Joint Subcommittees on Materials & Metallurgy, Thermal-Hydraulic Phenomena, and Reliability & Probabilistic Risk Assessment - November 15, 2001
Official Transcript of Proceedings
NUCLEAR REGULATORY COMMISSION
Title: Advisory Committee on Reactor Safeguards
Joint Meeting of the Materials and Metallurgy,
Thermal-Hydraulic Phenomena and Reliability
and Probabilistic Risk Assessment
Subcommittees
Docket Number: (not applicable)
Location: Rockville, Maryland
Date: Thursday, November 15, 2001
Work Order No.: NRC-112 Pages 1-156
NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers
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Washington, D.C. 20005
(202) 234-4433 UNITED STATES OF AMERICA
NUCLEAR REGULATORY COMMISSION
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ADVISORY COMMITTEE ON REACTOR SAFEGUARDS
JOINT MEETING OF THE
MATERIALS AND METALLURGY, THERMAL-HYDRAULIC
PHENOMENA AND RELIABILITY AND PROBABILISTIC
RISK ASSESSMENT SUBCOMMITTEES
+ + + + +
THURSDAY
NOVEMBER 15, 2001
+ + + + +
ROCKVILLE, MARYLAND
+ + + + +
The ACRS/ACNW Joint Subcommittee met at
Nuclear Regulatory Commission, Two White Flint North,
T2B3, 11545 Rockville Pike, at 8:30 a.m., William J.
Shack, presiding.
SUBCOMMITTEE MEMBERS:
WILLIAM J. SHACK Chairman, ACRS
DR. THOMAS S. KRESS Co-Chair, ACRS
DR. DANA POWERS Member, ACRS
MR. MARIO V. BONACA Member, ACRS
ACRS STAFF PRESENT:
Mr. Michael T. Markley, ACRS
ALSO PRESENT:
Mr. Ralph Meyer
Mr. Steve Bajorek
Mr. Norm Lauben
Ms. Carolyn Fairbanks
Mr. Alan Kuritzky
Ms. Mary Drouin
Mr. Tom King
I N D E X
AGENDA ITEM PAGE
Opening Remarks by Chairman Shack. . . . . . . . . 4
Update on Rulemaking Changes - Tom King. . . 6
Background - Risk-informing 10 CFR 50.46
Presented by Mary Drouin . . . . . . . . . . 9
Acceptance Criteria Overview - Steve
Bajorek. . . . . . . . . . . . . . . . . .15
Revisions to Decay Heat Standard - Norm
Lauben . . . . . . . . . . . . . . .16
Risk Informed Regulation Consideration on
Appendix K
Analysis Requirements - Steve Bajorek. . .34
Acceptance Criteria - Ralph Meyer. . . . .93
Recess at 10:48 a.m., until 11:09 a.m. . . 107
Status of technical work on 10 CDF 50.46
Presented by Mary Drouin . . . . . . . . . 108
Reliability Evaluation - Alan Kuritzky . 109
Large-Break LOCA Analyses - Carolyn
Fairbanks. . . . . . . . . . . . . . . . 133
Adjournment. . . . . . . . . . . . . . . . . . . 161
P-R-O-C-E-E-D-I-N-G-S
8:31 a.m.
CHAIRMAN SHACK: The meeting will now come
to order, the Joint Meeting of the Subcommittees on
Human Factors and Safety Research Program, previously
scheduled for today, has been postponed. This is a
joint meeting of the Advisory Committee on Reactor
Safeguards, Subcommittees on Materials and Metallurgy,
Thermal-Hydraulic Phenomena and Reliability and
Probabilistic Risk Assessment.
I am William Shack, Chairman of the
Subcommittee on Materials and Metallurgy. Graham
Wallis, Chairman of the Subcommittee on Thermal-
Hydraulic Phenomena and George Apostolakis, Chairman
of the Subcommittee on Reliability and PRA were unable
to attend this meeting, and we are proceeding with
this meeting on their behalf.
The Subcommittee members in attendance are
Mario Bonaca, Thomas Kress and Dana Powers. The
purpose of this meeting is to discuss the status of
NRC staff and industry initiatives to risk-inform the
technical requirements of 10 CFR 50.46 for emergency
core cooling systems for light water nuclear power
reactors.
The subcommittees will gather information,
analyze relevant issues and facts and formulate
proposed positions and actions as appropriate for
deliberation by the full Committee. Michael T.
Markley is the cognizant ACRS staff engineer for this
meeting.
The rules for participation in today's
meetings have been announced as part of the notice of
this meeting previously published in the Federal
Register on November 6th, 2001. A transcript of the
meeting is being kept and will be made available as
stated in the Federal Register Notice.
It is requested that speakers first
identify themselves and speak with sufficient clarity
and volume so that they can be readily heard. We have
received no written comments or requests for time to
make oral statements from members of the public
regarding today's meeting.
I guess we're going to hear an update from
the staff on some of the technical work they've been
doing to support the rulemaking for changes, and I see
Tom King is in attendance here, and I'd like to note
this is probably one of the last times we're going to
get to see Tom at a subcommittee meeting, since he's
going on to retirement.
We certainly enjoyed having you for many
extended discussions.
MR. KING: Thank you, but you know, you
may see me again. So don't be too optimistic over
there.
DR. POWERS: Well, in light of his
advancing years, should we get him a bottle of Geritol
or something like that?
CHAIRMAN SHACK: Well, that's one of the
politer bottles that you buy.
MR. KING: I'll take a bottle. It doesn't
have to be Geritol, though.
(Laughter)
CHAIRMAN SHACK: Since I don't see Mark
Cunningham, we'll assume that Tom King is going to
speak to --
MR. KING: Yes. We were going to provide
the status report on where we stand at this point.
You know, the SECY paper was out. We've not received
an SRM yet from the Commission, but we're proceeding
as if we're going to go forward with the rulemaking,
that the Commission's going to approve proceeding.
We're doing the technical work to see what
would that rulemaking look like. Today's meeting is
to provide you a status report on the options and
issues that we're dealing with in doing that technical
work and try and solicit some at least informal
feedback from the subcommittee on questions, views,
concerns you may have.
So with that, I'll turn it over to Mary
and the others who are going to give the presentation.
DR. POWERS: Tom, is there anything going
on that you might call Option 4, which would be the
complete reexamination of the regulations?
MR. KING: The short answer is, yes, there
is. There's a meeting this afternoon where NEI is
going to come in and give us their views on this clean
sheet of paper approach for -- particularly directed
toward future plants.
DR. POWERS: Yes.
MR. KING: We owe the Commission a paper
in June of '02 with our recommendations on whether or
not to proceed to do that, and if so, what are the
options. And if we can, what's our recommended option
for doing that.
So there is some work underway. This is
clearly as a policy question. The Commission's going
to have to make a decision and our target date is June
to get them something.
DR. POWERS: I think we might want to
alert the Planning and Procedures Committee that it
sounds like in the April, May, June time frame that we
ought to try to help staff where we can on the
development of that paper.
MR. KING: Yes. I think I -- in fact, I
ran into Med in the elevator and I said we need to sit
down and schedule several meetings with subcommittees
and the full committee, PBMR, GTMHR.
DR. POWERS: Is it the type of thing, Tom,
where we ought to have sort of an ad hoc committee?
I mean, it doesn't really fit within any of the
existing subcommittee structures. What I'm fishing
around for is how to be most helpful to you and not a
pain in the neck on this, because this is not a lot of
time to prepare that paper.
MR. KING: Yes. The idea of the paper is
to look at the pros and cons, look at the options,
give the Commission a recommendation. But assuming
the recommendation is to go forward, we also want to
give them at least a conceptual idea of what this new
clean sheet of paper approach would look like, so at
least they know what they're being asked to approve.
DR. POWERS: Yes.
MR. KING: So there is some technical work
that goes along with this.
DR. POWERS: Sure; sure. And we may want
to pursue that a little bit in December just to line
out schedules and things like that, from our own part.
MR. KING: Okay.
MS. DROUIN: We ready?
CHAIRMAN SHACK: Yes.
MS. DROUIN: My name's Mary Drouin, with
the Office of Research.
MR. KING: Who?
(Laughter)
MS. DROUIN: Cute, Tom.
DR. POWERS: Are you related to the
outstanding individual that produced the ITE Insights
Report that has had such a tremendous impact?
MS. DROUIN: Yes.
DR. POWERS: Okay.
MR. KURITZKY: We'd just like to get you
off to a good start.
(Laughter)
MS. DROUIN: And I greatly appreciate
that; really, I do. Before we get started we'll go
around and let everyone at the table introduce
themselves.
MR. MEYER: I'm Ralph Meyer, from
Research.
DR. POWERS: Are you new in this?
MR. MEYER: What?
DR. POWERS: Are you new in this
organization?
MR. MEYER: Lots of jokes this morning.
MR. KURITZKY: I'm Al Kuritzky. Work with
Area Branch.
MR. BAJOREK: Steve Bajorek, Research.
MS. FAIRBANKS: Carolyn Fairbanks,
Research with the Materials Engineering Branch.
MR. LAUBEN: Norm Lauben. I'm very new,
about 30, 40 years.
CHAIRMAN SHACK: Yeah, I know; I know.
DR. POWERS: Well, you know, as a rookie
trainee, maybe you'll listen to these experienced
hands and, you know, get some insights here.
MS. DROUIN: Okay. I think the last time
that we were in front of the subcommittee on 50.46,
the Option 3 part, was back in the summer as we were
writing our SECY paper.
And at that time, you know, we made the
commitment to maintain contact throughout the program
and solicit input and feedback from the committee as
we move forward. There are a lot of issues associated
with risk-informing 50.46.
So we did want to come in at this point,
since we have been proceeding with the technical work.
We had said in the SECY to the Commission that we
would not wait on the SRM to continue with the
technical work. We were going to move forward.
The rulemaking aspect, though, is
contingent upon when the SRM comes out. So we've had
about four months behind us in proceeding forward, and
we thought it was very timely at this point to give
you, you know, our status, what our -- kind of our
early thinkings are and issues we may have come
across.
So I'm not going to spend a lot of time
going through the background. We'll just quickly, you
know, refresh your memory of what our changes were,
what our recommended changes were to the Commission on
50.46.
We primarily are going to focus on the
technical work that we've been doing in support of the
recommended changes we made to the Commission and then
quickly go over what our schedule is at this point.
Again, primary purpose for being here is
to solicit feedback from the committee and comment,
one, on our overall approach because we're still --
have not quite solidified our approach. We are
converging on it and we thought, again, this would be
a good time.
We are encountering some, you know,
technical and implementation issues that we wanted to
bring to your attention and still, on some of our
recommended changes, whether we still feel that
they're feasible or not.
At this point, of course, we're not
requesting any letter from the committee. On the
background, you know, starting way back with SECY-300,
which instigated the program, 264-R Plan, 86 and 198
were two different updates of the framework.
198 gave our recommendations for 50.44,
and then our most recent SECY 133, which provided our
recommendations for risk-informing 50.46. Now, I'll
personally use the term "50.46," and when I use it, I
use it loosely.
It encompasses Appendix K and also GDC 35.
This here shows in a figure, an overview of 50.46,
plus Appendix K and GDC 35. I think it's a good
breakdown of the regulation in terms of how the
different requirements are grouped.
When you come over from the right -- or
from the left to the right, sorry. I still haven't
learned my left from my right yet. And you look at
the requirements, they tend to be divided up into what
we call these four functional groups.
The first one we're looking at the ECCS
reliability. Now, of course, when you look at the
50.46 and Appendix K, you're not going to see the word
"reliability" there, but for example, when you look at
GDC 35 and you look at the single failure criteria
requirement and the LOCA/LOOP, what that in essence
does in an indirect way of sitting with the
reliability of the ECCS as is.
So we have those requirements and this box
actually says what the technical requirements are.
The next LOOP tend to deal with the acceptance
criteria of the emergency core cooling system. The
next group is the evaluation model.
And finally, the last one is dealing with
the LOCA break size. And it's those different groups
that in 133 that we made recommendations to. Now,
when we go back to 133 we had two sets of
recommendations.
We had some that we called short-term
considerations and we had those that we considered
long-term. The short-term considerations dealt with
those first three boxes, looking at the ECCS
reliability, looking at the acceptance criteria and
the evaluation model.
In terms of the acceptance criteria in the
evaluation model, those we were going in and making a
recommendation to put a permanent change right into
the rule. That change would, though, be voluntary.
So it would be entered in through like an "or" gate.
Then an alternative to that would be an
alternative on the reliability side, and that is
dealing with GDC 35. We thought we could do those in
the short-term, and the technical work that we had
proposed on the short-term would be finished in the
April and July time frame of 2002.
On the long-term considerations we felt
there was still a lot more work done even to determine
if the feasibility was doable. And so we were looking
at the outside, two to three years to just finish the
feasibility study.
And again, in doing anything that -- in
terms of looking at Option 3, part 50, we have our
framework document which sets the guidelines and rules
of how we make the decisions that we make.
So at this point we're going to get right
into the technical work we were at, and we're going to
start first with the acceptance criteria in the
evaluation model, and so I'm going to turn it over to
Steve Bajorek.
MR. BAJOREK: Okay. Thank you, Mary.
Want to just slide over?
MS. DROUIN: Want us just to change it for
you?
MR. BAJOREK: Well, no. Let me --
MS. DROUIN: Okay.
MR. BAJOREK: -- let me just kind of
introduce what we're going to do next. The next
segment should be in a package that we just handed
out. We have three presentations in this. We're
going to start off with Norm Lauben.
He's going to talk about revisions to the
decay heat standard, how we deal with the
uncertainties. I'm going to talk about the use of the
evaluation models and the impact that may have on how
we do those analyses.
And Ralph Mayer is going to talk about the
50.46 performance-based criteria, and I think also
deal with a couple of cladding-type of issues that
have been brought up before. But Norm.
MR. LAUBEN: Yes. Let's see.
MR. BAJOREK: How's the --
MR. LAUBEN: I was happy to sit here, if
you want to change the slides for me.
MR. BAJOREK: Give me your --
THE REPORTER: Mr. Lauben, can you use the
microphone there?
MR. LAUBEN: Yes. I'll tell you what.
Why don't you move over a chair. Then I can just use
this microphone. And as long as I don't hit anyone in
the eye, I can use my laser beam.
MS. DROUIN: High tech. You might set a
fire.
MR. LAUBEN: Yes, right.
Carolyn, you may want to get out of the
way.
(Laughter)
MR. LAUBEN: Okay. Let's see. Yes,
that's -- let's see. This is what we're talking
about. That's who you are and that's who I am. So we
can go to the next slide. The real context for this
is going to be in Steve's presentation.
So mostly what I'm going to talk about are
the decay heat standards and their uncertainties and
some of the issues that we have uncovered with respect
to them, and how that all fits. But the context in
terms of conservatism and so forth is really, really
in Steve's presentation.
But so the hard part is to come after my
presentation, I hope, unless you all have questions
that I'm not expecting. Okay. This is just kind of
a review, first of all.
10 CFR 50.46 and Appendix K was
promulgated in '74, required the use as a draft, '71
ANS decay heat standard with a multiplier of 1.2 and
the assumption of infinite operating time for use in
ECCS evaluation models.
It's very simple. The '71 standard did
virtually have a curve with a table of uncertainties
that we chose 1.2 out of, and the assumption of -- you
could have finite operating time if you wanted to do
summation calculations, but we chose infinite
operation, which made the '71 standard very simple to
implement.
It was not -- there was no difficulty at
all in that. Anyway, number one, the research and
analysis since 1973 has shown that the most
significant conservatism in Appendix K is the decay
heat requirement.
The 1988 ECCS rule change allowed use of
a realistic evaluation model analysis option with an
uncertainty evaluation. In other words, instead of
using the conservative Appendix K, now you can use the
best estimate option.
So there's always two choices. One is the
best estimate option that was allowed since 1988. The
other was the Appendix K conservative option which was
the only option from 1974 to '88. But then after '88
it was still grandfathered. So licensees still have
a choice today of whether they want to use the best
estimate option or the Appendix K option.
Regulatory Guide 1.157, which accompanied
the '88 rule change, declared the acceptability of
using the '79 ANS decay heat standard for a realistic
option.
It said there's a few more physical things
that you need to consider, such as neutron absorption
efficient products and things of that sort. So it
says it's now become a little bit more complicated.
The '79 option now has three isotopes --
fissionable isotopes that you have to worry about, not
just one. So it's now more complicated. It has three
different ways of applying the standard. You can use
summation calculations -- excuse me.
Yes. You can use a summation calculation
for groups of decay products and you can also use some
integrated values for post-fissions, or you can use
integrated values for infinite decay heat and a
summation methodology where you can change that
infinite irradiation into finite irradiation.
So there's lots more choices that you have
to use when you start to use the '79 or then
eventually the '94 option. But okay. Regulatory
Guide 1.157 only applies to the best estimate option.
That Regulatory Guide does not apply to
Appendix K. Appendix K is self-standing. There's no
regulatory guides associated with it today or in the
past. It's just -- it's self-standing. You abide by
those rules and that's it. So 1.157 applies to the
best estimate option.
There's nothing to prevent a licensee or
an applicant from using all or part of an even newer
standard, the 1994 decay heat standard today, if you
want to, because there's no -- there are -- there's
really no requirements to -- as it says in the second
bullet.
The only technical requirement in the
realistic option has to do with the things that Mary
has addressed, i.e., the break spectrum in GDC 35.
Otherwise -- and those things apply to both the best
estimate and the realistic option. Okay. Back to --
CHAIRMAN SHACK: The current best estimate
models have been improved and they're really based on
the '74 guide or --
MR. LAUBEN: No. No. No. No. No. No.
