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 1

1

2

3 4 DISCLAIMER

5

6

7 UNITED STATES NUCLEAR REGULATORY COMMISSIONS

8 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS

9

10

11 The contents of this transcript of the

12 proceeding of the United States Nuclear Regulatory

13 Commission Advisory Committee on Reactor Safeguards,

14 as reported herein, is a record of the discussions

15 recorded at the meeting.

16

17 This transcript has not been reviewed,

18 corrected, and edited, and it may contain

19 inaccuracies.

20

21

22

23

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(202) 234-4433 W ASHINGTON, D.C. 20005-3701 www.nealrgross.com 1

1 UNITED STATES OF AMERICA

2 NUCLEAR REGULATORY COMMISSION

3 + + + + +

4 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS

5 (ACRS)

6 NUSCALE DESIGN-CENTERED SUBCOMMITTEE

7 + + + + +

8 OPEN SESSION

9 + + + + +

10 TUESDAY, FEBRUARY 6, 2024

11 + + + + +

12 The Subcommittee met via hybrid Video

13 Teleconference, at 1:00 p.m. EST, Walt Kirchner,

14 Chairman, presiding.

15 COMMITTEE MEMBERS:

16 WALTER L. KIRCHNER, Chair

17 RONALD G. BALLINGER, Member

18 VICKI M. BIER, Member

19 CHARLES H. BROWN, JR., Member

20 VESNA B. DIMITRIJEVIC, Member

21 GREGORY H. HALNON, Member

22 JOSE A. MARCH-LEUBA, Member

23 ROBERT P. MARTIN, Member

24 DAVID A. PETTI, Member

25 THOMAS E. ROBERTS, Member

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1 ACRS CONSULTANT:

2 DENNIS BLEY

3 STEVE SCHULTZ

4

5 DESIGNATED FEDERAL OFFICIAL:

6 MICHAEL SNODDERLY

7

8 ALSO PRESENT:

9 ANTONIO BARRETT, NRR

10 ANDREW BIELEN, RES

11 ALLYSON CALLAWAY, NuScale

12 KRIS CUMMINGS, NuScale

13 SARAH FIELDS, Public Participant

14 MAHMOUD JARDANEH, NRR

15 STACY JOSEPH, NRR

16 JOSHUA KAIZER, NRR

17 ZHIAN LI, NRR

18 JEFF LUITJENS, NuScale

19 KEVIN LYNN, NuScale

20 SCOTT MOORE, ACRS

21 REBECCA PATTON, NRR

22 ADAM RAU, NRR

23 HAROLD SCOTT, Public Participant

24 GETACHEW TESFAYE, NRR

25 SARAH TURMERO, NuScale

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1 TABLE OF CONTENTS

2

3 Opening Remarks................. 4

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

5 Methodology and Rod Ejection

6 Methodology Topical Reports

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

8 Topical Reports

9 Opportunity for Public Comment.........45

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

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

2 12:59 p.m.

3 CHAIR KIRCHNER: The meeting will now come

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

5 on Reactor Safeguards, NuScale Design-Centered

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

7 this meeting. Members in attendance today are Ron

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

9 Greg Halnon, Thomas Roberts, and Charles Brown.

10 Do we have anyone listening in?

11 MR. BLEY: Vesna.

12 MEMBER DIMITRIJEVIC: Yes, I am here. Hi,

13 good morning.

14 CHAIR KIRCHNER: Welcome, Vesna. Good

15 afternoon.

16 MEMBER DIMITRIJEVIC: Good afternoon.

17 Right.

18 CHAIR KIRCHNER: Mike Snodderly is the

19 Designated Federal Officer for this meeting. The

20 subcommittee will review the staff's evaluation of two

21 NuScale topical reports on subchannel analysis

22 methodology. We are going to review two -- pardon me.

23 Let me find my place again. The subcommittee will

24 review the staff's evaluation of two NuScale topical

25 reports on subchannel analysis methodology and rod

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1 ejection accident methodology.

2 The committee reviewed and commented on

3 Revision 1 of the subchannel analysis methodology

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

5 rod ejection methodology topical report back in 2020.

6 Since that time, NuScale has revised these

7 methodologies to include a statistical subchannel

8 analysis methodology that utilizes an approach, a

9 statistical approach in defining critical heat flux

10 analysis limits. It is NuScale's intent that a

11 statistical treatment of uncertainty in certain areas

12 will reduce some of the conservatisms and treatments

13 with a defendable basis to provide a better

14 representation of the actual core physical response.

15 One objective of this meeting is to help

16 prepare the full committee for its upcoming review of

17 Chapters 4 reactor and Chapter 15 transient accident

18 analysis of the NuScale standard design approval

19 application that includes a power upgrade from 50

20 megawatts electric to 77 megawatts electric for each

21 module.

22 The ACRS was established by statute. It

23 is governed by the Federal Advisory Committee Act

24 (FACA). The NRC implements FACA in accordance with

25 its regulations found in Title 10 of the Code of

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1 Federal Regulations, Part 7. The committee speaks

2 only through its published letter reports. We hold

3 meetings to gather information and perform preparatory

4 work that will support our deliberations at a full

5 committee meeting.

6 The rules for participation in all ACRS

7 meetings were announced in the Federal Register on

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

9 public website provides our charter, bylaws, agendas,

10 letter reports, and full transcripts of our full and

11 subcommittee meetings, including the slides presented

12 there. The agenda for this meeting was also posted

13 there. A portion of this meeting will be closed to

14 protect NuScale proprietary and export controlled

15 information pursuant to 5 U.S. Code 552(b)(c)(4).

16 As stated in the Federal Register notice

17 and in the public meeting notice posted to the

18 website, members of the public who desire to provide

19 written or oral inputs to the subcommittee may do so

20 and should contact the Designated Federal Officer five

21 days prior to the meeting. A communications channel

22 has been opened to allow members of the public to

23 monitor the open portions of this meeting. The ACRS

24 is now inviting members of the public to use the MS

25 Teams link to view slides and other discussion

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1 material during these open sessions. The MS Teams

2 link information was placed in the agenda on the ACRS

3 public website.

