ML19211C779

Transcript of the Advisory Committee on Reactor Safeguards Nuscale Subcommittee Meeting - June 19, 2019

ML19211C779
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Issue date:	06/19/2019
From:	Michael Snodderly Advisory Committee on Reactor Safeguards
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Snodderly, M, ACRS
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NRC-0389
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Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION Title: Advisory Committee on Reactor Safeguards NuScale Subcommittee: Open SessionDocket Number:(n/a)Location:Rockville, Maryland

Date: Wednesday, June 19, 2019Work Order No.:NRC-0389 Pages 1-257 NEAL R. GROSS AND CO., INC.

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

Washington, D.C. 20005 (202) 234-4433 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.

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

-3701 www.nealrgross.com 1 1 2 3 DISCLAIMER 4 5 6 UNITED STATES NUCLEAR REGULATORY COMMISSION'S 7 ADVISORY COMMITTE E 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 t ranscript has not been reviewed, 17 corrected, and edited, and it may contain 18 inaccuracies.

19 20 21 22 23 1 UNITED STATES OF AMERICA 1 NUCLEAR REGULATORY COMMISSION 2+ + + + +3 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 4 (ACRS)5+ + + + +6 NuSCALE SUBCOMMITTEE 7 OPEN SESSION 8+ + + + +9 WEDNESDAY 10 JUNE 19, 2019 11+ + + + +12 ROCKVILLE, MARYLAND 13+ + + + +14 The Subcommittee met at the Nuclear 15 Regulatory Commission, Two White Flint North, Room 16 T2D10, 11545 Rockville Pike, at 8:30 a.m., Jose March-17 Leuba, Chair, presiding.

18 19 COMMITTEE MEMBERS:

20 JOSE MARCH-LEUBA, Chair 21 RONALD G. BALLINGER, Member 22 DENNIS BLEY, Member 23 CHARLES H. BROWN, JR. Member 24 MICHAEL L. CORRADINI, Member 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 2 VESNA B. DIMITRIJEVIC, Member 1 JOY L. REMPE, Member 2 PETER RICCARDELLA, Member 3 GORDON R. SKILLMAN, Member 4 MATTHEW W. SUNSERI, Member 5 6 ACRS CONSULTANT:

7 STEPHEN SCHULTZ 8

9 DESIGNATED FEDERAL OFFICIAL:

10 MIKE SNODDERLY 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 3 CONTENTS 1 Opening Remarks.................4 2Overview of Topical Report, "EvaluationJune 24, 20198 3 Methodology for Stability Analysis of the 4 NuScale Power Module," and Section 15.9 5"Stability." 6 Topical Report, "Evaluation Methodology for...35 7 Stability Analysis of the NuScale Power 8 Module," Safety Evaluation and Section 9 15.9 "Stability"................59 10 Opportunity for Public Comment.........43 11Overview of Chapter 15, "Transient Analysis".110 12 Adjourn....................257 13 14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 4 P R O C E E D I N G S 1 (8:30 a.m.)

2 MEMBER CORRADINI: Why don't we get 3 started. So this is the second day of our three-day 4 committee meeting on NuScale, I'm not going to run 5 through the pro forma discussion except to mention 6 that we have a closed line for NuScale subject matter 7 experts that should be open.

8 Could the NuScale -- back in Corvallis?

9 MEMBER BLEY: That you're on the line in 10 Corvallis.

11 MEMBER CORRADINI: That you're on the 12 line.13 PARTICIPANT: NuScale's on the line.

14 MEMBER CORRADINI: Okay, all right. And 15 then we have the public line which is on mute mode.

16 And then I just want to remind everybody since I was 17 the offender last time, turn down your volumes. Turn 18 down your cell phones. Put them on mute, something, 19 so they don't talk back to you.

20 MEMBER BROWN: Are you going to do that?

21 MEMBER CORRADINI: And then other than 22 that I want to just proceed. We have an agenda today 23 where we are going to first go over the topical 24 report, and then transition into Chapter 15 from the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 5 applicant. And tomorrow we'll have the whole day to 1 talk with staff about Chapter 15.

2 So I'll turn it over to Dr. March-Leuba 3 who is going to lead us through the two days.

4 CHAIR MARCH-LEUBA: Thank you, Dr.

5 Corradini. So we're going to start with the stability 6 report, topical report, which -- but before you start, 7 let me give a summary for my colleagues of the way I 8 think this is going to go.

9 And so the stability report is an 10 excellent technically speaking. It is -- I found a 11 microphone, yes.

12 It's expanding the methodology for BWR 13 stabilities that we've known for 40 years now, and 40 14 years ago we would not be able to have done this. But 15 now we know all the problems and issues and we know 16 how to arrest them.

17 And better than that we have a particular 18 mass of people that can review your work, understand 19 it and intuitively say yes or no, whereas, it's not a 20 one person saying something, it's a community of 21 people saying.

22 So based on that methodology, we have 23 identified that the limited stability concern for 24 NuScale is natural circulation oscillation inside the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 6 core because of buoyancy concerns. So when you 1 generate a lighter mass on the riser you get more 2 flow, which then cools down the riser and you can have 3 oscillations. They become the normative oscillation.

4 And they analyzed it using all this methodology that 5 we know and they have decided there is no safety 6 significance to it.

7 And there could be a possibility of 8 instabilities if we get into boiling in the riser and 9 they prevent that with an exclusion region. It's one 10 that accepted a long time one of the solutions in BWRs 11 in which you don't allow boiling in the riser.

12 So, I think that it's perfectly covered 13 and I would like it to go fast so we can we move to 14 the difficult part of which are the next one on 15 Chapter 15.

16 Now one thing I'm concerned about is on 17 top of the primary system instability we have 18 secondary system instabilities. So you have these 19 long thin tubes in the steam generator where the 20 steam, the bubbles are inside of the tube and what is 21 all the experience we have is with the bubbles outside 22 of the tube.

23 So there's a large, very large friction 24 two phased flow of friction we calling that stability 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 7 domain that is very large and very destabilizing. So 1 to try to stabilize that NuScale has put, as we always 2 do, an inlet restriction, and we will talk about those 3 details in the closed session. But the possibility 4 exists with non negligible likelihood. We're not 5 talking 10 to the minus 7, we're talking maybe 50/50, 6 that the steam generat or will operate with flow 7oscillations in the secondary.

8 And I'm not sure we covered the solution 9 on the open session or the closed session, but the 10 staff on NuScale have reached a solution and concluded 11 that this would not be of safety significance to the 12 core and would not violate GDC 12. And during the 13 closed session when we have our discussion, I would 14 like to reach an agreement among yourselves and that 15 is we agree with the conclusion.

16 MEMBER BLEY: What's the potential from, 17 I would imagine there would be problems with steam 18 generator supports and vibrations and that.

19 CHAIR MARCH-LEUBA: That's what I want to 20 discuss with them. So I noticed in the presentation, 21 NuScale has maybe one bullet in the whole 22 presentation, so I will ask you to speed up through 23 the next four slides, so we can get to the question 24 and answer area.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 8 And we may have to do it in the closed 1 session, so it's up to NuScale to tell us when to stop 2 and move to the closed session, because things get 3 proprietary real fast.

4 NuScale, please go ahead.

5 MR. PRESSON: Thank you for that opening, 6 Dr. March-Leuba. And good morning, I'm Matthew 7 Presson with licensing at NuScale Power, project 8 manager for this topical report. Presenting today 9 will be Dr. Yoursef Farwila, our stability expert, and 10 supported by myself in licensing, and Ben Bristol, the 11 supervisor of system thermal hydraulics.

12 And with that as requested, we'll get on 13 with the presentation.

14 DR. FARWILA: Thank you. Good morning, 15 everyone, Mr. Chairman and all the members. I was 16 introduced already and I already know most of you. So 17 let me speak through the presentation.

18 Our agenda is very simple today. The 19 topic is simple. Just make a quick introduction and 20 tell you about the stability solution type and 21 describe how we investigated it with theoretical, 22 numerical and experimental benchmarks and how we use 23 these tools in a procedure and methodology to 24 demonstrate the stability of the module, summarize, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 9 and try to save as much time for your questions.

1 Start with the main message, the NuScale 2 power module design was found to be stable in its 3 entire range of normal operation. This is 4 unconditional stability as long as we are in normal 5 operation.

6 CHAIR MARCH-LEUBA: But you are referring 7 to the primary system, correct?

8 DR. FARWILA: The primary system, yes, 9 anything that affects the core. So it is not going to 10 be unstable or growing power oscillations or flow 11 oscillations that go through the core. Outside of 12 that, other systems are essentially outside of the 13 scope or touching in the scope and we'll be having a 14 chance to discuss how much that connection is.

15 CHAIR MARCH-LEUBA: Can you remind us what 16 GDC, the general design criteria 12 says about 17 oscillations?

18 DR. FARWILA:

GDC 12 says you're not 19 allowed to have oscillations unless you can detect and 20 suppress them so that the SAFDLs cannot be violated 21 with whatever thermal limits or other limits, cannot 22 be violated.

23 CHAIR MARCH-LEUBA: The way I read it is 24 you can either detect and suppress them or they cannot 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 10 violate SFADLs. So you may, according to GDC 12, you 1 may allow oscillations that do not violate SAFDLs.

2 Specified acceptable fields and limits.

3 DR. FARWILA: Right. That's what I 4 thought I said.

5 CHAIR MARCH-LEUBA: Mm-hmm, yeah. Okay.

6 MEMBER BLEY: I know our role here is 7 reactor safety. On the other hand, if you sell me a 8 plant with steam generators that starts coming apart 9 because of this, I'm not going to be very happy with 10 you; neither is anybody else. Although that's not 11 what we delve into, maybe sometime you can talk about 12 what the effects on steam generators could be.

13 CHAIR MARCH-LEUBA: Yeah, I think we would 14 want to save that discussion for the closed meeting, 15 so I'm going to speed you up so we can have more time 16 for that one.

17 DR. FARWILA: All right. Okay, part of 18 the main message also is to stress that outside of 19 normal operation, for any reason, the reactor can be 20 destabilized when the riser flow is voided, but even 21 then these unstable flow oscillations are limited by 22 nonlinear effect, so the magnitude of those 23 oscillations is going to be limited and there is still 24 not going be any critical heat flux violations.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 11 So now we identified where the stability 1 threshold is. That's already protected by scram upon 2 loss of riser inlets of cooling. We put a margin for 3 that eventuality, so, essentially, the hard stability 4 solution is to do nothing.

5 CHAIR MARCH-LEUBA: Going back to bullet 6 number two, you say that even if unstable flow 7 oscillations were to develop SAFDLs wouldn't be 8 violated. Is this because of a specific 9 characteristic of NuScale or is it because NuScale 10 operates with so much CHF margin that even if the CHF 11 oscillation never hit limits?

12 DR. FARWILA: Actually, the critical heat 13 flux ratio is going to increase. You are running a 14 lot of ahead of the presentation, but that's all 15 right. When you void the riser that gives you a much 16 greater feedback.

17 So for a unit of enthalpy added you get a 18 lot of density difference and that density contrast is 19 what drives the flow and the instability. So the flow 20 itself starts to become higher, so the average flow 21 gets higher and the magnitude of the oscillation is 22 bounded by in the upper part of the flow the voids 23 would collapse.

24 So once the voids collapse you cannot 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 12 increase more than that and the overshoot in the other 1 side would be about the same magnitude.

2 CHAIR MARCH-LEUBA: My question was a 3 little loaded in the sense that if in the future we 4 have a 20, 30, 50 percent power increase, power 5 upgrade that would eat into the CHF margin, you would 6 still have this effect.

7 DR. FARWILA: Yes, of course.

8 CHAIR MARCH-LEUBA: But it would have to 9 be evaluated.

10 DR. FARWILA: Definitely. Any change in 11 the way the reactor is operated is specified that we 12 will have to repeat the stability analysis. But the 13 same tools that we have with the phenomena in it would 14 be covered.

15 CHAIR MARCH-LEUBA: Thank you.

16 DR. FARWILA: So these conclusions that 17 are presented in the main message, they are based on 18 extensive first principles experimental and 19 computational. We just don't believe codes blindly.

20 We have to verify them by other ways, other methods.

21 We have to have first principles understanding.

22 MEMBER BLEY: Is this, the trip on loss of 23 subcooling in the riser, is that based, was that 24 always there or is that something that's been added 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 13 and might have been moved into Chapter 7 as part of 1 the instrumentation?

2 DR. FARWILA: It's always there.

3 MEMBER BLEY: Okay, thank you.

4 DR. FARWILA: So just going back, when we 5 first started with this it was a surprise. I mean why 6 do you need to have a stability analysis at all? It's 7 a PWR and PWRs, usually in the FSARs you have a 8 paragraph talking about stability and dismiss it.

9 But in our particular case you can see 10 that we have published reports with the experiments 11 that you can have instabilities in natural circulation 12 flow. And you can see here that there are several 13 configurations with horizontal cooler, horizontal 14 heater and you have vertical cooler and vertical 15 heater and vertical both.

16 And experiments could show that only in 17 the first one that you can have instabilities but none 18 of the others, but you could say the configuration of 19 the experiment is different from what we have. I mean 20 you can, not scale it properly and we don't know much 21 about it, but anyway this last configuration is very 22 similar to the NuScale instability.

23 But instead of taking that for granted, of 24 course an investigation of the modular stability is in 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 14 order and in order to really verify that and 1 understand it. So the way we started with this, that 2 first box in there in the original if you see it in 3 the printout it was painted gray.

4 So we were in the gray area when we know 5 only that we just have a design. We have expertise.

6 We know the theory, but it's still in the gray area 7 until we go to more colorful boxes with developing a 8 code and have independent models to verify and 9 experimental data to benchmark it and understand it.

10 And once we are confident with the tools 11 we have, we go to the next step and analyze the module 12 in different modes of operation, different powers, 13 just all the range that you have and essentially do 14 perturbations to see if perturbations would grow. And 15 also I'll tell you more about that later, look at 16 stability during transients, not just from a steady 17 state.18 And so we concluded from this that reactor 19 is stable within normal domain and most important 20 thing, identified what is the threshold for 21 instability which is riser voiding. That gets us to 22 the green area where we have a stability solution 23 which, luckily, does not introduce any additional 24 hardware as the threshold is already protected by the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 15 module protection system.

1 Like any new reactor with new phenomena we 2 start with a PIRT. That PIRT committee met for a week 3 and was extra conservative, everything counts, 4 everything, a lot of times were ranked high.

