ML24051A186

Transcript of Advisory Committee on Reactor Safeguards: NuScale Design-Centered Subcommittee Meeting, February 06, 2024, Pages 1-76 (Open)

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Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION

Title:

Advisory Committee on Reactor Safeguards NuScale Design-Centered Subcommittee Open Session Docket Number:

(n/a)

Location:

teleconference Date:

Tuesday, February 6, 2024 Work Order No.:

NRC-2701 Pages 1-49 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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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 NUSCALE DESIGN-CENTERED SUBCOMMITTEE 6

+ + + + +

7 OPEN SESSION 8

+ + + + +

9 TUESDAY, FEBRUARY 6, 2024 10

+ + + + +

11 The Subcommittee met via hybrid Video 12 Teleconference, at 1:00 p.m. EST, Walt Kirchner, 13 Chairman, presiding.

14 COMMITTEE MEMBERS:

15 WALTER L. KIRCHNER, Chair 16 RONALD G. BALLINGER, Member 17 VICKI M. BIER, Member 18 CHARLES H. BROWN, JR., Member 19 VESNA B. DIMITRIJEVIC, Member 20 GREGORY H. HALNON, Member 21 JOSE A. MARCH-LEUBA, Member 22 ROBERT P. MARTIN, Member 23 DAVID A. PETTI, Member 24 THOMAS E. ROBERTS, Member 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 ACRS CONSULTANT:

1 DENNIS BLEY 2

STEVE SCHULTZ 3

4 DESIGNATED FEDERAL OFFICIAL:

5 MICHAEL SNODDERLY 6

7 ALSO PRESENT:

8 ANTONIO BARRETT, NRR 9

ANDREW BIELEN, RES 10 ALLYSON CALLAWAY, NuScale 11 KRIS CUMMINGS, NuScale 12 SARAH FIELDS, Public Participant 13 MAHMOUD JARDANEH, NRR 14 STACY JOSEPH, NRR 15 JOSHUA KAIZER, NRR 16 ZHIAN LI, NRR 17 JEFF LUITJENS, NuScale 18 KEVIN LYNN, NuScale 19 SCOTT MOORE, ACRS 20 REBECCA PATTON, NRR 21 ADAM RAU, NRR 22 HAROLD SCOTT, Public Participant 23 GETACHEW TESFAYE, NRR 24 SARAH TURMERO, NuScale 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 TABLE OF CONTENTS 1

2 Opening Remarks.................

4 3

Discussion of Subchannel Analysis........ 10 4

Methodology and Rod Ejection 5

Methodology Topical Reports 6

Staff's Evaluation of NuScale.......... 26 7

Topical Reports 8

Opportunity for Public Comment

......... 45 9

10 11 12 13 14 15 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

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

12:59 p.m.

2 CHAIR KIRCHNER: The meeting will now come 3

to order. This is a meeting of the Advisory Committee 4

on Reactor Safeguards, NuScale Design-Centered 5

Subcommittee. I'm Walt Kirchner, the lead member for 6

this meeting. Members in attendance today are Ron 7

Ballinger, Jose March-Leuba, Bob Martin, David Petti, 8

Greg Halnon, Thomas Roberts, and Charles Brown.

9 Do we have anyone listening in?

10 MR. BLEY: Vesna.

11 MEMBER DIMITRIJEVIC: Yes, I am here. Hi, 12 good morning.

13 CHAIR KIRCHNER: Welcome, Vesna. Good 14 afternoon.

15 MEMBER DIMITRIJEVIC: Good afternoon.

16 Right.

17 CHAIR KIRCHNER: Mike Snodderly is the 18 Designated Federal Officer for this meeting. The 19 subcommittee will review the staff's evaluation of two 20 NuScale topical reports on subchannel analysis 21 methodology. We are going to review two -- pardon me.

22 Let me find my place again. The subcommittee will 23 review the staff's evaluation of two NuScale topical 24 reports on subchannel analysis methodology and rod 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 ejection accident methodology.

1 The committee reviewed and commented on 2

Revision 1 of the subchannel analysis methodology 3

topical report in 2018 and also on Revision 1 of the 4

rod ejection methodology topical report back in 2020.

5 Since that

time, NuScale has revised these 6

methodologies to include a statistical subchannel 7

analysis methodology that utilizes an approach, a 8

statistical approach in defining critical heat flux 9

analysis limits. It is NuScale's intent that a 10 statistical treatment of uncertainty in certain areas 11 will reduce some of the conservatisms and treatments 12 with a defendable basis to provide a better 13 representation of the actual core physical response.

14 One objective of this meeting is to help 15 prepare the full committee for its upcoming review of 16 Chapters 4 reactor and Chapter 15 transient accident 17 analysis of the NuScale standard design approval 18 application that includes a power upgrade from 50 19 megawatts electric to 77 megawatts electric for each 20 module.

21 The ACRS was established by statute. It 22 is governed by the Federal Advisory Committee Act 23 (FACA). The NRC implements FACA in accordance with 24 its regulations found in Title 10 of the Code 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

6 Federal Regulations, Part 7. The committee speaks 1

only through its published letter reports. We hold 2

meetings to gather information and perform preparatory 3

work that will support our deliberations at a full 4

committee meeting.

5 The rules for participation in all ACRS 6

meetings were announced in the Federal Register on 7

June 13th, 2019. The ACRS section of the U.S. NRC 8

public website provides our charter, bylaws, agendas, 9

letter reports, and full transcripts of our full and 10 subcommittee meetings, including the slides presented 11 there. The agenda for this meeting was also posted 12 there. A portion of this meeting will be closed to 13 protect NuScale proprietary and export controlled 14 information pursuant to 5 U.S. Code 552(b)(c)(4).

15 As stated in the Federal Register notice 16 and in the public meeting notice posted to the 17 website, members of the public who desire to provide 18 written or oral inputs to the subcommittee may do so 19 and should contact the Designated Federal Officer five 20 days prior to the meeting. A communications channel 21 has been opened to allow members of the public to 22 monitor the open portions of this meeting. The ACRS 23 is now inviting members of the public to use the MS 24 Teams link to view slides and other discussion 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 material during these open sessions. The MS Teams 1

link information was placed in the agenda on the ACRS 2

public website.

3 We have received one set of written 4

comments from Harold Scott. Those comments have been 5

distributed to the members, and they have been 6

provided to the staff at NuScale for awareness. The 7

comments will be read into the record during the 8

public comment portion of this meeting and attached to 9

the transcript. We have not received any additional 10 requests to make oral statements from members of the 11 public regarding today's session.

12 Written comments may be forwarded to 13 Michael Snodderly, today's DFO. There will be an 14 opportunity for public comment, as well, and we have 15 set aside ten minutes in the agenda at the conclusion 16 of the open session of this meeting for comments from 17 the public listening to the meeting.

18 A transcript of the open portions of the 19 meeting is being kept, and it is requested that 20 speakers identify themselves and speak with sufficient 21 clarity and volume so that they can be readily heard.

22 Additionally, participants should mute themselves when 23 not speaking, including their cell phones.

24 And with all of that, we'll take a breath 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 and turn to, proceed with the meeting. And I'll call 1

on Kris Cummings of NuScale to begin today's 2

presentations. Kris.

3 MR. CUMMINGS: Great. Thank you very 4

much. So my name is Kris Cummings. I'm a licensee 5

engineer with NuScale. I have been with NuScale for 6

about four years. Prior to that, I have had roles 7

with test vendors and reactor vendors Holtec and 8

Westinghouse and have been familiar with these 9

particular types of analyses in the past.

10 I want to thank the ACRS for having us 11 here. This is what I consider, in essence, the 12 kickoff of the ACRS review of the SDA application and 13 the associated methodologies that support that 14 application. So thank you for having us here. It has 15 been a pleasure working with the NRC staff during the 16 review of this process, and I think we've had some 17 good dialogue with them during the process and come to 18 what we feel is a good resolution of the issues and an 19 approved methodology.

20 I want to note that we took some of the 21 ACRS's comments from the DCA period under advisement, 22 and so we submitted these two topical reports about a 23 year in advance of when we submitted the SDA. So that 24 allows all of us, the NRC, the ACRS, and ourselves, 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

9 get, in essence, a methodology approved, you know, 1

well in advance of the approval of the SDA 2

application. So we took that advice from the DCA time 3

to heart.