4 We have received one set of written

5 comments from Harold Scott. Those comments have been

6 distributed to the members, and they have been

7 provided to the staff at NuScale for awareness. The

8 comments will be read into the record during the

9 public comment portion of this meeting and attached to

10 the transcript. We have not received any additional

11 requests to make oral statements from members of the

12 public regarding today's session.

13 Written comments may be forwarded to

14 Michael Snodderly, today's DFO. There will be an

15 opportunity for public comment, as well, and we have

16 set aside ten minutes in the agenda at the conclusion

17 of the open session of this meeting for comments from

18 the public listening to the meeting.

19 A transcript of the open portions of the

20 meeting is being kept, and it is requested that

21 speakers identify themselves and speak with sufficient

22 clarity and volume so that they can be readily heard.

23 Additionally, participants should mute themselves when

24 not speaking, including their cell phones.

25 And with all of that, we'll take a breath

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1 and turn to, proceed with the meeting. And I'll call

2 on Kris Cummings of NuScale to begin today's

3 presentations. Kris.

4 MR. CUMMINGS: Great. Thank you very

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

6 engineer with NuScale. I have been with NuScale for

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

8 with test vendors and reactor vendors Holtec and

9 Westinghouse and have been familiar with these

10 particular types of analyses in the past.

11 I want to thank the ACRS for having us

12 here. This is what I consider, in essence, the

13 kickoff of the ACRS review of the SDA application and

14 the associated methodologies that support that

15 application. So thank you for having us here. It has

16 been a pleasure working with the NRC staff during the

17 review of this process, and I think we've had some

18 good dialogue with them during the process and come to

19 what we feel is a good resolution of the issues and an

20 approved methodology.

21 I want to note that we took some of the

22 ACRS's comments from the DCA period under advisement,

23 and so we submitted these two topical reports about a

24 year in advance of when we submitted the SDA. So that

25 allows all of us, the NRC, the ACRS, and ourselves, to

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

2 well in advance of the approval of the SDA

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

4 to heart.

5 So today we're focused in particular on

6 the two methodologies that you mentioned and the

7 changes that we made to those methodologies associated

8 with the revisions were supplement to these topical

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

10 front of the ACRS, as you mentioned, for Chapter 4 and

11 Chapter 15. So we're focused, again, today on the

12 methodologies that will support the analysis or do

13 support the analysis in the SDA application.

14 With that, that is my opening comments,

15 and so what I would like to do is have my colleagues

16 here that are presenting give an introduction of

17 themselves. Yes, an introduction.

18 MS. TURMERO: Hi. So my name is Sarah

19 Turmero. I'm a licensing engineer for NuScale, and I

20 have been with the company in this position for about

21 a year and a half. And before coming to NuScale, I

22 was a reactor engineer at Waterford 3. And I will be

23 covering the open portion of the statistical

24 subchannel analysis methodology slides.

25 MEMBER MARCH-LEUBA: The microphones are

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1 extremely sensitive if you are close to them. They

2 are more concerned with minimizing background noise,

3 so do talk into them.

4 MS. TURMERO: Okay. Thank you.

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

6 licensing engineer with NuScale. I have been here

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

8 in licensing at an operating plant, a BWR operating

9 plant, and I also have previous licensing experience

10 with new plants, the Japanese designed the U.S. APWR

11 that was in process a few years ago and came to the

12 ACRS several times. So that's my background.

13 MR. LUITJENS: My name is Jeff Luitjens.

14 I'm in the nuclear fuels group. The last few years,

15 11 years at NuScale, jumping around from validation,

16 code development, testing. My background, Ph.D. in

17 nuclear engineering, focus on CHF, and today I am here

18 to provide information on the subchannel.

19 MS. CALLAWAY: My name is Allyson

20 Callaway. I'm the senior manager of nuclear fuels.

21 I have been at NuScale for 13 years in various

22 capacities within the fuels and neutronics

23 organization.

24 MS. TURMERO: So to kick off, I just want

25 to acknowledge that we are the proud recipient of

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

2 Energy and are thankful to identify their support of

3 our program.

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

5 off with the statistical subchannel analysis

6 methodology topical report. So for the history of the

7 statistical subchannel analysis methodology, it starts

8 with the originally approved subchannel analysis

9 methodology that was approved by the NRC in December

10 of 2018 and previously presented to the ACRS in August

11 and September of 2018. And this was the topical

12 report that was used for the NuScale US600 design

13 that's codified in 10 CFR Part 52, Appendix G.

14 And so the statistical subchannel analysis

15 methodology was submitted in December of 2021, and it

16 serves as a supplement to the originally-approved

17 methodology. So the staff performed a review and

18 audit of the topical report where there was one

19 request for supplemental information, no requests for

20 additional information and multiple audit questions.

21 The topical report was revised during the review

22 process to address staff feedback and the most recent

23 revision is Revision 4. That was submitted in

24 November of 2023.

25 So an overview of the previous subchannel

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1 methodology. VIPRE-1 was used for steady state and

2 transient analysis. The methodology fulfilled the

3 requirements of VIPRE-1 generic safety evaluation

4 limitations, and the topical report covered the

5 methodology application and treatment of uncertainties

6 where the objective of the topical report was to

7 provide a methodology to determine fuel thermal

8 margins, such as critical heat flux and fuel center

9 line melt.

10 And here on the slide, we have an outline

11 of the general methodology approach, and we'll be

12 going over the differences from the original topical

13 report to the statistical method.

14 So the changes from the original method,

15 of course, the treatment of uncertainties. There's a

16 statistical treatment of uncertainties for a set of

17 parameters instead of a deterministic approach.,

18 radial and axial nodalization, and axial domain. And

19 what remains unchanged is the fuel conduction, grade

20 and frictional losses, cross-flow and mixing, and the

21 qualification or the validation and applicability of

22 the topical report.

