490th Meeting - March 8, 2002
Official Transcript of Proceedings
NUCLEAR REGULATORY COMMISSION
Title: Advisory Committee on Reactor Safeguards
490th Meeting
Docket Number: (not applicable)
Location: Rockville, Maryland
Date: Friday, March 8, 2002
Work Order No.: NRC-272 Pages 272-371
NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers
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NUCLEAR REGULATORY COMMISSION
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ADVISORY COMMITTEE ON REACTOR SAFEGUARDS
490TH MEETING
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FRIDAY,
MARCH 8, 2002
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ROCKVILLE, MARYLAND
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The Committee met in Room T2B3, Two White
Flint North, 11 Rockville Pike, Rockville, Maryland,
at 8:30 a.m., George Apostolakis, Chairman, presiding.
PRESENT:
GEORGE E. APOSTOLAKIS Chairman
MARIO V. BONACA Vice Chairman
F. PETER FORD Member
THOMAS S. KRESS Member
DANA A. POWERS Member
VICTOR RANSOM Member
WILLIAM J. SHACK Member
JOHN D. SIEBER Member
. ACRS STAFF PRESENT:
MAGGALEAN W. WESTON
PAUL A. BOEHNERT
SAM DURAISWAMY
SHER BAHADUR
CAROL A. HARRIS
JOHN T. LARKINS
MICHAEL T. MARKLEY
. C-O-N-T-E-N-T-S
AGENDA ITEM: PAGE
Phase II, Pre-Application Review of . . . . . . 275
the AP1000 Design
Applicability of Exemptions and DAC. . . . . . . 299
Applicability of AP600 Testing . . . . . . . . . 307
Containment Issues . . . . . . . . . . . . . . . 332
Applicability of Reactor Codes . . . . . . . . . 339
Response of Westinghouse . . . . . . . . . . . . 344
. P-R-O-C-E-E-D-I-N-G-S
(8:28 a.m.)
CHAIRMAN APOSTOLAKIS: The meeting will
now come to order. This is the second day of the
490th Meeting of the Advisory Committee on Reactor
Safeguards. During today's meeting, the Committee
will consider the following; Phase II, Pre-Application
Review of the AP1000 Design, Future ACRS Activities,
a Report of the Planning and Procedures Subcommittee,
Reconciliation of ACRS Comments and Recommendations
and Proposed ACRS Reports.
A portion of the meeting may be closed to
discuss Westinghouse proprietary information. This
meeting is being conducted in accordance with the
provisions of the Federal Advisory Committee Act. Mr.
Sam Duraiswamy is the designated federal official for
the initial portion of the meeting.
We have received no written comments or
requests for time to make oral statements from members
of the public regarding today's sessions. A
transcript of portions of the meeting is being kept
and it is requested that the speakers use one of the
microphones, identify themselves and speak with
sufficient clarity and volume so that they can be
readily heard. I will begin by asking Dr. Kress, a
member in this issue, to lead us through the Phase II
Pre-application Review.
MEMBER KRESS: Thank you, Mr. Chairman.
I remind the members that the application review for
AP1000 is being done in three phases. Phase 1 was for
Westinghouse and the NRC to identify what would be the
key issues in the certification and Phase II was for
Westinghouse to ponder those key issues and come to
some sort of position on them. There are four of
these basically and today that's what we're going to
hear about, the four key issues and the staff's
position on these.
And I think we'll be asked for a letter,
of course, on our feelings about these issues. So,
with that, I'll turn it over to Jim Lyons.
MR. LYONS: Thank you, Dr. Kress. I'm Jim
Lyons, Director of the New Reactor Licensing Project
Office and we're glad to be here this morning to
discuss the completion of our review of the AP1000
pre-application review. We are getting ready to start
the review of the design certification which
Westinghouse is proposing to send in either later this
month or, I guess, next month. We are looking forward
to receiving your letter and with that, I'll turn it
over to Larry Burkhart, who will make the
presentation.
MR. BURKHART: Good morning, I'm Larry
Burkhart, the AP1000 Project Manager and as has been
said already, we're here to discuss the staff's
assessment of the pre-application review. Phase II,
the end of Phase II brings to a conclusion the end of
the pre-application review.
Briefly, the agenda, obviously,
introduction, what I am doing now, Mike Corletti from
Westinghouse will give us an overview of the AP1000
design, with some highlights on the differences
between the AP600 and that AP1000. We will provide
our assessment of the four issues that were decided to
be reviewed for the pre-application review. I'll talk
about those details in a second.
We have staff from NRR and the Office of
Research who were involved in that assessment and
after our assessment, Westinghouse will give their
presentation and their comments.
Some background; the AP600 was certified
in December of 1999. About that time, Westinghouse
expressed interest in applying for basically a larger
version of the AP600, the AP1000, based on the AP600
design. Early in the year 2000, we discussed a three-
phase approach that Dr. Kress mentioned. Pre-
application review involved Phases 1 and 2. Phase 1,
the scoping review, was completed in July of 2000 and
Phase II is to be completed by the end of March,
that's what we're talking about right now, and Phase
III is the actual design certification review, which
could come in as early as March, late March or early
April.
So getting to the point of what we're here
to talk about today, the scope of the Phase II review
is limited to four issues; the applicability of the
AP600 testing program to the AP1000 design
certification review, the applicability of the AP600
analysis codes to the AP1000 design, acceptability of
using the DAC approach in the INC control room and
piping design areas and that's in lieu of providing
detailed design, and acceptability of requesting
certain exemptions that were granted for AP600. There
are three exemptions which I'll talk about later.
The staff's assessment on these four
issues will be documented in a SECY to the Commission
and that would involve discussions of the design
acceptance criteria, the DAC, and the other three
issues would be documented in a letter directly to
Westinghouse and both of these are on tap to be issued
by the end of this month.
One last introductory slide, interaction
we've had with Westinghouse, as you imagine, have been
numerous. We had eight correspondences, which
involved requests for additional information that
actually covered 74 different questions. We issued
those RAIs between January and October of 2001 and
Westinghouse completed their answers to those RAIs by
November of 2001. We've had several public meetings
and tele-conferences and our interactions with the
ACRS included a briefing on Phase 1 in August of the
year 2000 and a couple weeks ago, three weeks ago, we
briefed two subcommittees as listed on the slide on
our assessments.
At that time our assessments were still
not completely finalized, as you'll see in the
discussion of design acceptance criteria. So moving
on, I would like to turn over the mike to Mike
Corletti, who will discuss the background of the
design, philosophy of design for the AP1000.
MR. CORLETTI: Good morning. It's a
pleasure to be here in front of you today. My name is
Mike Corletti, with AP1000 Project. I have quite a
few slides there in that package. I think I'm just
going to try to highlight on a few of those, but
they're there in case you have questions about the
background of the design.
As Larry said, we are designing AP1000 to
be based extensively on AP600 and to the extent that
you see here is a comparison of the general
arrangement of both AP600 and AP1000. And you will
see, we are maintaining the design within the space
constraints, within the general arrangement of the
nuclear island. So the system configuration of the
passive systems is the same as AP600 I'm going to show
and here, we typically say to people, "Can you tell
the difference between the two"? I think you'll see
that the steam generators are larger but other than
that from as far as the structural design here,
there's not really much difference on this view.
However, when you go to a 70 percent
upgrading, there are some changes that you have to
make. Here's a good view of the -- a section view of
the AP600 compared to the AP1000. The containment has
been -- the height of the containment is increased
approximately 25 feet basically to accommodate the
larger mass and energy releases associated with the
design basis accidents, and also to allow for steam
generator removal, if necessary.
Here's a comparison of some key selected
parameters. You'll see the power output, electric
power output essentially 1117, which is more than
1,000 megawatts and we'd like to say that the 1,000
doesn't necessarily stand for 1,000 megawatt. That's
$1,000.00 a kilowatt which is basically what we're
designing the installed cost of AP1000 to be.
MEMBER POWERS: What is W 3XL?
MR. CORLETTI: The 3XL is the Dole and
Tihange plants in Belgium. They are 14-foot core
plants, 157 fuel assemblies. Pretty much this is the
core, the reactor vessel that we've started with for
AP1000 and I have comparison to AP600. AP600, if you
remember, was a very low power density core. We
essentially had a 1,000 megawatt reactor vessel and a
1,000 megawatt core and we were running it at 600
megawatts.
To improve economic competitiveness, we've
basically taken the Doel Tihange core and as our basis
for AP1000 and we have increased its rating to -- a
comparable power rating to our operating three loop
plants. You'll see some of the other key parameters.
They both, AP600 and AP1000 uses a 17 by 17 fuel. As
I said, we've gone to the 14-foot -- 14-foot active
fuel length. One difference of AP600 and AP1000
compared to most operating Westinghouse PWRs is we use
gray rods for load follow, so we don't use boron for
load follow, which minimizes waste production.
CHAIRMAN APOSTOLAKIS: What did you say
about the AP1000, what does 1000 means?
MR. CORLETTI: Oh, I'm sorry, that was our
marketing. Typically, we started with 1,000 megawatts
electro-power rating but you see the -- we've actually
gone to 1117 but the driver for going from AP600 to
AP1000 was to get a cost competitive product and where
our U.S. utilities now are -- the target cost that we
need to deliver on an overnight capital cost is
essentially $1,000.00 a kilowatt, installed capital
cost. This is our major driver for developing --
taking AP600 and developing it to an AP1000.
MEMBER KRESS: Tell me, what is it -- what
is the need that drives the pressurizer volume
increase?
MR. CORLETTI: The pressurizer volume
increases there, to handle thermal transients,
transients that would occur.
MEMBER KRESS: So it's thermal capacity.
MR. CORLETTI: Yes, and it provides
basically a much more forgiving plant. AP600, you'll
remember, is designed to the utility requirements
document. One of those requirements was to eliminate
the PORV function stemming from the Three-Mile Island
accident. So the vendors all -- we've incorporated a
larger pressurizer to mitigate these transients
without opening -- without opening the safety valves,
right, without the need for opening the PORVs.
MEMBER KRESS: So that's what takes the
volume up.
MR. CORLETTI: That's what drives the
sizing of the pressurizer and for AP1000 it even got
larger. So it really provides a good operational
benefit for -- to mitigate transients.
VICE CHAIRMAN BONACA: A couple of other
things; at the surface area, there is a big increase
over the hedge.
MR. CORLETTI: There's a big increase,
right. The steam generator is what we call Delta 125
and it is similar to the -- it is based on the
replacement steam generator that we had supplied for
Arkansas but also essentially a small generator when
you compare it to the CE type -- you know, the CE,
System 2 type steam generators, where they fix their
designs on two loops and with very large steam
generators. This generator is within that size.
In the development of AP1000 shortly after
we started, we had merged with Combustion Engineering
and we really had the benefit of working with the
Combustion Engineering steam generator designers and
the Westinghouse designers in bringing a larger
generator within their operating -- it had been within
their design experience.
VICE CHAIRMAN BONACA: The other thing I
notice there, you have very similar core between the
Belgium reactors and this but you have much less of
reactor cool and pump flow.
MR. CUMMINS: Excuse me, this is Ed
Cummins. When you compare steam generators and pumps
to Tihange, you need to consider that there are three
steam generators and three pumps in Tihange and two in
AP1000.
VICE CHAIRMAN BONACA: Yeah, thank you.
MR. CORLETTI: Yeah, see the vessel flow
is essentially the same.
VICE CHAIRMAN BONACA: Yeah, okay, right.
MR. CORLETTI: With AP1000 we have four
pumps, four reactor coolant pumps.
VICE CHAIRMAN BONACA: The other one has
three, all right.
MR. CORLETTI: Right.
VICE CHAIRMAN BONACA: That makes a
difference.