No. No. No. No. Oh, excuse me. No. No. No.
What I said was that Reg. Guide 1.157, that's the
guidance as to what's acceptable to the staff with
respect to the best estimate option.
The best estimate option in 50.46 doesn't
say very much. It says, do a best estimate with a
high degree of certainty that your peak clad
temperatures won't exceed the limit. That's really
what it says, or that the criteria won't be exceeded
with a high probability. That's really all it says.
DR. KRESS: Does it explicitly call out
95.95?
MR. LAUBEN: No, it does not. That's
called out -- the 95 percent probability is called out
in the Regulatory Guide.
DR. KRESS: Yes, okay.
MR. LAUBEN: Not in the rule. The rule
doesn't say anything about that. The rule just says,
high probability that the criteria won't be exceeded.
You have to go to the Reg. Guide before you first see
the words, "95 percent" used.
DR. KRESS: So if somebody wanted to, they
could come in with less confidence level if they could
justify it?
MR. LAUBEN: If they could justify it.
DR. KRESS: Had a reason for it?
MR. LAUBEN: That's true of any regulatory
guide. You don't have to abide by a regulatory guide.
You can -- it's something that's acceptable to the
staff, but if you want to do something else, risk the
prolonged review that would be required for something
that's not in a regulatory guide, you can do it.
That's the rules.
DR. KRESS: Okay.
MR. LAUBEN: So at any rate, the
Regulatory Guide's been in place since '88 for best
estimate option. And it did say that the '79 standard
was acceptable. That's because the Regulatory Guide
came out in '88.
The '94 standard wasn't available at the
time, obviously. Okay. The last bullet. The '94
ANS-5 standard is potentially more accurate and less
conservative than the '71 draft standard, but requires
more choices to be specified by the user, as I
mentioned.
Instead of three fissionable isotopes, the
'94 standard has four fissionable isotopes. Still a
lot more than the one that was implied by the curve
that was in the '71 standard. So there's much more to
be -- choices that you have to make when you're using
the more modern standards.
More choices in '94 than there was in '79,
and certainly, many, many more choices than you had to
make from '71 standard. In fact, the '71 standard had
so few choices that the options could be contained in
two or three sentences in Appendix K.
Okay. If NRX makes it -- okay. Here's
the problem. You have a lot of choices now that you
have to make with the '94 standard, if you want to use
that. So the question is, who's going to make the
choices?
If NRC makes the choices ahead of time,
that may make life easier, but it also means that we
would have to make choices that would conservatively
bound any number of things that you have to consider
when you're applying the decay heat standard.
So let's see. What is -- let's see. If
NRC makes a choice -- yes, right. Okay. Anyway, if
NRC makes the choices, however, it's likely to make
the process more predictable and stable.
That is, if the choices are made at a time
by the NRC, no one argues with them, then there's no
-- there's very little potential for review, now, when
somebody comes in and says, I'm applying the '94
standard and here are the things that I choose to
implement out of that standard.
If each applicant or licensee selects the
options, then obviously, there's a lengthy review
process involved. Okay. Now, here are --
CHAIRMAN SHACK: Is there really a lengthy
review process? I mean, is it --
MR. LAUBEN: Yes, there could be. It
depends on -- it would depend on how the licensee or
applicant came in and decided to implement the
standard. He may be very -- he may want to get a lot
out of this, so he may be very tight in how he defines
his operating cycles, because that's one of the things
that you have to choose in here.
Or he may want to do a bounding histogram
that he could have, in which case it might not be. It
just depends on how much margin he's trying to shave
by using it, and that's the point of us making some of
these choices first.
And I can go through -- these are the six
that I identified as being the most important choices
that you have to make. Operating time. Well, in the
old standard infinite operating time is easy.
That's conservative. It's easy to use.
It actually reduces -- it reduces the complexity of
your uncertainty analysis. It makes life very easy
and it's obviously a conservative assumption, too.
But like I say, if you wanted to use a bounding
histogram of operating cycles, you could do that.
But if it was tightly bound then you may
run the risk of it doesn't apply to the next cycle of
operation or something like that. And that's part of
the problem, how tightly do you want to do this?
You going to leave it up to the individual
licensees or are you going to leave it up to -- or
should the NRC decide ahead of time? Part of the
reason I'm bringing this up is that -- and we didn't
mention this, but there was a petition by NEI to use
the '94 standard, just use it.
Well, they didn't say how they would use
it. They just said use it. So that -- the
implication is not clear. Do you mean for the NRC to
make choices ahead of time, or do you choose to come
in and make your own choices?
And if you're going to make your own
choices and each licensee makes a different choice,
then it does increase the potential for review.
CHAIRMAN SHACK: Let me put the question
a different way. You know, suppose you're just using
this to determine that decay heat --
MR. LAUBEN: That's all --
CHAIRMAN SHACK: -- that seems to me one
question. Well, is in fact -- I mean, do you feel
that your calculation of decay heat is now covering
some other non-conservatism somewhere else? I mean,
that would seem to me --
MR. LAUBEN: Yes.
CHAIRMAN SHACK: -- the difficult thing to
assess when you're trying --
MR. LAUBEN: Indeed
CHAIRMAN SHACK: -- to trade these off.
MR. LAUBEN: Indeed.
CHAIRMAN SHACK: Just looking at the decay
heat --
MR. LAUBEN: Yes.
CHAIRMAN SHACK: -- by itself I would
think --
MR. LAUBEN: Yes. Yes.
CHAIRMAN SHACK: -- looking at these would
be a relatively straightforward thing.
MR. LAUBEN: Relatively straightforward
thing. I agree. And Steve's going to address the
other part.
CHAIRMAN SHACK: Right. Okay.
MR. LAUBEN: I left the hard stuff for
him. But indeed, you're right. It should be
relatively straightforward, but the point is, even --
there are still some issues that need to be addressed,
just to do the straightforward part.
And that's what I'm attempting to address
here, that in the petition there was no mention of how
you even deal with the straightforward part. So I
bring these issues up here. I've brought them up in
a couple public meetings in the past, but there didn't
seem to be as much interest then, however. Okay.
Okay. Second one, fission fractions per
isotope. Well, this requires some -- okay. Well,
like I said, the '71 standard assumed 235U only. Three
additional isotopes in the '94 standard; fission
fractions vary with time and space.
You need a physics calculation to
determine what those fission fractions are for each
isotope. They vary with time. They vary with space.
They're burnup dependent and enrichment dependent.
So it's not -- you know -- it's not a
straightforward thing. You can make simple choices,
simple bonding choices like all 235U. That's a simple
bonding choice. Okay.
Neutron capture. This effect was added in
'79 and '94. The effect is burnup dependent and adds
to the decay heat. There's also some uncertainty in
it, although the amount is low until you get up to
beyond the times of interest that I think we're
interested in, like 10,000 seconds or so.
However, it's still something that needs
to be considered and addressed, and you can choose
times that are very high and then, you know, you're
conservative, because it's a T to the fourth effect in
the equation. It's there for neutron capture.
Okay. Fission energy. Each fissionable
isotope has different recoverable fission energies.
The standard in the past has always been to shoot 200
MEV per fission, because that's conservative. You can
actually reduce conservatism by using higher values
because that number appears in the denominator.
So you can, if you can justify it, choose
other numbers for other fissionable isotopes. So
that's another choice you have to make, or somebody
has to make, either the NRC ahead of time or the
licensees or whoever.
Okay. Actinide heavy element decay. The
same basic equations are in all three standards for
actinide decay. However, required 235U fission yield
is not specified and is burnup dependent. It was not
even specified in the '71 standard -- excuse me -- it
wasn't even specified there.
It was assumed I think that the value was
.7, but I don't -- you can -- I can't find the
documentation of it anywhere. In the examples in the
'79 and '94 standard I think it was like .7. There
are codes that use a default value of one. But the
point is, it's another choice to be made.
Okay. Tabular data. As I think I
mentioned earlier, there are three tables now for each
fissionable isotope, four fissionable isotopes. That
means you have 12 tables. You have 12 tables you can
go to and that depends on your method that you choose
to evaluate the decay heat.
That's quite different than just one table
that you had in the previous '71 standard. Okay. So
those are the key choices you have to make. At least
-- like you say, they're not -- they don't have to be
that difficult.
They can be chosen in a bounding way, but
if you want to reduce your conservatism you may not
want to make them quite as bounding as somebody else
might want to make them. Okay. So that's it. I
guess we can go to the next slide, then.
Okay. The issue here is uncertainty and
conservatism. Well, as we all know, now that we have
a decay heat standard that has many more variables in
it, your uncertainty analysis becomes a different
issue than it did before.
There are RMS equations or something like
that, that you have to go through and use to determine
your overall uncertainty in this. There are
uncertainties with two of the table types, the post-
fission type and the infinite irradiation tables, that
could be used.
They're different because they come out
with different values when you do this. But in
addition to the uncertainties in those tables for
those methods, you now have to look at other
uncertainties like uncertainties in power, or any of
the other variables that we're talking about,
uncertainties in fractions of fissionable isotopes.
So all these things now have
uncertainties, uncertainties in neutron absorption.
What if -- although the standard says, don't bother
doing that because we've picked conservative values
for you. So but the point is how to deal with
uncertainties now becomes an issue.
It wasn't an issue before, but how to
combine them and deal with them does become an issue.
There are equations in the standard, however. Let's
see. Let me see. I don't want to get ahead of myself
here.
Okay. Oh, yes, okay. Let me not get
ahead of myself then. Okay. Bullet number 3 here.
Use of the '94 standard with nominal inputs and
uncertainties could result in a substantial reduction
of overall conservatism in the Appendix K analysis.
And number 4, thus the magnitude of one or
more non-conservatisms is too large. If it is, the
appropriate overall conservatism may be in jeopardy.
I think this is Steve's presentation. I'm jumping the
gun a little bit.
But the point is here, is that if you now
reserve the conservatism in your analysis you now have
to worry about those other things that create
uncertainties in your analysis that you didn't have to
worry about before, because you don't have a bounding,
conservative -- it may be in jeopardy.
Let me just say that. It may be in
jeopardy. Okay. The current version of Appendix K
makes no break size distinction concerning application
of the decay heat requirement. Longer transients,
such as small breaks, would derive substantially
larger benefit from a reduction in decay heat,
compared to faster large breaks.
Large breaks, some of them, depending on
-- depending on a particular plant that you're looking
at, some large breaks can be over so quickly, peak
clad temperature can turn around so quickly, that it's
virtually a stored energy issue and not a decay heat
issue.
So large breaks that turn around quickly
are going to be -- are not going to be decay heat
dominated the way some small breaks that may be
uncovered, albeit later, for a longer period of time
become much more decay heat dominated.
Among the required features of Appendix K,
decay heat is the only one, except for the ones that
Mary talked about, i.e., the break size and the GDC 35
types of things. The only thing that really applies
to small breaks in Appendix K specifically is decay
heat.
Or let me put it this way, largely. There
are some other things that can influence it, too, but
I mean it's by and large virtually the entire
predominant feature of Appendix K, is decay heat for
small breaks.
Okay. RES is evaluating -- okay. Number
5 -- or 6. This may be somewhat new. We are
evaluating potential errors in the uncertainty methods
in the '79 ANS and '94 standards. Therefore, previous
sensitivities may not be appropriate.
Some of our assessments before -- the
uncertainties -- in other words, some of the
equations, I don't want to say for certain that
they're wrong, but I've had a number of physicists and
statisticians tell me that they are.
But wrong may not be a good adjective. It
may be that they were -- that they used methods that
were designed to enhance the uncertainty, and that it
has to be looked at more carefully. I think in fact
we've talked with the ANS Standards Subcommittee on
this subject and they -- those members agree also.
They believe that this should be fixed.
So our choice is either to convene a group of experts
under ANS and work this through or make the exceptions
ourselves. I tend to -- would tend to prefer to work
this through the ANS committees.
I think that's a better way, get a new
standard out which everyone agrees on these
methodologies and so forth. So that's something, like
you say, not necessarily that difficult to do, but
still something that you sort of need to establish
your baseline by doing these straightforward things
first.
And I think that's what we -- so that's
what we mean when we say, number 7, we're going to do
some additional work. We need to get some of these
things straightened out.
And now, as I said a couple times, number
8 there, the context of the decay heat work and the
-- is really the basic subject of Steve's
presentation. So I don't know if there are any other
questions or not. Okay. Thank you.
MR. BAJOREK: Those go back to Norm.
Thank you, Norm. Where I'm going to pick up now,
then, is if we start to change the decay heat model,
going from '71 or '79 to something that's technically
better, what are the consequences that we're going to
see in two different evaluation models that have been
presented to the staff, the classic Appendix K model
and how this might impact best estimate analyses, as
well.
Our directive to do this comes from the
SECY-01-133, and what I've summarized here in the
first three or four bullets are some of the items that
specifically discuss this.
What basically 01-133 asks us to do is to
take a look at Appendix K, identify those models which
are unnecessary conservatisms, come up with revisions
to them, but also keep in mind that Appendix K may not
cover everything.
We do have new knowledge in front of us
and there may be issues related to Appendix K where
there may be non-conservatisms involved. So we've
been asked to look for the unnecessary conservatisms,
as well as look at features that may not be
appropriately counted for.
DR. KRESS: Is there such a thing as a
necessary conservatism?
MR. BAJOREK: I think there is, and I
think Norm hinted on it. We see that the '71 decay
heat model is very overly-conservative technically,
compared to what it should be to an accurate
correlation.
But that excess conservatism has been used
in evaluation models to account for other things. It
forgives a lot of sins, okay, uncertainties in other
models, processes where you may have questions, but
from a regulatory viewpoint you may feel comfortable
with because you know there's so much conservatism in
the Appendix K, as well as in things like the single
failure criteria.
I'm going to talk about a few things that
we would consider as non-conservatisms in a couple of
minutes here. Principally, the focus of the efforts
in our branch have been by the norm to take a look at
the decay heat standard itself, what its
implementation should be, and then to look at options
to deal with incorporation of a revised decay heat
standard and how we should deal with some of these
things that we're terming as non-conservatisms.
Well, I think the first question is, well,
what is this thing that you would refer to as a non-
conservatism? And I would say that there are three
potential sources. First, there may be models in
Appendix K that even though they're intended to be
conservative, later information has shown them not to
be.
Now, the only example that we're aware of
is in the case of the Dougal-Rohsenow Model for post-
critical heat flux heat transfer. Information that
was uncovered in the '70s and '80s showed that it was
non-conservative.
And in the '88 rule change there were
restrictions placed on the Dougal-Rohsenow Model. It
could only be grandfathered and if there was a change
to the analysis, you had to justify its conservatism.
And to my understanding, most evaluation
models have basically replaced that at this time. So
that's not really an issue anymore. However, Appendix
K, while it gives prescriptions for several thermal-
hydraulic models, it doesn't account for everything.
And there has been the concern that these
models, which have not been specifically discussed by
Appendix K, may have a large uncertainty when they're
applied in an evaluation model. This was the focus of
another SECY paper, 86-318, that actually looked at an
issue very similar to what we're doing right now.
The premise for 86-318 was reduce the
decay heat by changing to an updated standard. I
think they were looking at the '79 standard at that
time. And the conclusion at that time was that, no,
that was not a good thing to do unless you accounted
for uncertainties in the other thermal hydraulic
models.
Now, it having been written in 1986, you
can see that this was basically a formulation for the
1988 rule change and the best estimate rule that
required people to actually address these
uncertainties.
But it still remains a concern that if we
start to do things with Appendix K, we still have to
do something to look at those uncertainties and assure
ourselves that there is some conservatism remaining in
that type of an evaluation model.
The third source of potential non-
conservatism are things that have arisen out of
thermal hydraulic test programs that were conducted in
the late '80s and the early '90s. These are processes
-- we'll talk about those in the next overhead.
These are processes that were identified
in the test programs that Appendix K didn't know about
in 1971, and had basically fallen through the cracks.
SECY 133 is asking us to identify what some of these
processes are and make sure that they are at least
compensated for by any revision in the decay heat
standard, plus some adequate multiplier.
A couple of examples that are considered
non-conservatism, and these are large break models.
The first one to refer to is downcomer boiling, and
this is something that was seen in the 2D/3D Program,
CCTF, SSTF that were run in Japan and also UPTF that
was run in Germany in the last '80s, early '90s.
They noted that some of the heat transfer
that occurred in the core wasn't as good as they
anticipated it to be. They thought the reflood rate
was going to be a little bit higher. In looking at
some of that data, part of it was attributed to things
that had gone on in the downcomer.
Later in the transient the fluid begins to
boil, takes awhile to get that energy out of the
walls. This voids part of the downcomer and two
things go on. One, you reduce your gravitational head
that drives fluid into the core.
And secondly, when that downcomer fluid
frosts up, part of it gets pushed back out the break.
So your result is a lower collapsed level in the
downcomer than you would have if you had made the
assumption it didn't boil and you were full up to the
cold leg.
Now, typically Appendix K evaluation
models don't really account for this. There are two
reasons. One, the models themselves are based on
equilibrium models that stem from work in the '60s and
early '70s.
They assumed that both the vapor and the
liquid were at the same temperature. Boiling does not
begin until you brought everything up to the
saturation temperature. Subcooled boiling, however,
is well-recognized to begin while you still have some
subcooling remaining in your bulk fluid.
So we know it will begin earlier. This is
also complicated by the simplified nodalization that's
used in many of these Appendix K evaluation models.
They lump everything in the downcomer together, as
opposed to allowing a thermal stratification to occur,
which is put in most of the realistic codes like RELAP
or TRAC or COBRA.
Now, the most vulnerable plants are ones
that have relatively high power, low containment
pressure. The large break transient extends for a
fairly long period of time. So you're depending on
your downcomer driving head during -- after your
accumulator period, okay, when boiling may occur to
start to recover your core.