23 MEMBER MARCH-LEUBA: Number one, we are

24 going to interrupt you all the time. When you say

25 statistical analysis of the uncertainties, you mean

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1 what is called best estimate plus uncertainty type of

2 approach where we do kind of a Monte Carlo propagation

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

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

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

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

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

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

9 plus uncertainty. I would say our overall methodology

10 is still deterministic. It's just in the CHF analysis

11 for subchannel we're talking about statistical

12 treatments.

13 MEMBER MARCH-LEUBA: In the previous,

14 Revision 2, I don't remember the number, the approved

15 one, we used bounding uncertainties for every single

16 pyramid, whereas here, for the CHF, you do a Monte

17 Carlo type of sampling?

18 MR. LUITJENS: Yes. For a set of those

19 uncertainties, you know, five or six, we do a Monte

20 Carlo type uncertainty kind of based on what's the

21 uncertainty value and what's the distribution

22 associated with that uncertainty. We do a Monte Carlo

23 --

24 MEMBER MARCH-LEUBA: The ACRS is here for

25 the public, so you're talking to, somebody is going to

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1 read this transcript, and they need to understand what

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

3 professors at university. Assume you're talking to

4 your students.

5 MEMBER MARTIN: Robert Martin, member.

6 Treatment of uncertainties specific to systems code,

7 my understanding is you run thousands of cases with

8 VIPRE, correct? You can --

9 MR. LUITJENS: So for the systems codes,

10 those are done deterministically, so we take the

11 bounding, you know, high flow, low flow. Those get

12 fed to the subchannel, and we analyze those and get

13 the limiting value.

14 MEMBER MARTIN: So those parameters are

15 deterministically treated while the other ones are

16 sampled --

17 MR. LUITJENS: Correct, yes. So

18 determining the CHF analysis --

19 MEMBER MARTIN: The deterministic

20 subchannel is the statistical.

21 MR. LUITJENS: Correct.

22 MS. TURMERO: Okay. And as Jeff had

23 mentioned, so the statistical subchannel analysis

24 methodology utilizes the statistical approach into

25 finding the CHF analysis limit, whereas many of the

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1 aspects of the methodology still use a deterministic

2 approach. And so our intent of introducing the

3 statistical treatment of uncertainties was to reduce

4 some of the overly conservative treatments with a

5 defendable basis and to provide a better

6 representation of the physical response.

7 So statistical versus deterministic. For

8 the deterministic approach, the event analysis input

9 uncertainties are biased independently in a limiting

10 direction. And so range of axial and radial power

11 distributions that's allowed by operations are not

12 treated statistically. There are variations that

13 could be from exposure, power, boron concentration,

14 control rod insertion, axial offset. And so in the

15 existing methodology, the radial power distribution is

16 artificially created to preserve the tech spec-allowed

17 measured radial peaking and minimizing the beneficial

18 cross flow, and the axial power distribution is

19 determined for the limiting shape allowed by axial

20 offset.

21 For the statistical approach, all of the

22 uncertainties associated with both critical heat flux

23 correlation and event analysis inputs are

24 statistically treated and accounted for with a 95-

25 percent probability at the 95-percent confidence level

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1 in order to determine the critical heat flux analysis

2 limit. And the statistical approach still requires

3 the use of a critical heat flux correlation, the

4 approved critical heat flux correlation with a 95/95

5 design limit.

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

7 Lynn.

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

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

10 of Member Vicki Bier. And, Sarah, since I have my

11 mike on, this is -- your previous slide said

12 actinically created. Perhaps I'm hanging up on the

13 word. What you're really saying is that, when you

14 apply the existing approved methodology, you

15 accurately, not artificially, model what the core

16 radial peaking is such that it's representative of the

17 actual conditions. It's not artificially created.

18 I'm just stumbling over the choice of words there and

19 not what I believe is what you're actually doing.

20 MR. LUITJENS: Yes, I think that's the

21 correct interpretation of artificially. What we're

22 really trying to capture is what do we allow from the

23 core design aspect to make sure we're capturing what

24 we could possibly see.

25 CHAIR KIRCHNER: Okay. Artificially

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

2 trying to accurately model what the radial power

3 distributions is when you conduct your analyses.

4 Okay. Go on.

5 MEMBER MARCH-LEUBA: By artificial, I

6 guess you mean bounding, right?

7 MR. LUITJENS: Yes. By artificial, we

8 mean bounding.

9 MEMBER MARCH-LEUBA: So the tech specs is

10 really what bounds your operation. You may never

11 reach that solution, but you have tech specifics, you

12 going to need to be under that or you'll be shut down.

13 Since we are the end of this presentation

14 and if you can say it in the open session, will this

15 exercise gain you a 2-percent margin, a 10-percent

16 margin, a 25-percent margin? Was it worth it? I

17 mean, if you get into a factor of 500 percent, I would

18 be worried that you were tweaking too much.

19 MR. LUITJENS: Yes. If you're talking

20 about the specific application, kind of going back --

21 MEMBER MARCH-LEUBA: Yes. You also might

22 need to --

23 MR. LUITJENS: So from a sense, we're

24 actually maintaining the same amount of margin for

25 different designs.

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

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

3 little power upgrade, but we came back and sharpened

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

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

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

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

8 MEMBER MARCH-LEUBA: Let me refresh the

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

10 license with your method and with the new method,

11 what's the change in margin that you calculate? Is it

12 in the 5-percent range or is it in the 100-percent

13 range?

14 MR. LUITJENS: Yes, I'd say that's really

15 hard -- it's hard to get that because you don't have

16 a limit that's made for that specific methodology, so

17 it's hard to go back --

18 MEMBER MARCH-LEUBA: Is it a big

19 difference in your mind?

20 MR. LUITJENS: I would say it would not be

21 a big difference.

22 MEMBER MARCH-LEUBA: I'm going to

23 stipulate in the open, this statistical methodology is

24 well developed and used everywhere. There's nothing

25 new here. You're just joining the 21st century, as

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1 opposed to just doing methods --

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

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

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

5 MR. CUMMINGS: Right.

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

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

8 the rod ejection methodology. Rod ejection accident

9 methodology was previously approved as Revision 1 by

10 the NRC in June 2020, and it was previously presented

11 to the ACRS at the full committee meeting in March and

12 the subcommittee meeting in February of 2020.