5 MEMBER CORRADINI: When did this occur?

6 DR. FARWILA: That occurred in 2015 or so, 7 so well, well before anything started.

8 MEMBER CORRADINI: Is that on the docket, 9 the PIRT?10 DR. FARWILA: I don't think so.

11 MEMBER CORRADINI: Okay, right.

12 DR. FARWILA: Right. It's probably not 13 very interesting reading.

14 MEMBER CORRADINI: Because you brought it 15 up so I thought I'd ask.

16 DR. FARWILA: Yes, of course.

17 We have a PIRT, you could say a post-code 18 PIRT. There is a pre-code PIRT and a post-code PIRT.

19 The post-code PIRT is worth reading. It's part of the 20 topical report.

21 MEMBER CORRADINI: Okay.

22 DR. FARWILA: Right.

23 MEMBER BLEY: It's a topical report?

24 MEMBER CORRADINI: That's what we have as 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 16 a separate.

1 MEMBER BLEY: That is the one we have, 2 okay.3 DR. FARWILA: Yes. So that's you could 4 say more the relevant one, not the one we started 5 with, with always conservatively as human things.

6 So anyway, we looked at, first, the 7 principles just to look at the riser only and see what 8 happens considering the cold leg as boundary 9 condition. And we look at the stability trends with 10 power because we got surprising results that the 11 higher the power, the more stable the reactor is. We 12 did not see this before in PWRs.

13 So you could say do I believe my code?

14 That's a taboo. We cannot believe a code without 15 understanding, so the understanding comes from first 16 principles and using other models and things like 17 that.18 So this analysis from first principles is 19 one of the important legs of this project and it 20 essentially, it informs the design of the stability 21 experiments as well because you can go to the facility 22 and you don't know what to measure and how to measure 23 it. Unless you know something from first principles, 24 there is always this organic relationship between an 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 17 experiment and the theoretical understanding that 1 comes with it. They feed off each other.

2 So anyway, regarding the PIRT, all medium 3 ranked phenomena were treated as highly ranked. There 4 was no complacency in this regard. So important thing 5 in theoretical understanding of instability is that if 6 you have positive feedback it's not allowed, of course 7 we don't allow it, and you cannot operate system with 8 positive feedback.

9 So we have negative feedback that's 10 engineered in, but this negative feedback if it's too 11 strong and delayed it can overshoot in the correction 12 and that can be oscillatory. And so a negative 13 feedback that is delayed and sufficiently strong will 14 be, can become in principle unstable. And when you 15 look at our module, the feedback is negative.

16 I mean if you have a perturbation 17 increasing flow, it cools off the riser and that 18 reduces the density head that drives the flow 19 essentially correcting that perturbation.

20 MEMBER BLEY: On your last slide when you 21 said you treated all ranked phenomena as highly 22 ranked, what did that mean to you? Did you require 23 experiments to verify those things, or what did you 24 do?25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 18 DR. FARWILA: Mainly put models that I 1 have high fidelity to represent these phenomena.

2 MEMBER CORRADINI: But you did do, you had 3 done -- I want to, here, get to the experiments, so.

4 DR. FARWILA: We did experiments, yes.

5 Actually, when the presentation was shortened, we are 6 not presenting as much. I can talk to them though.

7 MEMBER CORRADINI: Okay.

8 DR. FARWILA: Yeah.

9 CHAIR MARCH-LEUBA: Now it would be nice 10 if you'd give us a two-minute summary of the 11 experiments.

12 DR. FARWILA: Of course, I will.

13 Okay, so we said that this feedback is 14 delayed because it takes time to fill the riser with 15 that different temperature in order to make an effect.

16 And the strength of the feedback is of course is 17 related to the thermal expansion and that's what 18 creates the density difference.

19 So if you have a different fluid that 20 expands more or if you have boiling that will be 21 stronger or if you take the whole thing to a different 22 planet where the gravitational constant is different, 23 it would behave differently. I didn't hear a laugh, 24 but we actually had models where I changed the g in 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 19 order to find out -- I needed to change it by a factor 1 of 10 in order to make things unstable.

2 So all right, getting to the main tool, 3 it's a code called PIM. And you can see the 4 geometrical simplification from this iconic picture to 5 more of an advanced schematic, more accurate schematic 6 to just the essential loop of really what happened.

7 So it's not looping like this, of course, you know, 8 it's looping like that.

9 But here are the essential element, a 10 small core almost like a point in the bottom of a tall 11 riser, and you have the cold leg filled with a helical 12 steam generator acting as the heat sink.

13 CHAIR MARCH-LEUBA: I don't remember the 14 details. Can you go back? Does PIM consider heat 15 conduction from the riser to the heat exchanger 16 directly through the wall?

17 DR. FARWILA: Yes, it does.

18 CHAIR MARCH-LEUBA: Okay, so it's capable 19 of doing that when the water level drops below the top 20 of the riser, it will still transfer heat?

21 DR. FARWILA: When the water level drops 22 to --23 CHAIR MARCH-LEUBA: Below the riser.

24 DR. FARWILA: -- below the riser, then PIM 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 20 is no longer applicable because you don't have 1 established continuity for natural circulation.

2 CHAIR MARCH-LEUBA: All right, but I think 3 that's -- some of the calculations we've seen you 4 still establish heat transfer from the pink to the 5 blue, even though you don't have natural flow?

6 DR. FARWILA: That must be in NRELAP5.

7 CHAIR MARCH-LEUBA: Okay, thank you.

8 And while we have this here, could you 9 describe how representative with experiments, the 10 experiments that you were talking about and just tell 11 us how representative they were with respect to this 12 reality?13 DR. FARWILA: The experiments were done in 14 the NIST-1 facility --

15 CHAIR MARCH-LEUBA: Mm-hmm.

16 DR. FARWILA: -- which is a scaled 17 hydraulic loop that looks very much like this except 18 for the height is -- was it one-third?

19 PARTICIPANT: Mm-hmm.

20 DR. FARWILA: And the diameter is much 21 smaller than one-third, so it's more of a long vessel 22 with a riser and --

23 MEMBER CORRADINI: We'll see that in July.

24 DR. FARWILA: Oh, oh. Wonderful.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 21 MEMBER BLEY: Out there? I thought you 1 said they did that at NIST.

2 MEMBER CORRADINI: NIST is the name of the 3 facility at Oregon State.

4 MEMBER BLEY: Oh, that's right. I had 5 forgotten that.

6 MEMBER CORRADINI: NIST is not NIST. NIST 7 is the name of the facility.

8 MEMBER BLEY: It's another NIST, got it.

9 MEMBER CORRADINI: NuScale Integral 10 something or other.

11 MEMBER BLEY: Yeah. Yeah, we -- okay.

12 CHAIR MARCH-LEUBA: Yeah. So, basically, 13 it's representative of the NuScale, you have different 14 time constants. You have to scale on the results.

15 MEMBER CORRADINI: Just so the members 16 remember, those that went, we won't ask for hands --

17 that there were prior experiments done in Corvallis 18 with a non-scaled facility. This was then rebuilt as 19 we were visiting in '15 or '16. I can't remember 20 which summer. They were rebuilding the facility to 21 have it based on some scaling discussion which we're 22 going to actually talk about later today in terms of 23 the scale.

24 DR. FARWILA: All right. We can address 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 22 the scaling in maybe in the closed session, the 1 scaling of the experiments and --

2 CHAIR MARCH-LEUBA: But in summary, the 3 results of the NIST instability experiments did it 4 show it was stable or unstable?

5 DR. FARWILA: It showed it too stable, 6 almost dead stable.

7 CHAIR MARCH-LEUBA: Okay.

8 DR. FARWILA: Okay.

9 CHAIR MARCH-LEUBA: He's disappointed.

10 This is what I will ask you to, is skip 11 through the next four slides.

12 DR. FARWILA:

Yes, I'm going to skip 13 these.14 MEMBER CORRADINI: Before you skip, so I 15 want to understand. So PIM is not a homogeneous 16 equilibrium model; it's non-equilibrium between the 17 phases?18 DR. FARWILA: Non-equilibrium mechanical 19 and thermal.

20 MEMBER CORRADINI: So you have different 21 temperatures and different velocities.

22 DR. FARWILA: Yes.

23 MEMBER CORRADINI: Okay. And you didn't 24 first do a non -- a linear analysis, a simple linear 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 23 analysis to show the regions of stability or 1 instability?

2 DR. FARWILA: We did and we published it.

3 MEMBER CORRADINI: Was that the published 4-- is that the reference that you had referenced a 5 couple slides ago, or is it some other reference?

6 DR. FARWILA: I did not put -- no, no.

7 This reference here is not ours.

8 MEMBER CORRADINI: Okay, so I'd be curious 9 about the reference, but you did do a linear analysis 10 to begin with?

11 DR. FARWILA: Yes, we did.

12 MEMBER CORRADINI: Okay. And then my next 13 question, you can do it when you want. I'm curious 14 about the regimes of stability and instability between 15 the linear analysis and the non-linear analysis.

16 Because in other applic ations for even just gas 17 instability flows in high-pressure gases, which was 18 done for gas-cooled reactor designs, you find that the 19 regions are hard to predict.

20 So I'm kind of curious how they laid on 21 top of each other, or at least if you looked at these 22 comparisons.

23 DR. FARWILA: Right. In the beginning we 24 thought maybe you have a frequency domain code.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 24 MEMBER CORRADINI: Right.

1 DR. FARWILA: But since we know how to 2 write time domain codes that are not hampered by the 3 problems we use to have with numerical dispersion 4 diffusion and all these things, we thought we would 5 just have a time domain code with the small 6 perturbations it's totally equivalent to a frequency 7 domain.8 MEMBER CORRADINI: Sure.

9 DR. FARWILA: But outside of the normal 10 operation we get limit cycles and non-linear 11 circulation in everything.

12 MEMBER CORRADINI: Okay, fine. Thank you.

13 DR. FARWILA: So, yeah.

14 Okay, so I'm going to skip through the 15 model since you already have the topical report and 16 have read this presentation before. Just one little 17 thing here. We looked at what was not modeled and we 18 do not model the pressurizer. It does not contribute 19 to the momentum.

20 And there are certain things that we 21 anchor to the more detailed code, NRELAP5, so we don't 22 have to model them directly. There are simple things 23 also that we know is conservative not to model, like 24 we take a pneumatic riser because whatever heat 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 25 exchange is going to go into them, the transient and 1 things like that, so anything that's not modeled is 2 either conservative or very low ranking.

3 MEMBER BLEY: Conservative always bothers 4 me because it's conservative with respect to something 5 but maybe not some other things. So it's conservative 6 with respect to the generation of oscillations?

7 DR. FARWILA: Yes.

8 MEMBER BLEY: Is that what you mean by 9 conservative?

10 DR. FARWILA: Of course.

11 MEMBER BLEY: Okay. Well, of course is 12 nice.13 DR. FARWILA: Actually, things that we say 14 conservative we've verified it to be conservative.

15 Like for this methodology we say we do not model heat 16 exchange through the riser, but it's modeled in the 17 code and you can see that there's a little bit of 18 stabilization when you have it, so we say, "Okay, 19 don't worry about it. Let's just continue," and use 20 the historical calculation when we did not have that 21 feature.22 DR. SCHULTZ: So with all of the features 23 that you've listed in the previous slides then, in 24 order to identify that conservatism you did 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 26 sensitivity studies associated with each of the 1 elements that you've described?

2 DR. FARWILA: This is why there's been a 3 lot of sensitivity studies, yes.

4 DR. SCHULTZ: Okay, thank you.

5 DR. FARWILA: Yeah. We had three years.

6 DR. SCHULTZ: Okay, that helps.

7 DR. FARWILA: All right, so how the 8 analysis was done, in the linear regime you have SS, 9 meaning steady state, so we have a steady state at a 10 certain power and for each power we have flow because 11 it's natural circulation. You cannot move power and 12 flow independently without a pump. So when we say in 13 the range of power, we also mean in the range of flow.

14 So we perturb a steady state and look at 15 the result. You will see the flow and power 16 oscillating and the oscillations are decaying, and 17 that by looking at the manner in which these decay we 18 know what the decay ratio is. So that's how we get 19 the stability parameters, the decay ratio and the 20 oscillation period.

21 And we find that as you said before, we 22 have unconditional stability in the entire operation 23 range and a curiosity there that decay ratio decreases 24 when you increase power and also when you increase 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 27 exposure. And we find --

1 CHAIR MARCH-LEUBA: And by exposure you 2 really mean the reactivity feedback is larger at the 3 end of cycle?

4 DR. FARWILA: Yes.

5 CHAIR MARCH-LEUBA: So increasing 6 reactivity feedback is good.

7 DR. FARWILA: When you have large negative 8 feedback it's stabilizing. And that also was done 9 from first principles in the paper we published in 10 Nuclear Science and Engineering. It was also in the 11 NURETH-16. It was invited for archiving later on.

12 MEMBER CORRADINI: The Chicago meeting.

13 DR. FARWILA: I don't remember where 14 because I didn't manage to go.

15 MEMBER CORRADINI: Yeah, okay. Fine.

16 DR. FARWILA: All right. These 17 observations all are in agreement with independent 18 reduced older models so we have additional way to 19 trust it.20 All right, the application methodology, we 21 apply these perturbations to steady state to get the 22 decay ratios. We vary power widely from five to 23 hundred percent. Actually, we do one percent also, to 24 see what could happen. But you cannot get CHF 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 28 response or worry about SAFDLs below 20 percent, but 1 we say 5 since we started with that.

2 We do beginning of cycle and end of cycle 3 and if we have any reason to suspect any more limiting 4 with later feedback, maybe closer to the beginning of 5 cycle but not the beginning of cycle itself, we 6 examine that as well.

7 And we have considered assumptions and not 8 only for the moderator temperature coefficient, but 9 also for decay heat fr action because decay heat 10 fraction is just like fission energy except for it has 11 a zero feedback from the moderators. So if the 12 moderator feedback is positive then it is more 13 conservative to have zero decay heat.

14 But if you have negative moderator 15 temperature coefficient then it is more conservative 16 to assume the largest possible in decay heat, like you 17 have been operating at high power for some time and 18 then you drop the power.

19 And I have a question.

20 MEMBER RICCARDELLA: Yeah. On the 21 previous slide, could you go back to that, please?

22 And in the bottom sort of bullets you have decay ratio 23 decreases with power, period decrease. Is that 24 decreases with increasing power?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 29 DR. FARWILA: Yes, with increasing power 1 and increasing cycle exposure.

2 MEMBER RICCARDELLA: Okay, and period also 3 decreases with increasing power.

4 DR. FARWILA: Period also decreases with 5 increase in power, yes.

6 MEMBER RICCARDELLA: Okay, thank you.

7 DR. FARWILA: You're welcome.

8 All right, so outside the normal 9 operation, the only transient we -- we did a scoping 10 of all the AOOs in a generic kind of way and the only 11 thing that became unstable was a depressurization 12 transient because only then you can void the riser.

13 And so we could get limit cycles and we could see that 14 the CHFR, the critical heat flux ratio actually 15 increases, not decreases.