So the longer this transient proceeds, the
larger this defect is going to be. The other one --
CHAIRMAN SHACK: Would this be a problem
even with the current best estimate models? Would
they account for this?
MR. BAJOREK: They account for it. Most
of the realistic codes have what they will call
mechanistic models for subcooled boiling. And what
this allows you to do is to boil in the downcomer well
in advance of the time when everything is at
saturation.
In fact, this is how this issue started to
arise, because in the realistic calculations people
were noticing, hey, there's not as much margin here as
everyone had hoped, and in looking at those
calculations the cause was this downcomer voiding that
was going on in the calculations.
Let me show you an example of what goes
on. This figure is from the calculation using
COBRA/TRAC for a combustion engineering system 80
plant. The plant in this case is at 3800 megawatts,
sort of a standard 3800 system 80 design.
What's shown in the figure is the upper
curve, the saturation temperature, and the lower,
which is the liquid temperature in the downcomer.
Now, early in time at 50 seconds or so, the
accumulators come on.
In this plant the accumulators are
enormous with respect to other types of designs. So
you get a very high amount of subcooling early in the
transient. Well, eventually enough heat comes out of
the vessel wall and core barrel, so at roughly 180,
about 180 seconds or so into the transient the
downcomer is effectively saturated.
This figure shows the collapsed level in
the downcomer. Now, early on at 50 seconds or so,
that's when the accumulators are active. They just
fill the downcomers all the way up to the spray
nozzles and up into the cold legs.
At by about 100 seconds, the level in that
downcomer is about to the bottom of the cold light.
So they're effectively filled. Liquid is still
subcooled at that time. If you recall from the last
figure, saturation occurs at about 180 seconds.
And what you notice in the collapsed
liquid level is now a fairly significant decrease,
dropping from cold level to two or three meters lower
in this calculation. Eventually, your pressure
decreases, the pump's safety ejection comes on and you
recover your downcomer level and subsequently the
core.
Now, on the system 80 3800 megawatt plant,
which this calculation is for, there's not a real big
concern. This shows the peak cladding temperature in
the core. The reflood peak is reached shortly after
the accumulators inject.
Turned around, the core quenches by 140,
150 seconds. So with regards to downcomer boiling
it's basically no harm, no foul. Downcomer boiling
doesn't take place until after you've gotten the
energy out of the core, not much of a concern.
Well, now let's try to uprate the unit.
Now, to do this I took calculations that had been
performed for a system 80+, effectively the same
geometry. There is a difference in downcomer
injection location, but if I compare the transients,
I basically see that same accumulator effect.
We fill the downcomer, okay, and the
downcomer again boils around, oh, around 150 seconds,
a little bit earlier, because now we're looking at a
plant 3800 to 3914 megawatt thermal. Now, the energy
has not been removed from the core by the time
downcomer boiling begins.
And you see that rather than the peak
cladding temperature decreasing, as it would have at
150, 160, it starts off and reaches a second peak, in
this case at about 400 seconds. Quench of the core
because of the reduced reflood rate does not occur out
until roughly 900 seconds or so.
The transient is significantly prolonged
because of the downcomer boiling process. We'll get
back to the net PCT effect in a second, but let me
mention the other non-conservatism that has been
talked about for several years, and this one's
referred to as fuel relocation.
During the transient the clad will swell
at several locations, usually just below your peak
temperature location. Experiments that have been run
in this country, in France, in Germany, have found
that upon ballooning, the pellet fragments above the
ballooned location relocate and move into this balloon
zone.
Now, if you're doing a calculation and you
don't account for fuel relocation, you have a
situation where you have a stack of pellets with the
balloon clad. The clad effectively behaves like a
fin. Ballooning in some ways is good for the clad
because you remove it from the heat source, push it
off into the fluid where it gets effectively good
cooling.
That's why you really shouldn't see your
PCT location at the burst or the balloon location.
However, the concern from these experiments is that
upon ballooning you don't maintain a concentric stack
of pellets.
The pellets are fragmented due to prior
operation. They come down, increase the local power
and increase the pellet to clad gap conductance, which
would significantly increase your PCT. Now, one of
the things that we've been working on has been
attempting to get estimates of what does all this
mean.
If we change the decay heat from '71 to
'79 or '94, how does that impact the analysis and how
does these non-conservatisms stack up? Decay heat,
we've gotten estimates from two different sources.
Westinghouse had a meeting with the staff about a year
ago and they were asked their estimate of what would
happen if they took their Appendix K model and reduced
the decay heat to the '79 standard.
Their estimates were 250 to 340 degrees,
and there had been some calculations done to
substantiate those numbers. We also had one of our
contractors modify a RELAP to do a similar
calculation. They looked at an older vintage
combustion engineering unit.
I think it was Millstone or Calvert
Cliffs.
MR. LAUBEN: Millstone.
MR. BAJOREK: And they estimated that it
was 372, so more or less consistent with the
Westinghouse estimate, 3- to 400 degrees due to the
decay heat relaxation. Both also estimated what would
be the benefit of going from Baker-Just to Cathcart-
Powell for the metal heat reaction.
Smaller in effect, less than 100 degrees,
and you can see the estimates of 50 and 75 degrees.
Now, for downcomer boiling and relocation we've gone
to information that the vendors have provided us,
information that has been obtained publicly.
We have three estimates for the downcomer
boiling. Westinghouse took a look at their
calculations for a four-LOOP ice condenser unit and
they estimated that the penalty by accounting for
downcomer boiling in your calculation relative to
ignoring it was roughly 400 degrees.
ISL did some RELAP calculations for us,
again taking a look at a system 80+ unit. This is
similar to what I just showed you, but their interest
there is looking at the Korean next generation, which
is even at a higher power than the Palo Verde and the
powers that we're looking at for a system 80+ in this
country.
Now, their estimate was 700 degrees, or I
should say that's our estimate in taking a look at the
first reflood peak and the second reflood peak. What
I think you should gather from that is a few hundred
degrees.
I don't think it's 700 degrees. I think
that's a RELAP problem. The interfacial drag is too
high. We've seen that consistently in other RELAP
calculations. Once you get some bubbles it pushes up
far too much liquid into the downcomer.
Okay. So I think that number's too large.
The calculation that I showed you there in the last
four figures, if I subtract away a power effect and
look at the difference in PCTS and attribute that to
the downcomer boiling, my estimate was slightly over
300 degrees on that one.
So for at least for the downcomer boiling
we're seeing three separate organizations using
different relisting codes, all basically agreeing that
downcomer, it's not a 10 or a 20-degree effect. It's
something larger.
And those values, three, four -- three or
400 degrees are basically on the same order of the
decay heat change that would be envisioned for
Appendix K models that do not account for this process
correctly.
Fuel relocation. A technical paper was
written by the French and they took a look at the
experiments. They estimated some filling fractions of
the balloon region, did some CATHARE, which is
considered a realistic code for relocation versus not
accounting for relocation.
Their estimate -- or I should say our
estimate comparing their numbers translates to 313
degrees by accounting for this fuel relocation. Those
are the two that we see public information, we've
heard talked about at technical meetings and the
vendors have made us aware of.
They know that some of these are going on.
It's a question on how you should really deal with
those. We don't want to say that we're clairvoyant
and we k now everything with respect to the non-
conservatisms.
So I made a couple of phone calls to a
couple of university professors; what would you
consider a non-conservatism. We got a few things.
Some fit into Appendix K. Some really don't. They're
more plant condition issues.
An example may be, do you account for
secondary to primary leakage during a LOCA. We know
that during steady-state operation there is a amount
of leakage allowed from the primary to the secondary
side.
Well, if you account for that during an
analysis you would be increasing the amount of steam
binding, okay, and potentially having a penalty. I
guess my point on the final one there is even though
we have a list of several things that we would account
for, we would consider non-conservatisms, we still
feel we want to do a little bit more work, not going
on a witch hunt, but trying to make sure that we are
at least informed on things that are recognized as
these major non-conservatisms.
DR. POWERS: You have looked or reported
some examinations of a comparison between Cathcart-
Powel and Baker-Just for the parabolic reconstants.
Has anybody looked at what effect would happen if we
had deviations from parabolic?
MR. BAJOREK: I'm not aware of it, but
Ralph is best to answer that one.
MR. MEYER: No, I don't have that.
DR. POWERS: It has always struck me that
one of the best justifications for using Baker-Just in
the face of several examinations that took place later
that suggested it was quite conservative was the fact
-- a couple of things.
One, you really don't know the surface
area that you're oxidizing, and the second loophole is
that we usually calculate these things in a fairly
stylized fashion and don't calculate the epitaxial
stresses that arise in cylindrical coordinates that
might cause delamination of the oxide, locally if not
globally, especially around things which cause
deformations of the ballooned region around grid
spacers and the like that would cause a deviation from
strictly parabolic kinetics, and that because those
things were challenging to do you just used Baker-Just
to cover your ignorance there.
But I don't know that anybody has ever
gone through and looked and said, how much ignorance
are we covering.
MR. BAJOREK: Right. Ralph.
MR. MEYER: Well, we are going to look at
that in the work that we're doing at Argonne right
now. I would say that based on the early results that
are now coming out of the program, I don't expect to
find much here because what we have found in the last
couple of months for the BWR high burnup rods that
have undergone oxidation kinetics measurements, the
oxide layer doesn't seem to have any protective effect
in altering the rate of oxidation.
And our results for the high burnup
cladding appear to be virtually identical to results
for fresh tubing. Now --
DR. POWERS: Well, I guess the question I
would ask is, have you ballooned that cladding around
a grid spacer and can you come to that conclusion?
MR. MEYER: Have we -- well, so far we
haven't made measurements with balloon cladding, but
we are going to make measurements with balloon
cladding. Now, you're asking about, is the location
of a balloon close to a grid spacer and I can't tell
you the answer.
What I can tell you is that we are
discussing right now whether the upper fasting point
for the fuel rods should be shaped like a grid so that
we would get any grid effects on this.
But I think the best answer we can give,
and I think it's an adequate answer, is that we are in
the process of testing under conditions that are just
as prototypical as you can imagine, and we would be
able to detect any deviation in the oxidation kinetics
that results from the deformation and related
processes, like flaking off of the oxide, because we
will have at the outset very careful measurements of
oxidation kinetics on undeformed irradiated tubing in
order to compare with the more integral tests that
we're going to do.
DR. POWERS: Have you tried to determine
the conditions by say modeling or some sort that would
optimize the conditions for delamination of the oxide?
I know that the French have set up what looks to me to
be a relatively impressive model of those epitaxial
stresses.
I have never taken their model and tried
to say, okay, now, what kinds of things lead to high
strains and stresses at the interface that would cause
delamination? But it looks like they have one that's
sophisticated enough so that you could do that sort of
thing.
MR. MEYER: Well, we don't have a model
with that level of sophistication, but I don't see why
you couldn't get that information more reliably from
a test rather than a model.
DR. POWERS: Well, I mean, the problem is
-- I mean, maybe you could if you're fairly
imaginative in the testing capabilities. It's just
that I worry that you can't test all -- I mean, I'm
just not smart enough to participate.
MR. MEYER: No, that's true, but the
indications right now are that the oxide isn't going
to affect the oxidation rate, that large amount of
oxide that has accumulated from corrosion and is
present at the time of this ballooning deformation.
Now, remember, the ballooning deformation
occurs at a relatively low temperature. So you
haven't gotten into the high temperature oxidation
region where you're going to build up 17 percent.
The ballooning deformation is over with
before you ever start accumulating the large amounts
during the high temperature portion of this transient.
So you're really only talking about the spallation of
oxide that's on there from the corrosion process
during burnup operation.
In that part of it there's already a
preliminary indication it doesn't make any difference.
CHAIRMAN SHACK: Well, of course, that BWR
cladding has a relatively thin oxide --
MR. MEYER: It has a relatively small
amount of oxidation, that's absolutely true. It has
only seven to ten microns of oxide on it, and we have
PWR cladding that we're going to test soon that has
100 microns and even more than that in some locations.
So you know, I can't say that this is a
general observation, but there is an expectation that
even the heavier corrosion layer thicknesses, that
it's cracked and it's pervious. Is that the right
word? The opposite of impervious.
DR. POWERS: I mean, the challenge one
faces in this is that when we look at analog systems
with fluoride structure oxides on metal surfaces, the
analog systems that come immediately to mind are
things like cerium metal, uranium metal and plutonium
metal.
In every one of those cases they suffer
catastrophic delamination of the oxide at very thin
levels, and zirconium just doesn't do that.
MR. MEYER: Yes.
DR. POWERS: And hafnium even more doesn't
do that. And you keep saying why, and what is it that
will cause delamination of this oxide? Is it so
extreme that it's outside the range of things that you
can have during a reactor upset condition?
And I don't know the answer to these
things but I keep struggling with it, because I can't
keep my oxides on plutonium, so why are you guys with
zirconium so successful at keeping your oxides intact?
MR. MEYER: Well, I haven't suggested that
it won't spall. What I have suggested, that it won't
make any difference if it does spall. And I think we
will be able to see both, whether it flakes off during
the deformation process and if it makes any
difference.
CHAIRMAN SHACK: Steve, just --
MR. BAJOREK: Sure.
CHAIRMAN SHACK: -- when I look at this
kind of one at a time thing it sort of suggests to me
that I'm not going to get anything from a best
estimate calculation, that everything's going to wash
out. That doesn't seem to jibe with experience.
MR. BAJOREK: The penalties that you see
for the realistic calculations are relative to what
you would have gotten from that calculation without
conservatism boiling. For this one, the peak cladding
temperature was probably around 1900 degrees.
So there was a benefit in there. I mean,
it came due to relaxing the decay heat, okay, but if
you had ignored the boiling processes in the downcomer
you would have been dealing with a peak cladding
temperature 15 -- you know -- 1500 degrees or so.
So yes, there is a reduction, but the net
reduction isn't as large as what had been anticipated.
These numbers, by the way, are for large break. Now,
I've got some numbers, some estimates here for small
break, but the situation there is a lot more nebulous,
quite likely because most plants are large break
limited, or I should say, the vast majority are vast
break limited.
There hasn't been a tremendous amount of
work looking at the sensitivities with regards to
small break. Estimates that we have gotten from --
basically one of our contractors looked at the issue
and did some of their calculations, found some
information from Combustion Engineering and
Westinghouse that basically estimated close to 1,000
degrees, 800 to 1,000.
Their calculations, based on RELAP, were
showing another range, five to 1,000 degrees by going
from '71 to the '79 standard. I don't have an
estimate for the metal water reaction.
If you were to do that separately, my
guess it would be larger than what you would see for
a large break, because it occurs over a much longer
period of time, but we're not aware of any unique
sensitivity studies at a high enough temperature
whether it would an effect.
MR. LAUBEN: It is about the same. I did
some with -- for the 2700 megawatt CE plant and it was
about the same.
MR. BAJOREK: Okay.
MR. LAUBEN: The same 50 to 75 degrees.
MR. BAJOREK: Okay.
MR. LAUBEN: Because intransient's usually
a little bit slower.
MR. BAJOREK: Well, you have lower decay
heat at the time.
MR. LAUBEN: Right.
MR. BAJOREK: So it's --
MR. LAUBEN: Right.
MR. BAJOREK: Okay. Let's go. Now, some
of the things that we might want to consider as non-
conservative issues, we've seen some cases with
nodalization, where whether you uniquely look at
cross-flow into the hot assembly.
I think, Norm, you have these RELAP
calculations that show you get a 600-degree effect.
And this kind of goes back to the idea that these
codes were written '60s, '70s. You were -- had them
on CRAYS, 7600s, and you tended to want to simplify
your nodalization compared to what you could do so.
So by incorporating more complexity into
your model you start to see more variations, simply
because of the number of processes that lie cross-flow
that you would take into account.
Now, one that has been recognized in the
past has been the consequences of operator action
during a small break. Right now, you don't have to
worry about it as much in small break if you have the
loss of off-site power, the pumps trip on reactor
trip.
If you have off-site power available,
which is another one of the avenues that is being
pursued under risk-informed regulation, now you have
to depend on the operators to trip the pumps according
to their EOPs.
This usually calls for them to recognize
that the rods are on the bottom, you've got a safety
injection pump and that you've lost, by looking at
your monitors, lost some cooling into your hot leg.
Once you recognize that the reactor pumps are tripped.
Now, this is going to depend on how
quickly they go through the EOPs, their recognition of
these various signals while there's a lot of confusion
going on. Calculations that had been performed in the
mid-80s looking at this, found that there were periods
of time where the operator could trip them while you
had a plant at an elevated pressure and lost
inventory.
Then if you tripped the pumps you
collapsed the froth over core -- over the core, you're
still at high pressure, meaning you weren't getting as
much safety injection into the system, and could get
a very high peak cladding temperature.
So it's one of the things that may need to
be considered. The other two have more to do with
model and correlation uncertainty. In taking a look
at the decay heat sensitivity, the contractor noted
that, hey, being off just a couple of inches in your
level swell, where your froth level is in the small
break, can result in several hundred degree increase
or decrease in what your peak cladding temperature is.
LOOP seal clearance refers to the effect
out in a small break when steam starts to slip through
one or more of the LOOP seals of a plant. This
redistributes the fluid. Some goes out the break.
Some goes to the vessel; some stays in the
LOOP seal. And what happens then is you get a
different two-phase hydraulic loss through the LOOPs.
If that loss is high you tend to suppress the core
level much more than if you had a nice, clean blow in
that LOOP.
People who have tried to model this in
codes have had a fairly difficult time doing this. I
don't put a basis down on this because I'm talking a
little bit more from personal experience in developing
a small break evaluation model.
