ML19133A166

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Transcript of Advisory Committee on Reactor Safeguards Thermal Hydraulic Phenomena Subcommittee Meeting - April 18, 2019
ML19133A166
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Issue date: 04/18/2019
From: Weidong Wang
Advisory Committee on Reactor Safeguards
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Wang W
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NRC-0298
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Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION

Title:

Advisory Committee on Reactor Safeguards Thermal-Hydraulic Phenomena: Open Docket Number: (n/a)

Location: Rockville, Maryland Date: Thursday, April 18, 2019 Work Order No.: NRC-0298 Pages 1-57 NEAL R. GROSS AND CO., INC.

Court Reporters and Transcribers 1323 Rhode Island Avenue, N.W.

Washington, D.C. 20005 (202) 234-4433

1 1

2 3

4 DISCLAIMER 5

6 7 UNITED STATES NUCLEAR REGULATORY COMMISSIONS 8 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 9

10 11 The contents of this transcript of the 12 proceeding of the United States Nuclear Regulatory 13 Commission Advisory Committee on Reactor Safeguards, 14 as reported herein, is a record of the discussions 15 recorded at the meeting.

16 17 This transcript has not been reviewed, 18 corrected, and edited, and it may contain 19 inaccuracies.

20 21 22 23 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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1 1 UNITED STATES OF AMERICA 2 NUCLEAR REGULATORY COMMISSION 3 + + + + +

4 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 5 (ACRS) 6 + + + + +

7 THERMAL-HYDRAULIC PHENOMENA SUBCOMMITTEE 8 OPEN SESSION 9 + + + + +

10 THURSDAY, APRIL 18, 2019 11 + + + + +

12 ROCKVILLE, MARYLAND 13 + + + + +

14 The Subcommittee met at the Nuclear 15 Regulatory Commission, Two White Flint North, Room 16 T2D10, 11545 Rockville Pike, at 8:30 a.m., Michael L.

17 Corradini, Chairman, presiding.

18 COMMITTEE MEMBERS:

19 MICHAEL L. CORRADINI, Chairman 20 PETER RICCARDELLA, Vice Chairman 21 MATTHEW W. SUNSERI, Member-at-Large 22 RONALD G. BALLINGER, Member 23 WALTER L. KIRCHNER, Member 24 JOSE MARCH-LEUBA, Member 25 JOY L. REMPE, Member NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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2 1 ACRS CONSULTANT:

2 STEPHEN SCHULTZ 3 DESIGNATED FEDERAL OFFICIAL:

4 WEIDONG WANG 5 ALSO PRESENT:

6 ALAN BILANIN, Consumer Dynamics, Inc.

7 VIC CUSUMANO, NRR 8 MIRELA GAVRILAS, NRR 9 PAUL KLEIN, NRR 10 STEVE SMITH, NRR 11 *Present via telephone 12 13 14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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3 1 P R O C E E D I N G S 2 (8:28 a.m.)

3 CHAIRMAN CORRADINI: Okay, the meeting 4 will come to order. This is a meeting of the Thermal-5 Hydraulic Subcommittee for the ACRS.

6 My name is Mike Corradini. I am Chairman 7 of today's Subcommittee meeting. ACRS Members 8 currently in attendance are Matt Sunseri, Walt 9 Kirchner, Ron Ballinger, Joy Rempe, and we're 10 expecting Jose March-Leuba.

11 Our consultant Steve Schultz is also with 12 us today. Member Dennis Bley will be on the phone on 13 the bridge line which we have a private line open for 14 use. And Weidong Wang of the ACRS staff is the 15 Designated Federal Official for this meeting.

16 Today's meeting, in today's meeting the 17 Subcommittee will review a staff technical report 18 entitled, Technical Evaluation of In-Vessel Closure 19 Based on Low Safety Significance. The Subcommittee 20 will hear presentations by and hold discussions with 21 the NRC staff and other interested persons regarding 22 this matter.

23 The Committee has received an email with 24 a paper from a public member, Alan Bilanin, et al and 25 they requested time to make an oral statement at the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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4 1 end of our public session which we will do so in 2 today's meeting.

3 Part of the presentations by the NRC staff 4 will be closed in order to discuss information that is 5 proprietary to the licensee and its contractors 6 pursuant to 5 U.S.C. 552(b)(c)(4).

7 Attendance at these portions of the 8 meeting that deals with such information will be 9 limited to the NRC staff and those individuals and 10 organizations who have entered into an appropriate 11 confidentiality agreement with them.

12 So consequently, after we have our public 13 session we will need to confirm we only have eligible 14 observers and participants in the room for the closed 15 portions of the meeting.

16 The Subcommittee will gather information, 17 analyze relevant issues and facts and formulate 18 proposed positions and actions as appropriate for 19 deliberation by the full Committee.

20 Let me just break from our normal thing 21 and point out that this is an information meeting. We 22 have a draft report that is in front of us which is 23 being looked at by staff and reviewed and revised.

24 Therefore, there is no anticipation that 25 we will write a letter from this meeting. Rather NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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5 1 there will be a subsequent meeting after we see a 2 revised version of the staff's report.

3 Rules of participation on today's meeting 4 have been announced as part of the notice in the 5 meeting previously published in the Federal Register.

6 A transcript of the meeting is being kept and will be 7 available as stated in the Federal Register notice.

8 Therefore, we request that participants in 9 this meeting use the microphones located throughout 10 the meeting room when addressing the Subcommittee. If 11 the participants would first identify themselves with 12 sufficient clarity and volume so they may be readily 13 heard.

14 And just so we all check you have all your 15 various appliances, things that beep and boop, et 16 cetera, make sure they're all turned off so that they 17 can do it to you silently then you can deal with it.