13 The Revision 1, the approved version, was

14 used for the NuScale US600 design, which is codified

15 in 10 CFR 52, Appendix G. Subsequently, we submitted

16 Revision 2 in December 2021, and the NRC staff

17 performed a review and audit of Revision 2. We had no

18 RSIs. We had one RAI with two questions, and then we

19 had multiple audit questions.

20 So during the course of that interaction

21 with the NRC staff, we ended up making some changes to

22 the methodology throughout the process. And so we

23 submitted Revision 3 in October 2023, which is the

24 current revision.

25 The previously-approved version, Rev. 1,

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1 provided the methodology for modeling the rod ejection

2 accident, which is the bounding reactivity-initiated

3 accident in accordance with GDC 28. The rod ejection

4 is a bit unique compared to other Chapter 15 events.

5 It has its own phenomenon and time scales that are

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

7 own unique acceptance criteria. And that sort of

8 lends itself to having its own special method.

9 The approved method used a combination of

10 codes and methods, three codes, SIMULATE-3K, NRELAP5,

11 and VIPRE-01, and it also had a adiabatic fuel model

12 which was used to perform the calculation for fuel

13 entropy and temperature using, essentially, a hand

14 calculation.

15 The acceptance criteria that we used in

16 Revision 1 was based on Regulatory Guide 1.77, which

17 was the reg guide at the time, and also from the SRP

18 in NUREG-0800. And, overall, we provided a

19 justification for the software, the acceptance

20 criteria, the applicability, and the treatment of

21 uncertainties.

22 When we moved into Rev. 2, what were the

23 changes? Well, the big change was Reg. Guide 1.77 was

24 replaced with Regulatory Guide 1.236, and that was in

25 June 2020. So, essentially, just after the old

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

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

3 failure acceptance criteria, so that was sort of the

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

5 While we were doing that revision, we

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

7 and one of the things we identified was that the

8 adiabatic fuel model calculation, the hand

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

10 use VIPRE to perform those calculations of fuel

11 entropy and temperature.

12 In addition, as you just heard, we were

13 looking at the statistical analysis for subchannel, so

14 we wanted to incorporate that, as well. So bringing

15 that limit and make any changes that we needed to make

16 to the rod ejection methodology to better talk and

17 interface with that new method. And then, finally,

18 changes that were incorporated during the process were

19 details and justification that we added based on our

20 interaction with the NRC staff.

21 So we did not change the actual STIMULATE-

22 3K analysis for uncertainty treatment or the overall

23 qualification of the method. So, again, the primary

24 driver was the new regulatory guide. The methodology

25 itself was not really impacted by the design changes

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

2 power was not really the driver for the change.

3 As far as a summary for our open session,

4 for the subchannel analysis, the statistical treatment

5 of uncertainties allows for improved results while

6 still maintaining an overall robust analysis approach.

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

8 from the new reg guide and simplified our analysis to

9 better work with VIPRE and the new subchannel method

10 while still maintaining a conservative result.

11 And as Kris discussed earlier, these

12 methodologies, at this stage we're talking about the

13 methodologies themselves, but those methodologies are

14 ultimately used to produce results that are identified

15 in Chapters 4 and 15 of the NuScale standard design

16 approval application for US460. Those results will

17 obviously be coming back to the ACRS when those

18 chapters are reviewed.

19 MEMBER MARTIN: You don't get off too

20 easy. NuScale is, fundamentally, a light water

21 reactor and, clearly, you've --

22 MR. BLEY: Can you use the mike?

23 MEMBER MARTIN: I'm pretty close to the

24 mike. Fundamentally, you follow NUREG-0800. Early on

25 in the development of your safety case, you would have

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1 had to evaluated unique aspects of your design with

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

3 section related to reactivity insertion accidents that

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

5 there anything unique about reactivity insertion

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

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

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

9 benefit design change might benefit the likelihood of

10 such an event. Does that come into your thinking

11 going into this at all, or you're just pretty much

12 pushing the button like any LWR on this particular

13 event?

14 MR. LYNN: Well, I think one unique

15 aspect, right, being a smaller core and looking at

16 that certainly factors into it. And I know one

17 interesting thing, when we went from the uprate for

18 the power, actually, the benchmarking that was

19 performed, some of the benchmarking to the SPUR

20 analysis, for example, actually, when we uprated, the

21 power level is actually more in line with some of the

22 experimental data that's out there that was performed.

23 So sort of one unique aspect of being

24 small and being low power, you know, we're sort of

25 moving up in the power range and actually bring it

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1 maybe more in line a little bit with some of those

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

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

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

5 unique aspects.

6 I know that during the previous ACRS there

7 was some discussion about unique aspects, including

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

9 containment being closer to the vessel than it is in

10 a operating plant; and, therefore, does that change

11 anything when it came to rod ejection. But, you know,

12 we addressed that previously, and so there's nothing

13 new this time around that would make us revisit that,

14 no changes that we've made that would make that a

15 different scenario than it was before.

16 MEMBER MARCH-LEUBA: But, I mean, there's

17 no change between the approved design and the new

18 concept, but raw injection can be worse can be worse.

19 What I'm asking, when we're asking the question about

20 NUREG-0800, what could be -- 800 tells you take the

21 worst rod and eject it, right; so, in that case, you

22 have to do that. But, typically, if I remember

23 correctly, rods are a lot heavier than typical PWR; is

24 that correct?

25 MR. LYNN: I don't have the answer to

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1 that, but I do know that -- Allyson, do you want to --

2 MS. CALLAWAY: Allyson Callaway. You're

3 asking if the rods are heavier in mass or --

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

5 dollars.

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

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

8 preclude fuel failures still, and so that effectively

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

10 just controlled through the power-dependent insertion

11 limits. So the effective worth that's being ejected

12 is still low.