This was a very complex issue when we saw
hundreds of degrees of variation. We have also seen
some experimental tests that have raised it as a
concern, mainly due to LOOP seal replug. Some of the
ROSA tests said that you've got very good heat
transfer in your steam generator.
What that means is later in the transient
you can put enough condensate into the LOOP seal to
replug it, force it to blow again. So in terms of the
non-conservatism, it's something that we feel would at
least have to be looked at in terms of the consequence
of reducing decay heat if we're going to be relaxing
the amount of conservatism that we see now.
The next thing that I want to move into
are options that we're currently looking at. And I
want to emphasize that we have not reached a staff
consensus on which option should be pursued.
MR. BONACA: I have a question on one of
the thoughts just --
MR. BAJOREK: Sure.
MR. BONACA: You just made a pretty strong
case for some of the conservatisms that you have in
Appendix K, I mean, in the tradeoffs. And in the best
estimate, when you do best estimate calculations, do
you have -- there is no modeling of downcomer boiling
in best estimate testing.
MR. BAJOREK: In best estimate you do.
MR. BONACA: You do?
MR. BAJOREK: Yes.
MR. BONACA: Okay. That's one of the --
what I --
MR. BAJOREK: The two fluid codes would
take a look at non-equilibrium.
MR. BONACA: Okay. So yes, all right.
MR. BAJOREK: Phases that allow voids to
develop. The RELAP, as we noted --
MR. BONACA: Yes, that's right.
MR. BAJOREK: -- in the calculations we
think isn't doing it very well, but it's doing it very
conservatively, which gave that 700 number. We think
that the COBRA formation is maybe doing that in a more
kinder, gentler fashion, but it's still significant,
three to 400 degrees.
MR. BONACA: I guess the point I'm making,
it would be interesting to have a comparison of these
effects also for the best estimate so we could have an
understanding of what tradeoffs have already occurred.
And now in the best estimate modeling do
you still -- are most -- what's happening to the decay
heat curve? Which one is being used?
MR. BAJOREK: Usually, the '79.
MR. BONACA: Seventy-nine.
MR. BAJOREK: Yes.
MR. BONACA: Not '94 effect.
MR. BAJOREK: No. In fact, what I wanted
to point out with this overhead -- this is not in your
package -- but to point out the work that we need to
do in coming up with an option for Appendix K and a
revision to the decay heat, just to make sure that
that revision satisfies a new option for the Appendix
K, but also addresses some of the issues in a best
estimate model.
And I think as you noted and as Norm
noted, for a best estimate evaluation model, Reg.
Guide 1.157 simply says for decay heat, calculate in
a best estimate manner. It considers by way of a
reference that the '79 decay heat is acceptable.
Now, you could take that Reg. Guide at
this time and use the '94, but it's certainly not
clear to anyone that goes through when we're
developing a model. Perhaps even a little bit more
cloudy is the metal water reaction.
Again, the Reg. Guide says to calculate it
in a best estimate manner and it cites Cathcart, et
al., Cathcart, Powel and who else may have been on
that, their data is acceptable and doesn't even cite
the correlation.
It just says "that data is acceptable,"
and leaves it go at that point for the licensee and
the review process to sort out what is truly a best
estimate model.
CHAIRMAN SHACK: What have people actually
done in the best estimate models today for the metal
water action? Do they use Cathcart-Powel?
MR. BAJOREK: Yes. Yes. They've been
using Cathcart-Powel. There is an uncertainty in the
application that I'm aware of in how it's applied. So
they're -- Westinghouse is using Cathcart-Powel.
There is an uncertainty about that calculation.
CHAIRMAN SHACK: In my simple-minded view
of this thing, you know, the thing I'm normally
looking at when I have a conservative calculation, you
know, when I decide how conservative it is I go out
and I get a better calculation and I compare the two.
Well, you know, now I've got a better
calculation. It would seem to me that, you know, I
look at all my best estimate calculations and I go off
and I do my simple Appendix K calculation, it would
seem to be relatively straightforward to do.
You know, suppose I change my Appendix K
calculation with the decay heat and I look at my best
estimate calculations, you know, and --
MR. BAJOREK: We have that. That was
discussed in the meeting last year. There's a figure.
I'm not sure if it's proprietary or not. That's why
I didn't -- that's why I wanted to stay with stuff
that I knew was public.
Those calculations showed that the
Appendix K evaluation model, okay, with '71 decay
heat, gave a peak cladding temperature that was just
larger than best estimate plus uncertainties. Okay.
When they reduced the decay heat, the
Appendix K calculation gave values that were closer to
the best estimate, but without the uncertainties.
It's somewhere in the middle. Now, you have to take
it a bit with a grain of salt, because I think the
plant types were slightly different and there were --
it was more of a apple versus a different type of
apple.
CHAIRMAN SHACK: Pear.
MR. BAJOREK: Yes. So it wasn't
straightforward, but the calculations suggested that
if you reduced the decay heat in that -- for that
plant in that Appendix K evaluation model, the PCT
would not -- would be more favorable than what you
would be getting out of a best estimate methodology.
And that raises some concerns going back
to the SECY paper 86-318, which says, hey, there are
models which can result in a fairly large uncertainty
and you should account for those in your overall peak
cladding temperature and your analysis methodology.
MR. LAUBEN: But you're right about -- as
long as you have the standard of a best estimate
calculation to compare with the Appendix K
calculation, you can do it. But if you don't have
that standard, what do you do?
And for some plants, some vendors, some
plants, you have the standard with which you can
compare, and the calculation Steve has was actually
done by the same vendor, that he was able to compare
one to the other.
So that was an apple -- as close as you
can get to an apple and an apple. But it's not as
easy to do if you don't have a best estimate standard
by which you can compare to the existing Appendix K
calculation. That's --
CHAIRMAN SHACK: Well, I guess I just
don't have a feel whether we have enough best estimate
results --
MR. LAUBEN: Yes.
CHAIRMAN SHACK: -- available now to be
able --
MR. LAUBEN: Good.
CHAIRMAN SHACK: -- to make the benchmark.
MR. LAUBEN: Yes.
MR. BAJOREK: One of the problems that
occurs --
MR. LAUBEN: Good question.
MR. BAJOREK: -- is because they are
complex analyses to perform, you know you're getting
margin. So immediately what you want to do is to use
that margin, okay, for an operating enhancing the core
peaking factors.
So if you do the work you don't want to do
it at the levels that you already have the Appendix K
calculation. And because of that you always wind up
in this apples versus oranges type of comparison.
Three options that we are looking at right
now, and as I mentioned in this previous figure, we
feel that in coming up with an alternative option to
Appendix K we have work that needs to be done.
We also need to do work on what I'll call
the realistic option, to clarify the use of the '94
standard for decay heat. How you would use Cathcart-
Powel, if that's to be recommended for metal water
reaction?
What is the difference and how should we
deal with uncertainties and conservatism in either of
these analyses? Option A, as I'll refer to it. In
the realistic option -- and this is going to be true
in the two or three options that we'll discuss -- we
would revise Reg. Guide 1.157, clarify that you can,
perhaps should use the '94 decay heat standard, take
the work that Norm is doing to recommend how it should
be implemented into those decay heat questions, which
we have work ongoing.
Recommend a specific metal water reaction
that should be used, and clean up. Perhaps, the more
nebulous part of that Reg. Guide is how you deal with
these uncertainties. This is why you need to quantify
the accuracy.
You need to deal with the uncertainties,
and then you were sort of left to the winds on how to
do that. And part of the difficulty in the
application is coming up with an appropriate
statistical method to account for those uncertainties.
And it's been one of the things that has
driven up the difficulty in that analysis. Now, in
this particular option the Appendix K revision would
involve replacing the ANS '71 standard with '94, plus
some uncertainty, okay, that would account for the
experimental uncertainty in the decay heat.
Okay. One, two, three sigma, something
along those order. It would address solely the decay
heat model uncertainty. We would ask licensees to
take a list that we would propose and they could
augment to address recognized non-conservatisms,
things like the downcomer boiling, fuel relocation,
other things that we may identify.
We think that the approach is consistent
with what was requested in the 0-133. That relax
where it is clearly non-conservatism -- overly
conservative decay heat would account for
conservatisms.
DR. KRESS: When you say "consider non-
conservatisms" what does that actually mean?
MR. BAJOREK: They would be required to
account for those in their Appendix K evaluation
model.
DR. KRESS: Okay.
MR. BAJOREK: Okay. We would envision
-- and this would depend on NRR, on how they wanted to
deal with this -- the licensee coming in with
basically an alternative approach to Appendix K, a new
evaluation model, which would have reduced decay heat,
but those Appendix K evaluation models would have to
have features to account for downcomer boiling, fuel
relocation and in the case of small break, the issues
that we would have to identify for that.
MR. BONACA: More and more that would look
like the best estimate.
MR. BAJOREK: Well, we're -- you're
jumping ahead just a little bit, but I want to let
-- what I want to say. I want to lay this out because
as a staff we have not reached a consensus on this.
I want to summarize what we're looking at and lay out
the pros and cons of each one.
And you raise a good point and we're going
to point that out. Now, one of the obstacles we see,
that this approach would result in a new methodology
and we think that it would be very likely that it
would require a review.
NRR would have to expend resources for
vendors. The licensees would have to deal with these
issues. They aren't straightforward and simple to
deal with. They would have to come up with new models
for those.
In some cases, experimental information to
address those may not be entirely satisfactory right
now. There's some 2D/3D data, UPTF, CCTF, that points
out the effect. I think it's questionable right now
whether it has the right range of conditions by which
you might want to develop a new model for.
So I think there are some questions there
that need to be answered and we are going to take a
look at that. We have to come up with a list of all
recognized non-conservatisms. We have a few.
I guess our fear is once we get this list,
if something else crops up or is recognized, there's
a difficulty in getting it in, okay, without violating
some type of a back-fit rule that we might want to
keep on ourself.
Because of the difficulty in coming up
with new models, licensing those and dealing with the
potential uncertainties in the remaining models, we
start to think that this may not be that attractive to
vendors and licensees.
Our fear is that when you start to look at
expenses to come up with this, make Appendix K look
more realistic, but still be conservative, deal with
modeling uncertainties, you start to tip the balance
close enough to best estimate, there may not be an
advantage to going this way right now.
On a philosophical point, one of the
stones that we would throw at this option is that this
would effectively delay the transition from codes that
were developed in the '60s and early '70s to more
modern thermal-hydraulics codes.
Okay. We would be instituting codes that
people have objected to because of their ad hoc models
and implications in the past. The second option is
one that has been suggested by NRR.
It retains many of the features of
Appendix K -- excuse me -- of Option A that we talked
about. We would still deal with Reg. Guide 1.157 as
we had in the previous overhead.
The idea here is to replace Appendix K,
take out the '71 model, replace it with '94, and apply
a conservative multiplier, not one that just accounts
for uncertainties in decay heat, but now has
additional conservatism built in, but sufficient to
cover the uncertainties that are observed in the
realistic calculations.
DR. KRESS: That sounds just like the
current Appendix K, only with a little better
quantification.
MR. LAUBEN: Right.
MR. BAJOREK: That's pretty much it.
CHAIRMAN SHACK: Well, and to come up with
the right multiplier you still have --
DR. KRESS: Yes.
CHAIRMAN SHACK: -- to do everything they
do.
DR. KRESS: You really have to do the --
CHAIRMAN SHACK: I mean, it's magic when
you're done, but --
MR. BONACA: It's one added superficiality
--
(All talking at once)
MR. LAUBEN: A lot of print.
MR. BAJOREK: It's a tough row to hoe.
CHAIRMAN SHACK: Yes.
MR. BAJOREK: Jump ahead on here. If we
were to do this, our estimate is that this would take
the staff something on the order of ten man years,
because we would need to, one, make sure that we get
realistic codes behaving the way we want to.
We're fairly close on that. We still have
work to do. But we need to satisfy ourselves that
they're handling fuel relocation, downcomer boiling
appropriately. Okay. That's an issue in itself.
In the past, we haven't developed
evaluation models here at the staff. So we would have
to take our realistic code, revise it, change the
decay heat, put Baker-Just back in, prevent rewet
during blowdown, change the steam cooling models,
change this and the other thing to make it mimic an
evaluation model.
DR. KRESS: Let me ask you another
question about that. If you did that, including the
uncertainties, and then you ended up with your answer
at the end, and you took the 95 percentile and used
that to get your multiplier on your decay heat curve,
how is that any different at all than just the best
estimate approach?
MR. BAJOREK: You would not know what the
uncertainties are here. You would be basing your
conclusions based on another set of calculations and
hoping those are mimicked by the Appendix K evaluation
model. Where things --
DR. KRESS: But you would have to make
Appendix K conservatism enough to cover all plants is
what --
MR. BAJOREK: That's right.
DR. KRESS: -- I think you're saying.
MR. BAJOREK: We jumped ahead.
DR. KRESS: Yes.
MR. BAJOREK: Where we say it may not be
technically achievable is that if we do this strictly
as it was proposed, come up with a multiplier. Well,
we could look at the worst plant.
DR. KRESS: Yes.
MR. BAJOREK: Like that one I showed you
earlier that has a very long transient.
DR. KRESS: Yes.
MR. BAJOREK: Treat it as an evaluation
model, put a multiplier on it; look at some other
issues, things that we might want. Well, I don't
think it takes a big stretch of the imagination to see
that you can wind up with a multiplier based on that
plant that when you apply it to lower power units
you're going to have something that's even more
restrictive than the Appendix K as it is today.
DR. KRESS: Yes. I am --
MR. BAJOREK: I'm aware of one attempt,
not in this country, to do something like that. Their
approach was to take a realistic code, say we want to
stay away from all this uncertainty calculation, but
let's make our heat transfer conservative.
Let's make our plant initially
conservative and do it for a range of plants. Well,
they want through the exercise and they eventually
went back to a realistic methodology, because the
answers they were getting when they applied them for
all of the units were now even worse than what they
had been getting in Appendix K.
That's where the work comes in, because to
make this any benefit, we think, to industry we would
have to break this down into a plant-specific type of
multiplier.
And when you start looking at the
different types of BWRs, PWRs, BNWs, CE units, large
break and small break, the magnitude of number of
calculations that you have to do and get right becomes
very large, and that's what propagates into this.
I estimated a ten-year effort. I've been
told that I was too low. It's substantial. Go to the
last bullet. One of the reasons we've noticed
downcomer boiling as a potential issue has been due to
plants being uprated.
In that first figure I showed you, the no
harm, no foul, that was primarily due to the
relatively low power of that unit. It quenched before
the downcomer boiled. As we start to uprate the
units, the transient link must get larger because you
have more decay heat, okay, to remain.
So as we start to uprate units beyond what
they are now, the multiplier, even if it captured the
downcomer boiling in today's power levels, may not
necessarily capture that effect if that plant is
uprated by another five or ten percent.
The margin is not going to go unused. It
will likely be absorbed in another power uprating. So
our fear is that even if we came up with multipliers,
they would be invalidated once the plants start to
deviate from the present-day operation.
Also been notified by some of the staff at
NRR, they said, well, even if you come up with
multipliers using TRAC or RELAP in our versions of
evaluation models, we've recognized over the years
that the sensitivity of evaluation models that we see
from Combustion, from Westinghouse, from GE and BNW
aren't necessarily the same from one to the other,
much less how the staff's models would behalf.
They approximate things, but the power
sensitivity could be different. Nodalization can have
effect, as well. So as a result they said, well, even
if you spend your ten staff years coming up with a set
of multipliers, we're still going to have to go back
to the vendors to either verify or come up with
equivalent multipliers for their codes, because they
may behave significantly different.
Okay. Third option, and this is one where
we see it as perhaps an opportunity to move ahead
technically. And we see this as an option that says,
rather than continue to sink more resources into
Appendix K, maybe this is a point to say, let's put
the best technology into the best estimate rule.
Let's put those resources into revising
1.157, clarify how we would use the decay heat; what's
an appropriate way to apply it; what's an appropriate
model for the metal water reaction?
Pursue the other 50.46 risk informed
criteria, because there's a tremendous amount of true
margin that can be gained by relaxing plant boundary
condition assumptions, break size, loss of off-site
power.
But retain in the realistic option of a
way of analyzing it to at least a conservative fashion
or at least to a fashion by which we know what the
true margin is.
So in Option C, by focusing our attention
on the best estimate rule, making it easier to use,
easier to apply, we feel that we'll at least maintain
the present-day margin in Appendix K, okay, and if we
go to a realistic type of calculation we'll know what
that margin is.
I think it's been said in some of the ACRS
meetings that safety is better served by having to
quantify measure of the margin, rather than some
nebulous amount of conservatism that we don't know the
extent of.
We already have clear guidelines for the
review. We would have to clarify those further in the
Reg. Guide 1.157. NRR wouldn't be able to apply their
reviews as they currently perform those. In the long
run, we feel that this would encourage vendors to
continue to develop and use realistic models and more
advanced thermal-hydraulic tools.
Westinghouse currently has an approval for
best estimate. Siemens-Framatome has submitted one
several weeks ago. NRR says that in about a year they
think they can get approval for that. We've been told
that General Electric would be coming in, in a
realistic local methodology early next year.
We're seeing most of the vendors already
going down this path.
MR. BONACA: They already had Safer-
Gester, right, so.
MR. BAJOREK: Safer-Gester, my
understanding is that it's more consistent with an
inter-methodology. There are some -- it's not a true
best estimate and now they're ready to go the rest of
the way.
MR. LAUBEN: It has a 600 degree penalty
associated with its use, too. So it's not truly best
estimate. So it's TRAC-G that they're coming in with
to get approval.
MR. BAJOREK: Now, the cons of doing this.
Reduction in regulatory burden is probably minimal.