16 So these stability conclusions are generic 17 but we intend to, are committed to confirm them if 18 needed, like if a plant upgrades to, or increased rate 19 of power or the plant operation changes, you have 20 anything different that may affect normal rate of 21 temperature, the activity or the fuel design itself 22 that could increase the rated flow or things of that 23 sort, so anything that would affect the nature of 24 natural circulation or feedbacks will be re-examined.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 30 MEMBER REMPE: So you said you did some 1 sensitivity studies with respect to power uprates. Do 2 you have any feel for how much of power uprate might 3 affect this conclusion? Like is ten percent enough, 4 or did you do a sensitivity study in that area?

5 DR. FARWILA: Okay, what, fortunately, for 6 this module, when you increase power you become more 7 stable.8 MEMBER REMPE: Okay.

9 DR. FARWILA: So power upgrades as long as 10 it does not create voiding in the riser we are 11 covered. But they have been analyzed. I did not 12 analyze them myself, but they have been analyzed.

13 MEMBER REMPE: So you don't have other 14 individuals who've done analyses to look at how much 15 of a power uprate would cause voids in the riser?

16 DR. FARWILA: No, I don't have that 17 number.18 MEMBER CORRADINI: It can be calculated, 19 but I'm more interested in your 50-megawatt machine 20 than other machines.

21 DR. FARWILA: All right.

22 MEMBER BLEY: You've said that several 23 times that it was kind of a surprise that as power 24 goes up, the oscillations go down.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 31 DR. FARWILA: Yes.

1 MEMBER BLEY: Because the code said so is 2 one thing, physically how do you explain that 3 phenomena?

4 DR. FARWILA: When the code said so, 5 everything stopped. We had to understand it from 6 first principles. And I probably should get into that 7 in the closed session.

8 MEMBER BLEY: Closed session, that's fine.

9 DR. FARWILA: All right. With the long-10 term stability solution, you already said that before.

11 It's a originally seclusion. It's one-dimensional not 12 two-dimensional like PWRs. And we just protect 13 against void in the riser and that's essentially that.

14 MEMBER CORRADINI: Okay. I think you have 15 to, for the members, explain what you mean by one-16 versus two-dimensional.

17 DR. FARWILA: Okay. For boiling water 18 reactors we have a power flow map, so essentially one 19 acts as power, the other acts as flow. And the 20 operator can take the state of the reactor, you can 21 vary power by putting control rods. You can change 22 flow by changing the pump or pump valves.

23 But in this reactor module we don't have 24 a pump, so if you change power, you change flow with 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 32 it. So essentially have, it's like a straight line.

1 It's power versus flow is unique curve, so that makes 2 it a one-dimensional seclusion.

3 MEMBER RICCARDELLA: You said a unique 4 curve.5 DR. FARWILA: Yes. I mean later on when 6 we say we want to exami ne the transients, so we 7 consider the power and flow as stage variables. So in 8 the phase space you access points other than that 9 unique line only through transients. So you have non-10 zero time derivatives that take you somewhere else and 11 maybe there are islands of instability we haven't seen 12 or anything like that, so that's really the rationale 13 for examining transients.

14 All right, so do I speed through this one 15 since we already know what the conclusions are and go 16 to questions? Because I think I'm almost out of time.

17 MEMBER CORRADINI: Well, I want you to --

18 well, I'm not sure. I don't really care about that.

19 I want to make sure I understand the experiments that 20 were done. So where is the point that we want to talk 21 about the experiments, in closed session or now?

22 DR. FARWILA: Best in the closed session.

23 MEMBER CORRADINI: Okay.

24 DR. FARWILA: There's a lot of more 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 33 proprietary information in the experiments.

1 MEMBER CORRADINI: Okay.

2 DR. FARWILA: Okay.

3 CHAIR MARCH-LEUBA: So anyone have 4 questions by the members?

5 I'm trying to speed up through the open 6 session so we can go into the closed session and talk 7 freely.8 MEMBER CORRADINI: Thank you all.

9 DR. FARWILA: Thank you.

10 CHAIR MARCH-LEUBA: Okay, Bruce. And 11 rules apply, you guys are authorized to go five miles 12 over the speed limit.

13 MR. BAVOL: Okay, good morning. My name 14 is Bruce Bavol. I'm a project manager for the NRC.

15 This is staff's presentation for the open session for 16 the Stability Topical Report, Safety Evaluation along 17 with 15.9, the Stability section of the Chapter 15.

18 To my right, Dr. Ray Skarda. To his 19 right, Dr. Peter Yarsky will be presenting, Rebecca 20 Karas is the branch chief for the Reactor Systems 21 branch. I'll mention briefly that the staff had 62 22 RAIs, all responses were resolved and closed.

23 Our full committee is scheduled for July 24 10th, and the staff plans to issue the final SER in 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 34 August, late August, and then the dash A approved 1 version of the SER and topical report in November 2 2019.3 With that I'll turn it over to the authors 4 to go over the outline and the rest of the 5 presentation.

6 MR. SKARDA: I'm Ray and I'll just start.

7 These are the eight items. The outline comprises 8 these eight items, the regulatory criteria that were 9 used to perform the stability topical, stability 10 methodology topical report review as well as 15.9 DCD 11 review, the long-term stability solution that was 12 proposed by the applicant, the instability modes and 13 the phenomena that are considered important to the 14 NuScale design.

15 The applicant developed as you saw their 16 own computer code PIM to perform the stability 17 analysis. The stability acceptance criteria and 18 uncertainty. Worst rod stuck out analysis which we'll 19 talk about a little bit later was not part of the 20 original submittal. We'll get to that. And then 21 finally we'll summarize the staff's conclusion with 22 respect to the review of the topical report as well as 23 the DCD 15.9.

24 So the five regulatory criteria that are 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 35 important to stability are shown here, and these are 1 also the ones that are called out in the standard 2 review plan 15.9A which is specific to NuScale. This 3 is talked about a little bit before, so briefly GDC 10 4 says don't exceed the SAFDLs.

5 GDC 12, no uncontrolled out powers, 6 uncontrolled power oscillations. GDC 13, 20 and 29, 7 compressing this would be these relate to 8 instrumentation controls, systems and functions that 9 ensure that the long-term stability solution 10 accomplishes its job of protecting against 11 instabilities. And that long-term stability solution 12 is shown on the next slide. That's the exclusion 13 region.14 The main thing here as you heard is that 15 the exclusion region criteria is simple and 16 straightforward. And if you look at the figure that 17 the whole main point of that is that you have to 18 maintain a five-degree submargin, a five-degree 19 Fahrenheit riser subcooling margin for operation.

20 If that is not the case, the modular 21 protection system precludes against instabilities and 22 forces a trip, generally either a hot leg temperature 23 trip or pressurizer pressure, low pressurizer pressure 24 trip.25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 36 MEMBER CORRADINI: So let me ask, I don't 1 remember. But where does NuScale operate normally in 2 terms of riser subcooling compared to the forbidden 3 region and the allowed region?

4 MR. SKARDA: Yeah. So it has to be --

5 their subcooling margin is the riser and it needs to 6 be five degrees Fahrenheit of larger.

7 MEMBER CORRADINI: But what is it in 8 normal operation. That's what I don't --

9 CHAIR MARCH-LEUBA: I seem to remember it 10 was 35 Fahrenheit.

11 MEMBER CORRADINI: That's what I thought.

12 I thought it was in the 10s that you used. Okay fine.

13 MR. SKARDA: Oh, what they're operating 14 at. Okay, I'm sorry.

15 MEMBER CORRADINI: And then my second 16 question is, when I get into the forbidden region and 17 I lose my safety margin, I go to the possible 18 instabilities, is it the riser that is avoiding or the 19 possible instabilities are essentially a SAFDL issue?

20 What I'm trying to understand is am I 21 worried about the void into the core or I'm reading 22 about SAFDLs being violated because I have an unstable 23 flow?24 MR. SKARDA: The subcooling margin 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 37 protects the SAFDLs through minimum, the NCF --

1 MEMBER CORRADINI: Okay, fine. That's 2 what I thought. Okay, thank you. Thank you very 3 much.4 MR. SKARDA: Next slide.

5 So okay, so there's in terms of excluding 6 instabilities the applicant looked at several types of 7 instability modes, identified those that were relevant 8 to the NuScale design. In the DCD, I think they, as 9 you saw earlier, the one that's more important to them 10 is this natural circulation with density wave 11 oscillation characteristics riser dominant and that 12 will be discussed in more detail in the closed 13 session.14 The applicant's findings are consistent 15 with the staff's findings based on an independent PIRT 16 that was also performed by the staff. Next slide.

17 So as I mentioned, the applicant developed 18 their own computer model and computer code to perform 19 the stability analysis, PIM. PIM's evaluation model 20 includes simple models for a thermal-hydraulics 21 reactor, kinetics, fuel thermal mechanical response 22 and steam generator to peak conduction and heat 23 transfer, which you saw earlier.

24 And it's been validated against the NIST-1 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 38 stability tests which were integral tests. The decay 1 ratio is the principle acceptance criteria with 2 respect to steady state operation at various power 3 levels. The main conclusion's here is that the K 4 ratio is insensitive to variations in most of the 5 important phenomena over, really, the range of 6 analysis related to the NuScale design.

7 The decay ratio acceptance criteria 8 affords adequate margin to account for biases and 9 uncertainty and that includes the numerical effects.

10 Primarily, dissipation is what I would call the main 11 one, dispersion. It's highly dissipative at least 12 with steady operation, so any change in phase is not, 13 it's just not going to be an issue from what we're 14 seeing. Next slide.

15 So I mentioned this worst rod stuck out 16 analysis, and this is something that is in combination 17 with an analysis that was done as part of 1506, the 18 return to power. There was some combination with that 19 instability analysis.

20 From the stability standpoint, it provided 21 an analysis at intermediate pressures from operating 22 pressure down to where ECC would actuate. You'll see 23 both in the SER for 1506 and so forth, just to provide 24 context that event is actually decay, DHRS overcooling 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 39 event.1 So you're really driving, you're trying to 2 drive this thing into sort of a recriticality mode.

3 So trying to make sure I say the right things here in 4 terms of the -- we talked about the strong moderator 5 feedback with in terms of recriticality which is 6 important in driving that power or that recriticality.

7 But the other side of that is it really 8 damps oscillations then. So in terms of an event, 9 you'd ideally like something that's going to drive the 10 initial event hard to that point and then you would 11 like to have weak moderator feedback in order to have 12 those oscillations persist longer.

13 And so that will be again discussed --

14 CHAIR MARCH-LEUBA: And we see those 15 details in Chapter 15 this afternoon and tomorrow.

16 MR. SKARDA: Yes. That's correct. That's 17 correct.18 CHAIR MARCH-LEUBA: But just because we're 19 seeing -- because it's an overcooling event because 20 you cannot reach criticality unless you are, I believe 21 it's under 200, I mean very cold, then your coolant 22 has shrunk and you are below the riser and therefore 23 you cannot have natural circulation anymore.

24 So you really your parenthetical 18-- we 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 40 talk about this is the closed session for 15.

1 MR. SKARDA: Yeah. In fact, the next --

2 so basically before that o ccurs, before he sees 3 actuation, for example, there's actually, actually 4 plenty of subcooling margin in this particular case.

5 Next slide.

6 And so as you were saying, I don't have to 7 say it. Yeah, once he sees this actuates you've 8 broken the natural circulation flow pattern and you're 9 really in a pool boiling kind of mode, but at very, 10 very low power.

11 So the bottom line is this analysis by the 12 applicant demonstrated that flow oscillations are not 13 safety significant. Even if they had large 14 amplitudes, it's really low power. Next slide.

15 So the stability report conclusions with 16 respect to PIM approval for performing stability 17 analysis, PIM's a simple model but it's anchored in 18 upstream, high fidelity models to improve accuracy.

19 The decay ratio is highly insignificant to variations 20 in important phenomena.

21 The PIM predictions, both steady state and 22 transient, have been confirmed by staff through 23 independent confirmatory calculations. And so PIM is 24-- staff's found PIM to be acceptable for performing 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 41 the safety related stability analysis for the NuScale 1 module. Next slide.

2 In terms of the long-term stability 3 solution, the primary instability mechanisms were 4 properly identified by the applicant and confirmed by 5 independent staff TRACE analysis.

6 During power operation of the NuScale 7 power module, NuScale power module is very stable.

8 The exclusion region-based, long-term stability 9 solution is effective in preventing the reactor from 10 becoming unstable during normal operation and 11 including effects of AOOs. And then as we mentioned, 12 the potential instability during return to power with 13 respect to worst rod out is not a safety concern and 14 the five GDCs related to safety are met.

15 So briefly summarizing the review of 16 section 15.9 of the DCD, analysis of perturbed steady 17 state conditions demonstrate that decay ratio remains 18 well below the acceptance criteria for power levels 19 greater than five percent of rate of power.

20 The certain transient analyses result in 21 new studies, stable state conditions, and in others 22 that would exceed the hot leg trip or low pressurizer 23 pressure trip, enforce the exclusion region.

24 With respect to the AOOs, those are the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 42 AOO classes that you find in other sections of 15.9, 1 increase in heat removal, decrease in heat removal 2 from a secondary system and so forth. The first two, 3 really, the bounding events that were performed there 4 were feedwater flow increases and decreases.

5 I won't go through -- some of these were 6 dispositioned, just questions, we can take those. But 7 the bottom line is the long-term stability solution is 8 effective in preventing the occurrence of instability 9 and again the five GDCs important to stability are 10 met. And I believe that's it.

11 We have some backup slides.

12 CHAIR MARCH-LEUBA: Probably the answer to 13 my question is let's wait for the closed session, but 14 anything you can say in open session with respect to 15 the secondary side, the steam tube instabilities?

16 DR. YARSKY: Let's defer that to the 17 closed session. But the staff has a slide 18 specifically on that topic.

19 CHAIR MARCH-LEUBA: I know. And, but in 20 open session can we say that you're satisfied with the 21 proposed solution by NuScale or do you still have 22 reservations?

23 DR. YARSKY: I would say in terms of 24 secondary side instability the staff was able to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 43 determine that it does not pose any safety concerns.

1 CHAIR MARCH-LEUBA: Okay. That's what I 2 wanted to put on the record for the open session.

3 Thank you.

4 Any more questions -- okay. At this point 5 we're going to transition to a closed session, but 6 before that we're going to ask for comments from --

7 can we open the phone line?

8 Any members from the public that want to 9 make a comment on the open session?

10 We're waiting to see if the phone line is 11 open.12 MEMBER CORRADINI: Is anyone on the public 13 line? Please at least acknowledge that you're out 14 there.15 MEMBER RICCARDELLA: Mike is still trying 16 to verify.

17 MR. LEWIS: That's the worst thing. I've 18 never heard such dancing in my life trying to keep 19 away from the major problems and listening to details, 20 details, detail and then talking them into oblivion 21 instead of answering them strongly.

