ML25272A180

Transcript of the Advisory Committee on Reactor Safeguards - Accident Analysis - Subcommittee Meeting, September 16, 2025, Pages 1-103 (Open)

ML25272A180
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Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION

Title:

ACRS Accident Analysis Subcommittee Docket Number:

N/A Location:

Teleconference Date:

9/16/2025 Work Order No.:

NRC-0461 Pages 1-57 NEAL R. GROSS AND CO., INC.

Court Reporters and Transcribers 1716 14th Street, N.W.

Washington, D.C. 20009 (202) 234-4433

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(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 ACCIDENT ANALYSIS SUBCOMMITTEE 7

+ + + + +

8 OPEN SESSION 9

+ + + + +

10 TUESDAY 11 SEPTEMBER 16, 2025 12

+ + + + +

13 The Subcommittee met via hybrid 14 Video-Teleconference, at 8:30 a.m. EDT, Robert Martin, 15 Chair, presiding.

16 17 MEMBERS PRESENT:

18 ROBERT P. MARTIN, Chair 19 VESNA B. DIMITRIJEVIC*

20 GREGORY H. HALNON*

21 CRAIG D. HARRINGTON 22 WALTER L. KIRCHNER*

23 SCOTT P. PALMTAG 24 DAVID A. PETTI*

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

2 THOMAS E. ROBERTS 1

MATTHEW W. SUNSERI*

2 ACRS CONSULTANT:

3 RONALD BALLINGER 4

5 DESIGNATED FEDERAL OFFICIAL:

6 WEIDONG WANG 7

8 ALSO PRESENT:

9 KEVIN BARBER, WEC 10 JEREMY DEAN, NRR*

11 AARON EVERHARD, WEC 12 JERROD EWING, WEC 13 BRIAN ISING, WEC 14 JEFFREY KOBELAK, WEC*

15 JOHN LEHNING, NRR 16 SCOTT KREPEL, NRR 17 JACK VANDE POLDER, NRR 18 BRANDON WISE, NRR 19 20

• Present via telephone 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

3 CONTENTS 1

PAGE 2

ACRS Subcommittee Chairman Open Remarks 3

Robert Martin...............

4 4

NRR Staff Leadership Opening Remarks 5

Scott Krepel 9

6 WEC Opening Remarks 7

Jerrod Ewing

............... 10 8

Open Session: Discussion WCAP-18850 9

Jeffrey Kobelak.............. 11 10 Open Session: Staff Safety Evaluation 11 John Lehning

............... 37 12 Jeremy Dean................ 38 13 Brandon Wise

............... 43 14 Jack Vande Polder............. 41 15 Opportunity for Public Comment

......... 55 16 Break

..................... 56 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

4 P-R-O-C-E-E-D-I-N-G-S 1

8:30 a.m.

2 CHAIR MARTIN: The meeting will now come 3

to order. This is the meeting of the Accident 4

Analysis Subcommittee on the Advisory Committee on 5

Reactor Safeguards. I am Robert Martin, I'm Chairman 6

of today's Subcommittee meeting. ACRS Members in 7

attendance and present are Craig Harrington, Scott 8

Palmtag, Thomas Roberts and myself. ACRS Members in 9

attendance via virtual via Teams, I'm going to check 10 here and see, make sure everyone is here, are Vesna 11 Dimitrijevic, Matt Sunseri, I don't see Vicki Bier, 12 Greg Halnon and Walt Kirchner and Dave Petti. We have 13 one of our consultants participating in person, it is 14 Ron Ballinger. If I have missed anyone, which I don't 15 think I have, either ACRS Members or Consultants, 16 please speak up?

17 Weidong Wang, the ACRS staff, is the 18 designated federal officer for this meeting. No 19 member or conflicts of identified for today's meeting.

20 We have a quorum.

21 During today's meeting the Subcommittee 22 will receive a briefing on topical report and staff's 23 Draft Safety evaluation for Westinghouse Topical 24 Report WCAP-18850, Adaptation of the Full Spectrum of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

5 LOCA, Loss Coolant Accident, Evaluation Methodology to 1

Perform Analysis Cladding Rupture for High Burnup 2

Fuel.

3 The Westinghouse full spectrum LOCA 4

evaluation model was licensed for the purpose of 5

allowing licensees to demonstrate compliance with the 6

emergency core cooling system acceptance criteria 7

described in Title 10 of the Code of Regulations Part 8

50.46. The original full spectrum LOCA EM, evaluation 9

model, was developed to analyze and demonstrate 10 compliance, safety regulations for fuel burnups up to 11 a certain limit.

12 With the Industry moving towards higher 13 burnup fuel, which offers economic and operational 14 benefits, a new methodology was required to address 15 the unique behaviors of this advance fuel cycle. The 16 primary objective of WCAP-18850 is to extend the 17 applicability of Westinghouse's existing FSLOCA, 18 particularly for the risk of cladding rupture and fuel 19 fragmentation, relocation and disbursement.

20 ACRS was established by statute and is 21 governed by the Federal Advisory Committee Act, or 22 FACA. The NRC implements FACA in accordance with its 23 regulations. Additionally, the importance of Sections 24 29 in 1(a), 2(b) of the Atomic Energy Act.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

6 The ACRS advises the Commission with 1

regard to the hazards of proposed or existing reactor 2

susceptibilities and adequacy of the proposed safety 3

standards. In addition, the ACRS is implementing 4

Executive Order 14300 ordering to reform the Nuclear 5

Regulatory Commission dated May 23rd, 2025. Section 6

4(b) of the EO states, in part, the functions of the 7

ACRS shall be reduced to the minimum necessary to 8

fulfill ACRS's statutory obligations and that review 9

by ACRS shall focus on issues that are unique, novel 10 and noteworthy.

11 The review and reporting on new reactor 12 facilities and proposed safety standards are the 13 minimum required functions of the ACRS under Section 14 29 and 2(b) of the Atomic Energy Act. The Commission 15 may refer additional duties to the ACRS in accordance 16 with the Act.

17 Per these regulations and the Committee's 18 bylaws, the ACRS speaks only through it's published 19 letter reports. All member comments should be 20 regarding as only the individual opinion of that 21 member, not a Committee position.

22 All relevant information related to ACRS 23 activities, such as letters, rules for meeting 24 participation and transcripts are located on the NRC 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

7 public website and can be easily found by typing about 1

us ACRS in the search field on the NRC's homepage.

2 The ACRS, consistent with the Agency's 3

value of public transparency and regulation of nuclear 4

facilities provides opportunity for public input and 5

comment during our proceedings. We have received no 6

written statements or requests to make an oral 7

statement from the public.

8 We have also set aside at the time of this 9

meeting for public comments. Portions of this meeting 10 may be closed to protect sensitive information as 11 required by FACA, and the Government and Sunshine Act.

12 Attendance during the closed portion of 13 this meeting will be limited to the NRC staff and its 14 consultants, Westinghouse, and those individuals or 15 organizations that have entered into an appropriate 16 confidentiality agreement. We will confirm that only 17 eligible individuals are in the closed portion of the 18 meeting.

19 The ACRS will gather information, analyze 20 relevant issues and facts and formulate proposed 21 conclusions and declarations as appropriate for 22 deliberation by the full committee. A transcript of 23 the meeting is being kept and will be posted on our 24 website.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

8 When addressing the Subcommittee, the 1

participants should first identify themselves and 2

speak with sufficient clarity and volume so that they 3

may be readily heard. If you are not speaking, please 4

mute your computer on Teams, by pressing *6 if you're 5

on the phone. Please do not use the Teams chat 6

feature to conduct sidebar discussions related to the 7

presentations, rather limit use to limiting chat 8

function to report IT functions.

9 For everyone in the room, please put all 10 your electronic devices in silent mode. And mute your 11 laptop microphone and speakers. In addition, please 12 keep sidebar discussions in the room to a minimum 13 since the ceiling microphone, particularly the one 14 behind me, are live.

15 For presenters, your table microphones are 16 unidirectional, and you'll need to speak into the 17 front of the microphone to be heard. Notice how close 18 I am at the moment.

19 Finally, if you have any feedback for the 20 ACRS about today's meeting, we encourage you to fill 21 out the public meeting feedback form on the NRC's 22 website. All right, we will now proceed with the 23 meeting. And to begin with, following the agenda, 24 public's agenda, I'm going to turn to Scott Krepel for 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

9 staff leadership opening remarks.

1 MR. KREPEL: Well thank you very much.

2 I'm Scott Krepel speaking through a sign language 3

interpreter, as I typically do, and I am the branch 4

chief for the thermal methods and fuel analysis 5

branch. And my staff is going to be presenting today 6

their review of the WCAP-18850. And we will be giving 7

a little bit of background about this topical report.

8 About one year ago my staff presented to 9

you all on another topical reported related to 10 incremental burnup. And so, that was to improve an 11 increase in the burnup limits that the LOCA methods 12 had been analyzed. So this topical report will go 13 beyond that level. And it will support the fuel that 14 the full high burnup for the Industry. And this will 15 feed into the ALS that you will hear about in the 16 future presentations.

17 But I want to emphasize that this method 18 is not intended to address the FFRD explicitly. And 19 so that will not be a topic of this discussion here 20 today. But we will find out more when we get to the 21 ALS presentation. So thank you.

22 CHAIR MARTIN: Okay. Thank you, Scott.

23 And just to go on record here, a couple acronyms.

24 ALS, Alternative Licenses Strategy. FFRD, Fuel 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

10 Fragmentation Relocation and Dispersal.

1 With that introduction we will now turn to 2

Westinghouse. I believe Jerrod Ewing you are on deck 3

here.

4 MR. EWING: I am indeed. Thank you, Mr.

5 Chairman. Thank you, Members, for the opportunity to 6

come in and discussion of our adaption of our Full 7

Spectrum LOCA method to high burnup fuel as part of 8

that EPRI alternative licensing strategy that Scott 9

talked about.

10 This is obviously a very important 11 initiative for the Industry as we like to add more 12 megawatts on the grid. And I'm very excited to be 13 able to present this to you all.

14 I want to thank Scott's staff for their 15 review. It's been a good look at our method over the 16 past year. And appreciate that.