18 We will now proceed with the meeting.

19 I'll start by calling on the NRR staff and Dr.

20 Gavrilas will kick us off, Mirela.

21 DR. GAVRILAS: Good morning. I'm Mirela 22 Gavrilas. I'm the director for safety systems in NRR.

23 And I have a list of questions that the staff gave me 24 and said talk about these by ways of introducing the 25 topic to the Subcommittee.

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6 1 So the first question they wanted me to 2 address is why we did this. We did this because our 3 relatively new office director came in with a fresh 4 set of eyes.

5 And one of his principle objectives is to 6 right-size the expenditure of resources in NRR and 7 throughout the business line. So he looked at this 8 and he said why don't we look at what's still needs to 9 be done under GSI-191 given its safety significance.

10 So that was the incident. That was the 11 driving force. The second is why this specific item 12 was chosen. Frankly, because it's been around a long 13 time and we feel that a lot has been done by industry 14 and the staff has had ample opportunity to understand 15 what's going on.

16 So it was definitely the right topic to 17 choose for this right-sizing effort. The next 18 question is why is this an adequate methodology? So 19 under adequate methodology a methodology is adequate 20 for its particular purpose.

21 So let me talk about the purpose of this 22 report. This report assesses the safety significance 23 of in-vessel effects. And its main purpose is one, to 24 close out the generic issue and two, is to inform our 25 compliance discussions.

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7 1 I want to remind the Committee that we 2 still have a generic letter out there that the staff 3 is still trying to figure out what to do about. We're 4 still evaluating if any adjustment of course is needed 5 in that arena. And this report is also helping with 6 that.

7 CHAIRMAN CORRADINI: Can I interrupt you?

8 DR. GAVRILAS: Absolutely.

9 CHAIRMAN CORRADINI: Just for 10 clarification, so the generic letter we're speaking of 11 is the --

12 DR. GAVRILAS: GL-2004-02.

13 CHAIRMAN CORRADINI: The 2004 letter. And 14 the report will help inform that but is not intended 15 to close that out?

16 DR. GAVRILAS: That's right. So the 17 report is going to, there is one big issue in that 18 report and generic letter which says are you in 19 compliance.

20 And then there's an explicit tell me how 21 bad in-vessel effects are. So both those are in the 22 generic letter. So this report goes to address both 23 those issues.

24 But again, the path for closure of that 25 letter has not been discussed. We want to address the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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8 1 compliance next. So this is the first step. The next 2 step is going to be compliance.

3 The third step is going to be what do we 4 do about the generic letter. Did that answer your 5 question?

6 CHAIRMAN CORRADINI: Yes.

7 DR. GAVRILAS: So we are here soliciting 8 the Members feedback on the technical issues. And by 9 way of admonition not every statement that the staff 10 will make is going to have, is going to be equally 11 defensible.

12 So some will be, will have better 13 documentation, better technical basis for some points 14 we make and some depth of the technical basis may be 15 uneven throughout. So we think that is appropriate 16 given the overall picture, the overall look at the 17 issue and the conclusion that the staff made.

18 So we're looking forward to your feedback.

19 Thank you.

20 CHAIRMAN CORRADINI: Okay. Thank you very 21 much, Mirela. So we turn it to Steve.

22 MR. SMITH: Yes.

23 CHAIRMAN CORRADINI: Are you the man on 24 the hot seat, so to speak?

25 MR. SMITH: I'm starting us off.

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9 1 CHAIRMAN CORRADINI: Okay, all right.

2 Steve, take it away.

3 MR. SMITH: Yes. I'm Steve Smith. I'm 4 going to start off the presentation and this is on the 5 safety significance of in-vessel downstream effects on 6 long-term core cooling.

7 Our other presenters are going to be Paul 8 Klein, Ashley Smith, Ben Parks, Steve Bajorek and Joe 9 Staudenmeier. We've also had input from a lot of 10 other staff at NRR and research and particularly DMLR, 11 DSS and DRA and then research really did a lot of good 12 TRACE work for us.

13 On the next slide, well I'm in control of 14 the slides so I can flip. This just shows what we're 15 going to be talking about today. I'm not going to 16 spend a whole lot of time on the first few slides.

17 And so if people are unfamiliar or have 18 questions please stop and we'll try to answer your 19 questions as we're going through the first few slides.

20 We're just going to talk about the background of the 21 generic safety issue and the generic letter pretty 22 quickly.

23 We'll talk about NRC and industry actions.

24 We're going to talk about the approach of the 25 technical evaluation report that we did to address in-NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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10 1 vessel downstream effects.

2 And we do have a new acronym that I'll 3 have to give Ben Parks credit for creating IVDEs 4 because it's too hard to write in-vessel downstream 5 effects all the time.

6 So before we move ahead we just want to 7 say thank you to the ACRS for listening to us today 8 and giving us some feedback. The paper we sent you, 9 it was not finalized.

10 We've got feedback that it was confusing, 11 it wasn't clear. So we're working on clarifying the 12 paper and, you know, any feedback we get from you guys 13 today we'll incorporate into the paper.

14 CHAIRMAN CORRADINI: And just so you guys 15 were on the record to say this is that of course this 16 is individual Member comments. Since we're not 17 writing a letter report I won't confirm or deny the 18 quality of the comments.

19 MR. SMITH: Okay. We'll consider the 20 quality as we attempt to incorporate them. Today 21 we're favoring the right side of the room. Tomorrow 22 it might be the left. We're not sure.

23 So on the next slide, Slide 3 this is just 24 a little bit of background. This issue has been 25 around for a long time. As Mirela pointed out the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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11 1 GSI-191 did not identify in-vessel effects.

2 And it also didn't identify chemical 3 effects. Those were identified and included in 4 Generic Letter 04-02.

5 So I'm going to move to the next slide 6 because I think Mirela covered all of that. This is, 7 Slide 4 is the licensee actions to address effects on 8 long-term core cooling.

9 There is a list of things that were done 10 here by all of the plants or a couple of them might 11 have only been done by some of the plants. But all of 12 the plants have taken significant steps to help deal 13 with the debris issue in containment.