MR. CORLETTI: So these are some of the
key parameters comparing AP600 and AP1000 in the
reference plan.
Just quickly here, we see the reactor
coolant system. As you'll notice, it is two loops but
four reactor coolant pumps which is a different
configuration than the previous Westinghouse plants.
As I said, the reactor vessel is based on the 3XL.
It's the same outside diameter as AP600 but is a
longer vessel. The Delta 125 steam generators, the
use of canned motor pumps which is based on our naval
applications, a very high, reliable canned motor
pumps, eliminate seals, no seal injection, no need for
seal support.
Simplified main loop piping, eliminate the
cross-over line. This elimination of the cross-over
line improves a small break LOCA performance is one of
the inherent features of the AP600 and the AP1000.
VICE CHAIRMAN BONACA: How do you deal
with the coast down?
MR. CORLETTI: For the reactor coolant
pump, for the Navy applications, they have a very --
do not worry about coast down. For AP600 we designed
a high integrity fly wheel, we built it and tested it
and we've incorporated that in this design.
VICE CHAIRMAN BONACA: Okay, a fly wheel.
A VOICE: It's depleted uranium, right?
MR. CORLETTI: The -- it is constructed of
depleted uranium. It is totally sealed.
MEMBER POWERS: Why a 60-year design
lifetime and not 80?
MR. CORLETTI: Well, the regulations only
allow us 40 at this point in time. We've designed it
for 60 --
MEMBER POWERS: And you're going to go for
20.
MR. CORLETTI: Perhaps 70 years from now
we'll be talking about plant life extension.
MEMBER KRESS: And big steam generators
let you go to a power upgrade.
MR. CORLETTI: Right. You go into high
burn-up fuel, I'll tell you that.
What you see here is the passive decay
heat removal heat exchanger. This is one of the key
features of the passive safety systems. It is used to
mitigate transients. It replaces essentially the
safety grade emergency feed water and ox (phonetic)
feedwater. So it's designed for events like a loss of
normal feed. The passive heat exchanger is located in
the refueling water storage tank, inside containment.
It's located above the core on a low steam generator
water level. Valves are actuated and by natural
circulation, the heat exchanger provides core decay
heat to mitigate any of the transients that were
designed for.
MEMBER KRESS: Does the water boil there
in the transient?
MR. CORLETTI: Yes, the IRWST, the heat
capacity is such that after about an hour and a half
of continued operation, the tank would begin to boil,
but with the passive containment cooling, where
condensate then is condensed on the steel shell and
returned to the IRWST, the passive decay heat removal
can provide core cooling essentially indefinitely.
MEMBER KRESS: Is there a pump that takes
that back or is it gravity?
MR. CORLETTI: No, it's by gravity. The
-- it's got an arrangement on the containment shell
that returns the condensate back to the refueling
water storage thing.
MEMBER KRESS: That's just like the AP600.
MR. CORLETTI: Exactly like the AP600.
Now, the heat exchanger has been increased in surface
area roughly 20 percent. How we've -- we've kept the
capacity though in relation to the core power and
we've achieved that by making the inlet and outlet
piping a larger diameter so that reduces the
resistance to the natural circulation driving head and
we've been able to maintain a capacity about the same
factor as the core power. Because this is designed to
remove core decay heat, we had to maintain that sort
of a --
MEMBER KRESS: These two valves --
MR. CORLETTI: Those are fail open air
operated valves, yes, and they receive a signal on low
steam generator water level. Again, with AP600 and
AP1000 with defense in depth, we typically have non-
safety active systems which is the first line of
defense. You would have a loss of normal feedwater.
The start-up feedwater pumps would be actuated to
supply feed water to the generators.
If they would then fail, then the passive
decay removal heat exchanger is actuated.
MEMBER KRESS: Now, you indicate that the
four-stage ADS comes out of that vertical line. I
thought it came out of the hot leg.
MR. CORLETTI: It shares a connection.
The ADS 4 on that loop is actually -- is t'd off of
this inlet line.
MEMBER KRESS: T'd off of this line.
MR. CORLETTI: Yes. So it is connected to
the hot leg, it's very close coupled to the hot leg.
MEMBER RANSOM: At one time there was a
concern about the ability to model the heat exchange
and the vertical heat exchanger tubes. Were any
experiments done to verify the --
MR. CORLETTI: Yes, as part of AP600, we
did a full height, full pressure, full temperature
tests of vertical tubes to develop a heat transfer
correlation which we then validated our analysis codes
to that heat transfer correlation and also
demonstrated it with blind tests at the Rosa facility
which is one of the test facilities that was conducted
by the NRC and we had very good predictions of heat
transfer using that correlation.
MEMBER KRESS: Now, what's the issue then
with thermal plume there?
MR. CORLETTI: There is a -- the staff had
asked questions in regards to are you able to have
steam blanketing on the outside of the tubes. We
essentially showed that for the tests that we ran and
for the tests at Rosa that really that our heat
transfer correlation which is based on a modified
Rosenal (phonetic) correlation, was sufficient to
predict overall heat transfer.
I think the concern they had was could it
degrade the heat transfer of the heat exchanger? And
I think that we showed that through our tests and
through -- we did several sensitivity studies where
we --
MEMBER KRESS: Well, I recall in one of
the presentations or something that I read that if the
velocity exceeded a certain level, you had a problem
with that.
MR. CORLETTI: Okay, that is a -- that
question is specific to the no trump code (phonetic),
the LOCA Code. There was an issue there that for the
correlation that we use in the NOTRUMP code, if the
velocity was too high, it could be non-conservative.
For AP600 the velocity was not in the non-conservative
region but there is an issue, with AP1000 with the
higher flow rates, will your correlation --
MEMBER KRESS: Will you get into that?
MR. CORLETTI: Right, and what we're going
to have to do there as part of -- as part of design
certification is provide -- is take -- essentially
adjust that heat correlation so it is not -- so it is
no longer non-conservative with respect to our test
data.
And I think what the staff is requiring us
to do is provide a justification for that modification
to that correlation. So we will plan on doing that as
part of the --
MEMBER KRESS: The correlation is HA times
a delta T. My understanding was you're going to
adjust the A.
MR. CORLETTI: Right.
MEMBER KRESS: But since it's a product of
HA, it doesn't --
MR. CORLETTI: Right, that's right and
this is only for the NOTRUMP code.
MEMBER KRESS: And under certain --
MR. CORLETTI: For the loss of coolant
accident which really the passive chart is not a big
-- you know, it's not dominate in the loss of coolant
accidents. For the transients, there we've used the
modified Rosenal correlation that we based on our test
data. That's not a concern there.
MEMBER KRESS: It's okay, there.
MR. CORLETTI: Yes.
MEMBER KRESS: And that's in -- what code
is that?
MR. CORLETTI: That's in the LOFTRAN code.
MEMBER KRESS: The LOFTRAN, okay.
MR. CORLETTI: Here you see the passive
safety injection system for the AP600. I think this
is probably familiar to most of you, but the features
of passive safety injection, the accumulators, we have
two accumulators that are exactly the same for both
600 and 1000 and they're really sized to mitigate the
large break loss of coolant accident. Their size is
consistent with our operating plants today.
You have the core makeup tanks which are
aligned at very high pressure in case of a leak from
the reactor coolant system and they're able to provide
high pressure injection. They replace the high head
safety injection function in today's plants. They
also provide boration capability to mitigate steam
line breaks.
We also have the refueling water storage
tank which is there and we're going to be talking a
little bit more later to provide long-term safety
injection. As the pressure is reduced following the
loss of coolant accident, as the core makeup tanks
would drain, automatic depressurization valves
connected to the pressurizer designed to reduce the
system pressure to allow gravity injection from the
refueling water storage tank.
The final stage of depressurization is
achieved with the four-stage valves which are
connected to the hot leg and how we've differed the
design from the AP600, essentially the same
configuration has been maintained. We've maintained
the same elevations. The core makeup tanks are
increased approximately 25 percent and the line
resistance has been reduced to increase their flow
rates about 25 percent.
The low pressure portion, low pressure
injection portions of the system, including the ADS
stage 4, and the IRWST injection lines and the sump
injection lines have all been increased to -- in
relationship to core power to accommodate the higher
core power associated with those.
MEMBER KRESS: What does FAI stand for on
that?
MR. CORLETTI: That's a fail as is valve.
MEMBER KRESS: Fail as is.
MR. CORLETTI: That's what that means,
yes. Those are -- those four-stage valves are Squib
valves. They're explosively operated valves that
operate one time type operation. When the core --
following the loss of coolant accident, after the core
makeup tank has essentially been emptied. So you've
had a very large loss of coolant accident.
MEMBER KRESS: What causes the signal?
MR. CORLETTI: On a core makeup tank?
MEMBER KRESS: There's a level signal?
MR. CORLETTI: Yes, there's a 25 percent
level signal, 25 percent level in the core makeup
tank.
MEMBER KRESS: And it's explosive Squib
valve that once it goes, it's opened.
MR. CORLETTI: Yes, it opens, it opens.
MEMBER KRESS: And the steam just goes
into the containment there.
MR. CORLETTI: Right, I think my next
slide, for all accidents, we use passive containment
cooling, so for an accident like a steam line break or
a loss of coolant accident where steam is released
into containment. Water tanks at the top of
containment there we have a line that opens. We pour
water on the steel containment shell. There enters
these baffles that you see on the shield building and
down and pass over the containment shell and by
evaporative cooling, provide containment cooling to
mitigate all design basis accidents.
MEMBER KRESS: That feed line from the
water tank, it has a valve in it that's not shown
here?
MR. CORLETTI: Yes, in fact, for AP1000 we
actually have added a third -- there's actually three
lines, so as part of our PRA studies, we've added a
third diverse line for passive containment cooling.
MEMBER KRESS: Wide open so --
MR. CORLETTI: Those valves open on high
containment pressure or high containment temperature.
MEMBER KRESS: Okay, that makes sense.
MR. CORLETTI: The tanks on --
MEMBER KRESS: And where are those
measurements made?
MR. CORLETTI: Those are made from
instrumentation inside containment.
MEMBER KRESS: You mean, you have a bunch
of them redundant?
MR. CORLETTI: Yes, redundant, redundant,
at least, I believe we have four, four containment
pressure measurements.
The tank is sized for three days of
containment cooling flow. After three days we would
have water tanks and the dedicated pump to provide
water to replenish the tanks to provide core cooling
but even after -- on AP600 after three days, our
studies showed that air cooling was sufficient. Air
cooling is also sufficient to keep containment
pressure below the service level cease limits for the
containment.
MEMBER KRESS: Now, these are based on
your separate effects test with the large containment
vessel?
MR. CORLETTI: Well, yes, we performed a
slew of separate effects tests as far as basically to
get heat transfer correlations to apply for the
passive containment coolant, heat transfer
correlations for heat transfer across the containment
shell. Essentially, we've used them in a steady state
heat transfer correlations.
MEMBER KRESS: Right.
MEMBER POWERS: Where are those
documented?
MEMBER KRESS: There was a test basis
document that --
MR. CORLETTI: Right, for AP1000 we
submitted a test applicability -- I mean, our
applicability document that went through all of the
test programs for AP600 and showed how they were still
applicable for 1000. For AP600, we had -- there's
several different tests, either test reports or the
final validation report for Gothic which the Gothic
report showed the validations of the tests.
MEMBER KRESS: We got all those when we
reviewed AP600.
MR. CORLETTI: Right.
MEMBER KRESS: I don't know if we still
have them or not. I've got --
MR. CORLETTI: You know, there were
several reports.
MEMBER KRESS: They might have just been
sent to the Thermal Hydraulics Section.
