Joint Subcommittees on Materials & Metallurgy, Thermal-Hydraulic Phenomena, and Reliability & Probabilistic Risk Assessment - July 9, 2001
UNITED STATES OF AMERICA
NUCLEAR REGULATORY COMMISSION
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS
JOINT MEETING OF THE ACRS SUBCOMMITTEES ON MATERIALS
AND METALLURGY, THERMAL-HYDRAULIC PHENOMENA, AND
RELIABILITY AND PROBABILISTIC RISK ASSESSMENT
July 9, 2001
The Subcommittee met at the Nuclear Regulatory
Commission, Two White Flint North, Room T2B3, 11545
Rockville Pile, at 1:30 p.m., William J. Shack, Joint
Meeting Chairman, presiding.
WILLIAM J. SHACK Subcommittee Chairman
GEORGE APOSTOLAKIS ACRS Chairman
MARIO V. BONACA
F. PETER FORD
THOMAS S. KRESS
GRAHAM M. LEITCH
JOHN D. SIEBER
ROBERT E. UHRIG
GRAHAM B. WALLIS
B. Shack . . . . . . . . . . . . . . . . . . 3
NRC STAFF PRESENTATION
Mary Drouin and Alan Kuritsky. . . . . . . . 3
Adrian Heymer, Terry Reick . . . . . . . . 124
ACRS GENERAL DISCUSSION AND ADJOURNMENT. . . . . 147 P-R-O-C-E-E-D-I-N-G-S
DR. SHACK: This is the Advisor Committee,
an ACRS Joint Committee on the ACRS Subcommittees on
Materials and Metallurgy, Thermal-Hydraulic Phenomena,
and Reliability and Probabilistic Risk Assessment.
The meeting will now to come order. I am
William Shack, Chairman of the Subcommittee on
Materials and Metallurgy. Graham Wallis is Chairman
of the Subcommittee on Thermal-Hydraulic Phenomena,
and George Apostolakis is Chairman of the Subcommittee
on Reliability and PRA.
Subcommittee members in attendance are
Mario Bonaca, Peter Ford, Thomas Kress, Graham Leitch,
Steve Rosen, Jack Sieber and Bob Uhrig.
The purpose of this meeting is to discuss
the status of risk-informed revisions to the technical
requirements of 10 CFR 50.46 for emergency core
cooling systems. 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
meeting have been announced as part of the notice of
this meeting previously published in the Federal
Register on June 27, 2001.
A transcript of the meeting is being kept and
will be made available as stated in the Federal
It is requested that speakers first
identify themselves and speak with sufficient clarity
and volume so that they may be readily heard.
We have received no written comments from
members of the public regarding today's meeting.
I don't really have any comments. We've
sort of discussed some proposed revised of 50.46
before, and I think we'll be going into a little more
detail on some of these options today. And I assume
that Mark or Mary will do the honors.
So now we'll proceed with the meeting, and
I'd like to introduce Mike Johnson of NRR who'll
introduce the topic and the presenters.
MS. DROUIN: My name is Mary Drouin with
Office of Research, the probabilistic risk analysis
branch. At the table also with me is Alan Kuritsky,
also from Office of Research, and the PI branch.
Today we're here to give you a status of
where we are in 50.46, and we're going to concentrate
primarily on the paper that is on its way to the
Commission. I will remind the committee the paper has
not been signed out at this point, so it's still
sensitive. Hopefully, it will be to the Commission
within the week.
For today's briefing, we are going to
concentrate on 50.46. We'll quickly go over, you know,
the purpose and what we would like to see out of
today's discussion, the feedback we'd like from ACRS.
Quickly to remind a little bit about
option 3 in the background and what we're supposed to
be accomplishing. And then hone in on the particular
activities that are associated with 50.46.
There are three primary things that we're
going to touch on: The feasibility of changing the
actual 50.46, going in and tentatively we have some
considerations to change the actual rule; also looking
at additional changes to 50.46, things that are more
in the long term; other Option 3 activities. And then
wrap up with what our tentative recommendations and
our schedule is for 50.46.
In regard to today's meeting, again, we're
focus in on 50.46 and the paper that is making its way
up to the Commission. And for today, as we go through
the different options that we're considering, we would
like to get feedback from the ACRS on these options,
any implementation issues that you feel that we may
overlooked or not addressed adequately enough and
whether or not was really have come to the conclusion
that this is feasible or not feasible. And, of
course, at this point we are looking for a letter from
the ACRS to accompany our paper to the Commission.
Just briefly on the background, we go back
to SECY-264, which was the original plan for the
Option 3 work. And we also had a framework. And the
two important things to remember was a big lesson on
50.44 is that part of Option 3 has two phases to it.
And this first phase is strictly a feasibility study.
Is it feasible to do the things that we would
ultimately recommend to the Commission. That does
mean that we have done all the technical work that
would be needed to support a rulemaking, because that
technical work is part of Phase 2 when we get into the
implementation once we have received approval from the
Commission to proceed forward. And there seems to have
been some confusion there. So, I just wanted to
quickly highlight that again that the Phase I when we
complete it and we make our recommendation to the
Commission, that does mean that all the technical work
We've done enough work to have a good
comfortable feeling that this is feasible, that it
will work out, but there's no guarantee that it would.
DR. WALLIS: Besides feasibility, are you
looking at desirability as some sort of criterion for-
MS. DROUIN: To me desirability is part of
DR. WALLIS: You can do all kinds of
feasible things, but they may not be desirable.
MS. DROUIN: That's right. So part of
that feasibility is that it's desirable.
DR. WALLIS: Okay.
MS. DROUIN: I mean, you might be able to
do something, but if nobody wants it --
DR. WALLIS: That's right.
MS. DROUIN: Right. So absolutely, that's
part of the feasibility.
DR. SHACK: Well, that was in your
prioritized bullet, right, that you've already decided
this particular one is a high priority candidate for
MS. DROUIN: Yes. Yes. And that looks at
the resources and the cost, and the benefits. I
wasn't going to spend time going through each of
these, I just wanted to really focus on the difference
between Phase I and Phase II. Okay.
Now, getting into 50.46. We talk about
50.46 and, and they used that number 50.46 rather
loosely. But when you go and you look at Part 50 and
you talk about the ECCS performance, which is really
more what we're talking about, then you're really
talking about 50.46, you're talking about Appendix K
and you're talking about GDC 35. These you have to
handle together. You can't just deal with 50.46 and
exclude Appendix K and GDC 35. They work together as
And when you look at these and what are
the ECCS requirement, they break down into these four
what I would call topical areas in terms of what the
requirements are trying to achieve.
One is the ECCS reliability. The
acceptance criteria for the ECCS, it's evaluation
model and then ultimately the LOCA size definition.
And as you come out of these boxes to the
right, then you start seeing -- and we tried to mimic
the words right from the regulation so what exactly
what is the technical requirement.
When you look at the ECCS reliability, and
this is where I come back to, it's not just 50.46,
because that reliability, this row here is showing up
in GDC 35. And that ultimately gets to the single
failure criteria and the requirement for your
simultaneous LOCA and LOOP requirement.
We come down into the next one, which is
the ECCS acceptance criteria and you ultimately get to
-- this one is in 50.46, the five criteria that they
have to meet from their performance. And you hear
about, you know, your peak cladding temperature, 2200
degrees, your long term cooling, your coolable core
Your next one, your evaluation model, now
this is a coupling here of both 50.46 and Appendix K,
which gets into what the analysis you have to do and
what model that you're going to have to use.
And then your last topic then gets into
the LOCA size definition, and this is showing up in
several places. It does show up exactly in 50.46. It
shows up in Appendix K, which actually defines, and
you'll see these same words in those three places of
what is defined as a loss of cooling accident in terms
of the pipe break size and location.
So in risk-informing this, these are the
things that we're dealing with, trying to look the
reliability, looking at the acceptance criteria or get
the evaluation model and look at the LOCA size. So
those are going to be the four things that we're going
to touch on.
So, at this point, I'm going to turn it
over to Alan, and he will start walking us through
each of these four areas.
MR. KURITSKY: Okay. As Mary said, I'm
Alan Kuritsky, I'm in the PI Branch in the Office of
Based on the staff's feasibility
assessment of 50.46 and GDC 35 and Appendix K we feel
that changes to the reliability and acceptable
criteria and evaluation models may be justified.
More specifically what we're looking at is
ECCS reliabilities resulting from the technical
requirements may not always be commensurate with the
risk significance of the various LOCA sizes.
DR. WALLIS: How do you make a measure of
this commensurate? What do you balance against what
to decide whether its commensurate or not?
MR. KURITSKY: Right now we've been using
as our metric core damage frequency.
DR. WALLIS: Balance versus?
MR. KURITSKY: In other words --
DR. WALLIS: When it gets below a certain
amount, it's not worth bothering, its a go/no go kind
MR. KURITSKY: Yes. For instance, if you
had a 10-5 frequency of initiating event and you had
10-3 ECCS reliability and it required some additional
failures in your calculation that would make it even
lower, you may say okay that's not commensurate. It's
either CDF or just a total frequency of the sequence
of events you consider.
DR. APOSTOLAKIS: I don't understand the
second bullet anyway. Can you explain it?
MR. KURITSKY: The one that we're just
DR. APOSTOLAKIS: Yes. What does it mean?
MR. KURITSKY: Well, just pretty much what
I was just saying. If you have a frequency of, let's
say, a class of LOCA that may be 10-5, okay. And then
the technical requirements may require -- let me use
this example first.
Technical requirements may require you
also consider for that class of LOCAs a simultaneous
loss of off-site power and a single worst additional
failure. If you have a 10-5 frequency of this
initiator and it's another 10-4 or 10-2 for something
as loss of off-site power, an additional maybe 10-2
for another single worst additional failure and you
end up with a frequency of that series of -- you know,
sequence of events which is already down to the 10-8/9
level and you're having that in the core damage, it's
just that sequence, that's the events. So to us that
means that, you know, you rely on what you require of
these, yes. You would not need to have as high
When I go to the loss of off-site power
assumption and that single failure, that all feeds
into the ECCS reliability. In other words, when
you're assuming that it has to operate with off-site
power failure, you're assuming it has to operate given
the failure of some piece of equipment, final has to
go to how reliability that system has to be. In that
case you may be requiring a greater reliability than
is really called for by the frequency of that
DR. APOSTOLAKIS: Now, if I look at the
first bullet and what you just said, and compare it
with the -- what is left out is the LOCA size
MR. KURITSKY: Yes, and that's going to
show up when we discuss the longer term, the
DR. APOSTOLAKIS: So the message you're
sending with this is that change as to the LOCA
definition model may not be just --
MR. KURITSKY: Right now we don't -- we
haven't established the feasibility level right now.
DR. APOSTOLAKIS: Okay.
MR. KURITSKY: And some we're still going
to look into.
DR. WALLIS: This is really focused on the
LOCA LOOP simultaneous requirement, isn't it?
DR. BONACA: One of those.
Mary, you wanted to say something.
MS. DROUIN: Also the thing that I wanted
to add is that we say it may be justified. The words
that are missing here are "in the short term." These
are things that can be done immediately.
DR. APOSTOLAKIS: Okay.
DR. SHACK: We're going to discuss the
solution of the large break LOCA in more detail,
MS. DROUIN: We're going to get into that
In answer to Dr. Wallis, if we go back and
we look at, you know, the flow chart. Remember the
liability, that's being set. So when we talk about
reliability, we're talking about the single failure
criteria, we're talking about the simultaneous LOCA
DR. SHACK: Although in your second bullet
you certainly are leaning on the frequency of the
breaks as a function of break size as far as the ECCS
MS. DROUIN: Yes, that comes into play.
DR. SHACK: You're certainly arguing that
certain frequencies are much more likely than others.
MS. DROUIN: Correct.
MR. KURITSKY: Okay. And then the last
bullet there also is that based on feasibility study
we recognize that there may be some unnecessary
conservatisms in the existing requirements we want to
DR. APOSTOLAKIS: Maybe you said?
DR. WALLIS: Are these just conservative?
MR. KURITSKY: Well, we say maybe because
EDO hasn't signed off on those yet.
DR. BONACA: Well, isn't bullet 2 and 3
the same? I mean, really what you're saying there is
excessive conservatism --
MR. KURITSKY: Yes, it is --
DR. BONACA: -- being imposed right now
because of the requirements?
MR. KURITSKY: Right. The third bullet
also is trying to capture things that aren't -- just
dealing with ECCS reliability. As Mary showed you in
that previous slide there's some other things.
DR. BONACA: I understand.
MS. DROUIN: And when you get into the
acceptance criteria, you know, that's separate from
the reliability that there's conservatisms in the
DR. WALLIS: It's only unnecessary
conservatisms, and when NEI were here they were saying
that the accuracy on some of these -- the focus on
some of these very unlikely events was diverting the
design into channels which were actually harmful when
it came to dealing with likely events. It's not just
conservative, it's that you're doing the wrong thing.
MR. KURITSKY: Yes, there are a couple of
examples that indicate --
DR. WALLIS: So you're going to bring that
sort of thing up, too. It's not just conservatism
that's the problem, it's doing the wrong thing because
you're responding to the wrong kind of -- the less
likely one and then you're impairing your ability to
deal the more likely.
MR. KURITSKY: There may be a more optimum
DR. WALLIS: Right. That's right.
MR. KURITSKY: It doesn't mean that the
current way is a safety concern, but there may be a
more optimum way.
DR. WALLIS: The optimum, and that's a
very good one if that can be made. The optimization
is a very clear one to me if you can make it.
MR. KURITSKY: Okay. Some of the
technical observations and conclusions that we've
arrived at during the feasibility study conducted by
the staff is that, as we've been mentioning, current
evaluation models of ECCS performance may be overly
conservative for large-break LOCAs. And that goes
right back to what we just discussed. That could be
because of the additional assumptions that you put on
in the models. And it also could be due to specific
features of Appendix K which we may feel a little
Current estimates of the frequency of
large-break LOCAs are uncertain and are not low
enough, at least the current estimates that we have
are not low enough to eliminate all large-break LOCAs
as design based accidents.
DR. APOSTOLAKIS: How long should they be?
MR. KURITSKY: Well, we haven't put our
finger on the exact number. Certainly it'd be below
DR. APOSTOLAKIS: Mean value?
MR. KURITSKY: I say confidently, so I'll
leave that up to whether we see it as a percentile or
whether we would be comfortable with a mean. But if
we could be comfortable with them being below 10-6,
that may be somewhere in that ball park. But we're
not anywhere near that right now, so we don't really
have to establish that threshold because we just know
we're not actually there.
DR. SHACK: Well, you know, when you said
that the current estimates are not low enough to allow
elimination, that's the current estimates based on
data and observations which will, in fact, will be
limited by the fact that you just -- you know, to get
those kind of times, you need a lot of observations
and a lot of hours.
MR. KURITSKY: Exactly.
DR. SHACK: Certainly the estimates from
probabilistic fracture mechanisms would certainly
suggest that they're low enough to meet your 10-6
MR. KURITSKY: Right, except that again --
I don't want to tread to that area because I'm not an
expert. That's your expertise. But our fracture
mechanics experts actually have some -- are not
necessarily as comfortable with the operational data,
the numbers coming from the operational data because
they don't necessarily address certain failure
mechanisms like primary wire first corrosion cracking
which has been showing up recently, and so there's
some concern on their part that the operational, the
numbers coming up from operational data are not, say,
maybe not conservative or they're not properly --
DR. SHACK: They haven't been updated
sufficiently to take into account new phenomena.
MR. KURITSKY: Right. Exactly.
DR. APOSTOLAKIS: Has probabilistic
fracture mechanics ever produced numbers that are 10-3
or 5 for anything? It's always 10-x, and X goes -- is
that an inherent property --
DR. SHACK: Well if you look at a 2 inch
pipe and a 28 inch pipe, you get very different
DR. APOSTOLAKIS: But never high numbers?
DR. SHACK: Well, the ones for the 2 inch
pipe would be high.
DR. APOSTOLAKIS: They would be?
DR. SHACK: Yes.
DR. APOSTOLAKIS: Then we would believe
DR. WALLIS: Can I go back to the first
bullet, I'm sorry.
When you say evaluation model, do you mean
the criteria in Appendix K or do you mean something in
the codes, which is what I think of as an evaluation
MR. KURITSKY: Well, I guess what I'm
thinking of is two things. One may be the assumptions
used in the model, which goes back to the single
failure criteria --
DR. WALLIS: Those are sort of criteria,
they're not technical assumptions in the code of some
MR. KURITSKY: Right. That's just --
DR. WALLIS: So regulatory assumptions?
MR. KURITSKY: Right. Right.
DR. BONACA: I understood, for example,
that your multiplier under the code, it's one of those
things, is it?
MR. KURITSKY: Okay. What I just
mentioned was the first type. And the second time is
what Mario just mentioned; it's multiple -- you know,
anything in Appendix K, some of the actual features,
required features in Appendix K we may feel are
actually conservative. Like, for instance, 1.2
multiplier on decay heat or, as we're going to mention
later, the few that we're going to look at.
DR. WALLIS: This might even get down into
the actual calculation model for a large break. I
mean, requiring something like a Moody model in
Appendix K may not be appropriate if you know how to
do something better.
MR. KURITSKY: Yes.
DR. WALLIS: Well, you seem to be thinking
more in terms of regulatory part rather than the
MR. KURITSKY: Right.
DR. WALLIS: -- code modeling part.
MR. KURITSKY: Right.
DR. WALLIS: Okay.
DR. KRESS: Those models and those
conservatisms were put there on purpose --
MR. KURITSKY: Right.