14 CHAIRMAN CORRADINI: And just to put it 15 here just so, and there's, maybe you're going to say 16 this, but there is a population of plants with what 17 I'll term the bounding or conservative assumptions 18 that one must make still may have challenges to get to 19 the resolution state at this point. Is that a fair 20 way of putting it?

21 MR. SMITH: Yes. We'll go into a little 22 bit more details.

23 CHAIRMAN CORRADINI: Okay, thank you.

24 MR. SMITH: The next page we talk about 25 sump strainer status. And we'll talk about it here NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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12 1 because most plants already have acceptable strainer 2 evaluations.

3 And then as you just talked about there 4 are some plants that may not have a good strainer 5 evaluation. So SECY-12-0093 allows plants to use 6 risk-informed option or the deterministic options 7 which most of the plants have used to come up with 8 their evaluations.

9 STP, South Texas, that was the first plant 10 that had a successful risk-informed LAR go through the 11 staff. And they have closed the issue based on that 12 LAR. So there's other plants that are moving along 13 with that.

14 CHAIRMAN CORRADINI: There are, that was 15 my question. So there are other plants that are 16 following that way?

17 MR. SMITH: Right. We have two in house 18 right now that we're working on. We have Vogtle and 19 Calvert Cliffs. And there's a few other plants that 20 are planning on coming in with a risk-informed 21 evaluation. And --

22 CHAIRMAN CORRADINI: If I might just make 23 sure I understand. So let's say we see the next 24 version of this technical report which clarifies 25 things and kind of evens out the analysis and the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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13 1 discussion, this would then be used in some way of 2 evaluating pieces of these applications?

3 MR. SMITH: It would be used only for in-4 vessel. The strainer evaluation --

5 CHAIRMAN CORRADINI: That's what I should 6 have said, okay.

7 MR. SMITH: -- is unaffected. So the last 8 bullet here says we expect the strainer performance to 9 be evaluated in the ways that are currently accepted.

10 The in-vessel we're only looking at in-vessel.

11 CHAIRMAN CORRADINI: Okay, thank you. So 12 just, not to bring up the South Texas, but my memory 13 is that when we did the South Texas there were a 14 number of conservative, I'll say bounding assumptions 15 used in the in-vessel that might be relaxed based on 16 analysis that evolve from the technical report?

17 MR. SMITH: That's correct.

18 CHAIRMAN CORRADINI: Okay, all right.

19 Thank you.

20 MR. SMITH: Okay. So the next slide, 21 Slide Number 6 it talks about what was done in the 22 past WCAP-16793. That's a previously approved in-23 vessel evaluation method.

24 It established a 15 gram per fuel assembly 25 fiber limit which was pretty much staff imposed by a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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14 1 condition limitation. Below 15 grams the testing 2 showed that there wasn't significant head loss even 3 when chemicals were included in the test.

4 So 19 units were able to close out using 5 WCAP-16793 and the 15 gram limit. And we have 6 completely closed the generic letter for those plants.

7 So those plants in STP that makes 21 units 8 are completely closed out as far as the generic letter 9 is concerned. The only thing that is not closed for 10 all plants is boric acid precipitation which we will 11 address in our TER in our discussions today at least.

12 MR. KLEIN: And it's probably worth 13 mentioning that boric acid precipitation was not part 14 of the generic letter of 2004-02.

15 CHAIRMAN CORRADINI: Right, that came up 16 following.

17 MR. KLEIN: I think that issue was 18 actually raised before that. But it's been carried 19 for a long time.

20 CHAIRMAN CORRADINI: Okay, all right.

21 MR. KLEIN: What was new was that --

22 CHAIRMAN CORRADINI: I know there was 23 testing that illuminated what were the contributors.

24 But I couldn't remember if it was before or after.

25 MR. KLEIN: I think the new part of it was NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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15 1 there was a question if a debris bed at the core inlet 2 could lead to faster boron precipitation because you 3 might not have exchange of the fluid between the lower 4 plenum and inside the core.

5 MR. SMITH: And the other thing is the 6 last bullet, STP as we talked about. They did a 7 plant-specific thermal-hydraulic analysis which was 8 relatively conservative to show that in-vessel effects 9 wouldn't be an issue for them.

10 One of the things, on the next slide one 11 of the things that you had asked for was to talk about 12 RoverD a little bit. And since that was what, that's 13 the methodology that the South Texas project used.

14 And I should define RoverD. It means risk 15 over deterministic. I should have put that on the 16 slide but I forgot. So since we just talked about STP 17 this is a good place to bring this up.

18 They were -- there are some aspects of the 19 TER that we're writing that are similar to RoverD.

20 One of those is the TER accepts the most frequent 21 smaller breaks because of low debris amounts. This is 22 similar to what was done with RoverD.

23 There are some differences. We don't 24 really use Reg Guide 1.174 as a methodology or a basis 25 for our decision. We do use some of the ideas from NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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16 1 Reg. Guide 1.174. But we don't really follow all the 2 guidance of that.

3 We don't use PRA at all in the TER. I 4 mean, we use some frequency numbers out of NUREG-1829.

5 But that's about as close as we get to that. And the 6 PRA was used to some extent in STP evaluation.

7 So basically RoverD was a more specific, 8 plant-specific analysis that was done and calculated 9 plant-specific risk numbers and the TER is more 10 general and draws conclusions about the fleet.

11 So the next page this talks about a WCAP 12 that was written, WCAP-17788 that the staff was 13 reviewing and working with the PWR Owners Group on.

14 This WCAP was intended to allow higher debris limits 15 based on plant-specific parameters.

16 It was also to address boric acid 17 precipitation which was not addressed in 16793. And 18 we would like to point out that this was a significant 19 effort.

20 This WCAP came in, in six volumes, each 21 volume addressed a different aspect of the issue. We 22 had an overall. We had thermal-hydraulic analysis, 23 chemical effects, cold leg break.