4 So today we're focused in particular on 5

the two methodologies that you mentioned and the 6

changes that we made to those methodologies associated 7

with the revisions were supplement to these topical 8

reports. I want to note we will be back again in 9

front of the ACRS, as you mentioned, for Chapter 4 and 10 Chapter 15. So we're focused, again, today on the 11 methodologies that will support the analysis or do 12 support the analysis in the SDA application.

13 With that, that is my opening comments, 14 and so what I would like to do is have my colleagues 15 here that are presenting give an introduction of 16 themselves. Yes, an introduction.

17 MS. TURMERO: Hi. So my name is Sarah 18 Turmero. I'm a licensing engineer for NuScale, and I 19 have been with the company in this position for about 20 a year and a half. And before coming to NuScale, I 21 was a reactor engineer at Waterford 3. And I will be 22 covering the open portion of the statistical 23 subchannel analysis methodology slides.

24 MEMBER MARCH-LEUBA: The microphones 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

10 extremely sensitive if you are close to them. They 1

are more concerned with minimizing background noise, 2

so do talk into them.

3 MS. TURMERO: Okay. Thank you.

4 MR. LYNN: My name is Kevin Lynn. I'm a 5

licensing engineer with NuScale. I have been here 6

almost three years. And prior to that, I was working 7

in licensing at an operating plant, a BWR operating 8

plant, and I also have previous licensing experience 9

with new plants, the Japanese designed the U.S. APWR 10 that was in process a few years ago and came to the 11 ACRS several times. So that's my background.

12 MR. LUITJENS: My name is Jeff Luitjens.

13 I'm in the nuclear fuels group. The last few years, 14 11 years at NuScale, jumping around from validation, 15 code development, testing. My background, Ph.D. in 16 nuclear engineering, focus on CHF, and today I am here 17 to provide information on the subchannel.

18 MS. CALLAWAY: My name is Allyson 19 Callaway. I'm the senior manager of nuclear fuels.

20 I have been at NuScale for 13 years in various 21 capacities within the fuels and neutronics 22 organization.

23 MS. TURMERO: So to kick off, I just want 24 to acknowledge that we are the proud recipient 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

11 financial assistant awards from the U.S. Department of 1

Energy and are thankful to identify their support of 2

our program.

3 And to get started, we're going to start 4

off with the statistical subchannel analysis 5

methodology topical report. So for the history of the 6

statistical subchannel analysis methodology, it starts 7

with the originally approved subchannel analysis 8

methodology that was approved by the NRC in December 9

of 2018 and previously presented to the ACRS in August 10 and September of 2018. And this was the topical 11 report that was used for the NuScale US600 design 12 that's codified in 10 CFR Part 52, Appendix G.

13 And so the statistical subchannel analysis 14 methodology was submitted in December of 2021, and it 15 serves as a supplement to the originally-approved 16 methodology. So the staff performed a review and 17 audit of the topical report where there was one 18 request for supplemental information, no requests for 19 additional information and multiple audit questions.

20 The topical report was revised during the review 21 process to address staff feedback and the most recent 22 revision is Revision 4. That was submitted in 23 November of 2023.

24 So an overview of the previous subchannel 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 methodology. VIPRE-1 was used for steady state and 1

transient analysis. The methodology fulfilled the 2

requirements of VIPRE-1 generic safety evaluation 3

limitations, and the topical report covered the 4

methodology application and treatment of uncertainties 5

where the objective of the topical report was to 6

provide a methodology to determine fuel thermal 7

margins, such as critical heat flux and fuel center 8

line melt.

9 And here on the slide, we have an outline 10 of the general methodology approach, and we'll be 11 going over the differences from the original topical 12 report to the statistical method.

13 So the changes from the original method, 14 of course, the treatment of uncertainties. There's a 15 statistical treatment of uncertainties for a set of 16 parameters instead of a deterministic approach.,

17 radial and axial nodalization, and axial domain. And 18 what remains unchanged is the fuel conduction, grade 19 and frictional losses, cross-flow and mixing, and the 20 qualification or the validation and applicability of 21 the topical report.

22 MEMBER MARCH-LEUBA: Number one, we are 23 going to interrupt you all the time. When you say 24 statistical analysis of the uncertainties, you mean 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

13 what is called best estimate plus uncertainty type of 1

approach where we do kind of a Monte Carlo propagation 2

of -- can you explain to a member of the public that 3

doesn't know what you've done what you've done?

4 MR. LUITJENS: Yes. So we're talking 5

about statistical here. We're focusing just on the 6

CHF analysis limit, not how subchannel talks to, you 7

know, the systems code. So it's not a best estimate 8

plus uncertainty. I would say our overall methodology 9

is still deterministic. It's just in the CHF analysis 10 for subchannel we're talking about statistical 11 treatments.

12 MEMBER MARCH-LEUBA: In the previous, 13 Revision 2, I don't remember the number, the approved 14 one, we used bounding uncertainties for every single 15 pyramid, whereas here, for the CHF, you do a Monte 16 Carlo type of sampling?

17 MR. LUITJENS: Yes. For a set of those 18 uncertainties, you know, five or six, we do a Monte 19 Carlo type uncertainty kind of based on what's the 20 uncertainty value and what's the distribution 21 associated with that uncertainty. We do a Monte Carlo 22 23 MEMBER MARCH-LEUBA: The ACRS is here for 24 the public, so you're talking to, somebody is going 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

14 read this transcript, and they need to understand what 1

you're saying. So don't assume you're talking to your 2

professors at university. Assume you're talking to 3

your students.

4 MEMBER MARTIN: Robert Martin, member.

5 Treatment of uncertainties specific to systems code, 6

my understanding is you run thousands of cases with 7

VIPRE, correct? You can --

8 MR. LUITJENS: So for the systems codes, 9

those are done deterministically, so we take the 10 bounding, you know, high flow, low flow. Those get 11 fed to the subchannel, and we analyze those and get 12 the limiting value.

13 MEMBER MARTIN: So those parameters are 14 deterministically treated while the other ones are 15 sampled --

16 MR.

LUITJENS:

Correct, yes.

So 17 determining the CHF analysis --

18 MEMBER MARTIN:

The deterministic 19 subchannel is the statistical.

20 MR. LUITJENS: Correct.

21 MS. TURMERO: Okay. And as Jeff had 22 mentioned, so the statistical subchannel analysis 23 methodology utilizes the statistical approach into 24 finding the CHF analysis limit, whereas many of 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

15 aspects of the methodology still use a deterministic 1

approach. And so our intent of introducing the 2

statistical treatment of uncertainties was to reduce 3

some of the overly conservative treatments with a 4

defendable basis and to provide a

better 5

representation of the physical response.

6 So statistical versus deterministic. For 7

the deterministic approach, the event analysis input 8

uncertainties are biased independently in a limiting 9

direction. And so range of axial and radial power 10 distributions that's allowed by operations are not 11 treated statistically. There are variations that 12 could be from exposure, power, boron concentration, 13 control rod insertion, axial offset. And so in the 14 existing methodology, the radial power distribution is 15 artificially created to preserve the tech spec-allowed 16 measured radial peaking and minimizing the beneficial 17 cross flow, and the axial power distribution is 18 determined for the limiting shape allowed by axial 19 offset.

20 For the statistical approach, all of the 21 uncertainties associated with both critical heat flux 22 correlation and event analysis inputs are 23 statistically treated and accounted for with a 95-24 percent probability at the 95-percent confidence level 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 in order to determine the critical heat flux analysis 1

limit. And the statistical approach still requires 2

the use of a critical heat flux correlation, the 3

approved critical heat flux correlation with a 95/95 4

design limit.

5 With that, I'll turn it over to Kevin 6

Lynn.

7 CHAIR KIRCHNER: Okay. You're going to do 8

a handover. Good. I just want to note the presence 9

of Member Vicki Bier. And, Sarah, since I have my 10 mike on, this is -- your previous slide said 11 actinically created. Perhaps I'm hanging up on the 12 word. What you're really saying is that, when you 13 apply the existing approved methodology, you 14 accurately, not artificially, model what the core 15 radial peaking is such that it's representative of the 16 actual conditions. It's not artificially created.

17 I'm just stumbling over the choice of words there and 18 not what I believe is what you're actually doing.

19 MR. LUITJENS: Yes, I think that's the 20 correct interpretation of artificially. What we're 21 really trying to capture is what do we allow from the 22 core design aspect to make sure we're capturing what 23 we could possibly see.

24 CHAIR KIRCHNER: Okay. Artificially 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

17 created could give one the wrong impression. You're 1

trying to accurately model what the radial power 2

distributions is when you conduct your analyses.

