ML19317C747
| ML19317C747 | |
| Person / Time | |
|---|---|
| Issue date: | 09/16/2019 |
| From: | Weidong Wang Advisory Committee on Reactor Safeguards |
| To: | |
| Wang, W, ACRS | |
| References | |
| NRC-0570 | |
| Download: ML19317C747 (108) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
Advisory Committee on Reactor Safeguards Thermal-Hydraulic Phenomena Subcommittee Docket Number:
(n/a)
Location:
Rockville, Maryland Date:
Monday, September 16, 2019 Work Order No.:
NRC-0570 Pages 1-84 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1323 Rhode Island Avenue, N.W.
Washington, D.C. 20005 (202) 234-4433
NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
(202) 234-4433 WASHINGTON, D.C. 20005-3701 www.nealrgross.com 1
1 2
3 DISCLAIMER 4
5 6
UNITED STATES NUCLEAR REGULATORY COMMISSIONS 7
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 8
9 10 The contents of this transcript of the 11 proceeding of the United States Nuclear Regulatory 12 Commission Advisory Committee on Reactor Safeguards, 13 as reported herein, is a record of the discussions 14 recorded at the meeting.
15 16 This transcript has not been reviewed, 17 corrected, and edited, and it may contain 18 inaccuracies.
19 20 21 22 23
1 UNITED STATES OF AMERICA 1
NUCLEAR REGULATORY COMMISSION 2
+ + + + +
3 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 4
(ACRS) 5
+ + + + +
6 THERMAL-HYDRAULIC PHENOMENA SUBCOMMITTEE 7
+ + + + +
8 OPEN SESSION 9
+ + + + +
10 MONDAY 11 SEPTEMBER 16, 2019 12
+ + + + +
13 ROCKVILLE, MARYLAND 14
+ + + + +
15 The Subcommittee met at the Nuclear 16 Regulatory Commission, Two White Flint North, Room 17 T2B10, 11545 Rockville Pike, at 1:00 p.m., Joy Rempe, 18 Chair, presiding.
19 20 COMMITTEE MEMBERS:
21 JOY L. REMPE, Chair 22 RONALD G. BALLINGER, Member 23 MICHAEL L. CORRADINI, Member 24 WALTER KIRCHNER, Member 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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2 JOSE MARCH-LEUBA, Member 1
HAROLD B. RAY, Member 2
PETER RICCARDELLA, Member*
3 MATTHEW SUNSERI, Member*
4 5
DESIGNATED FEDERAL OFFICIAL:
6 WEIDONG WANG 7
8 ALSO PRESENT:
9 STEVE BAJOREK, RES 10 JOSH BORROMEO, NRR 11 MIRELA GAVRILAS, NRR 12 PAUL KLEIN, NRR 13 JANE MARSHALL, NRR 14 SCOTT MOORE, Executive Director, ACRS 15 BENJAMIN PARKS, NRR*
16 DAVID RUDLAND, NRR 17 ASHLEY SMITH, NRR 18 STEVE SMITH, NRR 19 20
- Present via telephone 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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3 P R O C E E D I N G S 1
(1:07 p.m.)
2 CHAIR REMPE: This meeting will now come to 3
order. This is a meeting of the Thermohydraulic 4
Phenomenon Subcommittee of the Advisory Committee on 5
Reactive Safeguards. I'm Joy Rempe, Chair of today's 6
subcommittee meeting. Members in attendance are Mike 7
Corradini, Ron Ballinger, and Harold Ray.
8 We also have Matt Sunseri and Pete 9
Riccardella, who have joined us on the line, and we 10 expect Walt Kirchner to arrive later during this 11 meeting. Members Matt Sunseri and Pete Riccardella 12 are connected using a public line, so they are on 13 mute, but I will try hard to remember to periodically 14 ask that that line be opened so they have an 15 opportunity to ask questions.
16 Weidong Wang of the ACRS staff is the 17 designated Federal official for this meeting. During 18 today's meeting, the subcommittee will review a staff 19 technical report, technical evaluation report of in-20 vessel debris effects. The subcommittee will hear 21 presentations by and hold discussions with the NRC 22 staff and other interested persons regarding this 23 matter.
24 This subject was first reviewed in our 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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4 April 2019 subcommittee meeting, and this meeting is 1
a follow-up for additional information. The rules for 2
participation in all ACRS meetings, including today's, 3
were announced in the Federal Register on June 13th, 4
2019.
5 The ACRS section of the U.S. NRC public 6
website provides our charter, bylaws, agendas, letter 7
reports, and full transcripts of all our full and 8
subcommittee meetings, including slides presented at 9
such meetings. The meeting notice and agenda for this 10 meeting were posted there, and we've received no 11 written statements or requests to make an oral 12 statement from the public.
13 Today's meeting is open to public 14 attendance. If necessary, part of the meeting will be 15 closed in order to discuss information that is 16 proprietary, pursuant to 5
U.S.C.
552b(c)(4).
17 Attendance at all portions of the meeting that deal 18 with such information will be limited to the NRC staff 19 and those individuals and organizations who have 20 entered in to an appropriate confidentiality 21 agreement.
22 Consequently, we'll need to confirm that we have 23 only eligible observers and participants in the room 24 for any closed portion of the meeting, if we decide to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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5 close it. During this meeting, our subcommittee will 1
gather information, analyze relevant issues and facts, 2
and formulate proposed positions and actions as 3
appropriate for deliberation by the full committee.
4 The rules for participation in today's 5
meeting were included in the June 13th, 2019 notice 6
published in the Federal Register, and a transcript of 7
the meeting is being kept and will be made available, 8
as stated in that Federal Register notice.
9 Therefore, we request that participants in 10 this meeting use the microphones located throughout 11 the room when addressing the subcommittee, and the 12 participants should first identify themselves and 13 speak with sufficient clarity and volume so that they 14 may be readily heard. And we'll now proceed with the 15 meeting, and I'd like to start by calling upon the NRR 16 staff.
17 MS. MARSHALL: Thank you, Chairman. Good 18 morning. My name is Jane Marshall, I'm the acting 19 director of the Division of Safety Systems, and we're 20 here to present the final staff technical evaluation 21 report on the safety significance of in-vessel 22 downstream effects in operating PWRs.
23 As you noted, this is a follow-up to the 24 April meeting where we presented the draft TER, and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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6 the subcommittee asked staff to return when the TER 1
was final, so that's our meeting here today. At that 2
meeting in April, the subcommittee members also made 3
some comments and asked questions about the TER, and 4
we appreciate the feedback and will discuss the 5
changes that we made to the TER in response to some of 6
those questions today.
7 The staff does not expect a letter from 8
ACRS on this TER. We also would like to note that 9
this topic is an indication of the way that the staff 10 is being asked to transform and use more risk-informed 11 approaches to regulation. So it may seem a little bit 12 different than some of the things we've done, 13 historically. We appreciate your interest and your 14 feedback on this issue.
15 CHAIR REMPE: And just to be clear, you've 16 not asked for a letter on this, right? And you don't 17 expect to have any sort of letter from us as you 18 continue to go through and evaluate each plant's 19 compliance --
20 MS. MARSHALL: Correct.
21 CHAIR REMPE: -- with it?
22 MS. MARSHALL: Correct.
23 CHAIR REMPE: Okay.
24 MS. MARSHALL: We do not expect.
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7 CHAIR REMPE: Okay. Thank you.
1 MS. MARSHALL: Thanks.
2 MEMBER CORRADINI: Can I get something 3
clear? In the executive summary, the final sentence 4
is, the staff is evaluating compliance in an effort to 5
separate from the TER. So, there is a slide in the 6
slide packet, is that final figure the one piece of 7
information on how compliance is to be met from a 8
logic standpoint?
9 MS. MARSHALL: I think that's probably the 10 only thing we have in there.
11 MEMBER CORRADINI: Okay. So we'll just 12 wait until then?
13 MS. MARSHALL: The flow chart?
14 MEMBER CORRADINI: Yes.
15 MS. MARSHALL: Yes.
16 MEMBER CORRADINI: The yes/no diamonds?
17 MS. MARSHALL: Yes.
18 MEMBER CORRADINI: Okay.
19 MS. MARSHALL: That's right.
20 CHAIR REMPE: So since we're kind of going 21 out of order and this is in the backup, I know you had 22 a meeting with the PWR owners group recently. How are 23 they receiving this guidance document and the 24 information in the technical report? Do they think it 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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8 provides a good pathway?
1 MS. MARSHALL: It does, and they seemed 2
very energized by it and very eager to move forward 3
and close out the issue, and they're moving forward 4
with this guidance. We've discussed it with them on 5
a couple of occasions.
6 CHAIR REMPE: Okay, good.
7 MS. MARSHALL: Yes.
8 CHAIR REMPE: Thank you. Go ahead.
9 MR. SMITH: All right, so we'll get 10 started. I'm Steve Smith, I'll be starting off the 11 presentation. This is just basically an informational 12 briefing. The other presenters are Ashley Smith and 13 Paul Klein. We do have one important member of the 14 team on the phone, Ben Parks. I just want to be sure, 15 Ben, can you hear us?
16 MEMBER CORRADINI: He might be muted.
17 MR. SMITH: Oh, he's muted?
18 CHAIR REMPE: So he can't talk?
19 MR. SMITH: The public --
20 CHAIR REMPE: Why don't you go ahead and 21 open it?
22 MR. MOORE: This is Scott Moore. The 23 public line is muted right now, so nobody on the 24 public line can respond.
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9 CHAIR REMPE: Let's go ahead and open it 1
and let him respond, just to make sure he's there and 2
then also, I'll give Pete and Matt a chance to speak 3
up. Okay?
4 MR. MOORE: Okay.
5 MR. SMITH: All right. Ben, can you speak 6
to us?
7 MR. PARKS: This is Ben, I can hear you.
8 MR. SMITH: All right, good, we can hear 9
you, too. Great. Thank you.
10 MR. RICCARDELLA: This is Pete. Why don't 11 you check and see if anybody else besides Matt and Ben 12 and I are on the public line, and if not, just leave 13 it open?
14 CHAIR REMPE: Is anyone else on the public 15 line, other than the three individuals?
16 MS. SMITH: It says there's nine. We're 17 getting an indication there are nine.
18 CHAIR REMPE: There are nine people, so I 19 think we are going to have to mute it, but we're going 20 to try and open it periodically for you guys, okay?
21 MR. RICCARDELLA: All right, thanks.
22 CHAIR REMPE: Okay.
23 MR. SMITH: All right, thanks for the help 24 with that. We also had input from other staff and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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10 NRR, particularly the MLR, DSS, and DRA, and of 1
course, research helped us out with the TRACE work 2
that you heard about before, and also with some work 3
in xLPR that we had talked about last time.
4 MEMBER CORRADINI: So let me ask the 5
question here, and you don't have to answer here, but 6
I'm looking -- I'm trying to understand the basis of 7
the low safety significance finding. Is it the RES 8
calculations that are sensitivities on the base? Is 9
it using the Westinghouse submittal in appropriate 10 engineering judgment calculations? What's the essence 11 of the technical basis for the finding?
12 MR. SMITH: Do you want to?
13 MR. KLEIN: I would say the essence is all 14 information compiled, including the WCAP that was 15 submitted, independent research work, plus the 16 combined experience and judgment of the staff that 17 have been working the issue for, you know, 10 to 15 18 years.
19 MEMBER CORRADINI: Okay, but it's not the 20 Westinghouse submittal, because you use some numbers 21 from the submittal within a context, but as I see it, 22 you're talking through a story. And once you talk 23 through the story, you do some sensitivities, and 24 given all of that, you feel good. So it's really the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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11 judgment of the staff given the pieces?
1 MR. KLEIN: I believe so. I think the 2
argument that we presented in April was that when you 3
look at the combined evidence, we don't believe that 4
you can block the core inlet, and although we didn't 5
write a CT evaluation on the WCAP, itself, we felt 6
very comfortable using that information as a defense 7
in depth argument that should the staff judgment be 8
wrong and you do block the core inlet, there are 9
alternative flow paths that could provide sufficient 10 cooling -- long-term cooling.
11 MEMBER CORRADINI: Thank you.
12 MR. SMITH: Specifically, I don't know if 13 you're asking about the risk values, the order of 14 magnitude values. Those are all calculated just based 15 on break frequency and certain pipe break sizes.