24 So there were several volumes and it was 25 a lot of work for both the industry and the staff.

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17 1 And there was a lot of good information that came out 2 of that.

3 So we attempted to use that information to 4 move ahead. And the next slide gives some information 5 on the review status of the WCAP.

6 And it shows, I think the main thing to 7 take away from this slide is that when we started work 8 on the TER this is where we stood, the status in the 9 middle column.

10 We had developed a large number of 11 conditions and limitations based on the review. And 12 it would have required significant plant evaluations 13 and a lot of review from the staff to make sure that 14 we agreed with the way that the issue was being 15 closed.

16 So instead of moving forward with that we 17 started working on the TER. So if you look in the 18 third column I think the main thing that could be of 19 interest is the second row down which is how we used 20 the TH analysis even though we had some unresolved 21 issues with it.

22 We still used the debris limits from the 23 WCAP. We used it to demonstrate, to help us 24 understand how the flows inside the reactor vessel go 25 and also to demonstrate alternate flow path viability.

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18 1 And alternate flow paths ended up being a 2 defense in depth measure for us. We didn't count on 3 them as the main way to cool the core. We assumed 4 that the flow was still going to come in through the 5 core inlet.

6 But the alternate flow path still provided 7 viability, a viable flow path. All right, next, yes.

8 CHAIRMAN CORRADINI: So if you're going to 9 do it later that's perfectly fine. I am very 10 interested in the brine rod testing because it's been 11 referenced in the memo or in the document a number of 12 times about various things observed that you're, I'll 13 use the word, taking credit for from the physical 14 phenomena standpoint.

15 So that will be discussed later, I assume?

16 MR. SMITH: I will discuss it now because 17 we don't really have specific discussions on it. I'll 18 try to give a high level idea of what was done with 19 that.

20 So the brine testing it was a program that 21 was basically meant to show if you form a bed at the 22 core inlet and you have a dense fluid which could, 23 meant to represent concentrated boric acid in the core 24 much denser than, you know, regular coolant what that 25 would do to the debris bed.

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19 1 So we didn't use any quantitative results 2 from it. But qualitatively it showed that if you had 3 a debris bed at the core inlet and had a dense fluid 4 above the, in the core area and a less dense fluid in 5 the lower plenum that you would get some exchange 6 flow.

7 And actually in some cases it would 8 disrupt the debris bed.

9 MEMBER KIRCHNER: So it wasn't a chemical 10 effects test it was a fluid density test?

11 MR. SMITH: That's right.

12 MEMBER KIRCHNER: So we're really talking 13 thermal-hydraulics, we're not talking chemistry?

14 MR. SMITH: Right.

15 MR. KLEIN: You know, I think the 16 potassium bromide solution was just a convenient way 17 to try and simulate the density that you get with 18 concentrated boric acid.

19 CHAIRMAN CORRADINI: The reason I asked 20 the question and I think we are going to have to 21 eventually get, because there are a couple comments 22 about inability to, now I can't find it, inability to 23 actually totally close off the core.

24 And then there was a reference to the 25 brine testing. So I guess I want to understand that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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20 1 connection. So maybe I'll wait because we'll see some 2 TRACE calculations in the closed session, right so we 3 will talk about that.

4 We can wait -- I'm not -- that was the one 5 thing on your list here on the table. And I guess, 6 well that was the main thing on your table that I 7 wanted to bring up.

8 So I had questions that I think are 9 related to calculations. So why don't we just wait.

10 MR. SMITH: Okay. And we may have to get 11 you the brine test report so you could understand.

12 CHAIRMAN CORRADINI: That's fine. At 13 least we can discuss it when the TRACE calculations 14 are discussed.

15 MR. SMITH: Okay. And we may get the PWR 16 Owners Group to come and discuss it if you have 17 detailed questions because they're the experts. Okay, 18 so this slide --

19 CHAIRMAN CORRADINI: I'm sorry. I found 20 it finally. It's on Page 11.

21 MR. SMITH: Okay.

22 CHAIRMAN CORRADINI: There is a paragraph 23 that talks about this test in relation to the 24 inability to 100 percent block the core. So that's 25 where I was kind of making the connection. So we'll NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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21 1 wait.

2 MEMBER REMPE: So since we've interrupted 3 you, is there something with respect to that table 4 that you want to talk about here or later about 5 uncertainties with respect to some of the results and 6 impact?

7 MR. SMITH: As far as the thermal-8 hydraulic analysis?

9 MEMBER REMPE: I'm thinking more the 10 chemical effects testing.

11 MR. SMITH: Paul discussed --

12 MR. KLEIN: We can discuss uncertainties 13 when get to the chemical effects slide in that area.

14 MEMBER REMPE: Okay.

15 MR. KLEIN: That's one of the things that 16 we had them look at. But I think in a more global 17 picture some of the uncertainties with the thermal-18 hydraulic analysis are what caused us to maybe 19 approach the overall logic in a different way instead 20 of just assuming that the core inlet blocked and that 21 alternate flow paths would provide cooling.

22 We thought with the uncertainty there it 23 might be more appropriate to move that to a defense in 24 depth mechanism even though we think it is a viable 25 cooling path particularly as you go longer out in time NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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22 1 before the core inlet could be blocked.

2 So we have a primary argument that it 3 won't be blocked and then the alternate flow path part 4 really becomes a defense in depth mechanism which we 5 thought would allow us to have more uncertainty.

6 MEMBER KIRCHNER: Could you just clarify 7 the very last, the bottom line? What do you mean by 8 using TER not applied to cold leg break?