17 And then also want to thank our partners 18 in EPRI as part of this. And our customers as well.

19 Can't forget them. So both those that are here in the 20 room and those that are on the phone. Thank you.

21 CHAIR MARTIN: Do you want to introduce 22 your speaker here --

23 MR. EWING: Sure.

24 CHAIR MARTIN: -- Jeffrey?

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11 MR. EWING: Yes. So we have Mr. Kobelak 1

will be presenting today. He is remote. I'll turn it 2

over to him.

3 MR. KOBELAK: Okay, thank you, Jerrod, and 4

thank you, Chairman Martin. I guess I did want to do 5

a quick sound check. Are you able to hear me clearly 6

in the room?

7 CHAIR MARTIN: We are. Go ahead.

8 MR. KOBELAK: Okay. Perfect. Thank you.

9 Thank you very much.

10 So as Jerrod said, thank you for allowing 11 us an opportunity on your agenda for the current 12 Subcommittee meeting to present on WCAP-18850. This 13 is a very important part of Westinghouse strategy 14 moving forward with, I'd say really three different 15 initiatives which kind of all mean the same thing. We 16 typically refer to this as either ATF, meaning 17 Accident Tolerant Fuel, HEF, meaning High Energy Fuel, 18 or LEU+, all kind of referring to operating fuel 19 products from a higher initial enrichment into a 20 higher burnup regime.

21 So as part of my presentation today for 22 the open session there are really four areas that I 23 would like to cover in detail. The first one I wanted 24 to talk a little bit about how this particular topical 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

12 report interacts with our high energy fuel strategy, 1

how it ties into the EPRI ALS for fuel dispersal. And 2

really also the fourth coming 10 CFR 50.46(a) aspects 3

of the increased enrichment rulemaking.

4 From there I'll move into an overview and 5

purpose of WCAP-18850. The third topic I'd like to 6

touch on is the focus areas within the topical report.

7 And in the open session I will keep this relatively 8

high level, but that will be a primary focus of the 9

closed session presentations, which will happen later.

10 And then finally, just a high level overview of the 11 limitation and conditions associated with the topical 12 report.

13 And I did want to point out there are a 14 lot of acronyms used throughout this presentation. I 15 did try to spell them out. For those who have a 16 printed copy, there are tables at the end with all of 17 the acronyms defined. And I will pause at the end of 18 every slide for any questions.

19 Okay. So I wanted to start out with an 20 overview of the integrated timeline for high energy 21 fuel, or LEU+ deployment. And what you can see on 22 this slide are bars indicating the relative timing of 23 some of the key activities associated with the high 24 energy fuel program.

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13 So that first bar which shows the prime 1

fuel futures, ADOPT fuel pellets and AXIOM cladding, 2

those are all now products which have been reviewed 3

and approved by the NRC available for region 4

deliveries, and in some cases already being delivered 5

as part of regions to utility customers.

6 The second bar there is the one that was 7

referenced by Scott in his opening remarks. The 8

incremental burnup topical report where we extended a 9

number of our codes and methods up to an incremental 10 increase in burnup which is in-between the limit of 62 11 gigawatt days per MTU and the limit that we're seeking 12 for WCAP-18850.

13 The review on that has already been 14 completed. And that is also an approved topical 15 report by the NRC.

16 Where we're at today is working primarily 17 on the next couple of lines here. So the next three, 18 or four really, are all things that are running in 19 parallel. So that third bar down is all of the 20 different codes and methods that are needed to be 21 developed for higher enrichment and higher burnup.

22 And that is the grouping of topical reports that 23 includes WCAP-18850, as indicated on this slide.

24 The fourth one is our chromium coated 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

14 cladding. So that's part of our encore ATF products.

1 And the first topical report to license chromium 2

coated cladding was already submitted to the NRC and 3

it's currently under review by the NRC.

4 And then the third, the third piece there 5

is the LEU+ manufacturing. So that's the facility 6

that will produce the higher enriched fuel. That is 7

also ongoing right now.

8 And then of course complementing many of 9

these activities is the ongoing testing. Whether it's 10 being done by Westinghouse or through cooperative 11 agreements with National Labs on various high burnup 12 and other ATF fuel samples that have been provided by 13 Westinghouse. So the primary purpose in this scheme 14 of WCAP-18850 is to demonstrate cladding rupture will 15 not occur in high burnup fuel thereby precluding any 16 concerns about the consequences of fuel dispersal.

17 CHAIR MARTIN: Okay. Jeff, this is Bob 18 Martin. Just as a point of clarification, and maybe 19 just, and really just for the record.

20 You currently have, Westinghouse currently 21 has, I believe the TR is WCAP-16996, correct? That is 22 your Full Strength LOCA that was approved a number of 23 years ago. This is in addition, because that goes up 24 to certain burnup limit, and then from that burnup 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

15 limit on you have this new topical report. And it is 1

a separate analysis that hangs on each of the 2

original, is that correct?

3 MR. KOBELAK: Yes, that is correct. Maybe 4

just one small clarification is that we are working on 5

extended that WCAP-16996 approved methodology to 6

higher enrichment and higher burnup to demonstrate 7

compliance with the ECCS criteria. So that's a 8

submittal that we're expecting to make at the end of 9

this year.

10 And then as you indicated, WCAP-18850 is 11 an additional separate method and separate analysis 12 that's done in addition to the ECCS analysis specific 13 to demonstrating no cladding rupture, to preclude fuel 14 dispersal. So taking fuel up the higher burnup for 15 LOCA requires both of those components. The analysis 16 for the ECCS criteria and the application of 18850, as 17 envisioned by Westinghouse.

18 CHAIR MARTIN: Okay. So that begs the 19 question, again, obviously you're kind of thinking 20 about it in that step, is why not just one analysis 21 method that covers all these questions?

22 How do you think you need the two 23 separate, or could you not incorporate into a single 24 methodology both the questions related to ECCS 10 CFR 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

16 50.46 compliance and the high burnup into, let's say 1

a single analysis evaluation model?

2 MR. KOBELAK: Yes, I'd say there is a 3

couple reasons for that. The first one is that the 4

fuel of interest for fuel dispersal is not necessarily 5

the same fuel that's going to be limited when 6

assessing the ECCS acceptance criteria. So the 7

population of fuel rods that we're interested in 8

relative to fuel dispersal is a different population 9

of fuel rods than what we're interested in when we're 10 trying to capture a limiting result anywhere in the 11 core to demonstrate compliance with the 50.46 12 criteria.

13 So I would say that's probably the 14 predominant reason. But there are at least one, or 15 maybe a handful of parameters, that are treated 16 differently for conservative reasons in demonstrating 17 compliance with the ECCS criteria versus cladding 18 rupture. So I'd say because of those two factors 19 primarily it was easier, and maybe even required, to 20 develop two separate methods rather than trying to do 21 it all within a single analysis.

22 CHAIR MARTIN: Yes, I appreciate that.

23 And I guess some of that information we might get into 24 in closed session --

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17 MR. KOBELAK: Yes.

1 CHAIR MARTIN: -- right?

2 MR. KOBELAK: Yes, I apologize. I kind of 3

went a little bit higher level with that second 4

response because it is the open session.

5 CHAIR MARTIN: Sure. I understand that.

6 I see that we have a question from our full Committee 7

Chair Walt. Go ahead.

8 MR. KIRCHNER: Yes, good morning. This is 9

Walt Kirchner. I'm looking at this slide. It's a 10 rather interesting choice of words. It's a view 11 graph. Are you designing fuel for dispersal?

12 MR. KOBELAK: Walt, could I maybe ask you 13 to clarify, when you say designing fuel for dispersal 14 what you mean by that?

15 MR. KIRCHNER: Well you just stated that 16 WCAP-18850, you were going to use to demonstrate no 17 rupture for cladding bursts. So, what fuel dispersal 18 are you talking about?

19 MR. KOBELAK: So, yes. So the intent of 20 WCAP-18850 is to demonstrate that there would be no 21 cladding rupture in the higher burnup fuel rods with 22 the intent of then demonstrating that there is no fuel 23 dispersal. And if there is no fuel dispersal, than 24 there is not a need to analyze the downstream 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

18 consequences.

1 So at least in the near-term leveraging 2

this WCAP-18850, in conjunction with EPRI ALS, or 3

potentially the 50.46(a) rulemaking as part of the 4

increased enrichment rulemaking, our intent would be 5

to demonstrate no cladding rupture and no dispersal in 6

the near-term without having change aspects of the 7

fuel design to particularly address fuel dispersal.

8 MR. KIRCHNER: So --

9 MR. KOBELAK: Did that answer your 10 question?

11 MR. KIRCHNER: I just wanted you to go on 12 record and say you're not designing for fuel 13 dispersal. You're developing a methodology to 14 demonstrate that you do not have fuel dispersal?

15 MR. KOBELAK: Yes, that is correct.

16 MR. KIRCHNER: All right, thank you.

17 CHAIR MARTIN: Kevin, you don't have to 18 raise your hand.

19 MR. BARBER: Yes --

20 CHAIR MARTIN: You're in the room.

21 MR. BARBER: Yes, I just wanted Jeff to 22 know that he may be giving me a second here since he's 23 remote.

24 CHAIR MARTIN: Okay, go ahead.

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19 MR. BARBER: I just wanted to note that we 1

were here as part of the increased enrichment 2

rulemaking ACRS Committee in December and January. We 3

presented in conjunction with NEI and the other 4

vendors and utilities in the Industry.

5 And just to be crystal clear, it's still 6

Westinghouse's intention, because we see by precluding 7

dispersal, precluding burnup of high, precluding 8

rupture of high burnup rod we are able to avoid a lot 9

of the uncertainties that are associated with coming 10 up with a high probability statement related to fuel 11 dispersal. I think that our intention is to avoid 12 quantification of uncertainties.

13 And we have talked about it with the staff 14 at a lot of the FFRD workshops we've had over the 15 summer, and we have later this week, to kind of spawn 16 from those ACRS meetings earlier this year. And 17 again, so from our point of view, especially with the 18 status with 50.46(a) rulemaking and the potential 19 demarcation of beyond design basis analysis and design 20 basis analysis.

21 Everything we're presented today is within 22 the context of the design basis analysis. So we're 23 looking at this in a high probability lens. And 24 because there is so much uncertainty from our point of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

20 view related to coolability aspects after the fuel is 1

dispersed, given the nature of the data that's 2

existing in the Industry.