16 MEMBER CORRADINI: I was going to get back 17 to that, but I was trying to get a bigger picture 18 about -- microphone, please? Sorry, excuse me, I 19 apologize. I was trying to get a bigger picture of, 20 is it the totality of everything, or if there are 21 individual pieces you sit on. So it sounds like it's 22 the totality of all the pieces with a judgment call 23 from the staff?
24 MR. SMITH: Right. The risk value's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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12 purely based on break frequency. Everything else is 1
integrated decision making.
2 MEMBER CORRADINI: Okay.
3 MR. SMITH: Yes.
4 MEMBER CORRADINI: Thank you.
5 MR. SMITH: So we can move to slide two, 6
and I just want to express our appreciation for our 7
continued interactions on this, and the input you've 8
given us, I think, has definitely improved our 9
product, in this case and in other cases.
10 The TER, when we came to you, it seemed 11 like there was a lot of lack of clarity. People 12 didn't really understand it. So we revised it based 13 on ACRS member and peer review comments to make it 14 more readable, and to clarify its intent, and to 15 clarify the information that was used and the extent 16 of each information source that was used.
17 And also to try to clarify the logic used 18 by the staff to reach the conclusions. We don't have 19 a lot of time. I guess we might have more time than 20 I thought we had, but we're not going to try to repeat 21 too many of the details that we went through last 22 time. And the first nine slides are just kind of 23 background on what we talked about before.
24 And after that, we'll get into the changes 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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13 that were made as response to some of the questions, 1
and peer review, and ACRS member comments that came 2
up. And if you have any questions, it appears that 3
you will feel free to ask them at any time.
4 MEMBER CORRADINI: I'm sorry, I'm just 5
asking all sorts of starting questions. Is this going 6
to be -- let me put it in a historical context. So 7
when I first started, which was a while ago, this was 8
talked about, literally the same topic. So I assume 9
the commission has been briefed on this, or they will 10 be briefed, so they understand the context of this?
11 The reason I'm asking the question such as 12 that is, it's a story, and I'm still struggling in the 13 current TER to see how the pieces of the story fit 14 together, whether it be a graphic, a walk through.
15 The closest thing is why I asked the question about 16 slide 22, because in some sense, your thinking about 17 compliance actually leads to some sort of logic thing.
18 MR. SMITH: Right.
19 MEMBER CORRADINI: So is this going to be 20 presented to the commission, or does it stop at the 21 NRR director?
22 MR. SMITH: From a high level, we brief 23 the commission every six months, the commission TAs, 24 on --
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14 MEMBER CORRADINI: Okay.
1 MR. SMITH: -- our path forward, and in 2
our last meeting, we did discuss with them what we're 3
doing with the TER, and they're comfortable at a high 4
level. Not in the amount of detail that we've gone 5
into with you, but they were comfortable with what we 6
did, and they didn't ask a lot of pointed questions at 7
the time.
8 MEMBER CORRADINI: Okay, fine. Thank you.
9 MR. SMITH: All right. So we're going to 10 move on to slide three. This is just a recap of what 11 we talked about in April. In that meeting, we talked 12 about actions that were taken by NRC and industry to 13 address the effects of debris over the last several --
14 many years.
15 We provided discussion of our TER, and we 16 took feedback from the ACRS members to help us make 17 improvements with the TER. On slide four, the first 18 bullet, we discussed this a little bit in April. The 19 NRR goal is to align NRC and industry resources with 20 the safety significance of issues.
21 The TER was an attempt to evaluate the 22 overall safety significance of in-vessel downstream 23 effects, and we took into account a lot of new 24 knowledge that we've gained over the past couple of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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15 years, and a lot of knowledge that's been around for 1
quite a long time.
2 And the one thing that we think is 3
important, and we'll have another slide on this, 4
defense in depth is maintained even if the core inlet 5
becomes blocked.
6 CHAIR REMPE: Just, again, to help me make 7
sure I understand, TRACE doesn't ever predict 8
blockage. You've just assumed blockage?
9 MR. SMITH: That's correct.
10 CHAIR REMPE: Okay.
11 MR. SMITH: TRACE assumed, you know, 12 various amounts of blockage, starting at a relatively 13 high amount, and then actually blocking the core and 14 let off completely.
15 CHAIR REMPE: But that's a user defined 16 input to do that?
17 MR. SMITH: Yes.
18 CHAIR REMPE: Okay.
19 MR. SMITH: Yes. I don't think it would 20 be -- I don't think we have the modeling capabilities 21 CHAIR REMPE: That's what I thought, but 22 I just wanted to make sure, because sometimes in the 23 TER, I got a little confused. So thanks.
24 MR. SMITH: Yes. To predict how much 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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16 debris is going to go where in the core, and when it's 1
going to block, you know, that would -- that's 2
something that's probably beyond our ability.
3 CHAIR REMPE: That's what I thought.
4 Thanks.
5 MR. SMITH: Okay. Slide five, this slide 6
provides just a scope of what the TER evaluation was, 7
and as Jane talked about, it was atypical for really, 8
two reasons. Instead of using deterministic methods, 9
which is what we're used to using when we talked about 10 5046, we used integrated decision making.
11 And we also divorced the consideration of 12 compliance from the safety significance determination.
13 And I think that the TER was confusing. It may still 14 be confusing because of such a change in the way that 15 we do things and the way we think about things. But 16 since the TER came out, GSI-191, the GSI was closed, 17 and there has been a lot of confusion, both inside and 18 outside the NRC.
19 The GSI was closed basically because it 20 was determined that the important technical issues 21 associated with it were well enough understood that we 22 didn't really need to study them anymore, and it fell 23 out of the GSI program. The GSI program said, okay, 24 you can exit, you can take this out of the GSI 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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17 program.
1 Some people think that because the GSI was 2
closed that there's no further action needed on this 3
issue, and that's not what the case is. There's 21 4
plants that have closed the issue. They don't have to 5
take any more action. But the rest of the PWRs have 6
to close the generic letter 0402 by providing specific 7
responses to the NRC.
8 Actually, they don't have to, but that's 9
what we've requested them to do, a generic letter.
10 You know, we've just asked them to provide us 11 information. They don't have to if they don't want 12 to, but they're doing that. We're working to develop 13 guidance, which we talked about a little bit earlier, 14 on how they can respond to the in-vessel part.
15 The strainer part of the issue, nothing 16 has changed. They still have to treat the strainers 17 the same as they've always been treated in the past.
18 We have existing guidance that's been accepted for a 19 long time, and that's what they're using to address 20 the strainers. And then once these plants provide the 21 information, then we'll close them out on a plant 22 specific basis, one by one.
23 MEMBER CORRADINI: So let me ask about the 24 second bullet. Is there a document or a process that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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18 one follows for integrated decision making? In other 1
words, if I go to Reg Guide XYZ, there is a process 2
flow? Or is this a new thing within the staff to try 3
this approach?
4 MR. SMITH: This is new. We did use a lot 5
of guidance out of Reg Guide 1.174.
6 MEMBER CORRADINI: Okay.
7 MR. SMITH: That's kind of the way we 8
thought about this, using defense in depth safety 9
margins, thinking about those sort of things.
10 MEMBER CORRADINI: Because I'm not against 11 it. I like the fact that you actually don't use 12 numbers only, but you actually have judgment. I just 13 was looking for some connection, because in section 14 whatever it is, you go through a series of steps, and 15 I'm trying to decide were those steps predetermined, 16 or did you organize these thoughts because of this 17 issue?
18 MR. SMITH: I guess we would have to see 19 what you're talking about, but I think we're doing a 20 lot of new kind of thinking when we did this.
21 MEMBER CORRADINI: Okay. Well, the reason 22 I'm saying that is not that I disagree with it, more 23 the fact that it would be good to then document the 24 fact that you've developed a process of thinking about 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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19 this that might be useable in other venues, where 1
something has, pardon the word, lingered, and --
2 MR. SMITH: We did think about that, and 3
I think that we and higher levels of management 4
understand that we need to get our processes caught up 5
with the way we're trying to do things.
6 MEMBER CORRADINI: Okay.
7 MR. SMITH: And I think there's other 8
people who are doing that at more generic of a level.
9 MEMBER CORRADINI: Thank you.
10 CHAIR REMPE: Okay. At this time, let's 11 just stop for a second and get the line open. Thank 12 you for the reminder. Is it open? Okay, can everyone 13 but Pete and Matt put your phone on mute? And Pete or 14 Matt, can you both chime in and say, do you have a 15 question, and say what it is if you do?
16 MEMBER SUNSERI: This is Matt, I don't 17 have any questions.
18 CHAIR REMPE: Thank you. Pete?
19 MEMBER RICCARDELLA: This is Pete. I 20 don't have any questions, either.
21 CHAIR REMPE: Okay. Please, everybody, 22 let's mute it again. Okay, go ahead.
23 MR. SMITH: All right, we're going to move 24 along to slide six, and this is a slide that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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20 highlights the primary reasons why the ECCS design 1
flow path won't be blocked. So the core inlet's not 2
going to become blocked at the following LOCA.
3 This was discussed in more detail in 4
April, and I'll just go through. We think that the 5
uniform bed formation is unlikely. There's very few 6
breaks that generate enough debris to cause a core 7
blockage. Long-term core cooling has been shown using 8
TH analyses, long-term core cooling is maintained with 9
a high level of blockage at the core inlet.
10 And then, we have some testing that shows 11 that if you don't have chemical precipitants, you can 12 incur a lot of fiber and particulate loading at the 13 fuel inlets without blocking the core and still being 14 able to get enough flow through. And then there's 15 other things that are done, like switch over for most 16 of the plants.
17 Some of the plants, like the BNW plants, 18 do a little bit different. BAT mitigation strategies, 19 and those are -- those have been well established in 20 there in all the plants' emergency operating 21 procedures that would bypass that BAT that would --
22 could occur at the core inlet.
23 CHAIR REMPE: When I was reading this, I 24 was wondering, what are you going to do for the plants 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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21 that are putting in chromium coated, accident tolerant 1
fuel or other types of accident tolerant fuel with 2
coatings that may not be qualified from testing 3
previously?
4 MR. SMITH: Right. So we didn't do 5
anything about that. I think that a plant who does 6
something like that would have to evaluate it using 7
the 5059 process when they do install those kind of 8
fuel assemblies in the core.
9 CHAIR REMPE: But not for a lead test 10 assembly, I guess, because that's already being 11 approved? So it'll be when they try to do a core 12 loading, that will need to be documented that they 13 need to consider this somewhere?
14 And it would be in -- what's going on with 15 the accident tolerant fuel people, the staff, not you 16 guys with this -- it would fall under the statement 17 about unqualified coatings and you look for --
18 MR. KLEIN: Well, ultimately, the plant's 19 responsible, if they make a change in the plant, to 20 evaluate the potential impact. So I think they will 21 have programs that are designed to consider blockages, 22 a strainer blockage of the core inlet, and any change 23 to the plant, our expectation would be that it's 24 evaluated in terms of those two issues.
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22 CHAIR REMPE: Okay.
1 MS. MARSHALL: If I may, Chairman, this is 2
Jane Marshall, that phenomenon was considered in the 3
first panel, the coating, and what would happen with 4
the coating. And for the lead test assemblies, given 5
the small number of lead test assemblies, there's not 6
that much material.
7 CHAIR REMPE: So it'll come in when you 8
start doing the core loading? Okay.
9 MS. MARSHALL: Yes. And that was 10 considered, and it has been valid.
11 CHAIR REMPE: Okay.
12 MEMBER CORRADINI: But there will be 13 testing required by the proposers to show there's no 14 flaking?
15 MR. SMITH: Right.
16 MS. MARSHALL: Right, and adhesion is one 17 of the phenomenon, yes --
18 MEMBER CORRADINI: Okay.
19 MS. MARSHALL: -- and they are testing.
20 MEMBER CORRADINI: Thank you.
21 MR. SMITH: All right, on slide seven, 22 this is a slide that we saw in April, but we thought 23 it was an important concept, and we feel that the 24 defense in depth that is available is significant for 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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23 this issue.