22 Further, there was a heck of a lot of 23 noise over this line. I presume everybody's shuffling 24 papers and hoping to cover me over.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 44 But this is exactly what I'm talking 1 about. You're going into a secret session, a closed 2 session, just to make it easier for the licensee to 3 cover all the problems that should be out there in the 4 public. I object strenuously and I plan to have some 5 more legal objections down the pipeline.

6 Thank you for listening to me. Good bye.

7 CHAIR MARCH-LEUBA: Just a moment. You 8 came on to the open line a little late so we didn't 9 hear your name. Can you state it for the record?

10 MR. LEWIS: Marvin, M-A-R-V-I-N, Lewis, L-11 E-W-I-S. I live in northeast Philadelphia. My email 12 is marvlewis@juno.com.

No period between the V and 13 the L and juno is spelled like the goddess, not the 14 city in Alaska.

15 CHAIR MARCH-LEUBA: Thank you very much.

16 Any other comments from the open line?

17 MS. FIELDS: Yes. First of all, I'd like 18 to know when the open session returns. Is that after 19 lunch?20 CHAIR MARCH-LEUBA: In principle, the open 21 session will start at 11:00 a.m. if we can make up 22 some time, for the open session for Chapter 11 and 23 we'll go one hour before lunch. Chapter 15, my 24 mistake. So in principle 11:00, but we may be late.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 45 MS. FIELDS: That's not the time frame on 1 the agenda. So you think you're coming back to open 2 session at 11 o'clock?

3 CHAIR MARCH-LEUBA: That's what we're 4 shooting for.

5 MR. SNODDERLY: This is Mike Snodderly.

6 I'll send you a email when we're going to start back 7 up in open session. But right now we plan to follow 8 the agenda and it'll be sometime around 11:00 a.m.

9 But I'll send you an email and I'll send it to all 10 that -- to that interested members of the public list 11 that I have.

12 MS. FIELDS: Okay, so I do have a comment.

13 I'm glad you brought up the issue of an increased 14 power and the possibility of a different type of fuel 15 because you may be aware there's a parallel process.

16 You have the NRC design certification 17 process which for the most part is based on a lot of 18 documentation, a lot of review. I've listened to 19 quite a few of the NRC's NuScale meetings and it's 20 been very, very valuable. But there's a parallel 21 process, the UAMPS process.

22 But I'd appreciate it if someone would 23 close their -- go on mute so there's not a lot of 24 background on the phone.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 46 CHAIR MARCH-LEUBA: Thank you, Sarah.

1 MS. FIELDS: All I hear is shuffling of 2 papers and I can hardly hear.

3 MEMBER CORRADINI: There's no shuffling 4 here. It must be on other lines.

5 MEMBER BLEY: And you're very clear coming 6 in.7 MS. FIELDS: Oh, okay. So this parallel 8 process, they anticipate a 20 percent of power uprate, 9 but they haven't outlined how they would get to that 10 power uprate and implying that it would be Utah 11 Associated Municipal Power Systems, which is the only 12 entity that currently plans to submit a COL 13 application using the NuScale design.

14 So they're talking about this, they're not 15 talking about how exactly they would get the power 16 uprates whether it would be a design change or whether 17 it would be part of the COL application or whether it 18 would be some future license amendment request.

19 There are other things, if you go online 20 there are articles about new types of fuel and NuScale 21 anticipating using some of these new types of fuel.

22 UAMPS has already announced when they're 23 going to get a NRC approval of their COL application, 24 when they're going to start site preconstruction 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 47 activities, when they're going to complete the 1 construction, when they're going to start operating 2 their first power module and when they're going to 3 start operating the c omplete array of 12 power 4 modules.5 The Department of Energy, one of their 6 staff people at a conference in Salt Lake already 7 announced, "Hey, this is happening." So there's a lot 8 of effort out there and also calling this a carbon-9 free power process.

10 And anyone who knows anything about the 11 nuclear fuel chain knows that carbon is used from the 12 moment that the uranium industry starts going out and 13 exploring for uranium and produces uranium, and all 14 along the fuel chain it uses fossil fuels to make the 15 fuel.16 And there's -- so calling it a carbon-free 17 power project is disingenuous and disinformation. So 18 on this you should be aware there's other parallel 19 world out there of public relations and trying to get 20 the public to accept this no matter what the cost 21 might be.22 I live 20 miles from a very low-income 23 community in Utah where the ratepayers there still do 24 not exactly how much this is going to cost. So 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 48 whatever's going on in your departments it comes down 1 to a ratepayer getting a bill for a project that over 2 the long term no one has a real perception of how much 3 it's going to cost each and every ratepayer over a 4 period of 50 years. So that's some of the background 5 of community concern.

6 Thank you.

7 MR. SNODDERLY: Thank you, Ms. Fields.

8 So we're going to go into a closed session 9 now. So, Makeeka, could you please close the open 10 phone line.

11 I'd like to ask Bruce and other members of 12 the staff, Rebecca, if there's anybody here from the 13 staff that does not have a need to know, we'd like to 14 ask you to leave the room now. And the same thing --

15 MEMBER CORRADINI: Well, I think we had 16 scheduled a break to allow this to happen easier.

17 MR. SNODDERLY: Okay, if you want, I think 18 we're ready to go if you want to --

19 MEMBER CORRADINI: Can we at least take 20 five minutes to make sure? That's what I would 21 suggest. Let's just take five minutes, make sure the 22 open line is closed.

23 MR. SNODDERLY: Okay.

24 MEMBER CORRADINI: All right. I think 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 49 we're going to lose members anyway to use --

1 MR. SNODDERLY: Yes, you are. Okay.

2 MEMBER CORRADINI: So five minutes.

3 (Whereupon, the above-entitled matter went 4 off the record at 9:28 a.m. and resumed at 11:30 a.m.)

5 MEMBER CORRADINI: Okay. Why don't we 6 come back in session. So, our plan is to start off 7 with the Applicant in terms of Chapter 15.

8 And we'll go through an hour. And then 9 break for lunch wherever we get in an hour. Jose?

10 CHAIR MARCH-LEUBA: Go for it.

11 MEMBER CORRADINI: Matthew, you're it.

12 MR. PRESSON: All right. Thank you again.

13 To reintroduce myself, I am Matthew Presson, Licensing 14 Specialist with NuScale Power, and Project Manager for 15 Chapter 15.

16 We are here today to discuss Chapter 15 of 17 the NuScale design certification application. And to 18 cover the unique aspects of how NuScale approaches 19 transient and accident analysis in our design.

20 The presentation today will be provided 21 primarily by the people joining us here at the table.

22 We have myself.

23 We have Megan McCloskey, Thermal Hydraulic 24 Analyst. We have Ben Bristol, Supervisor of System 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 50 Thermal Hydraulics. And Paul Infanger, Licensing 1 Specialist with Chapter 15.

2 And potentially joining us on the phone as 3 needed, will be Dr. Pravin Sawant, Supervisor of Code 4 Validation and Methods. Dr. Brian Wolf, Supervisor of 5 Code Development.

6 Dr. Selim Kuran, Thermal Hydraulic 7 Software Validation. Mark Shaver, Supervisor of 8 Radiological Engineering. And Greg Myers, Licensing 9 Specialist for Containment.

10 All right. For the scope of our 11 discussion today, there's a lot of information that is 12 summarized in Chapter 15, where we deal with 13 postulated transients and events.

14 There are also a number of topical reports 15 that define methodologies that we use in Chapter 15, 16 that we have not yet presented to the ACRS.

17 Therefore, our presentation today will be 18 focused on the material provided in the FSAR, citing 19 Chapter 15 itself, and the results of those 20 methodologies which are again, provided in that 21 chapter.22 We will discuss the high level details of 23 these methods so that we have a basic understanding.

24 And we are happy to summarize those topical reports 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 51 here.1 But any detailed discussion of those 2 methods will need to wait until we present the topical 3 reports for your review later this year.

4 CHAIR MARCH-LEUBA: Are we expecting those 5 in the October time frame?

6 MR. PRESSON: I believe October. Yeah.

7 So this is a big old slide. It is a copy of slide 77.

8 Later on in this presentation, those acronyms and 9 events will be covered in the presentation that 10 follows.11 But we did want to open this entire 12 discussion on Chapter 15 with the summary of doses, 13 just to cover the health and safety of the public.

14 And how it applies to NuScale design.

15 As you can see, the dose consequences for 16 our postulated events, and even the beyond design 17 basis events listed there, remain very low in the 18 NuScale power module.

19 So for all of our discussions on 20 postulated events that follow, the NuScale power 21 position is that we have a safe design.

22 MEMBER SKILLMAN: What is the purpose for 23 the bolding on the rem TEDE for dose?

24 MR. PRESSON: So again, we'll get into 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 52 those details later. But those are bolded to show the 1 highest doses that we had.

2 MEMBER SKILLMAN: Thank you. Okay, I 3 thought that something, yes.

4 MR. PRESSON: This is a quick review of 5 what we'll be going over today. Our design overview, 6 as well as the Chapter 15.

7 The intellectual assumptions for the 8 Chapter 15 analysis. So, some thermal hydraulics 9 analysis, methodologies. Some selected transient 10 results. Our radiological analysis.

11 Some on Chapter 6.2.1 containment response 12 analysis. That's where we follow it up with the --

13 from the loco model it is built off of. And the long 14 term cooling.

15 And with that, again, our overview of 16 safety and non-safety systems with Megan McCloskey.

17 MS. McCLOSKEY: Thank you. All right, so 18 before we dive into Chapter 15, I think for members of 19-- particularly after the discussion yesterday and 20 this morning, are familiar with the NuScale power 21 module design and the internal reactor design with the 22 core and steam generator and pressurizer in one 23 vessel.24 When we get to the transient results later 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 53 this afternoon, we'll see examples of module 1 protection system actuations in response to events.

2 And for Chapter 15 design basis analysis, 3 we're primarily concerned with confirming the 4 effective operation of the safety-related systems for 5 safety related decay heat removal. We have two 6 systems, the emergency core cooling system, and the 7 heat removal system.

8 So to set the stage, on those we have just 9 a couple of slides that I think we can go through 10 quickly on the operation.

11 CHAIR MARCH-LEUBA: I know we say this all 12 the time, but people are on the phone, and they're 13 probably not hearing you.

14 MS. McCLOSKEY: Okay.

15 CHAIR MARCH-LEUBA: Can you just speak or 16 get the microphone, maybe -- people are -- away from 17 the paper.

18 MS. McCLOSKEY: Yeah. I was concerned 19 about the paper shuffling.

20 All right. For the emergency core cooling 21 system design, we have two reactor recirculation 22 valves on the side of the reactor pressure vessel.

23 And three reactor vent valves on the top head of the 24 containment.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 54 And these -- when demanded, these valves 1 open to establish a boiling condensing flow path to 2 transfer decay and residual heat from the reactor 3 pressure vessel by venting steam from the reactor 4 pressure vessel into containment where it condenses on 5 the inside surface of the containment wall.

6 And then is transferred through the 7 containment wall to the reactor pool ultimate heat 8 sink. The --

9 CHAIR MARCH-LEUBA: Yesterday we asked 10 this question when we were talking about the ECCS 11 valves. I had read into a figure, what is the water 12 level after you open the ECCS valve, and assuming 13 initial inventory normal now.

14 Where does the water level settle? I read 15 ten feet above active fuel.

16 MS. McCLOSKEY: Yes. That's the --

17 CHAIR MARCH-LEUBA: That's usual?

18 MS. McCLOSKEY: The nominal equilibrium 19 water level.

20 CHAIR MARCH-LEUBA: Okay. Thank you.

21 MS. McCLOSKEY: Yeah. Typically there's 22 more than 20 feet above the top of active fuel when 23 the ECCS valves open under a normal expected 24 progression.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 55 MEMBER CORRADINI: And how far -- how far 1 above active fuel are the RRVs?

2 MS. McCLOSKEY: I don't have that number.

3 MEMBER CORRADINI: It's around eight feet, 4 six feet.5 MR. BRISTOL: It's six feet long.

6 MEMBER CORRADINI: Okay. All right.

7 CHAIR MARCH-LEUBA: Eight feet? You think 8 it's eight feet?

9 MEMBER CORRADINI: No. They said six 10 feet.11 MR. BRISTOL: Six.

12 CHAIR MARCH-LEUBA: Oh. I thought it was 13 four. But you know better.

14 MEMBER BLEY: And you said that if a coil 15 breaks level at about ten feet?

16 MS. McCLOSKEY: Yes.

17 CHAIR MARCH-LEUBA: And the ECCS valves 18 will open, based on the instrument, that level 19 instrumentation on the containment. Is that correct?

20 MS. McCLOSKEY: Yes. The containment --

21 or sorry, the ECCS valves are actuated by the module 22 protection system either due to a high containment 23 level signal. Or after if there's a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> loss of 24 AC power supply.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 56 CHAIR MARCH-LEUBA: But that -- that's not 1 the MPL. I mean, it's --

2 MS. McCLOSKEY: Yes.

3 CHAIR MARCH-LEUBA: The timer -- you lose 4 DC power to the solenoids at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

5 MS. McCLOSKEY: If DC power is available, 6 then after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> the load for maintaining the ECCS 7-- to the ECCS valve solenoids is shed.

8 CHAIR MARCH-LEUBA: Yeah.

9 MS. McCLOSKEY: So that's the timer.

10 CHAIR MARCH-LEUBA: So is it -- really the 11 activation is really on the water level.

12 MS. McCLOSKEY: Yes.

13 CHAIR MARCH-LEUBA: And we had a 14 discussion, I wanted to put it on the record again, 15 about the probability of failure of that level 16 instrumentation in the containment.

17 Which is an advanced sensor, which has not 18 been used in nuclear reactors before. And it is a 19 complex sensor. It's a rhythm-based sensor which we 20 haven't seen any details, but it's likely to have, be 21 a digital instrument.

22 Probably microprocessor based. So, it 23 would be subject to common core failures. So all four 24 level sensors may fail if it's a digital system.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 57 Or you have to consider a common core 1 failure from the digital point of view. And to 2 complicate things, the containment is always empty.

3 So you're not exercising that 4 instrumentation. So, it can fail and you never know 5 it's blind.

6 So, we are going to have to address that 7 thoroughly in Chapter 7 next time it comes here.

8 MS. McCLOSKEY: Right. In the scope of 9 the Chapter 15 analysis, since the module protection 10 system and the instrumentation are safety related, we 11 do assume that they function.

12 CHAIR MARCH-LEUBA: Right. But it's more 13 of a Chapter 7, Chapter 19 issue.

14 MS. McCLOSKEY: Yes.

15 CHAIR MARCH-LEUBA: But, I just wanted to 16 put the concept on the record again.

17 MS. McCLOSKEY: Yes.

18 MEMBER CORRADINI: Just so I remember, so 19 there are four different level sensors for the 20 containment water level?