DR. KRESS: -- because of the
MR. KURITSKY: And the idea being that
more recent information may allow us to be in a better
position to --
DR. KRESS: If you think you know better
what the large-break LOCA frequency might be, so that
MR. KURITSKY: Well, that's a whole
another issue. In the Appendix K part we may know
more about, you know, heat transfer or we may know
more about downcomer boiling or something. There's
different things that we know more about now then we
did back in, say, 1974 time frame.
DR. KRESS: So that's sort of somewhat
separate from actually making a risk-based move. It's
just the fine tuning Appendix K as it is now.
MR. KURITSKY: Right. And, in fact, we're
going to actually mention when we get a little further
along how we are actually kind of separating off our
purposed changes in two groups. One, which we're
really changing the Appendix K or 50.46, which would
then apply to everybody and then the other would be,
you know, coming from a risk-informed alternative to
Appendix K or a 50.46 and then that would be
something that would be voluntary.
So you're right, some of these things are
just fine tuning what's there already.
DR. SHACK: Where did we leave off?
MR. KURITSKY: Okay. The third bullet
just kind of follows on from the second bullet. The
current estimates of the LOCA frequencies aren't
sufficiently low that we can rule them out from the
design bases, but they are low enough that when we
combine them with the reliability of the ECCS we don't
see them as being risk significant.
DR. WALLIS: But if you made the large-
break LOCA no longer a part of this rule, then the
reliability might get lost because it no longer has to
confront the break. So these aren't independent
MR. KURITSKY: Right. That's right.
That's right. Okay.
And lastly, we note from our plant
equipment that has been there and designed for the
LOCA design or large LOCA and LOCA design-basis
accidents. However, it actually gets a lot of use in
the defense against a spectrum of beyond-design-basis
accidents. So we have to be very conscious that if we
do make some changes to what's covered in the design
basis, that we don't allow for something to be --
change, removed that we are currently taking credit
for that has good significance.
DR. APOSTOLAKIS: Can you give an example?
MR. KURITSKY: Well, I'm just trying to
think. Almost any equipment that's used in design of
a large-break LOCA, whether it be a low pressure
injection pump or whatever that's used to meet the
success criteria, the current ECCS acceptance criteria
for large-break LOCA and, you know, that's also used
for, let's say, in a seismic event beyond design basis
seismic event that could result in a loss of coolant
greater than a small LOCA, so therefore you would need
to have low pressure injection --
DR. APOSTOLAKIS: Well, then you're back
to a large LOCA, just that the cause changed.
MR. KURITSKY: Right. The idea being that
it was in the design basis because of a large-break
LOCA, but yet it's used for a response to something
that may be beyond the design basis, in an issue
that's not considered within the design basis.
DR. BONACA: But actually the report
identifies the view on design basis, but also in
transients, for example, certain transients that will
lead you to the need for some injection, right? You
mean, your knowledge, at least in the report, shows
pretty big spectrum of applications of ECCS injection
for some issues.
MR. KURITSKY: Right. Right. Yes, to
require further initiation.
DR. BONACA: I mean ultimately they end up
in a LOCA of some type, or maybe, you know, examples
of station blackout issues and things that drive need
for -- any requirements for ECCS.
MR. KURITSKY: Right.
DR. SHACK: I mean this notion that the
large-break LOCA is also the surrogate for all the
other LOCAs, whether it's man ways or seismically
induced equipment failures and supports and things is,
again, even if you could show that the large pipe
break was infrequent, you'd also have to show that all
other sources of large LOCAs would be equivalently
MR. KURITSKY: Actually, that's very good.
The -- that's one of the one main things he's getting
at too, things like that.
DR. SHACK: Well, I think -- and, again,
you know, we're talking about ancient history here.
But I mean the Livermore studies had the indirect
failures essentially as contributing more to the
large-break LOCA, you know, back when the did those
things in the '80s than the pipe failures themselves.
MR. KURITSKY: Right.
DR. WALLIS: Back to number three, not
only is the large-break LOCA less likely, but it may
be easier to handle than small-break LOCAs. This is
one reason that the AP600 opens up a valve, because
you depressurize and it's easier then to refill. It
may well be that, although it appears in the big pipe
break is a worse thing to happen, in fact it's easier
to handle with your ECCS. Is that a true statement?
MR. KURITSKY: And that's also why you've
seen a lot of PRAs, you see the contribution to core
-- in small breaks is greater than for large breaks.
DR. WALLIS: Not just because they're less
MR. KURITSKY: They're more likely, in
DR. WALLIS: They're more likely and
they're more difficult to handle.
MR. KURITSKY: And they can be, because
you have to depressurize, right.
DR. WALLIS: Right.
DR. KRESS: And that's why I think the
rule calls for looking at a spectrum of breaks, too,
because it doesn't limit it to the large.
DR. APOSTOLAKIS: Again, going to the last
bullet, are we regulating now beyond design basis
MR. KURITSKY: No, we're not regulating
beyond there, but it just --
DR. APOSTOLAKIS: Then where do we go?
MR. KURITSKY: Because this equipment
helps reduce the --
MS. DROUIN: This is more of a cautionary
type statement in consideration of our defensive tab,
which is going to come out on the next slide.
DR. APOSTOLAKIS: Okay.
DR. KRESS: Well, but we've always
regulated beyond design basis.
DR. APOSTOLAKIS: We have?
DR. KRESS: We always have.
DR. APOSTOLAKIS: Like when?
DR. KRESS: The design basis regulates
beyond design basis.
DR. APOSTOLAKIS: It's meant to be a
DR. BONACA: I think for the regulation
the ELPs are very much beyond design basis, too. I
mean, they have considerations and multiple -- sort of
support where directions are given to the operator on
what he has to put up and how -- and so there is a use
for whatever equipment you have.
DR. APOSTOLAKIS: Yes, but you're not
asking for new equipment or new design.
DR. BONACA: No.
DR. APOSTOLAKIS: Yes, that's my point.
DR. BONACA: But you're asking for
mitigation on whatever you got. I mean, we've been
banking on this system for what it is. And so by the
DR. APOSTOLAKIS: Is an earthquake part of
the design basis? But the stuff you're talking about
is really beyond the -- earthquake right?
MR. KURITSKY: Yes, and PRAs, yes.
DR. APOSTOLAKIS: Well, not in PRAs. I
mean reality. You're not going to have a large-break
LOCA with an earthquake that's safe shutdown.
MR. KURITSKY: Right. Right.
DR. APOSTOLAKIS: And so that's something
legitimate to worry about what's going to happen
beyond the SSE?
DR. KRESS: You always worry about that.
DR. APOSTOLAKIS: Well, we should worry
about it. We make it part of the regulations. I
thought the whole idea of the design basis accidents
was we defined an envelop beyond which we don't go.
DR. KRESS: That's exactly right.
DR. BONACA: Yes, but after TMI, we
discovered that we needed some -- I think many of the
things right now we have really conquered whatever we
got, and I think the U.S. regulatory system has not
imposed additional requirements, in other countries
DR. APOSTOLAKIS: I think what Mary said
makes more sense to me, that this is a cautionary.
Yes. But strictly speaking if I start worrying about
beyond design basis accidents, I would deny 99 percent
of the industry. It's like defense-in-depth and risk-
informed regulation. In the name of defense-in-depth,
no. In the name of protecting me from accidents that
go beyond design basis, I deny. Because I'll find
some weird occurrence --
DR. KRESS: It depends on your criteria
for what you mean by protection.
DR. APOSTOLAKIS: We don't have criteria
how to handle these, do we?
DR. KRESS: No, that's the problem.
DR. SHACK: But if they contribute enough
to CDF you certainly --
DR. KRESS: Yes, I understand, George, but
CDF itself is beyond design basis. Core damage is
beyond design basis.
DR. APOSTOLAKIS: And we are not
regulating on the basis of CDF. We are not.
DR. BONACA: And the program, severe
accident management guidelines are based on utilizing
whatever we got for events that go beyond design
basis. And, so, I mean there has been a commitment of
the industry to use, the OPs use it and in some cases
PWRs, APGs are intertwined between design basis and
DR. KRESS: The whole idea, though, is to
see if we can change the regulation.
DR. APOSTOLAKIS: Sure.
DR. KRESS: And in a risk-informed manner,
and then you're automatically going beyond design
basis whether you like it or not. You're not
regulating to it, you're using it as a tool to see how
to change the regulation. The regulation is always
addressed beyond design basis.
The way it does it, is like you said, they
generally use the frequency of the currents and the
cut off for the design basis. So if you dream up a
design basis accident which has a frequency of the
currents less than 10-6 per year, you usually don't
worry about it. That wasn't a strict rule. Some of
them do go beyond 10-6, but for example, the design
basis that includes a LOOP for the large-break LOCA.
DR. APOSTOLAKIS: I think the 10-6 applies
to the initiator, not the sequence.
DR. KRESS: No, it's the initiator, but
you know, you can forget about it at that point.
DR. APOSTOLAKIS: Not the sequence.
DR. KRESS: Well, no, I think it applies
to the whole sequence when it comes to design basis.
DR. BONACA: I would agree that the
statement that Mary made is the correct one, because--
DR. APOSTOLAKIS: But Alan said their view
that it's not low enough. The frequency of the large-
break LOCA is not low enough to forget about it, not
DR. KRESS: Maybe not low enough.
DR. APOSTOLAKIS: Maybe.
DR. KRESS: Your assessment might not be.
DR. APOSTOLAKIS: Well, I'm just trying to
understand the rules of the game. Are we really
regulating -- I mean, we're attempting to regulate
using risk information, are we attempting to do things
in a traditional --
DR. WALLIS: That's the whole idea. It's
the whole idea.
DR. KRESS: Yes, that's the whole idea.
DR. APOSTOLAKIS: Yes.
DR. BONACA: But, for example, if they go
into the notice that has been used for a certain
scenario beyond design basis and the probability of
that scenario combined with blah, blah, blah is
extremely low, then surely you would exclude the
importance of the ECCS for that scenario.
DR. APOSTOLAKIS: Okay.
DR. BONACA: And you may just consider the
MS. DROUIN: Correct.
DR. BONACA: So you're just looking at
DR. APOSTOLAKIS: Again, okay, this is
Option 3 risk-informed. So why then do we care about
the frequency of the initiator itself? Shouldn't the
frequency of sequences --
DR. WALLIS: But if the initiator is small
enough, you don't care about the sequence, do you?
DR. APOSTOLAKIS: But not the other way.
DR. WALLIS: Because the sequence isn't
going to be large.
DR. APOSTOLAKIS: But it can be large,
large and they're small enough, and I would still not
care on the basis of other things.
DR. WALLIS: That's why you look at --
DR. KRESS: You could go that step, too.
DR. APOSTOLAKIS: Yes. But we're not
going that way?
DR. KRESS: Well, I think the first step
is to --
DR. WALLIS: We're doing both.
DR. KRESS: Yes, we're doing both. I
think if we listen to them, they'll tell us they're
MS. DROUIN: If you go back to -- I didn't
bring a copy of it with us, but if you go back to our
framework document --
DR. KRESS: Yes, it's in there.
MS. DROUIN: It's in there. And, I mean,
I'm going to just bring it down for a second because
our second bullet on the next slide says it follows
the guidelines and the framework. And so if you go
back to the framework to that figure that shows the
quantitative guidelines, we deal with initiated
frequency, we deal with the CDF.
DR. KRESS: We had three ranges of
MS. DROUIN: That's right.
DR. KRESS: And they had to -
DR. APOSTOLAKIS: All right. I remember
DR. KRESS: Yes. Okay. And then they had
the CDF, and then they had the LERP.
DR. APOSTOLAKIS: Okay.
MS. DROUIN: So we deal with all of those.
MR. KURITSKY: Okay. Now we're on this
DR. APOSTOLAKIS: And we're done with it.
MS. DROUIN: Want me to go back to the
DR. KRESS: No, please don't.
MR. KURITSKY: Okay. And we mentioned in
the previous discussions -- we're looking at two
different types of changes to make. The first set of
MS. DROUIN: In the near term. These are
the near term ones.
MR. KURITSKY: The near term. Near term.
DR. APOSTOLAKIS: Within a year, or
something like that? Right now?
MS. DROUIN: We're going to get to the
schedule. Bear with us.
MR. KURITSKY: That's the last side, so it
keeps your attention.
In any case, we're looking at two types of
changes. The first set of changes would be to the
actual technical requirements of the current 50.46 and
Appendix K. Again, like Mary said, we use 50.46 very
loosely but it can mean that 50.46 and one or more of
these accompanying regulations. And particularly
terms of the acceptance criteria and the evaluation
model, we'd be looking to make changes to the existing
And then a second set of changes would be
part of a voluntary risk-informed alternative to 50.46
and GDE 35 and/or GDE 35, and that would deal with the
reliability requirements. That goes to the assumption
about the simultaneous loss of off-site power and the
single failure criteria.
DR. KRESS: Can we view what's going under
A as allowing utilization of what margins already
exist? Cutting down on those margins?
MR. KURITSKY: Using new information to
help us, you know. Going back to what you had said
before about how new information -- back then there
was, say, certain margins --
DR. KRESS: Yes, but regardless of what
information you use, you're cutting down the margins.
Because you maybe have a better appreciation of what
the margins are. You can ease up on them, because you
have a better idea of what the margins are?
MR. KURITSKY: Right. Where there were
margins that were applied on the past based on not
knowing certain things.
DR. KRESS: Yes.
MR. KURITSKY: Now we have the knowledge,
we don't need as much --
DR. KRESS: Yes, you have a better idea of
what the margins are, you can ease up on them a
DR. WALLIS: But the result will be that
the reactors are less safe?
MR. KURITSKY: No, I wouldn't say that.
That's a requirement.
DR. WALLIS: If they make changes in their
operating procedures or design as a result of
regulations, it will be in the direction of cutting
down on safety margin? It may be to establish a
safety margin which was reasonable all the time,
because it was too conservative before.
MR. KURITSKY: Right.
DR. WALLIS: But the effect will be to
reduce safety margin.
MR. KURITSKY: Except that where margin
was applied based on not understanding a certain
process, and now better understanding that process
tells us that we can now model that process better.
DR. WALLIS: It means that you were too
MR. KURITSKY: Right.
DR. KRESS: That they were unsure about
what the uncertainty was.
DR. WALLIS: That's right.
DR. KRESS: Now they have a better idea,
they say well we were too conservative. We can use
some of that.
DR. SHACK: But, again, it's not simply a
matter of conservatism. You know, your steam
generators -- I mean, your diesel generators may work
ore reliability now for small breaks --
DR. WALLIS: Then something has changed
which is better.
DR. SHACK: I think that you actually can
argue that there is a safety benefit to changing this
rule as well as a --
DR. WALLIS: It would help if we could do
that. It really would help.
DR. BONACA: No, the question is how do
you do that. I mean --
DR. WALLIS: Now, B you start with a fresh
sheet of paper?
MR. KURITSKY: Well, not really. B is the
more risk-informed piece. We're actually using risk--
DR. WALLIS: B sounds very interesting.
MR. KURITSKY: B is using the risk -- A
really isn't, as I think Dr. Kress pointed out, isn't
really looking at risk-information. It's just kind of
cleaning up what's there.
DR. WALLIS: A you can see achieving. A
is something achievable. How much is doubt, but A is
B is much more iffy and much more
MR. KURITSKY: What have a schedule for
this, which if you believe it is 12 months.
DR. WALLIS: You're just looking at the
record then, so maybe I went too far. There is no C,
which is development of a fully risk-informed --
MR. KURITSKY: No. We're just focusing in
the near term.
DR. WALLIS: Okay. I understand.
DR. APOSTOLAKIS: But he's talking only
about the reliability requirement.
DR. WALLIS: That's right.
MS. DROUIN: We talk about the reliability
MR. KURITSKY: Any rule change in 12
MS. DROUIN: When we talk about
reliability requirements, again we're talking about
the single failure criteria and the LOCA LOOP.
DR. BONACA: Right. And I think your
report already makes a convincing case that for a
large-break LOCA you assume also a LOOP. It's an
MS. DROUIN: Yes.
DR. BONACA: And so, I mean, that's a
pretty clear cut.
DR. APOSTOLAKIS: Now I'm confused myself.
So A deals with acceptance criteria in the evaluation
MR. KURITSKY: Yes.
DR. APOSTOLAKIS: But if you develop a
risk-informed alternative, you're not going to deal
with acceptance criteria and evaluation.
DR. KRESS: Well, you might.
MR. KURITSKY: In the long term you may.
right now in the short term we don't have a change
proposed dealing with the evaluation model. We had
thought about some of them, but we couldn't establish
their feasibility in the short term.
DR. APOSTOLAKIS: And why can't you change
the reliability requirements in the short term for the
MR. KURITSKY: Well, we are going -- you
mean, as opposed to making a risk-informed
DR. APOSTOLAKIS: Yes. I mean, you
mention explicitly acceptance criteria and evaluation.
Why don't you say and the reliability requirements?
I mean, they're very explicitly stated on slide 5:
"On site power operation and assuming a single
failure," and so on. I mean these would easily change
in the current rule, right?
MR. KURITSKY: Right. But we want to
allow people, the licensees, to choose to keep the
current requirements if they want to. If they want to
do their analysis assuming a lost of off-site power,
simultaneous loss of off-site power and a single worse
failure, they may do so. This is going to be an
alternative if they want to use either of the two
methods that we're going to discuss shortly.
DR. APOSTOLAKIS: The question is in A.
MS. DROUIN: It wouldn't be mandatory.
DR. APOSTOLAKIS: Huh?
MS. DROUIN: It wouldn't be mandatory. B
is not a mandatory. It's a voluntary.