1 On the left side in the red, when you hit 2
the red left side of the thing there, that means that 3
our assumption that the core is not going to become 4
blocked is wrong, okay? So from thereon out, we need 5
defense in depth. We didn't credit the alternate flow 6
paths from the WCAP in our evaluation of whether the 7
core would become blocked or not, but we did believe 8
that the alternate flow paths would provide a good 9
means to get coolant into the core.
10 The next three columns are just operator 11 actions that can be taken if the core inlet was to 12 become blocked, and then the last column talks about 13 containment integrity. The strainer evaluation is 14 separate from the in-vessel evaluation and the 15 deterministic strainer evaluations, and the staff's 16 opinion show that the strainers will function under 17 all design basis accident conditions.
18 So we expect that they would still 19 function to allow containment spray to function, and 20 you would still have your containment function -- your 21 containment cooling function intact. And this is the 22 end of my presentation. Ashley's going to take over 23 with the next slide.
24 MS. MARSHALL: Chairman, that might be a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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24 good point.
1 CHAIR REMPE: Okay. Actually, before I 2
open up the line, or while you're opening up the line, 3
didn't you used to have this defense in -- my notes 4
indicated you used to have this defense in depth 5
discussion in the executive summary, but in the most 6
recent version, I didn't find it. Is there a reason 7
that that was -- or did I just miss it, my notes 8
aren't correct?
9 MR. SMITH: We did change the executive 10 summary quite a bit, and I don't remember the reason 11 that we would've taken defense in depth out of there.
12 CHAIR REMPE: Okay. I just was curious.
13 Anyways, I think the lines are open. Pete, Matt, do 14 you have any questions?
15 MR. RICCARDELLA: No questions here. This 16 is Pete.
17 CHAIR REMPE: Not hearing anything from 18 Matt, we'll close the line and move on here. Okay?
19 MEMBER CORRADINI: So, let me ask a couple 20 questions at this point, before we go to the TRACE 21 analysis.
22 CHAIR REMPE: Thank you. Go ahead.
23 MEMBER CORRADINI: Okay. So here's where 24 I'm looking for some sort of story board that takes me 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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25 through the physical events with some sort of timing, 1
and you don't have to do it, but if I were not 2
embedded in this for a dozen years, I don't think I'd 3
follow this stuff.
4 So, that's why I go back to the final 5
slide. The way you talk through this picture, it's 6
fine, but I think you've got to have something that 7
actually talks through the accident. You've got three 8
different -- approximately three different plant 9
configurations, cold leg, hot leg, and then UPI, and 10 then you've got different plans on how they might 11 quantitatively change.
12 This strikes me that you want to go 13 through that in some sort of fashion, otherwise, I 14 would not understand if I was somebody that -- let me 15 put it in a different way. If I didn't believe that 16 the staff had thought this through, I'd challenge this 17 until I saw some sort of logical talking through the 18 points that, on a conservative basis, you still are 19 okay, because as you said here, if the core is 20 blocked, because I have a series of steps that occur, 21 I then have alternative defenses.
22 But I still don't see that initial talking 23 through, relative be to the time to block, the time to 24 switch -- or, sorry the time for switchover, the time 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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26 for blockage, the time for, then I want to call hot 1
leg switchover, the time for chemical precipitation, 2
which in some sense, you have assumed times that are 3
on the early end of each of those to give you margin.
4 And yet, I kind of have to still dig. It 5
seems like a picture, a talking picture along with 6
this sort of story board would be very helpful to the 7
general public understanding the reason why you have 8
so much margin. Because I think there is margin, it's 9
just hard to extract it from the TER.
10 MR. SMITH: I can understand that. I 11 think maybe the people who worked on it have been 12 working on it so long, it maybe is more apparent to us 13 what we were doing.
14 MEMBER CORRADINI: I'm kind of surprised 15 the commission staff doesn't ask you to explain it in 16 simple form.
17 MR. SMITH: I guess we could consider 18 doing that. I guess we'll have to talk about --
19 MEMBER CORRADINI: All right, and I'm not 20 trying to add work to what you have. If everybody 21 understands it within the staff, that's fine, but I'm 22 thinking about not the staff, but the general public 23 understanding the decision relative to the reasons 24 that there is significant margin at each stage of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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27 process. If you see where I'm going with this.
1 MR. SMITH: Yes, I think in the last 2
meeting we did go through the scenarios for the 3
various types of plants, but probably didn't explain, 4
you know, in detail how the margins apply to each one 5
of those --
6 MEMBER CORRADINI: Okay.
7 MR. SMITH: -- types of plants.
8 MEMBER CORRADINI: Okay, fine.
9 MR. KLEIN: I think one of the biggest 10 things, and maybe we didn't communicate it well in the 11 TER, but it's clear that the first WCAP owners group 12 program that just assumed precipitate for them, and 13 then they tried to use bounding parameters in order to 14 run the tests.
15 When they went to the WCAP 17788 and did 16 the actual tests in the enclave and followed the time 17 dependent temperature profiles, it became clear from 18 the results that chemical effects for, except maybe 19 one or two plants, would come well after the point 20 where a bed would get disrupted at the core inlet.
21 And I think that was one of the big 22 changes in the owners group program that we saw, and 23 it gave us confidence that -- but it sounds like we 24 could've communicated that whole timeline better in 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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28 the TER.
1 MEMBER CORRADINI: Okay, thank you.
2 MS. SMITH: Okay, we're on slide eight, 3
for those following along. So various sensitivity 4
studies were completed by the Office of Regulatory 5
Research to support the conclusions in our TER. Some 6
were completed prior to the TER effort, and some were 7
to support the TER effort, and we presented specific 8
details of all those analyses in our April meeting.
9 Overall, we wanted to highlight a couple 10 of the conclusions we had that boric acid 11 precipitation was not found to inhibit long-term core 12 cooling, and ultimate flow paths are a viable option 13 to maintain long-term cooling -- long-term core 14 cooling for both cold and hot leg breaks.
15 CHAIR REMPE: So during our discussion at 16 the prior meeting, there was a table given to us where 17 you had comments from industry as well as the staff, 18 and the staff apparently had some concerns about the 19 applicability of TRACE for these analyses. And I know 20 you've modified the TER to talk more about the 21 applicability of TRACE, but I guess it wasn't obvious 22 to me still, what were the models this particular 23 staffer or staffers were concerned about, and how did 24 you address it?
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29 Because again, I asked the question at the 1
prior meeting, it was like, well, this came from the 2
staff and we're addressing it, but I wasn't sure what 3
the concern was and where the staffer was concerned 4
about it.
5 MS. SMITH: What I remember is the concern 6
was how we were relying more on TRACE than maybe the 7
industry was, and we made it more clear in the TER 8
that we were using TRACE to support our conclusions 9
and not necessarily saying TRACE shows the conclusion.
10 CHAIR REMPE: Okay, so they didn't have 11 concerns about the models just not being applicable 12 for particular phenomenon? Because that's kind of how 13 the comment read, and so --
14 MS. SMITH: That wasn't my understanding.
15 CHAIR REMPE: -- okay, so maybe I 16 misunderstood what was written in the table. Okay, 17 thank you.
18 MEMBER CORRADINI: Let me ask the 19 question, maybe you're going to get to it later. So, 20 how was the TRACE scenario developed so that -- is it 21 a best estimate? Is it a bounding? Or is it just 22 something to look at? Because there are certain 23 timings it's assumed relative to switchover, to 24 ramping up to complete blockage, to where the blockage 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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30 is, to et cetera, et cetera, et cetera. So how does 1
one characterize the TRACE calculation?
2 MS. SMITH: We had the idea to do the 3
TRACE calculation as a sensitivity study, so we tried 4
to use a lot of the same inputs that we had from 5
industry codes. I don't know if Steve wanted to chime 6
in on any of that, but that -- we had the same inputs 7
as far as timing, some switchover, the things that you 8
had mentioned, so that we could show that our results 9
were -- we could compare to what the industry had.
10 MR. BAJOREK: This is Steve Bajorek, 11 Office of Research. I characterize the TRACE 12 calculations as being more bounding. One of the first 13 things we did, I think in consultation with the owners 14 group, is we picked out a plant class that we thought 15 would be conservative with respect to the alternate 16 flow paths.
17 We picked the Westinghouse plant that had 18 originally been down-flow converted to up-flow, so you 19 didn't have communication from the barrel baffle 20 region to the core. This would be something that 21 would tend to starve the core. We picked areas, flow 22 areas, and these are something that you can change in 23 a user-defined function.
24 That gave us a way of bounding the K over 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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31 A squared, the net resistance to the bottom of the 1
core, in order to be more conservative than what we 2
thought industry should be. Now, for decay heat, we 3
were -- best estimate, we used 79 decay heat, but we 4
also did sensitivities to go back to a 73 decay heat 5
to show what would happen if we were to add more power 6
in the reactor.
7 And actually, with respect to boric acid 8
precipitation, the higher power actually helps you.
9 It increases the entrainment and helps you to, you 10 know, flush out the core for a longer period of time.
11 But other than that, these calculations were well on 12 the conservative time.
13 And when we started this, I think that the 14 time at which we initiated blockage of the core was 15 conservative with respect to what we thought it was 16 going to be. The ramp up time about consistent with 17 what it would.
18 CHAIR REMPE: So I want to understand what 19 you said. First of all, this entrainment phenomena 20 with the decay heat effects, is that validated 21 anywhere, or is it just, oh, this is common sense, but 22 you didn't notice it until you saw it in TRACE?
23 MR. BAJOREK: Well, no, I mean, TRACE has 24 been validated for large and small break, and at 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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32 entrainment carryover, very important for us.
1 CHAIR REMPE: Okay.
2 MR. BAJOREK: Okay, so we've used tests 3
like FLECHT, FLECHT-SEASET, RBHT, in order to show 4
that our entrainment models are approximately correct 5
for carrying over, and --
6 CHAIR REMPE: But it's not the boric acid, 7
per se, it's just the --
8 MR. BAJOREK: I'm not aware of any test 9
where you --
10 CHAIR REMPE: Right.
11 MR. BAJOREK: -- orated things to try to 12 do that, but one of the things that we did before we 13 did the TRACE calculations is, we updated our 14 thermophysical properties so that when you got high 15 concentrations of boric acid, it was appropriately 16 reflected in the fluid density, which can increase 17 about 10 percent greater than pure water. And the 18 viscosity, which is approximately 30 percent greater 19 once you get to the precipitation of it.
20 CHAIR REMPE: Okay.
21 MEMBER CORRADINI: Let me just make sure 22 I understand. So I'm not sure I should mention 23 numbers, but there's a number assumed in the TRACE 24 calculation for switchover from clean water to recirc 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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33 out of the sum. Then, there's another ramp up time 1
from the K-loss being normal to the K-loss being 2
essentially infinite over some other time window.
3 How are those determined? Because I don't 4
know how one gets those numbers, so I'm trying to 5
understand -- I mean, they might be conservative, I'm 6
just trying to understand where'd they come from?
7 MR. SMITH: I think the time at which the 8
resistance started ramping up was around 20 minutes, 9
which is when most plants would -- that's the earliest 10 time for most plants to switch over. So that's the 11 conservative time, and then the value used, I think it 12 was -- I forget how many seconds it was to ramp 13 from --
14 MEMBER CORRADINI: I'm not sure I can say 15 it, but it was --
16 MR. SMITH: -- zero to --
17 MEMBER CORRADINI: -- longer.
18 MR. SMITH: -- you can say that. So that 19 was just something that we thought was a reasonable 20 time to get the debris out of the pool and either 21 collect it on the strainer or in the --
22 MR. BAJOREK: This is Steve Bajorek again.
23 We did vary that. We looked at what we thought would 24 be a best estimate time for the ramp up, and we also 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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34 did calculations where we made it much, much shorter 1
than what it was going to be, and it didn't really 2
affect things that much.
3 MEMBER CORRADINI: Okay.
4 MR. BAJOREK: We also looked at the hot 5
leg switchover time. I went to the extreme, and he 6
said what happens if it doesn't occur, ran the 7
calculations out for I think it was something like 36 8
hours that basically showed that by the time you --
9 your real concern is keeping the core covered, okay?
10 By the time you precipitate, you would be 11 uncovering the core. That would be more of your 12 concern. So even within the absence of hot leg 13 switchover, you have lots of time and lots of time 14 relative to typical assumptions from when hot leg 15 switchover's going to occur.