9 MR. SMITH: We didn't use --

10 MEMBER KIRCHNER: Because you examined 11 cold leg breaks obviously in the TER.

12 MR. SMITH: We talk about that. But we 13 really didn't use information from the WCAP in our 14 analysis.

15 MEMBER KIRCHNER: Okay, thank you. That's 16 what you mean but the TER itself is meant to be --

17 MR. SMITH: Right, it was --

18 MEMBER KIRCHNER: -- inclusive of all 19 these phenomenon.

20 MR. SMITH: Yes, and the cold leg break 21 volume, which is Volume 3 it was mostly talking about 22 how to calculate how much debris arrives at the core 23 for that situation. So we didn't really use that 24 information.

25 All right. The next slide is just very NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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23 1 high level slide on where we stood with the TH 2 analysis when we started working on the TER.

3 I'm not going to spend a lot of time here 4 because we have several slides that talk about, you 5 know, the TH analysis. So this talks about the in-6 vessel downstream effects safety significance 7 approach.

8 As Mirela said, NRR's concept we're 9 transforming to align our resource and industry's 10 resource expenditures with the safety significance 11 associated with various issues. So we took a look at 12 this issue to determine what the safety significance 13 was and safety significance is and determined how much 14 effort we should put into it.

15 You know, should we continue with the WCAP 16 review or should we try something that might be, take 17 less resources from all parties. And this second 18 bullet, it just lists the most significant technical 19 information that we looked at when we were doing this 20 evaluation.

21 Go to the next slide. So when we started 22 on this task the Agency really didn't have a 23 definition for what is low safety significance. So we 24 started looking at existing guidance to come up with 25 something we could use as a metric.

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24 1 So we looked at Reg Guide 1.174 which is 2 use of PRA in licensing basis changes. That's a 3 paraphrasing of what the title is, it's long.

4 And then we also looked at NUREG/BR-0058 5 and that's regulatory analysis. And both of those 6 things give us some ideas about, you know, what's 7 acceptable as far as risk is concerned.

8 So looking at both of those an issue would 9 be safety significant if you could reduce core damage 10 frequency by more than ten to the minus five per year.

11 Our evaluation shows that in-vessel downstream effects 12 do not meet this threshold.

13 And in addition to that we believe that 14 there is some significant defense in depth beyond, 15 you, now even if we just consider what happens if the 16 core becomes blocked. That's where we look at the ten 17 to the minus five number.

18 And then if that happens there's still 19 defense in depth.

20 CHAIRMAN CORRADINI: So, but let me ask 21 the question about the third bullet. Since you said 22 earlier you're not doing this as a risk calculation.

23 So how do you determine a risk number?

24 MR. SMITH: Basically we look at -- we're 25 using this as a metric. So basically it's just going NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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25 1 to be based on a break frequency. And then we can 2 also look at other things.

3 We can say, you know, we have conservatism 4 here or we don't so we think that it's actually 5 greater than the break frequency number, you know, or 6 the risk is less than the break frequency number that 7 we're going to calculate.

8 CHAIRMAN CORRADINI: So let me say it back 9 to you so I don't misunderstand. So you're point is 10 from a bounding standpoint the break frequency number 11 is, and everything else being conservatively assumed 12 is essentially the upper bound or the risk of the 13 event.

14 MR. SMITH: Right. So if the break --

15 we're assuming if the break occurs you go to core 16 damage. So it's very simple, like you said.

17 CHAIRMAN CORRADINI: And then you're 18 evaluating what we'll call additional margins?

19 MR. SMITH: There's additional margins in 20 that calculation. And then if the core was to block, 21 you know, if you get this ten to the minus six or ten 22 to the minus seven break to occur and it causes the 23 core inlet to block you have defense in depth beyond 24 that.

25 CHAIRMAN CORRADINI: Thank you.

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26 1 MEMBER KIRCHNER: So what would be, so 2 let's think about it outside of this specific 3 application of IVDE because we're seeing as PRA is 4 being used to inform both submittals from applicants 5 as well as the staff's reviews basically you are 6 saying here that the break frequency is less than that 7 number that you have on the view graph and so you just 8 screen out the, let me restate what I was trying to 9 say.

10 We've seen examples of using that to just 11 screen out even analyzing anything in that particular 12 area. Just say it's not part of the design basis 13 events.

14 MR. SMITH: So we're not saying that at 15 this point.

16 MEMBER KIRCHNER: No, you're not because 17 you're putting a lot of effort into this particular 18 area.

19 MR. KLEIN: I think the TER specifically 20 says it's, the evaluation is specific to in-vessel 21 downstream effect and we're not intending to set a 22 precedent for people to just use that blanket 23 approach.

24 MR. SMITH: Yes, and so, you know, just 25 saying you don't have to consider it, that's not what NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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27 1 this is intended to do. That's the compliance work 2 that's being done.

3 So that's when that will be decided. We 4 don't really know. We've had a lot of discussions.

5 We have some theories about what would be good ways to 6 do this.

7 But I don't think ignoring the issue is on 8 the table.

9 MEMBER KIRCHNER: Actually I agree with 10 you. But I'm just suggesting that we've seen 11 incidences where someone comes forward with a number 12 much lower than that and therefore it's not even 13 evaluated.

14 MR. KLEIN: I think we're very sensitive 15 to that.

16 MEMBER KIRCHNER: Okay. Thanks.

17 CONSULTANT SCHULTZ: In that regard the 18 third bullet can be misconstrued. I think that's one 19 thing that Walter is getting at.

20 That is to say it can be considered a 21 blanket statement that can be applied in many 22 different areas. But when you explain what you are 23 doing this only sets a starting point for further 24 determinations where you're investigating the 25 technical events which lead to a conclusion in NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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28 1 consideration of much lower risk profiles.

2 MR. SMITH: Yes, I agree. And we don't 3 want anyone to take the third bullet here and put it 4 in the headline of a newspaper, you know. We've got 5 to keep all this in context of what we're doing 6 otherwise we're going to get in trouble, you know.

7 CHAIRMAN CORRADINI: But, that's fine.

8 But I view this as a selective application trying to 9 risk inform where you're using some sort of bounding 10 analysis to at least see where you sit and then 11 evaluate margin which I mean, from my perspective 12 you're not looking for absolute assurance.