MEMBER POWERS: None of this is very
hopeful because there's a mountain of information
here. Could somebody point me toward where all this
stuff is?
MR. CORLETTI: Sure.
MEMBER KRESS: Well, we'll get -- these
are sort of just for our information now because we'll
get a chance to go over all this again when we talk
about the recertification. This is just to orient us
more or less. I don't think there's any decisions
that have to be made regarding these things at this
point.
MR. CORLETTI: Yes, right. I think during
the review the crux of the review from this issue was
that were the tests that we performed for AP600, was
AP1000 still within the range of those tests that were
performed.
MEMBER KRESS: Yeah, that's the issue,
that's the issue.
MR. CORLETTI: And I think the staff's
going to report on their findings on that.
Just a couple slides just showing some of
the performance of the passive systems. You'll see,
here's a comparison for a large break LOCA showing the
large margins that the passive plants provide for
mitigation of a large break.
For AP600, peak clad temperature was less
than 1640 degrees fahrenheit. For AP1000 it will be
higher but we will be well within the regulatory
limits for it. Essentially, here the dominate
phenomena is not the passive systems, it's really the
accumulators and the core-stored energy.
This slide here shows a comparison for
small breaks, for small break LOCA margin. One of the
key features of the passive safety systems was that
the improved performance for small break where we
would not have core uncovery for these events, for our
current PWRs, for two-inch, three-inch sized breaks
where they're limited on safety injection flow
typically you would have a fairly decent, fairly
significant heat-up, still under the regulatory
limits.
Here you see for the passive plants
essentially you have no core uncovery for the range of
small breaks. A couple others I just will real
quickly go; this just shows a comparison of our PRA.
This is another one of the benefits of the passive
systems, you see very low risk margins for AP600. We
expect AP1000 to have similar results.
MEMBER POWERS: I'm unfamiliar with the
requirement for -- NRC requirements. What are you
referring to there?
PARTICIPANT: The one times tenth to the
minus four core damage frequency for initiating
events.
MEMBER KRESS: It don't think it's a
requirement.
MR. CORLETTI: Probably it's a guideline,
I think. It's probably not a requirement.
MEMBER KRESS: Yeah, a guideline is a
better word.
MR. CORLETTI: Yes, I think that's fair.
And this last slide really shows you a comparison of
the size of the 600 compared to an evolution style
plant, I'm sorry, AP1000, compared to an evolutionary
plant. This is Sizewell. And you see with the
passive systems, that we've been able to achieve a
much simpler design and a much smaller plant footprint
because due to the modular construction the plant, the
whole plant is designed in modules and very much
smaller footprint than those in the past, such as the
Sizewell.
MEMBER KRESS: What's the power of
Sizewell?
MR. CORLETTI: Sizewell, yeah, we are
cheating a little bit there, about 3800 megawatts
thermal, we're 3400 megawatts thermal.
MEMBER KRESS: Not that much difference.
MR. CORLETTI: Yeah. I think Larry
talked about the scope of Phase II of this pre-
certification review that we've just finished and I
think the four major questions that we were looking to
answer in regards to the applicability of our test
program that we completed for AP600, as we said, we
completed a very thorough test program that was
extensively reviewed by ACRS and the staff. We're
looking to see the applicability of that test program
to AP1000.
And also then the AP set of analysis codes
that were validated against those tests, we plan on
using those codes too, in the design certification for
AP1000. And then the other two issues, the one is on
the issue of the use of piping design acceptance
criteria and the issue of the exemptions approved for
AP600.
That's all I have. I think I'm going to
turn it over to the staff now.
MR. BURKHART: Dueling slides. You've
seen this slide before. It's not a new one. It
reflects what Mike just stated as the scope of review
and here we'll start the staff's assessment. I will
discuss the applicability of the exemptions and the
DAC approach and Steve Bajorek from the Office of
Research, will discuss the applicability of the AP600
testing program and Ed Throm and Walt Jensen from NRR
will discuss the analysis codes.
PARTICIPANT: Do you have copies of these
slides, sir?
MR. BURKHART: Yeah, this was a previous
slide I had in my introduction. Okay, exemptions, the
applicability of the exemptions; the three exemptions
that Westinghouse plans to request for the AP1000,
this is a rundown of what the requirements are.
Section 50.34 (f)(2)(iv) additional TMI related
requirements regarding technical information contained
in application requires the safety parameter display
console, 50.62, requirements of the reduction of the
risk from ATWS requires diverse and automatic
initiation of auxiliary feed water, emergency feed
water and the third GDC 17 which requires two
physically independent offsite power sources.
A little more information added on this
slide, based on the design, the passive design of the
AP600, mostly, these exemptions, the request for
exemptions were granted for the AP600 and based on
meeting the special circumstance, that application of
the regulation is not necessary to achieve the
underlying purpose of the rule. And based on our
review, we believe that due to the similarity in
design between the AP600 and AP1000, that it's
appropriate to ask for these exemptions and expect
that they will be justifiable and the exemptions are
basically applicable. We will do the complete
detailed review during Phase III, the design
certification review.
Design acceptance criteria; I'd just like
to go over the requirements and how we've used the
design acceptance criteria approach in the past in
design certification reviews. The requirement in Part
52 is as stated; "An application must contain a level
of design information sufficient to enable the
Commission to judge the Applicant's proposed means of
assuring that construction conforms to the design and
to reach a final conclusion on all safety questions
associated with the design before the certification is
granted".
Not a prescriptive requirement, but pretty
clear on the intent. And after Part 52 was issued,
there were issues that came up on the level of detail
that was being provided in the ABWR and the System
80+. And where we start to get some clear direction
and guidance on the use of the DAC approach was in
SECY-92-053 and this is again during the review of the
System 80+ ABWR. The staff observed that applicants
weren't providing the level of information that we
thought we would get and this is where the DAC
approach first was discussed.
And the DAC, Design Acceptance Criteria,
are defined as, "A set of prescribed limits,
parameters, procedures, and attributes upon which the
NRC realized in a limited number of technical areas
that making a final safety determination to support a
design certification". And it was conceived that, you
know, this concept would enable the staff to make a
final safety determination as required by Part 52,
subject only to satisfactory design implementation,
verification by the combined licensee for appropriate
use of inspections, tests, analysis and acceptance
criteria.
And the staff concluded that you should
restrict the use of DAC to two cases where a design
area is characterized by rapidly changing technology
and thus, if you finalize a design at the design
certification phase, it may be obsolete by the time a
plant is actually built or design areas for which as-
built or as-procured information was not available.
And how we use it in design
certifications, for the ABWR the System 80+, we
approved the DAC approach for the I & C and control
room or human factors engineering areas due to the
rapidly changing technology aspects. We also, for
both of these design certifications, approved the DAC
approach for the piping and radiation protection areas
based on the lack of as-built or as-procured
information being available.
MEMBER KRESS: So you were able to approve
the piping DAC for ABWR and System 80+ without it
being a safety issue apparently.
MR. BURKHART: Correct, we were able to
come to a conclusion on all safety questions, right,
as required by Part 52.
MEMBER KRESS: And you feel like you can't
do that with AP1000?
MR. BURKHART: We're getting to that.
MEMBER KRESS: Okay.
MR. BURKHART: Our conclusions may be a
little bit different than what we discussed back in
February.
MEMBER KRESS: Okay.
MR. BURKHART: Okay, so chronologically
moving on to the AP600 design certification review, we
allowed the use of DAC in the I & C and control room
areas just as we did for the ABWR and System 80+, same
reason. However, piping back was not requested and it
wasn't used. And even though the as-built or as-
procured information wasn't available, Westinghouse
completed the piping design and they basically assumed
that information.
The DAC approach as proposed for the
AP1000, a little history here; originally,
Westinghouse proposed or it was discussed that DAC,
the DAC approach would be used in the I & C, the
control room, the piping, the structural and the
seismic areas for hard rock and non-hard rock sites.
And that was definitely expanding the use of DAC as
compared to what we had done before. And we had some
discussions with Westinghouse on our ability to come
to conclusion on all safety questions due to coupling
all of these together, especially the piping
structural and seismic areas.
We had some conversations and some public
meetings and voicing our concerns, and basically on
February 13th, Westinghouse revised their proposal for
the use of DAC to limit DAC in the I & C, control room
and piping areas. They would basically provide
sufficient information to preclude the use -- the need
to use DAC in the seismic and structural areas and in
that same letter, they provided more information
supporting why they should be able to use DAC in the
piping area.
So our assessment, we think the DAC
approach is acceptable for the I & C and control room
design areas, the same reason as we approved it for
the previous three design certifications, rapidly
changing technology. In the piping area, we do
recognize that Westinghouse completed the piping
design in the AP600 and due to the similarity, we
think there will -- we will realize the benefits of
standardization that they'll carry over from the AP600
to the AP1000 due to the similarity.
Westinghouse noted in their February 13th
letter that it gained very little regulatory benefit
by performing a detailed piping design because they
were still subject to pretty much the same ITAAC as
the ABWR and System 80+. And due to the similarities
in design, we find that the completed AP600 piping
layout and design provides a sufficient level of
detail to assure that the benefits of standardization
will be achieved for the AP1000 piping.
MEMBER RANSOM: I have one question on the
instrumentation and control, are these hard wired
plants, or have they gone to fiber optic pipe systems?
MR. BURKHART: Mike, do you know the
answer to that?
MR. CORLETTI: Yes, we do use a digital I
& C. We are hard-wired from the sense of to the data
highway but we have gone to the digital.
MEMBER RANSOM: So you have two
independent systems then?
MR. CORLETTI: We have three actually. We
have a safety related protection monitoring system.
We have the plant control system and we have a diverse
actuation system which is digital also but is diverse
to the protection system and it provides certain
protection type functions.
MEMBER RANSOM: Thank you.
MR. BURKHART: So based on the arguments
on the previous slide, we find that the piping DAC
approach is acceptable for the AP1000. However, just
as with any DAC, it's contingent upon being able to
agree with Westinghouse on adequate DAC. Again,
that's for any design acceptance criteria used. There
will be changes in piping size and we will have to
identify areas of concern. We think we can -- we can
be able to make -- come to a conclusion on all safety
questions but there are some areas where some changes
may cause us to focus, again, areas for Phase III,
design certification review and some of those areas
are listed here.
Now, the impacts of using design
acceptance criteria; it has a potential to increase
the likelihood of post-construction hearing petitions,
and to expand the scope of a hearing. Compliance with
a DAC can be subject of a hearing just prior to
operation, including those DAC that were intended to
be verified early in the construction process.
MEMBER KRESS: In other words, you're
moving towards what you used to do when you had to
have a construction permit and an operating permit.
MR. BURKHART: A little and I do want to
say that we're -- with allowing pipe DAC for
Westinghouse, we're not expanding the use of DAC
compared to what's been used before.
MEMBER KRESS: Because you did it before.
MR. BURKHART: Because we did it before.
In fact, Westinghouse -- well, ABWR and System 80+
used it for radiation protection. They're not using it
in this case. So the reason for approving the piping
DAC is a bit different than the reason we use for
approving the DAC approach for the ABWR and System
80+. That was, again, for as-built or as-procured
information not being available. We think because of
all the work that's been done on the AP600 and the
similarity of the design between the 600 and the 1000,
which the exact extent of that similarity will be
determined in the Phase III review, but because of the
work that's been done and the degree of
standardization we'll probably get from the AP600
design, that's why we're finding it acceptable for the
AP1000.
Well, that concludes the assessment of the
exemptions and the design acceptance criteria. Now,
Steve Bajorek from the Office of Research, to discuss
the staff's assessment of the applicability of the
AP600 testing.
MR. BAJOREK: Okay, thank you, Larry.