16 MEMBER CORRADINI: Okay. And then to kind 17 of get back to Joy's question, TRACE can track 18 concentration of boron in the water, and that's about 19 as far as it goes. You essentially then look, if you 20 get close to the precipitation point, but you don't 21 model precipitation, nor do you model the debris.
22 MR. BAJOREK: We don't model the debris, 23 okay? When you get to the precipitation limit, TRACE 24 will take the excess boric acid and play it out on a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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35 structure.
1 MEMBER CORRADINI: Okay.
2 MR. BAJOREK: And we saw that in the 3
calculations when you dried out -- like, in the upper 4
head, TRACE would say, hey, you're going to deposit a 5
film of boric acid. Now, if you recovered that region 6
with water, it would just go back into solution.
7 So as you get up to precipitation, TRACE 8
is not getting the dynamics correct, at that point.
9 It's just telling you that hey, this is the point in 10 time when precipitation is likely to occur.
11 MEMBER CORRADINI: Okay. So I have a 12 couple more questions. So you arbitrarily increase 13 the K-loss such that it looks like it was blocking, 14 and then at something like -- and I can't remember, in 15 the document somewhere, it's something around, as I 16 think one of the slides said, 99 percent -- you're 17 still okay.
18 Is there a physical reason why it doesn't 19 go to 100 percent? Because there used to be a member 20 here that always believed it would go to 100 percent 21 like a felt hat (phonetic).
22 MR. BAJOREK: Well --
23 MEMBER CORRADINI: You know what I'm 24 getting at.
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36 MR. BAJOREK: -- some sensitivities, that 1
was just a sensitivity that was done. Actually, some 2
increased the blockage to 100 percent. I don't 3
remember that --
4 MEMBER CORRADINI: But then you have to 5
rely on alternative flow paths?
6 MR. BAJOREK: That's right.
7 MEMBER CORRADINI: Okay. What I guess I'm 8
getting at is, so that was your -- that was how you 9
essentially evaluated margin was essentially take it 10 as a series of parametric steps, then assume 100 11 percent, and then show that alternative flow paths 12 would provide you enough?
13 MR. BAJOREK: That's correct.
14 MEMBER CORRADINI: Okay. And the reason 15 the alternative flow paths don't clog?
16 MR. BAJOREK: Because they're too large.
17 MEMBER CORRADINI: So are we allowed to 18 say what's large and what's not large? Is there a 19 boundary between large and not large?
20 MR. BAJOREK: The --
21 MEMBER CORRADINI: We can go to closed 22 session, if you want.
23 MR. BAJOREK: Yes, I don't know if we can 24 say this on --
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37 MEMBER CORRADINI: That's fine.
1 CHAIR REMPE: Okay.
2 MEMBER CORRADINI: That's fine. That's 3
fine.
4 MS. SMITH: It's based on testing.
5 MR. BAJOREK: It's based on testing.
6 MEMBER CORRADINI: So it's actually --
7 there was testing where there was -- there were 8
certain gaps --
9 MR. BAJOREK: Yes.
10 MEMBER CORRADINI: -- and then as the gaps 11 grew, there was no way to block them?
12 MR. BAJOREK: Right, and as we reviewed --
13 as we did a review of the WCAP, we actually came back 14 and said, hey, we don't think you should be crediting 15 some of these, and they took them out of the 16 calculations.
17 MEMBER CORRADINI: I see. Okay.
18 MS. SMITH: We asked do you have testing 19 to show this opening size would be a viable option for 20 debris to pass through? And they said we don't have 21 testing to sort of show that, so we'll take it out, 22 and they revised their conclusions.
23 MEMBER CORRADINI: Okay.
24 MR. KLEIN: I think another point to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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38 mention, too, is that the amount of fiber per time 1
continues to decrease dramatically. So as you get to 2
a point where the core inlet may become more blocked, 3
you also have a strainer that's being covered and 4
allowing much less fiber to pass through it.
5 MEMBER CORRADINI: Okay. Okay, thank you.
6 MS. SMITH: All right, and then next, on 7
slide nine, this is just a reminder from our April 8
meeting that the staff conclusion in the TER is that 9
in-vessel downstream effects are of low safety 10 significance, based on our current state -- based on 11 our current knowledge state.
12 All right, next slide. All right, so this 13 is really the new information that we're presenting 14 the next few slides. They're items that we wanted to 15 highlight based on comments from ACRS members at the 16 April meeting, as well as peer review and Peter 17 Barrano's (phonetic) comments. The first item here is 18 the definition of safety significance criteria.
19 We added this chart that's from the side 20 into the TER as a revision based on ACRS member 21 comments. Instead of using risk values from just Reg 22 Guide 1.174 and new Reg 0058, we looked at a variety 23 of NRC programs to ensure the definition of risk we 24 were using to define safety significance within the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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39 bounds of our available guidance.
1 And you can see as indicated at the arrow 2
at the bottom, the staff determined the order of 3
magnitude of the occurrence frequency that can 4
challenge on control flowing would be 1 times 10 to 5
the -6 per year or less.
6 MEMBER CORRADINI: So help me out. I know 7
the last one, since one of our members has been 8
educating us about 0058, and I know the first one.
9 What are the two in the middle?
10 MR. SMITH: The significance determination 11 process, that's something the region gets into more 12 when they --
13 MEMBER CORRADINI: So this is at the 14 region level?
15 MR. SMITH: -- they look back at scenarios 16 that occurred at a plant, and they do a PRA, and they 17 use that. And then the other one is LIC-504, which 18 that's a -- one of the management directives that we 19 use to -- or one of the procedures we use to evaluate 20 this and similar kinds of occurrences.
21 MEMBER CORRADINI: So the blue arrow is 22 supposed to tell me what?
23 MS. SMITH: That's just where we ended our 24 evaluation. It's just a --
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40 MR. SMITH: That's the order of magnitude 1
or break frequency that we estimated would be -- could 2
cause adequate fiber to be generated to block the core 3
inlet.
4 MEMBER CORRADINI: And that corresponds to 5
the pipe size that you use in the table one --
6 MR. SMITH: Yes.
7 MEMBER CORRADINI: -- as a break point?
8 MR. SMITH: Yes.
9 MEMBER CORRADINI: Okay. All right, I 10 understand now. Thank you.
11 MS. SMITH: All right, next slide.
12 MEMBER CORRADINI: Do you want to ask the 13 folks out in the -- I'm assuming that Dr. Riccardella 14 cares about break size, so this might be a good chance 15 to see if he cares.
16 CHAIR REMPE: Can we open the line?
17 MEMBER CORRADINI: Because I don't know 18 break size -- yes.
19 CHAIR REMPE: Do you have any questions --
20 MEMBER RICCARDELLA: This is Pete --
21 CHAIR REMPE: -- do you have any 22 questions, Pete?
23 MEMBER RICCARDELLA: I do. Can you hear 24 me?
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41 CHAIR REMPE: Yes, we can.
1 MEMBER RICCARDELLA: Okay. So the blue 2
arrow, what break size are we talking about for that 3
blue arrow?
4 MR. KLEIN: All right, so the blue arrow, 5
it's not just for a single break size. It's for a hot 6
leg break, and the actual break size that we evaluated 7
was for a six-inch pipe, so it's a 5.19 inch break, 8
and that's for a hot leg break. And then the cold leg 9
break, we assumed anything smaller than 12 inches 10 would not generate adequate debris to cause a blockage 11 of the core inlet.
12 MEMBER RICCARDELLA: So anything smaller 13 than what?
14 MR. KLEIN: A 12-inch break.
15 MEMBER RICCARDELLA: Okay. And, you know, 16 another question I have is, the metric isn't actually 17 RISP or CDF, it's Delta CDF. Would you explain that, 18 please?
19 MR. KLEIN: Yes, so the Delta CDF, 20 basically, we assume that if the break occurred, it's 21 sort of a conditional --
22 MEMBER RICCARDELLA: Yes.
23 MR. KLEIN: -- we assume that if that 24 break occurs, that you would go to core damage. So 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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42 the Delta CDF is between a plant that could generate 1
enough debris at that size break, so a plant that 2
would have no potential debris effects.
3 MEMBER RICCARDELLA: No debris at all, 4
okay.
5 MR. KLEIN: Yes.
6 MEMBER RICCARDELLA: Okay. Got it. Thank 7
you. I'll be interested, Joy, in talking later when 8
we get into discussion of the risk analysis and later 9
slides.
10 CHAIR REMPE: Is this the xLPR slide, or 11 is it --
12 MEMBER RICCARDELLA: Yes.
13 CHAIR REMPE: -- okay. I'll try and 14 remember. And then Matt, do you have any questions?
15 MEMBER SUNSERI: I don't, but can you hear 16 me?
17 CHAIR REMPE: Yes, we can. Thank you.
18 MEMBER SUNSERI: Okay, thanks.
19 CHAIR REMPE: Go ahead.
20 MS. SMITH: Okay, we'll go to slide 11.
21 We already talked about this a little bit, but we had 22 comments about how TRACE was used to inform 23 conclusions in our TER. Edits were made in the 24 document like Joy had mentioned to clearly state what 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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43 TRACE is used for in the model. We're confident that 1
the results support our conclusions.
2 We also had details of the various 3
sensitivity studies added in a table. That was the 4
same table that we presented to ACRS in April, and 5
that showed the purpose of each study and more 6
descriptive things about each study. Okay, I'm going 7
to turn it over to Steve to talk about another thing 8
we wanted to highlight.
9 MR. SMITH: Okay, so one of the ACRS 10 members, or maybe more than one, requested that we do 11 a sensitivity on the fuel assembly fiber amount that 12 could be accommodated. They said, well, suppose you 13 couldn't use the WCAP 17788 numbers, which shall not 14 be named, and you used the 15 gram per fuel assembly 15 value from WCAP 16793, which is what we know is 16 conservative, and that included chemicals and all 17 that.
18 So, we went back and looked at the data 19 that we had from a high fiber plant in South Texas, 20 and we didn't really have enough data on how much 21 debris is generated from these break sizes. There was 22 the four-inch breaks, there was only one break that 23 generated enough debris to cause the 15 gram per fuel 24 assembly value to be exceeded.
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44 So there was actually one four-inch break 1
that -- four-inch pipe break which would be a little 2
bit smaller, 3 point -- I forget what the 3 point --
3 what the wall thickness is there. So there was one --
4 and the majority of the debris for those breaks comes 5
from latent debris. So latent debris kind of 6
dominates the term at these really low fiber levels.
7 Anyway, what we did instead -- so we 8
looked at it that way, and then we looked at it from 9
another perspective is that if the fiber penetration 10 value, we used a -- the most conservative for our 11 initial. We had a few sets of fiber penetration data 12 that we could use.
13 If we used the most conservative value, 15 14 percent, and we did exceed the 15 gram per fuel 15 assembly limit, and if we used the second most 16 conservative value from the fiber penetration testing, 17 which was 12 percent at that particular amount of 18 debris, it would be below -- you would end up below 19 the 15 grams per fuel assembly, even with the 6-inch 20 break.
21 So that's the couple different ways we 22 looked at it. We really didn't have enough data to do 23 a good sensitivity study on exactly what pipe size you 24 would have to reduce to. So we couldn't really 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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45 calculate a frequency. It's probably confusing.
1 MEMBER CORRADINI: Well, I was going to 2
ask you if you could repeat some of that, because I 3
don't get it. So what you did was to vary the pipe 4
size, and then with a particular plant, look at what 5
the fiber generation would be and then what was 6
captured on the sum screens versus what's passed 7
through?
8 MR. SMITH: That's correct.
9 MEMBER CORRADINI: Am I understanding this 10 correctly?
11 MR. SMITH: That's correct, and we only 12 had information from one plant, that was South Texas.
13 MEMBER CORRADINI: Right, because the 14 RoverD analysis that they did.
15 MR. SMITH: Yes.
16 MEMBER CORRADINI: But their approach to 17 this -- I'm not sure if we can say it. Their general 18 approach to it -- let me try it that way -- their 19 general approach to it was alternative flow paths 20 after a certain point, if I remember correctly. That 21 is, their RoverD approach to a deterministic in-vessel 22 debris evaluation was essentially alternative flow 23 paths got them past the point of concern.