There would be benefit in clarification of the best
estimate rule and how you do this, but it's not a
tremendous leap. There's still a lot of work involved
there.
The expectations of SECY-01-133 may not be
met in going this approach. I think you go through
there, there was an expectation that we would make a
definite revision to the Appendix K. So that -- we
would need to make I think a very strong argument on
why we wouldn't think that the Appendix K revision is
necessarily the right way to go as part of supporting
this option.
Where we plan to go from here, we feel
that we need to get a -- agree on a list of non-
conservatisms, lay that out in a little bit better
fashion. We've talked about a few. Let's try to make
that list complete.
We want to go back and look at the
experimental data, because if we have to start asking
people to look at these non-conservatisms, we should
be well aware of whether the current database supports
development of those models.
The reason I suspected we may have a
problem in doing that, I did a kind of a quick scaling
evaluation CCTF. In taking a look at a parameter that
relates the energy that would be available in the
downcomer and core barrel walls, versus the energy
that would be required to raise the entire downcomer
to saturation.
In kind of a very crude fashion, looking
at energy available versus energy that would be
necessary. For the PWR, if you'll look at the energy
that's available in the core barrel in the vessel
wall, it's about seven and a half times the amount of
energy that would be required to raise this bulk of
fluid in the downcomer to saturation.
That's a lot of stored heat. CCTF where
we did see evidence of downcomer boiling -- you don't
have to get the whole thing up to saturation, just
part of it -- we're looking at something closer to
one.
So this is why I said, well, when we look
at the experimental data, we need to take a look at
the tests versus what we were expecting in the PWR,
because when we go down this path now of treating
these non-conservatisms for Options A or B, the folks
who want to go down that are going to have to
demonstrate that the experimental data is adequate to
come up with models for that. That may require them
to participate in new test programs.
Third, once we lay this out it's probably
advisable for us to hold a public meeting to discuss
what this alternative approach to Appendix K would
look like, and I think as someone pointed out, well,
are you getting so close to best estimate now that
you're going to throw a party and no one's going to
show up.
And if we get that word from the vendor
then maybe what's recommended in 0133 should be
revised somewhat. That's all I have, but we're
interested in your comments.
MR. BONACA: You made a case again for the
fact that in Appendix K you have tradeoffs that you
car calling for.
MR. BAJOREK: I couldn't hear you. I'm
sorry.
MR. BONACA: Yes. I'm saying that you
made a case for the fact that there are tradeoffs in
Appendix K right now that are an impediment to simply
moving on to 1994 ANS standard.
MR. BAJOREK: Right.
MR. BONACA: But the industry has
requested it and the way it came out was almost as if
in fact those issues were not there. Is there
consensus on the part of the industry, the technical
community, regarding these tradeoffs, these issues?
Or do you have to go to this public meeting before
that will be surfacing?
MR. BAJOREK: I think we have to go to the
public meeting to really surface that.
Norm, it was the vendors that came to you
last year and pointed some of this out.
MR. LAUBEN: Well, we have -- let's see.
We have the questions that we've -- you know -- they
came with the request for rulemaking. We have
proposed some questions to them about their proposal.
But as Steve said, it isn't clear what
venue it's -- addressing those questions would take.
Would it be a public meeting? Would it be publishing
the questions and then having them respond to it, or
what I think -- I think eventually it has to be some
kind of a public meeting so that all interested
parties get a chance to address their concerns about
this.
So I don't know. Last -- let's see. A
couple of years ago we did ask -- informally now.
This was not formally at all. At some public meetings
we asked questions about, you know, similar to the
ones that I had on decay heat.
How would you -- you know -- this is not
as simple as it was, but we -- at that time there was
no apparent interest in the decay heat change. And so
--
MR. KURITZKY: Yes. I think in all
fairness to the industry and that --
MR. LAUBEN: Yes.
MR. KURITZKY: -- those public meetings
were focused on --
MR. LAUBEN: Right.
MR. KURITZKY: -- on all the different
options.
MR. LAUBEN: Yes, right. Right. Right.
MR. KURITZKY: And industry was really
interested in the larger picture, local redefinitions
--
MR. LAUBEN: Right.
MR. KURITZKY: So they really didn't want
to spend time looking at other types of changes. So.
MR. LAUBEN: Right. So they're interest
in decay heat is relatively -- is subsequent to those
meetings. And I think we have to somehow get, you
know, stakeholder involvement in this, right.
MR. BONACA: The other question I had was,
you made a statement that typically, best estimate
results plus uncertainty, comes quite close to the
Appendix K, and that's the experience I've had, too,
I mean, in looking at that.
And that's -- and of course, the point of
comparison you used was PCT, peak core temperature,
okay. I'm trying to understand if there are other
measures of merit that you're using in these
comparisons to see what is appropriate to make
reductions in what is not.
Or rather than appropriately, what is
convenient or not convenient. Is PCT the only
criteria you use in there to compare the two
approaches and --
MR. BAJOREK: We should probably look at
clad reaction. I think in the shorter transients
usually that the equivalent clad reaction is not as
limiting as PCT. That may not be the case as we get
out to fairly long duration transients. It probably
should get looked at, because we haven't done that
yet.
MR. BONACA: And one last question I have
is, again, I mean, if I have the best estimate, which
typically, I mean, it has certainly conservatism built
in plus uncertainty, and I come up with the results
very close to the Appendix K and typically pretty
close to 2200 degrees fahrenheit, I mean, typically,
these plants don't have a lot of margin there, really,
what is the opportunity for margin reductions or for
reducing regulatory burden?
MR. BAJOREK: It would probably be in --
I think reduction in break size would certainly amount
to --
MR. BONACA: Well, that -- yes, that was
something we didn't want to -- I mean, that's a
different issue, talking about purely that we walk
down this path with the belief that there were
opportunities purely in the artificiality of Appendix
K, but then, you know, this comparison you're
referring to, it's a solid one.
I mean, I've seen it many times for
different plants and it's there.
MR. BAJOREK: Well, I guess, you know,
some of that -- they wouldn't necessarily wind up in
the Reg. Guide -- well, they could wind up in the Reg.
Guide. And when we developed the best estimate for
Westinghouse, in a number of cases the range over
which you addressed the uncertainty bounded all of the
data.
Appendix K doesn't have to do that. You
just have to be conservative relative to the mean. So
what happens when you go to best estimate under that
type of a regulatory requirement, Appendix K really
gets an advantage.
If the Reg. Guide were revised relative to
treatment of the experimental data that you have to
bound 95 percent or within two sigma, and made your
uncertainties smaller, first, you would make it clear
for people developing new pools what they had to come
up with.
And secondly, I think there would be a
fair amount of margin gained by, you know, getting
away from the wings of some of this experimental data.
I can think of several models where you would get a
lot of benefit in taking that approach, but that's
something that would have to come from probably a Reg.
Guide as opposed to a regulation.
That, again, goes back to -- as I
mentioned on that one slide, the problem with 157 is
the discussion and treatment of the uncertainties. It
kind of leaves it too wide open, and if that were
clarified there would probably be a fair amount of
benefit in that.
CHAIRMAN SHACK: I'm not sure I understand
that last argument. Are you just saying you just cut
the uncertainty analysis at the 95th percentile? That
would certainly help.
MR. BAJOREK: I don't have a pen.
MR. BONACA: What you seem to say, that
you have more opportunities in the best estimate than
you have in Appendix K, of course.
MR. LAUBEN: Here's one that works on
slides.
DR. KRESS: Just do it on the screen.
(Laughter)
MR. BAJOREK: Are you telling me to?
DR. POWERS: He's hoping somebody else
will to --
DR. KRESS: Yes.
MR. BONACA: To be the second.
DR. KRESS: I hate to be the only idiot in
the crowd.
MR. BAJOREK: If we take a look at an
uncertainty distribution in some model, we may see
some bias away from perfection. We've got everything
on here. But we also see a scatter in how well you
get a prediction to the experimental measurement. It
may take some distribution.
Well, if you want to range the uncertainty
for that model, well, you have to make a decision, do
I range it over best to worst, or do I say, hey, I
don't necessarily have to address the wings out in
here.
Most specifically, can I get away from
some of these worst situations? And in the
calculations that I see, what drives your 95th
percentile PCT frequently comes from this part of the
distribution, then an experimentalist may say it's a
bit of an outlier and isn't representative of the bulk
of the data.
But right now, the Reg. Guide is not very
clear on where you draw that limit.
DR. KRESS: Well, it looks to me like
there's not a very lot to be gained by changing the
Appendix K part of the rule. It looks like what we
didn't know before was that the non-conservatisms were
pretty much balanced out by the conservatisms.
And you know, that's -- you maybe don't
have them all quantified exactly right, but it's a
good guess that it's getting close.
MR. BAJOREK: Whoever picked out the
1.2 --
DR. KRESS: Yes, did a pretty good job.
MR. BAJOREK: -- did a pretty good job.
DR. KRESS: Yes. So since it would be a
big deal to change it and you have to worry about
back-fits, I guess, because it could require some
plants to redo their analysis and do things over, my
leaning right now is for your Option C.
But I would encourage you to continue on
with this action plan, because it does two things for
you. One, it bolsters your case because it does give
you a better look at what these non-conservatisms are
compared to conservatism, and it gives you information
that could be very insightful when you go into
evaluating the best estimate models.
MR. BAJOREK: Right.
DR. KRESS: So that's kind of my
inclination right now. I don't know how these other
guys feel about it.
MR. BONACA: Absolutely. I totally agree
with that. It seems to me Option C is the one that
has some opportunities.
CHAIRMAN SHACK: Well, clearly, there's a
difference of opinion, because somebody submitted a
petition to change it. So --
MR. BAJOREK: Yes.
DR. KRESS: Yes, but weren't they mostly
interested in changing the large break LOCA definition
in that? Or did they want --
MR. LAUBEN: No. No. I mean, this
petition is strictly for the decay heat.
MR. BAJOREK: Strictly decay heat.
MR. BONACA: Well, that's why I asked the
question about the technical community, because I
mean, the case you made today would discourage a
change without your investigation of this -- and you
have data that says that in fact you have -- you may
not be able to support the intention of that
multiplier literally.
DR. KRESS: And anyway, you have the best
estimate option which --
MR. LAUBEN: Right.
DR. KRESS: -- let's them do what --
MR. BAJOREK: It's there, now.
DR. KRESS: It's there now.
MR. BAJOREK: It's there now. It's not
clear and there are things that could be done to make
it perhaps less onerous.
DR. KRESS: Yes. You have -- yes. That
might be the place to focus your attention, I think.
MR. BONACA: I mean, any use of these
changes would require a new analysis, anyway.
MR. BAJOREK: Yes.
MR. BONACA: And you know, Appendix K may
be less expensive one. I don't know.
MR. BAJOREK: Generally, it is.
CHAIRMAN SHACK: Well, I guess just to
follow along here.
MR. BAJOREK: Okay.
CHAIRMAN SHACK: I guess it seems to me we
have realistic analyses, you know. People can make
comparisons, you know. Your case is reasonably
convincing in terms of discussion, you know, but I
just have to see more of these comparisons.
Now, Mario says he's looked at them and,
you know, they're there, but it seems to me that
really is the thing. You have best estimate
estimates. You have other estimate you can really get
a much more concrete comparison of what the effect
would be.
MS. DROUIN: I was going to say, Steve
covered the evaluation model. We now have the
acceptance criteria. I did notice, though, that on
the agenda you had a break at this point, whether you
want us to go ahead and get into the acceptance
criteria, or do you want to take a break now?
CHAIRMAN SHACK: Ralph's discussion looks
reasonably short. I think I'd just as soon keep on
going and then take the break.
MR. MEYER: Looks short, but the
discussion may be -- looks short, but may be
deceptive. All of the discussion so far has been on
analytical methods for calculating the peak cladding
temperature which are laid out in Appendix K.
There are in fact five acceptance criteria
specified in 50.46, not just peak cladding
temperature. These are the speed limits, so to speak,
and they are listed here on this slide.
The objective in examining the acceptance
criteria in 50.46 for possible modification is to see
if we can remove some or all of the prescriptive
nature of these criteria, which are related
specifically to zircaloy cladding and to ZIRLO, which
are written into the present rule, and take them out
so that the rule could apply generally to any
zirconium-based alloy that's used for fuel rod
cladding.
I think that this can be done simply by
removing number 2 on this list, the maximum cladding
oxidation, which is specified at 17 percent, and I
want to discuss that. So I have in fact just one
option here.
It's either do it or don't do it. You
could, I guess, make some variations on this, but this
seems like a logical approach, relatively simple in
procedure, that would solve the problem.
DR. KRESS: What does it change, Ralph?
MR. MEYER: What?
DR. KRESS: It just changes the -- it's a
perceptions change.
MR. MEYER: What you would do here is to
take the 17 percent equivalent cladding reactive limit
out of 50.46 and replace it with a performance-based
requirement that says simply that you should retain
some post-quench ductility in the cladding.
DR. KRESS: Yes, but isn't the 17 percent
a surrogate for that?
MR. MEYER: That's -- well, 17 percent was
a measure of that for zircaloy.
DR. KRESS: I see. It may not be the same
surrogate for other things.
MR. MEYER: That's correct. It may not be
the same, for example, for M-5. Even ZIRLO wasn't
tested carefully against this limit, although the rule
was changed to include it.
DR. KRESS: And if you made the change,
the licensee would have to come in, if you had a
different clad, and show you the database.
MR. MEYER: That's correct; that's
correct.
DR. KRESS: I think that'd be a good
change. That would clarify a lot of things.
MR. MEYER: Yes. Most of this is on the
next slide, but before you move to the next slide,
let's --
DR. POWERS: Before we get too excited
about making this change.
MR. MEYER: Yes.
DR. POWERS: What you want to do is to
preserve some ductility so that you can cool this core
and keep it cool and not have it fall apart on you.
MR. MEYER: Right.
DR. POWERS: We test for ductility in a
variety of fashions and we get different results when
we test in different ways.
MR. MEYER: Yes.
DR. POWERS: How do we know that the test
that we propose to use for ductility is the one that's
applicable for the core and the post-quench
environment?
MR. MEYER: Could you say a little more so
I understand what's in your mind a little better?
DR. POWERS: Okay. What I know is if you
test it one way it says there's lots of ductility.
Test it a different way there's not so much ductility,
okay. That's laboratory tests of remaining ductility.
Okay. Now, what we want to have is the
core not fall apart after we have gone through the ECS
injection or something like that and we've got
-- everything's cooled down, and it doesn't because
there's some ductility there.
How do we know that the ductility we
derive from whatever test we endorse is ductility that
actually exists in the clad under the conditions of
the post-quench environment?
MR. MEYER: Well, the -- first of all, the
testing that was done back in the early '70s and late
'60s was in fact done under a post-quench environment.
That is, the cladding pieces were taken through a
high-temperature steam oxidation.
They were cooled down. They were quenched
and then they were tested at a relatively low
temperature. And there -- while it's true that you
could use other methods than the ring compression
method that was used back in the '70s, and there would
be some scatter in the result, from reviewing what had
been done earlier, it still appears to be a reasonable
approach.
And in fact, we are at the present time in
an ad hoc expert group that has participation from a
number of international groups. We are exploring
several different test methods for determining
ductility.
All you're trying to do here is to have a
screening test where you can differentiate between
fully brittle material and material that has some
residual ductility. From what I've seen so far, I
think the ring compression test will continue to be a
good way of doing this.
You can do it with a hardness indentation.
You could do it with some sort of plastic extrusion
method of providing the loading on the rings. But
it's materials property, and basically, any way you
test it except for some variations introduced by the
testing method, you're going to get about the same
answer.
So I guess the answer to your question is,
we are aware of the concern about the appropriateness
of the test. We have an effort underway to see if
some other procedure would be better than the one that
was used in the early '70s.
At the present time the general
configuration of ring compression test still appears
to be a good approach, and the details of the test
method that would be used for this would be laid out
in a regulatory guide.
And I guess we can just -- you're jumping
to the bottom line here and going --
CHAIRMAN SHACK: Going at it a different
way because I think Dana's coming from -- there's two
problems here. One, given a given temperature strain
history I end up with a certain condition of cladding,
and to determine the ductility --
MR. MEYER: Yes.
CHAIRMAN SHACK: -- then it really is an
experimental problem of what is the right test.
MR. MEYER: Right. Right.
CHAIRMAN SHACK: And that's one we can
address.
MR. MEYER: Yes.
CHAIRMAN SHACK: I think in a fairly
straightforward way. I think Dana's concern is with
temperature strain history you put the clad through --
MR. MEYER: Oh. Oh. Oh. Okay.
CHAIRMAN SHACK: -- before you get to the
test.
MR. MEYER: Okay. Okay. Well, we're also
poking into that and the way -- we haven't completed
this, and you'll see that the last column on this
second slide here is that we will not have done enough
work to actually put this thing through a -- its paces
for one or two more years because we haven't finished
the work yet.
But we know pretty much now how this would
play out. You would use a temperature -- you would
simulate the several of the high-temperature LOCA
transients. You would have a slow temperature rise up
to some temperature at which you would soak it for a
period of time to accumulate the oxidation.
You would cool it at some steam cooling
rate. I forget the number, but I think it's on the
order of five or ten degrees a second, down to 800
degrees centigrade, at which point you would then
flood it and quench it.
And we are exploring the effect of
different heating and cooling rates and the effect of
different temperatures at which you hold the specimen.
And it's likely that one would want to prescribe tests
at a series of temperatures, not just at a single
temperature, up to and including the peak cladding
temperature of 2200 fahrenheit, which is 1200, 1204
degrees centigrade.