3 As Jeff mentioned, you know, we're working 4

closely, obviously with the National Labs and skip 5

program and invitees, et cetera. We're still trying 6

to keep that same, on that same track where we were 7

nine months ago. And so, just to be crystal clear, 8

for Walt's question, we, at this time, have no 9

intention of coming up with any fuel dispersal high 10 probability calculations.

11 MR. PALMTAG: So this is Scott Palmtag.

12 I just want to follow-up a little bit on the strategy 13 here. So this is all for AXIOM fuel? Chromium coated 14 fuel.

15 MR. BARBER: Yes, and, Scott, we have 16 actually, Jeff is going to give a, maybe, Jeff, if you 17 can jump to the next slide?

18 MR. KOBELAK: Yes, I was going to say, 19 I'll cover that in just a moment, if we can hold the 20 question. I'm going to get to the applicability of 21 the method.

22 MR. ROBERTS: This is Tom Roberts. I want 23 to follow-up on what Kevin and Jeff are saying in 24 response to one question.

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21 If I understand right, there is two 1

branches, at least two branches, they're looking at.

2 One is ALS, which says there would not be a 3

calculation of anything beyond what you could show no 4

plant rupture for. So that would be 1(a) 50 topical 5

report where we can find the method you used.

6 The second approach would be, if you used 7

50.46(a) but it requires some sort of calculation for 8

the larger break, beyond transition break. I think 9

what you said at that future work, that you're not 10 covering that today. And you would cover that either 11 in future topical or some other way. But that would 12 not be a no rupture, I would think, in your current 13 thought. That it would not be demonstrated in these 14 methods with the, you know, the beyond transition 15 break, size break that you could show no rupture, is 16 that right?

17 MR. BARBER: Yes. Yes, that's right. Go 18 ahead, Jeff.

19 MR. KOBELAK: Yes. So I guess I could 20 jump to this slide because I was just about to come to 21 this one. I think I tend to agree that, yes, what you 22 said is consistent with our planned approach. So I 23 put this slide in here just to kind of differentiate 24 the potential approaches exactly as you would outline.

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22 So one possibility of using this 1

WCAP-18850 is under EPRI ALS. So for EPRI ALS we 2

would define a transition break size, which is 3

essentially aligned with the largest connecting line 4

to the main loop RCCS piping.

5 And for all LOCAs that are at break sizes 6

equal to or smaller than the connected line pipping, 7

we would demonstrate no cladding rupture using this 8

method. So that's the top left blue box on this 9

slide.

10 And then for breaks that are larger than 11 that transition break size, we would aim to credit the 12 EPRI ALS method that's currently under review by the 13 staff to demonstrate that a large break LOCA with fuel 14 dispersal was not a credible event. So no explicit 15 analysis is needed. So that's the ALS option that you 16 mentioned.

17 Under the increased enrichment rulemaking, 18 10 CFR 50.46(a) framework, I think that that's a 19 little bit more uncertain until we see what the final 20 state of that rule is. But for the small breaks that 21 are under the transition break size the approach would 22 essentially be identical. We would aim to demonstrate 23 no cladding rupture.

24 And for breaks that are larger than that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

23 transition break size where we would be able to use 1

design basis analysis methods, I think one option 2

could be to potentially leverage the margin that comes 3

out of that more best estimate or nominal analysis and 4

potentially demonstrate that rupture doesn't occur.

5 If that's not the case I do think that it would likely 6

reduce the extent of potential dispersal and then we 7

could look at other means to address coolability.

8 From my perspective, that's something that 9

would be done on a longer timeline given, as Kevin 10 mentioned a lot of the uncertainties that we're still 11 trying to resolve around important phenomena for 12 coolability with dispersed fuel.

13 MR. ROBERTS: Okay, thanks, Jeff.

14 MR. KOBELAK: Did that --

15 MR. ROBERTS: Yes, thank you.

16 MR. KOBELAK: No problem. Did that cover 17 your question?

18 MR. ROBERTS: Yes. Have you done some 19 sort of a quick look analysis that it's plausible to 20 show no rupture for the large break? Or is that --

21 MR. KOBELAK: Yes, Kevin --

22 (Simultaneous speaking.)

23 MR. KOBELAK: Kevin, Kevin actually has 24 done some work on that. We have a paper that will be 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

24 presented at top fuel. I don't know, Kevin, if you 1

want to take a moment just to provide a high level 2

summary?

3 MR. BARBER: Yes. So, I mean, I think 4

that was another hot topic during the December and 5

January ACRS meeting on the rulemaking what exactly it 6

to mean to be beyond design basis in a LOCA 7

methodology. So that's something that we've looked at 8

in, for both Ps and BWRs, which is interesting because 9

obviously FSLOCA is with a state of the art as far as 10 best estimate plus uncertainty methodology, and that's 11 only applicable to PWRs. But we also have 12 methodologies that are Appendix A based that the staff 13 is actually looking at right now for some updates for 14 boilers.

15 And so, you know, it was a very different 16 starting place. Whether you have an appendix A 17 methodology or something like that, that's LOCA.

18 So at the time being, that's in the paper 19 that Jeff mentioned is going to be presented at Top 20 Hill next month, will primarily focus on adaptations 21 to the FSLOCA method. And looking at all the 22 uncertainty contributors that we have in the, as 23 approved topical report and trying to look at 24 different ways of defining what we would consider to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

25 be best estimate true nominal or something that's 1

reflective of beyond design basis analysis 2

requirement.

3 And in that paper we looked at different 4

Westinghouse PWR designs. Obviously from our 5

experience base we understand that some different 6

plants denied attributes leading to more limiting LOCA 7

events or a higher P, calculated PCTs and local 8

oxidation, et cetera.

9 So we used, we looked at a handful of 10 plants to look at this. And as you kind of start 11 ratcheting back these different uncertainty 12 contributors we do see a potential path for avoiding 13 cladding rupture in that beyond design basis accident, 14 with the criteria that would be expected for the 15 treatment uncertainties in that scenario.

16 There are some of the more limiting plant 17 design that are kind of very close to that threshold 18 of cladding rupture. And I think that's something 19 that as a couple will become public for comment, I 20 think the current schedule that the Agency had 21 communicated to Industry and to the public that they 22 will be able to see in February in 2026 to provide 23 public comment.

24 At that point we're hoping to get a little 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

26 more clarity on exactly what we may or may not be able 1

to credit in that beyond design basis circumstance.

2 But we do see, indeed, a large majority of the PWRs 3

expecting to not predict cladding rupture for the 4

large break conditions.

5 MR. ROBERTS: Okay, thank you.

6 MR. BARBER: Just one other note, for the 7

Members knowledge. So one of the things would be 8

taken back from recent meetings here is that we were 9

trying to provide more information in the open 10 session. There are going to be slides that are quite 11 similar to Jeff's presented in the closed session, so 12 if there is, we'll have another kind of opportunity to 13 ask maybe more direct questions related to proprietary 14 information in a few hours.

15 MR. PALMTAG: This is Scott again. So 16 going back to the accident question. So is this all 17 for the accident fuel? And I guess where I'm really 18 going is, are the older fuel designs going to go to 19 the higher burnup or are you only allowing the AXIOM 20 fuel to go to the higher burnup?

21 MR. KOBELAK: So let me, let me, yes, let 22 me just jump to that real quick and then I'll come 23 back. So here is where we're aiming as far as the 24 applicability of what can operate within this higher 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

27 initial enrichment, higher burnup regime.

1 So for cladding we are focused on the 2

AXIOM cladding. At least for near-term applications.

3 We also would expect that the chromium coated cladding 4

could operate in this regime. That that's listed as 5

future because it's not yet approved by the NRC it's 6

currently under review. But we would certainly expect 7

that cladding to be appropriate as well.

8 At present we are not looking to support 9

some of the older alloys, like Zirc-4, ZIRLO. For the 10 extended cycle lengths, and the higher fuel duty, the 11 corrosion and hydrogen becomes less desirable to 12 operate into high burnup than some of the more modern 13 alloys.

14 For fuel we are including both our 15 standard UO2 and ADOPT fuel pellets. No real change 16 to burnable absorbers. We would allow unpoisoned rods 17 if by gad and discrete burnable absorbers within this 18 regime.

19 As far as the specific enrichment and 20 burnup, we'll talk about that more in the closed 21 session. But needless to say, higher than five weight 22 percent and greater than 68 gigawatt days per MTU.

23 And then as far as plant classes, I know 24 it goes a little beyond the question, but this method 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

28 was designed for two-loop, three-loop and four-loop 1

Westinghouse plants as well as C-design plants.

2 MR. PALMTAG: Okay. And just to, I think 3

you said, just to clarify, the existing fuel that the 4

Zirc-4 cladding will not be allowed to go to high 5

burnup fuel?

6 MR. KOBELAK: That's correct. Zirc-4 7

would not. ZIRLO would not. At least as current 8

envisioned, or is supported, by these methods.

9 MR. PALMTAG: Okay.

10 MR. BALLINGER: This is Ron Ballinger. As 11 a practical matter, nobody is using Zirc-4 anymore 12 anyway, right? And that includes ZIRLO. So are there 13 any plants that you would, that are using this 14 material?

15 MR. KOBELAK: There are a handful --

16 (Simultaneous speaking.)

17 MR. BALLINGER: -- by the time it gets 18 approved?

19 MR. KOBELAK: There are actually a still 20 a handful of plants that use ZIRLO cladding material.

21 I think that there is relatively near-term plans for 22 those plants that transition off of them. But there 23 is still some plants that use that material.

24 MR. BARBER: Yes, maybe to expand a little 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

29 bit on Jeff's response. I mean, the majority of the 1

Westinghouse is, utilizes optimizes ZIRLO cladding.

2 And when we licensed AXIOM, and AXIOM 3

presented to the Committee, we showed some comparisons 4

and how optimized ZIRLO and AXIOM cladding performed 5

at these high burnup, high duty scenarios. And one of 6

the, one of the goals at AXIOM was to enable a higher 7

burnup operation to the reasons that Jeff had noted.

8 The corrosion and the hydrogen pick up.

9 I

think the well-established fuel 10 performance aspect, fuel cladding performance aspects 11 that have been discussed with Westinghouse and the 12 Committee and the staff. And certainly others within 13 the Industry. So that's why we were very specific in 14 our, in the slide that Jeff just had up there, and the 15 applicability of what materials and what plant classes 16 would potentially be applied in this method.