21 MS. McCLOSKEY: Four -- there are four 22 channels, I think.

23 MEMBER CORRADINI: Four channels.

24 MEMBER BLEY: And if this instruments are 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 58 safety related, and I thought they were, do we have 1 any source of safety-related electric power that 2 supply them?

3 MS. McCLOSKEY: No. The --

4 MEMBER BLEY: You don't. Okay.

5 MS. McCLOSKEY: Because if the -- if the 6 DC power that's supplied from the highly reliable 7 supply is lost, then our -- it is postulated to be 8 lost.9 The safety systems actuate in the NuScale 10 design. So, the safety --

11 MEMBER BLEY: Well, a level sensor won't 12 actuate. It --

13 MS. McCLOSKEY: No. But the -- the power 14 to the ECCS valve solenoids will wake up.

15 MEMBER BLEY: They will. Yeah. That's 16 right.17 MS. McCLOSKEY: And so then eventually the 18 valves will open to establish cooling, so.

19 MEMBER BROWN: And just to make sure I 20 understand. The radar-based system that we -- that I 21 think Jose is talking about, is actually during normal 22 operation, measuring the level up in the pressurizer.

23 Isn't that correct?

24 MEMBER CORRADINI: They're different 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 59 things.1 MS. McCLOSKEY: Yeah. That's -- I think 2 you're ---

3 MEMBER CORRADINI: Two different things.

4 Inside vessel, outside vessel. You're talking --

5 MEMBER BROWN: I'm inside the reactor 6 vessel.7 MEMBER CORRADINI: They're -- but that's 8 not what we're asking about.

9 MEMBER BROWN: But it's outside.

10 CHAIR MARCH-LEUBA: Yeah. I'm talking 11 containment.

12 MEMBER BROWN: You're talking about -- oh, 13 you're talking about the containment water.

14 CHAIR MARCH-LEUBA: So we have four 15 sensors in the pressurizer, four sensors in 16 containment.

17 MEMBER BROWN: Okay. I didn't know you 18 were talking -- I just kind of had a disconnect.

19 MEMBER CORRADINI: I'm still -- I'm still 20 awake. That's all it should be.

21 MS. McCLOSKEY: So actually it's on 22 containment level.

23 MEMBER BALLINGER: I mean, we're also 24 making an assumption here, you are anyway. That when 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 60 the containment doesn't have any water in it, those 1 sensors are not working.

2 MEMBER BLEY: That's true. We don't know 3 the answer to that.

4 MEMBER BALLINGER: I mean, most 5 electronics have diagnostics that run all the time and 6 things like that.

7 So, we have to be careful when we talk --

8 when we get to Chapter 9 that we don't make the --

9 CHAIR MARCH-LEUBA: Chapter 7.

10 MEMBER BALLINGER: Chapter 7 rather.

11 MEMBER BROWN: Well, I mean, there -- the 12 reason I'm asking, the con -- the radar base one is 13 measuring the pressurizer level are above the reactor 14 vessel.15 And they're, at least based on the 16 picture, I thought I remembered, they're going down to 17 measure the pressurizer level up in that upper part of 18 the reactor vessel.

19 For the containment ones, are they up on 20 that upper head area outside the pool? Are they --

21 are they located somewhere else?

22 I mean, it's a --

23 MS. McCLOSKEY: I'm not sure of the 24 sites.25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 61 MEMBER BROWN: Well, you said that the 1 water level in the reactor within the containment is 2 about ten feet above the reactor core.

3 MEMBER BLEY: After everything settles 4 down.5 MEMBER BROWN: After everything settles.

6 Are you still depending on those? I mean, that's a 7 pretty long shot for the radar detectors to be 8 measuring the water level in the containment.

9 MEMBER BLEY: They're supposed to be 10 measuring it all the way down at the bottom.

11 MEMBER BROWN:

That's a -- what I'm 12 saying. That's a long shot.

13 MR. BRISTOL: This is Ben Bristol. So, 14 yeah. A couple of points. I think as the ACRS is --

15 we've described before, there's performance 16 requirements that are established based on the safety 17 analysis for the instrumentation.

18 We've documented what those performance 19 requirements are. And it is yet to be demonstrated by 20 the final sensor selection that, yes, those 21 performance requirements can be met.

22 In addition to the common cause failure, 23 there is consideration given to the sensor design as 24 an input to the diversity and defense in depth 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 62 analysis of the MPS system to ensure that common cause 1 sensor failure is either analyzed within the bounds of 2 the Chapter 15 analyses that are otherwise ensured 3 that it's a low probability.

4 CHAIR MARCH-LEUBA: That's a very good 5 answer. Thank you. We just put in a marker that 6 whenever Chapter 7 comes back, or Chapter 19, we'll 7 bring you back again.

8 MR. BRISTOL: Okay.

9 MS. McCLOSKEY: Can we go onto the next 10 slide? The second system for decay heat removal is 11 the Decay Heat Removal System that removes heat after 12 a loss of normal secondary site cooling.

13 When the Decay Heat Removal System is 14 actuated, the containment isolation valves, the main 15 steam and feed water lines close.

16 And the actuation valves on -- for the 17 Decay Heath Removal System open to establish an 18 alternate heat removal path through the steam 19 generators so that energy is transferred from the 20 primary side to fluid inside the steam generator 21 tubes.22 That steam is transported through the 23 Decay Heat Removal System actuation valves over to the 24 condensers that are located in the reactor pool. Then 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 63 the condensate is transferred back to the steam 1 generat -- to the steam generators.

2 MEMBER BLEY: My copy of slide nine shows 3 water in the containment. That is wrong. Right?

4 Your copy doesn't. It's all white.

5 The copy they gave us shows water in the 6 line.7 MS. McCLOSKEY: No. There's no water in 8 containment. That's the -- that's the pool.

9 MEMBER BLEY: That's slide nine.

10 MS. McCLOSKEY: That's the pool.

11 MEMBER BLEY: Oh. You're right.

12 MS. McCLOSKEY: That's the pool.

13 MEMBER BLEY: Never mind.

14 MEMBER CORRADINI: White is air. It's 15 steam.16 MEMBER BLEY: Never mind. Never mind.

17 MEMBER BROWN: Oh, talk about a shot.

18 MEMBER CORRADINI: White is like you.

19 MEMBER BALLINGER: But you are right in 20 one sense. There's water -- our slides show water in 21 the vessel.

22 MS. McCLOSKEY: Inside the reactor vessel.

23 MEMBER CORRADINI: It was supposed to be 24 in --25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 64 MEMBER BROWN: In the reactor vessel, yes.

1 MEMBER BALLINGER: It's light blue here, 2 dark blue in there.

3 MS. McCLOSKEY: Yes.

4 MEMBER BROWN: It's very light blue.

5 CHAIR MARCH-LEUBA: Through all the 6 documentation there are references to the old and the 7 new actuation logic for DHRS. Will you tell us what 8 is the actuation logic for the DHRS?

9 What signals tip it? What signal tells 10 MPS to trip the DHRS valve? To open it?

11 MS. McCLOSKEY: There are a couple of 12 signals. One of them is high secondary side steam 13 pressure.14 Loss of power also actuates the valve.

15 And --16 MR. BRISTOL: High RCS temperature.

17 MS. McCLOSKEY: High RCS temperature.

18 MR. BRISTOL: High RCS pressure.

19 MS. McCLOSKEY: And pressure.

20 CHAIR MARCH-LEUBA: Oh, high pressure 21 inside the vessel.

22 MS. McCLOSKEY: Um-hum.

23 CHAIR MARCH-LEUBA: High temperature 24 inside the vessel, or high temperature outside in the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 65 secondary.

1 MS. McCLOSKEY: Right.

2 CHAIR MARCH-LEUBA: Okay.

3 MS. McCLOSKEY: Indications that secondary 4 site cooling is not effective.

5 CHAIR MARCH-LEUBA: The language indicates 6 that you use to trip on more things. Then I assume 7 that you have identified that they're not necessary?

8 MR. BRISTOL: So, -- this is Ben. The 9 signals used to be combined. There was two functions, 10 and we'll get into this in a little bit more detail 11 later.12 But there was an isolation function that 13 was required to mitigate some events for the secondary 14 side. And then there was a DHR actuation that was 15 required.16 The analysis that we did showed that those 17 two didn't necessarily need to come at the same time.

18 And as part of the start up procedure that ended up 19 being a consideration that was fairly limiting, 20 particularly at the lower temperature conditions.

21 CHAIR MARCH-LEUBA: Um-hum.

22 MR. BRISTOL: So the decision was to 23 decouple the secondary isolation as its own function, 24 so that on conditions that we knew that we needed to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 66 preserve inventory, secondary isolation would occur.

1 But not immediately cause DHR actuation.

2 And not continue to require DHR to be active for the 3 MPS logic.

4 So what it does, is it allows for DHR to 5 actuate and then clear once we have established 6 cooling based on the trip signals.

7 MEMBER BROWN: So you could not actuate 8 DHS, the Decay Heat Removal System totally. You just 9 isolate the main steam isolation valves?

10 MR. BRISTOL: That's correct.

11 MEMBER BROWN: And the feed water valves?

12 MR. BRISTOL: Feed water isolation valves.

13 MEMBER BROWN: And the feed water 14 isolation valves.

15 MR. BRISTOL: Yes.

16 CHAIR MARCH-LEUBA: And only if the 17 secondary steam starts heating up, then you need 18 additional cooling.

19 MR. BRISTOL: That's correct.

20 MEMBER BROWN: So the other path is not 21 established until you met some other preconditions?

22 MR. BRISTOL: That's correct.

23 CHAIR MARCH-LEUBA: That's in the area.

24 MEMBER BROWN: Okay. All right. Thank 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 67 you.1 CHAIR MARCH-LEUBA: And I assume all the 2 analysis in Chapter 15 represent the new logic, not 3 the old logic.

4 MR. BRISTOL: Well, it's a -- that's a 5 great question. It's one of the design changes that's 6 being implemented in the current analysis effort.

7 I think the NRC has asked us to describe 8 that.9 CHAIR MARCH-LEUBA: Are you redoing 10 everything?

11 MR. BRISTOL: We are in the middle of 12 updating the FSAR analysis. They're very similar from 13 a transient progression to what we've seen before.

14 MEMBER CORRADINI: But this is -- this is 15 what is identified in many cases as Rev 3.

16 MR. BRISTOL: That's correct.

17 MEMBER BROWN: That will also be reflected 18 in Chapter 7 Rev 3 relative to this differentiation of 19 what logic is required?

20 MR. BRISTOL: That's correct.

21 MEMBER BROWN: Okay.

22 CHAIR MARCH-LEUBA: Let me just stipulate 23 here before we go any further. That NuScale has so 24 much margin that for any error it doesn't matter what 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 68 you analyze, you're always going to get the same 1 answer, really good.

2 And so, but it is nice to do the paperwork 3 properly. Okay.

4 MEMBER CORRADINI: And you'll continue to 5 cheerlead that.

6 MS. McCLOSKEY: All right. So, in terms 7 of the scope of Chapter 15, the design basis 8 initiating events consider internal events that could 9 affect a module operating at power.

10 The Chapter 15 analyses that we do are 11 performed for a single module response. In terms of 12 shared systems for the NuScale design, the reactor 13 pool ultimate heat sink is the important shared system 14 there.15 And so our long term cooling analyses 16 consider effects of the reactor pool temperature and 17 the level on the module response that account for up 18 to 12 modules rejecting heat to the reactor pool.

19 We went through a systematic process to 20 assure that we had identified an appropriate scope of 21 design basis events for Chapter 15. Particularly 22 considering the systems and components that are unique 23 to the NuScale design, such as the containment 24 evacuation system for the ECCS valves.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 69 MEMBER DIMITRIJEVIC: Excuse me. Could I 1 ask you? Because I just want to make sure I 2 understand what you just said before.

3 MS. McCLOSKEY: Um-hum.

4 MEMBER DIMITRIJEVIC: You said that you 5 considered that changes in pool temperature are only 6 for long term cooling for all units. Right?

7 Just for long term cooling?

8 MS. McCLOSKEY: That was an area of focus 9 for long term cooling, to assure that we had bounded 10 effects of multiple -- of potentially multiple modules 11 rejecting heat to the pool.

12 MEMBER DIMITRIJEVIC: In long term 13 cooling.14 MS. McCLOSKEY: In long term.

15 MEMBER DIMITRIJEVIC: But you did not I 16 suppose, analyze that one unit, you know, can be long 17-- or that even by the one unit just goes to transit.

18 MS. McCLOSKEY: We have considered -- the 19 long term cooling analyses also consider potentially 20 only one unit rejecting heat to a cold pool.

21 So that is -- that is covered.

22 MEMBER DIMITRIJEVIC: All right. Well, my 23 question is, can we have 11 units injecting pool --

24 heating the pool, when one unit just going to DHRS or 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 70 ECCS operations?

1 So, you know, when -- I was wondering how 2 did you model that pool temperature? And what case 3 would you consider for it?

4 As I understood you only considered 5 difference from the beginning only for long term 6 cooling operations.

7 MS. McCLOSKEY: Well, and let me clarify 8 here. We -- okay, in terms of multi-module effects, 9 if one module were to experience a transient or an 10 accident scenario, --

11 MEMBER DIMITRIJEVIC: Right.

12 MS. McCLOSKEY: That potentially affected 13 the reactor pool temperatures for other modules, they 14 would, I believe that they would still be under the 15 control of the applicable technical specifications for 16 those modules, to assure that to consider whether they 17 would remain operating, or what actions operators can 18 take. 19 I'm not sure if that gets at your 20 question.21 MEMBER DIMITRIJEVIC: Well, I mean, I was 22 thinking about situations like where you have a common 23 thing like loss of offsite power. Or, you know, you 24 can have a loss of all AC power for all units.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 71 And they may be entering the transients in 1 the different phases. You know, because they would, 2 you know, I'm not sure, but how we end operation that 3 will go.4 So that, you know, I mean, they will all 5 three probably. But I'm not sure how they will go to 6 different phases.

7 It's even, you know, will they go in the 8 ECCS operation all in the same time? And how will 9 actuate.10 So, I was sort of wondering, can we have 11 some normal occurrence like loss of offsite power 12 where they will all be in the accident position of 13 certain taking, you know, depending on the pool?

14 MS. McCLOSKEY: We -- we'll get to some of 15 the example, some of the discussion in long term 16 cooling later this afternoon.

17 We considered different scenarios for long 18 term cooling, both maximum temperature cases as well 19 as minimum temperature cases. And that considers a 20 range of pool conditions.