13 MEMBER MARCH-LEUBA: Because of the --

14 MS. CALLAWAY: Power-dependent insertion.

15 MEMBER MARCH-LEUBA: -- safety controls

16 over the rods are positioned.

17 MS. CALLAWAY: Right.

18 MEMBER MARCH-LEUBA: Similar to what BWRs

19 do, correct? They're all worth minimizers.

20 MEMBER ROBERTS: A general question. What

21 I think I heard -- this is Tom Roberts -- at least

22 from Jose is that, for the subchannel analysis, this

23 is basically what many people do. And for the rod

24 ejection, I think what you said is this is following

25 the reg guide revision. So would you characterize

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1 neither of these topical reports as novel in scope or

2 innovative in terms of nuclear safety?

3 MR. LYNN: Yes, we would agree.

4 MEMBER ROBERTS: Good. Thank you.

5 CHAIR KIRCHNER: Other members, any

6 comments, questions --

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

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

9 concur with your evaluation that this is a small

10 evolution. A few more years of learning and tweaking

11 on the calculations, nothing groundbreaking in my

12 opinion.

13 CHAIR KIRCHNER: Okay. Then we'll turn to

14 the staff for their presentation in the open session.

15 Thank you. Okay. When you're ready. Stacy, are you

16 leading off? Just pull it closer to you, please.

17 MS. JOSEPH: I'm going to turn it over to

18 my branch chief, Mahmoud Jardaneh, to give some

19 opening remarks, and then I'll kick off.

20 MR. JARDANEH: Thank you. Good afternoon,

21 Chair Kirchner, and good afternoon, ACRS subcommittee

22 members. I'm Mahmoud Jardaneh, M.J. for short. And

23 I serve as the branch chief of the New Reactor

24 Licensing Branch in the Division of New and Renewed

25 Licenses in NRR. I recently assumed this position and

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

2 the licensing review of the NuScale US460 design and

3 engaging with you in this and future NuScale meetings.

4 Thank you for the opportunity today for

5 the staff to present their review of the NuScale rod

6 ejection accident and subchannel analysis

7 methodologies topical reports associated with the

8 standard design approval application (SDAA). These

9 two topical reports are the last two of eight topical

10 reports submitted prior to the application. The

11 remaining SDAA topical reports are reviewed as part of

12 the application, and we will inform the ACRS when

13 their safety evaluation reports are available for the

14 ACRS.

15 In addition to the safety evaluation of

16 these topical reports, we have completed the Phase A,

17 the advanced safety evaluation, without open items for

18 five SDAA chapters, and advanced safety evaluations

19 for them will be available for ACRS in the coming few

20 weeks.

21 In today's meeting, the staff will focus

22 on the differences from the last time we presented on

23 the previous revisions of these topical reports that

24 supported the now-certified NuScale US600 design.

25 Once again, thank you for the opportunity, and we look

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1 forward to a good discussion. Thank you.

2 CHAIR KIRCHNER: Thank you. And, Stacy,

3 next.

4 MS. JOSEPH: Thank you very much. Thank

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

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

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

8 manager for the two licensing topical reports that

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

10 PM for the NuScale SDAA review, Getachew Tesfaye, as

11 well as the staff members from both the Office of

12 Nuclear Reactor Regulation and the Office of Research,

13 who contributed to the reviews of the statistical

14 subchannel analysis methodology and the rod ejection

15 accident methodology.

16 A discussion on the statistical subchannel

17 methodology will be led by Joshua Kaizer and Antonio

18 Barrett from NRR; and for rod ejection, Adam Rau and

19 Zhian Li will be leading the discussion from NRR,

20 along with insights from Andrew Bielen from the Office

21 of Research. Andrew will be joining us virtually

22 today on Teams and will be presenting during the

23 closed session.

24 Thank you to NuScale for giving the

25 overview and the histories of the topical reports that

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

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

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

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

5 Josh and Adam will walk through the regulatory basis

6 for each of the reports and the conclusions the staff

7 made at the completion of their reviews.

8 The statistical subchannel methodology was

9 submitted to the NRC in December 2021 and was accepted

10 for review after NuScale addressed the staff's request

11 for supplemental information in April of 2022. The

12 staff conducted an audit between July 2022 and

13 December 2023; and, as NuScale previously mentioned,

14 the topical report was revised during this time period

15 to address staff feedback. NuScale submitted the

16 final revision to the topical report just this past

17 November, and the staff's advanced SER was issued

18 shortly later.

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

20 Kaizer.

21 MEMBER MARCH-LEUBA: These four revisions,

22 were they a consequence of deficiencies that the staff

23 identified during the review, where there were points

24 of finding of signs that was not completed and the

25 extra features, or can you explain why we were not

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1 happy with Revision 1?

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

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

4 to jump in and correct me. Everyone does quality

5 control of their documents a little bit differently,

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

7 Westinghouse topical report, you can generally expect

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

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

10 1. And that is one way to do it.

11 Other people decide to update the topical

12 report, as information comes in, change the

13 information in the topical report. A lot of times,

14 that information would have been in the RAIs, it would

15 have been in the Dash A version. Everything that we

16 kind of saw here, there were some areas where we said,

17 hey, we need more information, but it's really up to

18 them whether they want to rev the topical, just

19 provide the information and say, okay, we're going to

20 attach it at the end of it. And I thought a lot of

21 this came out of the QA program NuScale uses for its

22 document generation, so there was nothing, I'd say,

23 extra special about this topical report that it

24 required four revisions before it even got there. It

25 was just this is the way they chose to address the

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1 information.

2 MEMBER MARCH-LEUBA: So there was no major

3 deficiency. It was just tweaking.

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

5 the regulatory basis for the statistical subchannel.

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

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

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

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

10 talks about the 95/95.

11 I can go into a lot more detail because we

12 actually did a presentation on this to the staff a

13 couple of years ago where we tried to track down where

14 does the 95/95 come from and all that kind of stuff.

15 But suffice to say, there is this 95/95 requirement,

16 well, not requirement, but there's 95/95 in the SRP.