3 Okay. Go on.

4 MEMBER MARCH-LEUBA: By artificial, I 5

guess you mean bounding, right?

6 MR. LUITJENS: Yes. By artificial, we 7

mean bounding.

8 MEMBER MARCH-LEUBA: So the tech specs is 9

really what bounds your operation. You may never 10 reach that solution, but you have tech specifics, you 11 going to need to be under that or you'll be shut down.

12 Since we are the end of this presentation 13 and if you can say it in the open session, will this 14 exercise gain you a 2-percent margin, a 10-percent 15 margin, a 25-percent margin? Was it worth it? I 16 mean, if you get into a factor of 500 percent, I would 17 be worried that you were tweaking too much.

18 MR. LUITJENS: Yes. If you're talking 19 about the specific application, kind of going back --

20 MEMBER MARCH-LEUBA: Yes. You also might 21 need to --

22 MR. LUITJENS: So from a sense, we're 23 actually maintaining the same amount of margin for 24 different designs.

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 MEMBER MARCH-LEUBA: It's the same core.

1 MR. LUITJENS: It's the same core with a 2

little power upgrade, but we came back and sharpened 3

our pencils on some of the approaches. We had 5 to 4

10-percent margin last time. We still have that same 5

amount of margin this time. So there's not an order 6

of magnitude change on the margins that we're seeing.

7 MEMBER MARCH-LEUBA: Let me refresh the 8

question. If you have a core and you are under a 9

license with your method and with the new method, 10 what's the change in margin that you calculate? Is it 11 in the 5-percent range or is it in the 100-percent 12 range?

13 MR. LUITJENS: Yes, I'd say that's really 14 hard -- it's hard to get that because you don't have 15 a limit that's made for that specific methodology, so 16 it's hard to go back --

17 MEMBER MARCH-LEUBA:

Is it a

big 18 difference in your mind?

19 MR. LUITJENS: I would say it would not be 20 a big difference.

21 MEMBER MARCH-LEUBA:

I'm going to 22 stipulate in the open, this statistical methodology is 23 well developed and used everywhere. There's nothing 24 new here. You're just joining the 21st century, as 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

19 opposed to just doing methods --

1 MR. CUMMINGS: Yes, Kris Cummings. I'd 2

say we came from the 70s to the 90s.

3 MEMBER MARCH-LEUBA: Yes. Nothing new --

4 MR. CUMMINGS: Right.

5 MR. LYNN: Okay Thanks, Sarah. My name 6

is Kevin Lynn. I'll be covering the open session for 7

the rod ejection methodology. Rod ejection accident 8

methodology was previously approved as Revision 1 by 9

the NRC in June 2020, and it was previously presented 10 to the ACRS at the full committee meeting in March and 11 the subcommittee meeting in February of 2020.

12 The Revision 1, the approved version, was 13 used for the NuScale US600 design, which is codified 14 in 10 CFR 52, Appendix G. Subsequently, we submitted 15 Revision 2 in December 2021, and the NRC staff 16 performed a review and audit of Revision 2. We had no 17 RSIs. We had one RAI with two questions, and then we 18 had multiple audit questions.

19 So during the course of that interaction 20 with the NRC staff, we ended up making some changes to 21 the methodology throughout the process. And so we 22 submitted Revision 3 in October 2023, which is the 23 current revision.

24 The previously-approved version, Rev. 1, 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 provided the methodology for modeling the rod ejection 1

accident, which is the bounding reactivity-initiated 2

accident in accordance with GDC 28. The rod ejection 3

is a bit unique compared to other Chapter 15 events.

4 It has its own phenomenon and time scales that are 5

looked at, very compressed time scales, as well as its 6

own unique acceptance criteria. And that sort of 7

lends itself to having its own special method.

8 The approved method used a combination of 9

codes and methods, three codes, SIMULATE-3K, NRELAP5, 10 and VIPRE-01, and it also had a adiabatic fuel model 11 which was used to perform the calculation for fuel 12 entropy and temperature using, essentially, a hand 13 calculation.

14 The acceptance criteria that we used in 15 Revision 1 was based on Regulatory Guide 1.77, which 16 was the reg guide at the time, and also from the SRP 17 in NUREG-0800. And, overall, we provided a 18 justification for the software, the acceptance 19 criteria, the applicability, and the treatment of 20 uncertainties.

21 When we moved into Rev. 2, what were the 22 changes? Well, the big change was Reg. Guide 1.77 was 23 replaced with Regulatory Guide 1.236, and that was in 24 June 2020. So, essentially, just after the old 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

21 methodology was approved, the new reg guide came out.

1 And that new reg guide had a change to the PCMI fuel 2

failure acceptance criteria, so that was sort of the 3

main driver for why we needed to (audio interference).

4 While we were doing that revision, we 5

looked it up. There's stuff that we can incorporate, 6

and one of the things we identified was that the 7

adiabatic fuel model calculation, the hand 8

calculation, could be removed and, instead, we could 9

use VIPRE to perform those calculations of fuel 10 entropy and temperature.

11 In addition, as you just heard, we were 12 looking at the statistical analysis for subchannel, so 13 we wanted to incorporate that, as well. So bringing 14 that limit and make any changes that we needed to make 15 to the rod ejection methodology to better talk and 16 interface with that new method. And then, finally, 17 changes that were incorporated during the process were 18 details and justification that we added based on our 19 interaction with the NRC staff.

20 So we did not change the actual STIMULATE-21 3K analysis for uncertainty treatment or the overall 22 qualification of the method. So, again, the primary 23 driver was the new regulatory guide. The methodology 24 itself was not really impacted by the design changes 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

22 we made going from DCA to SDA, and the increase in 1

power was not really the driver for the change.

2 As far as a summary for our open session, 3

for the subchannel analysis, the statistical treatment 4

of uncertainties allows for improved results while 5

still maintaining an overall robust analysis approach.

6 And for the rod ejection, we've incorporated changes 7

from the new reg guide and simplified our analysis to 8

better work with VIPRE and the new subchannel method 9

while still maintaining a conservative result.

10 And as Kris discussed earlier, these 11 methodologies, at this stage we're talking about the 12 methodologies themselves, but those methodologies are 13 ultimately used to produce results that are identified 14 in Chapters 4 and 15 of the NuScale standard design 15 approval application for US460. Those results will 16 obviously be coming back to the ACRS when those 17 chapters are reviewed.

18 MEMBER MARTIN: You don't get off too 19 easy. NuScale is, fundamentally, a light water 20 reactor and, clearly, you've --

21 MR. BLEY: Can you use the mike?

22 MEMBER MARTIN: I'm pretty close to the 23 mike. Fundamentally, you follow NUREG-0800. Early on 24 in the development of your safety case, you would have 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 had to evaluated unique aspects of your design with 1

respect to NUREG-0800. Is there anything in this 2

section related to reactivity insertion accidents that 3

is unique? Anyway, if I can get my composure back, is 4

there anything unique about reactivity insertion 5

accidents? As an integral PWR, yes, as an integral 6

PWR, it's a little bit different regarding the design 7

in this aspect. I would think it would, in some way, 8

benefit design change might benefit the likelihood of 9

such an event. Does that come into your thinking 10 going into this at all, or you're just pretty much 11 pushing the button like any LWR on this particular 12 event?

13 MR. LYNN: Well, I think one unique 14 aspect, right, being a smaller core and looking at 15 that certainly factors into it. And I know one 16 interesting thing, when we went from the uprate for 17 the power, actually, the benchmarking that was 18 performed, some of the benchmarking to the SPUR 19 analysis, for example, actually, when we uprated, the 20 power level is actually more in line with some of the 21 experimental data that's out there that was performed.

22 So sort of one unique aspect of being 23 small and being low power, you know, we're sort of 24 moving up in the power range and actually bring it 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 maybe more in line a little bit with some of those 1

cases in some of the more operating plants. So that, 2

you know, change, although it is an uprate, you know, 3

it sorts of brings us into line with that, but they're 4

unique aspects.

5 I know that during the previous ACRS there 6

was some discussion about unique aspects, including 7

the design of our containment, you know, and the 8

containment being closer to the vessel than it is in 9

a operating plant; and, therefore, does that change 10 anything when it came to rod ejection. But, you know, 11 we addressed that previously, and so there's nothing 12 new this time around that would make us revisit that, 13 no changes that we've made that would make that a 14 different scenario than it was before.

15 MEMBER MARCH-LEUBA: But, I mean, there's 16 no change between the approved design and the new 17 concept, but raw injection can be worse can be worse.