21 And it's actually the minimum temperature 22 case where you have the most heat removal outside of 23 the containment vessel, where we have our most 24 challenge in terms of level and margin to warm 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 72 precipitation.

1 And so we've considered both ranges, both 2 ends of that spectrum for a range of cooling that 3 occur.4 MEMBER DIMITRIJEVIC: Right. Well we will 5 see as you present them then. And we will get a 6 better idea of how does that fit and all 7 MR. BRISTOL: Yeah. And I'll just add 8 that the pool temperature does a specified range in 9 tech specs. So the analyses are initiated from, 10 within that range.

11 MEMBER DIMITRIJEVIC: Um-hum.

12 MR. BRISTOL: So, we don't necessarily 13 initiate a transient from something outside of that 14 range. In the condition of the loss of offsite power 15 to the, you know, to the entire plant, all the modules 16 immediately go to DHR cooling conditions.

17 MEMBER DIMITRIJEVIC: Okay.

18 MR. BRISTOL: So they don't -- they 19 wouldn't come in at stages kind of like you were 20 talking about.

21 MEMBER DIMITRIJEVIC: Right. Well, I was 22 trying to think, --

23 MR. BRISTOL: Sure.

24 MEMBER DIMITRIJEVIC: Because when we were 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 73 have some discussion about operator actions through 1 that. You know, because they cannot, they have enough 2 time to go from one unit to units.

3 So, I will think of a type of accident I 4 was thinking. But, even in these cases, they all come 5 to DHRS when -- I mean, will temperatures stay in the 6-- okay. Well, we had to go to ECCS, right?

7 MEMBER BROWN: No.

8 MR. BRISTOL: Yes.

9 MEMBER DIMITRIJEVIC: You are having 10 something goes wrong with the DHRS, I'm just trying to 11 think about accidents which can cause that.

12 MR. BRISTOL: So the range of DHRS 13 performance includes analysis of a range that's 14 outside of the tech specs. The transients aren't 15 necessarily initiated from outside of that pool 16 temperature range.

17 But, there is consideration given to that.

18 And I think we'll get into that maybe a little bit 19 later, --20 MEMBER DIMITRIJEVIC: All right. All 21 right. Well, let's do that.

22 MR. BRISTOL: As we get into the details 23 of the methodology.

24 MEMBER BROWN: During normal operation 12 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 74 modules, everything is working just fine. We're 1 inside a vacuum inside the containments.

2 Is it expected that there's -- the pool 3 temperature just stays constant? It doesn't heat up 4 a little bit just due to some type of heat effects 5 coming through the containment and out to the pool.

6 And then stabilizers because the pool stabilizes after 7 some point if you've got them all?

8 Is there a range of operation, 12 modules 9 where if you start cold, start them all up, and the 10 temperature would rise up just because of the reactor 11 operations themselves? Even though they're within a 12 vacuum?13 MR. BRISTOL: Yes. Yeah, there is some 14 heat loss, known heat loss from the module to the pool 15 that's considered.

16 I think the spent fuel pool is one of the 17 larger heat loads. I'm not extremely familiar with 18 that analysis.

19 MEMBER BROWN: Yeah. Put the spent fuel 20 pool aside. It's a -- I understand that cooling.

21 MR. BRISTOL: Sure. The pool has a 22 cooling system that takes into consideration the 23 normal heat loads and off-normal heat loads of DHR 24 sometimes.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 75 MEMBER BROWN: But there will be some heat 1 up even though you've got the reactor vessel and 2 everything within that vacuum area. There's going to 3 be some, has to be, heat conducted through there.

4 MR. BRISTOL: Yeah. The pool definitely 5 has a heat load.

6 MEMBER BROWN: Yeah. Okay. All right.

7 MR. BRISTOL: A normal heat load that's 8 considered part of the systems then.

9 MEMBER BROWN: So, but the rest of your --

10 I'm trying to springboard off of Vesna's comment. And 11 then you've also considered if you lost power, then 12 you -- everybody goes to DHRS.

13 Then you'd have to be able to handle that 14 in terms of the general -- and the pool has no cooling 15 now. It's got the total, the total mass of water.

16 It has to be able to accomplish decay heat 17 removal for all 12 modules. And not go outside of an 18 acceptable band.

19 MR. BRISTOL: That's correct. And that's 20 where we get pretty quickly into the short term 21 transient response, pool temperature of the pool.

22 The pool is a big enough heat sink. It 23 doesn't have a huge temperature transient where the 24 long term cooling analysis is primarily where we have 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 76 the consideration of the coping period, and what are 1 all the heat loads.

2 And ensuring the --

3 MEMBER BROWN: Yeah. I'm not worried 4 about an accident rate.

5 MR. BRISTOL: Sure.

6 MEMBER BROWN: I was interested in the 12 7 modules now are all in DHRS. Then you could have an 8 accident. And you have to consider that as well?

9 MR. BRISTOL: No. We would consider the 10 loss of power being the initiating event. And after 11 DHR actuation then we're in long term cooling 12 conditions.

13 So we wouldn't postulate a new initiating 14 event during that event progression.

15 MEMBER BROWN: Even long term?

16 CHAIR MARCH-LEUBA: He's already dumping 17 all of the heat from the core into the pool through 18 DHRS. What worse can you make this?

19 MEMBER BROWN: I don't know.

20 CHAIR MARCH-LEUBA: You're dumping 100 21 percent --

22 MEMBER DIMITRIJEVIC: This is what I was 23 trying to actually get to.

24 MEMBER BROWN: Yes. I thought that's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 77 where you were trying to get to.

1 MEMBER DIMITRIJEVIC: I was trying to go 2 to ECCS where something goes wrong when we -- actually 3 we have additional accidents.

4 But then I, I realized that that's 5 additional accident. And you would not look in that.

6 But, I mean, it could be like some safety valve refuse 7 to close or something, I mean, you know.

8 MEMBER BROWN: No idea. You're right.

9 MEMBER CORRADINI: I guess I'd ask a 10 different question instead of asking all these things.

11 What's the rate of rise if I had to assume the decay 12 heat of all 12 modules into the pool?

13 MS. McCLOSKEY: It --

14 MEMBER CORRADINI: I calculate it to be 15 less than a degree, substantially less than a degree 16 an hour. On the order of a degree an hour.

17 That's what I would ask.

18 MS. McCLOSKEY: I don't know the specific 19 rate of rise. But if you take realistic initial 20 conditions for the pool level and temperature and 21 decay heat loads for the 12 modules, then the --

22 assuming boil off of -- assuming the heat loads to the 23 reactor pool, there's more then 30-days worth of level 24 above the top of the Decay Heat Removal Systems.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 78 MEMBER CORRADINI: Okay. Fine. All 1 right. That's another way of doing it. Okay. Thank 2 you.3 MS. McCLOSKEY: Yeah.

4 MEMBER CORRADINI: I appreciate that.

5 MR. BRISTOL: It's very slow, yeah.

6 MS. McCLOSKEY: It's very slow.

7 MEMBER CORRADINI: I figure that.

8 MR. BRISTOL: Yeah.

9 MS. McCLOSKEY: Yeah.

10 CHAIR MARCH-LEUBA: Thirty days.

11 MEMBER CORRADINI: I mean, I didn't want 12 to interject -- oh, I'm sorry. I didn't want to 13 interject with their questions on the right.

14 But I have a different question. Are you 15 guys done?

16 You were at initiating events, you were 17 giving us a long list. In Table 15.01 and 15.02, you 18 identify a thing called an IE.

19 And I didn't understand why you need an IE 20 versus an AOO and a DBE, because in 15.02 your table 21 for acceptance criteria is essentially, the IE's 22 acceptance criteria is the same as the DBE.

23 So why did you make the distinction to 24 begin with? I'm clueless.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 79 MS. McCLOSKEY: Part of the distinction 1 comes in the radiological dose acceptance criteria.

2 MEMBER CORRADINI: Not in the thermal 3 hydraulic. So, --

4 MS. McCLOSKEY: Not in the thermal 5 hydraulic dose acceptance criteria.

6 MEMBER CORRADINI: So, for the IE, the 7 acceptance criteria is more like an AOO?

8 MS. McCLOSKEY: For -- in terms of the 9 radiological dose, it's -- the radiologic -- the 10 acceptance criteria are aligned with a small fraction 11 of the acceptable dose for accidents.

12 MEMBER CORRADINI: But not the full dose?

13 MS. McCLOSKEY: But not the full dose.

14 MEMBER CORRADINI: And it's not the AOO 15 which is essentially mainly just preserving the 16 SAFTLs.17 MS. McCLOSKEY: Right. So when we get --

18 MEMBER CORRADINI: Where would I find 19 that? I guess I was looking, and I missed that.

20 MS. McCLOSKEY: You -- in the Table of the 21 dose analysis results for the different acceptance 22 criteria.23 MEMBER CORRADINI: Oh.

24 MS. McCLOSKEY: For the steam generator 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 80 tube failure. And for small lines outside of 1 containment, you'll see the acceptance criter -- yeah.

2 Yes, that sample.

3 MEMBER BROWN: The acceptance criteria do 4 change as the --

5 MS. McCLOSKEY: The acceptance criteria.

6 MEMBER CORRADINI: That's the one where 7 it's 6.3 and not 5 or 25?

8 MS. McCLOSKEY: Correct.

9 MEMBER CORRADINI: Oh. Because the only 10 two that you identified in 15.01 was the small line, 11 and another one, which I can't remember.

12 MS. McCLOSKEY: The steam generator tube 13 failure.14 MEMBER CORRADINI: Thank you. Thank you 15 very much. Okay. Thank you. Appreciate it.

16 MS. McCLOSKEY: So, and --

17 MEMBER CORRADINI: I'm done.

18 MS. McCLOSKEY:

Okay. In terms of 19 identifying the scope of initiating events for Chapter 20 15, we started with the PRA initiating events, because 21 this was examined, then summarize the scope of events 22 that could cause a reactor trip or transient.

23 But from there we examined the systems 24 that were identified in the PRA as relevant to causing 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 81 a reactor trip or transient in -- for additional 1 detail in order to identify the specific impacts on 2 the module, in order to categorize and classify the 3 design basis events for Chapter 15.

4 CHAIR MARCH-LEUBA: Sorry to put you on 5 the spot, but can you give me an example that you 6 identify through PRA that was not on the SRP of 7 Chapter 15?

8 MS. McCLOSKEY: An example might be, would 9 be the containment flooding and loss of containment 10 vacuum events. Because those are --

11 CHAIR MARCH-LEUBA: Okay. That's good 12 enough.13 MS. McCLOSKEY: One potential cause of 14 loss of containment vacuum is --

15 CHAIR MARCH-LEUBA: Well, that will not be 16 on SRP 15. But it would be in the PRA.

17 MS. McCLOSKEY: Right. When we went 18 through the design basis events that we identified and 19 categorized them, our categories are consistent with 20 those for operating light water reactors.

21 Except that the category of decrease in 22 RCS flow events is not applicable due to the natural 23 circulation design of the plant.

24 We also have NuScale specific phenomena 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 82 and -- or event progressions. PWR stability we've 1 discussed already this morning.

2 And then return to power analysis are part 3 of the Chapter 15 analysis. And we'll discuss that 4 later this afternoon.

5 MEMBER CORRADINI: Where is a good time 6 for me to ask about the evolution of NRELAP from 1.3 7 to 1.4? Since that appears in a lot of the open items 8 as an addendum.

9 You decide where in the discussion today 10 you want to explain that. And then the second one 11 that I want to get explained is the scale distortion 12 in NIST 1 and NIST 2 experiments.

13 MS. McCLOSKEY: Okay.

14 MEMBER CORRADINI: So, you don't have to 15 answer it now. You just decide where you want to 16 inject it. And then I can ask my questions. Okay?

17 MS. McCLOSKEY: Okay. I think -- all 18 right. Well, probably the closed session is 19 appropriate for any discussion of the details there.

20 MEMBER CORRADINI: Okay.

21 MS. McCLOSKEY: But, most of the 22 discussion of scale distortions between the NIST 1 23 facility and the plant, we would defer detailed 24 discussion of that to the topical report --

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 83 MEMBER CORRADINI: Which is yet to be --

1 MS. McCLOSKEY: Methodologies. Right.

2 With the LOCA topical report methodology when we 3 present that to the ACRS committee.

4 MEMBER CORRADINI: Okay. But that's 5 nowhere in, nowhere in the short term future?

6 MS. McCLOSKEY: I believe it's this fall 7 in the October time frame was the schedule for 8 meetings.9 MEMBER CORRADINI: At the earliest.

10 CHAIR MARCH-LEUBA: Did you say LOCA or 11 non-LOCA?12 MEMBER CORRADINI: Both are still out 13 there as open.

14 CHAIR MARCH-LEUBA: I know. But which --

15 which were you talking about? You were talking about 16 LOCA?17 MEMBER CORRADINI: Both.

18 MS. McCLOSKEY: LOCA.

19 MEMBER CORRADINI: Okay. And then the 20 RELAP 1.4 trans --

the transition from 1.3 to 1.4, 21 because staff has yet to finish its review of that.

22 Or I'm not sure if you've yet to even 23 issue the differences.

24 MS. McCLOSKEY: Yes. The differences are 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 84 issued. And the staff has also audited that 1 information.

2 So, I think we can say a little bit --

3 MEMBER CORRADINI: In closed session.

4 MS. McCLOSKEY: In the closed session 5 about the details of the code changes.

6 MEMBER CORRADINI: Okay. All right.

7 That's fine. That's good. We'll just wait until 8 closed session. Thank you very much.

9 MS. McCLOSKEY: And the effects. The 10 design basis events, this has already been mentioned 11 here. We are classified as anticipated operational 12 occurrences, infrequent events or accidents.

13 Events that could potentially occur one or 14 more times during the lifetime of the plant, are 15 classified as anti -- as AOOs.

16 Events that are not expected to occur are 17 classified as infrequent events or postulated 18 accidents. Or in some cases they were conservatively 19 classified as AOOs.

20 And one example of that is the inadvertent 21 opening of an ECCS valve. We don't expect that event 22 to occur during the lifetime of the plant.

23 But it was conservatively classified as an 24 AOO. And we demonstrate that those acceptance 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 85 criteria are met. Because that bounds a transition of 1 other events to ECCS cooling if a loss of power were 2 to be assumed.

3 And in some cases we also simplified the 4 event classification by applying a deterministic 5 criteria where the event was similar to other PWRs.

6 Particularly where event consequences are small and 7 calculating a NuScale specific event frequency is not 8 warranted.

9 So again, failures such as in the 10 containment evacuation system are classified as an AOO 11 event.12 MEMBER CORRADINI: So, there was an open 13 item, or an RAI, it maybe an open item. I don't 14 remember if I've got it down right, in terms of how 15 you classified return to power.