And so we are doing those kind of tests in
the near future on a high burnup cladding and the
archive under-radiated fresh material that corresponds
to that to try and map out what these effects are and
what would be the best rates and temperatures to
conduct this temperature history for the ductility
test.
So that would all be set out in the
Regulatory Guide. Now, in the relatively near term we
could set out in a draft guide the conditions that we
in fact are planning to use in the laboratory.
But if you rush this through before we're
able to actually do those tests in the laboratory and
see if the result appears satisfactory, then you run
the risk that we might have to change something.
MR. MEYER: Now, there is -- may I move to
another point? There is one thing that I wanted to
emphasize here, and that is that the peak cladding
temperature of 2200 degrees and the cladding oxidation
limit of 17 percent really arose as a pair of numbers
originally, and these both came from these ductility
tests, the ring compression tests.
The 17 percent -- okay. So you have some
flexibility if you want to move away from these
precise numbers you could say, well, let's work with
2300 degrees fahrenheit and maybe we would get 15
percent for zircaloy.
So there would be some flexibility in
working with both of those numbers, but you'll notice
that I've suggested that we keep the 2200 degree
fahrenheit number, and I've suggested that for what I
think is a good reason.
And that is during the ECCS hearing this
was the most contentious part of the debate about the
acceptance criteria. And in fact, a second line of
concern was raised about the peak cladding
temperature, and that had to do with rapid oxidation
at higher temperatures.
And so the Commission reached a decision
to limit the temperature a relatively low value so
that you didn't have the concern of rapid oxidation.
And at the same time it fit in with the -- with
Hobson's ring compression test data on the ductility.
And so I think that if you were to alter
that temperature that you would probably open this up
to a lot of contention. And I don't believe there's
a need to change that because we can work with that as
a fixed number, and then let the maximum cladding
oxidation figure vary in order to capture the effects
of both cladding alloy variations and burnup effects.
And so it might go up or it might go down.
And it might be different for high burnup, low burnup,
different cladding alloys. And so you pull that out.
You put it into a Regulatory Guide. Everything else
can stay fixed and then the -- in 50.46.
And the 50.46 would not be pegged to
zircaloy or ZIRLO and could be used for all zirconium
based alloys.
CHAIRMAN SHACK: Why not just pull them
out to the Reg. Guide?
MR. MEYER: Well, you could --
CHAIRMAN SHACK: Use the coolable geometry
and the long-term cooling as the fundamental
requirements, which they really are.
MR. MEYER: Yes.
CHAIRMAN SHACK: And then how you assure
that, put that in the Reg. Guide because if you get
new data some day --
MR. MEYER: Well, you could do that. I
think that you would also need to address the question
of rapid oxidation at higher temperatures. And to me
this would open up the possibility of litigation
unnecessarily.
There's no reason that we couldn't work
with that 2200 figure on the embrittlement criteria.
Leave it fixed. It was, you know, a hard fought
number in the beginning and it does not cause, as far
as I can see, any problems with the technical adequacy
of an embrittlement criterion that you would derive
with that as a fixed number, because you've got two
parameters to work with. So we can do it all with the
other one.
CHAIRMAN SHACK: It's just that, you know,
you don't really have the database on M-5 or even
ZIRLO. I'm not sure that people were worried about it
as much.
MR. MEYER: No. It hasn't been worried
about too much in the past, but we're worrying about
it now. And in fact, just for your interest, I could
say that we've made excellent progress in our
discussions with Framatome about an agreement to begin
testing their M-5 cladding.
And we're now down to the point of some
legal language in a memorandum of understanding with
all the basic issues having been agreed upon between
us and Framatome. So I think the time is coming soon
that we will begin to test, first, the Framatome M-5
cladding on irradiated material at first, and then
hopefully, Westinghouse, their low cladding, although
those negotiations are simply on hold waiting the
outcome of the negotiations with Framatome.
DR. KRESS: You're fairly confident,
though, that the 2200 will keep you below a runaway
oxidation.
MR. MEYER: Yes.
DR. KRESS: That's well enough below it
that it's safe.
MR. MEYER: Yes. I'm not aware of
anything that would be significantly altered by making
these small alloy changes. I mean, it's still based
--
DR. KRESS: Just not enough that has
changed.
MR. MEYER: -- and zirconium and zirconium
oxide.
CHAIRMAN SHACK: I mean, 2200 is more than
runaway oxidation. It really is sort of oxygen pickup
that --
MR. MEYER: Sure. 2200 first of all is
part of the embrittlement criteria.
CHAIRMAN SHACK: Yes.
MR. MEYER: And how it came about -- put
my backup slide. I've got my backup slide to make me
look smart here. When you ran a piece of zircaloy
cladding through a high temperature transient and
brought it back down, if you -- you're looking at the
outer surface on the left and the inner surface on the
right, it went through a phase change.
It was hexagonal close-packed in its alpha
phase at normal temperatures. And some of it changed
to a body center cubic structure at high temperatures,
and then you quenched it and brought it back down.
And you could tell what had been body
center cubic and it turns out that the body center
cubic phase is the one that provides your strength and
ductility. And so what you really are interested in
is maintaining a ductile prior beta region in the
cladding.
And the gross amount of oxidation
correlated pretty well with the thickness of a ductile
prior beta layer. Above 1200 degrees centigrade, 2200
degrees fahrenheit, you've got additional oxygen
diffusion into this prior beta region that pretty much
upset that handy little correlation.
And so that was the reason that you didn't
go above 1200 degrees centigrade, because your use of
gross oxidation as a surrogate for this one layer fell
apart. Now, you could deal with that by backing down
the total amount of oxidation in say 15 percent or 14
percent, and let the temperature go up.
But the Commission did not do that. They
stuck with that number and then they said, and by the
way, we don't want to make it any higher because there
is this consideration of rapid oxidation at higher
temperatures and we don't have much information on
that.
And it was a huge -- that was a huge part
of the hearing. It was a huge part of the Commission
opinion, and it seems like the sensible thing to do is
to leave it alone and to work with the oxidation
thickness for the embrittlement criteria.
CHAIRMAN SHACK: Any additional questions
for Ralph? If there are none, this seems like a good
place for a break and I suggest we come back at 11:05.
(Whereupon, a recess was taken
at 10:48 a.m. until 11:09 a.m.)
CHAIRMAN SHACK: So in that quandary, we
can start again.
MS. DROUIN: Okay. He has it on. It's
not working.
CHAIRMAN SHACK: Time to change bulbs.
(Pause)
MS. DROUIN: Okay. We just have one slide
here to bring in the status of what's happening on the
rulemaking side with NRR. Unfortunately, Sam Lee
couldn't be here today. There was a petition that was
sent in, in September by NEI.
The primary purpose was, as we saw with
50.44, if there's a part that can be -- that appears
to be -- that can -- that appears -- man, I just can't
get these words out of my mouth -- that can be
separated out and move on a faster track, they like to
see that be done that way.
And so they have submitted a petition to
separate out the decay heat part and put that on a
faster track and make a separate rulemaking activity
out of that. We had noted in our SECY that all of
these things could be one rulemaking or several
rulemakings, and that would be decided as we move
forward.
But in their particular petition, you
know, it would allow the licensees optional adoption
of the latest standard and allow adoption by the
licensees of any subsequent revisions to the standards
that are endorsed by the NRC as we go forward in time.
Right now, the staff is currently
evaluating the petition. It's in the normal process.
Okay. Now, today so far we have talked about the
status on the evaluation criteria and the evaluation
model.
Those were two very important parts
because we are right now deviating on the
recommendations that we had made on the evaluation
criteria and the evaluation model. We had made one
set of recommendations, and now, as we move forward in
the technical work we are now proposing somewhat
different things.
On the reliability part, we've still got
a lot more work to do here, and as we've seen in the
criteria in the evaluation, we're coming up against
some technical issues that we had not anticipated. So
with that, I'll turn it over to Alan.
MR. KURITZKY: Okay. As Mary said, the
previous discussion dealt with the proposed changes in
SECY 133 dealing with the ECCS evaluation model and
the acceptance criteria.
We also proposed changes in the near-term
to the reliability requirements, particularly those
that are included in, you know, GDC 35, dealing with
the loss of off-site power requirement and also the
single failure criterion.
In the SECY what we recommended was a
risk-informed alternative to those ECCS reliability
requirements. The idea was that we would replace the
existing requirements of GDC 35 with requirements that
were more risk-informed and more realistic.
Particularly, we would be deleting the --
oh, we'll call it the requirements or the assumption
that you have a loss of off-site power when you have
a LOCA, and also the need to model the single worst
additional failure.
Instead, we would be offering two
performance-based options that would get at -- that
would help assure ECCS reliability. A first option
would be a generic -- would be something that was done
in a generic fashion by plant type that the NRC staff
would do ahead of the game.
We would put together, we would define by
plant group or plant type what minimum ECCS equipment
would be required for that group or type, and we would
-- that would also include whether or not you need to
consider the loss of off-site power for -- to prevent
accidents.
And the equipment requirements themselves
would be tied to different groups of accidents. You
may have one set for large LOCA ones and for small
LOCA, et cetera. The idea under Option 1 is that's
something that the NRC staff would do ahead of time so
that if a licensee wanted to implement it they would
not have to do any technical analysis.
It would be pretty much cut and dried.
They can choose to go with it. They don't have to do
any analysis and nor does -- do any review, and it's
-- it'll go quickly.
However, if a licensee decides that they
feel they are not getting as much unnecessary burden
reduction as they feel they could get, you know, doing
a more detailed analysis, a more plant-specific
analysis, they don't like the group they're in, they
feel some bad actor was dragging their group down,
they will have the option to go ahead and do a plant-
specific analysis and that will be based on guidance
that we would include in a Regulatory Guide.
We would give them an ECCS function
reliability threshold that would be derived from,
well, what we're envisioning is probably something
derived from the core damage frequency threshold
that's in our framework, our Option 3 framework, the
qualitative guidelines we have there.
And then the licensee would go through and
do analysis using their own data, you know, whatever
analysis they want to do analysis mix they want, their
own PRA, and try and justify some -- they would have
to meet some reliability threshold for the ECCS
function, and it could be with whatever equipment they
have at their plant, whatever set they feel is
necessary.
And again, that would also cover whether
or not they would need to consider the simultaneous
loss of off-site power assumption for different acts
and classes. To kind of explain that a little bit
better I have -- this just shows you the --
CHAIRMAN SHACK: Now, your own Reg. Guide
would also give them some way to calculate LOCA
frequencies, right?
MR. KURITZKY: Well, what the Reg. Guide
wold do would give them guidance on LOCA frequencies,
exactly. That's going to be one of the main things.
You'll see as we get to the technical issues, that's
one of the main things we are still wrestling with.
But that's -- yes, you're right. It would give them
guidance or --
CHAIRMAN SHACK: Or a set of numbers or
something.
MR. KURITZKY: Yes. It could give them a
set of numbers or it could --
THE REPORTER: Excuse me. Would you pull
your microphone up.
MR. KURITZKY: It can give you -- it would
give you a set of numbers or it could tell you things
you have to consider when you want to calculate your
own numbers. They say that latter part about things
you have to consider, some of that stuff may have to,
you know, I don't know whether it's something we'll do
now in the short-term, whether it's something that
would have to wait till we get to the long-term thing
of looking at the spectrum of LOCAs.
Just to kind of clarify a little bit about
what we're looking at from coming from these two
options, for Option 1 we're envisioning that we would
have matrices that we have produced, and the matrices
would have plan group or plan type along one side.
You know, it'd have different acts and
classes along the other side. And it would delineate
what minimum system requirements you would have or
equipment requirements you would have for the ECCS
function.
And these -- the purpose of specifying
that equipment is if a plant finds out that they have
more equipment than the minimum required, it would
give them fuel or additional justification for making
some kind of operational relaxation, whether it be in
technical specifications or whether or not it would
allow some kind of design change.
That would be up to us to decide, you
know, the NRR to decide in the implementation phase.
But in addition, there would be a second matrix that
would identify the actual sections that are used in
the ECCS thermal-hydraulic performance calculations.
And specifically, it's the GDC-35
requirements of the single additional -- single worst
additional failure, and considering both with or
without off-site power available.
This matrix would again be the same thing,
plant type and accident type on the other side, and it
would specify whether or not you do need to consider
a loss of -- a conditional or a current loss of off-
site power with that particular accident class, and
also whether or not -- what failures you'd need to
consider.
It could be a single failure. It could be
multiple failures. It would also allow you to address
passive failures. It would give us the opportunity to
finally try and resolve the footnote that's been in
Appendix A to Part 50 for -- since I was a small boy,
because all that would fall into this reliability
threshold. And so --
DR. POWERS: It seems to me that the
assumption is the ECCS requirements right now were
installed in response to the possibility of some
stochastic event during normal operations, and you're
trying to address that. That doesn't seem to me,
then, to span the entire spectrum of reasons for
having an ECCS.
MR. KURITZKY: Well, as far as I
understand, the ECCS -- we're looking at all the
different types of acts and issues that you could have
at the plant.
DR. POWERS: No, you're not. You're not
looking at all of them. You're not looking at any
kind of sabotage. You're not looking at any kind of
external threat whatsoever here.
MR. KURITZKY: External threat. You're
referring to a sabotage threat or external events like
seismic activity?
DR. POWERS: Clearly, I'm talking about
sabotage.
MR. KURITZKY: Sabotage, yes. Yes.
Sabotage isn't --
DR. POWERS: Well, doesn't that -- I mean,
doesn't that make you -- I mean, why can you exclude
that?
MR. KURITZKY: That's an interesting
question. I mean, as I understand it -- I'm not privy
to all that's going on in the Agency on that topic.
There's a lot of work going on there and that's going
to impact -- I assume that's going to impact a lot of
the work that the Agency does.
It can impact a lot of the regulations.
I don't know how that's all going to fall out. I
would say I wouldn't want to hold up everything else
waiting to see how that falls out. So what we're
going to do is based on current risk insights.
And unfortunately, as we all know, they do
include sabotage as an initiator. I mean, it does not
include sabotage is -- that's my answer.
DR. POWERS: I mean, it seems to me that
until you can establish that the only reason we have
any CTS in each plant is for stochastic events that
are covered by the PRA kinds of analyses, you can't go
around doing this.
MR. KURITZKY: Well, I don't know. I
guess my opinion is that I don't necessarily agree
with that. I feel that we have enough knowledge that
we can propose some changes based on what we feel are
reasonable events.
I think you make a good point and that's
one thing that just has been kind of overlooked by
PRAs, and it's not a question of something that's
overlooked because of the frequency is so low, which
we can make some probabilistic argument why we don't
need to worry about it, but it's one that obviously we
can't make that argument about. I guess that may be,
you know, policy --
MS. DROUIN: I'm confused by your -- I
wasn't even sure what your question was in all of that
data. But what I'm more confused by is your concern
doesn't seem to be addressed by the current set of the
way the regulation is written right now anyway.
DR. POWERS: Why not?
MS. FAIRBANKS: I guess if I can
interrupt, I was going to say that later when I had a
slide come up that we were going to be providing from
our branch some support to PRAB. And one of the
things that we were trying to look at, too, was some
of these indirect causes.
And we had actually considered potentially
sabotage or maybe that would be the subset of
something like an indirect crane hit to piping, which
could cause a large break LOCA. But to fully risk
inform --
DR. POWERS: Well, I think you -- I mean,
I don't think there's an analogy, a good analogy
there, because one of the reasons for saying -- you
got a large break LOCA and a simultaneous loss of
power, it is clearly a, gee, this is a deliberate
sabotage event and I want to be able to respond to
that with my system.
And I don't think you can do both of them
with a stochastic event. I mean, that's why he's
interested in dropping out the simultaneity, because
it's hard to come up with a finite, nonvanishing
probability, is to have both at the same time. But
you can when you come to sabotage.
MS. FAIRBANKS: Yes, you're right.
MS. DROUIN: If you give the sabotage a
probability of 1.0 -- the frequency --
DR. POWERS: No, I don't think I have to
do that. I have to say that in any event even those
of a vanishingly small probability can in fact occur,
and if they do occur I want something to protect me.
MS. DROUIN: So regardless of how small
the occurrence is, I mean, to me that's not being
risk-informed, and that's where we are right now. We
have two events there that are extremely low
frequency.
MR. KURITZKY: And I think also in the
off-site thought, Mary's point is that -- or to
address more your question, Dr. Powers, is that the
-- if we do make some of these changes, it does not
mean that -- you mentioned you'd like to have
something to protect you in case that event does
occur.
And it's not that these changes that we're
going to make here are necessarily going to strip away
all that protection. Your reliability may be somewhat
reduced, but it doesn't strip that away.
So then it's the question of that
reliability times the probability or the frequency of
a sabotage event that results in the loss of off-site
power and large break LOCA, plus your residual
mitigated capability, is that frequency -- previously
something that gives us heartburn in that -- without
a quantification of sabotage frequency, I can't say
one way or the other.
DR. POWERS: I guess I'm wondering if
suppose somebody even figured out how to calculate the
sabotage frequency, would I want to give up that
protection?
MR. KURITZKY: Well, what protection
specifically are you giving up?
DR. POWERS: Be able to cool the core.
MR. KURITZKY: Well, what I'm saying, I
don't envision that what we would be changing would
necessarily give up your ability to cool the core.
DR. POWERS: I am --
MR. KURITZKY: You still have low pressure
injection pumps that are most likely going to be on
the -- so it's not -- you know -- there is a
mitigative capability remaining in the plant.
MR. BONACA: I think this is somewhat of
a broader issue of how the -- you know -- the issue of
security has always been dealt with. I think that the
fact that there is a security has always been
eliminating consideration of sabotage as initiator for
this.
I mean, it's an issue but it's broader
than this specific one, I think.
MR. MARKLEY: I think the point here that
you're driving toward is that it was built on internal
threats.