18 What I'm asking, when we're asking the question about 19 NUREG-0800, what could be -- 800 tells you take the 20 worst rod and eject it, right; so, in that case, you 21 have to do that. But, typically, if I remember 22 correctly, rods are a lot heavier than typical PWR; is 23 that correct?

24 MR. LYNN: I don't have the answer 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 that, but I do know that -- Allyson, do you want to --

1 MS. CALLAWAY: Allyson Callaway. You're 2

asking if the rods are heavier in mass or --

3 MEMBER MARCH-LEUBA: No, no, in the 4

dollars.

5 MS. CALLAWAY: Because there's fewer, each 6

ejected rod relative has more worth than a PWR. We 7

preclude fuel failures still, and so that effectively 8

limits how much worth can be ejected, and that's all 9

just controlled through the power-dependent insertion 10 limits. So the effective worth that's being ejected 11 is still low.

12 MEMBER MARCH-LEUBA: Because of the --

13 MS. CALLAWAY: Power-dependent insertion.

14 MEMBER MARCH-LEUBA: -- safety controls 15 over the rods are positioned.

16 MS. CALLAWAY: Right.

17 MEMBER MARCH-LEUBA: Similar to what BWRs 18 do, correct? They're all worth minimizers.

19 MEMBER ROBERTS: A general question. What 20 I think I heard -- this is Tom Roberts -- at least 21 from Jose is that, for the subchannel analysis, this 22 is basically what many people do. And for the rod 23 ejection, I think what you said is this is following 24 the reg guide revision. So would you characterize 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 neither of these topical reports as novel in scope or 1

innovative in terms of nuclear safety?

2 MR. LYNN: Yes, we would agree.

3 MEMBER ROBERTS: Good. Thank you.

4 CHAIR KIRCHNER: Other members, any 5

comments, questions --

6 MEMBER MARCH-LEUBA: Since we're in the 7

open session, I want to put on the record that I 8

concur with your evaluation that this is a small 9

evolution. A few more years of learning and tweaking 10 on the calculations, nothing groundbreaking in my 11 opinion.

12 CHAIR KIRCHNER: Okay. Then we'll turn to 13 the staff for their presentation in the open session.

14 Thank you. Okay. When you're ready. Stacy, are you 15 leading off? Just pull it closer to you, please.

16 MS. JOSEPH: I'm going to turn it over to 17 my branch chief, Mahmoud Jardaneh, to give some 18 opening remarks, and then I'll kick off.

19 MR. JARDANEH: Thank you. Good afternoon, 20 Chair Kirchner, and good afternoon, ACRS subcommittee 21 members. I'm Mahmoud Jardaneh, M.J. for short. And 22 I serve as the branch chief of the New Reactor 23 Licensing Branch in the Division of New and Renewed 24 Licenses in NRR. I recently assumed this position 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

27 look forward to being a member of the team working on 1

the licensing review of the NuScale US460 design and 2

engaging with you in this and future NuScale meetings.

3 Thank you for the opportunity today for 4

the staff to present their review of the NuScale rod 5

ejection accident and subchannel analysis 6

methodologies topical reports associated with the 7

standard design approval application (SDAA). These 8

two topical reports are the last two of eight topical 9

reports submitted prior to the application. The 10 remaining SDAA topical reports are reviewed as part of 11 the application, and we will inform the ACRS when 12 their safety evaluation reports are available for the 13 ACRS.

14 In addition to the safety evaluation of 15 these topical reports, we have completed the Phase A, 16 the advanced safety evaluation, without open items for 17 five SDAA chapters, and advanced safety evaluations 18 for them will be available for ACRS in the coming few 19 weeks.

20 In today's meeting, the staff will focus 21 on the differences from the last time we presented on 22 the previous revisions of these topical reports that 23 supported the now-certified NuScale US600 design.

24 Once again, thank you for the opportunity, and we look 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 forward to a good discussion. Thank you.

1 CHAIR KIRCHNER: Thank you. And, Stacy, 2

next.

3 MS. JOSEPH: Thank you very much. Thank 4

you, M.J., and good afternoon, members of the ACRS, 5

NuScale, colleagues from the NRC, and members of the 6

public. My name is Stacy Joseph, and I'm a project 7

manager for the two licensing topical reports that 8

we're here to discuss today. I'm joined by our lead 9

PM for the NuScale SDAA review, Getachew Tesfaye, as 10 well as the staff members from both the Office of 11 Nuclear Reactor Regulation and the Office of Research, 12 who contributed to the reviews of the statistical 13 subchannel analysis methodology and the rod ejection 14 accident methodology.

15 A discussion on the statistical subchannel 16 methodology will be led by Joshua Kaizer and Antonio 17 Barrett from NRR; and for rod ejection, Adam Rau and 18 Zhian Li will be leading the discussion from NRR, 19 along with insights from Andrew Bielen from the Office 20 of Research. Andrew will be joining us virtually 21 today on Teams and will be presenting during the 22 closed session.

23 Thank you to NuScale for giving the 24 overview and the histories of the topical reports 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

29 we'll be discussing. We'll try not to repeat too much 1

of what you've already heard today. So in this open 2

session, I'll quickly run through the time lines for 3

each of the topical reports, the reviews, and then 4

Josh and Adam will walk through the regulatory basis 5

for each of the reports and the conclusions the staff 6

made at the completion of their reviews.

7 The statistical subchannel methodology was 8

submitted to the NRC in December 2021 and was accepted 9

for review after NuScale addressed the staff's request 10 for supplemental information in April of 2022. The 11 staff conducted an audit between July 2022 and 12 December 2023; and, as NuScale previously mentioned, 13 the topical report was revised during this time period 14 to address staff feedback. NuScale submitted the 15 final revision to the topical report just this past 16 November, and the staff's advanced SER was issued 17 shortly later.

18 With that, I'll turn it over to Josh 19 Kaizer.

20 MEMBER MARCH-LEUBA: These four revisions, 21 were they a consequence of deficiencies that the staff 22 identified during the review, where there were points 23 of finding of signs that was not completed and the 24 extra features, or can you explain why we were not 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 happy with Revision 1?

1 MR. KAIZER: Sure. That's for the NRC 2

staff. This is my answer to that, and NuScale is free 3

to jump in and correct me. Everyone does quality 4

control of their documents a little bit differently, 5

so, if you're looking at a GE topical report or a 6

Westinghouse topical report, you can generally expect 7

to see Rev. 0, it comes in the door. Maybe if there's 8

a major change to the topical, they might make a Rev.

9

1. And that is one way to do it.

10 Other people decide to update the topical 11

report, as information comes in, change the 12 information in the topical report. A lot of times, 13 that information would have been in the RAIs, it would 14 have been in the Dash A version. Everything that we 15 kind of saw here, there were some areas where we said, 16 hey, we need more information, but it's really up to 17 them whether they want to rev the topical, just 18 provide the information and say, okay, we're going to 19 attach it at the end of it. And I thought a lot of 20 this came out of the QA program NuScale uses for its 21 document generation, so there was nothing, I'd say, 22 extra special about this topical report that it 23 required four revisions before it even got there. It 24 was just this is the way they chose to address 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

31 information.

1 MEMBER MARCH-LEUBA: So there was no major 2

deficiency. It was just tweaking.

3 MR. KAIZER: Correct. Okay. So I'll give 4

the regulatory basis for the statistical subchannel.

5 It mostly comes from GDC 10 of Appendix A, so, 6

basically, saying, hey, you need SAFDLs. Critical 7

heat flux is a SAFDL. This gets a little bit broken 8

down more in the standard review plan, SRP 4.4, which 9

talks about the 95/95.

10 I can go into a lot more detail because we 11 actually did a presentation on this to the staff a 12 couple of years ago where we tried to track down where 13 does the 95/95 come from and all that kind of stuff.

14 But suffice to say, there is this 95/95 requirement, 15 well, not requirement, but there's 95/95 in the SRP.

16 Everybody says, yes, we want to satisfy that. And for 17 direct correlations, it's a

little bit more 18 straightforward when you start to do statistical 19 stuff. It is a little more challenging, but, like a 20 lot of people have pointed out, this was a concern and 21 a challenge that we have long since resolved. I think 22 the earliest I've seen it used, I thought the topical 23 was, like, sometime from the 1980s, the late 80s. So 24 using 95/95 in the statistical sense is something 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 we're very familiar with, especially in DMB.