DR. APOSTOLAKIS: No, but in A you're
explicitly talking about acceptance criteria and
evaluation. And I'm wondering why you don't also
mention reliability requirements. They're very
explicit. I mean, you can say don't do this anymore.
You don't have to have a risk-informed alternative to
do that. You can easily say as part of the current
50.46 we're changing this. No?
DR. BONACA: Well, they have to have a
basis determinable to that, that's what they're trying
to do now. They're trying to develop the basis for
which they can tell them as part of 50.46 don't do
that. Don't take --
DR. APOSTOLAKIS: Why are two of the four
mentioned and not a third one?
DR. SHACK: Well, hold on, maybe they'll
get to that. I'm interested, too.
DR. KRESS: The current regulation
addresses reliability very, very indirectly. In fact,
by using the single failure criteria --
DR. APOSTOLAKIS: Yes, and off-site power.
DR. KRESS: Right.
DR. APOSTOLAKIS: Right.
DR. KRESS: It doesn't specify what the
reliability has to be.
DR. APOSTOLAKIS: No.
DR. KRESS: And if you're going to change
that, I don't now what you do. You have to have a
basis for saying what the actual reliability is and
from erring it and determining. I mean, I don't think
they ought to get into that with A. I sort of think
that's something that leads to D.
DR. BONACA: A is more like, you know,
they're saying for example 2100oF. Okay. It may be
inappropriate to measure the real objective, which is
the coolability of the core; that's what they're
DR. KRESS: Yes.
DR. BONACA: And you may show that you can
have higher temperature than that and still meet those
requirements. So within the models existing right now
they find there are ways to meet the same objectives
with less -- so that's really much more into the
evaluation model and 2100, which is one of the
The other one, it's more of this
reliability requirements which are really right now
there isn't a solid basis for understanding why you're
imposing LOOP in addition to single failure, in
addition to the blended -- that's -- okay. And if you
kind of develop an understanding of extremely low
probability, then you can eliminate that. But you
don't want to eliminate that blended break, so then
you can eliminate a LOOP.
DR. WALLIS: It's interesting, but we're
still trying to infer why they might have divided it
into classes A and B. Maybe we should ask them why.
MS. DROUIN: Going back, A is we're going
to the acceptance criteria in the evaluation model and
the current 50.46. And with current knowledge we're
doing some clean up work in the current rule. That's
all it is. It's really that simple.
Now we get more into of what Option 3 is
about and bringing risk-information and coming with
our risk-informed alternative, which is supposed to be
voluntary. So this would be creating a separate
regulation that a licensee could choose to implement
or not. It'd be like -- I mean, in 50.46 where we
came up with a alternative, here's our risk-informed
DR. APOSTOLAKIS: So the second bullet
then really refers to B only?
MS. DROUIN: In B you don't need A,
because you've already done it. It will be there.
DR. APOSTOLAKIS: But A will not be done
following the guidelines in Option 3
MS. DROUIN: I'm sorry?
DR. APOSTOLAKIS: A will not be done
following the guidelines in Option 3?
MS. DROUIN: It certainly won't contradict
DR. APOSTOLAKIS: It's just in there?
MS. DROUIN: As I said, it's not really
DR. APOSTOLAKIS: Okay.
MS. DROUIN: It's more just clean up
DR. WALLIS: Well, are you going to look
at something like 2100o?
MS. DROUIN: Yes.
DR. WALLIS: Are you going to say what
risk benefit is there from that and suppose it were
2250 or 2300, what would be the additional risk? And
then you're going to make choice based on risk? Is
that the kind of thing you're going to do?
MR. KURITSKY: Well, I think --
MS. DROUIN: Well, we're going to get into
it, so why don't we move on to the next slide.
DR. KRESS: But before you leave, are we
going to talk about in this meeting about this
framework document and all?
MS. DROUIN: No, we hadn't --
DR. KRESS: Could I ask one question about
MS. DROUIN: No.
DR. KRESS: Why? In your table of
framework where you have three ranges of initiating
event frequencies and then you have the conditional
MS. DROUIN: Yes.
DR. KRESS: It wasn't quite clear to me
whether those ranges of initiating event frequencies
referred to just one initiator or the summation of a
set of initiators.
MR. KURITSKY: The summation of the set?
You mean --
DR. KRESS: So you're going to take all
initiators and group them into these three sets, in
some there are frequencies and that's the range you're
talking about in that range of frequencies?
MS. DROUIN: Yes.
DR. KRESS: Okay. I just wanted to get
clarification of that. Because it's something that
bothered me when I looked at it.
MS. DROUIN: We are planning on reissuing
an updated version because we did receive comments
from the ACRS. We did get some public comments. And
we've gone through and we're trying to clarify all
this, and we hope we have a new version out in August.
It doesn't change any of the technical basis or
concepts, just better --
DR. KRESS: Just clarifies it?
MS. DROUIN: Better explanations of the
numbers and how they're used.
The next set of slides that Alan's going
to get into is going to go into detail of what we're
doing in A and what we're doing in B.
MR. KURITSKY: Okay. First in A, which is
the possible changes to the existing 50.46 and
Appendix K. One of the first things we're looking at
is replacing the current prescriptive ECCS acceptance
criteria with a performance-based requirement. And
the performance-based requirement would be that you
would have to demonstrate adequate post-quench
cladding ductility and adequate core-coolant flow area
to ensure that the core remains amendable to cooling.
DR. KRESS: Well, let me ask you a
question about that. The current version is based on
failure to develop for zircaloy clad, I presume. And
it has to do with how much oxidation you had as far as
clad embrittlement and how much bowing and swelling
you might have as with respect to the temperature.
Well, if you were to write a general rule
that says you demonstrate the coolability, well won't
whoever makes that demonstration have to go through
the same -- if they're using, say, a different kind of
clad, it's got to go through the same experimental
program and same database? I mean, develop it all
over again for their new clad?
MR. KURITSKY: In fact, that's exactly --
you see the last bullet. The whole purpose -- the
main purpose of this change to these acceptance
requirements is to allow uses of other cladding
DR. KRESS: Yes.
MR. KURITSKY: What currently they have to
do is if they want to use a different material, is
they have to apply for a license exemption, okay. And
what we want to do is have that changed so that the
rule will be more general, you know, it would be more
performance-based nonprescriptive. And in the rack
out we would specify some conditions they'd have to
meet, and one of them would be what they would have to
go through in order to demonstrate that adequate post-
quench ductility, which would be that criteria.
DR. KRESS: Okay. So you'd spell that out
in a reg guide?
MR. KURITSKY: Right. Right.
DR. KRESS: Okay.
MR. KURITSKY: And as a matter of fact was
the main purpose of this change, this clean up, so to
speak. So it's not limited just to zircaloy and
DR. WALLIS: I like this. I think,
though, that you have to think very carefully about
what the performance is to be.
MS. DROUIN: Yes.
DR. WALLIS: The performance-based
requirement. And amenable to cooling, I challenged
last time because you can always cool some things some
And then your thing about a core
temperature and acceptably low value, well there's
nothing magically about temperature. It's got to be
something other than temperature. It's got to be some
consequence to safety.
DR. KRESS: What the temperature does to
the geometry, yes.
DR. WALLIS: To geometry or the
coolability, or to eventually release of fission
products. There's got to be something here about
MR. KURITSKY: Right now this is just
taking this thing --
DR. WALLIS: You've got to think very
carefully about what these performance measures are to
MR. KURITSKY: Right. Right. Right now
we're working on it. That's taking an existing -- the
five criteria that are there right now, this is the
long term cooling criteria --
DR. WALLIS: But you see hydrogen release
isn't covered by any of this, is it?
MR. KURITSKY: Right. And the idea being
that hydrogen is not really controlling and it's going
to be adequately taken care of with the 50.44.
DR. WALLIS: So they can release as much
hydrogen as they like?
MR. KURITSKY: Well, no. But the control
of hydrogen is going to be covered under 50.44.
DR. KRESS: Well, they have an oxidation
limit in this rule which could be converted into
hydrogen, but it doesn't produce much hydrogen because
what it has to do is embrittle of the clad. So that
will actually control the amount of hydrogen. It'll
be a lot less.
DR. WALLIS: But you know we can't produce
a great deal of hydrogen.
DR. KRESS: Not with that level, no.
DR. WALLIS: Not with that level. So
something else happens first.
MR. LEITCH: You overly embrittle the clad
before you get much hydrogen.
DR. WALLIS: At least with the cladding we
know today, right?
DR. KRESS: Yes, that's true. Good point.
DR. SHACK: But it would still be covered
DR. KRESS: Yes, the hydrogen part will be
covered under 50.44.
MR. KURITSKY: Okay. I think the major
area of change under A, which is the changes to the
existing criteria or existing 50.46 is changes with
regards to the evaluation -- the test evaluation
model. And that's to make them use more realistic
And in the near term what we're
specifically looking at would be changes to Appendix
K to use more, as we mentioned before, more current,
more realistic information. And specifically this
could involve taking the main pieces -- what's
currently for the -- the '71 ANS decayed standard
using a multiplier of 1.2 to account for uncertainty.
And we'd be looking to use instead something like the
'94 ANS standard and then coming up with an NRC-
prescribed uncertainty treatment because the '94
standard has a lot more options and perimeter and
uncertainty treatments. It's a little more
complicated than just applying factor, which is done
for the '71 standard. So that's one of the main
pieces that we're looking at under changes to Appendix
But we also wanted to take a look at these
other few things that are on the list. There's a
couple of items that we're looking. We want to look
at more recent data to see whether or not they want to
delete the limitation on the PWR reflood steam cooling
for small reflood rates. And then also the
possibility of deleting the prohibition on the return
to nucleate boiling during blowdown.
And lastly, we're also looking at the
Baker-Just -- what currently is used at the Baker-Just
zirconium steam model and we'd be looking at possibly
using the Cathcart-Pawel zirconium steam oxidation
model just for heat generation. Replacing that plan
for fuel embrittlement, that would be covered on the
other. And we're looking at demonstrating adequate
ductility, but for the heat generation part, we would
be looking at replacing Baker-Just with the Cathcart-
So those are some of the clean up items
that we're looking under at under Appendix K.
And then the important thing to note at
the bottom is that as part of this update we'd also be
looking at recognized nonconservatisms and model
limitations that exist right now and to make sure that
those are accounted for and that the safety focus is
still, you know, maintained such that the impact of
these nonconservatisms, recognized nonconservatisms
and model limitations wouldn't -- what's that phrase--
significantly erode the conservatism remaining in the
Appendix K model.
DR. KRESS: Well, when you start getting
rid of only conservatisms, replacing them with more
realistic best estimate type, should one start
thinking about these best estimate calculations need
to be accompanied by uncertainties so we really know
how close we are to limits?
MS. DROUIN: Yes.
DR. KRESS: Would that part of this change
MS. DROUIN: You're not going to be able
to do that without thinking of the uncertainties
associated with them.
MR. KURITSKY: Okay. As part of these
changes that we -- these proposed changes that we're
considering, there'd be additional technical work that
would have to be done. As Mary mentioned, right now
this Phase 1 work is a feasibility study and there is
additional work that would have to be done under Phase
2 in order to support rulemaking.
And the main thing that would need to be
done under Phase 2 for these A changes would be work
to support the removal of the unnecessary
conservatisms from Appendix K, which means for each of
those items that we just listed as possible changes on
the previous slide, we'd have to go through and look
at data or look at different calculations and
sensitivity analysis and uncertainty consideration to
determine what we feel comfortable -- what changes
we'd feel comfortable making.
Also as part of the ECCS acceptance
criteria changes we discussed a couple of slides ago,
and I think we mentioned, too, we'd have to go through
and identify what would be necessary for -- what
guidance would be necessary for demonstrating adequate
DR. WALLIS: Again, that's a funny
criterion. I mean, ductility is a means to an end,
not an end in itself.
MR. KURITSKY: And this, again, not my
area, but my understanding is that we're saying as
long as we can hold the core in its shape --
DR. WALLIS: But how much is it allowed to
distort, and what does this do to the cooling
capabilities and such? It's not a simple question.
It can stretch into all kinds of shapes and still be
okay, but then someone has to analyze to see what the
consequences are of those events and so on.
MR. KURITSKY: Right. And I think that's
what the other -- I mean, that's -- the adequate post-
quench ductility is one of the two pieces. The other
piece was adequate core-coolant flow area.
DR. WALLIS: You're saying the same as
nonreleasing fission product, isn't it?
DR. KRESS: But that's part of the post-
MR. KURITSKY: That's the ultimate, right.
DR. WALLIS: Well then why don't you put
that in as a criterion instead of these means to an
MR. KURITSKY: Well, I guess, again this
is not my area of --
DR. WALLIS: But if you can't cool it, it
gets hot and then eventually releases product. It is
ductile, it splits and it releases fission products.
The end is releasing fission products, isn't it?
MR. KURITSKY: Yes.
DR. WALLIS: So why don't you put that in
as a criteria, otherwise you get into something which
is too wishy-washy.
MR. KURITSKY: Well, I think -- and again
DR. WALLIS: It'll blow out like a great
big balloon, and that doesn't make it okay.
DR. KRESS: It's because you can't --
because if you had limits on fission products --
DR. WALLIS: Yes.
DR. KRESS: -- you couldn't quantify very
well, and you have to back off to the next level.
Say, well let's put the limit on ductility and if we
got a certain level of ductility, we know we're not
going to release fission products. So it's one of
those things were you back off to where you can deal
with something you can deal with. Because you're not
going to be able to calculate the amount of fission
products you get out a given ductility level.
DR. WALLIS: Right. But then if you
can't, you get conservative about your ductility then?
DR. KRESS: You get more conservative
about your ductility, yes. You back off to where you
can -- to something you can deal with.
DR. WALLIS: Well, I'm just saying don't
back off until you have to.
DR. KRESS: Yes, well I think it's a good
DR. WALLIS: Because if you're doing
something which is a much better measure of
performance than --
DR. KRESS: You should always turn to high
level and see where you can deal with it, yes.
DR. WALLIS: Right.
DR. BONACA: But I thought that's why you
need the time, right, to develop so this criteria --
Yes, that's why Bill Shack's right about
the one year.
DR. SHACK: No, no. The one year is after
they finish the technical work.
DR. KRESS: To write the rule? To change
the rule? Well, they could probably do that.
MR. KURITSKY: Actually, the work for this
actually is currently ongoing at Argonne National Lab.
And so we'll be able to borrow off that and use it for
DR. KRESS: Well, that adds a couple of
years to it.
MR. KURITSKY: I was told it would be done
DR. APOSTOLAKIS: December 2003.
MR. KURITSKY: They may have left that
MR. LEITCH: On your previous slide one of
the bullets said deleting the prohibition on return to
nucleate boiling during blowdown. Why can we
eliminate that prohibition?
MR. KURITSKY: Well, we don't know if we
can. What we're saying is --
MR. LEITCH: Well, why do you suspect you
MR. KURITSKY: It's just we want to look
at more recent data on heat transfer during blowdown
and on minimum film boiling temperature. Actually,
the expert is here.
MS. DROUIN: Norm's going to --
MR. KURITSKY: Norm is here.
MR. LAUBEN: I think that there's
certainly a lot of question as to whether you really
could eliminate that, because minimum film boiling
temperature of the data is quite large, although you
could choose a low enough one and be -- might be okay.
But this request was made by one of the
industry representatives, and if they have some
interesting science to provide us, we'll be willing to
look at it. But the people I've talked to thus far,
I would have to say there's not a lot of optimism in
this particular one. That's why the word "could" is
up there. But we don't want to exclude from making a
case for that, that's all.
Oh, excuse me. I guess I'm supposed to
say I'm Norm Lauben from the Office of Research.
MR. KURITSKY: Okay. If there are no
other questions on this slide, we can go to the next
MS. DROUIN: Just I want to add, going
back again, all we've done now is determine it's
feasible. Over the next year as we do the technical
work, we'll be coming to the ACRS, I'm sure, on
numerous occasions as we get into the details of this
and, hopefully, during that time period, you know, a
lot of these questions that you're raising are very
good and, hopefully, we're start beginning having
answers to them.
DR. KRESS: One with respect to this Part
A, it would be interesting to know if you made these
changes what would be the resulting changes that the
licensees would make in the way they operate their
plant or even plant hardware. And then how would one
look at those changes and perhaps give it the 1.174
treatment that would say these changes are acceptable
to us from a delta risk standpoint? Is that part of
this A activity or is it a thinking part of it?
MS. DROUIN: I'm sorry, I didn't follow
DR. KRESS: Well, if you make these
changes in the regulations, Part A, then the plants
are going to do something. They're going to up the
power, they're going to maybe even relax some of the
ACC requirements; I don't know what they're going to
do, but they're going to do some things. You have a
made a list of what these possible changes might be,
and then looked at that list of changes and give it
the reg guide 1.174 treatment to say that list of
changes would likely result in a delta risk of so
much, and therefore maybe we'd better think about it
again or something?
MS. DROUIN: If you go back to the earlier
slide where we said we're going to follow our
guidelines, our framework guidelines, which are
DR. KRESS: Yes, but for A --
MS. DROUIN: Yes.
DR. KRESS: For A you're going to follow
MS. DROUIN: Oh, absolutely, yes.
DR. KRESS: Oh, okay.
MS. DROUIN: Yes.
DR. KRESS: And they're sort of consistent
MS. DROUIN: They're totally consistent
with 1.174, yes.
DR. KRESS: Okay. I didn't realize you
were going to the guidelines for the A part.
MR. ROSEN: Mary, as long as we're on A
and B, could you go back to that slide for a minute
and let me ask you a question? Slide 9, I think it
From a licensee's perspective -- no, I'm
sorry. It's slide 8 that I want to look at. Okay.