24 MR. SMITH: They did a thermohydraulic 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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46 analysis, you're correct.
1 MEMBER CORRADINI: Okay. Okay. So --
2 MR. SMITH: They assumed that the core 3
inlet was blocked at a very early time.
4 MEMBER CORRADINI: Much earlier than --
5 MR. SMITH: Yes.
6 MEMBER CORRADINI: Okay. Okay. All 7
right, I think -- I don't remember who made this 8
comment, but I'm just trying to understand what you 9
did. Okay, so South Texas was, in some sense, a 10 calculational example?
11 MR. SMITH: That was the only place that 12 we had --
13 MEMBER CORRADINI: Enough information?
14 MR. SMITH: -- fiber generated per break 15 size, but they only did it for six-inch pipes and then 16 four-inch pipes, and two, you know? So between six 17 and four, we just didn't have enough data to come up 18 with some sort of a frequency, you know, a meaningful 19 frequency number.
20 MEMBER CORRADINI: Okay. All right, thank 21 you. Okay.
22 MR. SMITH: Okay, we'll move on to slide 23 13 and xLPR a little bit more about pipe break 24 frequency.
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47 MR. KLEIN: All right, I'll take this one.
1 So, during the April subcommittee meeting, we were 2
asked if the staff could use xLPR and try to benchmark 3
the new Reg 1829 break frequency that was assumed in 4
the staff TER.
5 So we had several members of the NRC staff 6
run the xLPR code investigate the effects of pipe 7
- size, degradation mechanisms, how things like 8
mitigation of susceptible wells and leak detection 9
would affect some of the numbers, and we have some 10 preliminary results that suggest the local frequencies 11 in 1829 are conservative, but we consider those 12 preliminary.
13 And I think that the effort was useful in 14 terms of the lessons learned with the xLPR code, as 15 well. So there's additional studies that are in 16 progress, and we can take questions. We have the 17 right people in the audience to address detailed 18 questions.
19 CHAIR REMPE: So before I open the line 20 for Pete's detailed questions, what are you going to 21 do with these sensitivity study results? I mean, the 22 TER is done, you're issuing -- you've already issued 23 guidance to the owners groups. What are you going to 24 do with it?
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48 MR. KLEIN: I don't think that xLPR 1
results are going to affect the TER. Like you 2
mentioned, it's already issued and on the street, we 3
don't feel a need to modify it based on the xLPR work 4
that's been done to date.
5 CHAIR REMPE: Okay. Is the line open?
6 Pete? Okay.
7 MEMBER RICCARDELLA: This is Pete. Is 8
there openly going to be a report, or white paper, or 9
something prepared on this study?
10 MR. KLEIN: I'm going to ask Dave Rudland 11 to maybe step up to the mic and address that.
12 MEMBER RICCARDELLA: That would be great.
13 Hi, Dave, how are you doing?
14 MEMBER CORRADINI: So since you're doing 15 it -- since Pete asked about this one, I was going to 16 ask about the TRACE one, so we might as well just get 17 it all out on the table.
18 MR. RUDLAND: Hey, this is Dave Rudland, 19 Senior Technical Advisor for Materials and the 20 Division Materials License Renewal. Pete, right now, 21 I don't know. We don't really have any large plans.
22 We're kind of continuing this study to look at both 23 these effects and those questions that came out of the 24 new scale DCD review, also. I'm going to be 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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49 presenting some of these results at our PFM workshop 1
at the end of October.
2 MEMBER RICCARDELLA: Oh, okay.
3 MR. RUDLAND: And we'll probably put 4
together some kind of report, but we haven't really 5
discussed what that would be at this particular time.
6 MEMBER RICCARDELLA: Okay, I wasn't aware 7
of that workshop. What's the date of that workshop?
8 MR. RUDLAND: It's the third week of 9
October. October 21 to 23, I believe. I don't have 10 my calendar with me.
11 MEMBER RICCARDELLA: Okay, a three-day 12 workshop.
13 MR. RUDLAND: Yes, it's a three-day 14 workshop, and held here in D.C.
15 MEMBER RICCARDELLA: At headquarters?
16 MR. RUDLAND: Yes, we're actually having 17 it at an off-site location, but in Rockville.
18 CHAIR REMPE: You can make a trip back the 19 third week of October, right Pete? It's a joke.
20 MEMBER RICCARDELLA: Yes, that's the week 21 we don't have subcommittee.
22 CHAIR REMPE: That's right, but you can 23 make the flight back. There was a question Matt had?
24 Matt, you got interrupted, did you --
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50 MEMBER SUNSERI: I have no questions, just 1
still following along. Thanks.
2 CHAIR REMPE: Okay.
3 MEMBER RICCARDELLA: Okay, thank you.
4 MEMBER CORRADINI: So can we pick up the 5
question about the TRACE sensitivities?
6 MS. SMITH: Yes, so the TRACE --
7 MEMBER CORRADINI: Is there going to be --
8 MS. SMITH: -- the TRACE sensitivities 9
were done as part of a user need that we had for the 10 boric acid precipitation studies, and then we just did 11 follow on studies to help us support conclusions in 12 the TER. Right now, there's no intention for a white 13 paper, but the report given to NRR, I have opposite 14 research for that user need I'm sure we could make 15 available if you're interested.
16 MEMBER CORRADINI: Okay.
17 MR. SMITH: It actually ought to be one of 18 the references in the paper.
19 MEMBER CORRADINI: There is a reference?
20 Did I miss it? I apologize.
21 MR. SMITH: It should be there. If it's 22 not, we probably messed up.
23 MEMBER CORRADINI: Okay. Well, to the 24 extent that it's available, I'd be interested.
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51 MR. SMITH: Okay.
1 MS. SMITH: Yes, we'll be sure to get it 2
to you, and I know it's in references. I don't know 3
offhand which number it is.
4 MEMBER CORRADINI: Well, I didn't look, so 5
6 MS. SMITH: Yes, we'll find out.
7 MEMBER CORRADINI: -- to be honest, I 8
didn't -- okay, thank you.
9 MS. SMITH: And provide it.
10 MR. SMITH: All right, we'll go to --
11 MEMBER RAY: Wait, I'm going to ask a 12 question. Are these studies of LOCA frequencies used 13 elsewhere, other than this work that we're talking 14 about today?
15 MR. KLEIN: The new Reg 1829 studies?
16 MEMBER RAY: Well, I guess. I'm really 17 talking about the reference to 1829, it says, are 18 conservative. I'm asking about the results that we're 19 talking about in this meeting, which are preliminary 20 results as it's described there on the third bullet.
21 Are they going to be used for anything else, other 22 than what -- GSI-191 related?
23 MR. KLEIN: Well, I think there's more 24 work that needs to be done, which is why we 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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52 characterized it as preliminary. So I think xLPR 1
still may need a few tweaks in order to optimize it 2
and the work that was done to do this evaluation is 3
helping that effort.
4 So I don't think the end goal with the 5
xLPR effort was really to have a grand result, but 6
it's more to look at the 1829 assumptions and say, 7
could the staff have erred on the LOCA frequencies?
8 And the preliminary results suggest that that's not 9
the case, that those frequencies are probably 10 conservative.
11 MEMBER RAY: Well, I'm thinking about risk 12 informing consideration of future plant designs, that 13 sort of thing. And I'm just wondering if these -- if 14 this work leads, ultimately, to some update or input 15 basis, whatever you want to say, that we may be using 16 and thinking about future plant designs.
17 MR. KLEIN: Dave, I'll defer to you for 18 long-term plans on xLPR.
19 MR. RUDLAND: Yes, this is Dave Rudland 20 again. The study we did was kind of focused here, 21 right? Just to kind of give us a feel for the 22 conservative nature of 1829, and in order to do the 23 job correctly, to really confirm all of the results 24 according to plan would be a much more expansive 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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53 effort. Now, I think it's a doable effort, but I just 1
think right now, we don't have the plans to expand it 2
all that far.
3 MEMBER RAY: Okay, well that really gets 4
to my point, is that this isn't something that once 5
done, it gets picked up and used elsewhere?
6 MR. RUDLAND: Yes, it would need to be 7
expanded much further if it were going to be used 8
generically.
9 MEMBER RAY: Thank you.
10 MEMBER RICCARDELLA: This is Pete, can you 11 guys still hear me?
12 MR. RUDLAND: Yes.
13 CHAIR REMPE: Yes.
14 MEMBER RICCARDELLA: I'd like to, you 15 know, at some point, I'd like to see almost a 16 statement. I was one of the co-authors, or one of the 17 experts on the new Reg 1829 extra panel, and I recall 18 we had tables of break sizes with kind of ranges of 19 frequencies for each size.
20 I just would like to see just from your 21 preliminary results what those -- how the xLPR ranges 22 compare. I mean, were they an order of magnitude?
23 You said they were conservative. Were they an order 24 of magnitude lower, a couple orders of magnitude?
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54 MR. RUDLAND: So this is --
1 MEMBER RICCARDELLA: Did the uncertainty 2
ranges overlap?
3 MR. RUDLAND: So this is Dave Rudland.
4 Pete, again, we didn't do an exhaustive enough search 5
to be able to really give ranges of uncertainty on the 6
failure frequencies. What we did was we did a 7
sampling of several different pipe sizes and 8
degradation mechanisms, from select cases from 1829, 9
just to look at that.
10 And again, you know, the numbers were 11 based on our assumptions of crack initiation 12 frequencies, and they turned out to be a couple of 13 order of magnitude below those that were in 1829. And 14 again, the details, I think, would be more -- the 15 details of the analyses and the results would be more 16 informative than just a table of frequencies.
17 MEMBER RICCARDELLA: Okay. And you said 18 that workshop is the week of the 23rd?
19 MR. RUDLAND: What I'll do, Pete, is I'll 20 take an action to send you the flier for the workshop.
21 MEMBER RICCARDELLA:
Thank
- you, I
22 appreciate that. That's all I have.
23 CHAIR REMPE: Okay, thank you. Go ahead.
24 MR. KLEIN: All right, move to slide 14.
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55 Okay, I'll take this one, too. This is the final 1
slide in our regular scheduled program here. So, the 2
purpose of the TER, as we mentioned, was to evaluate 3
the CET significance of in-vessel downstream effects.
4 Based on the current knowledge base and 5
the TER, the NRC was able to close GSI-191, and Steve 6
explained the difference between closure of GSI-191 7
and licensee resolution, which will be addressed 8
separately as part of the generic letter process. I 9
think we're really, at this point, ready to address 10 any additional questions.
11 There's an ML number listed for the NRC 12 staff review guidance, and that review guidance is 13 intended to help the staff address licensee responses 14 as they're submitted to the NRC staff. And we have 15 tried to develop that guidance with both a number of 16 internal NRC staff and also external stakeholders.
17 And most of the core team that worked on 18 the TER was also involved in the staff guidance, and 19 we have a schematic, if you'd like us to put that up 20 and begin discussions on the staff guidance, if that 21 would be helpful.
22 CHAIR REMPE: I would like to see it.
23 This is slide 22, right? Have you discussed it? It's 24 in the guidance, which is publically available, so 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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56 let's go for it.
1 MR. KLEIN: So, I'll start this, Steven, 2
and maybe you, and Ashley, and Ben can jump in, but in 3
terms of just the philosophy of how to do review 4
guidance, I think the general staff philosophy was we 5
wanted to try to design a flow chart that would allow 6
the plant with the least challenges to work through 7
the process and maybe get the NRC staff closure in the 8
most direct manner.
9 So we tried to set it up so that those 10 plants with the most favorable attributes were able to 11 pursue one of the early passed resolution, maybe one, 12 two, or path three, which path one would include the 13 plants that were able to close out under a previous 14 WCAP because the staff understands what that amount of 15 fiber that it's just extremely difficult to block the 16 core inlet, including chemical effects.
17 And then paths two and three were designed 18 for plants that have very favorable attributes in 19 terms of alternate flow paths, or alternate ways to 20 get flow into the core. So we felt the plants that 21 were of the BNW plant design or upper plenum injection 22 plants, if they met the fiber limits that were within 23 WCAP 17788, that would lead to a direct closure path 24 for those type of plants.