1 And I

wanted to add the staff's 2

conclusions, we found an acceptable method for 3

combining all these uncertainties. We did have two 4

limitations and conditions. The first one was, 5

basically, saying that your correlation has to be 6

approved. This was just a carryover from the 7

original, the NuScale, the subchannel analysis 8

methodology. It's kind of a general statement you'll 9

see a lot of times. Any time you see a CHF 10 methodology, hey, your CHF correlation has to be 11 approved for the fuel you're using, so that's not that 12 really big of a deal.

13 The next one, a little bit more complex, 14 but we just basically said you have a whole bunch of 15 models in this methodology that NuScale wanted to say 16 we're going to model this, we're going to capture the 17 uncertainty of this parameter. We're not really ready 18 to tell you yet how we're going to do that. And so we 19 kind of looked through it and said, okay, that's 20 reasonable, but, before you actually apply this, you 21 have to tell us how you're going to model this and we 22 have to approve it. And there's a number of ways we 23 can do that. We can either approve the equation or we 24 can approve the direct uncertainty itself. So those 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 were the two conditions, limitations, on the staff's 1

SER, and that was pretty much the majority of the 2

review.

3 MEMBER MARCH-LEUBA: Revision number 2 is 4

more a condition from the first --

5 MR. KAIZER: Yes.

6 MEMBER MARCH-LEUBA: -- license, and then 7

the second can just --

8 MR. KAIZER: Correct, yes. And there's a 9

bunch of ways that we can resolve those issues. We're 10 just saying, hey, these have to be reviewed and 11 approved by the staff.

12 MEMBER MARCH-LEUBA: It's not really 13 limiting.

14 MR. KAIZER: Correct.

15 MEMBER MARCH-LEUBA: We need to look at 16 the test at least once.

17 MR. KAIZER: Yes.

18 MEMBER MARTIN: With statistical methods, 19 the presentation of information will be a little bit 20 different from a deterministic presentation of 21 information. And there might be a tendency to just 22 kind of globally look at results from thousands of 23 cases in a statistical sense. Do you still expect or 24 require that NuScale present some deterministic 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 representative type of results of what exists after 1

95/95, or you'd be satisfied with for just the 2

statistical presentation of information?

3 MR.

KAIZER:

I want to ask one 4

clarification on your question because this is 5

something that I get into a lot of conversations about 6

this, and I don't quite understand sometimes when 7

people use -- to me, the deterministic analysis is any 8

analysis where you put in the input and you get out 9

the same output, and a non-deterministic analysis will 10 literally be if I give my computer code three, one 11 time I get the number five, one time I get the number 12 seven.

13 So I have always viewed that even 14 statistical methodologies are deterministic in nature.

15 It's just what we're doing is we're feeding them, 16 instead of a constant, a random variable, and they're 17 going to give me a different outcome. But if I give 18 it that same initial input, I get the same thing. So 19 I want to clarify that when I hear deterministic in 20 this sense, I'm thinking more of do they have to do, 21 like, the worst-case scenario type thing.

22 MEMBER MARTIN: No. That's a trick 23 question, and we're aligned on that perspective.

24 Deterministic is a term, because of Chapter 15 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 accident analysis in the old school, was truly 1

bounding in a sense, and we've evolved to a different 2

approach now.

3 But, yes, I was just really wondering 4

whether, if an old school reviewer picked it up, would 5

they recognize it?

6 MR. KAIZER: Well, one of the challenges 7

with statistical CHF is it's been around for so long.

8 I mean, you're talking 1980s, so I took over this 9

position from Tony Attard. I think he started in the 10 NRC in the mid 90s, so, yes, he would have already 11 been familiar with that.

12 The other thing about statistical 13 subchannel is it's not a replacement method, it's an 14 alternative approach, so we'll talk about their normal 15 subchannel analysis methodology. And I never thought 16 of the statistics in it as giving you, I'd say the 17 major benefit that I feel like you would get from a 18 statistical LOCA where you're like ranging that break 19 size. I mean, normally, what you're doing is you are 20 taking a whole bunch of uncertainties and, instead of 21 just adding them as straight adders, you're saying, 22 okay, we can treat these as random variables and 23 combine their things statistically.

24 So it is a statistical method, but I don't 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 think of it as something as far afield from a 1

deterministic one because you're still going to find, 2

I

mean, you're treating the uncertainties 3

statistically but not --

4 MEMBER MARTIN:

I think you're 5

overthinking my question.

6 MR. KAIZER: Okay.

7 MEMBER MARTIN: An uncertainty is a 8

tendency with statistical methods that kind of present 9

the cloud of results, and that is useful to some 10 extent. But my point about kind of old school 11 approach is people still kind of want to see, you 12 know, plots of behavior because the trends give you a 13 feeling of rate processes and what have you, and, you 14 know, certainly, an expert analyst gets insight. It 15 just doesn't come out of a statistical presentation 16 of, you know, various metrics that might be valuable 17 to measure against acceptance criteria. But to really 18 assess as evidence, which, of course, ultimately, all 19 these analyses are, there needs to be a tangible 20 event. But when you're running thousands of cases, 21 it's difficult to do so, so you're really looking for 22 something representative. In this case, that's 23 something at the 95/95 confidence probability.

24 As a throwback, I just wouldn't expect it 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 to kind of look like a traditional analysis. For 1

instance, what's difficult, where this kind of comes 2

from, you know, comparing it to LOCA where they may 3

only run 59, certainly, you can look at a limiting 4

case. But in those limiting cases, the samples 5

themselves, you

know, particularly,

say, less 6

important than the more dominant ones, they may not 7

look right, you know, because they're in the wrong 8

direction of what might be otherwise considered 9

conservative.

10 Now, maybe in a case like running 11 thousands of cases, that would be so much of an issue.

12 Truly, a 95 case would capture the more bounding 13 conditions, you know, associated with the major 14 parameters that you are looking at. So, again, it's 15 a simpler question. You know, are there, basically, 16 you know, results that, while they may be, you know, 17 of one representative event, they're still there, just 18 to throw back to the old ways these things were 19 presented in safety analysis reports. I still think 20 that's value in that. That's my point. There's still 21

value, as opposed to statistically presenting 22 information.

23 MR. KAIZER: Okay. I have just a -- is 24 there a question that I should be answering? 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

38 reason I'm asking is because, like, this, to me, is a 1

very interesting topic, as a lot of times things 2

usually are. And I want to make sure I'm not going 3

into down a rabbit hole that the ACRS, you guys, 4

aren't asking us to go down to answer the question or 5

just accept the comment.

6 MEMBER MARTIN: It's simply an expectation 7

of content of a safety analysis report. And my 8

expectation is that it truly looked like an analysis, 9

even though there is, of course, the statistical 10 component to it. It should still look like, you know, 11 here's an event and this was the outcome, these were 12 trends, inputs in affect, you know, the transient over 13 time.

14 MR. KAIZER: I think what I would expect 15 that in the transient analysis that they're 16 performing, but I don't know if I would necessarily 17 expect that in the method they would use to generate 18 the statistical limit.

19 MEMBER MARTIN: That's fine. That's fine.

20 MR. KAIZER: Yes, okay.

21 MEMBER MARTIN: But a reasonable person 22 coming from the outside picks up the safety analysis 23 report. They want more than just a --

24 MR. KAIZER: 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

39 MEMBER MARTIN:

statistical 1

presentation of information. They want something that 2

they understand really from kind of a science, 3

engineering basis, as opposed to a math based.

4 MR. KAIZER: Correct.

5 CHAIR KIRCHNER: Josh, could you put your 6

limitations and conditions in number two in some 7

perspective, given this is an open meeting? There are 8

numerous equations that are referenced in the 9

submodels and such. What you're really saying is, 10 when it comes to applying this methodology in Chapter 11 15, we are going to go back and review what?

12 MR. KAIZER: Sure. So there are a lot of 13 input parameters or input variables that impact your 14 statistical limit, and there's a question of how do 15 you treat the uncertainty of those. When we say how 16 do you treat the uncertainty, what equation are you 17 going to use? Are you going to assume it's normally 18 distributed, uniform distributed? If you are, what 19 are the parameters of that distribution? Are you 20 going to assume there's a linear relationship?

21 There's a whole bunch of questions.

22 In the initial topical report, NuScale 23 gave examples of how they would treat those 24 uncertainties, but they hadn't finalized 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 information yet. So we pretty much said, okay, for 1

these variables, and I think we listed however many 2

there were, there was a handful, okay, that you would 3

have to come in and tell us how you're going to 4

capture that uncertainty. And there's just a bunch of 5

different ways to do it. The one way is, well, we're 6

going to assume a conservatively high or low value.