From a licensee's perspective what you've
described now seems to be we've put them in a position
that once they did the changes to their modeling and
processes that A would allow, they would get some
improvement, some value from that which would then be
the baseline for whether they would go ahead with the
risk-informed alternative. In other words, they might
get so much value out of A, that going ahead with the
risk-informed alternative might even not be necessary
or even desirable. Could you comment on that?
MS. DROUIN: I think that --
MR. KURITSKY: That possibility exists.
I mean, I --
MS. DROUIN: Yes, but I don't think it's
very probable. Because I think these are two very
separate distinct entities when you look at the
acceptance criteria and the evaluation model versus
what gets imposed because of GDC 35. I mean, I think
they're two separate benefits.
A licensee could certainly come along and
say "You know, I've gotten these benefits from A and
I don't care for anymore benefits." But I think both
of them offer independent benefits.
MR. ROSEN: Okay. Thank you.
MS. DROUIN: Were we on 12.
MR. KURITSKY: I think we're on 12, yes.
The type B changes that we're considering,
which are the ones that involve developing a voluntary
risk-informed alternative to 50.46 and/or GDC 35 would
involve -- the technical requirements that are used to
ensure or that -- well, the changes that we would be
recommending would include technical requirements to
ensure an ECCS reliability that's commensurate with
the frequency of the challenge. And that goes back to
the discussion we had early on in the presentation
where we would be trying to match up the ECCS
reliability with the frequency of the LOCA initiators
DR. WALLIS: Now reliability includes
functionality? I mean reliability per se to me just
means does the pump work or not. But, I mean, does it
perform? Does the whole thing work, it's
functionality. That's got to work. That's got to be
there, too. It's got be functional and reliable.
MR. KURITSKY: Yes, again --
DR. WALLIS: Conceivably if you said don't
worry about this size break and that size break,
people would change the size of the accumulator or the
size of the pumps or something, so they couldn't
handle a big break. It wouldn't even function.
MR. KURITSKY: Right. In my mind
reliability means it has to be reliable to accomplish
its function. So to me I see functionality being part
of it. But I'm sure that, you know, people are going
to have to defend wording interpreting, so that point
is definitely true, I mean that has to be accounted
DR. KRESS: When you say commensurate with
the frequency of challenge, the only reason that seems
to me like it's a useable concept is because you
somehow know the next step, and that's the conditional
core damage frequency. So you could back off from
some criteria like 10-4 to take conditional and then
say now what is the frequency that I can live with.
MR. KURITSKY: That's exactly right.
Based on the options in the framework guidelines we
come up with some, say, GDF limit and then we can back
off of that. Looking at different -- the frequency of
different groups of initiators, whether it be a
spectrum of LOCA sizes or whatever, and then come up
with what should be the commensurate reliability that
we're looking for.
DR. APOSTOLAKIS: Well, at the same time,
though, we are not trying to bring all the plants up
to the 10-4 goal, are we?
MR. KURITSKY: This is voluntary.
DR. KRESS: It's voluntary.
DR. APOSTOLAKIS: Yes, I know. But, I
mean, you're giving now -- I mean, is that a good idea
to say here you keep the goal and as long as you're
under the goal, it's fine? I thought the idea was not
to push everybody toward the goal.
DR. KRESS: Well, you know, this is a
question about the framework document. The framework
document really starts from 10-4.
DR. APOSTOLAKIS: Yes.
DR. KRESS: And works -- well, it actually
starts from LERC and even works its way backwards, but
it has 10-4 built into it as a defense-in-depth
DR. APOSTOLAKIS: But that's at the high
DR. KRESS: Yes, but they back off to a
frequency that's consistent with that based on the
success criteria of ECCS and the conditional core
damage frequency that you get when the ECCS fails.
And that's another question I was going to have, do
you factor success criteria into that some way?
Because, you know, they may discover they can do away
with one of the trains, but success criteria has that
built into it sometimes, how many trains are
operational of ECCS.
MR. KURITSKY: Well, in fact, the way this
will work, let me just jump to the second book,
because we're looking at two different options.
MS. DROUIN: Why don't we just get right
MR. KURITSKY: Okay. We're looking at two
different options for how we would accomplish this
ECCS system liability requirement. And the first
option, and it says a deterministic system reliability
requirement based on risk information. And as an
example we put up there an ECCS requirement that only
one train of ECCS would be required for some set of --
DR. KRESS: That is a success criteria.
MR. KURITSKY: Right, sum set of LOCAs.
And that actually is what you'll be using to establish
maybe a less stringent reliability requirement for
initiators that are much lower frequency. And those
various LOCA frequency intervals and the associated
ECCS reliability requirements would be something that
the NRC would be establish based on generic
information. And so once we would come out and
specify what you would need. For this LOCA interval
you would need to have this reliability requirement,
you know, one train or two trains. Well, you need to
consider loss of power, you would not.
DR. KRESS: But would you specify that in
terms of some confidence level in order to factor a
defense-in-depth concept in?
MR. KURITSKY: Well, certainly -- I'd
DR. KRESS: I mean you're not going to
stick to means, are you?
MR. KURITSKY: The framework you
definitely need to consider uncertainty. To get a
mean you, obviously, have to consider uncertainty.
DR. KRESS: Yes. You have to have the
uncertainty to get to mean.
MR. KURITSKY: And the framework document
does talk of means. I mean, the values that are
provided in the framework document are based on mean
DR. KRESS: See, that bothers me because
you could have a given mean, large uncertainty or
small uncertainty, you ought to treat the two
MR. KURITSKY: Right. But that's why this
is something the staff has to -- on this particular
one it will not be up to the licensee to come up with
that value. We'll be doing that evaluation ourselves.
So if we run into a situation where you can have a
very wide uncertainty that could give you a -- mean or
whatever, and we are well aware of that.
DR. APOSTOLAKIS: Or they could specify an
DR. KRESS: Or a confidence level.
DR. APOSTOLAKIS: Yes. They say they're
going to specify a threshold. So, the earlier comment
that it's going to be based on 10-4 is not really
valid. I mean, it's got to be the location issue. It
has to be a large LOCA contribution of some kind, and
they will specify that. And, presumably, they work
with mean values. The value that they will choose
will allow for the uncertainty also. It'll be low
enough to allow for the uncertainty.
And you want it more explicit, that is
what you're saying?
DR. KRESS: Yes.
DR. APOSTOLAKIS: They might give you
reason why --
DR. KRESS: Because I think people would
treat it differently if --
DR. APOSTOLAKIS: They might then give you
a reason why they selected this mean value and do some
sensitivity studies to show what the 96 percentile
does, for example. Because in these cases it's the
high tail that drive the mean, really.
DR. KRESS: Yes.
DR. APOSTOLAKIS: So it's -- but I think
the appropriate NRC specified threshold should address
this question. That's going to be a challenge to do
DR. KRESS: Yes.
MR. KURITSKY: Okay. And just to jump
down. So for number 1, the NRC would establish those
requirements and they would be, I guess, maybe in a
reg guide or whatever, but once we establish then --
DR. APOSTOLAKIS: Now, all this is with
the current definition of large-break LOCA, right?
MR. KURITSKY: Well, right now we're not--
DR. APOSTOLAKIS: You're not touching
MR. KURITSKY: Yes. And this is not just
relegated to large-break LOCA.
DR. APOSTOLAKIS: All LOCAs?
MR. KURITSKY: This would be all LOCAs.
DR. APOSTOLAKIS: Well, the interest is
really in the large-break, isn't it?
MR. KURITSKY: Right, that's obviously
where you would find --
DR. APOSTOLAKIS: So this is the current--
MR. KURITSKY: It's the current
DR. APOSTOLAKIS: The current definition,
MR. KURITSKY: Yes.
Okay. And so, like I said, in the first
DR. APOSTOLAKIS: And now you don't expect
-- I mean, you said there earlier that the issue of
the frequency or the size will be visited later?
MR. KURITSKY: Yes.
DR. APOSTOLAKIS: And if you reach certain
conclusions, then you don't expect these things to
MR. KURITSKY: No. As you'll see when we
discuss that later, that of course --
DR. APOSTOLAKIS: But it's frequency,
MR. KURITSKY: -- had a large synergistic
beneficial impact with these.
DR. APOSTOLAKIS: Yes. Yes.
DR. WALLIS: I don't quite understand why.
If you've got two trains of ECCS for LOCAs of a
smaller size, you don't know what kind of LOCA you're
going to get anyway, so saying you're only going to
have one for a large LOCA, I don't quite know what you
mean, unless you mean in a probabilistic sense, in
which case you're putting in an improbable LOCA with
a improbability of failure of a train, say you're
going to sort of beating a dead horse, really. I
mean, you're putting in a weaker requirement for a
LOCA which isn't required anyway. I don't think you
gain anything for that.
If you have to have two trains for some
other kind of LOCA, you need the two trains.
MR. KURITSKY: Right. Like, as an
example, look at accumulators. You only need them for
large LOCAs. So if you could show that for large
LOCAs you only need one train step, then you would
only need to have one accumulator, let's say, or you
know, something along those lines.
So, you're right. If it's a high pressure
injection pump that's used for small LOCAs and large
LOCAs and transients, just the fact that you only need
one for this case but you need two or more for other
cases, you're right. It doesn't buy anything. But if
there's specific equipment that is associated with us
a particular subset of LOCAs or subset of initiators
that you can then demonstrate --
DR. WALLIS: You might get rid of those
MR. KURITSKY: Well, what we're saying is
that you would say, for instance, especially you only
need to have one train for LOCAs above size X and if
accumulators are only needed in your plant for LOCAs
above size X, you would only need to have one train of
DR. WALLIS: Why?
MR. KURITSKY: If you only had one
accumulator, and now whether or not --
DR. WALLIS: Because one accumulator is
able to handle the large LOCA and the second one's
just a backup?
MR. KURITSKY: Right.
DR. WALLIS: Okay.
MR. KURITSKY: And if there's four, you
need two then it means that, you know, two need two,
you wouldn't need the other two.
DR. APOSTOLAKIS: How would you
accommodate in this risk-informed approach or allow
for the statement you made earlier the plant equipment
that is designed to the requirements of design basis
LOCA also provide defense-in-depth against a spectrum
of beyond design-basis accidents? It seems that this
is strictly based on LOCA.
MR. KURITSKY: Well, actually, it's not
here on the slide, but in the description on
attachment 2 we mention that -- and it applies both
to 1 and 2 here -- is that changes that are made at
the plant based on these things need to consider the
impact not just on LOCAs but on all initiators because
ECCS, of course, is used for a wide swath of
initiators, it's not just LOCAs. So, obviously, no
change is going to be made without considering the
risk impact and the risk significance of those changes
across all initiators.
So, it can impact what you have to assume
for your thermal-hydraulic ECCS performance
calculations. It may -- if you can find things like
an accumulator only applies to a subset of LOCAs, you
can change those requirements, then you can get some
benefit from that. But you need to consider the
impact across all initiators.
MR. ROSEN: But it might also impact
allowed outage times?
MR. KURITSKY: Well, that's what one of
the benefits may be. In other words, I wouldn't say
necessarily that if you had three accumulators in your
plant and now this thing says you only one, you may
not take get rid of one, but you could certainly have
the case for a greatly relaxed allowed outage time on
DR. WALLIS: You wouldn't go from green to
MR. KURITSKY: Yes. I don't exact with
that oversight program what's what, but -- okay.
So anyway, so getting back, under option
1 it's something the NRC will specify. We'll
establish it and it will be specified. And so a
licensee who chooses this option will go ahead, they
will not require any NRC review and approval, because
it would already be there, they can pick it.
And I make that point because in under
option 2 what you're doing is actually allowing the
plant to use plant specific LOCA frequency information
and plant specific ECCS reliability information to
come up with -- you know, to do the same type of thing
but do it on a plant specific basis. So they'll come
up with commensurate ECCS reliabilities based on the
frequency of LOCAs or challenges that they have at
their plant, and that can allow them more relaxation
than what would be obtained through the generic
application the NRC would do.
DR. WALLIS: So people are going to be
exercising these thermal-hydraulic codes a lot to look
and see if they can gain anything by saying well, you
know, if we didn't have this functional, then this
would happen and maybe we could tolerate that, and
maybe something else could happen. There's be a lot
of exploring to see what would happen if you backed
off on all sorts of requirements.
MR. KURITSKY: Right. But I think for the
most part the way it would probably work out is you're
talking about relaxation of allowed outage times. And
you already know from your calculations that you need
this one train or this two trains. And so anything
more than that --
DR. WALLIS: But that you need a train,
who is going to decide whether you need the train? Is
that the calculation of the licensee or the NRC? The
NRC is going to run in some codes to decide that one
MR. KURITSKY: No. I think that the ECCS
performance calculations that are already done
determine how many trains you need.
DR. WALLIS: Oh, they've already been
MR. KURITSKY: I think everybody has to
have those done.
DR. WALLIS: And they have explored all
MR. KURITSKY: Well, they know what the
minimum -- they know the minimum number of trains that
they need or the amount of equipment they need.
DR. WALLIS: Okay. So much of the
technical work has already been done?
MR. KURITSKY: In that regard, yes.
DR. WALLIS: Okay.
DR. KRESS: Based on the current Appendix
MR. ROSEN: Or best estimate.
DR. KRESS: Best estimate.
DR. WALLIS: When you start changing some
of these things, you may need to run those again,
though, when you change these --
MR. KURITSKY: That's right.
MR. LAUBEN: This is Norm Lauben again.
I think in general because of the single
failure requirement currently, and it's the state of
the single active failure, usually it turns out that
the whole thing is designed so one train will do the
trick in terms of pump ECCS. But I think in terms of
accumulator outage times, there may be a dearth of
information about how many accumulators you'd need
under various circumstances. Because you do require
some accumulators even for large small breaks or
certain evaluation models show that.
DR. WALLIS: Small large breaks, too.
MR. LAUBEN: Excuse me?
DR. WALLIS: And small large breaks.
MR. LAUBEN: And small large breaks,
So I think there might be studies that the
vendors would -- and utilities would need to do also
with respect to their accumulator outage.
DR. WALLIS: And the, of course, when
you've changed the decay heat curve and the decay heat
multiplier and all these other things, you have to run
them again and again.
MR. ROSEN: Well, where the margins would
show up, would be in the margin to the peak clad
temperature requirements that utilities have to keep
track of all the time anyway. And with these changes,
my first take on it is that they'd show up with much
larger margins than they now show. Is that correct?
MR. KURITSKY: I think with the A changes,
yes. That's basically would be in, you know, getting
increased peak clad temperature.
MR. ROSEN: And some plants are now quite
MR. KURITSKY: Yes.
MR. ROSEN: -- by the conservatisms in the
existing model requirements.
DR. WALLIS: It's going to be very
interesting for the codes. Because up to now, the
codes have been accepted based on the way things have
always been done. When we start changing these decay
heats and these zirconium steam models, and all those
things, it's going to change everything, isn't it?
So, there's got to be then a careful evaluation of
whether the codes are now adequate for this new
environment and what the uncertainties are and so.
DR. SHACK: Now, bullet 2 would let me get
rid of the simultaneous LOOP and large-break?
MR. KURITSKY: You mean the second option?
DR. SHACK: Yes.
MR. KURITSKY: Yes. It's essentially the
same thing, only it's more of a plant specific type of
calculation. So the NRC would establish some CDF
threshold and they would do their calculation
underneath that threshold.
The first one is meant to do something
where we wouldn't require any reviews. We'd go
through and establish it ahead of time and licensees
who wanted to choose it could just go do it without
having to get review and approval. One allows them to
do that in order to be comfortable, we can do that
across the board, we have to be more conservative.
The second one allows them to be a little more plant
specific if they want to sharpen their pencil and use
their PRA models or do reliability analyses. And,
again, that goes to -- coming with the LOCA
frequencies, it goes to the issue we mentioned before
where it may be some kind of updating of operational
data to come up with the new LOCA frequencies, or it
may involve some PFM analysis and more detailed things
along the lines of large-break LOCA redefinition. So
that would be something they could consider. Maybe it
would take a little longer, but that's something that
they could use their --
DR. WALLIS: And that would be consistent
with the loss of their performance-based regulation
would you just had some -- at a high level a
requirement and then it has to be met somehow.
MR. ROSEN: The first one's more
prescriptive and the second one will be more
MR. ROSEN: Plants with more robust
designs, like three safety trains, would particular be
able to take good advantage of that second bullet.
MR. KURITSKY: And the first bullet, too,
for that matter. Because they may show that maybe two
of their trains can have relaxed aspects or something.
MR. ROSEN: Conversely, plants with less
robust designs might not get any improvement out of
this because they're bumping up against the limits now
and even with the changes, they might not get more
margin, much more margin?
MR. KURITSKY: And the same thing with the
A changes. I know it's very plant specific. Some
plants, you know, may get a lot of benefits, some may
not get that much benefit depending on how close you
are to bumping up to the margins right now.
DR. WALLIS: Well, 2 ought to be more
acceptable to the public if you could say that these
plants -- we are now assuring that these plants have
a certain NRC specified CDF threshold.
MR. KURITSKY: The first one --
DR. WALLIS: That's much more direct than
saying that it's got to have all these prescriptive
requirements, but we don't know what the consequences
MR. KURITSKY: Right. Only -- yes. Maybe
as far as when the public sees it. But for us to go
ahead and come up with those prescriptive requirements
under 1, we're going to be using a CDF threshold as
our metric, too. You're right, it's not as much in
the public in that sense, but it's the same thought
process, the same procedures can be used in 1.
DR. WALLIS: Well, at least it's clear
what your measure of safety is. Your measure of
safety now is analysis specified CDF threshold. It's
not some statement that if they follow our
requirements, that's adequate for the safety. I mean,
this is a definite statement that you have an NRC
DR. SHACK: Progress, right?