17 Everybody says, yes, we want to satisfy that. And for

18 direct correlations, it's a little bit more

19 straightforward when you start to do statistical

20 stuff. It is a little more challenging, but, like a

21 lot of people have pointed out, this was a concern and

22 a challenge that we have long since resolved. I think

23 the earliest I've seen it used, I thought the topical

24 was, like, sometime from the 1980s, the late 80s. So

25 using 95/95 in the statistical sense is something

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1 we're very familiar with, especially in DMB.

2 And I wanted to add the staff's

3 conclusions, we found an acceptable method for

4 combining all these uncertainties. We did have two

5 limitations and conditions. The first one was,

6 basically, saying that your correlation has to be

7 approved. This was just a carryover from the

8 original, the NuScale, the subchannel analysis

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

10 see a lot of times. Any time you see a CHF

11 methodology, hey, your CHF correlation has to be

12 approved for the fuel you're using, so that's not that

13 really big of a deal.

14 The next one, a little bit more complex,

15 but we just basically said you have a whole bunch of

16 models in this methodology that NuScale wanted to say

17 we're going to model this, we're going to capture the

18 uncertainty of this parameter. We're not really ready

19 to tell you yet how we're going to do that. And so we

20 kind of looked through it and said, okay, that's

21 reasonable, but, before you actually apply this, you

22 have to tell us how you're going to model this and we

23 have to approve it. And there's a number of ways we

24 can do that. We can either approve the equation or we

25 can approve the direct uncertainty itself. So those

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1 were the two conditions, limitations, on the staff's

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

3 review.

4 MEMBER MARCH-LEUBA: Revision number 2 is

5 more a condition from the first --

6 MR. KAIZER: Yes.

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

8 the second can just --

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

10 bunch of ways that we can resolve those issues. We're

11 just saying, hey, these have to be reviewed and

12 approved by the staff.

13 MEMBER MARCH-LEUBA: It's not really

14 limiting.

15 MR. KAIZER: Correct.

16 MEMBER MARCH-LEUBA: We need to look at

17 the test at least once.

18 MR. KAIZER: Yes.

19 MEMBER MARTIN: With statistical methods,

20 the presentation of information will be a little bit

21 different from a deterministic presentation of

22 information. And there might be a tendency to just

23 kind of globally look at results from thousands of

24 cases in a statistical sense. Do you still expect or

25 require that NuScale present some deterministic

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1 representative type of results of what exists after

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

3 statistical presentation of information?

4 MR. KAIZER: I want to ask one

5 clarification on your question because this is

6 something that I get into a lot of conversations about

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

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

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

10 the same output, and a non-deterministic analysis will

11 literally be if I give my computer code three, one

12 time I get the number five, one time I get the number

13 seven.

14 So I have always viewed that even

15 statistical methodologies are deterministic in nature.

16 It's just what we're doing is we're feeding them,

17 instead of a constant, a random variable, and they're

18 going to give me a different outcome. But if I give

19 it that same initial input, I get the same thing. So

20 I want to clarify that when I hear deterministic in

21 this sense, I'm thinking more of do they have to do,

22 like, the worst-case scenario type thing.

23 MEMBER MARTIN: No. That's a trick

24 question, and we're aligned on that perspective.

25 Deterministic is a term, because of Chapter 15

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1 accident analysis in the old school, was truly

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

3 approach now.

4 But, yes, I was just really wondering

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

6 they recognize it?

7 MR. KAIZER: Well, one of the challenges

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

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

10 position from Tony Attard. I think he started in the

11 NRC in the mid 90s, so, yes, he would have already

12 been familiar with that.

13 The other thing about statistical

14 subchannel is it's not a replacement method, it's an

15 alternative approach, so we'll talk about their normal

16 subchannel analysis methodology. And I never thought

17 of the statistics in it as giving you, I'd say the

18 major benefit that I feel like you would get from a

19 statistical LOCA where you're like ranging that break

20 size. I mean, normally, what you're doing is you are

21 taking a whole bunch of uncertainties and, instead of

22 just adding them as straight adders, you're saying,

23 okay, we can treat these as random variables and

24 combine their things statistically.

25 So it is a statistical method, but I don't

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1 think of it as something as far afield from a

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

3 I mean, you're treating the uncertainties

4 statistically but not --

5 MEMBER MARTIN: I think you're

6 overthinking my question.

7 MR. KAIZER: Okay.

8 MEMBER MARTIN: An uncertainty is a

9 tendency with statistical methods that kind of present

10 the cloud of results, and that is useful to some

11 extent. But my point about kind of old school

12 approach is people still kind of want to see, you

13 know, plots of behavior because the trends give you a

14 feeling of rate processes and what have you, and, you

15 know, certainly, an expert analyst gets insight. It

16 just doesn't come out of a statistical presentation

17 of, you know, various metrics that might be valuable

18 to measure against acceptance criteria. But to really

19 assess as evidence, which, of course, ultimately, all

20 these analyses are, there needs to be a tangible

21 event. But when you're running thousands of cases,

22 it's difficult to do so, so you're really looking for

23 something representative. In this case, that's

24 something at the 95/95 confidence probability.

25 As a throwback, I just wouldn't expect it

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1 to kind of look like a traditional analysis. For

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

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

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

5 case. But in those limiting cases, the samples

6 themselves, you know, particularly, say, less

7 important than the more dominant ones, they may not

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

9 direction of what might be otherwise considered

10 conservative.

11 Now, maybe in a case like running

12 thousands of cases, that would be so much of an issue.

13 Truly, a 95 case would capture the more bounding

14 conditions, you know, associated with the major

15 parameters that you are looking at. So, again, it's

16 a simpler question. You know, are there, basically,

17 you know, results that, while they may be, you know,

18 of one representative event, they're still there, just

19 to throw back to the old ways these things were

20 presented in safety analysis reports. I still think

21 that's value in that. That's my point. There's still

22 value, as opposed to statistically presenting

23 information.