MR. BONACA: Right.
MR. MARKLEY: And not external threats.
MR. BONACA: Correct.
MR. KURITZKY: Okay. So as I was
mentioning, we have these two types of matrices that
would really -- that we're looking at, we're
envisioning would come from this: the one we
specified with the minimum equipment, ECCS equipment
that the plant -- or plant type or plant group would
have to have for each different type of accident
initiator category.
And the second matrix would specify the
assumptions, failure assumptions to be used in doing
the thermal-hydraulic calculations by the types of
failures we'd have to consider, and also what
equipment -- also whether or not you'd have loss of
off-site power or not.
For Option 2 we would be producing a
Regulatory Guide. I guess I should have used the
words "contain the requirements," since there are
requirements, but I guess it would provide the
guidance to licensees for performing a plant's
specific analysis like I had discussed previously
where they would essentially be going through the same
things that we're going to be going through, trying to
come up with the option on matrices.
The same issue that we are going to
wrestle with we would have to lay out in that
Regulatory Guide, at least to get to know how -- at
least one way that we would approve them in doing the
analysis.
And that would allow them, like I said
before, to try and get additional margin or additional
unnecessary burden reduction if they feel that the
first option didn't give them -- or didn't get them
where they wanted to go.
CHAIRMAN SHACK: Now, what -- you know,
when we redo this, what changes do you see the
licensees actually making in response to this? Is it
tech spec requirements on the --
MR. KURITZKY: I think one thing is
probably tech spec requirements; allowed outage times,
maybe some relaxation of allowed outage times. I
think the LOCA/LOOP assumption may allow them to
extend the -- or relax the diesel generator start time
that -- the tech spec requirements for the ten-second
diesel start time.
Those are the two main things that I can
envision, relaxation of tech specs which includes, of
course, the diesel start time. What's not clear is
that if they are -- if they can do the calculation to
show that they can extend the diesel start time,
whether they would in fact push for a change on that
start time or allow the diesels to start later, or
whether or not they would just keep that margin for
some other usage or find that margin for some other
usage.
But that would be up to the licensees to
decide. So we will just have to make sure that
whatever that chance could entail, we're happy with
that they would do with it.
MS. DROUIN: You go back to the issues and
when we come back if they want to hear about that.
(Pause)
MS. DROUIN: We were going to skip the
next slide in and get into -- because it just seems to
go more along better with the discussion -- the issues
that we're encountering.
MR. KURITZKY: It's off the slide 13.
Okay. In doing the technical work and pursuing the
technical work since we submitted the paper, SECY 133,
we have encountered a number of issues that we have to
wrestle with, technical issues, implementation issues.
We're also looking out for policy issues.
Some of the issues may border or be on some fine line
between technical and policy. But right now we have
a quite a long list, maybe 20, 30 issues that we've
come up against.
Some of them were relatively easy to
resolve and we've already resolved them internally, or
have those resolutions to them internally. Others we
still are wrestling with. We'll require more broad-
based discussions and probably public stakeholder
input.
And certainly, we welcome and one of the
purposes of this meeting is to get ACRS input on some
of these issues. The three of them that I have listed
on this slide are three of the more important ones
that we're wrestling with.
The first one we all were just starting to
discuss a little while ago was the LOCA scope and
frequency. We are planning -- or at least at this
point the most up-to-date column, state of the art
LOCA frequency numbers are in NUREG CR 57.50, and
that's our starting point for getting LOCA frequencies
for this effort.
However, the new NUREG CR 57.50 LOCA
frequencies are just for pipe break LOCAs. They don't
consider nonpipe break failure methods, such as steam
generator man-way, or heavy load drops.
So we have to determine some way to
include those other types of LOCA initiators or LOCA
causes into our calculations. In addition, we need to
address the methodology in NUREG CR 57.50. We need to
determine whether or not it adequately addresses aging
effects and other unknown -- mechanisms that may show
up sometime in the future that would serve to
undermine the service data that is the basis for the
NUREG 57.50 numbers.
We are planning to have meetings with
contractors from the engineering folks, the
probabilistic factual mechanics experts meeting with
people involved with NUREG 57.50 to try and internally
come up with something that may be acceptable to all
parties, at which point we also want to go out to the
public and get their input on how we're going to
address the LOCA frequencies.
And obviously, it's a big driver. It's
going to drive both pieces that I was talking about
previously, the LOCA/LOOP and the reliability. Both
-- the LOCA frequency is a parameter in the equation
for both of them.
So it's obviously a very important issue
that we need to come to some resolution on. Another
issue that's very important that we need to resolve
deals with the conditional loss off-site power
probability given a LOCA, going to that LOCA/LOOP
assumption.
And unfortunately -- but fortunately,
there is no data on LOCA/LOOPs. We're happy about
that, but as analysts it makes it a little trickier.
We have, instead, had to use as surrogates for an
actual loss of off-site power conditional on LOCA,
we've had to use just regular reactor trip events, and
also, ECCS actuations.
Now, ECCS actuations more closely resemble
the conditions you would have, at least electrically,
electrical load-wise, from a LOCA. However, again,
there's very few ECCS actuation events.
There's more readily available data on
reactor trips. The problem we have with reactor trips
is that the electrical loading conditions aren't
nearly as severe or not as severe as you would have if
you had a LOCA, because you don't have the ECCS loads
coming onto the safety buses.
And that concern is further exacerbated by
the fact that we have a situation now where there are
plants sometimes operating with a degraded grade of
voltage, and when that condition occurs, given that we
have the degraded voltage relays or trip relays on the
safety buses, you can run into a situation where just
an extra load from the ECCS pump starting could be
enough to trip those relays, and even though power may
still be available on the grid, for all practical
purposes the plan is experiencing a loss of off-site
power because it's going to separate from the grid and
have to run on the diesels.
So that again is one of the data
limitations we have right now that we're working with.
And the third issue that we have up here involves
giving credit for non-safety grade -- non-ECCS systems
in the calculation.
The reliability threshold that we're
basing this on is probably going to come from a CDF
threshold from the framework. The CDF threshold is
based on values from a PRA.
PRAs and doing the core damage frequency
calculations do credit non-ECCS equipment for serving
a function, or a RCIC pump or in a BWR you could have
a service -- cross-tie, or you know, a fire, a fire
protection pump.
So what we have to determine is what
credit are we going to give for non-ECCS systems in
this -- in our calculations or in trying to come up
with these matrices?
We don't want to get up in a situation
where a licensee may try and meet the entire
reliability threshold with non-safety grade systems
and then say, okay, I can have a lot of relief on my
true ECCS systems because I have all this reliability
from my -- you know -- additionally, my other nine
ECCS systems.
So we may have to come up with a -- as we
mentioned -- a sub-threshold, which would at least
assure a minimum reliability of the pure safety-grade
ECCS systems. So that's just another one of the
issues that we're wrestling with.
MR. BONACA: This is mostly on BWRs,
right?
MR. KURITZKY: Exactly.
MR. BONACA: And those which rely heavily
on the procedures that you have in place on how
integrated those systems are in the procedures?
MR. KURITZKY: Yes, that's the thing.
Certain systems -- like I think, I don't know, maybe
the RCIC system, my understanding, may have a little
better pedigree than some of the other systems. But
again --
MR. BONACA: You know, if they're trained
and they're used that way and there is a real hardened
use for that, I think is different than purely if you
have some hypothetical, you know, ideas that was
implemented in the PRA but is not supported by
procedures.
MS. DROUIN: Yes, I mean, because the --
a lot of these it's not hypothetical, but particularly
when you look at boilers, they give a lot of credit to
systems whose primary function, you know, is not --
MR. BONACA: Not ECCS.
MS. DROUIN: -- is not the core coolant.
MR. BONACA: Oh.
MS. DROUIN: You know, the service for the
cross-tie, the fire water system, enhanced CRD. And
they do have procedures in place at the plants for
using these systems in those, you know, extreme cases.
But they aren't there for ECCS -- they are
not ECCS systems. And with boilers in particular,
they would have a very difficult time if we did give
them credit for meeting any kind of CDF threshold
value.
But as Alan said, on the other hand, you
don't want them to come in and have so much credit
that we'd back off on the ECCS.
MR. BONACA: Right.
MS. DROUIN: And have a reliability of --
that's unacceptable to us.
MR. KURITZKY: And I guess one of the
other things that will come up when we -- or that we
have to consider when we look at the non-ECCS systems
is that right now the ECCS performance calculation is
just to look at the safety where you need the actual
ECCS systems.
And so when you make sure you meet your
20-200 DUEF (phonetic) threshold you have, relying on
just those ECCS systems. If we're going to credit
RCIC or service or cross-tie or something like that,
you know, there are at present no calculations
demonstrating that they can meet 20-200.
MR. BONACA: Right.
MR. KURITZKY: So we wouldn't want to have
the calculations need to be run. So we would want to
credit systems where it would be fairly obvious that
the function could be accomplished. So that's
-- those are three of the biggest issues that we're
facing.
MR. BONACA: And I guess the same would be
under the fit for PWRs.
MS. DROUIN: Yes. Yes.
MR. BONACA: How credible is it that you
complete the fit, first of all, for the given plant
and then what credit do you give the function so that
you don't degrade the reliability of the ECCS?
MR. KURITZKY: Okay. So
CHAIRMAN SHACK: How would you -- or how
do you propose to address the LOCA frequency for the
non-pipe break LOCAs? Is this a database thing again,
you would look at experience and try to do estimates
on that?
MR. KURITZKY: That's kind of up in the
air right now. As I mentioned, we're going to try and
get some meetings together with some of our -- the
engineering folks and the PRA folks to kind of has
some of this out.
It may not -- you know -- it may be some
kind of bounding. We may put some kind of bound on
the numbers from 57.50 to try to account for some of
these other mechanisms. Some of them specifically may
have some data on them.
For instance, seismic LOCAs, you know,
seismically induced pipe breaks, okay, or at least not
data, but the analyses show that they're very low
contributors. On the other hand, seismically indirect
-- you know -- seismic indirect LOCAs where you've
failed the supports on something and that falls and
breaks a pipe, well, the models show that to be on the
order of what you're getting from just the pipe break
LOCAs.
So in some of them we have some kind of
-- you know -- we don't call it data, but we have some
kind of models that give us some feel for what kind of
contribution they're going to make. Other ones are
really kind of floundering right now.
The shut-down conditions, drain-down
events, we really don't have very good weight of data
for that. There's not very many studies that are out
there, at least not -- and not in this country
particularly.
So it's -- right now we don't know exactly
how we're going to address that. That's why that
issue is out, you know, we're taking input from
anybody who wants to give us input on issues like
that. I don't have a proposal right now. Okay.
Well, let me just --
MS. DROUIN: No, let's keep going, time-
wise.
(Pause)
MR. KURITZKY: Okay. So let me just move
on to the other piece that we had in SECY 133 was the
long-term piece looking at the possibility of
redefining large-break LOCA or the spectrum of breaks
that would be considered in the 50.46 analyses, and
Carolyn Fairbanks.
MS. FAIRBANKS: Yes. We've just really
initiated the work on this long-term objective out of
risk-informing 50.46. The objective here, which would
be at a time line of about the end of three years
would be to have a tech basis developed for redefining
the large-break LOCA.
We've developed a program approach here.
The approach that we were taking was really trying to
parallel the work that's being done to revise the PTS
rule, pressurized thermal shock rule. We wanted to do
this and we've had a meeting with industry a couple
months ago to relay that and to say that this is our
objective in following this example, to have a level
of rigor in our approach that's equivalent to that
that's being pursued with PTS.
So far we are doing some work on tasks one
and tasks three. There are some existing codes on
probabilistic break codes, probabilistic fracture
codes. We're adding at this point some sub-critical
crack growth modules.
As Alan described, there are some issues
as far as indirect failures that --
DR. POWERS: I'm just a little confused
when you say the word "codes." You're not talking
about the SME code or anything like that?
MS. FAIRBANKS: No. No. No. This would
be programs.
DR. POWERS: Computer programs.
MS. FAIRBANKS: Programs, computer
programs.
DR. POWERS: And --
MS. FAIRBANKS: Modeling.
DR. POWERS: -- and so which ones are
those?
MS. FAIRBANKS: We're starting off
initially, we're just about done I think adding some
subcritical crack growth modules to the squirt code,
which is a probabilistic break code. There are a
number of other codes, P-squirt, PROLBB, and we're not
really sure --
DR. POWERS: I'm wondering --
MS. FAIRBANKS: Pardon me?
DR. POWERS: -- I'm wondering just which
of these codes predicts the cracks like in plants like
Summer and places like that.
MS. FAIRBANKS: We have to add that in.
Jumping a little bit ahead, the --
DR. POWERS: How about the cracks that we
have not seen today but will appear next year?
MS. FAIRBANKS: Jumping a little ahead
again, those are things that are we going to consider,
and they are difficult to do. A year ago nobody would
have thought we would be having to add in some BWSCC
modules; Summer occurs, and we're going to be doing
that.
We're not far along, not far enough along
yet to have that done, and if we look back
historically, we do see that new degradation
mechanisms do arise, some more significant than
others, but there is a history.
You know, we have a little interesting
plot, about every seven years there's something new.
DR. POWERS: Yes.
MS. FAIRBANKS: And so I don't think
anyone would feel comfortable in risk-informing this
without accounting for some possible future
degradation mechanism. How we're going to approach
that we haven't quite settled yet, but that's
certainly one thing that's going to be incorporated
into this work.
MR. KURITZKY: And I think also the point
that -- of course, we definitely need to focus on, but
also, each of these clear mechanisms shows up, you
know, I think one time Mike Mayfield showed a slide
that showed like every seven years a new mechanism
shows up that they hadn't thought of before.
But in all cases these mechanisms that
have shown up, we don't have a LOCA so far, knock on
wood, and we'd identify the mechanism and then we do
some analysis of it. We come up with some type of
response or something that's implemented to try and
control it.
And so we've managed to avoid having a
LOCA. So in fact, yes, we do need to consider that
there could be other mechanisms that are going to crop
up and get us as time goes on.
But we also, you know, keep in mind that
once that mechanism -- unless that mechanism shows up
and it acts fast enough that we end up with a LOCA
condition right away -- we'll evaluate it and try and
address it so that, you know, corrective actions will
be taken to minimize its impact on the LOCA frequency.
That's just one other thing we need to consider.
MS. FAIRBANKS: That's something that we
really think, is considering our input, too, with LOCA
frequency for the LOCA/LOOP.
DR. POWERS: It sounds like, if I follow
your logic, we should get rid of these things. I
mean, you say we got a lot of band-aids, and we don't
really need band-aids, because nothing ever results in
a LOCA. So why worry about it?
MR. KURITZKY: Like I say, with the band-
aids, your band-aids is what -- the corrective actions
that come up when we discover these things, we need
those band-aids. That's what keeps the LOCA frequency
low.
If we didn't put these -- if primary
-- crack and popped off and we just said, well, that's
a new mechanism, okay, very -- that's good, let's keep
going the way we're going, then I would expect to see
an increase in that LOCA frequency.
I'm not saying we wouldn't see one now
anyway because of this mechanism, but the idea that we
find it, now we address it, we put in corrective
actions to minimize it.
So you wouldn't expect to see, even if
there is going to be some delta in the LOCA frequency,
it wouldn't be of a magnitude as if you just let the
thing go off on its own and didn't address it. So
there's some kind of self-correcting or self-
modulating type of mechanism there.
MS. FAIRBANKS: Also shoes that as we're
approaching this we're looking at all of the different
type of crack growth modules to incorporate axial,
circumferential and surface cracks. They will all be
incorporated into the modeling.
We had a -- as I said earlier, we had a
meeting to convey this approach to industry, and right
now we're trying to support PRAB to the best we can
with our knowledge and our plants, that we're using it
in development of our break frequency and pipe size
diagrams to support the --
DR. POWERS: What is PRAB again?
MR. KURITZKY: PRA -- it's probable --
MS. DROUIN: That's us. What Carolyn is
getting there is that --
DR. POWERS: I thought it was a code for
a second.
MS. DROUIN: -- our technical work on the
reliability side, we're supposed to be finished, you
know, early in the spring time frame. We don't want
to move forward with a recommendation and then say a
month or six months later they come in on their long-
term work and the frequency numbers that we're using
are totally not in agreement with them.
So we're trying to have some kind of
convergence here between what they're doing on the
large pipe break size versus what we're trying to do
on the reliability.
MS. FAIRBANKS: And it is a complex issue,
because in the approach for this we're even at the
initial point of deciding which pipe break sizes we're
going to look at, which lines those would be on, what
is the -- what are the operating conditions, what are
the environments for that size of diameter, which
degradation mechanisms would be potentially involved
in those.
And so you're not necessarily going to get
a curve when you're looking at the break size versus
frequency. I think that is really just wrapping up
where we are at this point. We are pursuing this --
MR. BONACA: Just to understand a little
better, just to know.
MS. FAIRBANKS: Okay.
MR. BONACA: For example, clearly, I mean,
you have a whole issue of crack growth and development
in two different size breaks, depending, you know, I
think there is a time parameter there. I mean, you
have a crack initiation result.
Now, are you looking also at how a seismic
event could result in a certain break size, given that
you have an identified crack?
MS. FAIRBANKS: Yes.
MR. BONACA: For example, there is some
event where you have a crack or multiple cracks and
now you do have a seismic event, and so you will be
looking at that?
MS. FAIRBANKS: Yes. We'll be looking at
all the modes.
CHAIRMAN SHACK: It's more difficult than
it is in the PTS case, though, where, you know, you
sort of assume that the only flaws you have to worry
about are due to fabrication. You know, when you
allow flaws to suddenly appear --
MR. BONACA: Right.