DR. WALLIS: That's progress.
MR. ROSEN: Okay. And, again, going back
to the fact that this is a feasibility study right
now, page 1, you know we got to work on feasibility,
establish the feasibility, now under Phase 2 we will
continue with additional technical work to support the
rulemaking. And just as under the A changes, under
the B changes we have a number of items that we have
Specifically, as we've all been
discussing, when it comes to this risk-informed
alternative, we need to determine acceptable methods
and assumptions for performing those LOCA CDF and
system reliability analyses. And that does mean that
we have to take a lot of consideration of
uncertainties, because that becomes a very big part of
determining how we're going to come up with threshold
and what types of analyses will be acceptable for
meeting those thresholds.
Again, the --
DR. APOSTOLAKIS: Excuse me. Option 3 is
separate from 1.174?
MS. DROUIN: Yes.
DR. APOSTOLAKIS: So there in Option 3 you
can actually increase the CDF more than what the
regulatory guide says? Because I mean if you
establish a threshold value that's high enough, then
for a particular plant the result may be a change in
CDF that's more than regulatory guideline 1.174.
MR. KURITSKY: The Option 3 doesn't
specify a limit on like reg guide 1.174 is on
increase. Just like you say, if there's a threshold,
theoretically someone may move up more than what would
be in reg guide 1.174 theoretically. But we do, I
believe, and the framework does say that any changes
that would tend to increase risk would have to be
limited. It's qualitative wording, but I think there
is some wording in the framework that limits -- says
that increased numbers have to be limited and they
must still remain below the framework guideline values
and also may have to be limited. But it's not as
clearly specified as reg guide 1.174, which has actual
MS. DROUIN: I mean, our goal is to stay
consistent with reg guide 1.174. The difference is
that between them is you have to remember is that reg
guide 1.174 is applied on a plant specific basis. Our
framework is applied on a generic basis.
Now, if because of some circumstance the
numbers are going to have to differ, then there will
have to be a real good basis for it. Because our goal
is to stay consistent. It doesn't mean that we can't
deviate, but there'd have to be a good technical basis
MR. ROSEN: But, Mary, after you're done
with this, 1.174 still stays in play, right?
MS. DROUIN: Absolutely.
MR. ROSEN: So then a utility could then
still make small changes to that based on 1.174?
MS. DROUIN: Absolutely. Absolutely true.
DR. WALLIS: I think you're going to have
to face the question of the risk that ECCS wouldn't
work based on uncertainties in the codes. Fit that
somehow into your risk analysis and in a formal way as
soon as you move away from conservatism.
DR. APOSTOLAKIS: It seems to me when you
talk about codes here, the issue of model uncertainty
would be that important, would it not, Graham?
DR. WALLIS: That's the issue, yes.
DR. APOSTOLAKIS: That's the issue.
Now, are you guys having an approach? I
mean we keep hearing now for two years at least that
the University of Maryland is developing something on
model uncertainties. Is that done? Now you have an
approach to this? How are you going to handle it.
MR. CUNNINGHAM: There's, I guess, two
issues of this.
This is Mark Cunningham from the staff.
DR. APOSTOLAKIS: That's one issue.
MR. CUNNINGHAM: That's one issue, who I
am, yes, sir.
And the second issue is where I'd rather
be, but that's -- the University of Maryland work on
model uncertainty is being feed into the PTS work that
we've talked to the Committee about on several
DR. APOSTOLAKIS: Yes.
MR. CUNNINGHAM: And how you deal with
model uncertainty there. Probably some of that same
thinking will go into play as we do the greater -- the
next phase of the technical work for the ECCS modeling
as well. So I think it's going to spell over into
What we've learned so far, if you will,
the PTS work we'll feed into this work the next time
around or over the next year or so.
DR. APOSTOLAKIS: But we haven't seen any
report, have we? Have we seen anything yet?
MR. CUNNINGHAM: I think that's right,
yes. It'll come in at least in the context of the PTS
documentation that you see.
MR. KURITSKY: Okay. As you mentioned,
there's a lot of work to be done in Phase 2 for
determining the methods to use between the LOCA CDF
and ECCS system reliability. We have to determine the
appropriate thresholds concerning many of the things
and the comments that the ACRS has just brought out,
and also the items that we already have considered.
Another thing that we have to do is
identify features that tend to decrease the likelihood
of loss of off-site power after a LOCA and determine
acceptable methods and assumptions for estimating the
plant-specific probability of loss of off-site power
given a LOCA. And the reason we have those two kind
of separate, because the first one really kind of
applies to Option 1 from the previous slide where
we're going to specify some generic requirements and
it may be that in order for a plant to take advantage
of certain requirement where they do not have to
consider loss of off-site power for a certain set of
LOCAs, they have to meet features.
Like, for instance, they'd have to have
the capability -- or they may have to have the
capability for communication with -- you know,
communication with the transmission system operator or
something like that. There may be some features that
plants would have to meet, and if they meet those,
then they can have the relaxation on the LOOP
And the second --
DR. WALLIS: Does the LOOP always follow
a LOCA and not precede it?
MR. KURITSKY: It can go either way.
Preceding the LOCA, there isn't as much -- at least to
date there hasn't been shown to be as much of a tie.
There's been shown more of a tie where when you have
a LOCA, you have a big inrush of loads when big pumps
start and so you can precipitate a LOCA.
Q So it's of common cause then?
MR. KURITSKY: Yes, right. And the other
way around, you don't tend to really have that much of
DR. WALLIS: So the loss of off-site power
doesn't set off a transient which lead to a LOCA?
MR. KURITSKY: Right. I mean, is there a
possibility they could have a greater chance of
popping open a valve or leaving it open or something?
I mean, there is some connection-- there's some
connection, but it's not as strong, nearly as strong
as -- at least to date from --
DR. WALLIS: Not perhaps the broken pipe,
but the stuck open valve or something might be more
likely if you lost off-site power?
MR. ROSEN: Right. Right.
MR. ROSEN: But what you're talking about
are all hypotheticals. I mean, we're not talking
about experience of losses of off-site power causing
LOCAs or LOCAs -- or LOCAs causing losses of off-site
power. You don't have much data on that.
MR. ROSEN: Yes, we don't. There's very
MS. DROUIN: That's correct.
DR. APOSTOLAKIS: You don't have much data
on LOCAs, period.
MR. ROSEN: That's right. I mean, we're
talking about this hypothetical space and trying to
think about -- what you were talking about here is
trying to think about mechanisms where losses of off-
site power, for example, can cause a LOCA. And you
have to go pretty far to figure that -- to think about
that. And there's no operating experience that shows
There's been lots of losses of off-site
power and no LOCA's as a result of it, or very few.
MR. KURITSKY: Right.
MR. ROSEN: I mean these are not causally
linked subjects in my mind. We can think about
possible ways to link them causally, but in fact
experience says they're not.
MR. KURITSKY: And going from LOCA --
going from LOOP to LOCA we don't have anything. Going
from LOCA to LOOP we don't have -- we don't have data
to show it because we don't have that many, because as
we said we don't have many LOCAs. We have some ECCS
DR. BONACA: Yes, because then it would be
ECCS acutations and sequencing that --
MR. ROSEN: You have lots of scrams,
MR. KURITSKY: Right.
MR. ROSEN: And how many LOOPs are caused
by a scram?
MR. KURITSKY: Right.
MR. ROSEN: When the plants scrams, how
many times has the LOOP gone done? And the answer is
very, very infrequently.
MR. KURITSKY: Right. But the issue is
not from just a regular scram, but from an ECCS
actuation. The drawdown on the voltage from all of
the safety injection pumps coming on line. There is
limited data as far as ECCS actuations, but again --
I don't say it's conjecture, but I mean --
DR. BONACA: The numbers they use here,
you know, are pretty low in frequencies.
MR. KURITSKY: Right.
DR. BONACA: I mean projected frequencies.
So it's not that it's very high.
MR. KURITSKY: Right.
DR. BONACA: But it justifies the thought
that for certain break sizes, you know, those
estimates tell you you don't overkill to assume loss
of of-site power. And an interesting thing is that,
of course, as you go to a smaller size break size,
then LOOP seems to be less of a necessity because the
loading is differently, probably you're not going to
have as much demand on the electrical system as you
will have in a large-break LOCA.
So, for both of them really it seems to me
when I read the report, it becomes questionable
whether we're using a loss of power assumption, except
it's a conservative assumption.
MR. ROSEN: One of the other features of
using a loss of off-site power assumption is a
regulatory principle. It neglects the fact that a
off-site power systems at all the different sites are
different, some more robust than others.
MR. ROSEN: Yes, that's very true. And
that's why we talk about in this last bullet
determinable acceptable methods for us being plant
specific for us being plant specific probability of
loss of off-site power because it can be very plant
MR. LEITCH: I thought some of the work
related to this had to do with the elimination of
single failure criteria. In other words, what we're
talking about here is simultaneous LOCA LOOP and be
able to do this with a single failure. And I thought
in some of the reading it was thought that perhaps the
single failure could be eliminated.
MR. KURITSKY: Well, in this -- what we're
doing with these reliability thresholds or CDF
thresholds is accounting for simultaneous LOOP -- LOCA
LOOP assumption and single failures, kind of all round
up into one.
MR. LEITCH: Yes.
MR. KURITSKY: So if you can demonstrate
that, you know, you're below some threshold and only
let's say, for instance, with just one train of
MR. LEITCH: Right.
MR. KURITSKY: You know, that you're below
this threshold, then you don't need to have like a
second train. So in other words, you don't have to
have to have that single failure criteria, you don't
have to have that extra redundancy built in. So it's
addressing that single failure criterion through
MR. LEITCH: Liability, yes. Okay.
MR. ROSEN: And that's perfectly
appropriate, because the single failure criterion was
a surrogate for a real reliability framework when we
weren't able to put one together and analyze it
because we didn't have the PRAs and because we didn't
have the data to support the reliability analysis that
we now have based on real experience at operating
DR. KRESS: And this is where I keep
harping on uncertainties. You've got two trains that
have a mean reliability of this level for that, and
then you are going to replace it with one train that
has reliability down here. Then you have to worry
more about the uncertainties in this train down here
because as the reliability gets lower and the
uncertainties does get bigger. So you can't just swap
MS. DROUIN: I mean, one of the biggest
challenges, you know, over the next year we're going
to be faced with is how to deal with the
DR. APOSTOLAKIS: Absolutely.
MS. DROUIN: And how to incorporate that
in, without a doubt.
DR. KRESS: And I know I keep harping on
that, and you keep giving me the same answer. So, I
MS. DROUIN: I may not have the answer to
you today, but we don't. We have lots of ideas, but--
DR. WALLIS: Well, I think it would be
good to try to implement some of those ideas in a
preliminary way to see if they work.
MS. DROUIN: Yes.
MR. KURITSKY: That's kind of what Phase
DR. WALLIS: Rather than sort of promising
to do it. I mean, I think you need to start trying
some of them out and seeing if they work or not, since
not too much of this is work to be done, but some of
it gets done and then you can say "Yes, we know. We
know we can do that."
MR. KURITSKY: And that's exactly what the
Phase 2 work is going to do.
DR. WALLIS: I was looking at this slide
here. I was wondering if eventually we're going to
see, or you're going to have to develop a work scope
for all this stuff.
MR. KURITSKY: Yes.
MS. DROUIN: Yes.
DR. WALLIS: It'll be interesting to see
how comprehensive and long it is.
MR. KURITSKY: We have a little bit in
attachment 2, the paper, there's a little more detail
MS. DROUIN: But that's still a high level
MR. KURITSKY: Yes, it's still high level.
MS. DROUIN: No, you're right. We're going
to have to sit down and work out all the things that
are going to be needed to be done. And once we get
the go ahead, yes. Okay.
DR. WALLIS: Consequently it becomes a
real thing and not a dream.
MS. DROUIN: That's right.
Now the long term changes. You heard about
the short term and now we will get into the long term.
MR. KURITSKY: Right. Based on our
feasibility study we also feel that additional changes
to 50.46 may also have merit, particularly possibly in
the definition of the spectrum of breaks and
The extent of potential change to 50.46 --
DR. KRESS: What do you mean by
MR. KURITSKY: The specificity of the
DR. KRESS: The speculation, rather.
MR. KURITSKY: The spectrum, specified
The extent of potential change to 50.46 is
dependent on our state of knowledge regarding the LOCA
frequencies for different break sizes. And as an
example, you know, if we could confidently demonstrate
that a set of LOCAs has a collective mean frequency,
again that means, of course, we take into account
uncertainties, but --
DR. KRESS: But you're adding them up?
That's what collective means.
MR. KURITSKY: Right, collectively means,
right. In other words, all breaks above 16 inches.
DR. KRESS: Well, let me ask you a
question about that. I would have thought that the
conditional core damage frequency would be a function
of the LOCA frequency, they're not independent.
For example, small-breaks have higher
frequency and small-breaks have a different
conditional core damage frequency. Therefore, there's
a link between CDF and frequency, but the numbers you
have, 10-4, 10-5, 10-6, seems to me to assume a
constant conditional core damage frequency.
DR. WALLIS: This is just initiation
frequency shown here.
DR. KRESS: Yes, but in order to arrive at
those numbers, you've assumed the constant core
damage, conditional core damage frequency, I think.
And it seemed to me like a little bit a issue that you
ought to think about.
MR. KURITSKY: Right. Well, I think --
the way something like this would work, and this is
just an example to illustrate how we would --
DR. KRESS: Yes.
MR. KURITSKY: If we had such data, what
we could work with. If, for instance, we could that
a set of LOCAs had a collective frequency of 10-4, you
know, lower than 10-4, then we may say that some
regulatory relief is appropriate. It may be reducing
it to one train of ECCS. Now, regardless of whether
that's a small or large-break, what we're saying is if
you had one train, you're going to get, let's say,
another 10-2, but your 10-4, so that may be
DR. KRESS: Yes. I would prefer it, I
think, more high level specification. Say, if a set
of frequencies can be determined such that the
convoluted frequency and the conditional core damage
frequency is less than 1/10th of the core damage
frequency, then you could do some of these things.
Let's ignore high level. You know, you
may be able to plant specifically back it off to some
numbers like this, but I think for that particular one
I would look for more of that kind of statement.
DR. BONACA: Yes. He had already give you
some kind of blanket credit to your ECCS system.
DR. KRESS: Yes. Right.
DR. WALLIS: Yes, sort of in the low
DR. KRESS: Yes. Yes.
DR. WALLIS: And so --
DR. KRESS: This is too -- I'm looking for
more of a performance one rather than a prescriptive
DR. WALLIS: But 10-6 you might go for
anyway no matter what the conditional core damage
DR. KRESS: Yes, 10-6. You might get the
one level like that or you just forget it.
DR. BONACA: Well, then I think the
implication there is that, you know -- I mean, even if
you just give 10-1 as credit for the ECCS system, you
would -- your sequence would be successful enough. I
mean, a likelihood, I mean it's so low, I guess. But
that makes it more clear, you're right.
MR. ROSEN: Yes. The point is we've
already done that. The NRC has already done that for
vessels. The vessel failure is so low we don't
DR. WALLIS: Or our estimate with current
knowledge is so low, yes.
DR. BONACA: On the other hand, I mean if
you take that last case, 10-6, I assume that these
would be double and can break. And you're saying that
-- if -- in the case there will be no credit or very
little credit given for the ECCS effectiveness because
if you step down the capability, not to be designed to
meet this kind of criteria for the LOCA, then you're
really hanging your hat on 10-6 for reactor here,
right? Assume that you said I don't need an ECCS
system for a large-break LOCA because the frequency of
that is so low, so therefore I step down --
DR. KRESS: Therefore it doesn't
contribute to CDF anyway?
DR. BONACA: That's right.
DR. KRESS: Because it's more than a
certain percent to --
DR. BONACA: So for that particular case
you're taking no credit for the ECCS system at all.
You're saying 10-6 is good enough and then live with
MR. KURITSKY: Don't need it.
DR. BONACA: That's right.
DR. WALLIS: This is long term work
anyway, isn't it?
MR. KURITSKY: Yes. Yes.
DR. WALLIS: So I think you understand
what we're saying how can it do it tomorrow.
MR. KURITSKY: Yes.
DR. BONACA: In other words, how can you
get that kind of constant.
MR. KURITSKY: Assuming we have a
schedule, that's longer term.
DR. KRESS: Yes, but my problem is how are
you going to demonstrate these set of LOCAs, how they
collective mean frequency? That seems like a pretty
MR. KURITSKY: That is --
DR. KRESS: I guess we'll leave that to
DR. BONACA: And to Peter.
DR. SHACK: Without Mayfield here to argue
this out, I mean you know we calculate these things
all the time for leak before break, for pipe wipe
restraints, we deal with environmental fatigue by
calculating things. And now all of a sudden it's --
DR. BONACA: Too hard.
DR. SHACK: -- too hard to do, you know.
I think to my mind somehow I just sort of
get the feeling that we're making this more difficult
than it has to be. You know, I look through some of
this work and, you know, you're not trying to
calculate the leak rate through every crack and every
pipe. You're trying to sort of block off the
feasibility of a very large pipe break, a double under
guillotine pipe break. And we've done an awful lot of
leak before break and pipe probabilistic fracture
mechanics. You know, we've studied in connection with
PTS initial flaw sizes.
I get a little worried, you know, you're
going to get bogged down on your short term, which
will turn out to be longer term than you think it is
and more difficult than you think it is and the pay
off there is really a whole lot less than it is here.
And to just go for it and concentrate the resources on
the thing that has the pay off.