7 You can do that, but, if it's statistical, you're 8

probably going to say, well, we think that this is 9

going to be normally distributed, and we think this is 10 the way to determine the mean and this is the way to 11 determine the variance. We think that it's best to 12 treat this as a uniform distribution, so here's its 13 lower limit, here's its upper limit. And that is, 14 well, I guess, the further details of that number two.

15 CHAIR KIRCHNER: Thank you.

16 MR. KAIZER: If there are no further 17 questions, I'll turn it over to Adam.

18 MS. JOSEPH: Just quickly. Thanks, Josh.

19 Stacy Joseph again. The time frame for rod ejection 20 topical report is similar to that of subchannel.

21 NuScale submitted Revision 2 of the rod ejection 22 topical report in December 2021. The staff issued an 23 RAI and received NuScale's response in September 2022.

24 The staff performed an audit between April 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

41 September 2023. And following completion of the 1

audit, NuScale revised the topical report to address 2

the feedback from the staff. The staff then completed 3

the review and issued the advanced SER on January 4th, 4

2024.

5 Adam.

6 MR. RAU: All right. Thank you, Stacy.

7 Okay. And so, as NuScale mentioned in their 8

presentation, the regulatory basis for the rod 9

ejection accident is GDC 28. It requires an 10 evaluation of limiting reactivity insertion accidents 11 for the effect on the reactor coolant pressure 12 boundary and for core coolability. In NuScale's case, 13 rod ejection is the limiting accident in their case.

14 So the regulatory guidance for this 15 accident is given in, primarily, Reg. Guide 1.236.

16 You know, it was mentioned in their presentation that 17 this is the new guidance that's come out since the 18 previous revision of the topical. There's additional 19 information in SRP 4.2, Appendix B, as well as 15.4.8, 20 as well.

21 And so the NRC staff conclusions for the 22 evaluation was that the rod ejection accident analysis 23 methodology is a systematic methodology for analyzing 24 this accident. We did place three limitations 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

42 conditions on the topical report that are primarily 1

concerned with, if I could draw a trend between them, 2

I would say articulating the scope of our approval for 3

this, and I think, hopefully, that comes through as a 4

through line through the three limitations and 5

conditions.

6 So the first is related to the 7

application. So when this is applied, it just states 8

that applicability needs to be demonstrated. So this 9

is, you know, a generic methodology that's applied to 10 a new design that maybe NRC staff hasn't had a chance 11 to look at yet, and that's just a question that would 12 have to be answered at that time.

13 So limitation and condition number two.

14 I know ACRS members had some questions on this, and, 15 you know, we'll definitely get a chance to talk about 16 the basis in the closed session. Just to try to say 17 a bit about it in the open session, I think the 18 motivation here is that there's a sensitivity to the 19 axial offset in the code, and so the -- well, again, 20 trying not to get into too many details in the open 21 session, we wanted to have a condition reflecting that 22 saying if this is applied to a design that operates 23 with control rods inserted for a long period of time 24 or has a load following scheme that involves this sort 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

43 of operation, that this is something that should be 1

addressed and may be outside the scope of staff's 2

approval.

3 MEMBER MARCH-LEUBA: Your efficient 4

evaluation that if we allowed 1:53:20 operation, the 5

uncertainty of the equation will increase because now 6

you will have the offset, the axial offset, and all 7

that --

8 MR. RAU: That's right, yes. Not sure if 9

I say uncertainty or bias or conservatism, but one of 10 those, something in that family would --

11 MEMBER MARCH-LEUBA: Another thing I 12 wanted to place on the open session is, in my mind, 13 there are two extremes. On one extreme, you can 14 provide a link to the control rod position to the 15 grade dispatcher and he controls the power of your 16 reactor at any time he wants. On the other extreme, 17 you have a power plant that is co-located with solar 18 and wind, and you know in the middle of the day you're 19 going to have lower power, and you have a pre-planned 20 hour2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> of shade during the day. And if you're in that 21 way, you can probably control the power with boron, 22 and it wouldn't cause such problems. And that's the 23 most likely one.

24 So I understand what limitations 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

44 there. And if you decide to do load following, come 1

talk to me and we'll decide if it's okay. Most 2

likely, it will be reprogrammed during the day and 3

many plants are doing that already.

4 MR. RAU: Yes. And, you know, hopefully, 5

we provided enough in the SE and the condition itself 6

that, you know, if that comes into a future reviewer, 7

they'll understand where we --

8 MEMBER MARCH-LEUBA: It's good, like, in 9

the SRP in NUREG-0800 you provided hints to the future 10 reviewers, which might be younger 20 years from now to 11 look for. My principle concern is if it's placing an 12 undue burden on NuScale because we are limiting them 13 to bystanders and say, well, we won't bother when 14 maybe you can do it.

15 MR. RAU: Yes, that makes sense. The 16 third limitation condition is just recognition that 17 the NRC staff considered some of the methodologies 18 cited in the topical report to be integral parts of 19 the methodology, so that particular nuclear analysis 20 methods that were cited, as well as the subchannel 21 methodology, you know, played into our review. And so 22 if these were to, you know, if you were to try to 23 change these out, we would consider this a change to 24 the methodology itself.

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 With that, I will turn it back over to 1

Stacy.

2 CHAIR KIRCHNER:

Members, further 3

questions, statements, comments? I note for the 4

record I detected Dennis Bley, our consultant, and 5

Steve Schultz also are participating today.

6 So then thank you. At this juncture, I 7

think we'll change to, turn to public comments. And, 8

with that, we have Harold Scott, I see, on our screen.

9 Good afternoon, Harold. Since you already submitted 10 a comment, do you wish to make any public statement?

11 You have to unmute yourself.

12 MR. SNODDERLY: Well, I think Harold did 13 request that someone, and I can do it for you --

14 CHAIR KIRCHNER: We can read it.

15 MR. SNODDERLY: Yes, that we would read it 16 for Harold, and then we'll follow up and see if --

17 CHAIR KIRCHNER: Okay. So, Harold, I'm 18 going to ask Mike Snodderly, the Designated Federal 19 Official, to read your comments into the record.

20 MR. SNODDERLY: Thank you, Chair Kirchner.

21 This is Mike Snodderly. This is an email that we 22 received yesterday, Monday, February 5th, from Harold 23 Scott. It reads as follows: My topic is amount of 24 proprietary marking redaction. Can you or another 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

46 staff read out this message during public comment 1

period NuScale meeting? I have trouble speaking.

2 What is it about plots of computer code output that 3

makes them proprietary? I think the public would find 4

value in seeing explicit margins. I would appreciate 5

ACRS members considering if the topic is a concern to 6

be raised with the commissioners. Thanks for 7

listening.

8 That was the end of the email. This email 9

will also be included in the official transcript.

10 CHAIR KIRCHNER: Now it's our, not policy 11 but practice, I think, is more accurate to say that 12 the committee doesn't respond in realtime. We address 13 comments raised by the public and usually include them 14 in our considerations for a letter. In this 15 particular case, though, I just would observe that the 16 committee in the past, as a general practice, has 17 encouraged all applicants to make as much material 18 publicly available as supports their safety case, and 19 we've had numerous interactions over the last years 20 with applicants to encourage them to do so.

21 So, Harold, your comment is duly noted.

22 It is not in our control to decide what is proprietary 23 or not, but it is in our, I think, the committee's 24 interests to encourage all applicants to make as 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

47 of their safety case publicly available, and that 1

would include such detailed plots as you were asking 2

for.

3 MR. SCOTT: Thank you very much. Thank 4

you. So thank you very much. Thank you.

5 CHAIR KIRCHNER: Thank you, Harold. Are 6

there any other members of the public or those present 7

here in the room who wish to make a comment? Please 8

come forward or unmute your line and identify yourself 9

and affiliation, as appropriate, and make your 10 comment. Sarah. Okay, Sarah. Go ahead.

11 MS. FIELDS: Yes, this is Sarah Fields 12 with Uranium Watch in Moab, Utah. To follow up on Mr.

13 Scott's email comment, I found recently that large 14 sections of applications related to so-called advanced 15 reactors and also the NuScale small modular reactor 16 project that you're reviewing now, they're just 17 redacting. You look at an application, you look at a 18 submittal, and most of it is redacted. So I think 19 information that used to be readily available to the 20 public is now being redacted.