Good morning, my name is Steve Bajorek. I'm from the
Office of Research. What I'm going to talk about
hopefully over the next 20, 25 minutes or so is the
research evaluation of the test programs that
Westinghouse is using for the AP1000 and that were
done primarily in support of the AP600. As Larry and
Mike Corletti mentioned, as part of the AP1000
application, Westinghouse has proposed to use the test
programs that were used for the AP600 in support of
all of the data needs for the AP1000.
Their contention is that the data from the
AP600 programs is adequate. It's sufficient and it
covers the range of conditions that one would expect
for accident scenarios in the AP1000. The research
role was asked to come in and for those tests that
effected the primary system, evaluate those tests,
perform an independent evaluation and come up with our
own opinion on whether that data is truly acceptable.
What we did is we broke our evaluation up
into what I would consider three overall segments.
One, which I'll refer to as a top down scaling
approach which takes a look at the major interactions
of the system between other subsystems, how it
interacts with safety systems and how the system
behaves as a whole. We supplemented that with
simplified calculations. You might think of a first
principles thermodynamic evaluation looking at the
RCS, the flows into and out of the system in order to
get a better handle on the transient behavior as the
AP600 or AP1000 transitions from its high pressure
performance as the ADS 1/2/3 are on all the way
through to the IRWST injection phase.
Finally, we did another evaluation that
has been referred to as a bottom up scaling approach
that looks at those individual two-phased processes
that you really can't address very well, either with
simplified numerical calculations or in the top-down
scaling approach which really homogenizes everything
that goes on in the system.
You could spend a couple of days just
going over different top-down scaling methodologies
and what they entail. Essentially, what is done in a
top down scaling approach is to look at the mass
momentum and energy equations for a particular flow
circuit in a system and non-dimensionalize those and
then you look at those non-dimensional terms which
appear in front of each one of the major components of
that mass momentum or energy equation. This gives you
a set of dimensionalist groups, what we would refer to
as pi groups that you can compare from one facility to
the next and make a decision if the important
processes in the AP600 or the AP1000 are those same
things that occurred in the major integral test
facilities.
MEMBER KRESS: Let me ask you a question
about that. When you take these pi groups, you ratio
the -- say from 1000 to the test or to 600 and you say
that if that ratio for any one of these umpteen pi
groups falls in a range of .5 to 2, then that's an
acceptable range so that the phenomena you would
expect to be the same. My question is, how did you
arrive at that range and why is it -- why is it the
same range for every pi group ratio?
MR. BAJOREK: It necessarily isn't the
same range for every pi group. Let me just briefly
describe the overall approach.
MEMBER KRESS: Okay.
MR. BAJOREK: It's to take a look at these
dimensionless groups and if you -- the ratio of those
is between .5 and 2. Essentially, if everything is
within an order of magnitude it was deemed acceptable.
Now, in answer to your question on where I got that,
I got that from the AP600 review, used that as an
acceptability criteria. It was the tighter of the
acceptability criteria that was used. In some cases
it was between .3 and 3. Now, we didn't just base our
conclusion on all pi groups falling within that range.
Indeed, if you take a look at the test,
some of them fall without that, outside of that range.
We independently evaluate each one of those groups to
come up with a determination; one, is it really
important to the problem. In the INEL methodology
that we applied, one of the nice features is that the
pi groups are such that ones with very large values
are indicators, these are important. Ones with very
small values are effectively unimportant.
So when we looked at those --
MEMBER KRESS: That's like saying it's a
coefficient multiplying something that determines the
influence of that something in the equation. And you
know, I think it's both the size of the coefficient
and the something that determines. I mean, you have
to have -- you can't look at the coefficient by
itself.
MR. BAJOREK: Okay. I guess, you know,
the best I can say is we tried to follow what was done
in the AP600. We stayed on the tighter side of that
criteria. And when we did this we looked at things.
If they were outside of the range and distorted, we
tried to come up with a rationale, did it really
matter? And if it didn't matter, or if they were such
that the process in the AP1000 was going to be more
benevolent, have more mass in the system, behave
better than the tests, then you would assume that that
distortion was a conservative one and it would be
acceptable.
A real concern are those things that we
could identify as being very important to how the
AP1000 behaves and were not represented well in the
experiments. And usually, I think we would fine in
these scale groups they were fairly close to 1, 1.2,
1.3.
MEMBER KRESS: And those things came out
of the PIRT?
MR. BAJOREK: Yes, yes, or they fell
outside of that range. If we changed that range a
little bit, we would come up with essentially the same
conclusions. So I think that, yes, we did look at the
sensitivity to that and things that we will identify
as being important we think would fall outside of an
acceptability criteria even if you made it much
looser.
Okay, with respect to the top-down
scaling, the news is basically good here, in the use
of the AP600 integral tests. We looked at two
different scenarios, a one-inch cold leg break, a
double-ended guillotine of a DVI line, which tends to
be perhaps the most important of the transients,
looking at small break processes and we found that for
five -- four of the five major periods of the small
break and a long term cooling transient, tests that
were done in support of AP600 cover what we would
expect for the AP1000.
I show here on these bullets the five
different periods. Early in time, we see that the
AP1000 scales very well with SPES. In fact, AP1000
scales better with SPES than the AP600 did based on
the changes that were made to the system. If you go
further out in time, there weren't a tremendous amount
of changes that were made effecting the IRWST. The
sizes were larger but elevations which effected
driving heads didn't change that much, so again we
reached the conclusion that AP1000 scales fairly well
with APEX, the facility at OSU for the late phases.
Now, we do have what I might call a
difference of opinion with Westinghouse on the one
phase that transitions from high pressure to low
pressure. I refer to this as the ADS-4 blowdown.
Westinghouse claimed in their submittals that APEX,
the OSU facility, was valid and that data was good
throughout that period. When we do our scaling
evaluation we find that APEX starts to fall just
outside of that acceptability range but SPES remains
within that range.
So with regards to the test programs, we
would conclude, yes, the tests are available. During
this period we think SPES is probably the better one
to base your conclusions on code accuracy as opposed
to APEX but once you get down to lower pressure, APEX,
again, becomes the facility that you should base your
decisions on.
MEMBER KRESS: Is this one of your
bottoms- up scaling?
MR. BAJOREK: No, this is a top down.
MEMBER KRESS: This is top down.
MR. BAJOREK: This is top down.
MEMBER KRESS: So you're dealing with the
momentum and energy equations.
MR. BAJOREK: Yes, yes.
MEMBER KRESS: And what pi groups come out
of that? Are they --
MR. BAJOREK: Essentially --
MEMBER KRESS: Froude number?
MR. BAJOREK: Well, in this one it is a --
well, there's actually about 65 to 70 scaling groups.
MEMBER KRESS: Total, yeah, so they don't
all apply to APEX.
MR. BAJOREK: Total. They don't all show
up in each one of the periods. They change as you go
throughout. The Froude number and things like that,
that's for bottom up and we'll get to that in just a
second.
Now, one thing that we do note with the
ADS-4 blow-down and this is perhaps more of a critique
on the methodology itself, is it does make some
assumptions on what goes on in the tests and in the
AP1000 and one of those is that you have a certain
exit quality leaving the ADS. We stayed consistent
with the methodology. We didn't want to invent
anything new at this point but we did note that during
this period, those assumptions and the scaling groups
are relatively sensitive to your assumption in what is
that flow quality? How much liquid is leaving during
this period. And we thought, well, this is something
that means we should look at it in a little bit more
detail.
We continued with the bottom up --
MR. CORLETTI: Steve, could I just make
one comment? This is Mike Corletti, Westinghouse. In
regards to our code validation, we did validate our
codes to both APEX and SPES and typically we wanted to
have at least one of the facilities be well-scaled in
all of the regimes, so we did actually have acceptable
validation for one well-scaled facility for AP1000,
even.
MR. BURKHART: That's right and that's
basically what my conclusions say. Based on top-down,
you don't need any more data. It may be how we look
at what validation you did that's the determining
factor in how good the code is doing. But we went on
and we still want to look at the bottom up processes.
As part of that we set up a simplified model. It
looked that the RCS essentially is one node, takes the
mass equation, the energy equation and sets up
essentially a thermodynamics problem to look at the
shrink and swell of the phases, the flows into and out
of the system.
The conclusion that we get out of those
calculations is that regardless of what we assumed for
exit quality out of the ADS, the pressurization of the
system didn't change all that much. Now, that's
important because it says the delay time between when
you have CMT flow and that essentially stops and
you're waiting for the IRWST to come into the system,
that period of time stays about the same. But what
the sensitivity also showed us that we would very
drastically reduce the mass in the vessel, in the
AP1000 relative to the AP600 or the experimental
facilities at a rate at which suggested maybe we're
going to see some core uncovery because of this
uncertainty in the exit quality through the ADS.
That starts to point at things in a bottom
up evaluation. It says, well what would contribute to
a high amount of flow leaving the system, things like
entrainment in the vessel and in the hot leg. So this
starts to support some of our conclusions in the
bottom up scaling where we look at precisely those
phenomena that get missed in a top-down scaling.
And these are things in two-phase flow
which tend to act as cliffs, flow regime transitions.
Are you homogenous or are you stratified or annular?
Are you flooding in the surge line or are you not
flooding in the surge line? Entrainment is another
process by which you have a gas flow, there's no
entrainment. Higher gas flow, no entrainment.
Suddenly you reach a critical point and you have a
great deal of entrainment. So we looked at the bottom
up processes for flooding, flow regime transition and
again, I think the message should be that the news is
really quite good here because when we looked at
regime transition, flooding, core level swell and void
fractions again, they're not too far off from the
ranges that we saw in the AP600 tests.
The exceptions, the things that start to
stand up as important items to look at in Phase III
are two-fold. Both are related to entrainment; one in
the hot leg. The other I'll refer to as a pool type
entrainment. And this is entrainment that occurs at
the top of the core, between the top of the core and
the upper plenum.
MEMBER KRESS: Now, did any of the tests
have a way to determine what that particular
entrainment was?
MR. BAJOREK: Yes.
MEMBER KRESS: You were able to get that
out of some --
MR. BAJOREK: Yes, I'll jump ahead a
couple of overheads, but after the AP600 tests were
completed, the NRC ran what they called no reserve
tests. Now, these were tests in which you had mass in
the upper plenum, they turned on the power, evaporated
and swept out that liquid. It showed from the test
results that there was an unexpectedly high amount of
entrainment from the upper plenum pool.
MEMBER KRESS: You could compare the level
change with the amount of energy going in and if it
wasn't going out as steam --
MR. BAJOREK: It was going out as liquid
and they used the separator tanks also to catch that.
MEMBER KRESS: I was going to ask you, you
could catch it.
MR. BAJOREK: Yes.
MEMBER KRESS: Okay.
MR. BAJOREK: Now it wasn't a primary
focus in the APEX tests that were run integrally for
looking at one-inch cold leg breaks and you can't
really get it out of those. There's too many things
going on. But in these no reserve tests, they noted,
yes, this is a process that was going on and what
became bothersome is that RELAP calculations,
simulations of those events under-predicted the
entrainment, where when they ran the tests they got a
lot of entrainment, actually got the level into the
core. RELAP couldn't predict that. It was getting
too high a level.
Now, those tests are not a good indicator
of whether you will have core uncovery or not. But
they are indicative of the fact that for flows similar
to AP600, AP1000, you will have a lot of entrainment.
One thing I want to point out, there's two different
entrainment processes. We talked about this at the
combined subcommittee meeting a couple of weeks ago
and I want to make sure that we're clear on the
distinction.