17 CHAIR MARTIN: Jeff, this is Bob Martin.

18 MR. KOBELAK: Okay, so -- oh, sorry.

19 CHAIR MARTIN: And I'm also kind of 20 looking at the clock here and looking at your slides.

21 I think looking at what, the slides in between where 22 you're at now and the applicability slide, you're 23 probably, I know the contact we have certainly sat in 24 on several meetings discussing ALS. In fact, you 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

30 identified three topical proportioned to EPRI. We 1

will be looking at those on some level. That one.

2 We had a conversation, I think at our last 3

full committee meeting just two weeks ago where I 4

reported in my impressions of those. So we understand 5

this slide.

6 The next slide, I think we talked 7

something about the background here. Objectives 8

already.

9 The next slide. I think we've already 10 kind of addressed, okay, we know the 50.46 limits, 11 right? Somewhat familiar with the code. Maybe there 12 is some nuance here that you might want to mention, 13 just knowing that there is a difference here between 14 this topical report and your previous that you might 15 want to throw in. Right? You're relying more on 16 WCOBRA/TRAC with this methodology more than, say with 17 ECCS.

18 MR. KOBELAK: Yes, Bob. Maybe, so in the 19 interest of time, if I keep my comments very brief, 20 yes, I would say that it's important to know that 21 WCOBRA/TRAC-TF2 is associated with the FSLOCA EM.

22 It's a very different code than some of the prior 23 codes that you and others may be familiar with. It 24 was updated specifically focusing on the core and fuel 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

31 rod models for high burnup and higher initial 1

enrichment.

2 And then it utilizes fuel performance data 3

from PAD5 for the fuel rod initialization. And PAD5 4

is similarly being updated to support higher 5

enrichment and high burnup.

6 CHAIR MARTIN: And just, can you all 7

agree, I think we saved a little bit of time.

8 MR. KOBELAK: Okay. You want me to resume 9

from Slide 12 then?

10 CHAIR MARTIN: Yes. If you've already 11 talked about it just kind of skip on through.

12 MR. KOBELAK: Okay.

13 CHAIR MARTIN: We can start with 16 if you 14 like, but --

15 MR. KOBELAK: Okay. Yes, not too much 16 more to say on this one. I think we've already talked 17 in the introductory remarks and earlier on about 18 incremental burnup, so I'll move on past this one then 19 just noting that that was approved by the NRC last 20 year.

21 I think we've also kind of covered this 22 slide at length. The purpose of this method. So I 23 will jump then to 16.

24 So this is just a very high level flavor 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

32 of the focus areas within the topical report. A large 1

portion of it is focused on ensuring that we have 2

appropriate fuel rod and core models to analyze higher 3

enrichment and higher burnup fuel.

4 Details will be provided in the closed 5

session, but just to mention here, the areas that we 6

looked at on the fuel rod are the pellet clad and gap 7

conductance model, cladding deformation and cladding 8

rupture. How the fuel rod is initialized.

9 And then a number of things that are kind 10 of newly important to the higher burnup fuel rod. So 11 susceptibility to find fragmentation where we see a 12 lot of this phenomena starting to occur. The 13 potential for fission gas release within the fuel rod 14 during the LOCA transition itself, in addition to the 15 preexisting fission gas in the fuel rods.

16 Looking at pre-birth fuel relocation. So 17 the ability of fuel to fragment and relocate within 18 the rod prior to rupture occurring. And then ensuring 19 that the fuel pellet thermal conductivity is 20 appropriate modeled up the higher burnup.

21 And on the core-wide front, the main focus 22 was on the kinetics and the decay heat. And the idea 23 there is of course to assess those models to make sure 24 that the energy addition being modeled during the LOCA 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

33 transient is reasonably to conservatively captured.

1 CHAIR MARTIN: And maybe I'll just fill in 2

a gap for you. These of course weren't just pulled 3

out of the air, right? There was an NRC PIRT done 20 4

some odd years ago. And I believe you also did maybe 5

your own PIRT type exercise to kind of at least 6

confirm some of the conclusions from the NRC's PIRTs, 7

as well as maybe new insights you gained from the past 8

20 years of maybe in-house testing and just Industry 9

experience, correct?

10 MR. KOBELAK: Yes, that's correct. We 11 leveraged both the Industry PIRT, and as you indicated 12 we did create our own internal PIRT focused on a high 13 burnup fuel rod response during a LOCA so those were 14 factored into determining this list. And I think the 15 NRC is planning to speak a bit more about that in 16 their presentation as well.

17 CHAIR MARTIN: Thanks.

18 MR. KOBELAK: Okay. Here, again, just 19 very high level as far as methodology in the areas of 20 focus within this topical report. So a lot of the 21 discussion centered around the treatment of regions 22 and ensuring that we have appropriate coverage of the 23 entire break spectrum. So when I say regions I'm 24 talking about basically portions of that break 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

34 spectrum which have common phenomena.

1 So as you go through the entire spectrum, 2

different phenomena become important at different 3

break sizes. And we wanted to make sure that all of 4

those were appropriately captured.

5 Reviewing the methodology uncertainties to 6

ensure that they remain appropriate or updating them 7

for higher burnup and higher enrichment fuel rods.

8 And of course, as was mentioned earlier, factoring in 9

information available since the original FSLOCA EM was 10 approved. And then some discussion regarding the 11 treatment of offsite power availability, while there's 12 a few other miscellaneous considerations.

13 And then finally, I have just a handful of 14 slides on the limitations and conditions. And again, 15 I think the NRC staff will cover this in much greater 16 detail in their presentation. But there were two 17 different types of limitations and conditions on the 18 topical report. A subset that were inherited from the 19 base Full Spectrum LOCA EM.

20 So any limitations and conditions from the 21 FSLOCA EM, which remained applicable, were generally 22 imposed on this topical report as well. There were a 23 number of limitations and conditions that weren't 24 applicable since we were focused just on the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

35 prediction of cladding rupture rather than the ECCS 1

criteria as a whole. So things like long-term core 2

cooling, those were not included.

3 And then there is a number that were 4

superseded. So for example, the burnup limit in the 5

FC LOCA EM was superseded by a new limit imposed on 6

this topical report.

7 In summary there is 11 limitations and 8

conditions on this topical report. I just wanted to 9

touch on them at a very high level. The first 10 limitation and condition covers the different PWR 11 designs, which are included within the applicability 12 of the topical report.

13 The second one covers some limitations and 14 conditions relative to the decay heat modeling to make 15 sure it remains appropriate and conservative.

16 Limitation and condition 3 covers the maximum allowed 17 fuel rod average burnup. Limitation and Condition 4 18 covers the fuel performance data that is allowed to be 19 used for initialization of the fuel rods.

20 Limitation and Condition Number 5 is 21 specific to a

particular uncertainty analysis 22 parameter. And Limitation and Condition Number 6 23 covers requirements related to the seed and the 24 uncertainty analysis inputs. As well as what needs to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

36 be done if we get an unacceptable analysis result and 1

reporting of the analysis ranges to the NRC.

2 Limitation and Condition 7

is a

3 requirement relative to the offsite power availability 4

analyzed. Limitation and Condition 8 just pulls 5

forward three of the limitations and conditions from 6

the base FSLOCA EM.

7 Limitation and Condition 9 covers the 8

applicable cladding materials and fuel designs that I 9

mentioned on an earlier slide. Limitation and 10 Condition 10 covers the allowable burnable absorbers 11 that I also presented earlier. And then Limitation 12 and Condition 11 covers the maximum initial fuel rod 13 enrichment.

14 So that was all the remarks I had for the 15 open session. Happy to take any other questions.

16 CHAIR MARTIN: A little gun shy to ask 17 some questions because of course it might touch on 18 proprietary content. It's not so unusual for it to be 19 a little quite during an open session when we know 20 there is a closed session later.

21 I will turn to my colleagues here in the 22 room or online. Are there any questions to 23 Westinghouse before we transition to the staff? Not 24 seeing any I will thank you all very much.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

37 And we'll make that transition over to the 1

staff's presentation. Give us a few minutes online.

2 MR. KOBELAK: Okay, thank you very much.

3 CHAIR MARTIN: Thank you.

4 Are you ready?

5 MR. LEHNING: Yes, we are ready. It's my 6

pleasure, and our pleasure, to be here in front of you 7

all this morning. My name is John Lehning from the 8

Nuclear Methods and Fuel Analysis Branch in the Office 9

of Nuclear Reactor Regulation, as are my colleagues 10 too who are here, and one who is virtual. One of us 11 who participated in the review, Patrick right now has 12 left the Agency but was a principle contributor. And 13 we present somewhat on his behalf.

14 We will tag team this presentation. We'll 15 introduce ourselves as we transition speakers. I'm 16 just going to help out, do the introductions right 17 now. So to my left, Brandon, do you want to introduce 18 yourself really quickly?

19 MR. WISE: I'm Brandon Wise in the Nuclear 20 Methods and Fuel Analysis Branch in the Division of 21 Safety Systems.

22 MR. LEHNING: And Jack?

23 MR. VANDE POLDER: I am Jack Vande Polder 24 in the Division of Safety Systems, Nuclear Methods and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

38 Fuel Analysis Branch.

1 MR. LEHNING: And remotely our lead 2

review, Jeremy is going to take it from here and do 3

the first five slides I think. So go ahead, Jeremy.

4 MR. DEAN: Great, thank you, John. My 5

name is Jeremy Dean, I'm the lead reviewer for this 6

topical report. As said, I'm in the same branch as my 7

colleagues and report to Scott Krepel.

8 So we're going to cover, here in the open 9

session, just at a high level, what the staff's review 10 of this topical report. So next slide, John.

11 Here is just a quick presentation outline.

12 This is more important in the closed session to show 13 where we spent most of our time reviewing. And then 14 the, trying to be brief, we'll try to skip through 15 these pretty fast.

16 Next slide. So Westinghouse submitted a 17 topical report, WCAP-18850, to extend Full Spectrum 18 LOCA to incorporate effects of high enrichment and 19 high burnup. During this one new phenomena is of 20 primary interest for this. For fuel fragmentation, 21 relocation dispersal.

22 And one means of addressing that is to 23 prevent rods that are susceptible to this phenomena 24 and just prevent their rupture from occurring. And 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

39 from the NRC staff's point of view, right, this is the 1

highest standard you can apply to this in regards to 2

health and safety of the public.