21 So if you're under the illusion that the 22 industry is making everything available possible 23 available to the public, you're mistaken. All this 24 stuff is just missing. Thank 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

48 CHAIR KIRCHNER: Thank you, Sarah. Any 1

further comments?

2 MEMBER MARCH-LEUBA: Yes. Mine is related 3

to this, too.

4 CHAIR KIRCHNER: Okay. This is Member 5

March-Leuba.

6 MEMBER MARCH-LEUBA: One consideration 7

that we need to have here is the export control is 8

often more restricted on proprietary measures, and all 9

of this, the science, are on export control. And if 10 you release this information, you can go to jail much 11 easier. Proprietary, NuScale can sue you. But if you 12 release export control information, you can go to 13 jail. So people are more careful because of that.

14 CHAIR KIRCHNER: Thank you. Further 15 comments from the public?

16 MR. SNODDERLY: Excuse me, Chair Kirchner.

17 CHAIR KIRCHNER: Yes.

18 MR. SNODDERLY: If I could add, Ms.

19 Fields, this is Mike Snodderly from the ACRS staff.

20 You might find it interesting, if you look at the 21 recent Revision 1 to the publicly-available non-22 proprietary version of Chapter 15, accident analysis, 23 and Section 15.4 on the rod ejection accident, there 24 is the description of the sequence of events 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

49 results that may give you, you may find them of 1

interest. So there are more results that are 2

available concerning the rod ejection accident 3

interview he publicly-available FSAR chapter. And if 4

you have trouble finding that, Sarah, you have my 5

email and I can help you find that.

6 MS. FIELDS: I was talking generally, not 7

specifically about this issue that you're discussing 8

today. I'm talking generally about applications.

9 MR. SNODDERLY: Okay. Thank you for the 10 clarification.

11 CHAIR KIRCHNER: Thank you. Not hearing 12 further comments, we are going to take a short break 13 here and go into a closed session with a different 14 Teams link. And those that need to know to 15 participate will have access to that Teams link. And 16 with that, we are on a break for 15 minutes. It is 17 currently five minutes after two. We'll take a break 18 until 2:20 Eastern Time.

19 (Whereupon, the above-entitled matter went 20 off the record at 2:03 p.m.)

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

LO-156239 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com January 25, 2024 Docket No.52-050 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738

SUBJECT:

NuScale Power, LLC Submittal of Presentation Materials Entitled Statistical Subchannel Analysis Methodology and Rod Ejection Accident Methodology Topical Reports, ACRS Open Session, PM-154736, Revision 0 (Open Session)

The purpose of this submittal is to provide presentation materials to the NRC for use during the upcoming Advisory Committee on Reactor Safeguards (ACRS) NuScale Subcommittee Meeting on February 6, 2024. The materials support NuScales Statistical Subchannel Analysis Methodology and Rod Ejection Accident Methodology topical reports of the NuScale Standard Design Approval Application.

The enclosure to this letter is the nonproprietary version of the presentation entitled Statistical Subchannel Analysis Methodology and Rod Ejection Accident Methodology Topical Reports, ACRS Open Session.

This letter makes no regulatory commitments and no revisions to any existing regulatory commitments.

If you have any questions, please contact Wren Fowler at 541-452-7183 or sfowler@nuscalepower.com.

Sincerely, Tom Griffith Manager, Licensing NuScale Power, LLC Distribution:

Mahmoud Jardaneh, NRC Getachew Tesfaye, NRC Mike Snodderly, NRC

Enclosure:

Statistical Subchannel Analysis Methodology and Rod Ejection Accident Methodology Topical Reports, ACRS Open Session, PM-154736, Revision 0 (Open Session)

Tom Grifffif th

LO-156239 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com

Enclosure:

Statistical Subchannel Analysis Methodology and Rod Ejection Accident Methodology Topical Reports, ACRS Open Session, PM-154736, Revision 0 (Open Session)

1 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Statistical Subchannel Analysis Methodology and Rod Ejection Accident Methodology Topical Reports February 6, 2024 ACRS Open Session

2 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Acknowledgement and Disclaimer This material is based upon work supported by the Department of Energy under Award Number DE-NE0008928.

This presentation was prepared as an account of work sponsored by an agency of the United States (U.S.)

Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. Government or any agency thereof.

3 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Statistical Subchannel Analysis Methodology, TR-108601-P Supplement 1 to Subchannel Analysis Methodology, TR-0915-17564-P-A, Rev. 2

4 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Statistical Subchannel Analysis Methodology - History

• Subchannel Analysis Methodology, TR-0915-17564-P-A, Rev. 2 o Approved by NRC in December 2018 and previously presented to ACRS August 24, 2018 subcommittee meeting September 6, 2018 full committee meeting o Used for the NuScale US600 design codified in 10 CFR 52 Appendix G

• Statistical Subchannel Analysis Methodology, TR-108601-P, Rev. 0 submitted in December 2021 o Serves as a supplement to TR-0915-17564-P-A, Rev. 2

• NRC staff performed review and audit of TR-108601-P o One request for supplemental information (RSI) o No requests for additional information (RAIs) o Multiple audit questions

• TR-108601-P was revised during the review to address NRC staff feedback

• Current revision is TR-108601-P, Rev. 4 - submitted November 2023

5 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Overview of Previous Subchannel Methodology in TR-0915-17564-P-A, Rev. 2

• VIPRE-01 used for steady-state and transient analysis

• Methodology fulfills requirements of VIPRE-01 generic safety evaluation report (SER) limitations

• Methodology application and treatment of uncertainties

• Objective: critical heat flux (CHF) and fuel centerline melt

• General methodology approach:

o Input uncertainties treated deterministically; no credit for statistical randomness o Conservative basemodel development o Generic cycle-independent radial power distribution o Bounding axial power shapes o Detailed radial and axial nodalization evaluations o Detailed checklist to ensure compliance with method

6 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Subchannel Methodology Changes in TR-108601-P

• Changes from TR-0915-17564-P-A, Rev 2:

o Treatment of uncertainties - statistical for a set of parameters instead of deterministic approach o Radial nodalization o Axial domain o Axial nodalization

• Unchanged:

o Fuel conduction o Grid and frictional losses o Cross-flow and mixing o Qualification (validation and applicability)

• The Statistical Subchannel Analysis Methodology utilizes a statistical approach in defining the CHF analysis limit; but, many aspects of the methodology continue to employ a conservative deterministic approach (e.g., axial and radial power profiles)

• The intent of introducing a statistical treatment of uncertainties in certain areas was to reduce some of the overly conservative treatments with a defendable basis and to provide a better representation of the physical response

7 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Subchannel Methodology: Statistical vs. Deterministic

• Deterministic: Event analysis input uncertainties (power distributions, boundary conditions, tolerances, etc.) are biased independently in the limiting direction o Range of axial and radial power distributions allowed by operations not treated statistically o Variations possible from: exposure, power, boron concentration, control rod insertion, axial offset, etc.

o As in existing approved methodology:

Radial power distribution: Artificially created to preserve measured Technical Specification allowed radial peaking and minimize beneficial cross-flow in analysis Axial power distribution: Search performed for limiting shape allowed by axial offset

• Statistical: All uncertainties associated with both CHF correlation and event analysis inputs are statistically treated in order to determine the CHF analysis limit o Statistical approach accounts for all uncertainties with a 95% probability at the 95% confidence level o Statistical approach continues to require use of an approved CHF correlation with a 95/95 design limit

8 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Rod Ejection Accident Methodology, TR-0716-50350-P

9 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Rod Ejection Accident Methodology - History

• Rod Ejection Accident Methodology, TR-0716-50350-P-A, Rev. 1 o Approved by NRC in June 2020 o Previously presented to ACRS February 19, 2020 subcommittee meeting March 5, 2020 full committee meeting o Used for the NuScale US600 design codified in 10 CFR 52 Appendix G

• TR-0716-50350-P, Rev. 2 submitted in December 2021

• NRC staff performed review and audit of TR-0716-50350-P o No RSIs o One RAI with two questions o Multiple audit questions

• TR-0716-50350-P was revised during the review to address NRC staff feedback

• Current revision is TR-0716-50350-P, Rev. 3 - submitted October 2023

10 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Overview of Previous Rod Ejection Methodology in TR-0716-50350-P-A, Rev. 1

• Methodology for modeling rod ejection accident (REA)

• Bounding reactivity initiated accident (RIA) from General Design Criteria (GDC) 28

• REA is unique in comparison to other Chapter 15 events o Phenomena, time-scales, acceptance criteria, methods