DR. BONACA: Yes, I totally agree with
that that there's a great pay off. To some degree
it's a little bit like, you know, a little bit
different but like, say, okay we're going to remove a
container. What I'm trying to say is that ECCS when
it comes down to makeup water and so, you know,
everything you think about --
DR. SHACK: Not a safer cow, right?
DR. BONACA: And you want to have water.
And to step it back, it's a little bit of a holy
DR. SHACK: Well, yes. And I suppose it
comes down to how feasible you really think the first
set of changes are. You know, if they could be
DR. WALLIS: Speaking of pay off, the pay
off is mostly to industry, isn't it, rather than to
NRC. So then maybe industry should be the ones to
demonstrate all these things with an optimism that
they can succeed.
DR. SHACK: Well, I think industry is sort
of they think they can do this. The NRC has to do
enough work to be able to judge what the industry
DR. BONACA: That's right. No, they don't
have to lead the way. They only have to sort of drag
industry into it by showing it can be done.
DR. SHACK: Right. But they certainly
have their own set of work to do in order to be able
to evaluate and to assess what industry proposes.
MR. ROSEN: Let me give the other side of
the argument, Bill, to your statement about jumping to
Part B forgetting about Part A.
I think what you need to do is demonstrate
some early success. And so that's what Part A is for.
DR. SHACK: Yes, we've been picking low
hanging fruit here for the 8 years I've been on the
DR. KRESS: The higher up the tree, the
sweeter grows the lemon, right?
DR. BONACA: Out of a lot of low hanging
DR. SHACK: Yes, a lot of low hanging
DR. WALLIS: When I pick the apples, I
usually forget the low hanging ones because they're
not worth eating. You go for the ones that are really
good at the top, right.
DR. KRESS: The ones at the top are
DR. BONACA: Still there is the holy grail
thing. I mean, once you say that I don't have to
design any more of my system. Because somewhere
you're going to capture the benefit of that for a
double ended break. You're making a trust issue. I
mean, and the consequences in case you could have a
low ended double ended break and not a capability to
deal with it, would be very significant. It would be
so -- I mean there is a -- you know, there is a real
issue of public acceptance in stepping back on that
kind of commitment. It has to be really looked hard
and tough, and you have to have a very high confidence
in the fact that you won't have that break.
Again, we depend on our colleagues with
the metallurgical background to give us that
DR. KRESS: Well, I think you can have
probably a large confidence on a break -- the largest
pack with the double ended guillotine. My problem is
you're going to back off to something else.
DR. BONACA: Absolutely.
DR. KRESS: And somewhere down there you
don't have that confidence, and I don't know where
that level is.
DR. SHACK: I see what you mean, yes.
Yes, and you know I think getting to industry 6 inch
break might be difficult, but I think you could
certainly back off from the double ended guillotine
break of the largest pipe down quite a ways with a
reasonable degree of confidence.
MR. ROSEN: And certainly back off from a
double ended guillotine break at the same time that
you get a LOOP and take a single failure rate.
DR. SHACK: That's easy.
MR. KURITSKY: But I mean they're going to
deal with that one, absolutely, because that's in the
sort term. And there you can do very conservative
estimates of those large break frequencies and still
get a lot of benefit.
MS. DROUIN: I believe so. Shall we go to
MR. KURITSKY: Okay. Just to -- off this
conversation that we were just having, the staff is
going to continue to meet with industry,
representatives of the industry in public meetings to
discuss the set of issues to resolve or a set of
issues that would be necessary to be able to come up
or satisfy the NRC they could come up with pipe
frequencies for different sizes.
Like was mentioned, yes, we know that the
double ended guillotine break of the largest pipe is
a low frequency event and we shouldn't not to drive
for it, but you can't take that away until you set
what's the limit you're going to stick with. And that
one, it takes a little more work, and that's the one
that both the staff and industry I think are going to
have to pursue.
As I think Dr. Shack may have mentioned
that industry will have to go ahead and do a lot of
work, but the NRC has to do enough work to satisfy
ourselves that what they're doing is reasonable and
DR. WALLIS: Do you resolve anything in a
MR. KURITSKY: Excuse me?
DR. WALLIS: Do you resolve anything in a
MR. KURITSKY: Well, the --
DR. WALLIS: You bring up subjects and you
state what your positions are, but I think you resolve
things in a different way than in a public meeting.
MS. DROUIN: This is not meant to say
we're going to resolve these in public meetings.
DR. WALLIS: That's what it says. We'll
meet "to address and resolve the technical issues" in
MR. KURITSKY: Right. Yes, that may be in
this thing. But also the fact what this is is it's
going to be, hopefully, a working level meeting. It's
going to involve -- the next one we have planned that
we're trying to set up right now, in fact, is going to
involve, hopefully --
DR. WALLIS: It may spell out what has to
be done to resolve the issue?
MR. KURITSKY: Right. Right. And it's
going to, hopefully, get the experts from industry and
NRC in this field to really hammer out what needs to
DR. WALLIS: Right.
MR. KURITSKY: And some of the example
issues are listed right here, the initial flaw
distributions, crack propagation, material response
and metallurgical properties, that kind of stuff. And,
of course, uncertainly analysis are things that have
to be dealt with.
And if this large-break LOCA redefinition
is found feasible, then the staff would recommend
additional changes to 50.46 including possibly wording
changes to Part 50 to reestablish what the limiting
break size is --
DR. WALLIS: Are there no thermal-
hydraulic issues that are for example in the second
bullet? It's all materials problems?
MR. KURITSKY: No, they're not only
material problems. But this -- at least the means that
we've talking issue set up is to address the
materials, metallurgical ones. It's not to say that
the other issues don't also have to be addressed, but
the first stepping stone that we're trying to get a
handle on is the materials.
MR. LEITCH: It seems to me that there's
a number of issues where double ended guillotine
breaks are as a bounding thing for all sorts of
things. I mean, just all kinds of analysis and so
forth have been done. I'm not sure that I can come up
with any real specific --
DR. BONACA: The containment ropes.
MR. LEITCH: We read on our reading for
tomorrow's meeting about the CRDM failure. Well, it
doesn't matter because it's bounded by doubled end
Is there a way to -- I mean, it seemed to
me you'd have to go back and replow those fields every
place where that was used as a --
MR. KURITSKY: Surrogate.
MR. LEITCH: -- surrogate for some other
event or issue that is, perhaps, even totally
unrelated to it but it turned to be a bounding
situation. I mean, that seemed to me would be a major
piece of work to go back and try to assure ourself
that we hadn't missed anything along the way.
MR. KURITSKY: That point's well taken, it
is something we have to do. I think in the big
attachment, attachment 1, we have somewhere in there
a list, a table of a whole bunch of LOCA initiators
that we feel -- you know, the large-break LOCA may
bound or be a surrogate for. You have to go through
them one by one to assure ourselves that either
because of the frequency of these other events or the
consequence of them that we're still bounding and
that we feel as important, and that's a very important
MR. ROSEN: I think that addresses Dr.
Wallis' point earlier. When we do that, pay some real
particular attention to what pops up when we take the
double ended guillotine break away, that we may find
the things that are really important that have fairly
significant consequences and relatively higher
frequencies and be able to address those as a
regulatory and the industry. And so that seems to me
to begins to get to the question of how do we -- what
are the --
MR. LEITCH: What is in it for NRC?
MR. ROSEN: What are the regulatory
benefits of this? And the answer is a sharpened focus
on the accidents and the consequences that are more
likely to happen in a double ended guillotine break.
DR. KRESS: And maybe deal with them in a
better way than just a double ended surrogate or
MR. ROSEN: Exactly.
DR. WALLIS: So it's better defense of
public safety because the folks doing the right
MR. ROSEN: That's exactly right.
DR. WALLIS: So there's actually a
positive side. It's not just backing off on a
conservative requirements. We're actually doing a
better job of preserving public safety. If you can
make that case, I think you've got a very good one.
DR. APOSTOLAKIS: Well, I think that's the
general theme of initially reforming the regulations.
We're focusing on what's appropriate --
DR. WALLIS: But it's always sort of at a
philosophical level. If you can show you've actually
done it, you have improved safety because of being
risk-informed, then you become much more credible.
It's not just a promise that it ought to happen.
DR. APOSTOLAKIS: You are opening up a
whole new subject now. That's what we've been doing
for the last 20 years; adding things.
DR. SHACK: Right.
DR. WALLIS: Mr. Chairman, is this the
presentation or is there another one? I notice there's
a break. Is there another presentation after the
break or is this one?
DR. SHACK: Are we going to have a
discussion of the attachment 2, the technical work?
MS. DROUIN: That's what we've been going
DR. WALLIS: Yes, and so there's no second
DR. APOSTOLAKIS: So what's going on now?
Where are we?
MS. DROUIN: We only have three more
viewgraphs to our presentation. We're almost done.
DR. SHACK: Then we can break and come
back and we have some -- I assume you'll have
something to say.
DR. WALLIS: We might just have some
comments. This is the first time we're hearing it.
DR. APOSTOLAKIS: Never stopped you
DR. SHACK: Okay. Why don't we finish
your presentation and then we'll take a break. You'll
have 15 minutes to think about it.
MS. DROUIN: Before we move on to the
other Option 3 activities, just to wrap up on this
long term one, different than the short term. And the
short term, again, we want to move forward immediately
with the technical work because we feel it's feasible.
Here we're trying to establish the feasibility. But
once we feel that it's feasible, then we would go in
and, as it shows here, potentially go through a
rulemaking to change the wording to allow a licensee
to come in and offer up a different pipe size break
over the large double ended guillotine.
DR. APOSTOLAKIS: That's just for Appendix
MS. DROUIN: Yes.
DR. APOSTOLAKIS: Because if you're going
to be risk-informed, you really ought to look at all
possible break sizes and evaluate the risk.
MR. KURITSKY: But let me just say, just
for the break size change would be -- Appendix K are
for all of them.
MS. DROUIN: Well, it goes with the 50.46
and Appendix K.
MR. KURITSKY: Right, 50.46 and Appendix
MS. DROUIN: Okay. I'll just quickly try
and go through the next two slides just to give you a
brief idea of where we are on the other Option 3
We talked about the single failure
criterion. The option that we're going forward in the
short term on the single failure only relates to ECCS.
But if you go into Appendix A, the single failure is
broader than ECCS. You'll see there I have listed on
the third bullet there's GDC 17, 34, 38 -- I can't
remember which all of these are. I know one of them is
containment heat removal, one's electric power --
MR. KURITSKY: Electric power, residual
heat removal, cooling systems.
MS. DROUIN: But the single failure
applies beyond ECCS, so one of the things that we were
planning hopefully to continue doing is looking at a
generic change to the single failure criterion that
would apply across the board and not just to ECCS.
DR. BONACA: Outside the LOCA analysis?
I mean --
MS. DROUIN: Correct.
DR. BONACA: -- for every accident that is
DR. APOSTOLAKIS: I think that's a big
change, is it not?
MR. KURITSKY: Yes, that is a big change.
That would be a big change.
DR. APOSTOLAKIS: A huge change.
DR. BONACA: But wouldn't you use then PRA
to identify the most likely failure that you should
design for? I mean, wouldn't you exchange it for a
criteria on that is based on PRA insights?
MS. DROUIN: We would still bring risk
information into the formulation of it.
DR. BONACA: Yes, because I know the
single thing about a single failure already you have
to take the most penalizing single failure that you
can find, so you have to do it -- irrespective of high
likely is the failure. It may be impossible to have
it, but you have to assume it. Not that far, but
MS. DROUIN: Not again, this would be --
DR. BONACA: But still you would have --
MS. DROUIN: -- to establish the
feasibility of doing this. We had not gone beyond
just thinking -- we do it's feasible to do it for
ECCS. Now we want to look at a whole global generic
change to see if that's feasible. And so that would be
the next --
MR. ROSEN: And here again, Graham's
already said it, but this question of desirability
comes back onto the table. Would you really want to
do it for all of the application of single failure
criterion across the whole plant safety systems?
You've got to think about the desirability as well.
MS. DROUIN: That's part of the
DR. KRESS: The problem I see you're going
to have is whether or not you can make this go away
with this single failure criteria, you'll have to ask
yourself if we did away with it for these GDCs that
are listed up there, what changes will take place in
the way the plant's operating or the way it's built
and then what effect will those changes have on risk
in a generic basis? That's the kind of questions
you're going to have to ask.
MR. ROSEN: Yes.
DR. KRESS: And I think that's a tough
MS. DROUIN: Absolutely.
DR. KRESS: Especially the first part;
what changes are going to result.
MS. DROUIN: But it's not doing away with
it, it would be replacing it.
DR. KRESS: With the reliability
MS. DROUIN: Yes.
MR. ROSEN: Yes, but which is in effect a
multiple failure criteria. But the failures will be
at the probabilities or the reliabilities encountered
at the plant, which is much more realistic. Yes.
DR. WALLIS: But you'd replaced it with a
performance based criterion, wouldn't you?
DR. BONACA: Remember, however, there is
MS. DROUIN: Perhaps.
DR. BONACA: All the analysis that you
have with single failures, particularly what you have
on analysis on a single failure, your reality behind
that you have tons of analysis assuming the worst
single -- well, until you find the single failure. And
those analysis had also as significant deterministic
design value in that you understood the behavior of
the plant; if you assumed this failure versus this
failure, versus failure and then finally you found the
bounding one, you put in the ECCS, or behind that you
have all the design basis of the plant.
So, this is a significant change. I mean,
clearly it would go in the direction of being more
risk-informed. You would identify a combination of
probable and combination of consequences, etcetera,
but you have to think about what you're going to lose,
and maybe you don't lose anything. You have to
perform -- you know, but it's a complex change.
DR. APOSTOLAKIS: I just don't know how
you can attack just a single failure criteria in
isolation. That is part of a bigger --
DR. BONACA: It's a big -- a big change.
DR. APOSTOLAKIS: That's fine. You can go
ahead and we'll see what comes out of it. Because I
don't -- I mean, a first reaction is that you can't
just do it to the single failure criterion. You are
really talking about risk-informing the whole thing.
So you have to look at the -- you have to look at a
lot of things.
DR. BONACA: Very ambitious. Yes, it's a
very big change.
MS. DROUIN: The other thing is that, you
know, we have started to look at the special treatment
requirement under Option 3. Now, under both of these
looking at the single failure criterion and the
broader aspect, the special treatment requirements,
both of these have right now been deferred because
right now over the next couple of years we're going to
focus our resources in supporting 50.44 and 50.46.
DR. APOSTOLAKIS: Oh so -- oh. So that,
what is it, Appendix D, was it?
MS. DROUIN: Yes.
DR. APOSTOLAKIS: 50.69?
MR. CUNNINGHAM: No, that's not being
deferred. That's the Option 2 or --
MS. DROUIN: Option 3 aspect.
DR. APOSTOLAKIS: I don't know what the
MR. CUNNINGHAM: The work that Mary is
talking about would be a step beyond what's in Option
2 today. It would be to change the -- Option 2 looks
at what's the scope of equipment that has to be
subject to --
DR. APOSTOLAKIS: Right.
MR. CUNNINGHAM: -- EQ and that sort of
thing. This would be what should the EQ be that would
go with it. What would be the environmental
qualification standards and that sort of thing. So
it's revisiting that aspect of it, not the scope.
DR. APOSTOLAKIS: And that's it?
MS. DROUIN: Okay. Schedule.
So in terms of the schedule those two
things have been deferred because we're going to focus
our resources into supporting. You know, right now
we're doing the technical work to support 50.44.
We're starting on the technical work to support 50.46
and completing the feasibility on the definition.
So in looking at the change which is was
our A -- I think it was our A. Now I'm getting all
this confused. But where we're going to go in and
modify the existing regulation.
In developing the proposed rule, the
schedule that we have tentatively set is 12 months
from the date of the SRM or two months after the
completion of the technical work. And that's the
development of the proposed rule.
DR. APOSTOLAKIS: Is that a magic number
or did someone look at all the things you have to do
and the people available and figure out how long it
would take to do the job?
MS. DROUIN: Yes.
DR. APOSTOLAKIS: Someone didn't just say
let's do it in a year. What's the magic about July 2,
2002 since everything is --
DR. WALLIS: No. By saying they can do
the job in 12 months, it looks like somebody's guess,
MS. DROUIN: We are continuing to do the
technical work. We are not waiting on the -- it was --
we are not waiting on the SRM to start our technical
work. We're going to continue to do the technical
We feel that in terms of the changes to
the acceptance criteria and the evaluation model we
can have that work done by July 2002.
DR. KRESS: Twelve months is a lot more
believable to me than 13.62 months. Because 12 months
is one of those round numbers --
DR. WALLIS: What's the uncertainty on the
DR. KRESS: You can do it one year rather
DR. APOSTOLAKIS: What's the risk of not
completing the job? You don't like the 12 months?
DR. SHACK: No, I don't mind 12 months.
It's just, you know, trying to think of other rule
changes that we've done in 12 months.
DR. APOSTOLAKIS: And you fail.
DR. WALLIS: By the time you have public
meetings and responses to comments and all that kind
of stuff --
DR. SHACK: And you have to come to the
ACRS and which we talk about -- and that'll last for--
MS. DROUIN: No, no. This is development
of proposed rule.
DR. BONACA: They don't say complete.
Yes, they don't say complete.
DR. WALLIS: So you would be ready for
public comment by then?
DR. BONACA: Development.
DR. WALLIS: Right.
MS. DROUIN: The development. A
significant subtly there.
DR. WALLIS: Well, we should cheer and say
"go for it," isn't that what we should do?
MS. DROUIN: Absolutely.
DR. WALLIS: Okay.
DR. BONACA: You agree we should cheer and
tell you "go for it?"