24 MR. KAIZER: Okay. I have just a -- is

25 there a question that I should be answering? The

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

2 very interesting topic, as a lot of times things

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

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

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

6 just accept the comment.

7 MEMBER MARTIN: It's simply an expectation

8 of content of a safety analysis report. And my

9 expectation is that it truly looked like an analysis,

10 even though there is, of course, the statistical

11 component to it. It should still look like, you know,

12 here's an event and this was the outcome, these were

13 trends, inputs in affect, you know, the transient over

14 time.

15 MR. KAIZER: I think what I would expect

16 that in the transient analysis that they're

17 performing, but I don't know if I would necessarily

18 expect that in the method they would use to generate

19 the statistical limit.

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

21 MR. KAIZER: Yes, okay.

22 MEMBER MARTIN: But a reasonable person

23 coming from the outside picks up the safety analysis

24 report. They want more than just a --

25 MR. KAIZER: Correct.

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1 MEMBER MARTIN: -- statistical

2 presentation of information. They want something that

3 they understand really from kind of a science,

4 engineering basis, as opposed to a math based.

5 MR. KAIZER: Correct.

6 CHAIR KIRCHNER: Josh, could you put your

7 limitations and conditions in number two in some

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

9 numerous equations that are referenced in the

10 submodels and such. What you're really saying is,

11 when it comes to applying this methodology in Chapter

12 15, we are going to go back and review what?

13 MR. KAIZER: Sure. So there are a lot of

14 input parameters or input variables that impact your

15 statistical limit, and there's a question of how do

16 you treat the uncertainty of those. When we say how

17 do you treat the uncertainty, what equation are you

18 going to use? Are you going to assume it's normally

19 distributed, uniform distributed? If you are, what

20 are the parameters of that distribution? Are you

21 going to assume there's a linear relationship?

22 There's a whole bunch of questions.

23 In the initial topical report, NuScale

24 gave examples of how they would treat those

25 uncertainties, but they hadn't finalized that

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1 information yet. So we pretty much said, okay, for

2 these variables, and I think we listed however many

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

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

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

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

7 going to assume a conservatively high or low value.

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

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

10 going to be normally distributed, and we think this is

11 the way to determine the mean and this is the way to

12 determine the variance. We think that it's best to

13 treat this as a uniform distribution, so here's its

14 lower limit, here's its upper limit. And that is,

15 well, I guess, the further details of that number two.

16 CHAIR KIRCHNER: Thank you.

17 MR. KAIZER: If there are no further

18 questions, I'll turn it over to Adam.

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

20 Stacy Joseph again. The time frame for rod ejection

21 topical report is similar to that of subchannel.

22 NuScale submitted Revision 2 of the rod ejection

23 topical report in December 2021. The staff issued an

24 RAI and received NuScale's response in September 2022.

25 The staff performed an audit between April and

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1 September 2023. And following completion of the

2 audit, NuScale revised the topical report to address

3 the feedback from the staff. The staff then completed

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

5 2024.

6 Adam.

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

8 Okay. And so, as NuScale mentioned in their

9 presentation, the regulatory basis for the rod

10 ejection accident is GDC 28. It requires an

11 evaluation of limiting reactivity insertion accidents

12 for the effect on the reactor coolant pressure

13 boundary and for core coolability. In NuScale's case,

14 rod ejection is the limiting accident in their case.

15 So the regulatory guidance for this

16 accident is given in, primarily, Reg. Guide 1.236.

17 You know, it was mentioned in their presentation that

18 this is the new guidance that's come out since the

19 previous revision of the topical. There's additional

20 information in SRP 4.2, Appendix B, as well as 15.4.8,

21 as well.

22 And so the NRC staff conclusions for the

23 evaluation was that the rod ejection accident analysis

24 methodology is a systematic methodology for analyzing

25 this accident. We did place three limitations and

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1 conditions on the topical report that are primarily

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

3 I would say articulating the scope of our approval for

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

5 through line through the three limitations and

6 conditions.

7 So the first is related to the

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

9 that applicability needs to be demonstrated. So this

10 is, you know, a generic methodology that's applied to

11 a new design that maybe NRC staff hasn't had a chance

12 to look at yet, and that's just a question that would

13 have to be answered at that time.

14 So limitation and condition number two.

15 I know ACRS members had some questions on this, and,

16 you know, we'll definitely get a chance to talk about

17 the basis in the closed session. Just to try to say

18 a bit about it in the open session, I think the

19 motivation here is that there's a sensitivity to the

20 axial offset in the code, and so the -- well, again,

21 trying not to get into too many details in the open

22 session, we wanted to have a condition reflecting that

23 saying if this is applied to a design that operates

24 with control rods inserted for a long period of time

25 or has a load following scheme that involves this sort

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1 of operation, that this is something that should be

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

3 approval.

4 MEMBER MARCH-LEUBA: Your efficient

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

6 uncertainty of the equation will increase because now

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

8 that --

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

10 I say uncertainty or bias or conservatism, but one of

11 those, something in that family would --

12 MEMBER MARCH-LEUBA: Another thing I

13 wanted to place on the open session is, in my mind,

14 there are two extremes. On one extreme, you can

15 provide a link to the control rod position to the

16 grade dispatcher and he controls the power of your

17 reactor at any time he wants. On the other extreme,

18 you have a power plant that is co-located with solar

19 and wind, and you know in the middle of the day you're

20 going to have lower power, and you have a pre-planned

21 hour2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br /> of shade during the day. And if you're in that

22 way, you can probably control the power with boron,

23 and it wouldn't cause such problems. And that's the

24 most likely one.

25 So I understand what limitations are

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

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

3 likely, it will be reprogrammed during the day and

4 many plants are doing that already.

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

6 we provided enough in the SE and the condition itself

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

8 they'll understand where we --

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

10 the SRP in NUREG-0800 you provided hints to the future

11 reviewers, which might be younger 20 years from now to

12 look for. My principle concern is if it's placing an

13 undue burden on NuScale because we are limiting them

14 to bystanders and say, well, we won't bother when

15 maybe you can do it.