13 We're looking for reasonable assurance of 14 safety. So it seems, personally it seems reasonable.

15 CONSULTANT SCHULTZ: In that regard it 16 sets the stage for that type of an approach.

17 CHAIRMAN CORRADINI: Right, right.

18 CONSULTANT SCHULTZ: But taken out of 19 context it can be misconstrued.

20 MR. SMITH: Yes. And I think part of --

21 this is a new idea for us. So I think it's important 22 for the ACRS to think about this as well because I 23 think this is kind of the way things are going now.

24 You know, this is what we're seeing is 25 where looking for things that are low safety NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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29 1 significance. We're going to try to define those, 2 figure out what the safety significance is and if they 3 don't appear to be safety significant we may treat 4 them differently than we would have in the past.

5 So I think the Agency is kind of moving 6 this direction. It may move back in a few years. I 7 don't know how things are going to go. But it's a 8 good thing to think about.

9 CHAIRMAN CORRADINI: Okay, thank you.

10 MR. SMITH: So this talks a little bit 11 about the TER scope. And this is kind of what we were 12 just talking about.

13 One of the hardest things we had to do 14 while we were writing the TER is to try to divorce 15 compliance from safety significance because we have 16 not really thought that way in the past. It's a new 17 way of thinking.

18 By considering only the safety 19 significance we are leaving probably a more difficult 20 task for the people who have to work on the compliance 21 part of this. The second bullet we did use integrated 22 decision making and this is what Mirela was talking 23 about when she opened up for us.

24 Engineering judgment is used more here 25 than probably what we're used to doing. The TER can NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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30 1 provide a basis to close the GSI, GSI-191 if we 2 understand the technical issues well enough we can 3 close that.

4 But then to close the Generic Letter 2004-5 02 for each plant individually we can consider -- we 6 may consider some of this information. You know, it 7 kind of depends how the compliance discussions go.

8 All right. So Slide 14, this is going to 9 take a little while. This is what you were -- I was 10 going to talk through the event here. So if I leave 11 anything out or I don't give enough details please 12 stop me.

13 I don't have hot leg switch-over on here.

14 I'll try to remember to hit that at the end because I 15 do have a couple more slides for the cold leg break 16 and hot leg break to talk about hot leg switch-over.

17 But it might be good to talk about it here.

18 CHAIRMAN CORRADINI: That would be fine, 19 thank you.

20 MR. SMITH: So this diagram is just sort 21 of typical. It would look different for different 22 plants. The heat exchanger could be on the other 23 loop.

24 The safety injection system might be 25 called something else. But it's kind of a good, it's NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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31 1 a good diagram for us to use and it's good for pretty 2 much all the plants.

3 The first thing that happens is you have, 4 I'm trying to get my pointer. Here you have a LOCA 5 that occurs here. Say a LOCA break occurs here.

6 And in the area of that break you damage 7 materials within the zone of influence. Materials 8 have different zones of influence. Stronger materials 9 have smaller zones of influence. Weaker materials or 10 less robust materials have larger zones of influence.

11 So materials in the zone of influence are 12 damaged. Usually it's insulation and coatings that 13 we're worried about. After that the RCS empties 14 during blow down.

15 For large LOCAs the SITs are going to 16 inject, safety injection tanks. And this helps 17 reflood and quench the core. And it also adds volume 18 to the sump because it's going to eventually spill out 19 of the reactor.

20 So it adds inventory to the sump. After 21 that the ECCS starts and injects. And the initial 22 injection is from the RWST or there's other names for 23 this, BWST or RWT.

24 And it injects and it supplies, if the 25 containment spray system starts it supplies the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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32 1 containment spray and it supplies the ECCS or safety 2 injection system. This takes a minimum of about 20 3 minutes.

4 Could be, usually it's going to be longer 5 than that. Occasionally, I guess it's possible to be 6 shorter.

7 CHAIRMAN CORRADINI: But it's designed 8 dependent upon the size of all the systems, et cetera, 9 et cetera?

10 MR. SMITH: The size of the RWST has a big 11 effect and how many pumps start. Like if you all your 12 pumps running it's going to empty faster. If you 13 have, you know, if you only have one train running 14 it's going to take a lot longer time.

15 Break size can have a big effect. As soon 16 as the break gets down below a specific size depending 17 on what the capacity ECCS is it may limit the flow.

18 For the more likely smaller breaks it's 19 going to take longer than 20 minutes because the 20 breaks are going to be small.

21 CHAIRMAN CORRADINI: But that's what you 22 guys use as a, I guess you would call it a switch-over 23 point?

24 MR. SMITH: The switch-over point is 20 25 minutes. That's what is considered for the switch-NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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33 1 over. And that's pretty, generally conservative I 2 would say or representative of the earliest that we 3 would switch over.

4 As that tank is emptying you have 5 containment spray running or just the LOCA break. And 6 that's going to wash materials down into the sump down 7 here around the strainers.

8 The strainers aren't in service yet. But 9 this blue arrow shows that the sump is filling up at 10 this time.

11 Some debris is going to settle, and some 12 will remain suspended and reach the strainer. And 13 materials that are damaged during the break and other 14 materials that are in containment are dissolving at 15 this time.

16 You generally have a high, an acidic --

17 the pH is acidic. And then if you have -- it depends 18 if you have sodium hydroxide. You have different pHs 19 so you dissolve -- aluminum is the main thing we're 20 worried about dissolving, and Paul is going to talk 21 about that a little bit later.

22 The unqualified coatings begin degrading.

23 And that's due to the harsh environment. They weren't 24 damaged by the jet, but they're all over the 25 containment. And they generally take hours to days to NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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34 1 degrade and fail and wash down to the sump.

2 CHAIRMAN CORRADINI: So that comes to my 3 next question which is at this point for your analysis 4 you're assuming, I'm not sure if we can say the 5 number, you're assuming hours or greater?