3 So WCAP-18850 provides a method of 4

applying FSLOCA, the original framework, to determine 5

with high probability that cladding rupture is not 6

going to occur during a loss coolant accident.

7 Next slide, John. So a little bit of 8

background on the original Full Spectrum LOCA. Just 9

a best estimate, realistic loss of coolant accident 10 and evaluation model that accounts for uncertainties.

11 It covers the entire break spectrum, up to a full 12 double ended guillotine break. It was approved in 13 2017, and applicable to Westinghouse three and 14 four-loops.

15 And as a sub note, they're working on 16 expanded their trivariate analysis for 50.46 17 acceptance criteria to other pressurized reactor water 18 designs. And to be clear, the FSLOCA methodology does 19 not address fuel dispersal, there is so many 20 complexities with dispersal of fuel into the coolant.

21 Whether it meets regulations, the uncertainties of 22 coolability and where that fuel goes. So those, there 23 are some models included for fragmentation relocation 24 in the initial model, but 18850 will not address that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

40 piece.

1 Next slide, John.

2 CHAIR MARTIN:

You didn't include 3

dispersal, that's the key, right?

4 MR. DEAN: Yes.

5 CHAIR MARTIN: Okay.

6 MR. DEAN: Absolutely.

7 CHAIR MARTIN:

If

anything, the 8

fragmentation relocation is really the, kind of 9

creating more local power at the rupture site, which 10 gives you --

11 MR. DEAN: Yes. So again, we'll get into 12 that in the closed section. But right, once the 13 pellet starts to become very, very small and 14 fragmented along it's green boundaries, it can 15 relocate axially in the fuel rod. In particular, if 16 it starts to balloon it can start to pack into the 17 region. And models need to be included for that.

18 MR. LEHNING: If you can hear me? This is 19 John Lehning speaking. I'll just add, we will touch 20 on a little bit of the distinction. And, you know, 21 obviously the full spectrum when it was approved, the 22 amount of knowledge we had was not quite up to what we 23 know now, and so we'll touch just briefly on some of 24 the distinctions there.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

41 MR. DEAN: Yes. Next slide, John, unless 1

there is any more questions on that one?

2 Really quickly on the review timeline.

3 18850 was submitted in February 2024. We did our 4

acceptance review in the spring. We spent the summer 5

reviewing and preparing for an audit in the fall with 6

numerous questions going into that. We were able to 7

resolve a lot of those and issued RAIs in November of 8

last year.

9 Westinghouse, just so you know, they 10 responded in two separate responses to answer all of 11 our questions. Then we took the latter part of the 12 spring into mid-summer to come up with our draft 13 safety evaluation. And now we're here ready to 14 present to you folks on the Subcommittee meeting.

15 Next slide. So I'm going to turn it over 16 to Jack here and let him talk about the regulatory 17 background and what's applicable there.

18 MR. VANDE POLDER: Hello, everyone. So 19 here are the key regulatory requirements and guidance 20 for LOCA. Of note, our 10 CFR 50.46 and general 21 design criteria 35. 10 CFR 50.46 is the main reason 22 which guided Westinghouse into their approach. And 23 then GDC 35 had the LOOP requirements, Loss of Offsite 24 Power, for Westinghouse in their review.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

42 Next slide please. So Westinghouse 1

WCAP-18850, the methodology must be capable of 2

predicting an occurrence of cladding rupture. The 3

methodology is based on the previously approved Full 4

Spectrum LOCA methodology. Westinghouse evaluated the 5

PIRT phenomena for increased burnup. And there were 6

two key model updates that were needed. Fuel rod 7

modeling and kinetics and decay heat modeling.

8 Next slide please. For further detail --

9 CHAIR MARTIN: One point of clarification.

10 So when you say two main areas, okay, fuel, but under 11 that title there are several --

12 MR. VANDE POLDER: Yes.

13 CHAIR MARTIN: -- updates.

14 MR. VANDE POLDER: Yes, there are several 15 updates.

16 CHAIR MARTIN: Okay. As opposed to, I 17 guess kinetics decay heat. There are obviously two 18 distinct phenomena due to the same site closure 19 models, okay.

20 MR. VANDE POLDER: Yes. So to the PIRT, 21 Westinghouse evaluated the FSLOCA PIRT and the 22 Industry high burnup PIRT. They didn't identify, 23 there were no new phenomena identified that needed to 24 be evaluated.

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43 They did find some, there were three 1

categories of areas. There were things that would be 2

conservative or would have no effect if left as the, 3

such as void generation or the water volume. There 4

were several things that need to be change, such as 5

the after mentioned fuel rod models and decay heat.

6 And then there are items that we precluded 7

by their methodology, such as time and location of 8

bursts. The NRC staff found that the PIRT evaluation 9

by Westinghouse was comprehensive and adequate.

10 Next slide. So the fuel rod models, it's 11 more complex than just one model as there are several 12

things, such as cladding

rupture, cladding 13 deformation. All the models that go into the fuel rod 14 modeling would be impacted or potentially impacted so 15 Westinghouse had to evaluate those. So the details 16 for these are a little too proprietary though so they 17 will be discussed in the closed section.

18 And I will be handed it off to my 19 colleague Brandon.

20 MR. WISE: Thank you. I am Brandon Wise 21 and I'm going to discuss the kinetics in the heat 22 model, as well as the cladding rupture methodology.

23 Westinghouse updated the WCOBRA/TRAC-TF2 24 kinetics and the heat models to be applicable to the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

44 higher burnup and higher enrichment readings. The 1

updates are performed used PARAGON2, which was 2

approved in June 2021. That topical report has an 3

enrichment and power applicability that bound 4

WCAP-18850.

5 These same updates were applied in 6

WCAP-18446, which is the incremental burnup extension.

7 And WCAP-18773, which is the high enrichment for PWR 8

topical report. In both those topical reports the 9

staff found that the methodology could prove the new 10 kinetics and decay heat model was acceptable.

11 The staff found that the model is 12 acceptable and that the heat sources that are being 13 modeled are appropriately characterized for the 14 purposes of cladding rupture calculations. For the 15 cladding rupture methodology I'm going to discuss some 16 of the important topics proposed in WCAP-18850.

17

First, the FSLOCA EM is the base 18 methodology with some modifications discussed in 19 WCAP-18850. The purpose of the methodology is to 20 preclude cladding rupture of fuel rods susceptible to 21 cladding fragmentation. The cladding rupture analysis 22 is performed parallel to a typical FSLOCA EM analysis 23 demonstrating compliance with 10 CFR 50.46 Bravo 133.

24 The cladding rupture -- sorry. CAP-18850 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

45 provides a new analysis region. That's region 1(b),

1 which lies between the small and large break 2

representing the intermediate break spectrum. And 3

closes a methodology for analyzing that region, which 4

is a mix between Region 1 and 2, being mostly related 5

to Region 1. Which is small break LOCA. WCAP-18850 6

also proposes a few changes to Region 1 and 2 7

uncertainty analysis for cladding rupture 8

calculations.

9 CHAIR MARTIN: Point of clarification on 10 cladding rupture. Historically LOCA evaluation models 11 have leveraged the latest NUREG-0630, right? Looking 12 over at John, he's nodding his head so I did remember 13 something from a long time ago.

14 And it's a very, it's a relatively simply 15 type of cladding cooling rupture model. Has 16 Westinghouse departed from that? Is that a 17 proprietary type thing?

18 And in general, are fuel vendors moving 19 away from that old lot?

20 MR. LEHNING: We will cover somewhat in 21 the closed session in more detail.

22 CHAIR MARTIN: Okay.

23 MR. LEHNING: I don't want to speak out of 24 turn here. I will say that I think just in general, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

46 in the broad sense, that vendors in general tend to 1

use that, I think as you know, maybe their own 2

versions or their own sort of data sets. It may 3

sometimes be cladding specific or other times they may 4

demonstrating the certain claddings fall within other 5

data that they have, but basically I would say that 6

the overall methods and approaches are highly 7

consistent with what was developed for that 8

NUREG-0630.

9 CHAIR MARTIN: Okay. Maybe some of the 10 parametrization is a little different based on, say 11 fuel specific testing?

12 I will say that if our Committee, I think 13 it was a couple years ago, so prior to a couple 14 members, did visit Westinghouse and we did get to look 15 through their testing program where they were 16 specifically looking at FFRD phenomena and trying to 17 improve their fuel designs.

18 And I can see how that, that work could 19 feed into a new model. Or at least maybe, maybe a 20 parametrization, re-parametrization, of an old model.

21 MR. LEHNING: And I'm sure Westinghouse 22 has a slide or two on that, and the staff does too, in 23 our closed presentation.

24 CHAIR MARTIN: Okay.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

47 MR. LEHNING: So we will talk more on --

1 CHAIR MARTIN: All right, thanks.

2 MR. WISE: Next slide please. So based on 3

the changes discussed on the previous slide the NRC 4

staff made the following findings. We found that the 5

adaptation of the FSLOCA EM is a base methodology 6

appropriate to prevent cladding rupture calculations.

7 Including in that there were several model 8

updates that were found to be acceptable for the 9

applicable burnup and enrichment range. We also found 10 that the methodology was supported by significant data 11 and has been acceptable for predicting the occurrence 12 of cladding rupture and rods susceptible to cladding 13 fragmentation.

14 Additionally the staff compiled a

15 definition of Revision 1(b) and its treatment of the 16 FSLOCA EM to be comprehensively described and 17 acceptable. Found that the proposed changes to 18 Revision 1 and uncertainty analysis is acceptable.

19 The exact details of these two topics are 20 closely provided here. And we discuss it in more 21 detail in the closed session. But we can say that the 22 proposed treatments are supported by sensitivity 23 studies compared to calculations of engineering 24 judgment that the staff found to be acceptable.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

48 Now I'll turn the presentation back to 1

Jeremy Dean, who will discuss limitations and 2

conditions.

3 MR. DEAN: Thank you, Brandon. So for 4

limitations and conditions the staff asked 5

Westinghouse to address all the 15 limitations and 6

conditions from their FSLOCA evaluation model.

7 We also, we did this for a couple of 8

reasons. One, it helps the NRC staff, you know, if 9

the applicant helps define the range of applicability 10 for their analysis rather than having the staff do 11 that for them, it's advantageous to them because we 12 would likely be more restrictive. And so in some 13 cases we did modify the suggested limitations and 14 conditions.