16 MR. RAU: Yes, that makes sense. The

17 third limitation condition is just recognition that

18 the NRC staff considered some of the methodologies

19 cited in the topical report to be integral parts of

20 the methodology, so that particular nuclear analysis

21 methods that were cited, as well as the subchannel

22 methodology, you know, played into our review. And so

23 if these were to, you know, if you were to try to

24 change these out, we would consider this a change to

25 the methodology itself.

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1 With that, I will turn it back over to

2 Stacy.

3 CHAIR KIRCHNER: Members, further

4 questions, statements, comments? I note for the

5 record I detected Dennis Bley, our consultant, and

6 Steve Schultz also are participating today.

7 So then thank you. At this juncture, I

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

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

10 Good afternoon, Harold. Since you already submitted

11 a comment, do you wish to make any public statement?

12 You have to unmute yourself.

13 MR. SNODDERLY: Well, I think Harold did

14 request that someone, and I can do it for you --

15 CHAIR KIRCHNER: We can read it.

16 MR. SNODDERLY: Yes, that we would read it

17 for Harold, and then we'll follow up and see if --

18 CHAIR KIRCHNER: Okay. So, Harold, I'm

19 going to ask Mike Snodderly, the Designated Federal

20 Official, to read your comments into the record.

21 MR. SNODDERLY: Thank you, Chair Kirchner.

22 This is Mike Snodderly. This is an email that we

23 received yesterday, Monday, February 5th, from Harold

24 Scott. It reads as follows: My topic is amount of

25 proprietary marking redaction. Can you or another NRC

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1 staff read out this message during public comment

2 period NuScale meeting? I have trouble speaking.

3 What is it about plots of computer code output that

4 makes them proprietary? I think the public would find

5 value in seeing explicit margins. I would appreciate

6 ACRS members considering if the topic is a concern to

7 be raised with the commissioners. Thanks for

8 listening.

9 That was the end of the email. This email

10 will also be included in the official transcript.

11 CHAIR KIRCHNER: Now it's our, not policy

12 but practice, I think, is more accurate to say that

13 the committee doesn't respond in realtime. We address

14 comments raised by the public and usually include them

15 in our considerations for a letter. In this

16 particular case, though, I just would observe that the

17 committee in the past, as a general practice, has

18 encouraged all applicants to make as much material

19 publicly available as supports their safety case, and

20 we've had numerous interactions over the last years

21 with applicants to encourage them to do so.

22 So, Harold, your comment is duly noted.

23 It is not in our control to decide what is proprietary

24 or not, but it is in our, I think, the committee's

25 interests to encourage all applicants to make as much

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1 of their safety case publicly available, and that

2 would include such detailed plots as you were asking

3 for.

4 MR. SCOTT: Thank you very much. Thank

5 you. So thank you very much. Thank you.

6 CHAIR KIRCHNER: Thank you, Harold. Are

7 there any other members of the public or those present

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

9 come forward or unmute your line and identify yourself

10 and affiliation, as appropriate, and make your

11 comment. Sarah. Okay, Sarah. Go ahead.

12 MS. FIELDS: Yes, this is Sarah Fields

13 with Uranium Watch in Moab, Utah. To follow up on Mr.

14 Scott's email comment, I found recently that large

15 sections of applications related to so-called advanced

16 reactors and also the NuScale small modular reactor

17 project that you're reviewing now, they're just

18 redacting. You look at an application, you look at a

19 submittal, and most of it is redacted. So I think

20 information that used to be readily available to the

21 public is now being redacted.

22 So if you're under the illusion that the

23 industry is making everything available possible

24 available to the public, you're mistaken. All this

25 stuff is just missing. Thank you.

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1 CHAIR KIRCHNER: Thank you, Sarah. Any

2 further comments?

3 MEMBER MARCH-LEUBA: Yes. Mine is related

4 to this, too.

5 CHAIR KIRCHNER: Okay. This is Member

6 March-Leuba.

7 MEMBER MARCH-LEUBA: One consideration

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

9 often more restricted on proprietary measures, and all

10 of this, the science, are on export control. And if

11 you release this information, you can go to jail much

12 easier. Proprietary, NuScale can sue you. But if you

13 release export control information, you can go to

14 jail. So people are more careful because of that.

15 CHAIR KIRCHNER: Thank you. Further

16 comments from the public?

17 MR. SNODDERLY: Excuse me, Chair Kirchner.

18 CHAIR KIRCHNER: Yes.

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

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

21 You might find it interesting, if you look at the

22 recent Revision 1 to the publicly-available non-

23 proprietary version of Chapter 15, accident analysis,

24 and Section 15.4 on the rod ejection accident, there

25 is the description of the sequence of events and

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

2 interest. So there are more results that are

3 available concerning the rod ejection accident

4 interview he publicly-available FSAR chapter. And if

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

6 email and I can help you find that.

7 MS. FIELDS: I was talking generally, not

8 specifically about this issue that you're discussing

9 today. I'm talking generally about applications.

10 MR. SNODDERLY: Okay. Thank you for the

11 clarification.

12 CHAIR KIRCHNER: Thank you. Not hearing

13 further comments, we are going to take a short break

14 here and go into a closed session with a different

15 Teams link. And those that need to know to

16 participate will have access to that Teams link. And

17 with that, we are on a break for 15 minutes. It is

18 currently five minutes after two. We'll take a break

19 until 2:20 Eastern Time.

20 (Whereupon, the above-entitled matter went

21 off the record at 2:03 p.m.)

22

23

24

25

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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 Tom Griffffffffffffffffffffffffffffffiffffffffffffffffffffth 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)

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

Enclosure:

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

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

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

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

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

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)

6 Non-Proprietary 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 proprietary marking (redaction)

can you or another NRC staff read out this message during public comment period NuScale meeting ? I have trouble speaking

What is it about plots of computer code output that makes them proprietary ?

I think the public would find value in seeing the explicit margins

I would appreciate ACRS members considering if the topic is a concern to be raised with the Commissioners.

Thanks for listening