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57 MEMBER CORRADINI: So let's just, if we 1
could, so take box one. So box one says, go find a 2
spectrum of break sizes that by 1829 are of high 3
enough frequency and show -- and therefore show that 4
you're less than 15 grams. If your answer is yes, 5
then you go to the right, if the answer's no, then you 6
go down and ask the next question?
7 MR. KLEIN: I think box one was intended 8
to be a deterministic path based on WCAP 16793. Since 9
the staff already had a CT evaluation written 10 independent of that --
11 MEMBER CORRADINI: The size of the hot leg 12 break. The worst break.
13 MR. KLEIN: Yes, worst break.
14 MEMBER CORRADINI:
Excuse me, I
15 misunderstood. I assumed you already had started 16 chopping it with size. No?
17 MR. KLEIN: No consideration of size under 18 path one. It would be the bounding break, can you 19 meet that amount, and that would be the path that --
20 what we had turned to option one plants had taken to 21 reach closure.
22 MEMBER CORRADINI: Okay. I misunderstood.
23 MR. SMITH: So this is the reason why it 24 becomes confusing, because for all of these, because 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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58 this is more of a compliance thing than a safety 1
significance thing, these plants all have to evaluate 2
the worst possible break for how much fiber can get to 3
the core, including single failure and all that. So 4
all these fiber amounts that are calculated in here 5
are more of a compliance thing. 5046 says you've got 6
to calculate the worst scenarios.
7 MEMBER CORRADINI: Well, you've lost me 8
now. I thought I had you, but now --
9 MR. SMITH: Okay.
10 MEMBER CORRADINI: -- I'm --
11 MR. SMITH: Sorry.
12 MEMBER CORRADINI: -- I'm decoupling.
13 MR. SMITH: I should have not said 14 anything.
15 MEMBER CORRADINI: You could've just 16 nodded and just let me go on my merry confused way.
17 So box one is the largest break, not the largest break 18 given a frequency?
19 MR. SMITH: No, it's the largest break.
20 It's not necessarily the largest, but the biggest 21 debris -- the one that generates and transports the 22 most debris to the core.
23 MEMBER CORRADINI: Okay. Okay. All 24 right, so this is almost a filter before -- excuse the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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59 word, but it's a filter before you go through 1
everything we just discussed? I'm having trouble.
2 MS. SMITH: It's separate. I think you're 3
getting confused because the TER had frequency 4
evaluation in it. When we did the compliance added, 5
that was kind of separate.
6 MEMBER CORRADINI: Well, I'm concerned 7
about inconsistency if I go through a compliance set 8
of logic, I'm going to find myself in trouble, even 9
though by the TER, it's of low safety significance.
10 That's what's confusing, so help me.
11 MR. SMITH: Right. The TER, we wrote to 12 determine the safety significance of the issue. We 13 determined the safety significance of the issue was 14 low, especially if the plant showed that they met the 15 key parameters in the -- that we considered when we 16 looked at that.
17 So then, after that, that kind of guided 18 us into how we would develop our staff review 19 guidance. Since it's a low safety significance thing, 20 how much detail do we really have to look at? And so 21 this is where Paul said, you know, we have to look 22 harder at some plants, but every plant has to consider 23 not based on what their break frequency is, unless 24 they come in and get an exemption and do a risk 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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60 informed evaluation like STP did. Every plant has to 1
consider the largest amount of debris that could reach 2
the core under 5046 rules, basically.
3 MEMBER CORRADINI: Okay, all right. Do 4
you want to add to this?
5 MR. LEHNING: Yes, this is John Lehning 6
from the NRR staff, too, and I just wanted to say, 7
where the risk part comes in is potentially on the 8
bottom, the lowermost yellow box there, the plant 9
specific evaluation.
10 So that is still an option, but basically, 11 the rest of this flowchart is based on the compliance 12 part, and for some plants that are able to show 13 compliance that way without an exemption, that may be 14 the easiest thing.
15 But it's not to say that we're throwing 16 away the TER. That may still be a part of the basis 17 for some of the plants that may not be able to do it 18 for the whole spectrum.
19 MEMBER CORRADINI: So can I say what you 20 just said differently? That is, by compliance, you 21 assume 5046 rules all the way through, and you get to 22 the yellow box, and then you might be able to apply 23 the risk significance to let them off the hook?
24 MR. LEHNING: Yes.
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61 MEMBER CORRADINI: To put it bluntly.
1 MR. LEHNING: Yes. If they wanted to use 2
a risk informed argument, they would have to come in 3
with a LAR and an exemption.
4 MEMBER CORRADINI: Uh-huh, but they could 5
reference the risk -- excuse me, they could reference 6
the TER and that calculational logic to show they fit 7
within that box? That's what I'm still trying to --
8 MR. LEHNING: They could use a similar 9
kind of logic. I mean, it's a little bit more -- when 10 you do a plant specific calculation, we determine an 11 order of magnitude when we came up with that 10 to the 12
-6, right? They would actually use their PRA, they 13 would come up with plant specific, you know, delta CDF 14 numbers --
15 MEMBER CORRADINI: Okay.
16 MR. LEHNING: -- based on, you know, 17 whatever break size they chose to -- or whatever 18 breaks they chose to put in the risk informed bucket.
19 MEMBER CORRADINI: Okay. Well, I thought 20 I had it. Let me say it differently. You're saying 21 that in some sense, the TER is a guide to how they 22 might have to do it if they find themselves in the 23 yellow box?
24 MR. LEHNING: It would certainly provide 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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62 things for them to look at.
1 MR. KLEIN: I think the TER also informs 2
path four, because if you go through the first three 3
paths and you hit the red box, then the question is, 4
you know, do you do something to disrupt an inlet bed 5
before chemical affects four?
6 And then if the answer is yes, then you go 7
into more of a WCAP 17788 analysis. So you might be 8
given more credit for that analysis and being within 9
the -- all the key parameters of the staff TER in that 10 block four, as well.
11 CHAIR REMPE: So the TER isn't just the 12 yellow box, it's the -- how you created box four? Is 13 that a true statement? Because the TER helps you 14 confirm that those parameters could get you out of 15 there? Or --
16 MS. SMITH: I don't know if Ben had some 17 examples that helped the implementation when we talked 18 with the group. In the plant specific evaluation box, 19 he talks about how plants may be able to make a plant 20 specific evaluation if they didn't meet boxes one, 21 two, three, and four. So that's why I'm wondering if 22 Ben has some insights that --
23 CHAIR REMPE: Okay.
24 MS. SMITH: -- may answer your question.
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63 FEMALE: And you opened the bridge line?
1 CHAIR REMPE: I think it's open, because 2
I hear noise, but Ben, are you there?
3 MR. PARKS: Yes, this is Ben Parks with 4
the staff. Can you hear me?
5 CHAIR REMPE: Yes.
6 MR. PARKS: Okay. So this whole flowchart 7
and the staff guidance document is all purely 8
deterministic. There's no risk consideration here.
9 In fact, I think we have a paragraph in the guidance 10 document that says it can't align with these 11 deterministic evaluations, you can't show that, you 12 know, if you get a core inlet blockage, you're still 13 okay, then you need to pursue a different approach.
14 And that's what Steve was talking about 15 with the risk informed LAR and the exemption to the 16 1546 requirement. So if you get down to path four and 17 you find that you don't meet the alternate flow path 18 evaluations that were in WCAP 17788 plane four, then 19 you need to do an evaluation to show, you know, that 20 you have a lower core power level than might have been 21 analyzed in 17788 for, you know -- you are much 22 greater than 20 minutes when you stopover.
23 Basically kind of, like, one approach or 24 one strategy there is you'd be chasing down and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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64 showing that you have less decay heat than the 1
industry's analyzed, and so a much less severe event 2
than it may seem. And that way, you have assurance 3
that even if you have a core inlet blockage, you don't 4
have core damage follow it.
5 MEMBER CORRADINI: So let me say it back 6
to you. We're following a deterministic set of 7
questions, and I get to box four, and we haven't 8
looked at 17788, it's too darn big. So therefore, 9
there's something within 17788 that says the core 10 fiber limit is above some set of numbers we don't need 11 to discuss, and the switchover point is greater than 12 20 minutes. And what's RTP?
13 MS. SMITH: Rate of terminal power.
14 MR. SMITH: Rate of terminal power.
15 MEMBER CORRADINI: Oh, okay, thank you.
16 Less than evaluated, and the flow resistance is by the 17 other holes in the core are -- the resistance are 18 less, you're okay, you go to the right, and you've 19 essentially succeeded. If I don't and I go down to 20 the yellow box on plant system evaluation, that tells 21 you you're in a state of uncertainty, and the staff --
22 the licensee could use the TER as a roadmap to do a --
23 its own sort of plant specific evaluation?
24 MR. SMITH: That's correct.
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65 MEMBER CORRADINI: So have I essentially 1
said it about right?
2 MR. SMITH: That's correct, and the only 3
time they --
4 MR. PARKS: Yes.
5 MR. SMITH: -- the only time they would 6
get into any kind of a risk evaluation is if they 7
couldn't
- show, you
- know, that
- actually, our 8
thermopower is low, so, you know, we had an early 9
switchover time. So we would actually be below the 10 value that was calculated in the WCAP 11 MEMBER CORRADINI: Okay, fine.
12 MR. SMITH: They could use those to 13 evaluate against each other, and if they couldn't do 14 that, then they might get into the point where they 15 have to come ask for an exemption and say, okay, 16 certain breaks, we can't mitigate.
17 CHAIR REMPE: But you never proved the 18 WCAP, but your evaluations that you did in support of 19 the TER gave you confidence that the criteria in four 20 were acceptable. So that's why I'm saying I thought 21 that basically, you wouldn't even have box four if you 22 hadn't have done all of this work for the TER. Is 23 that a true statement?
24 MS. SMITH: We evaluated the top of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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66 report up to a certain point, and there were some 1
areas that we felt was going to take a significant 2
amount of time and effort to resolve, so we were given 3
direction to go with this other path. So it's not 4
that we never agreed with what was in the top report.
5 We didn't finish our evaluation.
6 CHAIR REMPE: Right.
7 MS. SMITH: And this allowed us to show 8
box four, okay, it sounds pretty good.
9 CHAIR REMPE: So if you had not done all 10 this work for the TER, you could've made the 11 conclusion for box four and said it was fine, it was 12 just there were other things that you couldn't. So 13 you didn't need all this, the trace calculations even 14 do say those questions would let you go to a yes. I'm 15 trying to understand and I'm asking both questions 16 both ways to see what you say.
17 MS. SMITH: Yes, TRACE helps us support 18 the conclusion that in box four, we think is okay.
19 CHAIR REMPE: So my first statement was 20 correct? Granted, the TER will inform the yellow box, 21 but the work you did for the TER also gave you 22 confidence that box four was -- could be accepted and 23 you could go directly to yes? So it did help you 24 confirm the adequacy of box four?
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67 MS. SMITH: Yes.
1 CHAIR REMPE: Okay.
2 MEMBER CORRADINI: Okay. So after all of 3
that, now I am confused. Table two of the document we 4
were supposed to read has a set of numbers, which we 5
don't need to talk about what they are. Are those the 6
numbers in box four?
7 MS. SMITH: The debris less than 17788 8
core inlet, yes.
9 MEMBER CORRADINI: Okay.
10 MS. SMITH: Yes.
11 MEMBER CORRADINI: But those were -- as I 12 understand it, were calculated using a set of 13 calculational procedures that was not exactly 17788?
14 I thought there were -- my reading of the document was 15 that you actually went through a set of what I'll call 16 conservative assumptions that were not necessarily the 17 same as 17788 to get those numbers. Am I wrong?
18 MR. SMITH: These numbers in that chart 19 all came from 17788.
20 MEMBER CORRADINI: Oh, and that is what is 21 being used as reference in the box four question?
22 MS. SMITH: Right.
23 MR. SMITH: Yes.
24 MEMBER CORRADINI: Got it. Okay.
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68 MR. SMITH: These numbers assume, you 1
know, a uniform debris bed at the core inlet and all 2
that, so --
3 MEMBER CORRADINI: Yes, yes, yes.
4 MR. SMITH: -- that's why we think there's 5
margin.
6 MEMBER CORRADINI: But that's what leads 7
you to the next step about having to then evaluate the 8
alternative flow paths with some empirical determined 9
resistance or size that you must be below?