15 So several were directly propagated.

16 These were limitations and conditions 3, 12 and 13.

17 Several were modified, 2, 4, 5, 6, 8, 11 and 15.

18 Next slide. The NRC's draft safety 19 evaluation ultimately resulted in 11 limitations and 20 conditions that the licensees must adopt. Again, 21 these were originally proposed by Westinghouse in 22 their submittal. And we modified several of these.

23 We covered three limitations and 24 conditions during, in this open session, but the most, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

49 I would say interesting and more restrictive, 8, will 1

be discussed during the closed session.

2 Next slide. And here are the ones that 3

were directly transferred. And we can talk a little 4

bit during the open session here, so.

5 Limitation and Condition 1 can only be 6

applied to Westinghouse two-loop and combustion 7

engineering plants after the base models have been 8

approved for these applications. And the applicable 9

differences and deviations are addressed. And what 10 that really means is the FSLOCA EM needs to then 11 include these new reactor types.

12 As Jeff alluded to in his portion, 13 Limitation and Condition 9, they're only applying this 14 to standard UO2 pellets and their ADOPT pellets. And 15 it's only applicable to AXIOM cladding.

16 And then Limitation and Condition Number 17 10 is just a repeat of Jeff's. That's it's applicable 18 to unpoisoned fuel, fuel with inoperable, fuel 19 burnable absorbers, particularly gadolinia. And it 20 doesn't preclude the other discrete burnable absorbers 21 that Westinghouse may use.

22 Next slide.

23 CHAIR MARTIN: Just a quick question. Bob 24 here.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

50 MR. DEAN: Sure.

1 CHAIR MARTIN: You mentioned, previous 2

slide, about limits, limitations and conditions 3

related to range of applicability. And of course, 4

maybe pushing that back to Westinghouse to incorporate 5

that under PR. Some range of applicabilities relate 6

to inputs that are easy to control. Were any of those 7

ranges of applicabilities related to a calculated 8

parameter, variable that might have to be tracked by, 9

tracked through the calculation and require maybe a 10 little bit more effort on their part to assure maybe 11 a wording or something like that?

12 Sometimes that happens more than often 13 than not it's the former. Where they're relatively 14 easy. But sometimes you're dealing with, say some 15 closure limit. And as a calculated result that is 16 constrained by a range of applicability and it has to 17 he checked.

18 MR. LEHNING: Jeremy, this is John.

19 MR. DEAN: Yes, go ahead.

20 MR. LEHNING: And I guess I, to answer 21 that one. And Westinghouse, feel free to jump in and 22 offer your perspective. I don't think that there are 23 any like that that are, and I'm sort of reading your 24 question as if maybe sometimes, I've seen where maybe 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

51 if a certain model gets activated, maybe you have to 1

go back and check through the files and output and 2

see.

3 CHAIR MARTIN: Yes.

4 MR. LEHNING: I don't think there are any 5

like that. I think all the ones that are associated 6

with it, that come to my mind, are ones where either 7

a parameter is set right at the beginning and it's 8

just to wrap around, there is nothing to check or so 9

forth. But, Westinghouse, if you have a different 10 view please feel free to address that.

11 MR. KOBELAK: No, John. This is Jeff 12 Kobelak from Westinghouse. I agree with your 13 assessment relative to the parameters. And maybe the 14 only other thing I would add are, there are one or two 15 that are kind of more procedural in terms of reporting 16 certain results to the NRC. Or at least reporting 17 results under certain conditions. And we have placed 18 those type of requirements into our analysis guidance 19 to make sure that they are not lost or forgotten as we 20 apply these methods.

21 CHAIR MARTIN: John, would those guidance 22 documents be something you reviewed?

23 MR. LEHNING: I don't know that we 24 reviewed any of the guidance documents of how 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

1 2

3 4

5 6

7 8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 52 Westinghouse does their calculations as part of this review. It might have been during some of the initial review of the base methodology. We may have, we did a lot of audits and that might have been.

I know some of the statistical parts of this, we did talk through at a high level. I don't know that we reviewed their actual documents, but we did get pretty detailed into that part for sure.

CHAIR MARTIN: Okay, appreciate that.

MR. DEAN: Yes, I concur with that. Most, it's really bias in certain parameters that are applicable to this, you know, sort of single variate for fuel rod burst that would be different than you would do for the tried varied analysis for 50.46 acceptance criteria.

All right, so conclusions. So during our review we found that WCAP-18850 does provide an acceptable approach for determining the high probability that cladding rupture will not occur.

We'll go into great detail in the closed session of how we were able to accomplish that. And of course, that's for fuel rods that are only susceptible to find fragmentation.

The staff conclusions are, of course, predicated on the methodology being used within its NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

53 approved range of applicability. And we'll outline 1

that a little bit more as well in the closed section.

2 And specifically addressing all the limitations and 3

conditions of Section 4 of the safety evaluation. I 4

believe that's the last slide.

5 CHAIR MARTIN: It is.

6 MR. DEAN: So any more questions we can 7

answer for you during this open session?

8 MR. ROBERTS: Yes, this is Tom Roberts.

9 I was wondering if you could resolve the arithmetic 10 for these license, LNC slides?

11 If you start with the first slide it says 12 there are 15 that were assessed, then the next part of 13 that slide says there were ten that were adopted or 14 modified. That's ten of 15. And then it says on the 15 next slide you adopted 11. Then the slide after that 16 lists three that aren't on that first slide, which 17 brings you up to, you know, I think it was 13. So 18 what is it arithmetic here?

19 MR. LEHNING: This is John Lehning --

20 (Simultaneous speaking.)

21 MR. DEAN: Go ahead, John.

22 MR. LEHNING: So the three that are shown 23 in the open presentation, those are part of the 11 24 that are on Topical Report WCAP-18850. There are 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

54 eight more that we will cover that will be in the 1

closed session.

2 Now the 15 that came from the original 3

base methodology it looks like, yes, I think if you 4

add those up, which I hadn't necessarily thought to do 5

before, but there are three, four, five, six, seven, 6

eight, nine, ten there. So none of those that are in 7

the WCAP-18850 propagated from the base method. And 8

apparently there is one that came in that essentially 9

is a new one that is not sort of covered in this 10 paradigm based on the way it's presented here. So 11 hopefully that's resolve the numbers.

12 And obviously out of this --

13 MR. DEAN: Remember also --

14 MR. LEHNING: -- 15 that there were five 15 that did not, were not applicable for whatever reason.

16 And obviously the different objectives of these 17 analyses, so some of them were perceived by 18 Westinghouse and the staff found acceptable that they 19 weren't necessary to do the calculation for this 20 cladding rupture.

21 MR. ROBERTS: So there were 15, five were 22 resolved as not applicable, and then one was added?

23 That's how you get to 11?

24 MR. LEHNING: That seems to be correct.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

55 I hesitate to, I mean, because like I said, we hadn't 1

really done that math but that is what I believe to be 2

true.

3 MR. DEAN: Hey, John --

4 (Simultaneous speaking.)

5 CHAIR MARTIN: -- details coming in the 6

closed session, I guess we can rectify the numbers 7

there.

8 MR. DEAN: -- just a little bit tricky 9

that one limitation and condition pulls over three 10 into one. So yes, at first glance it looks like maybe 11 we didn't add it up right, but I assure you we did.

12 MR. ROBERTS: That is all right. Okay, 13 thank you.

14 CHAIR MARTIN: Any further questions or 15 topics of discussion from the Committee? Consultant 16 stab at this? Anything on your mind, Ron?

17 MR. BALLINGER: No.

18 CHAIR MARTIN: Okay. I think at this 19 point we need to go to public comments. Looking over 20 here? Okay. So if there is any member of the public 21 that has a burning question, this is your opportunity 22 to speak up.

23 Please use, if you're on Teams, please 24 raise your hand and we will give you a couple minutes 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

56 here to provide your comment. Is there anyone out 1

there? Gave it a good 15 seconds, huh? All right, 2

not seeing any I believe we can close our open 3

session.

4 And of course there is some logistics that 5

we have to take care of going into the closed session 6

to make sure everyone that is here is allowed to be 7

here. And for those of you that can be here 8

virtually, I believe there is going to be a, there is 9

a different link so be aware of that.

10 And we're going to have a break. Right 11 now it is 9:41. We're going to break until 10:00.

12 It's what's on the schedule. So meeting is recessed 13 until 10:00.

14 (Whereupon, the above-entitled matter went 15 off the record at 9:41 a.m.)

16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com

NRC Staffs Review of Westinghouse Topical Report WCAP-18850-P, Adaptation of the FULL SPECTRUM LOCA (FSLOCA )

Evaluation Methodology to Perform Analysis of Cladding Rupture for High Burnup Fuel Open Presentation to Advisory Committee on Reactor Safeguards, Accident Analysis Subcommittee September 16, 2025 J. Dean, U.S. NRC B. Wise, U.S. NRC J. Vande Polder, U.S. NRC J. Lehning, U.S. NRC

Presentation Outline Topic

1. of Slides Introduction / Background 4

Review History 1

Requirements and Guidance 1

Technical Evaluation (open portion) 7

• Modeling Basics (1)

• Phenomenon Identification and Ranking (1)

• Fuel Rod Modeling Updates (1)

• Kinetics and Decay Heat Model Updates (1)

• Cladding Rupture Methodology (3)

Applicability, Limitations and Conditions 3

Conclusions 1

Acronyms 1

Presentation Total 18 2

Introduction

• Westinghouse proposed WCAP-18850-P to extend its approved FULL SPECTRUM LOCA methodology to higher fuel enrichment and burnup levels 3

• One means of addressing fuel dispersal is preventing rupture of fuel rods susceptible to fragmentation

• WCAP-18850-P provides a method for applying FSLOCA framework to determine with high probability that cladding rupture will not occur during a LOCA

FSLOCA Background WCAP-16996-A

• FSLOCA is a realistic LOCA evaluation model that accounts for uncertainty

• Methodology addresses scenarios across entire postulated spectrum of break sizes

• Current methodology applicable to Westinghouse 3-and 4-loop pressurized-water reactors was approved in 2017

- Extensions currently being pursued for additional pressurized-water reactor designs

• Licensed FSLOCA methodology does not address fuel dispersal

- Models are included for fragmentation and relocation 4

Review Timeline 5

WCAP-18850-P Submitted Feb May Acceptance Review Complete Oct Audit Nov RAI RAI Responses

1. 1 #2 Jan Mar July Draft SE Sep ACRS SC Meeting NRC Westinghouse 2024 2025

Key Regulatory Requirements and Guidance for LOCA

• 10 CFR 50.46

• General Design Criterion 35

• NUREG-0800, Standard Review Plan

- Chapter 15.6.5, Loss-of-Coolant Accident

- Chapter 15.0.2, Review of Transient and Accident Analysis Methods 6

• Regulatory Guide 1.157, Best-Estimate Calculations of Emergency Core Cooling System Performance

• Regulatory Guide 1.203, Transient and Accident Analysis Methods

Loss-of-Coolant Accident Analysis Methods

• WCAP-18850-P methodology must be capable of predicting occurrence of cladding rupture during a LOCA

- Modeling based on FULL SPECTRUM LOCA methodology (WCAP-16996-P-A)

- WCOBRA/TRAC-TF2 code 7

• Westinghouse evaluated PIRT phenomena for impacts of increased burnup

• Key model updates in two main areas

- Fuel rod modeling

- Kinetics and decay heat modeling

Phenomena Identification and Ranking

• WCAP-18850-P evaluated the FSLOCA PIRT and an industry high burnup PIRT.