• Combination of codes and methods:

o SIMULATE-3K: Transient nuclear physics simulations o NRELAP5: Transient systems thermal-hydraulics o VIPRE-01: Transient detailed core thermal-hydraulics o Adiabatic Fuel Model: Conservative analytical model of fuel enthalpy and temperature

• Unique acceptance criteria from Regulatory Guide (RG) 1.77, NUREG-0800

• Justification for software, acceptance criteria, applicability, and treatment of uncertainties

11 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Rod Ejection Accident Methodology Changes

• Changes from TR-0716-50350-P-A, Rev. 1:

o Replacement of RG 1.77 with RG 1.236 (issued in June 2020) o Change to pellet clad mechanical interaction (PCMI) fuel failure acceptance criteria from RG 1.236 o Calculation of fuel enthalpy and temperature via VIPRE-01 instead of adiabatic fuel model o Subchannel statistical analysis limit o Other minor changes to accommodate updated statistical subchannel method o Incorporate content from previous RAIs and add new detail, justification, and explanation to address NRC staff questions during review

• Unchanged:

o SIMULATE-3K analysis and uncertainty treatment o Qualification (validation and applicability)

• Primary driver of the revision was the new RG 1.236

• REA method effectively not impacted by design changes o Increase in power was not a driver of the changes

12 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Summary and Conclusions

• Subchannel:

o Statistical treatment of uncertainties allows for improved results while maintaining overall robust analysis approach

• Rod ejection:

o Incorporate changes from RG 1.236 issuance o Simplify analysis structure to use VIPRE-01 for fuel calculations o Interface with updated subchannel method

• Improvements in methods while maintaining conservative results

• Results from calculations utilizing these methodologies are contained in Chapters 4 and 15 of the NuScale standard design approval application (SDAA) for the US460 design

13 PM-154736 Rev. 0 Copyright © 2024 NuScale Power, LLC.

NuScale Nonproprietary Template #: 0000-21727-F01 R10 Acronyms ACRS Advisory Committee on Reactor Safeguards CFR Code of Federal Regulation CHF Critical Heat Flux GDC General Design Criteria NRC Nuclear Regulatory Commission PCMI Pellet Clad Mechanical Interaction RAI Request for Additional Information REA Rod Ejection Accident RG Regulatory Guide RIA Reactivity Initiated Accident RSI Request for Supplemental Information SDAA Standard Design Approval Application SER Safety Evaluation Report

Presentation to the ACRS Subcommittee Staff Review of NuScale Topical Reports TR-108601-P, REV 4, STATISTICAL SUBCHANNEL ANALYSIS METHODOLOGY, SUPPLEMENT 1 TO TR-0915-17564-P-A, REVISION 2, SUBCHANNEL ANALYSIS METHODOLOGY TR-0716-50350-P, REV 3, ROD EJECTION ACCIDENT METHODOLOGY February 6, 2024 (Open Session)

Non-Proprietary 1

NRC Technical Review Areas/Contributors 2

Non-Proprietary Statistical Subchannel Analysis Methodology Rebecca Patton (BC), Reactor Systems NRR/DSS/SRNB Antonio Barrett, NRR/DSS/SRNB Joshua Kaizer, NRR/DSS/SFNB Peter Lien, RES/DSA/CRAB II Rod Ejection Accident Methodology Rebecca Patton (BC), Reactor Systems NRR/DSS/SRNB Zhian Li, NRR/DSS/SRNB Ryan Nolan, NRR/DSS/SRNB Adam Rau, NRR/DSS/SNSB Andrew Bielen, RES/DSA/FSCB Project Managers Stacy Joseph, TR PM Getachew Tesfaye, Lead PM

SSAM Staff Review Timeline NuScale submitted its Topical Report (TR) TR-108601-P, Rev 0 on December 30, 2021 (ML21364A133) as supplemented by letters dated April 25, 2022 (ML22115A222) and December 13, 2022 (ML22347A314).

Staff performed an audit between July 13, 2022 and September 27, 2023 (ML23295A001).

Following the audit, NuScale submitted Revisions 3 and 4 on October 12, 2023 (ML23285A341) and November 6, 2023 (ML23285A341) of the TR.

Staff issued the Advanced Safety Evaluation Report (SER) on November 6, 2023 (ML23277A007) 3 Non-Proprietary

SSAM Regulatory Basis General Design Criterion 10, Reactor design, of Appendix A The reactor core and associated coolant, control, and protection systems shall be designed with appropriate margin to assure that specified acceptable fuel design limits are not exceeded during any condition of normal operation, including the effects of anticipated operational occurrences.

Standard Review Plan, Section 4.4, Thermal and Hydraulic Design.

..there should be a 95-percent probability at the 95-percent confidence level that the hot

[fuel] rod in the core does not experience a DNB [departure from nucleate boiling] or boiling transition condition during normal operation or AOOs.

4 Non-Proprietary

SSAM Staff SER Conclusions The SSAM is an acceptable methodology to calculate the margin to fuel thermal limits such as the critical heat flux ratio through a statistical combination of the uncertainties.

There were two limitations and conditions:

1. An applicant referencing [the SSAM] in the safety analysis must also reference an approved CHF correlation which has been demonstrated to be applicable for use with [the NSAM]. (Carry over from NSAM)

2. The SSAM relies on multiple submodels to calculate the statistical critical heat flux analysis limit. While some of these submodels have been reviewed and approved as part of the NRC staffs review and approval of the SSAM, the submodels listed in the SER would need to be reviewed and approved before the application of this methodology for a licensing analysis.

5 Non-Proprietary

6 Non-Proprietary NuScale submitted its Topical Report (TR) TR-0716-50350-P, Rev 2 on December 21, 2021 (ML21351A400).

NuScale supplemented its submittal by letter dated, September 14, 2022 in response to requests for additional information (RAI), RAI No. 9936 from the NRC staff.

Staff performed a limited scope audit between April 19, 2023 and September 27, 2023 (ML23295A001).

Following the audit, NuScale submitted Revision 3 of the TR on October 20, 2023 (ML23293A292)

Staff issued the Advanced SER on January 4, 2024 (ML23310A166)

Staff Review Timeline TR-0716-50350-P, Rev 3 Rod Ejection Accident Methodology

Regulatory Basis General Design Criterion 28, Reactivity Limits, of Appendix A Criterion 28Reactivity limits. The reactivity control systems shall be designed with appropriate limits on the potential amount and rate of reactivity increase to assure that the effects of postulated reactivity accidents can neither (1) result in damage to the reactor coolant pressure boundary greater than limited local yielding nor (2) sufficiently disturb the core, its support structures or other reactor pressure vessel internals to impair significantly the capability to cool the core. These postulated reactivity accidents shall include consideration of rod ejection (unless prevented by positive means), rod dropout, steam line rupture, changes in reactor coolant temperature and pressure, and cold water addition.

Standard Review Plan Sections 4.2 and 15.4.8 and Regulatory Guide 1.236, Pressurized-Water Reactor Control Rod Ejection and Boiling-Water Reactor Control Rod Drop Accidents for reactivity-initiated accidents.

7 Non-Proprietary

Staff SER Conclusions TR-0716-50350 P, Revision 3 provides a systematic methodology for performing rod ejection accident (REA) analysis subject to the following limitations and conditions:

1. An applicant or licensee referencing this report is required to demonstrate the applicability of the REA methodology to the specific NPM design. The use of this methodology for a specific NPM design requires the NRC staff review and approval of the applicant or licensee determination of applicability.

2. The REA methodology is limited to evaluation of REAs for fuel that has not experienced significant depletion with control rods inserted, such as from non-baseload operation.

3. The staffs approval is limited to the use of the rod ejection methodology with TR-0616-48793-P-A, Revision 1 (Reference 14), Nuclear Analysis Codes and Methods Qualification, and TR-108601-P, Revision 4 (Reference 13),

Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology.

8 Non-Proprietary

Questions/comments from members of the public before the closed session starts?

9 Non-Proprietary

From:

Harold Scott To:

Michael Snodderly

Subject:

[External_Sender] public comment for 2/6/24 ACRS SC Date:

Monday, February 5, 2024 12:14:24 PM My Topic is amount of proprietarymarking(redaction) can you or anotherNRC staff read out this messageduring publiccommentperiodNuScale meeting ? I have troublespeaking What is it aboutplots of computer code output that makesthem proprietary ?

I think thepublic wouldfind valuein seeingtheexplicit margins I would appreciate ACRS membersconsideringif thetopicis aconcern to be raisedwith the Commissioners.

Thanksfor listening