10 MR. SMITH: Right.
11 MEMBER CORRADINI: Or the resistance must 12 be below, or the size must be above?
13 MR. SMITH: Yes.
14 MEMBER CORRADINI: Okay. All right. Got 15 it. I think I got it.
16 CHAIR REMPE: So let's open up, I think 17 the line's still open, but Pete or Matt, do you have 18 any more questions?
19 MEMBER RICCARDELLA: This is Pete. I just 20 had one. So do I understand you to say that if a 21 licensee gets into the yellow box at the very bottom, 22 that that requires a license amendment?
23 MR. SMITH: It may.
24 MR. KLEIN: Yes, not necessarily. It 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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69 would only do that if they couldn't evaluate the key 1
parameters and show -- say there's some switchover 2
really came at the earliest potential switchover 3
actually came at 30 minutes, and their rated thermal 4
power was lower than what was evaluated, they could 5
show that their decay heat was below the value that 6
was evaluated in the WCAP.
7 And that would be a relatively simple 8
calculation, and in that case, you know, the plant 9
specific evaluation would be relatively simple. Now, 10 if they couldn't do that, and they had to say, okay, 11 it's going to -- we have x number of breaks that won't 12 get us below this core fiber limit, and we're going to 13 have to take those out, then they would have to use a 14 risk informed LAR.
15 MEMBER RICCARDELLA: Oh, I see, you have 16 to take those out, or you just have to assume --
17 MR. KLEIN: Assume core --
18 MEMBER RICCARDELLA: -- so an overall risk 19 informed -- or risk based approach would require a 20 license amendment?
21 MR. KLEIN: Yes.
22 MEMBER CORRADINI: But an individual 23 calculation to show on any one of the things that 24 brought you down to the no question might be 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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70 calculable on a case by case basis?
1 MR. SMITH: Right.
2 MR. KLEIN: Correct.
3 MEMBER RICCARDELLA: So that would be 4
effectively a yes to four then, really.
5 MR. SMITH: Yes.
6 MEMBER RICCARDELLA: In effect.
7 MR. SMITH: Yes.
8 MEMBER RICCARDELLA: Okay. Yes.
9 MR. KLEIN: So the thought was that 10 licensees that enter block four, the further out of 11 bounds they were, the more likely they might get into 12 a situation that required an LAR. But if they were 13 slightly out of bounds, they might be able to show 14 that they really are inbounds by taking credit for 15 other features of the plant.
16 MEMBER RICCARDELLA: So refresh my memory.
17 Did South Texas do a license amendment?
18 MS. SMITH: Yes.
19 MR. SMITH: Yes.
20 MEMBER CORRADINI: We reviewed that. It's 21 called RoverD, Rover.
22 MR. SMITH: RoverD.
23 MEMBER RICCARDELLA: Yes. Understand. I 24 remember reviewing it, I just didn't remember if it 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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71 was part of a license amendment or not.
1 CHAIR REMPE: Okay. Do any of the members 2
or the -- here in the room or members on the phone 3
have any more questions or comments? We do need to 4
also go to public comments before we might possibly 5
close the meeting.
6 So at this point, too, could members speak 7
up and say if they think they need to have a closed 8
meeting? Looking around the table and it's pretty 9
quiet. What about Pete and Matt, do you guys have any 10 additional questions or comments for a closed meeting?
11 MEMBER RICCARDELLA: Nope, nothing further 12 from me.
13 CHAIR REMPE: Okay.
14 MEMBER SUNSERI: This is Matt. I don't 15 have any additional questions. I thought the 16 flowchart and the technical evaluation report were 17 quite helpful, actually. Thanks.
18 CHAIR REMPE: Okay. Thank you. So at 19 this point, let's see if any of the public in this 20 room have any questions or comments. And with that, 21 I'm not hearing any, I'll go around and ask members if 22 they have any final closing comments.
23 MEMBER CORRADINI: People on the line?
24 CHAIR REMPE: Oh. Are there public 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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72 members on the line that want to speak up and make a 1
comment? So not hearing anything, I guess we'll go 2
around the table for closing comments, starting with 3
Member Ballinger.
4 MEMBER BALLINGER: No further comment.
5 CHAIR REMPE: Harold?
6 MEMBER RAY: No, I don't think so.
7 CHAIR REMPE: Mike?
8 MEMBER CORRADINI: So, I guess I have a 9
number of comments. Since you've been doing this for 10 a long time, it's kind of not going out with a bang, 11 but a whimper, and that worries me, for two -- for 12 three reasons. One, you have an integrated decision 13 making process which is not standard operating 14 procedure.
15 You have essentially developed something 16 which could be beneficial, so it seems to me some sort 17 of documentation of that integrated decision making 18 processes would be beneficial for the rest of the 19 staff, because there are going to be other things that 20 linger that could be transformed to use at the 21 technique, right?
22 But I think you've got to somehow at least 23 talk through the process, because I thought the 24 process, as you walked through in terms of what were 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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73 the safety margin -- or what were the set of 1
assumptions, what were essentially the defense in 2
depth measures, what was the safety margins in each of 3
the defense in depth was a way to get you to the final 4
end state that I thought was good, so that's the first 5
thing.
6 My second thing is documentation of the 7
pieces -- Pete talked about xLPR. I don't know enough 8
to appreciate that, but at least with the TRACE 9
calculations, if they truly are conservative, even 10 though it's a small community, I think some sort of 11 documentation of that would be useful.
12 MR. SMITH: It's reference 21.
13 MEMBER CORRADINI: It's reference 21. So 14 there is something out there we can look at?
15 MS. SMITH: Yes, I don't know if that's 16 public, though, so --
17 MEMBER CORRADINI: Yes, I'm sure it isn't.
18 MEMBER RAY: Mike, I'm going to just 19 interject into your question. You used the word it, 20 and you said it was going out with a whimper. What do 21 you mean by it, because --
22 MEMBER CORRADINI: GSI-191.
23 MEMBER RAY: Well, all right, but that 24 doesn't end the ongoing process, that closure.
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74 MEMBER CORRADINI: No. The evaluation for 1
the generic letter is going, but what I guess I'm 2
getting at is, what's bothering me is, you have a 3
technical basis document that strikes me as 4
incomplete. It's incomplete because the decision 5
making process is not -- incomplete because I would 6
think there are pieces of the calculation that ought 7
to be properly documented.
8 And the third part of it, to me, is that 9
if this was the public and the public just by 10 weariness is not around to listen to it, would be 11 confused as to why it's significantly conservative.
12 I mean, I really do think you guys have a case, and 13 I'm not arguing with the case.
14 I'm just not clear that the document is 15 clear so somebody can look at it and say, a-ha. We've 16 already been worrying about this for a decade when we 17 shouldn't
- have, or they've developed enough 18 experimental information that now, we feel confident 19 that it is a low safety.
20 So those are the three things that -- I 21 know it's more work, it takes resources, I understand 22 all that, but it just strikes me that these would be 23 beneficial for the technical basis, not for the 24 evaluation. I think now I finally understand why 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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75 that's different.
1 MS. MARSHALL: Okay, well, if I may, this 2
is Jane Marshall with NRR DSS. A lot of the risk 3
informed decision making processes that we use are 4
documented in other procedures in other places for 5
NRR. So they're not necessarily repeated in this 6
document.
7 CHAIR REMPE: And the staff tell us this 8
is a new way of doing things earlier in this meeting 9
today?
10 MS. MARSHALL: It's a new way, broadly, a 11 new way of looking at things across all of NRR's 12 processes, not just isolated to GSI-191 resolution.
13 We're looking at risk informing as many of our 14 processes --
15 CHAIR REMPE: Right.
16 MS. MARSHALL: -- as we can, and you know, 17 I would like to highlight, there is a difference 18 between risk informing and risk based, as long as we 19 get through. So, and I know it's easy for some of the 20 members of the public to look at those as the same 21 thing, so I wanted to highlight they are separate 22 processes. NRR has an inner office instruction and 23 some other guidance to staff on risk informing these 24 processes.
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76 MR. BORROMEO: This is Josh Borromeo from 1
the staff. Jane, I think the office instruction you 2
are talking about is LIC-206. It's recent formed 3
decision making for LARs.
4 MEMBER CORRADINI: And this followed that 5
procedure?
6 MR. BORROMEO: Probably not, because it 7
was released in June, I think, of this year. June 8
2019.
9 MS. MARSHALL: It follows the ideas, but 10 not the processes.
11 MR. SMITH: This isn't a LAR.
12 MS. MARSHALL: Yes.
13 MEMBER CORRADINI: This is what?
14 MR. SMITH: The TER isn't a LAR, either.
15 So a lot of the license amendment requires --
16 MEMBER CORRADINI: Oh, oh, I'm sorry.
17 MR. SMITH: -- and that's the same with 18 Reg Guide 1.174. It's written for license amendment 19 requests, but we still use the ideas from these things 20 21 MEMBER CORRADINI: Okay.
22 MR. SMITH: -- when we did the evaluation.
23 MEMBER CORRADINI: What I guess I'm 24 getting at, to put it in a simple thing, I think this 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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77 is a good piece of work. It kind of is now going to 1
sit somewhere quietly, but I do think since when I 2
started with the committee, this was a lot of 3
discussion --
4 MR. SMITH: Right.
5 MEMBER CORRADINI: -- in 2005 and 2006.
6 And it just strikes me you essentially put a cap on it 7
technically, and it would be good to essentially wrap 8
it up in these three areas. But I think the staff has 9
done a very good job, personally.
10 CHAIR REMPE: I can come back to your 11 comments, but let me let Matt and Pete have a chance 12 to give their final comments, and then I'd like to 13 discuss what you're saying a bit more, Mike, okay?
14 MEMBER CORRADINI: Mm-hmm.
15 CHAIR REMPE: Matt, do you have any final 16 comments?
17 MEMBER SUNSERI: No, I don't have anything 18 else to add, Joy, thank you.
19 CHAIR REMPE: Okay. Pete, do you have any 20 comments?
21 MEMBER RICCARDELLA: Nope, nope, I don't.
22 I just, I'm happy to see the staff actually making use 23 of the xLPR work. Preliminary as it might be, it's 24 important.
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78 CHAIR REMPE: So I know you just joined 1
us, but Walt, did you have any comments you wanted to 2
make while you're on the table?
3 MEMBER KIRCHNER: No, thank you.
4 CHAIR REMPE: Okay. So you've listened to 5
what Mike has said. Does the staff -- I mean, he's 6
made discussion a couple of pretty good suggestions, 7
such as documenting the cases and how much margin 8
there is, and to provide someone who's less familiar 9
with the topic an easier to understand path of what 10 occurred here, and to better justify your approach and 11 why it's valid.
12 Does the staff have the opportunity they 13 might consider these suggestions? Or you're saying, 14 nope, we're done and that's it, we've already got the 15 guidance document out, the industry's happy with it, 16 they said it's going to be easy to follow?
17 MR. SMITH: I see Mirela's stepping up to 18 the table, so I'm going to let her answer.
19 MS. GAVRILAS: So this is Mirela Gavrilas 20 of the staff. I think the points that you guys are 21 raising are very important, because it is a paradigm 22 shift. It's not happening in a vacuum, though. I 23 mean, all the principles that have been involved in 24 this decision making are related to 1174.
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79 What is new is the fact that we actually 1
used them for decision making for a decision that's 2
other than a licensing action, and while it didn't 3
occur to us for this -- in this specific context that 4
we should take the next step and see what we can 5
document so that it becomes a generally useful tool 6
for the -- for future decision making, I think you're 7
making a very good point, and we'll certainly consider 8
that.
9 With regard to the margins that actually 10 gave the staff the confidence to call this a low 11 safety significance scenario or phenomenon, we will 12 want to document that, as well. So I think that 13 you're right. We'll go back and see in the context of 14 knowledge management if we can document the various 15 margins that actually led to the elements of 1174 that 16 actually led us to conclude that this is low safety 17 significance. So we will do that, because it is of 18 value to do. Folks are going to be using this similar 19 approach in the future.
20 CHAIR REMPE: Because as Mike emphasized, 21 GSI-191 was a pretty hot topic there for a lot of 22 years, and again, you may appreciate having that 23 documented now before staff may retire or move to 24 other topics that they're interested in.