One is entrainment in the hot leg and
we're looking over at this region of the figure where
gas that leaves the core goes into the hot leg. The
principal view that people have is that there's a
stratified level in the hot leg. The high gas
velocities entrained droplets from this stratified
layer and it gets swept into the ADS. Where we did
have some discussion and what I think a better view is
called for is, where we really expect the most
entrainment is when the levels are fairly high in the
hot leg.
It's not quite entrainment from a
stratified layer but what we've seen or I should say
some of us have seen in -- of some flow visualizations
that have been done at OSU is that you get entrainment
there but you also get most of your entrainment from
plugs intermittent flows that occur in the hot leg.
Now, trying to predict that, trying to scale that
leaves us at a loss. When we take the best
correlation that we can find, best we can say at this
point is we'd expect a lot more entrainment in AP1000
than what we would expect in the tests or in the
AP600, but we can't put a good number on that.
MEMBER KRESS: In other words, it's kind
of self-limiting as the level gets down --
MR. BAJOREK: It may well be. I think my
point on this is this is something that we cannot say
at this point has been well scaled in the tests but
keep in mind, when it occurs, there's a lot of water
in the system. This is up close to the top of the hot
leg.
MEMBER KRESS: Yes, so one asks the
question, does it really --
MR. BAJOREK: It is --
MEMBER KRESS: -- from the standpoint of
safety?
MR. BAJOREK: My point here is, is the
data acceptable to evaluate these models in the code?
That's one question. Well, even if they aren't, then
those models are not doing a great job, the other
question that needs to be answered, I think, in Phase
III is how safety significant is that? The answer
that's still open, okay, and we have our opinions on
that at this point is, well, is this really going to
be important to the safety of the plant and uncovery
of the core if you aren't predicting this properly.
My opinion is probably not, but we've got
to get --
MEMBER KRESS: It's kind of a race.
You've got the decay heat driving stuff off and if you
-- and it's going down and if you've thrown out too
much already, you're starting from lower level, it
means you're going to dip farther into the core
depending on how much that was.
MR. BAJOREK: Right, right. Now, this
process goes away when you start to get down into the
core and --
MEMBER KRESS: Does this -- does the fact
that you now have a 14-foot core instead of a 12-foot
one impact on this at all?
MR. BAJOREK: Not this because the upper
plenum hardware has remained the same.
MEMBER KRESS: Oh, the same.
MR. BAJOREK: Unless I've missed it, Mike.
Upper plenum elevations and that hardware is identical
to the AP600.
MEMBER SIEBER: What's the distance from
the top of the core to the bottom of the hot leg?
MR. BAJOREK: I estimate it as 1.82 meters
based on some numbers that I had, six feet or so.
MEMBER SIEBER: Six feet.
MR. BAJOREK: Yeah, and that's to the top
of the active part of the core. The core plate is a
few inches off of that.
Now, I think what you were referring to,
Dr. Kress, was the other entrainment process that
starts to become dominant if you have scenarios that
lead to a two-phase level that drops below the top of
-- the bottom of the hot leg.
MEMBER KRESS: Yeah, that's what I was
concerned about.
MR. BAJOREK: Now, this gets away from the
slugging and stratified entrainment in the hot leg but
it's a different physical process by which you have
gas bubbling through a pot, in this case liquid
trapped in the upper plenum, entrains these droplets
and if that gas velocity is high enough, it sweeps
those out through the ADS.
Now, where this starts to get our
attention is in the double-ended guillotine break of
the DVI line, where calculations done by both the
staff and Westinghouse suggest that that level will
drop and reach a minimum, I think it's about a foot
above the core, more or less. Our question now is, if
you do not predict that adequately, are you looking at
a level that remained in the upper plenum or
potentially drops into and uncovers the top part of
the core?
So we focused more of our attention on
scaling this process from a bottom up viewpoint. And
on page 8, I put a little bit of that -- those numbers
and some of the scaling criteria that we used to take
a look at this process. First, this is something that
does show up being highly ranked in the PIRT. Okay,
this is Westinghouse's and what we also believe to be
correct it this is a truly important process,
especially for this double-ended guillotine break of
the DVI line.
And as I mentioned just a few minutes ago,
tests that were done after the AP600 program, did show
what when you had the two-phase level below the bottom
of the hot leg, I did have significant amounts of
entrainment and that we had a very difficult time
trying to determine how much should be entrained in a
calculation using RELAP. Now, there's a flock of
correlations that have been proposed to take a look at
this. The chemical industry very interested in
separations processes, so we see an amount of work.
Principally, what happens is it depends on
one, what's the gas velocity as you bubble through
this pool and secondly, how far to you have to entrain
a droplet before it goes up and out of your system.
So it's basically two parameters which are dominant in
these correlations.
MEMBER KRESS: E is defined as the ratio
of the mass of liquid to the mass of vapor?
MR. BAJOREK: Right. It's a mass of the
liquid -- it's the liquid flux over the gas flux.
Okay, and it's a dimensionalist way of representing
the entrainment. Looking at the correlations that we
find to be closest to the AP1000 in the test and we
did find those to be in the same range, okay, we find
that this relative entrainment scales to Jg the gas
velocity to the third, maybe the fourth power.
MEMBER KRESS: That's looking at these
correlations you say exist.
MR. BAJOREK: Yes.
MEMBER KRESS: I mean, it doesn't come out
of this. It just --
MR. BAJOREK: These are correlations that
were done. There was some work done in Russia to take
a look at this. Ishii had done some work at Argonne.
There had been some other work. They all basically
suggest that E scales with Jg to the third, fourth or
higher power.
So I defined a scaling ratio based on
those correlations and if you assume, as I think we've
just heard, AP600 has the same upper plenum hardware,
same geometry but you increase the power by 75, 76
percent, you can very quickly estimate that the AP1000
should have at least five times the amount of
entrainment that occurred in the AP600.
MEMBER KRESS: Now, this is decay heat
driving this.
MR. BAJOREK: This is decay heat driving
the --
MEMBER KRESS: So you wouldn't quite
expect the same ratio of decay heat as due to the
power, would you?
MR. BAJOREK: Well, no, we did take that
into account. Yes.
MEMBER KRESS: Oh, the 75 is --
MR. BAJOREK: Yeah, the decay heat goes up
by 75 percent.
MEMBER KRESS: Okay.
MR. BAJOREK: So the power -- depending on
when you look in the transient, that's scaled power
still goes up by 75 percent. Now, there are some
differences in pressure and in what that scale power
was in the facility and we sharpened our pencil and we
looked at those and we found that SPES or AP1000 would
have over 100 times the amount of entrainment as the
SPES facility, roughly 20 times what you saw in ROSA
facility.
APEX, only about six, somewhere between --
well, I estimated 6.3. APEX is a lot closer. It still
is a bit of a concern because the way APEX got closer
was not because of the gas velocity being correct for
the entrainment but the fact that it was a one-quarter
facility. So we're looking at it in -- from the
viewpoint that APEX is closest at this point. It's
distorted in a non-conservative direction but the one-
quarter height may actually save some of those test
results so that eventually they may be able to be
applied to the AP1000.
But our conclusion to date is looking at
this process, which was ranked high by Westinghouse,
using the best information we have, we find that none
of these test facilities were appropriately scaled to
capture this phenomena which we think is going to be
important in determining whether we have uncovery or
not in the AP1000. So by conclusion --
MEMBER KRESS: So your concern, though, is
only on this upper plenum entrainment --
MR. BAJOREK: That's basically --
MEMBER KRESS: -- and not at the ADS-4.
MR. BAJOREK: We think we still need to
take a look at entrainment in the hot leg. The
question is, well, how does this effect other parts of
the transient and you may want to use those results to
make other decisions, not just on whether you have
core uncovery or not.
MEMBER KRESS: So there's two areas of
entrainment, the ADS-4 and then the other one is --
MR. BAJOREK: The other is the hot leg. In
one case, I think it's a lot easier to make the
argument it may not be safety significant. And I
think that's the distinction. So by conclusion, we
should lost sight of the fact that by and large those
tests for AP600 are still valuable. They cover --
they answer an awful lot of questions for the AP1000.
We feel there are a couple of issues, a
couple of problems that stand out as exceptions to
that. Both involve entrainment. As we looked at the
RAIs, information that was submitted to Westinghouse
and results of our own independent investigation, at
this point we conclude that Westinghouse has not
demonstrated that the test data is adequate for
validation for these processes and we suggest that
they and we need to come up with either alternative
data, a different criteria for scaling or some new
test results in order to close out these issues and we
think this is going to be something that we need to
look at in Phase III.
MEMBER SIEBER: Has that decision been
made yet, which of the three approaches?
MR. BAJOREK: No, we've -- in the SECY, I
believe the language is such we're leaving this open
for discussion. We're not saying you've got to go out
and run tests because there may be other entrainment
tests that can be used. They may not just be what was
done in the original AP600 test.
MEMBER SIEBER: But of all the phases,
this is the most important because it results in the
loss of inventory.
MR. BAJOREK: Yes, this one is going to
basically show us do you have core uncovery and some
clad heat-up or not in the AP1000. Now, again, I
think there's -- you can do some other work looking at
how quickly you should lose liquid from the upper
plenum. Again, you may be able to demonstrate that
the uncovery that you expect is not going to be
significant or that it's going to take so long to get
that last bit of liquid out of the upper plenum,
again, your concern may not be justified.
But at this point, the data doesn't bound
the types of things that we expect in the AP1000.
MEMBER KRESS: If more data were needed,
can APEX be used to produce that data?
MR. BAJOREK: I think so. In fact, I
think that a series of tests could be run in the APEX
you should do something to the no reserve but you do
it under steady state. Okay, they still had
complications in the no reserve because they started
from a high pressure and flashed a lot of liquid. Run
some steady state tests to get the effluent and the
exhaust flow rate and bench mark these correlations
which we still have questions about. I mean, these --
MEMBER KRESS: What would you do about the
H difference?
MR. BAJOREK: The H difference, I think,
can be addressed, although I would not do that in the
APEX facility itself. There is a sister facility out
at OSU called ATLAS. It has the same diameter vessel.
MEMBER KRESS: ATLAS. That's the one we
saw.
MR. BAJOREK: That's the one we saw but
they didn't have anything in their upper plenum, okay,
or above the core. But they do have some nice
visualizations and working with plexiglass and lower
pressure is a lot easier than messing around with
APEX, where you have all the instrumentation. I think
it would be very feasible to put in upper core plate,
simulated upper internals, a couple of DP cells and
try to get at some of these same things. There you
could, I think, fairly easily change your upper plenum
geometry, okay.
You could put in what I'd call a donut in
the upper plenum to restrict some of the flow and
change your gas velocities or change the height of the
core plate and get at some of those things. So an
answer, yeah, I think APEX would help. I think maybe
that sister facility may be a better place of
exercising some of these parameters that apparently
effect the correlations.
MEMBER SIEBER: Just stepping back and get
the big pictures. ADS operates to get the pressure
down enough so that you can inject from the
accumulators. Roughly, what is that period of time
from the time that ADS-4 begins to operate until the
accumulators inject and I'm sure it's a function of
break size.
MR. BAJOREK: Yeah, it's -- I believe that
what happens in like a double headed guillotine
transient is that the accumulators come in while
you're still depressurizing. The length of time then
between ADS -- or excuse me, accumulator injection and
the time you actually get the IRWST is on the order of
several hundred seconds. Mike, do you remember that?
MR. CORLETTI: Yeah, the core makeup takes
time to drain in about 20 minutes and then after that,
the ADS-4 is actuated and IRWST injection can occur
immediately to some time there's a delay a hundred,
couple hundred seconds. It ranges, as I said, based
on the break size. But it's not a long duration and
essentially once you get the IRWST injection, we're
flooding in the vessel in the hot leg and so we're up
to, you know, a lot of water, a lot of water in the
system.