6 MR. SMITH: Right.

7 CHAIRMAN CORRADINI: For the precipitation 8 to occur.

9 MR. KLEIN: And we'll address that 10 specifically in the chemical effects part. But it 11 would be hours. And for most plants greater than 24 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

13 CHAIRMAN CORRADINI: Okay.

14 MR. SMITH: So by the time this external 15 water source is depleted the strainers are submerged 16 and you switch from injection to recirculation. So 17 that's the 20 minute time frame for the large break.

18 And this can be automatic or manual or a 19 combination. It depends on the plant design. And 20 the, you continue injecting to the cold leg which is, 21 there we go, you continue injecting to the cold leg 22 here, which is the same place that the injection was 23 injecting.

24 I don't know if I mentioned that or not.

25 But anyway, for the first part of the event you always NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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35 1 inject to the cold leg. So the strainer is now in 2 service. The green line coming from this tank is 3 valved out.

4 This is valved in. So this is supplying 5 both the safety injection and the containment spray if 6 the containment spray is running.

7 So what happens at this point is you have 8 fluid circulating through the system. It's coming --

9 it's going through the strainers. Anything that goes 10 through the strainer and goes to the ECCS system has 11 an opportunity to reach the core inlet.

12 And it's different for a cold leg break 13 and a hot leg break and we'll talk about that a little 14 bit later. But anything that goes through the 15 containment spray system is going back to the sump 16 strainer and it's, as the debris builds on the 17 strainer it's more likely to get filtered out.

18 So the less percentage of flow that's 19 going to the core the less debris you get there. And 20 over time just the amount of debris goes down. So --

21 CHAIRMAN CORRADINI: But if I might again, 22 you'll get this in, but the assumption, the bounding 23 assumption that you're using is you don't take credit 24 for it, for the fines?

25 MR. SMITH: All the fines are assumed to NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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36 1 transport to the strainer. Now some collect on the 2 strainer and don't go through. But we take credit for 3 filtering on the strainer.

4 CHAIRMAN CORRADINI: Okay. Then I've got 5 to come back.

6 MR. SMITH: We'll talk about that a little 7 bit later on.

8 CHAIRMAN CORRADINI: Okay, thank you.

9 MR. KLEIN: What's not credited is any 10 fines that would get held up on gratings or that might 11 have a chance to get hung up on debris interceptors or 12 sometimes at the strainer you'll get a pile of debris 13 at the inlet.

14 And we've seen that could trap fines. So 15 no credit is given for any of those features.

16 MR. SMITH: Okay. And then basically the 17 last thing that happens here is the sump, as the event 18 goes on the sump begins cooling. This increases your 19 NPSH margin.

20 But it also leads to potential for 21 chemical precipitation and higher head loss across the 22 strainer.

23 And then I'm going to say after a few 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> usually between, I think it's between like six 25 and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> approximately maybe a little bit earlier NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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37 1 than six the plant will go to hot leg switch-over 2 which will inject water to a different point so it 3 will bypass any debris bed that might have occurred at 4 the inlet of the core.

5 CHAIRMAN CORRADINI: So that's what I 6 guess I -- thank you for bringing up. So is that part 7 of an emergency procedure so that is they have 8 procedures that say at this point based on some 9 monitoring of some parameter go to switch-over?

10 MR. SMITH: Yes. It's not based on a 11 parameter. It's based on timing. It's calculated to 12 prevent boric acid precipitation.

13 CHAIRMAN CORRADINI: So the intent is to 14 go to switch-over before you expect precipitation?

15 MR. SMITH: That's correct.

16 MR. KLEIN: That's not the original intent 17 of the procedure. The original intent was to prevent 18 boric acid precipitation because you weren't sure if 19 you had a hot leg or a cold leg break.

20 So the hot leg switch-over or equivalent 21 was originally intended to prevent boric acid 22 precipitation.

23 CHAIRMAN CORRADINI: In the system?

24 MR. KLEIN: In the system, in the reactor 25 vessel for a cold leg break.

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38 1 CHAIRMAN CORRADINI: Okay, fine.

2 MR. KLEIN: The advantage is that if 3 precipitation, chemical precipitation occurs after the 4 time a hot leg switch-over we would expect the debris 5 bed to be disrupted before it precipitates. And we'll 6 talk to that later in some slides.

7 CHAIRMAN CORRADINI: Okay, thank you.

8 MR. SMITH: Yes, I'm sorry. I thought you 9 were asking about boric acid precipitation. There's 10 two precipitations so we've got to be careful.

11 CHAIRMAN CORRADINI: It's within the core 12 or within the system. I understand, thank you.

13 MR. SMITH: Okay. So the next slide, 14 better use the buttons. Yes, we're supposed to close 15 the meeting now because we could get into discussions 16 about specific.

17 CHAIRMAN CORRADINI: We don't want to do 18 something that's inappropriate.

19 MR. SMITH: I'm glad somebody saved me 20 there, saved me from a faux pas. So that's the end.

21 I guess of the non-proprietary, so if maybe this would 22 be a good time for questions.

23 CHAIRMAN CORRADINI: I was going to say I 24 want to go around to make sure the Members have a 25 chance to answer questions in public session. If we NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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39 1 don't have comments from the Members, we'll turn and 2 ask for public comments.

3 Okay. So, Paula, can you make the magic 4 occur. Okay, so first I know there is a public 5 comment from someone in the room.

6 So, Mr. Bilanin, are you here? Just go to 7 the mic and identify yourself.

8 MR. BILANIN: Can you hear me?

9 CHAIRMAN CORRADINI: Yes.

10 MR. BILANIN: My name is Alan Bilanin.

11 I'm head of Continuum Dynamics Incorporated. In the 12 late 90s we conducted the technical program that 13 formed the basis of utility resolution guidance 14 document for the boiling water reactors.