CHAIRMAN SHACK: -- and to grow, life gets
a great deal more difficult than the --
MS. FAIRBANKS: And repair welds, many
things are going to come --
CHAIRMAN SHACK: Yes.
MS. FAIRBANKS: -- up to complexity.
CHAIRMAN SHACK: But I guess in your case,
though, I mean, the frequency you need to get rid of
a large break LOCA as a design basis accident is
really probably a whole lot lower than you need --
although I guess you want to use the most realistic.
I mean, it's not as though you're going to
just stick a sort of a conservative estimate, because
you can move on. But in reality, you could have a
fairly conservative estimate for the large break LOCA
and still be able to obtain some relief, I would
think, in the simultaneous LOOP, wouldn't you?
MR. KURITZKY: The thing -- difference
being is that right now, since we don't have LOCA
frequencies by pipe size, which is something that we
idealistically hope that we can maybe get in the
longer-term, right now we have to deal with the large-
break LOCA category from a PRA stance, which is
essentially something six inches per PWR, every six
inches and above.
So we have to make it hold for everything
six inches and above. In the future we may be able to
show that the ultimate frequency you need to get rid
of a design based axiom, yes, we need to be lower.
But you may be able to do it with, say, a
14-inch pipe or a 12-inch pipe, and that frequency may
be much lower, while the six-inch break, you know, you
may give up something. So you're right. You can
definitely get a much lower frequency to get it out of
the design basis.
But because we can't do it by a pipe size
right now, we have to do it for everything that's,
say, six inches and above that we can't afford to have
too many layers of, you know, conservatism piled on
there to, you know, address various
uncertainties before we would start to run into a
-- we lose our flexibility also.
MR. BONACA: Although you mentioned before
you are going to include consideration of heavy loads,
for example, in heavy loads then the frequencies
associated with a procedural violation of some type is
a measured one, perceive that, you know, it's -- I
think it's more likely that you have that happening
than certainly you have just a mechanistic double-
ending break. So that may drive up your frequency
quite a bit.
MR. KURITZKY: Well, except that it's not
just a question of having heavy load drop. It has to
be -- the operations have to be taking place during
power. You have to be doing something that's inside
the containment where you're over --
MR. BONACA: I'm talking about maybe
you're -- you know -- you're in shutdown conditions.
MR. KURITZKY: Yes, for the -- oh, for a
shutdown.
MR. BONACA: You haven't removed the head
yet. You have the fuel there and whatever. You're
moving some heavy load and, you know, a heavy load
have enough to do damage.
MR. KURITZKY: Yes. In fact, at shutdown,
that's one of the -- like I mentioned before -- that's
one of the things we're really struggling with right
now because of all types of -- the drained elements or
LOCA initiates that could have occur at shutdown.
MR. BONACA: You know, that could drive
your frequency there, because I mean, that's a
procedural violation of some type.
MR. KURITZKY: Something we have to
consider.
MS. FAIRBANKS: I think we can move along.
MS. DROUIN: Move along?
MS. FAIRBANKS: No other questions.
MS. DROUIN: Okay. Well, at this point
we've gone through the four different areas covered by
50.46 and tried to give you an update and status of
where we are at. Just going back to what we had said
in the SECY in terms of our schedule, we had for the
evaluation model and the acceptance criteria that that
technical work would be done, you know, on or before
July 2002.
That work right now is still on schedule,
and as you've seen, you know, we're deviating a little
bit from what we said in the SECY in terms of what we
would do there. On the risk-informed alternatives to
the reliability requirements, our work there is due in
April.
It's going to be very tight to us trying
to meet that schedule, a lot of issues there we're
still trying to --
MR. KURITZKY: Oh, that's 2002? I thought
it was 2003.
(Laughter)
MS. DROUIN: On the definition of the
break size.
DR. POWERS: I just have to interject.
One of the commissioners has bet me that he will not
have to vote on this during his term of office.
MR. KURITZKY: How many years do they have
left?
DR. POWERS: If I told you that I'd reveal
which commissioner it was, but several.
MS. DROUIN: You mean, for the break size?
DR. POWERS: He said he would not have to
vote on any revision to 50.46 in his term of office.
MS. DROUIN: Well, if he doesn't vote,
then he, you know, we can't go forward with that break
size. I mean, he's kind of set the -- he's stacked
the deck -- yes.
CHAIRMAN SHACK: He said it would never
come to him to vote. Looks like -- I mean, we're
still working on the SECY. The vote is a long way
down the road.
(Laughter)
MS. DROUIN: Yes.
DR. POWERS: I think I'm going to owe him
some money here.
CHAIRMAN SHACK: But the most substantive
thing that's changed since 133 is the skepticism about
the possibility of relief for the K curve.
MS. DROUIN: Yes.
CHAIRMAN SHACK: I mean, you were more
optimistic in 133 than you are --
MR. KURITZKY: Right.
MS. DROUIN: Correct.
CHAIRMAN SHACK: -- from today's
presentation.
MS. DROUIN: Correct.
CHAIRMAN SHACK: But everything else is
more or less following, which you laid out --
MR. KURITZKY: Right.
CHAIRMAN SHACK: -- in 133.
MS. DROUIN: That's correct. But you
know, our technical work on 50.46 is not tied to any
commissioner's vote. It's the rulemaking. So -- but
we plan to have all of our technical work done as we
laid out in 133. The public has been very interested
in this program, followed it closely.
We have had a lot of meetings with the
various stakeholders. We can -- we plan to continue
having a lot of meetings with the stakeholders. We
just have listed a couple there that's happened back
in August on the LOCA frequencies.
We had another one on the LOCA and new
frequencies. We just had a second one in October. We
plan to have another one at the end of November. So
I mean, almost on a monthly basis you can see we're
meeting with the stakeholders on this program.
They've been following it very closely,
giving us a lot of good data, also working with us.
So on that note, that kind of sums up where we're at
on the status for 50.46.
CHAIRMAN SHACK: You want to make any
comments? Okay.
MS. FAIRBANKS: No comments.
SECRETARY HORN: We were scheduled to have
a presentation from NEI, Tony -- Mr. Angelo, but he's
had other commitments and so can't make it today. And
I think we're done with the formal presentations.
Final comments from members of the
subcommittee?
MR. BONACA: I think it was an informative
presentation, particularly when it came down to the
Appendix K tradeoffs that are really in the Appendix
K model, and then for which we need the credit,
really, from the K-8 curve.
I mean, that was quite a bit of
information. I think that that was quite valuable.
I don't have any other specific comments, except it
may be a long time before we have that relief, and
this work seems to be --
CHAIRMAN SHACK: Where's that low-hanging
fruit?
MR. BONACA: Yes.
MR. KURITZKY: Drying up.
MR. BONACA: And I thought it was in
general a very good presentation.
DR. KRESS: I thought so, too, and RP --
it looks like Option C on that Appendix K is probably
the best one, plus continuing with the action plan to
get that additional information. I worry about using
frequencies to eliminate the LOCA/LOOP combination,
because I've been considering this a defense in depth
type of approach.
For sabotage and other things, I think
there are other ways you can get LOCA/LOOPS at the
same time, but I haven't thought enough about it to
get a firm position on that.
MS. DROUIN: One of the things I didn't
say and we tend to forget about our framework
document, but we do follow the framework very closely.
And the framework does not allow us, regardless of
what the numbers say, to violate those six elements of
defense-in-depth.
DR. KRESS: That's true, yes.
MS. DROUIN: So you know, we tend to talk
a lot about the numbers and we tend to, you know, not
verbalize so much the framework, but everything does
pass through that framework and you cannot violate one
of those defense-in-depth elements, regardless of what
the numbers tell us.
DR. KRESS: I guess we're supposed to
decide on what to do about the full committee?
CHAIRMAN SHACK: No. I don't think we had
--
DR. KRESS: We don't.
CHAIRMAN SHACK: -- planned to have a
presentation to the full committee.
MR. MARKLEY: Just a Subcommittee report.
CHAIRMAN SHACK: Just a subcommittee
report.
DR. KRESS: Okay. Good.
MR. BONACA: You know, just to interject
on the issue of LOOP. I mean, I agree that's an issue
of defense-in-depth that makes you uneasy when you
think about eliminating it if you really want to cover
all the bases.
But one of the big challenges of the
licensees is really the frequent start of the diesels,
you know, cold and the wear of the diesels, and also
the very strict and demanding requirements imposed on
a lot of systems like, you know, HVAC and so on and so
forth.
I mean, does it mean that you -- I mean,
could we possibly have still a design capability for
LOCA and LOOP with less demanding requirements imposed
on the equipment from a perspective of testing?
Couldn't you look at the risk significance
of reducing some of the tests imposed on the equipment
that really are the driving force right now for the
licensees on requesting some relief?
MR. KURITZKY: Well, I think in regards to
that, I mean, most plants' technical specifications
have already been changed so that that fast start of
the diesel --
MR. BONACA: Yes.
MR. KURITZKY: -- only has to be done --
used to be done once a month, but it's down to, I
think, once every six months.
MR. BONACA: That's true.
MR. KURITZKY: Assuming you pass it. So
there has been some relief in that regard already.
What it comes down to is do you still have to have
your diesel designed and your equipment designed to
come up at a certain time.
And that's governed by what kind of flow
rates -- you know -- what kind of flow rates have to
break and how quickly you have to get water back in
the core cylinder. And how big a break you're going
to consider and what the frequency of that event is,
you know, determines the time when that diesel has to
come on board.
But as far as the testing, I think most
plants I think already have managed to reduce that,
you know.
MR. BONACA: I've not seen, but some of
the systems like the HVAC system and the time you need
to draw a vacuum in the enclosure buildings, I mean,
that's stuff that is tremendously demanding on the
plants and on the equipment.
And so anyway, but that's just a thought
that one could also determine the risk increase
associated with the relaxation of some of the
requirements, and they may find that you can still
have a high expectation of success of a LOCA and LOOP,
you know, coping with both of them by imposing less
restrictive requirements.
I agree with the -- on the start of the
diesel. That's one thing that has been done. But
again, many of the other systems have not been relaxed
at all, their testing.
MR. KURITZKY: That's something we can
look into.
CHAIRMAN SHACK: Well, I guess, you know,
when I -- I'm not as concerned as Tom is about the
defense-in-depth, because when I looked at the
proposed changes I don't see that those really affect
your defense-in-depth very much.
You know, if you were proposing to remove
some equipment, but the kind of changes I foresee, at
least from this part, I think eliminating the large
break LOCA as a design basis accident could have a
more substantive impact than what one would consider
defense-in-depth. But this part doesn't seem to me to
impact it as much.
MS. DROUIN: Well, you may have some PWRs
out there who would like to get rid of their
accumulators, and they could.
CHAIRMAN SHACK: Under this.
MS. DROUIN: Under this.
MR. KURITZKY: Well, so far we have to
wait and see, but it doesn't even look like they're
going to get too much in that regard, because most of
the IPEs or the PRAs are going to correct the
accumulators for the smaller breaks, also, what's
called medium breaks.
And so therefore, you may not -- from a
reliability point you still may not make the grade.
But it's possible that maybe for A, if you have a
spare accumulator, you know, that you may be able to
relax the allowed out of time on it.
But again, whether or not somebody takes
something out of a plant or whether this gets
relaxation in their technical specifications, I think
we're going to have to decide, the staff will have to
decide whether or not -- you know -- even if the
numbers come out that show that you could do that, we
have to decide whether or not that meets the defense-
in-depth filter or whether or not we're just
comfortable with that.
And we may want to put some kind of
limitations on that, some kind of restraints.
CHAIRMAN SHACK: Dana?
DR. POWERS: I guess I opened the Pandora
with the sabotage concern, the defense-in-depth, and
I think I still wrestle with defense-in-depth and what
we're -- where it is and how it is in the regulations
and how far it goes.
I come back to the earlier presentation,
I look forward to seeing what comes out of these
studies on the oxidation of clads and your
circumstances. And it looks to me like what -- after
a lot of complications of phenomenological discussions
-- that the basis idea that you will only go after the
17 percent oxidation and replace it with an
embrittlement criterion seems like a pretty good idea
to me.
I mean, I feel sorry for those that have
to demonstrate that they have retained ductility,
because I think that's a much harder analytic tool
than just showing that you don't hit 17 percent
oxidation using Baker-Just kinetics than in a fairly
simple temperature transient.
But I think it's a much more defensible
thing and the challenge that the industry would face
in showing that the oxidation kinetics of every type
of clad that came along was bounded by Baker-Just
might prove as much of a challenge as the calculation
of ductility.
But I guess it's -- I mean, I think before
you finalize on this we just have to wait for the
experimentalists to get their act together and get
some data, and it takes a lot of data.
CHAIRMAN SHACK: Other comments?
MS. DROUIN: I have a question. You know,
we were asked last time, you know, to keep the ACRS
informed, you know, of the status. I look down the
road to the future of, you know, where our next
milestones are and, you know, the technical work on
the reliability parts to be done at the end of April,
the acceptance criteria and evaluation model in July.
My question is to, when would you all be
interested in seeing us again, and would it be at the
Subcommittee level, the full committee level?
DR. POWERS: You know, my initial
reaction, of course, Mary, is the committee is always
delighted when you want to come talk to us because you
always have something interesting to tell us, but I
think that really it's up to you.
And I think you've got a good strategy
here that you're trying to pursue and I think it's
when you think you have enough substance in there to
get some opinions instead of some speculations and
questions --
MS. DROUIN: Okay.
DR. POWERS: -- that we want to hear. And
I would suggest this is before the full committee
because everybody has a stake in this. And so you
want to ask not only for a time, but enough time so
that you can -- you're not rushed in getting your
points across.
So don't let them short-change you on
time, in other words. But I think it's really up to
you because you know your schedule and the various
challenges. It's when you think you've got enough to
-- this to mark some point on it, rather than any
-- rather than judging on the calendar list, judge
based on the progress of the work.
MS. DROUIN: No. No. I agree and I
didn't know if there was --
DR. POWERS: Sure.
MS. DROUIN: -- something here in
particular that you wanted to hear back again on, but
absolutely, when we feel we've got --
DR. POWERS: Your current milestones sort
of suggest something like April or May --
MS. DROUIN: Yes.
DR. POWERS: -- when you've finished the
reliability. But obviously, if you're not there,
you're not there.
MR. BONACA: And the other thing, the
other criteria I would use is if you feel there is
some surprise for us. For example, today I think was
a very valuable presentation because at least for me
I thought that the decay heat curve was a low-hanging
fruit, and now I've been, you know, educated on that.
And I think that was an important time to
hear about that. Otherwise, we would be still
proceeding in our mind with the thought that, here it
comes, you know.
MS. DROUIN: And that's why we felt it was
important to come now.
MR. BONACA: Yes.
MS. DROUIN: Because we were deviating
from what we had in the SECY, and what we had told you
guys in our letter.
DR. POWERS: I guess one of the real
problems that the NRC will face, Mario, is just that
lots of people think that decay heat curve is a
"gimmee." I mean, I've even characterized it as the
"gimmee."
MR. BONACA: Yes.
DR. POWERS: And there's going to be --
they're not going to have had the benefit of the
discussions that we went through and so they're going
to persist in taking that.
I'm wondering if maybe you shouldn't think
seriously about formulating that into a paper that you
could give to -- before the ANS or some body like that
and try to socialize the opinion to at least in some
sense take the weight off your back, because you're
going to have a lot of people says, ah, NRC, they'll
never change this.
I mean, you're just -- it's going to be
conventional wisdom and maybe you ought to reach out
a little bit to the -- at least the technical
community and advertise that position.
MR. BONACA: I think that's an excellent
recommendation because I thought that the presentation
that you provided, Steve, it was outstanding in that
sense. I think it was very pointed.
It showed some of the effects and really
was a good -- you know -- I mean, you come out of it,
you can ask some pointed questions to that, but then
you come up with an understanding of what the issues
are.
And I think that that would be valuable
because I think there is -- in my judgment there is a
widespread belief that that's an easy tradeoff and how
come the NRC's not moving on this.
MR. BAJOREK: By the way, a lot of those
figures that I did show, we're intending to put that
in a OCONEE paper, submitting that at the end of the
month.
DR. POWERS: You know, that's not -- I
mean, that's the kind of forum where you need to
socialize these ideas and what-not and put it before
the technical community. If they find fault with it,
of course, you learn something.
But if you're of sound position, then they
learn something. So I mean, there's no loss here.
MR. KING: We'll take a commitment to do
that, figure out the right forum and the right
vehicle.
DR. POWERS: Yes, you know, because
otherwise, you get this very unfair accusation because
people just haven't seen that sort of stuff.
MR. KING: Right.
DR. POWERS: They haven't thought about it
as much as you have.
CHAIRMAN SHACK: Yes. I mean, in July you
just sort of had a general statement that, you know,
you have to consider the compensation non-
conservatisms, but now you have actually something
fairly specific, and you know, I think it makes it a
much more substantive case than saying, there may be
non-conservatisms that won't be bounded.
DR. POWERS: And it gives the model
builders some grist to think about, too. They may
find that, well, you're talking about RELAP having
some less than desirable features perhaps in the code.
So maybe people developing models can think about it.
We'll see.
MR. BONACA: The other thing which is
significant here is that so many of the comparisons
were based on calculations performed by licensees.
DR. POWERS: Sure.
MR. BONACA: And so those are facts,
really, and not speculation on the part of the staff,
really. It's coming out of presentation and some
meters provided by the licensees.
CHAIRMAN SHACK: If there are no
additional comments we can adjourn the Subcommittee
meeting.
(Whereupon, this ACRS/ACNW Joint
Subcommittee meeting was concluded at 12:09 p.m.)
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Page Last Reviewed/Updated Tuesday, August 16, 2016