MEMBER SIEBER: Now, once ADS-4 operates,
it's there forever, right? It's open.
MR. CORLETTI: It's open, yes.
MEMBER SIEBER: Open to the containment
forever. All right, okay.
MR. CUMMINS: This is Ed Cummins. There
is actually a black valve that you could close but
that's not the intention. The intention is that the
steady state safety case remains open.
MEMBER SIEBER: Right.
MEMBER KRESS: But even then, steam
condenses on the walls and goes back to the IRWST.
MEMBER SIEBER: Yeah, there's a reciro
path that -- yeah.
MR. BAJOREK: Okay, well, thank you and I
think the next presentation is by Ed Throm and he's
going to talk about the containment issues.
MR. BURKHART: This is Larry Burkhart just
to be clear, our assessment on the codes testing and
exemptions issues we documented in a letter to
Westinghouse, not in a SECY.
MR. THROM: Good morning, my name is
Edward Throm and I'm with the Plant Systems Branch and
I'll be going over the WGOTHIC computer program review
that was done for the AP1000 Phase II evaluation.
WGOTHIC is the computer program that Westinghouse uses
to evaluate the design basis accident response of the
containment to double-ended guillotine primary LOCAs
and main steam line breaks.
The code is described in WCAP 14.407 and
basically WGOTHIC is an extension of the numerical
applications incorporated GOTHIC 4.0 computer program
and what Westinghouse did was included a model in the
code called a Clime which represents the heat transfer
modeling to look at the condensation on the inside
surface, through the wall and the evaporation of the
PCS water flowing down the outside of the vessel.
The staff's evaluation was presented in
NUREG-1512. It covered the scaling studies, the part
studies, the testing program, a description of those
parts of GOTHIC that we reviewed, our review of the
Clime model and our overall conclusions on the
acceptability of what we came to call an evaluation
model for doing these types of analysis.
The evaluation model basically consists of
the use of the lumped parameter modalization process
in the WGOTHIC program. We believe that the lumped
parameter approach is applicable based on looking at
the buoyancy of the jets Froude number scaling, also
in looking at international test programs such as the
Patel model containment and the HDR which showed that
you would get a fairly well-mixed environment for all
parts of the transient.
One issue that we had to deal with was the
large scale test facility. It was not really scaled
for transient applications, so there were a lot of
questions on the circulation, stratification and
mixing of the steam environment within the
containment.
Westinghouse has addressed these in
conservative manners. Two address circulation, for
example, after the blow-down period, they don't take
any credit for steam that might get into the dead-
ended compartments below the deck. So they're not
trying to take any credit for any mixing that the code
might be calculating because of the uncertainties.
Stratification is also a concern with potentially
creating an air blanket on the operating deck which
will be a relatively large heat structure, so they
don't take any credit for the operating deck as a heat
structure in the analysis.
Also for horizontal surfaces that may get
condensing pools on them, they also don't count those
as heat structures. The other things that are done in
the evaluation model, is the PCS flow and mass and
heat transfer models are conservatively used. They
use minimum PCS flows in the massive heat transfer
models. They apply multipliers onto essentially bound
the uncertainty in all the data that went into
developing these models.
The AP1000 is a little bit different than
the AP600 as been noted before. The power level is
quite a bit higher, about 75 percent. The vessel
itself is about 25 feet higher. It's a slightly
larger volume. In looking at the PIRT and looking at
the fact that the AP1000 is using the same mechanism
for heat removal, we didn't see any changes in the
PIRT rankings of the important phenomena. There were
a couple of issues that we were concerned with in
going up to the AP1000.
One of them was whether or not the shell
temperature would get above 212 degrees Fahrenheit
before the PCS water came on. If that were to occur,
then we would have a problem with the model for the
film. We'd have to consider boiling of the film and
potentially breakup of the film. Westinghouse did
calculations that showed that at the time the PCS
water would be credited in the calculation. The shell
is only going to be about 180 degrees, so we don't
have to be concerned with that particular problem.
The other one was in looking at the
increased power and basically size of the AP1000 and
the stored energy and mass is somewhat larger than the
AP600. So the question was, are the massive heat
transfer correlations still being used within their
applicable range. And that was pretty much the focus
of the review was to go out and look at the mass and
energy, the heat fluxes that had to be addressed in
the correlations.
Okay, then in summary, no new phenomena
were identified in the process and the PIRT rankings
remained unchanged. The heat transfer models and
correlations are being used within their applicable
range. This is based on scoping studies that
Westinghouse performed provided to the staff in
December of last year in which they looked at most of
the dimensionalist groups and found that the expected
performance of the AP1000 wold fall within the
applicable ranges of all the data upon which these
correlations were based.
So we basically feel that WGOTHIC when
used with the evaluation model, is applicable to the
AP1000. The lumped parameter, mixing, we expect it to
be a well-mixed environment. They're still using the
same conservative approaches in addressing circulation
stratification and heat transfer. In Phase III there
are some things that we need to go back and look at
because the scoping analysis were not done completely
in accordance with the evaluation model but they're
very close.
They have not applied what they call their
evaporated flow model. And this is just a model that
adjusts the PCS flow to only take credit for the
amount of water that you could evaporate. The
standard review plan has mechanisms or guidelines for
calculating the mass and energies from both LOCA and
steam line releases. The LOCA analysis that was in
the scoping analysis is not quite in conformance with
what we expect to see in the design certification
analysis but we don't believe that that's a problem.
Also in the scoping analysis that Westinghouse did,
they looked at the ADS-4, IRWST and sump flows based
on the AP600. There's going to be some changes to
those in the long term and defining the mass and
energies that you have to account for in the process.
So during Phase III we will go back and
look at those evaluations again and we will --
Westinghouse, I believe, is committed to providing us
with similar evaluations to demonstrate that the codes
are still being applied within the applicable ranges.
I don't see any particular problem with
the expected changes in those but we reserve the right
to assure ourselves that we haven't gone outside the
applicability of the code. We have done Contain 2.0
audit calculations for the scoping analysis. We got
a very good comparison for the steam line break where
the passive containment cooling system is not really
a contributor to the peak pressure calculation.
We did do the large break LOCA
calculation. We did not do it for a licensing case
but we did it for the one of the reference cases that
Westinghouse provided us back in December 2000 we
calculated a peak pressure of about 54 psia compared
to that calculation which would have calculated about
60 psia. The contained two code is designed to be a
best estimate code for all practical purposes.
We did to a sensitivity study that tried
to mimic the penalties or multipliers that
Westinghouse applies to the heat transfer correlations
and we got about a two psi increase which we would
expect. We've not yet attempted to model or remove
any of the other heat structures from the contained
code to see if we could actually predict all of the
conservative features that are in the evaluation model
that Westinghouse uses with WGOTHIC. We do plan to
perform audit calculations as part of the Phase III
review once the mass and energies are finalized and
Westinghouse provides us with the detailed information
to make sure we've got all the volumes and heat
structures that we do apply in the code properly
marked.
So we believe that the WGOTHIC code is
applicable to the AP1000. That it will be used within
its range of applicability in terms of the mass and
heat transfer models that Westinghouse developed for
the PCS. That's all I really wanted to say this
morning.
MR. BURKHART: Great. Now, we'll turn it
over to Walt Jensen to discuss the applicability of
the reactor codes.
MR. THROM: Thank you.
CHAIRMAN APOSTOLAKIS: No, if he wants to
stand, he can stand. Do you want the mobile
microphone?
MR. JENSEN: I'm Walt Jensen of the
Reactor Systems Branch of NRR and I was responsible
for the review of the LOFTRAN, NOTRUMP codes that will
be used by Westinghouse for analysis of AP1000. The
LOFTRAN code is used by Westinghouse for non-LOCA
transients, including steam generator tube rupture and
it's used with other codes to assess the maximum
reactor system pressure, fuel temperature and the DNBR
that might be obtained.
The NOTRUMP code is used for small break
LOCA but in the time between a break occurs and stable
flow is established from the IRWST. After that the
WCOBRA track code is used for long term cooling
evaluation. And the staff did detailed reviews of
both these codes for operating plants in the mid-
1980's and again for AP600 and wrote an SER in 1998.
The review process that we took just these
codes that have already been reviewed in some detail
in the past. We looked at the differences that might
effect the analysis between the AP600 and the AP1000
plants. In particular the PRHR heat exchanger carries
a greater heat exchanger carries a greater heat load.
Steam generators are larger and the ADS-4 is larger
and carries more flow and has a greater role in small
break LOCA mitigation than it did for AP600.
We looked at the scaling, which you've
just heard about, of the tests that were used to
qualify the codes for AP600 to see if they would still
be qualified for AP1000. We obtained the Westinghouse
standards for generating input to the codes and this
is important because both codes are very versatile and
allow many user options. And Westinghouse has
established the set of options that should be used to
analyze the passive plants and we reviewed those.
And then we performed independent audit
calculations using RELAP5. We looked at a main steam
line break, small break LOCA. We got similar results
as Westinghouse for small break LOCA, but we did get
a very minimal amount of core uncovery for the double-
ended DVI injection line break. We took a look at the
limits in NOTRUMP and analyzing the PRHR heat
exchanger and we looked at the hot leg velocity and
how it might effect the entrainment going out of ADS-
4.
First, conclusions with LOFTRAN, we found
LOFTRAN was capable of analyzing the anticipated
transients and accidents, non-LOCA, for AP1000.
However, the steam line break is still open.
Westinghouse has not performed the steam line break
for AP1000 and we are concerned that the voiding in
the reactor system might extend beyond the capability
of the LOFTRAN code, though they have done one
preliminary calculation of steam line break that shows
there to be very low voiding.
The NOTRUMP code, we also found that to be
acceptable with the following exceptions that are
still open, and number one is the liquid entrainment
out of the -- which began in the core into the upper
plenum and out of ADS-4. Westinghouse has proposed to
bench mark the NOTRUMP code which has a very
rudimentary entrainment model against the WCOBRA tract
that they've modified with correlations to predict
entrainment and then they will bench mark that WCOBRA
tract code against experimental data which is still
under discussion with the staff.
Perhaps we will do some sensitivity
studies with RELAP to see the effect of entrainment on
the core. The conservatism of the PRHR heat exchanger
model is still under review. There's a limitation in
NOTRUMP to limit the code to flow rates in the primary
side of the PRHR heat exchangers to less than 1.5 feet
per second and this is based on a limit in the heat
flux comparisons with the experimental data by the
time correlations that's used in NOTRUMP that was
found to be non-conservative in comparison to the
experimental data for high heat flows.
So we'll be looking at that but
preliminary studies here show that the PRHR heat
exchanger flow has a very small effect on the course
of a small LOCA. And finally, we only looked at a few
breaks with either RELAP or NOTRUMP and the
entrainment issue is still open and this will effect
the results. So if core uncovery is calculated, we
will have to take up the review of the core uncovery
models in NOTRUMP and in the SBLOCTA code that's used
to evaluate the final core temperature when the core
is uncovered.
So that's where we stand at the end of
Phase II and we will be continuing the review in Phase
III. Thank you.
MR. BURKHART: Thanks, Walt. Just a quick
summary, again, the scope of Phase II was limited to
four issues. You've seen this slide before, this was
from my introductory slides. As you've heard in
general, the AP600 testing program and analysis codes
are applicable to the AP1000 design. We've noted some
exceptions and where we will focus our efforts on the
review during the design certification review.
We've also shared that the staff finds the
DAC approach in the I & C, human factors, control room
design and piping areas acceptable and also that the
three exemptions that are proposed for AP1000 are
applicable. And that concludes our presentation of
the staff's assessment. I'll turn it over to Mike for
Westinghouse's presentation.