DR. SHACK: Short letter.
MS. DROUIN: In terms of the development
of the voluntary risk-informed alternative, and that's
where we're coming in and changing -- it's really
changing GDC 35, that's going in and attacking the
single failure criterion as it applies to ECCS, it was
those two options. The generic and more plant
Again, we're going to continue, we aren't
going to stop our technical work. We're going to
continue on that and we feel that can be done by April
2002. And the development of the proposed, again, 12
months from the SRM or two months after the completion
of the technical work.
DR. BONACA: Yes, that second bullet seems
to be pretty optimistic to me. Because that change in
the GDC 35 is a very -- not GDC 35, all the other
places where you have single failure criteria --
MS. DROUIN: No, no, no. Only for GDC 35.
DR. BONACA: I understand. Okay.
MS. DROUIN: This does not include the
others. Just for GDC 35.
And, again, we aren't going to stop, we're
going to continue with the feasibility in looking at
the redefinition of the large-break LOCA and the
completing of the feasibility. There's a lot of
complexities and we feel that could go up to three
years to complete feasibility.
DR. APOSTOLAKIS: Now I thought we said at
one point that maybe being a risk-informed regulatory
system you will not need GDCs. Didn't we say that
once? GDCs are remanents of the old system, so that
a possibility that you don't need at all a GDC.
MR. KURITSKY: So those would be interim
DR. APOSTOLAKIS: Huh?
MR. KURITSKY: These will be interim
MS. DROUIN: You know, when you look at
this what form it takes, your alternative risk-
informed regulation, whether you characterize it as a
GDC or as a -- I mean --
DR. APOSTOLAKIS: Or something else?
MS. DROUIN: It's premature to say. But
you are not getting rid of the current GDCs that are
on the books. Those are there.
DR. APOSTOLAKIS: Yes. They are, yes.
MS. DROUIN: Now, whether you have a risk-
informed alternative to it or you characterize it some
other way, those are decisions to be made.
MR. KURITSKY: And just for this specific
point, the changes to the reliability requirements,
even though the GDC 35 is where they're specified,
depending on how we ultimately decide it should be
applied, it may actually be a change in 50.46 that
tells you whether or not you have to meet the
requirements in GDC 35. So that way whether or not
the actual wording change occurs in GDC 35 or in
50.46, we haven't decided that yet.
DR. WALLIS: I don't know if we're going
to cheer or not, but it seems to me you're much more
positive and optimistic about the chances of success
than you were last time we met. Maybe that's because
you've had the time to figure out what you need to do
to do the job. And it turns out that it looks
MS. DROUIN: Well, I'd say that's true,
yes. You know, whether we come up against something
that throws off track, but know at this point we've
given it a lot more thought, we've done more work and
we do feel for these first two bullets that that's
DR. WALLIS: And you're going to have
enough support from management to get this done?
MS. DROUIN: Mark?
MR. CUNNINGHAM: Well, of course. Mary
said something a little bit ago that plays into this.
In the context of Option 3 the focus over the next
couple of years is going to be changes to 50.44 and
50.46. That was to make sure that the resources we've
got available here are focused where we want them to
be. And, you know, these other things could devote
resources away. So from that standpoint that
commitment is there.
From a budgetary standpoint the commitment
is there, too. We've got money today where we can
start each of these three efforts in parallel. And as
we've got money in the fiscal '02 and '03 budget to
support these, so we've anticipated that in our budget
preparations and we think it's there.
DR. WALLIS: Now this is an RES activity?
MR. CUNNINGHAM: No, it's a staff
activity. The technical work that you would talk
about here, perform the technical work, that will be
done principally in RES. The rulemaking will be done
DR. WALLIS: Yes. Is there a good tie in
with the people who are actually going to use this
product in the regulatory world?
MR. CUNNINGHAM: Yes. Yes. They're the
ones that are going to be writing the rule itself and
the reg guides and that sort of thing.
DR. WALLIS: Are we going to hear from
MR. CUNNINGHAM: You will hear from them,
you know, at some point we'll talk about when the next
meeting on this subject would be.
DR. WALLIS: Good to hear on that, too, to
know that they're fully behind you and they really
appreciate the product.
MR. ROSEN: It's not going to change what
they want --
MR. CUNNINGHAM: So it's just in the next
-- in Phase 2 Research will be behind it and all are
supporting them. It becomes their lead to do it.
And, yes, I expect that sometime in a few
months from now the committee would want to hear from
the staff again in terms of now -- given -- presumably
this paper goes forward, now what's happening.
MR. ROSEN: Is the risk-informed licensing
panel in this process?
MS. DROUIN: Yes.
MR. CUNNINGHAM: Yes. They basically
concurred in these recommendations.
Just to be clear, some people understand
how it works. This is -- Mary and Alan said, this
paper is with EDO. NRR has concurred in this as well
as Research. So this is not just Research's opinion
on this. NRR has concurred in the paper.
DR. WALLIS: Well, looking at this from a
personal perspective at what might have been achieved
by the time I leave the ACRS, if I can go back to talk
to my friend and they say "Well, what have you been
doing in Washington that made any sense that actually
achieved something." I can say "Well, those guys
managed to risk-inform 50.46."
MR. CUNNINGHAM: 50.46, yes.
DR. WALLIS: And maybe we had something to
do with it. That would be something that I'd like to
be able to say.
MR. CUNNINGHAM: Okay. I think we'd like
you to be able to say it, too.
MS. DROUIN: Any other questions?
DR. SHACK: No more questions?
I think maybe it's time for a break and we
can come back at 4:00 or a few minutes after and hear
(Whereupon, at 3:44 p.m. off the record
until 4:05 p.m.)
DR. SHACK: Well, now that Adrian's had 15
minutes to think about, I think we can get his
DR. APOSTOLAKIS: Maybe you can start by
telling us what's new in what you heard that we didn't
know before. I mean, I -- we -- I didn't know, at
MR. HEYMER: Good afternoon. My name is
Adrian Heymer. I'm a project manager with NEI on
I have with me today Bob Osterieder from
Westinghouse Group and Terry Reick from the BWR Group,
Terry Reick's from Exelon in their Chicago offices.
And Bob's a project manager for Westinghouse looking
after risk-informed activities for the Westinghouse
We are just going to give you some initial
feedback on what we heard. What was new, I think, was
someone's suggestion, and it was mentioned earlier
about climbing apple trees and picking the fruit. And
as we've told you before, we really think there is
significant benefit in taking a look at redefining the
We recognize there is a significant amount
of work to be done, and we're willing to work with the
NRC staff in trying to develop some of that work and
being that work to the staff. And so, we're looking
forward to working with them. We've been trying to
arrange some dates where we can start sitting down and
get a better understanding of what we would have to
develop or the level to which material that we would
to develop. And we can move forward with that.
We did find a little confusing in some of
the material, and I think that was clarified briefly
in a discussion. But if you're going to impose new
requirements, I think you got to be careful about how
you word such requirements. Because in some cases not
everybody might want to pick up on those new
requirements. I'm talking about the A(1) I think it
was of the slide. Some people might like to stick
with the criteria that have already been established
and not make any changes.
As regards the A(1) I think it's clear
that we can move forward. There is an existing
standard on the books from 1994 on decayed heat and we
think we can move forward with a rulemaking very
expeditiously in that area.
There are some other things that are
linked into that part associated with ECCS acceptance
criteria. And that's where, I know it's been mentioned
before, but we were a little surprised that that
should be blended together along with the same time
frame as the ECCS rulemaking.
Terry, did you want to comment?
MR. REICK: Yes, on the Option A I had a
couple of questions that came up when I listened to
Decay heat clearly is something that BWR
Owners Group has looked at and thought that we should
move forward with.
The one thing that bothered me was one of
the bullets talked about NRC's prescribed uncertainty
treatment. And our understanding is we talked about
in our committee was that the multiplier of 1.2 as
stated in the ECCS criteria 50.46 talks about it as an
uncertainty value. I know we had some discussion on
uncertainty versus margin in here. It's an
uncertainty value because back in 1972/71 we didn't
know decay heat very well, and there's a lot of work
that's been done since then that has clarified it.
And, in fact, the 1979 standard came out and said here
is the decay heat as we now know it based on some
experimentation and here is now the uncertainty that
we attach to it. And they said uses a two sigma value
So, we see this change it should be very
simple. We think take the 1.2 multiplier out in the
1971 standard and replace it with the current standard
which has uncertainty built into it.
To summarize it another way --
DR. WALLIS: It's not quite the same
thing, though. 1.2 factor is a conservative treatment
and the full treatment on uncertainty in risk-informed
approach is not --
MR. REICK: Well, I wasn't --
DR. WALLIS: -- the conservative limit,
but to look at the whole spectrum and make an
MR. REICK: Now, I wasn't there back in
the ECCS hearings, but if you read the ECCS rule it
talks about the 1.2 being a factor because of the
uncertainty in decay heat.
DR. WALLIS: Yes.
MR. REICK: It doesn't talk about it as
being conservatism, it talks about uncertainty and the
decay heat value.
DR. WALLIS: But essentially it's saying
we think the uncertainty is like this, so we'll be
conservative and we'll step outside the uncertainty
MR. REICK: But it's an uncertainty in the
decay heat, not the uncertainty in the other 50.46
requirements and assumptions. And if we know decay
heat better now and the standard has come out that
says here is how the uncertainty should be applied to
it, our position is let's apply that uncertainty.
Whereas, the words --
DR. WALLIS: It would be a factor of 1.05
or something, say 1.2.
MR. REICK: Like 1.07 -- 1.08 I think they
used the two sigma. Whereas, this in here says NRC
prescribed uncertainty. So, essentially what I'm
hearing is the NRC wants to take the margin created
because we became more certain and then use that
margin themselves as opposed to going to what the best
DR. WALLIS: Well, this is the old
business of who knows the margin?
MR. REICK: Whose margin is it?
DR. APOSTOLAKIS: Is that they're saying?
What are they saying?
MR. REICK: Well, if you look on their
page 10 --
DR. APOSTOLAKIS: Page 10.
MR. REICK: On the second bullet it says
"within NRC prescribed uncertainty treatment." So our
position is use the uncertainty that the standard came
up and define. They said here's the best --
DR. APOSTOLAKIS: Oh, but you yourself
said though that the 1.08 is a two sigma?
MR. REICK: Yes.
DR. APOSTOLAKIS: They might three sigma?
MR. REICK: Right. They want three sigma.
But what I'm saying is the industry came up with a
standard that they thought was best estimate of with
an uncertainty, and that ought to replace was back in
early 1970s. But it sounds like there may be some of
that uncertainty that staff wants to take up because
of other unknowns or other nonconservatives that they
have in their minds.
So our position is just simply replace the
standard and that should be an easy rule change.
DR. WALLIS: So whatever it is it will be
NRC prescribed, because they make the rule?
MR. REICK: Correct.
DR. APOSTOLAKIS: So it might be what you
MR. REICK: Right. And our position is
just put the new standard that talks about the
uncertainty of decay heat.
DR. APOSTOLAKIS: Have they objected to
what you're proposing or are you speculating now?
MR. REICK: We're speculating because we
don't know what the detail is yet.
DR. APOSTOLAKIS: You don't know. Okay.
MR. REICK: And that type of reasoning I
think would apply in any other changes under A; that
is if it was uncertainty that was in the ECCS aspects
back in the early '70s and we've reduced that
uncertainty and that created margin, that that's
margin we should have rather than taking the margin
away for something else. That was the item on decay
Yes, I guess I'd like to add a little bit.
I think the decay heat changes are
certainly something we believe are going to be very
appropriate. The Westinghouse Owners Group has a bit
of a concern with the rest of the changes related to
acceptance criteria. And I think some very
distinguished gentlemen on this panel last time said
that's like changing the works of Shakespeare if
you're going to change acceptance criteria. And we're
very concerned that the -- owing the decay heat in
with other changes to acceptance criteria could be a
very lengthy process and requiring a lot of
discussions with this Committee. And I guess we're
just generally concerned that the effort would be so
big that we'd rather that effort be spent on the
redefinition. But I think, you know, as stated here
we think some people feel it can be done in a year.
And with relatively smooth sailing, I would say to get
there in a year, but I think this is going to be a
much longer process to get into the acceptance
criteria in general and try to change those. It was
a long process originally and we think it's going to
be a long process now.
And I guess we think it would be more
prudent to look at the decay heat independent or aside
from and then get into the other acceptance criteria
if we're going to go that route and we're concerned
with spending what we think will be a sizeable amount
of resources on that. and maybe it won't be, but our
experiences don't show us that. I guess our point --
DR. BONACA: You don't think about just
the consideration of LOOP and single failure. That
would be a great area of opportunity for the industry,
MR. OSTERIEDER: It could be in the area
of opportunity. Partly some of the discussion today
has enlightened us a bit and we need to think about
it. We're not --
DR. SHACK: That's B, right?
MR. OSTERIEDER: That's B, right. Right.
and I guess we'll have a few more comments on that, so
I don't know if there's any other on A.
MR. REICK: I'd like the acceptance
criteria. Maybe Norm can help on this. Because I'm
confused a little bit because I'm on another
committee. I'm a committee for robust fuel with EPRI
and in the industry and we've been working with the
Argonne acceptance criteria. And recently there was
a discussion that came out and said that the current
acceptance criteria was based on post-quench cladding
ductility, and it was based on experiments done many
years ago that showed 2200 and 17 percent was based on
a post-quench ductility. And all I read from this is
that we're going from the current criteria to
demonstrate adequate post-quench cladding ductility.
I see no change.
DR. WALLIS: Part of the idea was that
cladding wouldn't be necessarily the same in the
future as if you had a performance based criteria.
MR. REICK: That's agreed.
DR. WALLIS: Then this could handle new
cladding, which maybe could go to 2500 or something,
whatever it is.
MR. REICK: I agree. What we've talked
about in the industry is that new cladding would go
through separate effects test. And by testing new
cladding relative to old cladding, they can see how
the effects would change, and thus base the criteria
on that. And typically we would say let's live with
the existing criteria because the new cladding is
better than the old cladding.
DR. WALLIS: Well, maybe the 2200 contains
one of these factors, like 1.2 so that if you actually
have more information, maybe you could get a better
I don't know why you'd want to go back to
a more primitive number when a better one might be
MR. REICK: Well, what I'm saying is my
understanding is the current criteria is only 2200 and
17 percent is already based on post-quench cladding
ductility. And so I don't understand what change is
being proposed here, and we're doing some testing on
DR. SHACK: Well, I think the answer is
that suppose you had a cladding that was more
corrosion resistent but was in fact embrittled more
under a radiation so that in fact the true criteria
for it was not an oxidation criterion anymore but
essentially an irradiation criterion.
The true thing that you really have to end
up with is some ductility. So, I think it was just
there attempt that, you know, if you were using
zircaloy, you could still use 17 percent and 2200 F.
But if you had a different material, the crucial thing
was, in fact, to maintain the ductility, not --
MR. REICK: What I'm hearing you say is
for existing claddings there is no change in criteria
because our current criteria is already based on
ductility. But for new claddings, there could be a
change in criteria.
DR. SHACK: I'm not the NRC, but that
would be my interpretation.
DR. BONACA: But my understanding --
MR. REICK: That's I -- that's what I
hear. That's what I'm hearing.
DR. BONACA: -- reading the material --
MR. REICK: That's the acceptance
DR. BONACA: Reading the material we have.
DR. WALLIS: Is this ductility independent
of burn up and does it change with radiation history?
MR. REICK: Yes, it does. And we're doing
DR. WALLIS: So if we go into a long burn
up should we change this criteria?
MR. REICK: That's a whole separate
discussion the industry is having with the NRC on when
you go to higher burn ups what criteria should change.
This is talking about existing burn ups and we're not
trying to lump them together. But there's a whole
separate committee that's working on that, extending
DR. WALLIS: But it's not independent of
this, surely. I mean, if you have a performance based
criteria and it can handle extended burn up and so on,
it seems a much more desirable thing.
MR. REICK: Yes. There will be a whole
separate rulemaking that'll take 3 to 5 years before
we get extended burn up. And this has been touted as
shorter term, but I see no relaxation for the industry
in changing acceptance criteria in the short term on
that. So the only thing left today as I see it is
decay heat. Now, that would take some additional
discussions with the staff and talking about. I just
see decay heat, and as I mentioned earlier, I think
decay heat is a simple change.
DR. SHACK: But I think the first one was
mostly just to give you the flexibility of doing
something like -- besides ZIRLO or zircaloy without
another rule change. I mean, as it is now every time
you come up with a new cladding --
MR. HEYMER: I'm not saying that would be
great. Our concern is that these discussions get
protracted out and out and out. And there are some
benefits that could be added in the short term, but
let's not lose sight of that fact and also not --
let's not be afraid to sort of chop certain things off
as we go down if we think we're running into some
DR. WALLIS: I'm not surprised to see the
NRC going for a more ambitious way of helping you guys
to reduce conservatism then you want to let them do.
MR. HEYMER: Well, I think it's not
necessarily a question of that. It's a question of
concern over timing.
DR. WALLIS: So you don't think they can
do it with the time available?
MR. HEYMER: Well, judging on my past
experience, we're probably going to struggle a little
bit on some of those.
DR. BONACA: Just before we move, and this
is just for clarification for me, I had understood in
reviewing this package that 22000F, the criteria as we
have right now, may be we're over restrictive criteria
to the term meaning what is an adequate post-quench
cladding ductility. Okay.
MR. HEYMER: And the advantage compared
with the rest -- because we haven't read the material,
everything made publicly available.
DR. BONACA: That would be my
understanding. So there would be still some benefit
even for current licensees by exploring ways or
criteria that would still provide adequate post-quench
cladding ductility but less restrictive than the
current criteria? That's my understanding, and maybe
I was wrong.