- No new phenomena identified

- Updates to WCOBRA/TRAC-TF2 and other models where appropriate

• Fuel Rod Models, Kinetics and Decay Heat, Burst Criteria

- Burst size, location, etc. determined to be unimportant.

• The NRC staff found that the PIRT evaluation is comprehensive and adequately identifies where model updates are needed to account for FFRD and high burnup and enrichment.

8

Fuel Rod Model Updates

• WCAP-18850-P addresses fuel rod models that could be impacted by increased burnup:

- Pellet-cladding gap conductance

- Cladding deformation

- Cladding rupture

- Fuel rod initialization

- Susceptibility to fine fragmentation

- Transient fission gas release

- Pre-burst fuel relocation

- Fuel rod material properties

• Proprietary details discussed further in closed session 9

WCOBRA/TRAC-TF2 Kinetics and Decay Heat Model Updates Westinghouse updated the models to incorporate increased enrichment and higher burnup

- Nuclear physics data provided by PARAGON2 (Approved June 2021)

Similar model updates were previously approved in:

- WCAP-18446-P-A (Approved June 2024)

- WCAP-18773-P (Final SE Issued July 2025)

The NRC Staff found the model updates to be acceptable because they were consistent with previous approvals. Unique characteristics associated with the expanded range of applicability and cladding rupture calculations were examined.

10

Cladding Rupture Methodology

• WCAP-18850-P

- Uses the FSLOCA EM as a base methodology and adapts it as appropriate

- The purpose of the methodology is to preclude cladding rupture of rods susceptible to fine fragmentation.

• The WCAP-18850-P cladding rupture analysis is performed parallel to the WCAP-16996-A FSLOCA base analysis that demonstrates compliance with 10 CFR 50.46(b)(1)-(b)(3).

- Defines a new break spectrum region, Region IB

- Proposes a methodology for analyzing cladding rupture in Region IB

• A mix of Regions I and II, with some unique characteristics

- Proposes changes to Region I and II uncertainty analyses 11

Cladding Rupture Methodology

• The NRC Staff

- Found the adaptation of the FSLOCA EM base methodology appropriate to perform cladding rupture calculations. Several models were updated to incorporate the increase range of applicability for burnup and enrichment

- Found the methodology to be supported by significant data and is acceptable for predicting the occurrence of cladding rupture of rods susceptible to fine fragmentation.

12

Cladding Rupture Methodology

• The NRC Staff

- Found the definition of Region IB and its treatment in the FSLOCA EM to be comprehensively described and acceptable.

- Found the proposed changes to Region I and II uncertainty analyses acceptable.

- The proposed treatments are supported by sensitivity studies, comparison calculations, and engineering judgment.

13

Review of Limitations and Conditions from FSLOCA (WCAP-16996, R1)

• Westinghouse assessed the 15 limitations and conditions from WCAP-16996, R1, for applicability to the derivative WCAP-18850-P methodology

• Applicable limitations and conditions from WCAP-16996, R1, were propagated into WCAP-18850-P topical report

- Direct propagation of FSLOCA L&Cs 3, 12, and 13

- Others adopted in modified form (FSLOCA L&Cs 2, 4, 5, 6, 8, 11, 15) 14

Limitations and Conditions for WCAP-18850-P

• The NRC staffs draft safety evaluation contains 11 limitations and conditions that licensees adopting the methodology must address

- These limitations were originally proposed by Westinghouse in WCAP-18850-P

- NRC staff modified several of these limitations

• Three limitations and conditions will be covered in the open presentation

- Remaining eight will be discussed during the closed presentation 15

Limitations and Conditions:

Methodology Applicability Per Limitation and Condition 1, the methodology can only be applied to Westinghouse 2-Loop and Combustion Engineering plants after

- The base model is approved for these applications

- Applicable differences and deviations have been addressed Per Limitation and Condition 9, WCAP-18850-P is only applicable to fuel products with

- Uranium dioxide or ADOPT fuel pellets

- AXIOM cladding Per Limitation and Condition 10, WCAP-18850-P is only applicable to

- Unpoisoned fuel

- Fuel with integral fuel burnable absorbers

- Fuel with gadolinia (this limitation does not preclude use of discrete burnable absorbers) 16

Conclusions

• The NRC staff found the WCAP-18850-P methodology provides an acceptable approach for determining, with high probability, that cladding rupture will not occur for fuel rods susceptible to fine fragmentation

• The NRC staffs conclusions are predicated upon

- The methodology being used within its approved range of applicability

- Licensees acceptably addressing limitations and conditions in Section 4.0 of the staffs safety evaluation 17

Table of Abbreviations 10 CFR Title 10 of the Code of Federal Regulations ACRS Advisory Committee on Reactor Safeguards FULL SPECTRUM LOCA, FSLOCA WCAP-16996-P-A, Revision 1, 'Realistic LOCA Evaluation Methodology Applied to the Full Spectrum of Break Sizes (Full Spectrum LOCA Methodology)

L&C Limitation and Condition LOCA Loss-of-Coolant Accident NRC U. S. Nuclear Regulatory Commission PIRT Phenomenon Identification and Ranking Table RAI Request for Additional Information SC Advisory Committee on Reactor Safeguards Subcommittee SE Safety Evaluation WCAP-18850 WCAP-18850-P/NP, Revision 0, Adaptation of the FULL SPECTRUM LOCA (FSLOCA) Evaluation Methodology to Perform Analysis of Cladding Rupture for High Burnup Fuel 18

Westinghouse Non-Proprietary Class 3 ADOPTTM, AXIOM, FSLOCA', and FULL SPECTRUM' are trademarks of Westinghouse Electric Company LLC, its affiliates, and/or its subsidiaries through the United States of America and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners.

Westinghouse Electric Company 1000 Westinghouse Drive Cranberry Township, PA 16066

© 2025 Westinghouse Electric Company LLC All Rights Reserved Westinghouse Open Session Slide Package for the ACRS Subcommittee Meeting on WCAP-18850-P/NP (Non-Proprietary)

September 2025 LTR-NRC-25-47, Enclosure 2 Page 1 of 27

1 Westinghouse Non-Proprietary Class 3

© 2025 Westinghouse Electric Company LLC. All Rights Reserved.

ADOPT, AXIOM, FSLOCA and FULL SPECTRUM are trademarks or registered trademarks of Westinghouse Electric Company LLC, its subsidiaries and/or its affiliates in the United States of America and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners.

© 2025 Westinghouse Electric Company LLC All Rights Reserved LTR-NRC-25-47, Enclosure 2 Page 2 of 27

Westinghouse Non-Proprietary Class 3 2

© 2025 Westinghouse Electric Company LLC. All Rights Reserved.

Jeffrey Kobelak Westinghouse Electric Company September 2025 Overview of WCAP-18850: Adaptation of the FULL SPECTRUM LOCA (FSLOCA) Evaluation Methodology to Perform Analysis of Cladding Rupture for High Burnup Fuel LTR-NRC-25-47, Enclosure 2 Page 3 of 27

3 Westinghouse Non-Proprietary Class 3

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Overview

• Interaction of WCAP-18850 with Westinghouse high energy fuel (HEF) /

accident tolerant fuel (ATF) / low enriched uranium+ (LEU+) program

- Fuel dispersal during a postulated LOCA and Electric Power Research Institute (EPRI) alternative licensing strategy (ALS)

• Overview and purpose of WCAP-18850 (Westinghouse Cladding Rupture Methodology)

• Focus areas within topical report

• Topical report limitations and conditions (L&Cs)

LTR-NRC-25-47, Enclosure 2 Page 4 of 27

Westinghouse Non-Proprietary Class 3 4

© 2025 Westinghouse Electric Company LLC. All Rights Reserved.

Westinghouse Activities for HEF / ATF / LEU+

Introduction to WCAP-18850 Methodology Overview Limitations and Conditions LTR-NRC-25-47, Enclosure 2 Page 5 of 27

5 Westinghouse Non-Proprietary Class 3

© 2025 Westinghouse Electric Company LLC. All Rights Reserved.