MR. CORLETTI: We'll have Bill Brown, will
be our next presenter, will be presenting some of the
issues in regards to the applicability of the tests in
response to Steve Bajorek's presentation.
MR. BROWN: Okay. PIRT scaling and
entrainments assessment; Steve's already covered a lot
of this which we pretty much agree on most points, and
that is that there is no new phenomena expected for
AP1000 and we've already submitted our scaling
analysis to demonstrate that our 5600 test facilities
are applicable to AP1000. We previously presented
this work to both the NRC and the ACRS subcommittee.
Obviously, there were some issues
discussed here with respect to entrainment, especially
in the upper plenum and because of that, we went back
and did some additional evaluation and some scaling
which I'll present here in a moment. Before I do
that, though, I thought it was maybe a little bit
helpful in that I tried to come up with a -- sort of
an integral effect type of a slide to put this
entrainment a little bit in a system level
perspective. I know we kind of have focused on this
a lot from a very separate effect level and it
certainly is something that is considered to be high
ranked or important during the ADS to IRWST transition
phase of the transient but I think we need to keep in
mind a couple of things that are going out during this
time frame as well as not only do we have stuff going
out but we've also got potentially a lot of stuff
going in.
And one of the biggest things to always
keep in mind is that we've got roughly a 600,000
gallon tank sitting up here after the core make-up
tank, which is continuing to drain through the ADS-4
as well, that is certainly willing to sit there and
feed whatever entrainment that might be going along,
but based on our testing and a lot of the analysis
that we had done on the AP600, what we would expect to
see here which we had seen in AP600, is more of a
situation where you might start off in a phase where
you've got the ADS-4 is on and been actuated and is in
here venting steam to reduce the RCS pressure.
We've got injection from a core makeup
tank and then later here with a significant amount of
water from the IRWST potentially available here to
inject. We've got liquid perhaps in a first phase
being entrained from the upper plenum due to the high
steam flow associated with the AP1000. We would
expect some amount of phase separation in the hot
legs.
Some of the de-entrained liquid here would
initially start to accumulate somewhat in the hot leg.
We would expect that this process would continue. As
Steve mentioned earlier, we probably wouldn't
initially get a significant amount of entrainment
through the ADS-4 at this point until we reach a
critical inception level within the tanks so that the
velocity is high enough and to draw it, sort of a
Bernoulli effect, sort of sucking the water out of the
hot leg, so that we continue replenishment here in the
IRWST.
The ADS-4 would still be venting and
eventually we hit this point where we begin to hit an
inception point we now begin to entrain the liquid up
into the vents. At that point, then, as we would draw
the liquid up into the vents at this point, now you've
got the vents now that were predominately venting
steam out probably got to clear this liquid out, so at
that rate we'd probably see a bit of a reduction in
the amount of injection but on the other hand, now you
don't have a nice path for the steam to go out any
more, so now you've temporarily got a lower velocity
of steam and so you've got an entrainments reducing.
So the system is kind of correcting itself
here a bit and it's clearing itself purging the liquid
out. So eventually you clear out, so again you get
the pressure back down, you've vented the steam here,
so now you can resume to inject more water and entrain
more liquid out here and the process would then repeat
and we would see this going on through the long-term
cooling phase.
So that just sort of sets up a little bit
of the, I think, more of a system level effect to put
the local entrainment into context for you.
MEMBER SIEBER: If I look at the slide 9
and compare it to your drawing, it looks like ADS-4
comes off the line at the next ER of EST to the hot
leg, instead of as you show it there where it comes
in.
MR. BROWN: The ADS-4 here?
MEMBER SIEBER: Yeah.
MR. BROWN: The ADS-4 comes off the top of
the hot leg.
MEMBER SIEBER: Now, the IRWST line comes
in the same place, right?
MR. CUMMINS: This is Ed Cummins. I think
the thing that you're looking at is the PRHR heat
exchanger.
MEMBER SIEBER: Okay.
MR. CUMMINS: The PRHR heat exchanger is
a tank within the IRWST. It is connected to one of
those two ADS four lines.
MR. BROWN: Off the top of this line right
here, you would have a connection from PRHR off of one
of these ADS-4s that continues up and then that comes
up into here which is the exchanger sitting in the
tank here.
MEMBER SIEBER: All right.
MR. CUMMINS: If you look at slide 10, in
your presentation, all the injection from the core
makeup tanks to the accumulators and the IRWST for
make up to the reactor vessel, is through two direct
vessel injection lines which are basically independent
of other lines.
MEMBER SIEBER: Okay, I see that. Thank
you.
MR. BROWN: In fact, we finally see in the
tests that the PRHR actually helps to provide
fissional depressurization because it does condense
more steam.
MEMBER POWERS: Can you give me a feeling
for during this period where you have entrainment what
the superficial gas velocity through the core region
is?
MR. BROWN: Through the core region
itself? Well, obviously not as -- I think really the
highest velocity you could get is through the upper
core plate. That's really the highest velocity that
you get. It's pretty substantial. I'm trying to
remember what that was off-hand. Steve, do you
remember? Is it 100 feet a second or something like
that? I think it's pretty high. And it's moving up
through there, yeah, yeah, to the core plate and then
you would expand into the upper plenum where you --
MR. BAJOREK: This is Steve Bajorek for
Research. I don't exactly remember the velocity at
the core plate. However, in the AP1000 your
superficial velocity through the upper plenum, the
free part was about two and a half meters per second.
So given that there was a restriction down at the core
plate, three to four maybe.
MR. BROWN: It's probably somewhere
between those to if you want to try to bound that,
yeah. It's definitely higher than AP600.
Well, I just wanted to start with that
one, just to sort of put it in sort of a system level
context, so Steve's gone over some of this before.
We've looked at the -- first of all in the upper
plenum entrainment. Some of the work by Katoaka-Ishii
looked at full entrainment in vessels and identified
a near surface region and a momentum controlled
region.
The near surface region, very, very close
to the water surface, was found to correlate simply on
a density ratio. The momentum controlled region,
where you would move further away from the surface of
the liquid, was found to be a function of density
ratio, hydraulic diameter, viscosity number, but
primarily most strongly upon superficial gas velocity
divided by a dimensionless height. So it's really a
combination of the two of the Jg star and an H star
which are really the dominant terms in the momentum
controlled regime.
And to help you a little bit we're trying
to put this again, in context in terms of what type of
events might this be of interest to us or what type of
events would we be looking at things where we have,
for example, a level in the hot leg, we would be more
interested in what is the near surface type of
entrainment where we essentially have water already in
the hot leg, we're not having to lift it up from the
vessel into the hot leg, it's already there, versus
events where we would get into a momentum controlled
regime where we've got to actually lift the water
droplet up into the hot leg.
If you think of some of the two slides
that Steve just presented, you can see a good -- he
had a better picture of that than I do. These would
give you an idea of the type of events that we've seen
not just from analysis but also from looking back at
the OSU tests for example, and all the test programs.
Typically, the half inch, the one inch, the two inch
cold leg breaks, the hot leg break, two inch DVI and
the doubled ended core make-up balance line break, all
typically have a level within the hot leg already. So
for those events we've got a level in the hot leg.
We're in this near surface entrainment regime and
looking at the scaling. This indicates that we're
simply a function of a density ratio and since we
essentially have pressure scale facilities, the
scaling is good.
So the one in which we have a momentum
controlled regime where we don't have a level in the
hot leg, really is the DE DVI line break. So this is
really the focus of all this. So we even talk about
entrainment, you know, trying to put it in a system
level context and now in terms of events, which ones
are we focused in on. So we really, if you look at
all these tests, we're well scaled as far as
entrainment is concerned.
In the hot leg, for example, we've got
mixture levels in there and it's really only the DE
DVI line break that we really need to focus in on. So
based upon looking at this type of pool entrainment,
similar to the work of Kataoka-Ishii, we would say
that the entrainment is well scaled in the test
facilities for small break LOCAs where we've got a
mixture level in the hot leg, which was most of the
small break LOCA events I just listed, where pressure
is preserved and therefore, density.
It's in this momentum entrainment,
momentum controlled regime in which we're dependent
upon the superficial gas velocity divided by height in
which we have a potential distortion in the AP600 test
facilities due to the fact that we do have a higher
superficial gas velocity in the AP1000 core.
MEMBER RANSOM: Excuse me, what is the
dimensionless height? Is that just a height through
the outlook flow?
MR. BROWN: Yes, it's basically, if you
did a measurement, yeah, it's basically how far do you
have to lift up a droplet in order to carry it away,
right.
MEMBER KRESS: How do you non-
dimensionalize it?
MR. BROWN: It's non-dimensionalized, I
think, it's got a square root of density difference,
gravity and surface tension. I think that's how it's
-- so essentially, again, if you have a pressure scale
facility, you're just looking at just dimensional H
really and the velocity. And we are at this time in
the transient, we've essentially depressurized in the
facilities. We're to the point where you're really
looking at just Jg divided by H, dimensional.
It gives you a little better idea, I guess
on the next page here. I tried to put this together
a little bit in another way to digest this
correlation. Some of the details are down below, but
essentially if you were to start off with the
correlation here that Steve presented earlier, that
you've got the Jg divided by H star cubed and the
viscosity number and the hydraulic diameter number,
you can eventually -- you can relate this for pressure
similitude and for saturated conditions in the vessel.
You can come up with an expression for Jg and come up
with a simple expression like this where you've got
core power, area, height, and the hydraulic diameter
ratio here as far as looking at entrainment in a pool
type situation. So this is really the basis for which
to look at.
And the key is, is obviously, this term
right here is really the -- obviously, the dominant
term, the core power and the height and the area.
When you try to take this scaling ratio and put some
numbers into it, similar to the question you asked Dr.
Powers about the velocity and so on, if you sort of
range the velocity through the upper core plate up
into the upper plenum, you would come up with a number
in this range of roughly a quarter to a half, which,
you know, based on our criteria, the half were here,
based on the criteria that was used previously by
Brookhaven for AP600, at roughly a third, it kind of
looks like we're -- you know, we're kind of close.
So you know, we find that we're certainly
in the range at which I think Westinghouse would say
that, well, there may be a possible distortion, we're
certainly on the non-conservative side, as Steve says,
but we don't think that this distortion is very far
off that we can't use this data for code validation
purposes for AP1000.
The next step, I sort of tried to ask
myself a little bit presented before to the
subcommittee was, well, what does this -- what might
this correlation look like? If I were to come up with
a little simple model of an upper plenum mode where I
had really no water in the hot leg and I was just
worried about I've got some mixture level sitting up
above the core in the upper plenum at the bottom of
the hot leg and what if I put in this pool entrainment
correlation and essentially assume that the core decay
heat was driving it off. I had just enough liquid
here or mass flow to make up and match decay heat at
that time. Well, what might happen and how long might
it take for this entrained liquid to effect the upper
plenum level?
So I come up with sort of a simple little
model here in which I had a transient conservation of
mass here for the upper plenum and I just started with
the upper core plate to the bottom of the hot leg as
this initial two-phase region. And I used a simple
void fraction correlation using the YEH correlation
here to determine void fraction in this area right
here. And then I used the upper -- for the upper
plenum entrainment, then I used the pool entrainment
correlation form from Kataoka-Ishii here to try to
determine what was the mass flux of the liquid that
was entrained out of this mass and then from a
conservation of mass on the core, and I just for
conservatism I decided not to even account for any of
the sub-cooling which might help me here and said,
well, even if I just simply have saturated conditions
in the core here, what might my steam generation rate,
steam velocity be?
So then I did this, and I put this into
MathCAD. This is the result I got which showed that
very, very quickly, extremely quickly, I approached
sort of a quasi-steady state level above the top of
the core plate here and within seconds, I reached an
equilibrium level. So, very, very quickly this very
strong function of entrainment, this Jg really dropped
me very rapidly but then, of course, remember that
it's Jg over H and so H very quickly restores you into
sort of a self-limiting type process and so at some
point you very rapidly settle out at a steady state
level.