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80 MS. GAVRILAS: And let me give credit to 1
Vic Cusumano, who is not here today, but what Vic 2
always says is, we got here because we worked very 3
hard for the past -- not just the staff, but industry 4
and everybody worked very hard to understand what's 5
going on so that we can make a conclusion that we've 6
presented to you today.
7 So, and we do want to make sure that we 8
actually document that knowledge in a manner that's 9
transparent and easy for others to follow and easy for 10 the public to understand. It's a very good comment, 11 we'll hear you.
12 CHAIR REMPE: Okay.
13 MEMBER RAY: Let me interject here, 14 though, then, because, you know, I went through the 15 AP1000 design certification as the secondary chair.
16 Another reason it occurs to me for doing what Joy and 17 Mike have discussed is, the logic associated with 18 closure of GSI-191, isn't it potentially relevant to 19 future applications for design certification, or 20 standard design approval, or whatnot?
21 In other words, if it -- the only thing, 22 as I understand it, that we're doing today is closing 23 GSI-191. If I'm a licensee, I've got to do the same 24 thing I've always had to do. I follow the flowchart 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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81 up there and do what I'm obligated to do.
1 But if I'm a potential applicant for a 2
design certification, for example, isn't there 3
information here that I would want to draw upon, 4
whether I was staff or applicant, in the future?
5 MS. GAVRILAS: I just want to be careful, 6
because we have the standard review plan for 7
applications, in general. We have an effort right now 8
to revise the standard review plan to consider risk 9
information.
10 In other words, what findings must the 11 staff make before they have reasonable assurance of 12 adequate protection in any of the regulations? So I 13 want to be careful to not convolute this effort with 14 what's going on there. We have to give some thought 15 where to put it.
16 We have a lot of risk initiatives going on 17 right now in the agency, and to put them all in a 18 cohesive structure is not trivial, it's not easy.
19 This is one of them, and I think we need to figure out 20 where it fits, but we're hearing you that we need to 21 figure out how we can take it beyond what it means to 22 closing GSI-191 and how we can apply what we learned 23 here to other type of regulatory decision making, 24 whatever that decision making may be.
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82 MEMBER RAY: That's fine, and also, as 1
they say, perhaps make it accessible by a potential 2
applicant, not just buried in some staff.
3 CHAIR REMPE: So is there a way we can 4
help you make sure that this gets done? I mean, we 5
aren't requested to write a letter on this, and we 6
probably won't get into the technical details of the 7
process, but to say some of the aspects that we feel 8
are important and should be documented in a letter.
9 Again, I'm a member speaking in a 10 subcommittee meeting, and it would have to go through 11 the full ACRS, but if we were to do something like 12 that, does that make this a little more concrete so 13 what we're asking gets done for those members who feel 14 like it should be done?
15 MS. GAVRILAS: So, we talk about it 16 amongst ourselves that it's, you know, the committee's 17 provocative to ask us to come in front of the 18 committee, and so we've given you the overview to the 19 subcommittee. And if the committee feels that it 20 would be of value to come and talk to the full 21 committee, and the committee wants to write the 22 letter, then by all means, we'll support it.
23 CHAIR REMPE: Okay, but does it help make 24 sure something gets done is what I'm asking. Yes, we 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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83 can do this, but does it matter as far as you feel 1
like, eh, we're going to do it no matter what, you 2
guys -- it's a waste of our time to come down and have 3
to do this --
4 MS. GAVRILAS: We are committed to 5
basically implicate risk in agency decision making to 6
the maximum extent possible. So this will be one of 7
the things that we will consider. Am I going to say 8
100 percent? I'm not quite sure what's on their to-do 9
list, so how quickly it gets done --
10 CHAIR REMPE: Yes.
11 MS. GAVRILAS: -- may depend, but I think 12 we'll strike the iron while it's hot, and we are 13 committed, the management in NRR is committed to 14 utilizing all the good lessons to have them share 15 about with internal and external stakeholders.
16 CHAIR REMPE: Do any members want to speak 17 up and say something we should do before we close 18 this, or just --
19 MEMBER CORRADINI: I'm out. I'm not going 20 to say a word.
21 CHAIR REMPE: Ron or Harold?
22 MEMBER RAY: No, I'm just thinking about 23 this for the first time. I would need some more time 24 to reflect on it.
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84 MEMBER CORRADINI: Can I ask Mirela a 1
slightly different way of the question? So have you 2
already thought down the line, you've done a TER, 3
which has shown a -- which has a technical basis for 4
the conclusion.
5 You now have compliance evaluation 6
guidance, which is being approved, or has been 7
approved, or whatever, right, and it's out on the 8
street. Except for what I'll call knowledge 9
management, which I think is important, are you 10 committed to that, regardless?
11 MS.
GAVRILAS:
To the knowledge 12 management?
13 MEMBER CORRADINI: Yes.
14 MS. GAVRILAS: Yes.
15 MEMBER CORRADINI: Okay, fine. That's 16 what I thought you said. I wanted to make sure.
17 Okay.
18 CHAIR REMPE: So I'm going to close this 19 meeting, unless I hear anything else from Matt and 20 Pete. Going, going, gone, and with that, I'll close 21 this hearing.
22 (Whereupon, the above-entitled matter went 23 off the record at 2:40 p.m.)
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Technical Evaluation of In-vessel Closure Based on Low Safety Significance for Generic Safety Issue - 191 ACRS Subcommittee Meeting September 16, 2019 Steve Smith, NRR/DSS/STSB Paul Klein, NRR/DMLR/MCCB Ashley Smith, NRR/DSS/SRXB
Presentation Outline
- Recap from April 2019 meeting
- Staff technical evaluation (TER) of in-vessel downstream effects (IVDEs) (ML19178A252)
- Comment/resolution since April 2019 meeting
- GL 2004-02 staff review guidance development 2
Recap from April 2019 Meeting
- Provided background
- Described industry and NRC actions related to Generic Safety Issue (GSI) - 191 and Generic Letter (GL) 2004-02
- Described the approach to address IVDEs
IVDE Safety Significance Approach
- Align agency/industry resources in accordance with safety significance of issue
- Staff TER - evaluate the overall significance of IVDEs, considering new and existing knowledge
- Safety significance criteria determination used various sources of information
- Defense in depth is maintained assuming complete blockage of core inlet 4
Technical Evaluation (TER) Scope
- Evaluation of IVDE safety significance only
- Integrated decision-making:
- Engineering judgment, qualitative, quantitative, and risk information used
- Not evaluating regulatory compliance
- TER provided supporting information to close GSI-191
- TER will be considered in closing GL 2004-02 5
Primary Flowpath Maintained
- Uniform bed formation is unlikely
- Breaks that reach core blockage debris threshold are very low frequency
- Long-term core cooling (LTCC) maintained with core inlet 99% blocked
- WCAP-16793 single fuel assembly tests - tolerate high quantities fiber/particulate without precipitates
- WCAP-17788 chemical effects timing - almost all plants go to hot-leg switchover (HLSO) (or equivalent) before precipitation, debris bed disruption expected 6
Overview - Defense-in-Depth 7
Core Inlet Blocked Defense-in-Depth Measures Alternate Flow Paths (AFPs)
Refill RWST/Direct Injection Operator Action: Start Reactor Coolant Pumps Hot Leg Switchover Containment Integrity AFP may provide adequate cooling Cleaner injection water may provide adequate cooling Disrupts debris bed Disrupts and bypasses debris bed Provides additional fission product barrier if fuel cladding fails Defense-in-Depth Outcomes
TRACE Analyses Various sensitivity studies completed by RES result in the following conclusions:
Boric acid precipitation (BAP) was not found to inhibit LTCC with significant blockage at the core inlet AFPs are a viable option to maintain LTCC for both cold-leg breaks (CLBs) and hot-leg breaks (HLBs) 8
Staff Technical Evaluation Conclusion 9
- Staff concluded that IVDEs are of low safety significance for plants that address the key parameters identified in the TER
Safety Significance Criteria Used available guidance to determine definition of risk 10 Frequency of LOCAs to challenge LTCC via IVDEs
Use of TRACE
- Clarified how TRACE was used to inform conclusions
- Added a table to describe various TRACE sensitivity studies performed 11
Break Size Sensitivity
- Compared WCAP-17788 most conservative limit to lower 15 g/FA limit from WCAP-16793
- The 15 g/FA value can be met using the same break size and other inputs except:
- Fiber penetration value is reduced from the most conservative value (15%) to the second most conservative value (12%)
- Penetration values from plant specific testing 12
LOCA Frequencies -xLPR
- Parametric study was conducted using xLPR Version 2 to estimate LOCA frequencies
- A variety of pipe sizes, degradation mechanisms, inspection schedules, and leak detection credit were investigated
- Preliminary results suggest that LOCA frequencies in NUREG-1829 are conservative
- Further sensitivity study is underway to investigate impacts of uncertainties in key variables (e.g., weld residual stress, loads, and cracking frequency)
GL 2004-02 Staff Review Guidance
Purpose:
Provide guidance to the NRC staff to evaluate licensee demonstration of compliance with 10 CFR 50.46(b)(5) for addressing debris impacts
- Status: Issued September 4, 2019 (ML19228A011) 14
BACKUP SLIDES 15
Comment/Resolution ACRS TER was revised to address ACRS comments:
- Clarified use of TRACE
- Staff verified 15 g/FA and 6-inch minimum break size
- Additional information added to clarify brine testing
- Clarified TER safety significance statement
- Clarified HLSO based on BAP is in emergency operating procedures
- Clarified tblock, tchem, and Kmax
- Clarified why the CLB bounds the HLB
- Clarified the use of STP assumption for lowest fibrous debris limit
- Additional language added regarding uniform resistance calculations
- Clarified that the use of risk numbers developed to define safety significance for use in the TER to define IVDEs only applies to this review 16
Comment/Resolution Staff Peer Review and PWROG
- TER was revised to address both staff peer review and PWROG comments, some of which are listed below:
- Clarity
- Purpose
- Safety significance threshold
- Reliance on TRACE
- Correction to description of how flows, break size and debris generation are related
- Applicability to new reactors
- Loss-of-coolant accident deposition model (LOCADM) as key parameter
- Sump switchover timing 17
Plant LOCA Response 18 Sump Containment Spray System (CSS)
Safety Injection (SIS)
Heat exchanger Tank CSS SIS Spray nozzles Valve Fuel Assemblies RWST Strainers
Overview - Safety Margin 19 Attribute LOCA Size for Debris Generation Recirculation Swapover Time Coating Failure Unqualified Debris Transport Fiber Penetration Core Inlet Fiber Chemical Effects Timing Hot Leg Swapover Timing Assumption 6-inch 20 minutes 100% Fine 100% Fines Transport 15%
Uniform 6 Hours 24 Hours Maximum Most Probable
<6-inch
>30 minutes
<100%
Time dependent Some fines trapped
<15%,
Decrease with break size Non-Uniform 24 Hours Plant Specific Margin Less debris is likely More debris settles before reaching sump, Lower decay heat Some fail as Chips
<100%
Depends on Plant Design More debris required to block core Core inlet unblocked w/o Chemical Effects Consider actual plant timing Time in Transient Initial Recovery Switchover and Early Recirculation Long-Term Effects
TRACE Analyses 20 CLB BAP HLB BAP/AFP HLB AFP CLB AFP Purpose Evaluate effects of debris buildup at core inlet on BAP Evaluate effects of debris buildup at core inlet on BAP and LTCC Evaluate PWROG conservatisms Evaluate PWROG conservatisms Model DEG, 4-loop W upflow, mid-peaked axial, ANS 79 DEG, CE, top-peaked axial, ANS 79 Cases/
Sensitivities 99.9% blocked LCP 100% blocked nozzle
-HLSO time, decay heat, axial skew
- 99.5-100%
blocked core inlet
-Decay heat
-Bypass
-Blockage timing
-Rate of blockage
-HPI flow
-Base case only
Key Parameters 21
- Initiating event frequency
- HLSO (or equal) to dilute debris, chemicals, BAP
- Chemical timing vs. AFP timing
- Chemical effects methodology
- SSO timing
- Particulate debris amounts
- Fibrous debris amounts
- Minimum ECCS flow
- FA debris capture characteristics
- AFP resistance value
- CLB driving head
- RCS liquid mass
- LOCADM
Staff GL 2004-02 Evaluation 22