MR. HEYMER: Well, hopefully, the SECY
would be released to the public and then we can
provide some input on the policy.
MR. REICK: My reading of this it doesn't
provide anything to current --
DR. BONACA: Okay.
MR. REICK: Cladding materials doesn't
provide any relaxation, because the current criteria
is based on post-quench ductility.
DR. BONACA: I understand. But the
reading seemed to me that the implication was that
that criterion was in amount to use to measure this,
was over restrictive. I don't know what else could be
MR. OSTERIEDER: The other point related,
I guess, we just have to be careful with any required
changes to acceptance criteria. If we're not careful,
we may end up causing everybody to reanalyze for
something that appears from what we heard today to be
-- give more margin but some plants may not want to
spend the effort. They may be satisfied with their
current analysis. So, we just wanted to state the
obvious, that we'd have to be careful that everybody
wouldn't have to be required unless we felt we were
doing this to -- for an issue that was not handled as
appropriately as it should have been in the past.
DR. WALLIS: This is a remarkable sort of
seesaw issue. I mean, when we meet sometimes you guys
are all eager to press ahead and do stuff and NRC's
dragging its feet. And the next time around the NRC's
all eager to press ahead and you guys say "Let's drag
out feet because they can't do it."
MR. HEYMER: We are happy and we're
willing to move ahead and push on as expeditiously as
possible. We just want to be careful that we don't
get ourselves bogged down into so many details that we
don't actually make some progress on stuff that is
relatively straight forward.
MR. SIEBER: Well, it seems to me that
there's a trade going on in squad 10. If you look at
the last bullet it talks about viewing with recognized
nonconservatisms and model limitations. And I sort of
got the impression that there was going to be a trade
off between the decay heat multiplier and the decay
heat curve versus the nonconservatisms which sort of
all in one full swoop consumes at least some of the
margin that they built in when they built in the 1.2
multiplier. So you may get a thing that you might
like and something you may not like as an output.
MR. HEYMER: As I say, we were just giving
you our first reactions.
DR. WALLIS: I guess the criterion for the
NRC to do this is not that it saves money for
industry. They're interested in public safety, and if
this is the right to do it, that's the right way to do
MR. HEYMER: And we fully agree with that.
It's just a question of if we can do it in the 12
months, great. We go on and do it. But if it takes
36 months, we'd much rather take some of the things
that are, in fact, the low hanging fruit.
MR. OSTERIEDER: I guess I just want to
make another comment on our being gungho in some cases
and not in others. I think we continue to be gungho
in large-break redefinition. Certainly we were a lot
more optimistic than the staff is. And we think that
this effort is a big effort. And if we're going to do
a big effort, we still think we should go for the
risk-informed redefinition; that's why we're gungho on
one and not the other.
As we've heard already, there's limited
resources and you can only put it in certain areas.
And if we're going to have a big effort, we're
thinking that the redefinition is the more appropriate
way to put the big effort.
DR. WALLIS: Well, whose resources are you
talking about? Is it the effort that you folks would
do to analyze these issues or is it the resources the
NRC's going to put into it?
MR. OSTERIEDER: Well, I thought I heard
in here that the NRC said that their effort, you know,
their manpower is allocated to these efforts. So I'm
concerned with their involvement.
DR. WALLIS: Yes.
MR. OSTERIEDER: Plus we've had a
difficult time, and this isn't really a resource
issue, I suppose, but just getting the next technical
meeting scheduled has been a bit of a challenge. But,
again, I don't know that that's a resource issue.
It's getting the right people together.
DR. WALLIS: I think the last time we met
industry was gungho and said we're going to put the
resources behind this to make a really case for what
we think should be done.
MR. HEYMER: And as regards the redefining
large-break LOCA, that still is the case.
DR. WALLIS: Still is the case.
MR. HEYMER: But there does become an
industry resource issue if regards to too much at
MR. OSTERIEDER: Right. And we have a
number of resources allocated and ready to go, and
we've kind of put the brakes on a bit if we're not
going to have the staff looking at this to any great
extent and we're going to be able to get the
initiatives developed and agreed to after we do our
work; that's what we're trying to sort out.
MR. HEYMER: As regards to the other
topics, on LOOP LOCA, yet again that's something that
there's an awful lot of information out there at the
current time. There's a lot of information out on
loss of off-site power, and there's been a lot of
studies done on plant centered events. There's been
a lot of work done as regards good reliability and
what the impact of that could be in the last 9 months
So, we are going to think that's a
relatively quick issue to get under our belt and we
look forward to working with the staff in that regard.
And in some cases, I think I'd be surprised if the
technical work can't be done in less than 12 months.
So, that's good.
On redefining the large-break LOCA, as Bob
said a few moments ago, that still is where we have
most of our resources focused and we're still very
interested in moving ahead with that.
One of the issues that we did have on the
table or the suggestions that we had made previously
was that there be an enabling rule, fairly straight
forward, which would then provide double ended
guillotine break or an alternative break size as
approved by the Commission. And it's just not quite
clear to me whether that's still in the works or
whether or not we're trying to come up with more
detail criteria to put into the rule. It seems more
like the latter, and that's something that we'll have
to discuss internal and get back with the staff.
That'll probably be a comment that we make once we get
the SECY and have had a chance to review it.
MR. OSTERIEDER: Right. And that is when
you asked earlier on whether some of the changes,
there was talk at the last meeting of the potential to
put something in. And we certainly were excited by
that potential knowing that we still have the
technical issues to deal with as we do in either case.
But now if we do move ahead and do something in the
nearer term, then I guess we need to ask for an
exemption or a petition or something to -- if the
wording isn't going to be changed in the near term by
the staff. So, that's a bit of a change from what we
were hoping from your last meeting and we have to
consider what that means.
MR. HEYMER: I think to sort of sum up,
we're pleased that the process is moving forward now.
We would probably like to see the emphasis still be
placed on redefining a large-break LOCA. I think as
somebody in this Committee mentioned, we're quite --
you know, industry to do the work and the NRC to
review it. And we're more than ready to work with the
staff to define what we need to do. We think we know
what that is at the moment, but before we actually
start pulling everything together and interacting with
the staff, we'd like to sit down with them so that we
can get a better scope on that. So we're really
interested in moving forward.
We think there are some near term
objectives that we can achieve, certainly within the
12 month time frame. And we look forward to reading
the SECY when it's released.
MR. REICK: Let me add a comment from the
DR. SHACK: Did you say B or P?
MR. REICK: BWR, boiling water reactors.
Our committee agrees with the large-break LOCA
redefinition of the priority, but we also looked at
the other NRC proposed options and prioritized within
our group other options. And we do like some of the
options in here, I want to make sure that comes
The LOOP LOCA coincidence can be a benefit
for the BWRs. And it was asked here what type of
examples do you have. And the LOOP LOCA is, I think
a good one to illustrate how we might benefit. For
the large-break we require and we rely on the diesels;
that is the LOOP in connection with the large-break
requires the diesel to start so that you can have your
low head pumps, your quick injecting pumps be
available. Because they're driven by electrical
For the small-break, we rely on steam
that's still available in the small-break to drive
some of our pumps. And we have separate -- we have a
separate diesel driven pump, separate from our main
grid. So we don't have to rely on off site power.
So we may be able to relax our criteria,
for example, on our fast start diesels. That is the
large-break we won't need them and we don't need them
for the small-break, and so we could relax the start
requirements and have them start at a more reasonable
time frame and, thus, improve the reliability of the
diesels. And that is the diesels would not have to go
through the fast starts and, thus, be degraded because
of the fast starts and they could be started -- maybe
they would start automatically, but it would be in a
three minute time frame as opposed to 10 seconds or
maybe they could even wait for a manual start when you
need them for a small-break. So there could be some
benefit in that. We're looking seriously at that.
The single failure criteria could fall
into that, but we're still -- we still need some
discussion on what the single failure would mean for
us. I think it's still a little hazy on how you might
factor that into your analyze.
DR. WALLIS: Could you put this in the
sort of rational that optomizing the use of the
diesels so that you have them available when you
really need them.
MR. REICK: Right.
DR. WALLIS: And they're most reliable
when you need them, so in fact safety's improved?
MR. REICK: That's correct.
DR. WALLIS: Could you make that case?
MR. REICK: They are -- that's the case
that we would make. They're most beneficial when you
need them and they're more reliable because of the way
you would operate them.
So we have -- you know, those are the key
things we've looked at, decay heat and the benefit to
a LOOP LOCA as opposed to single failure after the
redefining the break size. There is some benefit in
the proposals here and we're pleased to move forward
That's all I wanted to say.
DR. SHACK: If there are no other
questions, the staff has asked for a letter, and I
think we'll want to put one together.
Do I have any thoughts or comments from
people about what we should say in a letter?
DR. WALLIS: Well, about the letter, we
don't have this document which isn't yet finished?
DR. SHACK: Well, we have a preliminary
version of it.
DR. WALLIS: But it's not --
DR. SHACK: It hasn't been approved by the
MR. CUNNINGHAM: That's correct, it's
still in the EDO's office. And we would -- obviously,
we don't anticipate changes, but as soon as we get the
signed version, then we would get it back to the
DR. WALLIS: Well, that would be before we
have to write the letter?
MR. CUNNINGHAM: I hope it's in the next
few days. Next week. Again, I don't anticipate major
changes, but we could certainly try to -- if there are
changes, we could lay out what the changes were and
that sort of thing to help out the Committee.
DR. SHACK: But I would think that, you
know, we could certainly talk about the options that
are discussed in attachment 1 in the overall document
of the options. And, you know, it might be a matter
of which had higher priorities. But that's something
we could comment on almost irrespective of what the
staff decided the priorities with the options.
So, I think we could move ahead on the
letter myself. Well, maybe that's something we can
discuss after people have had a chance to think about
it a little bit.
DR. APOSTOLAKIS: Well, they're coming
back to address the full Committee, right?
DR. SHACK: Right.
MR. LEITCH: We're almost all here anyway.
DR. BONACA: Maybe next week before,
however, we could get a feedback.
DR. APOSTOLAKIS: If we don't like the
letter this time, it'll be in September, right? Even
if we slip one day, that's it. The Commission will
MR. ROSEN: I didn't hear any very
negative views expressed, so I think we in general are
in agreement with the approach. So I think it would
DR. BONACA: I think there is some opinion
we have with priority for redefining the large-break.
DR. SHACK: Well, I mean the staff has
said it's going to go forward. You know, they haven't
stopped that work and it's, you know -- at this point
it's just sort of a skepticism about whether -- but I
think the short term benefits they're talking about
are definitely benefits also. I mean, especially the
Appendix -- or the B one.
MR. SIEBER: Well, if somebody's pressed
on the final acceptance criteria, it would certainly
be handy to have some of that margin that would come
out of the short term benefits.
DR. WALLIS: I would favor encouraging the
staff, that we go ahead with what they've laid out
here and not trying to meddle too much in redirecting
MR. SIEBER: Well, it's pretty early in the
game, too. This is all feasibility study.
DR. SHACK: Right.
MR. SIEBER: And so the decisions as to
what you finally will pursue and how much effort you
put into it won't be made for another year. So, you
know, there isn't too much that can be said other
than, again, encouragement.
DR. KRESS: Well, I think they're on the
right track. I see some details --
MR. ROSEN: The A&S standard has only been
out 7 years. I mean, it's pretty young. It's really
time for us -- of course, I'm kidding.
DR. KRESS: Well, I think there's some
unanswered questions on how you deal with margins in
the deterministic end of the thing. As we use more
realistic calculations, we approach these limits. But
those limits were set knowing that you had a pretty
good margin in the first place. And there may be some
question about the appropriateness of the limits as
you approach them.
I think Graham raised this issue that are
the limits independent of the margins. And I think
there are some questions that -- but that's for
something later on.
MR. SIEBER: The more important question
is who owns the margin.
DR. KRESS: Oh, I think definitely we
ought to have an ACRS position on that. And my
position, of course, will be that the licensee owns
MR. SIEBER: Well, provided you get the
licensee to fix up nonconservatisms that may exist
that the margin in the old days took care of one way
or another. And so to me you can't do it piecemeal,
you have to do like a package.
DR. KRESS: Well, I think I would agree
with that. I think as a general principle the
licensee owns the margins. Now there's a question
about what margins are actually there and how do these
limits get set, and what do the uncertainties do when
they overlap the margins. There's a lot of little
questions, but I think as a general principle the ACRS
thinks the licensee owns the margins.
MR. SIEBER: I didn't see any of that
discussion in the feasibility study.
DR. SHACK: But I don't think the staff
disagrees with that.
DR. KRESS: Yes, I don't think they do
DR. SHACK: They're acceptance limits and
that's why they're called acceptance limits. Yo know,
there's a debate on whether you've calculated things
properly perhaps, but that's a review process.
MR. SIEBER: But the concept of defining
what the margins are --
DR. KRESS: I think there's some debate
MR. SIEBER: Right. And I think that
ought to be dealt with as part of this project.
DR. KRESS: That's part of the 8.
MR. SIEBER: Yes.
DR. WALLIS: Well, this would be the
margins of the two signal or the three signal level,
that sort of thing.
MR. SIEBER: Well, that would be one
DR. KRESS: Well, here once again is a
good place for some formal decision criteria to enter
the picture. Right, George?
DR. WALLIS: Well, this is one of the
questions we wrestle with all the time is whether or
DR. APOSTOLAKIS: Never disagree with you.
DR. BONACA: Well, so much of it we have
to see for the work they do. For example, the issue
of single failure or elimination of it, it's very
significant in that it drops so many of the issues of
LOCA; what you inject, what assumption you make, what
is the break. All these. And so --
DR. KRESS: But I think they're well aware
DR. BONACA: Yes, they're well aware of
it. So what I'm saying all we can do is to follow
progress and I'm sure they'll ask the right questions
before we ask them.
So, you know, in the broader sense of
eliminating, that's even a bigger --
MR. ROSEN: But that's long term.
DR. BONACA: That's long term.
DR. KRESS: But you know it's the right
direction. You're getting rid of some of these vague
things that are closely related to risk somehow and
actually getting them pinned down as to how much value
they really are and what do they mean --
DR. BONACA: For the existing plants,
however, those decisions were integral with the design
of the plant. Many of the single failures were
eliminated by designing the plant in a different way
because that resulted in acceptable results. So, you
had a lot of alternations between the analysts and the
people designing the plants and how they ended up the
way they are. So, you know, I think for a newer plant
the design, I think today, with PRA you would have a
much better approach in evaluating all the possible
outcomes and considering also the probabilities for
the sequences so that you know --
DR. KRESS: And there's where I keep
harping on you to use your uncertainties correctly.
DR. BONACA: Yes, and I agree with that.
But anyway, that it is along --
MR. ROSEN: I think you just made a very
important point that I hadn't heard discussed before.
The changes go back to 50.46 and all the other risk
informed changes are changes that will apply to new
plants as well.
DR. KRESS: Yes.
MR. ROSEN: And we're about to see I think
-- I hope -- we hope some new plants.
DR. APOSTOLAKIS: Well, I don't know.
50.46, I mean, everything we're discussing today is
really water, isn't it? Water? ECCS and all that?
MR. ROSEN: But what about changes to the
single failure corrector?
DR. APOSTOLAKIS: That, yes.
DR. BONACA: But I would expect under the
current regulatory environment, an applicant could
come in and provide a study of single failure based on
a PI, and that would be much more credible how you
eliminate certain --
DR. APOSTOLAKIS: It's not even a single
failure. It's a single failure of hardware, right?
And put the operator there to defeat everything. And
that's not the same --
DR. BONACA: But the point I'm making is
that you assume -- see -- in search almost of a design
that was acceptable, you assume those kind of
failures. Now you would do it through a PRA.
DR. WALLIS: If we're looking ahead to new
plants we should encourage the staff to get
performance-based and not sort of specific based
entirely on the existing fleet of plants.
MR. UHRIG: But what impact would this
have on the certified plant?
DR. KRESS: They have their own rule.
DR. WALLIS: But this business about the
cladding and stuff, how would it apply to a peddle bed
reactor? But if you had something which said that
you've got retain fission products, then that applies
DR. KRESS: Yes, I think that's a good
point that you make. I mean, why you worry about the
ductility of the event.
DR. WALLIS: Ductility of the cladding of
a peddle bed reactor, yes.
What is the ductility of these ceramics?
DR. KRESS: Sounds pretty good.
DR. SHACK: But you put in a nice buffer
layer to absorb all the changes.
Are there any particular items we want
brought up at the full Committee, they should be
DR. APOSTOLAKIS: This was a nice
presentation for a full Committee.
DR. KRESS: Yes, and it wasn't that long,
was it? They might have to shorten it some.
DR. APOSTOLAKIS: Yes, they can shorten it
a little bit. But other than that --
DR. SHACK: I'm sure that's not a problem
DR. WALLIS: Will NEI have a presentation
or have you had time to think about before the full
MR. HEYMER: Since we haven't seen the
SECY and we're not really available on Wednesday
because we have an interaction with the senior NRC
management, we weren't planning to say anything more
than what we've said today.
DR. SHACK: Okay.
DR. BONACA: I have a question, Mr.
Chairman, which is shall we give back this document
DR. APOSTOLAKIS: No. This pre-
MR. MAYFIELD: That's right. You just
can't share it with anyone else. It's for your use
DR. BONACA: Then I will not share it with
DR. APOSTOLAKIS: We never share anyway.
DR. SHACK: Well, if there are no more
serious items to be discussed, I think we can adjourn
the Subcommittee meeting.
(Whereupon, at 4:45 the Subcommittee was
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