So it kind of gives you a feeling of what
the -- how the correlation and the behavior should be
for this type of entrainment. So what I concluded
from this was that are entrainment was sufficiently
scaled in the upper plenum for all possible events
with the exception of maybe the DE DVI line break in
which we didn't have a hot leg -- a level up in the
hot leg for very long there during this phase. And
that the entrainment scaling was really of concern
during this transition phase of the DE DVI vent where
we were subject potentially to this momentum
controlled regime. That this distortion in OSU does
not appear to be so large that would render our codes
unusable and that the momentum controlled regime, the
entrainment in the upper plenum here seems to be
somewhat of a self-limiting process because we've got
the Jg relative to H and because of this, we don't
expect to really see that there's going to be a
serious safety issue here with AP1000.
We also looked at hot leg entrainment as
well, and we expect to see a stratified type pattern,
although certainly Steve says we may see some slugs in
there and that's possible. I don't expect to see
cliescent (phonetic) stratified flow but we certainly
expect to see something that's stratified.
There's a Froude number type correlation
with a length to diameter of up-take type of
correlation which is responsible for predicting the
onset of entrainment from the flow into the hot leg,
into the ADS-4 and this was used to scale this.
The results of the scaling indicated that
our Froude number seemed to be acceptably scaled to
AP600 and AP1000. The real difference was in the
dimensionalist ratio of liquid level in the hot leg
relative to the ADS-4 pipe, which would indicate,
which I would agree with Steve, we would expect to see
-- we would expect to see entrainment begin at a lower
level in the hot leg in AP1000 relative to AP600 and
OSU.
However, I guess I'd say on the other
hand, the fact that we've got a level in the hot leg
and we're looking at those type of events, it's not
something I think that's quite as much of a concern.
We probably would accumulate less water in the hot
legs, however, usually having the hot water -- having
the level in the hot leg would tend to indicate we've
got core coverage. So we're certainly not as
concerned about that event than we would where we're
going to go below the hot leg potentially in events
such as a DE DVI event.
So some of our plans for trying to address
this situation in Phase III, we're going to
demonstrate through calculation and analysis that the
entrainment phenomenon in the upper plenum and hot leg
during this limiting small break LOCA does not
challenge the safety and see it as sort of using a
term of extreme entrainment here would be addressed on
one of several ways; assessing margins relative to the
regulatory limits, adjusting upper plenum/hot leg
correlations to increase entrainment, assessing upper
plenum de-entrainment due to the reactor vessel
internals, also potentially increasing pressure drop
in the ADS vents such as whenever the liquid is being
discharged through there and we plan to submit a
topical report to address this later this year in
June.
The overall conclusions that I have from
the testing and scaling, again, no new phenomena in
AP1000. The separate effects and integral effects
tests are acceptably scaled. Upper plenum
entrainment, there's a local effect that appears to be
self-limiting. We don't think additional testing is
required.
MEMBER POWERS: Can I ask a question?
MR. BROWN: Yes.
MEMBER POWERS: Which you showed was a
simple calculation --
MR. BROWN: Yes.
MEMBER POWERS: -- in which you had an
entrainment and then you had water feed.
MR. BROWN: Uh-huh.
MEMBER POWERS: And you said, gee, it
starts at one level and it comes to another level.
MR. BROWN: Right.
MEMBER POWERS: It seems to me that that's
an unremarkable conclusion for a first order
differential equation with a source and a think term
to come to another level. That has nothing to do with
the entrainment correlation. It has to do with the
fact that you've got a loss term and a gain term.
They balance each other if you go out long enough in
time.
MR. BROWN: That's true, but I think I'm
just trying to demonstrate the fact that I think
sometimes when the entrainment is presented, people
tend to forget about the fact that there is -- that in
looking at certainly the relative order, that there
certainly is a restoring term in there for H as far as
how far that level is.
MEMBER POWERS: But that calculation
doesn't show that. I mean, the calculation only tells
me a loss term and a gain term and the relative
magnitudes of those two will determine where that
balance is.
MR. BROWN: Yeah, and well, we're not
trying to make -- at this point, not trying to make
any claims about the absolute value of where that
steady state level is. I'm not trying to make any
claim about that at all. I mean, certainly this is a
very simple calculation.
MEMBER POWERS: I thought what you were
claiming that this was self-limiting because as that
H got bigger and bigger it reduced that J over H term
to --
MR. BROWN: Right.
MEMBER POWERS: -- the point that -- and
that's just not obvious to me that that's the case at
all.
MR. CUMMINS: Hello, this is Ed Cummins.
I think what Bill did in his calculation just for
simplicity, he set the in-flow equal to the out-flow
so that the mass was -- the core was covered and what
he was trying to assess was the effect of -- the
separate effect of entrainment, which is the same
thing that Steve was trying to assess. It's not the
whole integral effect.
So if you assess the separate effect of
entrainment, what is the effect of H and Jg working
together for the entrainment phenomenon and I think
those things suggest that at some level Jg dominates
and then after awhile H corrects it.
MR. BROWN: The point is to try to find
out at what H do we come to some kind of a steady
state. I mean, I agree that it's a steady state
calculation. I mean, eventually we're getting to that
point, but there is an H associated with that Jg in
which you balance and the question I have the interest
is, is well is it something that looks like it's, you
know, a foot or two away or is it 20 feet deep or how
far into this thing does it look like it goes and so
that was of some use.
MEMBER POWERS: I can make that carried
out, just by changing your inlet term.
MR. BROWN: Well, it was driven by the
decay heat in this case. I mean, the decay heat was
driving the mass flow which was representative at this
point in the transient. So yes, if I picked a
different decay heat, sure I would get a different
value and this certainly should decrease over time.
MR. CUMMINS: If you deal with -- Ed
Cummins again. If you deal with the entire system
performance, then the top down scaling is appropriate
and whether you get in-flow and out-flow depends
mostly on the relative pressure drop between the
forced states and the pressure available from the
IRWST. But as we, I think pretty much agree with the
staff, the top down scaling for the AP1000 is
acceptable and we happen to be now looking at a bottom
up scaling for a particular phenomena which is pool
entrainment from the upper head pool and what we were
trying to show that performance with some simple
calculation to give you a feel for what the
characteristics were.
MR. BROWN: I mean, it's very similar to
some of the things we had done in AP600, looking in
the containment. I mean, we all felt eventually that
we would, for example, remove the energy through the
containment shell. What the question is, is at what
temperature would the inlet -- the flow through there
balance and that's simply what I was trying to get at
was, okay, given that this entrainment occurs, what
would be the height at which I would reduce to given
the core power which would, again, influence the
velocity, at what height at which I would be able to
balance the entrainment relative to the flow that was
coming in? That's all I was trying to get at.
MEMBER POWERS: And again, let me control
the source term and I can make that height anything
you want.
MR. BROWN: Again, I would agree that if
we put a different flow rate in there, we'll come to
a new value. It's just that I was using typical
values that we got from our safety analysis code at
the time in which ADS-4 went off to represent to you
what might that look like at the time when ADS goes
off. And so we went into the code and said, okay,
what's the decay heat during that period and said,
okay, this is how many BTUs per second we're putting
into this point, this is the energy that's driving
this. What does that -- what might that steady state
height come out to be?
Any other questions?
MR. CUMMINS: Yeah, I think it's important
that we have not completed the calculation in the
topical report we plan to submit. When you use the
appropriate decay heat for the point of -- the point
of time for the transient, I think, you're right, you
could put any heat level in you want and drive any
answer, but when you put the appropriate decay heat
level, we'll have -- essentially we'll see a delta on
what the level could be.
MR. BROWN: Yeah, and we were curious
about that ourselves, so we decided to try it and see
what it looked like.
MEMBER KRESS: Do you have this model
built into your code?
MR. BROWN: Not this specific one like
this, no, but again, this was again, sort of a --
MEMBER KRESS: I mean, the entrainment.
MR. BROWN: -- yeah, what would this look
like if we were --
MR. CUMMINS: Ed Cummins again. I think
when we deal with both injection and venting, we go
back to the system level performance and we get away
from the local effects. And if you remember I think
both the staff and Westinghouse feel that on a system-
wide basis, the AP1000 scaled well to the test and on
a system-wide basis we would expect that the level
predicted would be scaled.
MR. BROWN: Anyway we do intend to do a
topical in which we would actually to certainly some
more rigorous calculations here and so on. This was
just in the time frame that we could get to present
was to get some sort of an order of magnitude of what
we were looking at relative to the best information we
had as far as decay heat and so on at the time, the
best estimate of a velocity we could get there.
Yes, Steve.
MR. BAJOREK: This is Steve Bajorek from
Research. I guess I just want to kind of add to it.
Our concern is a couple fold on this. As we look at
things from a top down system-wide level, okay, we
would agree that most things are okay. However, when
we have to look at these bottom up processes, we have
to limit ourselves to the steady state behavior and on
that basis we are restricted because the correlations
that are developed, we have questions on whether they
apply strictly to the geometry that we're now trying
to extend those two.
Secondly, when it goes back to the system-
wide effects, we have to add flashing terms back into
this. And when we look at both of those occurring
simultaneously, this leads to our concern and question
that even on a system-wide basis, should we be
concerned with additional liquid being flushed out of
this upper plenum.
So I think at this point we would still
disagree with the statement that APEX is well-scaled
for this particular process.
MEMBER KRESS: Okay, we have what --
MR. BROWN: Michael just has a --
MR. CORLETTI: Yeah, and I could probably
summarize right from here. I think Bill's pretty much
summarized our conclusions. Our conclusions with the
tests in regard to the applicability of the tests
remembering the four issues we were asking the staff
to approve here was the applicability of our AP600
test to AP1000. We believe we've shown that by and
large these tests are applicable and we believe are
sufficient for certification for AP1000.
The one issue that does remain is this
effect of entrainment. We believe we'll be able to
demonstrate that when you take it in context with the
large margins we have, and not only margin to core
uncovery but also margin to regular limits as far as
peak clad temperature are essentially -- for instance
for one of the loss of core accidents for AP600 where
we did have core uncovery that's for the 10-inch
break, we had a core heat up of 400 degrees PCT
because it was a very short duration.
We had -- essentially, this plant is not
a small break LOCA limited plant and we will be able
to show a very large margin to regulatory limits in
that regard. So I think in that context, this is why
we believe we'll be able to demonstrate that in our
topical report with that sort of a bounding
calculation.
With regards to our analysis codes, we are
-- our conclusions were that they are largely
applicable to -- they are applicable to AP1000 and
then will be able to be used for design certification.
There are certain conditions that the staff has pretty
much made clear. They've spelled them out here and
our plan is to follow those conditions as far as
design certification.
In regards to the other issues on the
piping DAC and I think we are in agreement with the
staff's position on that.
MEMBER KRESS: Okay, thank you very much.
I think that brings us to the end of this session.
We're running a little late. At this time I'm going
to declare a break until 11:00 o'clock and some of us
will not come back, including our chairman.
MEMBER POWERS: And I won't be back here
either.
MEMBER KRESS: So we won't have a quorum.
so I guess we're recessing now till 1:00 o'clock.
MEMBER POWERS: And I don't think you need
the Reporter any more, do you?
MEMBER KRESS: And I think this is the end
of the need for a Reporter. We'll recess until 1:00
o'clock.
(Whereupon, at 10:44 a.m. the above-
entitled matter was concluded.)
Page Last Reviewed/Updated Monday, July 18, 2016
Page Last Reviewed/Updated Monday, July 18, 2016