WCAP-18850 will be leveraged to address fuel dispersal within codes and methods for LEU+

5 WCAP-18850 EnCore High Energy Fuel Program Integrated Timeline for LEU+ Fuel Deployment High Burnup LTR-NRC-25-47, Enclosure 2 Page 6 of 27

6 Westinghouse Non-Proprietary Class 3

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Fuel Fragmentation, Relocation, and Dispersal (FFRD)

Figures 4-41 and 4-42 of NUREG-2121 55 GWd/MTU Rod Average Burnup Large Fuel Fragments 72 GWd/MTU Rod Average Burnup Fine Fragmentation Addressing fuel dispersal for design basis accidents such as LOCA is one key element of code and method updates LTR-NRC-25-47, Enclosure 2 Page 7 of 27

7 Westinghouse Non-Proprietary Class 3

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Fuel Dispersal EPRI ALS versus Draft Increased Enrichment Rulemaking 7

Westinghouse has aligned with industry to support the EPRI ALS for Fuel Dispersal

• Accounts for the extremely low likelihood of occurrence for a postulated large-break LOCA (LBLOCA)

• WEC performed analyses following the WCAP-18850 methodology demonstrating no burst for small-break LOCA (SBLOCA) & intermediate-break LOCA (IBLOCA) scenarios SBLOCA LBLOCA IBLOCA Demonstrate No Cladding Rupture Credit Leak-before-Break (No Dispersal Analysis)

ALS 7

SBLOCA LBLOCA IBLOCA Demonstrate No Cladding Rupture Best-Estimate or Nominal Analysis 50.46a WCAP-18850 can be leveraged to demonstrate no rupture under 10 CFR 50.46a framework

• Directly applicable for breaks below the transition break size (TBS)

• Break above the TBS would be analyzed in a beyond design basis manner starting from the WCAP-18850 methodology Commonality between EPRI ALS and Draft IE Rulemaking in approach for breaks below the TBS for PWRs LTR-NRC-25-47, Enclosure 2 Page 8 of 27

8 Westinghouse Non-Proprietary Class 3

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Current Status of EPRI ALS

• Submitted February 2024

• Accepted May 2024

• Audited October 2024

• RAI Responses March 2025

• Draft SER July 2025

• ACRS Subcommittee September 2025

• Potential ACRS November 2025 WCAP-18850:

Methodology for Cladding Rupture Calculations Westinghouse Submittal EPRI Submittals 3002028673:

Alternative Licensing Strategy for Fuel Dispersal 3002028674:

LOCA Cladding Rupture Calculations 3002023895:

xLPR Estimation of PWR LOCA Frequencies

• Submitted April 2024

• Accepted June 2024

• Audits Completed June 2025

• RAI Responses Complete (except uncertainty analysis reruns)

• Draft SER Expected February 2026

• RAI Responses Complete

• Draft SER Expected December 2025

• RAI Responses in progress

• Draft SER Expected February 2026 LTR-NRC-25-47, Enclosure 2 Page 9 of 27

Westinghouse Non-Proprietary Class 3 9

© 2025 Westinghouse Electric Company LLC. All Rights Reserved.

Westinghouse Activities for HEF / ATF / LEU+

Introduction to WCAP-18850 Methodology Overview Limitations and Conditions LTR-NRC-25-47, Enclosure 2 Page 10 of 27

10 Westinghouse Non-Proprietary Class 3

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Objective

• Provide an overview of the Westinghouse methodology to perform cladding rupture calculations for high burnup fuel

- Initial driver was to support the EPRI ALS for fuel dispersal

- Topical report is generically applicable to perform rupture calculations

• Builds on prior Westinghouse methods that are NRC approved

- FULL SPECTRUM LOCA (FSLOCA

) Methodology (WCAP-16996-A, Revision 1)

- Incremental Burnup Extension (WCAP-18446-A)

LTR-NRC-25-47, Enclosure 2 Page 11 of 27

11 Westinghouse Non-Proprietary Class 3

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Background:

FULL SPECTRUM LOCA EM

• The FSLOCA evaluation model (EM) is NRC-approved to demonstrate compliance with the 10 CFR 50.46 ECCS acceptance criteria

- Peak cladding temperature (PCT) less than 2,200°F

- Maximum local oxidation (MLO) less than 17%

- Core-wide oxidation (CWO) less than 1%

• WCOBRA/TRAC-TF2 (TF2) is the thermal-hydraulic system code associated with the FSLOCA EM

• Fuel performance data utilized for fuel rod initialization in TF2 is from PAD5 FSLOCA EM Approved by NRC in 2017 LTR-NRC-25-47, Enclosure 2 Page 12 of 27

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Background:

Incremental Burnup

• Incremental burnup topical report leveraged the FSLOCA EM framework to perform cladding rupture calculations for higher burnup, lower power fuel rods

- Demonstrate no cladding rupture with high probability

• WCOBRA/TRAC-TF2 code was reviewed and updated as part of incremental burnup

- Revised models appropriate to higher burnup fuel

- New models necessary to analyze higher burnup fuel Incremental Burnup Approved by NRC in 2024 LTR-NRC-25-47, Enclosure 2 Page 13 of 27

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Introduction to Cladding Rupture Methodology (WCAP-18850)

• Code and method used to perform the cladding rupture calculations adapted from the FSLOCA EM and Incremental Burnup program

- WCOBRA/TRAC-TF2 code was modified to analyze higher burnup fuel with higher initial enrichment

- Considers all higher burnup fuel rods in the core

• Not just peripheral rods as in incremental burnup

- Analysis is focused on cladding rupture

- Lessons learned from licensing of incremental burnup were accounted for in the development of the cladding rupture methodology LTR-NRC-25-47, Enclosure 2 Page 14 of 27

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Applicability of Cladding Rupture Methodology

• Cladding: AXIOM Cladding (current), coated cladding (future)

• Fuel: Standard UO2, ADOPT fuel pellets

• Burnable Absorbers: Un-poisoned, IFBA, Gadolinia, Discrete BAs

• Initial Enrichment: Greater than 5 w/o enrichment

• Fuel Rod Average Burnup: Greater than 68 GWd/MTU

• Plant Classes: 2-loop, 3-loop, 4-loop W-NSSS plants, CE-NSSS plants LTR-NRC-25-47, Enclosure 2 Page 15 of 27

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Westinghouse Activities for HEF / ATF / LEU+

Introduction to WCAP-18850 Methodology Overview Limitations and Conditions LTR-NRC-25-47, Enclosure 2 Page 16 of 27

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Topical Report Focus Areas Fuel Rod and Core Models

• Pellet-Cladding Gap Conductance

• Cladding Deformation

• Cladding Rupture

• Fuel Rod Initialization

• Susceptibility to Fine Fragmentation

• Transient Fission Gas Release

• Pre-Burst Fuel Relocation

• Fuel Pellet Thermal Conductivity

• Kinetics and Decay Heat Models were assessed and/or updated primarily to ensure that all fuel rod phenomena associated with higher burnup levels were appropriately captured to support high probability, licensing basis calculations Models were assessed and/or updated to ensure energy addition from kinetics and decay heat models is reasonably-to-conservatively modeled LTR-NRC-25-47, Enclosure 2 Page 17 of 27

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Topical Report Focus Areas Methodology

• Treatment of regions

- Coverage of entire break spectrum

• Methodology uncertainties

- Assessed relative to higher burnup, higher enrichment, and information available since the approval of the FSLOCA EM

• Offsite power availability

• Miscellaneous considerations Additional Details will be Provided in the Closed Session Presentation LTR-NRC-25-47, Enclosure 2 Page 18 of 27

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Westinghouse Activities for HEF / ATF / LEU+

Introduction to WCAP-18850 Methodology Overview Limitations and Conditions LTR-NRC-25-47, Enclosure 2 Page 19 of 27

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Type of Limitations and Conditions

• Two different types of limitations and conditions

- L&Cs inherited from the FSLOCA EM

• L&Cs which remain applicable are generally inherited into this topical report

• Some are not applicable (e.g., long-term cooling)

• Some are superseded (e.g., prior burnup limitations)

- New L&Cs imposed on this topical report LTR-NRC-25-47, Enclosure 2 Page 20 of 27

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Limitations and Conditions

• L&C #1: Applicability to different PWR designs

• L&C #2: Conditions related to decay heat modeling and uncertainty

• L&C #3: Maximum fuel rod average burnup

• L&C #4: Fuel performance data should be from a code that is approved for the intended analysis conditions, and explicitly accounts for thermal conductivity degradation (TCD)

• L&C #5: Condition related to an analysis uncertainty parameter

• L&C #6: Conditions related to the seed and uncertainty analysis inputs; also requirements for unacceptable analysis results and reporting of analysis ranges LTR-NRC-25-47, Enclosure 2 Page 21 of 27

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Limitations and Conditions

• L&C #7: Requirement to perform the Region II (LBLOCA) analysis with offsite power available (OPA) and loss-of-offsite power (LOOP)

• L&C #8: L&Cs number 3, 12, and 13 from the FSLOCA EM (WCAP-16996-P-A, Revision 1) remain applicable to WCAP-18850

• L&C #9: Applicability to cladding materials and fuel designs

• L&C #10: Applicability to various burnable absorbers

• L&C #11: Maximum initial fuel rod enrichment LTR-NRC-25-47, Enclosure 2 Page 22 of 27

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Questions LTR-NRC-25-47, Enclosure 2 Page 23 of 27

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Acronyms / Codes / Labels Acronym Definition ACRS Advisory Committee on Reactor Safeguards ALS Alternate Licensing Strategy (for FFRD)

ATF Accident Tolerant Fuel CE Combustion Engineering CFR Code of Federal Regulations CWO Core-Wide Oxidation ECCS Emergency Core Cooling System EM Evaluation Model EPRI Electric Power Research Institute FFRD Fuel Fragmentation, Relocation, and Dispersal LTR-NRC-25-47, Enclosure 2 Page 24 of 27

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Acronyms / Codes / Labels Acronym Definition FSLOCA FULL SPECTRUM LOCA HEF High Energy Fuel IBLOCA Intermediate-Break LOCA IE Increased Enrichment IFBA Integral Fuel Burnable Absorber L&C Limitation and Condition LBLOCA Large-Break LOCA LEU+

Low Enriched Uranium+ (between 5 and 10 w/o)

LOCA Loss-of-Coolant Accident LOOP Loss-of-Offsite Power LTR-NRC-25-47, Enclosure 2 Page 25 of 27

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Acronyms / Codes / Labels Acronym Definition LTA Lead Test Assembly LTR Lead Test Rod MLO Maximum Local Oxidation NRC Nuclear Regulatory Commission NSSS Nuclear Steam Supply System OPA Offsite Power Available PAD Performance Analysis and Design PCT Peak Cladding Temperature PIE Post-Irradiation Examination PWR Pressurized Water Reactor LTR-NRC-25-47, Enclosure 2 Page 26 of 27

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Acronyms / Codes / Labels Acronym Definition RAI Request for Additional Information SBLOCA Small-Break LOCA SER Safety Evaluation Report TBS Transition Break Size TCD Thermal Conductivity Degradation TF2 WCOBRA/TRAC-TF2; thermal-hydraulic code licensed as part of the FSLOCA EM W

Westinghouse LTR-NRC-25-47, Enclosure 2 Page 27 of 27