16 So, how is that being classified?

17 MS. McCLOSKEY: That is a -- it's not an 18 initiating event. It's an event progression.

19 MEMBER CORRADINI: Right.

20 MS. McCLOSKEY: And so it's not -- the 21 event classification applies to the initiating events.

22 But we demonstrate that the AOO acceptance criteria 23 are met.24 MEMBER CORRADINI: Ah. Okay. So, the way 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 86 you look at it is if it were an AOO.

1 MS. McCLOSKEY: Well, that's what defines 2 the acceptance criteria. Yes.

3 MEMBER CORRADINI: Okay. Fine. Thank 4 you.5 CHAIR MARCH-LEUBA: Because the initiating 6 event is loss of offsite power for more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

7 And no non-safety grade power back up coming up.

8 But yet if you -- it's perfectly 9 acceptable to make it an AOO.

10 MS. McCLOSKEY: Right.

11 MEMBER CORRADINI: I'm going to ask the 12 same question of the staff. So I'm just trying to ask 13 it here and get there and see if there's consistency.

14 MS. McCLOSKEY: Um-hum.

15 MEMBER CORRADINI: Because it was left 16 out. Okay, an AOO. Thank you very much.

17 MS. McCLOSKEY: So next slide. This slide 18 and the next several slides summarize the design basis 19 events and their respective categories.

20 So we have the event, the event 21 classification, the evaluation model used to do the 22 system thermal hydraulic analysis if applicable. And 23 the end reliant code used there.

24 Whether the event is analyzed for 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 87 subchannel analysis with the VIPRE-01 code. And then 1 whether the event is part of the Chapter 15 2 radiological dose analysis.

3 The NuScale specific events are 4 highlighted. And so here loss of containment vacuum 5 or containment flooding is a unique event.

6 The loss of containment vacuum could be 7 postulated due to a malfunction in the containment 8 evacuation system. Containment flooding is postulated 9 due to a break in piping that carries reactor 10 component cooling water to the control rod drive 11 mechanisms on top of the reactor head.

12 So although these events, these postulated 13 events don't directly interface with the primary or 14 the secondary side of the module, they would -- they 15 could result in a slow increase in heat transfer from 16 the reactor vessel compared to the evacuated -- the 17 vacuum conditions normally in containment.

18 And so it's included here as an increase 19 in the removal event.

20 CHAIR MARCH-LEUBA: And anywhere you say 21 in RELAP 5 you mean you plan to do it with the newest 22 version of the model, correct?

23 We have results for 1.3 and you plan to do 24 it for 1.4?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 88 MS. McCLOSKEY: Yes. We're in the 1 progress of -- we're in the process of revising those 2 analyses to 1.4.

3 CHAIR MARCH-LEUBA: And remind me again, 4 when you use VIPRE in a transient, you use VIPRE for 5 every entire step? I don't remember the -- I remember 6 the methodology for steady state.

7 But for transient, how do you apply VIPRE 8 during the transient?

9 MS. McCLOSKEY: The boundary conditions 10 from the NRELAP 5 results are provided for power, fl 11-- total RCS flow, pressure, and core inlet pressure.

12 CHAIR MARCH-LEUBA: At every time slice?

13 Ms. McCLOSKEY: Well, I think --

14 MR. BRISTOL: No. So there's an edit 15 frequency that's generated from RELAP and transmitted 16 to, you know, around a second or half a second.

17 CHAIR MARCH-LEUBA: Okay. But then even 18 time slice.

19 MR. BRISTOL: Yeah. That's right, yeah.

20 Yeah.21 CHAIR MARCH-LEUBA: And how many roles do 22 you have play with VIPRE? How many roles of the, 23 subchannels does VIPRE simulate? You don't remember?

24 MR. BRISTOL: I don't.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 89 CHAIR MARCH-LEUBA: Okay. It's been a 1 year since we reviewed it. But, just I was asking.

2 MR. BRISTOL: That's fair. We can follow 3 up with that if that's of interest.

4 CHAIR MARCH-LEUBA: It would be nice to 5 know. I know we know, but I don't remember.

6 MEMBER CORRADINI: But you have -- you do 7 track the hot channel versus the average channel.

8 That's what I would assume.

9 MR. BRISTOL: Um-hum.

10 MEMBER CORRADINI: At the time when we did 11 this, you had a nodalization approach to as where you 12 determined the hot channel. And then you essentially 13 had less and less subchannel nodalization --

14 MR. BRISTOL: Um-hum.

15 MEMBER CORRADINI: as you went. It went 16 away from the grouping of hot channels. So I assume 17 that's what was done here.

18 MR. BRISTOL: Fifty-two rods. Is the 19 answer.20 MEMBER CORRADINI: Okay. Thank you.

21 MS. McCLOSKEY: All right.

22 MEMBER BROWN: Before you leave that, the 23 last item, go back.

24 MS. McCLOSKEY: Um-hum.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 90 MEMBER BROWN: How much of an effect 1 overall is there if you just lose the vacuum and it's 2 just air? Can -- does that significantly heat up the 3 pool?4 MS. McCLOSKEY: No. It's a --

5 MEMBER BROWN: So it's -- you could 6 operate that way? Or do you require a shut down if 7 that occurs?

8 MS. McCLOSKEY: We would be outside the --

9 MEMBER BROWN: But just air. It's air, 10 not water. It's not -- it hasn't been flooded.

11 MS. McCLOSKEY: We would be outside the 12 limits established for monitoring containment leakage.

13 MEMBER BROWN: Okay.

So it would be a 14 containment leakage issue then.

15 MS. McCLOSKEY: Um-hum.

16 MEMBER CORRADINI: They'd have to shut 17 down.18 MEMBER BROWN: That's what I guess I would 19 translate. Okay. Thank you.

20 MS. McCLOSKEY: In Section 15.2 are the, 21 you know, it results in a decrease in heat removal 22 from the secondary side.

23 And here the NuScale specific event is 24 inadvertent operation of the Decay Heat Removal 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 91 System. Because the Decay Heat Removal System is 1 sized for decay heat removal, so inadvertent operation 2 of -- actually causes a decrease in heat removal.

3 There are several different variations of 4 this event that we analyze. That maybe a single 5 valve, actuation valve opening.

6 It maybe an inadvertent signal that 7 actuates the DHRS train valves and closes the 8 secondary isolation valves on one train or on both 9 trains.10 And we have some example results on the 11 transient for the single valve opening later this 12 afternoon.

13 In terms of the reactivity and power 14 distribution anomalies, these events are similar to 15 the scope for light water reactors. The flow related 16 events are not applicable to the design.

17 And for the 15.4.6, the inadvertent 18 decrease in warm concentration, it's postulated due to 19 a CVCS, chemical volume and control system malfunction 20 that causes a boron dilution transient to occur.

21 That's analyzed as part of the non-LOCA evaluation 22 model.23 And then in -- we analyzed the control rod 24 ejection accidents. There's a separate topical report 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 92 for the wad ejection analysis where the power response 1 is calculated using the SIMULATE-3K code.

2 And the system response is analyzed with 3 NRELAP-5. And then VIPRE is used to assess crit --

4 margin to critical heat flux ratio.

5 MEMBER CORRADINI: And I think we're going 6 to see that topical in September.

7 MS. McCLOSKEY: I don't know.

8 MEMBER CORRADINI: Well, that's all right.

9 MS. McCLOSKEY: I mean, later -- yeah, 10 we'll see the topical later in the --

11 MEMBER CORRADINI: Later in the fall time 12 frame.13 MS. McCLOSKEY: Later in the year. Yep.

14 MEMBER CORRADINI: All right. Thank you.

15 MEMBER BLEY: I know you answered Mike on 16 this earlier, but I kind of didn't follow it then.

17 Most of these are AOOs. But, you have an 18 IE in there. And I forget why you said that was.

19 MS. McCLOSKEY: And I forgot about that 20 one when we were talking about IEs.

21 MEMBER BLEY: That's okay.

22 MS. McCLOSKEY: That's the inadvertent 23 loading of a fuel assembly in it.

24 MEMBER BLEY: So that just means that's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 93 when you picked up the most PRA? Or why is it falling 1 under?2 MS. McCLOSKEY: That is one where the 3 radiological acceptance criteria are a fraction of 4 those acceptable for the accident dose.

5 MEMBER BLEY: Okay.

6 MS. McCLOSKEY: It was that. It wasn't 7 the steam generator tube failure. I was mistaken 8 earlier.9 MEMBER CORRADINI: That's okay. I just 10 wanted to know what it was. And you answered it.

11 That's fine.

12 MEMBER DIMITRIJEVIC: Well, you have, I 13 mean usually we have a thorough, infrequently it's an 14 accident. And I thought that your postulate an 15 accident is something where we normally have an 16 accident. And the IE will be what you call infrequent 17 event.18 But you actually classify everything with 19 AOO, right?

20 MEMBER CORRADINI: No.

21 MS. McCLOSKEY: No.

22 MEMBER DIMITRIJEVIC: No, no. There is 23 the one postulated accident where there is the one IE.

24 So, I mean, is there some reason why you 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 94 decided to just classify everything as AOO and then 1 have a couple of exceptions which don't correspond to 2 this other usual division?

3 MEMBER CORRADINI: We haven't gotten to 4 15.6 yet. There's a lot of postulated events in 15.6.

5 MS. McCLOSKEY: In most cases the 6 initiating events are similar to those for operating 7 PWRs.8 MEMBER DIMITRIJEVIC: Right.

9 MS. McCLOSKEY: And so we classified them 10 consistently.

11 MEMBER DIMITRIJEVIC: But no. For the 12 loss of offsite power is infrequent event. Which you 13 call AOO here. I mean, and well also --

14 MS. McCLOSKEY: Loss of offsite power is 15 typically analyzed as an AOO.

16 MEMBER DIMITRIJEVIC: Oh, really?

17 MS. McCLOSKEY: Yes.

18 MEMBER DIMITRIJEVIC: That's unusual. I 19 mean, not from my time. But anyway -- well, maybe my 20 time is, my time isn't right.

21 Well, the thing is so what is then like 22 infrequent event, like steam generator tube rupture.

23 What -- how would you classify that?

24 MS. McCLOSKEY: I was mistaken earlier as 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 95 we -- a steam generator tube rupture is actually 1 classified as a postulated accident. And that's on 2 the 15.6 slide.

3 MEMBER DIMITRIJEVIC: And most LOCAs you 4 classify right, as a postulated accident, right?

5 MS. McCLOSKEY: Yes. Yes.

6 MEMBER CORRADINI: They have a long list.

7 We're only half way through their list.

8 MEMBER DIMITRIJEVIC: Okay. I'm going to 9 check with the -- with the one with the specifications 10 in the PLA specimen. I'm going to see.

11 I mean, for me this is like almost 12 everything you've done is AOO. Which is like really 13 spec.14 MS. McCLOSKEY: And this is in the design 15 basis event space. In terms of events that are unique 16 to NuScale that we conservatively classified as an 17 AOO, in some cases because we have sufficient margins, 18 it wasn't valuable to do a specific analysis of the 19 event frequency in order to justify classifying it as 20 something other than an AOO.

21 And so we treated it as an AOO.

22 MEMBER DIMITRIJEVIC: All right. Because 23 obviously some of those are not going to occur during 24 the, you know, hopefully during the plant life, so.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 96 MS. McCLOSKEY: Right.

1 MEMBER DIMITRIJEVIC: All right. Okay.

2 I mean, and you think that this is conservative from 3 your perspective. So, you know, what you need to so 4 express this, that's all right.

5 MS. McCLOSKEY: We go to 15.5 in terms of 6 events that increase reactor coolant system inventory, 7 for the NuScale design as a chemical volume control 8 system is the only system with capability to increase 9 RCS inventory during normal operation.

10 Then in --

11 MEMBER SKILLMAN: Well, what about control 12 rod drive cooling?

13 MS. McCLOSKEY: The control rod drive 14 cooling doesn't interface with the primary system.

15 And so it's -- that's a failure in the lines carrying 16 cooling to the control rod drives, is treated in the 17 containment flooding analysis.

18 MEMBER SKILLMAN: Okay.

19 MS. McCLOSKEY: In 15.1.

20 MEMBER SKILLMAN: Okay. Thank you.

21 MS. McCLOSKEY: In the -- in 15.6 then, we 22 have the events that decrease reactor coolant system 23 inventory.

24 The inadvertent operation of an emergency 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 97 core cooling system valve or also -- we also call that 1 inadvertent opening of a reactor safety valve, is 2 addressed here.

3 And that's analyzed with the valve opening 4 event methodology that's an extension of the LOCA 5 analysis methodology. But we analyze it to 6 demonstrate that AOO acceptance criteria are met.

7 CHAIR MARCH-LEUBA: Is that going to be on 8 the same topical report as LOCA?

9 MS. McCLOSKEY: Yes. The methodology --

10 CHAIR MARCH-LEUBA: So there's like an 11 appendix?12 MS. McCLOSKEY: Is now described in 13 appendix B of the LOCA topical report.

14 CHAIR MARCH-LEUBA: And has it always been 15 an AOO? Or is this a recent modification?

16 I'm asking in conjunction with an IAB, you 17 know, an inadvertent actuation block valve.

18 MS. McCLOSKEY: Um-hum.

19 CHAIR MARCH-LEUBA: If you consider this 20 an AOO and you survive it, why do we need an IAB?

21 MS. McCLOSKEY: The -- since we -- since 22 the NuScale design doesn't have a safety-related power 23 supply, then in design basis event space, any event 24 where you assume loss of power --

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 98 CHAIR MARCH-LEUBA: Oh.

1 MS. McCLOSKEY: To occur, could be 2 postulated to transition to ECCS cooling.

3 CHAIR MARCH-LEUBA: But this one -- so 4 this event, 15.6.6 is loss of AC power, which trips --

5 well, I mean you trip the solenoid on the ECCS valve.

6 But IAB still holds it closed?

7 MS. McCLOSKEY: No. 15.6.6 postulates in 8 an inadvertent opening of one ECCS valve.

9 CHAIR MARCH-LEUBA: And release of 10 pressure.11 MS. McCLOSKEY: While, the RCS is 12 operating at normal operating pressure and 100 -- and 13 2 percent power.

14 CHAIR MARCH-LEUBA: And using AOO 15 acceptance criteria.

16 MS. McCLOSKEY: Yes.

17 CHAIR MARCH-LEUBA: So then the question 18 is, why bother with the IAB?

19 MS. McCLOSKEY: So --

20 MEMBER CORRADINI: I think the answer 21 yesterday was they don't want to have too many invalid 22 actuations. They want to have valid actuations.

23 So that was their protection from an 24 investment standpoint.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 99 CHAIR MARCH-LEUBA: I thought the answer 1 is they were not sure. They were not -- that they 2 could survive this.

3 MEMBER CORRADINI: Oh. We can -- I'm not 4 sure, I can't remember who from the audience came up 5 and helped us. But that's what I remembered.