15 Our strainer designs are both in some PWRs 16 and most BWRs as well. Recently we've been working 17 with BWRs on a concept called good debris which has 18 the potential for improving net positive suction head 19 margins at the same time increasing the time between 20 suppression pool cleaning.

21 While conducting those tests we've noticed 22 that if you deployed good debris you can significantly 23 reduce downstream effects.

24 My question has anyone considered other 25 defense in depth strategies for resolving strainer NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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40 1 downstream effects such as seeding the sump with these 2 engineering materials that in PWRs will both enhance 3 the NPSH margin and reduce the fiber bypass?

4 It would seem that the use of these 5 materials might permit plants to show that the current 6 emergency core cooling systems can meet the design 7 basis accidents which they were originally, under 8 which they were originally licensed.

9 CHAIRMAN CORRADINI: Thank you very much.

10 And just so the Members are aware, the paper we 11 received is by Mr. Bilanin, et al that discusses this 12 that's being presented.

13 So we were given something we can read 14 after the fact. So anything else from the audience in 15 the room? So why don't we turn to the phone line.

16 The phone line should be open and volume up.

17 Is anybody on the phone line to make a 18 public comment? Could somebody at least identify that 19 the public line is open so we know you're out there?

20 PARTICIPANT: Yes. The phone is open.

21 CHAIRMAN CORRADINI: Okay. Anybody on the 22 line, go ahead I'm sorry, excuse me.

23 PARTICIPANT: Just confirming that the 24 public line is open.

25 CHAIRMAN CORRADINI: Okay. Anybody who NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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41 1 would like to make a public comment? Okay, hearing 2 none let's close the public line. And then I'm going 3 to ask the staff to look in the room and politely ask 4 those that are not bona fide to leave.

5 And we'll take a minute or two to 6 reorganize ourselves and then we can get into closed 7 session.

8 (Whereupon, the above-entitled matter went 9 off the record at 9:14 a.m.)

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Technical Evaluation of In-vessel Closure Based on Low Safety Significance for Generic Safety Issue - 191 ACRS Subcommittee Meeting April 18, 2019

Presentation Outline

  • Industry and NRC actions
  • Approach to address in-vessel downstream effects (IVDEs)
  • Staff technical evaluation (TER) of IVDEs 2

ECCS Debris Effects Background

  • GSI-191 for PWRs issued in 1996 to address strainer performance

Licensee Actions to Address Debris Effects on LTCC

  • Installed larger strainers
  • Removed unnecessary debris sources
  • Removed some problematic materials
  • Implemented administrative controls

- Control materials in containment

  • Implemented procedural changes
  • Improved chemical effects attributes 4

Sump Strainer Status

  • Most plants have acceptable strainer evaluations
  • Some plants are using risk-information to demonstrate adequate strainer function
  • No change to methodology for demonstrating strainer performance 5

IVDE - WCAP-16793 Summary

  • Industry program (WCAP-16793) for the evaluation of the effects of debris in the reactor vessel (RV) on long-term core cooling (LTCC)

- Test program based on bounding assumptions that cover all plant designs

- NRC SE approved fiber limit incapable of blocking flow

- 19 PWR units used guidance to demonstrate in-vessel debris would not inhibit LTCC

- 5 additional low fiber units meet WCAP-16793 limits

  • Awaiting higher limits for margin or risk-informed LAR

- 21 of 65 units closed at this time

  • STP used plant-specific thermal-hydraulic (TH) analysis and risk evaluations to address IVDEs 6

RoverD Applicability to TER

  • Similar - some breaks are shown to be acceptable based on low debris amounts
  • RoverD used staff approved deterministic thresholds combined with PRA to assess acceptability
  • TER safety significance values are order of magnitude
  • TER considered DID and SM similar to RoverD
  • TER uses integrated decision making, more engineering judgement, because models for some aspects of IVDEs have not been developed 7

IVDE - WCAP-17788 Summary

  • Plant-specific evaluations with event timing considerations
  • Higher debris limits
  • Performed fuel assembly (FA) testing, chemical effects testing, TH analysis 8

WCAP-17788 Review Status Technical Area Status Use in TER Overall Conditions & Limitations Assumptions Approach (C&Ls) Understanding methodology TH Analysis Unresolved Issues Establish debris limits Demonstrate RV flows Demonstrate AFP viability Chemical Limited C&Ls Precipitate timing evaluated against Effects Testing HLSO timing FA Testing Limited C&Ls Establish debris limits Brine/Heated Reviewed as Supporting Provide experimental evidence of Rod Testing Information phenomena Cold-leg Break C&Ls Not applied 9

WCAP-17788 - Staff TH Assessment

  • Code models not previously reviewed for phenomena unique to post-LOCA long-term cooling with debris blockage
  • Modeling inputs not bounding of all plants
  • Code outputs exhibited anomalies and behavior that was not fully understood
  • PWROG did not support further WCAP efforts 10

IVDE Safety Significance Approach

  • NRR - align agency/industry resources in accordance with safety significance of issue
  • Staff TER - evaluate the overall significance of IVDEs, considering:

- WCAP-17788

- Break frequency (NUREG-1829)

- TRACE RES analysis

- WCAP-16793-NP-A

- Autoclave and historical chemical effects testing

- Risk-informed analyses (STP and Vogtle)

- Strainer testing 11

Safety Significance Criteria Determination

  • Both tie back to Commissions Quantitative Health Objectives
  • An issue would be safety significant if resolution would reduce core damage frequency (CDF) by

>1x10-5 per reactor year

  • Staff evaluation shows that IVDEs do not meet this threshold
  • Defense in depth (DID) is maintained assuming complete blockage of core inlet 12

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

- Separate staff effort on compliance

  • TER provides basis to close GSI-191

Plant LOCA Response Spray nozzles Fuel Assemblies Tank RWST Heat exchanger Valve Strainers CSS SIS Sump Safety Injection Containment Spray System (CSS)

(SIS) 14

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