6 MEMBER BLEY: It was Storm. And -- oh, 7 you'll cover it. Go ahead.

8 CHAIR MARCH-LEUBA: Say your name.

9 MR. RAD: So, some of this information is 10 in --11 MEMBER BLEY: Your name?

12 MR. RAD: I'm sorry, this is Zachary Rad, 13 Director of Reg Affairs, NuScale Power. Some of that 14 information in detail would be in the proprietary 15 session.16 But, the objective here, so analyzing the 17 inadvertent opening as an initiating event is 18 basically just following the Chapter 15 protocol.

19 What we don't want is to have an 20 inadvertent opening of one, and another one opens 21 because of the basic design. I mean, so that's why 22 the IAB is in there. Multiple openings would be 23 negative.24 MEMBER CORRADINI: Thank you.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 100 MS. McCLOSKEY: The other event I'll 1 highlight here is the small line break outside of 2 containment. That event is traditionally analyzed in 3 PWRs for radiological dose analysis.

4 And we also analyze it for dose analyzes 5 here. The small line break event in the NuScale 6 design is mitigated by closing the containment 7 isolation valves typically on a low pressurizer level 8 signal.9 And then you have sufficient inventory 10 remaining in the reactor coolant system to support 11 cooling through the Decay Heat Removal System. And so 12 that's why you'll see that's part of the non-LOCA 13 event analysis.

14 MEMBER CORRADINI: A long list.

15 MS. McCLOSKEY: In terms of the thermal 16 hydraulic and fuel acceptance criteria, this table 17 summarizes acceptance criteria for minimum critical 18 heat flux ratio, the primary and secondary site 19 pressures, containment pressure, and event 20 progression.

21 This is generally consistent with the 22 standard review plan guidance, except that the NuScale 23 analysis methodologies are developed to demonstrate 24 that fuel cladding integrity is maintained, and MCHFR 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 101 remains above the limit for AOOs, infrequent events, 1 or postulated accident conditions.

2 The secondary side system pressure, design 3 pressure is equal to the primary system design 4 pressure at 2100 psi. And so you'll see in our 5 analysis results we have, we retain significant margin 6 to the secondary pressure limits.

7 The containment design pressure is 1050 8 psi. And we have those results in FSAR 621 to discuss 9 later this afternoon.

10 So, given all of these different 11 acceptance criteria and different event types, the 12 next two slides summarize the NuScale topical and 13 technical reports, describing the analysis 14 methodologies, to just lay out what these connections 15 are.16 For a typical non-LOCA event, we built the 17 plant model in NRELAP-5. And that's used to calculate 18 the system from a hydraulic response to demonstrate 19 that the primary and secondary pressure criteria are 20 met. And that a safe stabilized condition is 21 achieved.22 And that's in the non-LOCA topical report.

23 The boundary conditions from that system from a 24 hydraulic analysis are then provided to for the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 102 subchannel analysis with VIPRE to demonstrate the 1 field cladding integrity are met.

2 And boundary conditions are from the --

3 are provided for the radiological analysis. And the 4 accident source term analysis topical report describes 5 the methodology to establish the source terms for the 6 radiological consequences.

7 MEMBER BLEY: Let me -- and Mike, I know 8 we have the topical on source terms later this year.

9 I think I know that.

10 MEMBER CORRADINI: We -- it has been 11 delivered to staff and they are starting to review it.

12 MEMBER BLEY: Okay. You don't know when 13 we're going to --

14 MEMBER CORRADINI: I'm not sure that we 15 have scheduled it.

16 MEMBER BLEY: Okay. What about the other 17 two topicals there? Have we --

18 MEMBER CORRADINI: We've already looked at 19 the subchannel topical report on how they've analyzed 20 it. We have not -- we -- it's somewhere in the fall 21 that we'll see the non-LOCA and the LOCA.

22 MEMBER BLEY: Okay.

23 MS. McCLOSKEY: In terms of LOCA and valve 24 opening events, we use NRELAP-5 to protect -- to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 103 predict the system and the hot channel response.

1 And in the NuScale methodologies the 2 acceptance criteria for these events are to 3 demonstrate margin too minimum critical heat flux 4 ratio. And that water level is maintained above the 5 top of the fuel.

6 The long term cooling analysis with ECCS 7 is analyzed with RELAP to demonstrate that water level 8 remains above the top of the core. And the core inlet 9 temperature remains sufficiently high that boron 10 precipitation is precluded.

11 And then the containment response is an 12 extension of the LOCA EM and also the non-LOCA EM for 13 the secondary side breaks to evaluate peak pressure 14 and temperature levels.

15 MEMBER CORRADINI:

So, let me get a 16 clarification. Because I know the topicals are being 17 submitted to us for review -- I'm sorry, submitted to 18 the staff, excuse me, for review.

19 The technical reports are essentially 20 addendums to Chapter 15 analysis?

21 MS. McCLOSKEY: Chapter 15 and Chapter 6, 22 yes.23 MEMBER CORRADINI: Okay. Which are not 24 being asked for the staff to look at them, only from 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 104 the standpoint of audit. And they want to do 1 confirmatory calculations.

2 But they are not being submitted to the 3 staff for separate review.

4 MS. McCLOSKEY: They are part of the DCA.

5 MEMBER CORRADINI: Okay. That's what I 6 thought. I just wanted to make sure.

7 MS. McCLOSKEY: So this is part of the 8 Chapter 6 and Chapter 15 analysis.

9 MS. KARAS: Yes, this is Becky Karas from 10 Reactor Systems. We do review the technical reports 11 in concert with the DCA review --

12 MEMBER CORRADINI: But we would find your 13 evaluations buried inside the SEs?

14 MS. KARAS: That's correct.

15 MEMBER CORRADINI: Okay. Fine. Thank 16 you.17 MEMBER DIMITRIJEVIC: For the Chapters.

18 MEMBER CORRADINI: For the Chapters, yes.

19 MR. SCHMIDT: This is Jeff Schmidt. It's 20 incorporated by reference to the DCA.

21 MEMBER CORRADINI: I'm telling this to the 22-- I'm saying it out loud so the members, if they get 23 interested, because we felt that we didn't have enough 24 paper to read so far.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 105 So, just in case. The 700 pages was a 1 quick read.

2 MEMBER BLEY: Half of it's pictures.

3 MEMBER CORRADINI: That made it quicker.

4 MS. McCLOSKEY: The module protection 5 system actuations in the NuScale design were developed 6 and designed with a focus on this scope of design 7 basis events and the event response and the actuations 8 that we need to support the passive full response to 9 design basis events without crediting operator 10 actions.11 And so we consider the design basis 12 events, the functions can be broadly classified into 13 four areas. The reactivity control either through 14 reactor trip or through isolation of the source of 15 dilute water that could be causing an inadvertent 16 dilution of event.

17 RCS and secondary site inventory control.

18 The containment isolation assures that sufficient 19 inventory is maintained to support ECCS cooling in the 20 event of a postulated pipe break or valve opening.

21 It also mitigates the loss of inventory 22 outside of the module, limiting dose consequences.

23 And the secondary isolation limits dose consequences 24 for events such as steam generator tube failure.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 106 And also assures that appropriate 1 inventory is maintained in at least one train of the 2 Decay Heath Removal System for DHRS cooling.

3 If normal secondary side cooling 4 unavailable, we've talked about the DHRS. And if 5 necessary, the emergency core cooling system 6 actuations.

7 And then finally primary side subcooling 8 and stability are protected by reactor trip.

9 CHAIR MARCH-LEUBA: So would this be a 10 good time to stop for lunch?

11 MS. McCLOSKEY: I think one more slide too 12 just --13 MEMBER CORRADINI: A good transition 14 point?15 MS. McCLOSKEY: It would be a good 16 transition point.

17 MEMBER CORRADINI: Okay. Thank you.

18 MS. McCLOSKEY: Because when we take those 19 overall functions of the module protection system and 20 look at the design basis event mitigation for the 21 different types of events that we've gone through, 22 that's what's summarized on this slide.

23 MEMBER CORRADINI: Okay.

24 MS. McCLOSKEY: That the increase in heat 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 107 removal, transients are most often cause by a 1 postulated secondary side malfunction. So secondary 2 isolation is important there.

3 Decrease in heat removal transients 4 generate Decay Heat Removal System actuations.

5 Reactivity in power transients rely on reactor trip, 6 and demineralized water isolation.

7 Increase in RCS inventory events are 8 mitigated with isolation from the increase in 9 inventory source. Decrease in RCS inventory events 10 rely on containment isolation to control the inventory 11 available for ECCS cooling, and to mitigate dose 12 consequences and reactor trip instability.

13 MEMBER DIMITRIJEVIC: Shouldn't you have 14 like a measure control function also complication.

15 Like the, you know --

16 MS. McCLOSKEY: The pressure in the 17 reactor coolant system is limited by the reactor 18 safety valves.

19 MEMBER DIMITRIJEVIC: Right.

20 MS. McCLOSKEY: And so those are passive, 21 passively actuated valves. They aren't controlled.

22 So it's not -- that's not a function of the module 23 protection system.

24 The module protection system provides 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 108 actuations --

1 MEMBER DIMITRIJEVIC: But module systems 2 have like inter-module protection function.

3 MEMBER CORRADINI: Is your green light on?

4 I'm not sure anyone can hear you.

5 MEMBER DIMITRIJEVIC: Oh, well. I will 6 just consider it as a multiple presentation fraction 7 where I was not pressure control part of the function 8 which we're looking at.

9 MS. McCLOSKEY: This was -- sorry, this 10 was focused on the module protection system.

11 MEMBER DIMITRIJEVIC: System, I see. All 12 right.13 MEMBER CORRADINI: So this is a good time 14 for us?15 MS. McCLOSKEY: Yes.

16 MEMBER CORRADINI: Okay. So, we're going 17 to try to catch up --

18 MR. BRISTOL: I have a quick follow up on 19 the --20 MEMBER CORRADINI: Okay. Go ahead Ben.

21 MR. BRISTOL: Common cause failure. For 22 the level sensors, that's actually addressed in DCA 23 Section 7.1.5.1.2. And in Table 7.1-13 kind of has 24 the functions and how diversity and common cause 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 109 failure is addressed for the very sensors.

1 CHAIR MARCH-LEUBA: Can you read us the 2 section again?

3 MR. BRISTOL: Yes. So the DCA Section 4 Number 7.1.5.1.2.

5 CHAIR MARCH-LEUBA: Level five, yes?

6 MR. BRISTOL: Yes. And the DCA Table is 7 7.1-13.8 CHAIR MARCH-LEUBA: Thank you. You know, 9 whenever you say that, we're going to look at it. And 10 then come back and say it doesn't say anything.

11 (Laughter) 12 MR. BRISTOL: Yeah.

13 CHAIR MARCH-LEUBA: I'm only kidding you.

14 MEMBER CORRADINI: That's not a given.

15 He's just being --

16 MR. BRISTOL: I'll be prepared for that 17 follow up. Thank you.

18 MEMBER CORRADINI: Okay. So why don't we 19 take a break until 1:15. So we'll have a very 20 efficient lunch.

21 (Whereupon, the above-entitled matter 22 went off the record at 12:33 p.m. and 23 resumed at 1:17 p.m.)

24 CHAIR MARCH-LEUBA: For your reference we 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 110 are starting on Slide 24, okay?

1 MS. McCLOSKEY: All right, so as we move 2 into a summary of the analytical assumptions that are 3 applied in the Chapter 15 analyses, this slide shows 4 a map of the analytical pressure and temperature, 5 operation limits, and module perfection system limits.

6 And Dr. Corradini, I think this morning 7 you had a question about the normal T hot operation 8 versus --9 MEMBER CORRADINI: It was somebody, I 10 don't remember. It doesn't matter.

11 MS. McCLOSKEY: Sorry, so there was a 12 question this morning and the normal T hot is shown 13 there in the green dot in the middle with the 14 operating range that's analyzed.

15 And then the T cold and T hot is about 590 16 degree compared to the hot leg temperature, module 17 protection system analytical limit of 610 degree to 18 protect the margin to subcooler.

19 CHAIR MARCH-LEUBA: My understanding is if 20 we make a mistake completing the flow, T hot will be 21 maintained at that point and T average will oscillate.

22 MS. McCLOSKEY: The plant control is based 23 on T ave and maintaining constant T ave.

24 CHAIR MARCH-LEUBA: What we were told is 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 111 if -- which we will -- you're assuming a flow, a flow 1 rate. And we will have the flow rate the plant wants 2 to have and if it's only 0.1 percent off there's no 3 difference.

4 But if it's a significant difference, we 5 will keep T hot where it is now or we will move T 6 cool. 7 MEMBER CORRADINI: I think they've got to 8 check on that.

9 MR. BRISTOL: So, for the consideration of 10 operating margin, yes, there is some thought that goes 11 into where the analytical limit, at which point a trip 12 would come in, how much margin needs to account for 13 censor uncertainty, how much additional margin needs 14 to count for normal transience.

15 And so, yes, most likely the 59595 16 condition would be maintained as comfortable operating 17 margin and then T ave would flow from there.

18 MS. McCLOSKEY: And we have the high and 19 low pressure operating limits shown on there, the plus 20 or minus 70 PSI from normal operating condition at 21 1850. 22 And then the margin to high pressure and 23 low low-pressure analytical limits are also shown --

24 (Simultaneous Speaking.)

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 112 CHAIR MARCH-LEUBA: And the red lines are 1 automatic scrams, correct? If a person goes below 2 1600, the protection system will scram?

3 MS. McCLOSKEY: Yes. I'll go on. In 4 terms of the analytical assumptions for Chapter 15 5 analysis, we'll talk about operator actions, single 6 failures, loss of power and then the scope of event 7 progression.

8 In the NuScale design for the Chapter 15 9 analyses no operator actions are required to achieve 10 the safety functions for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> after an initiating 11 event occurs.

12 We do consider operator errors in 13 identifying the scope of initiating events, such as 14 inadvertent signals that could occur.

15 But any operator actions that are allowed 16 by procedure will make the consequences of an event 17 less severe, and therefore are bounded by the Chapter 18 15 analyses.

19 The scope of multiple operator errors or 20 errors that result in a common-mode failure are beyond 21 design basis.

22 In the Chapter 15 analyses, we assume the 23 limiting single failure of a safety-related component, 24 and so we went through a systematic evaluation of our 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 113 systems and the safety-related components to identify 1 failures that could affect the transient progression.

2 And due to both the simplified design in 3 terms of reducing the number of safety-related 4 components and redundancy of the safety-related 5 components, that reduces the overall scope of failures 6 that need to be evaluated in the Chapter 15 events to 7 determine the worst single failure for a particular 8 analyses.

9 And this slide summarizes the results of 10 that evaluation for the safety-related systems, 11 relevant single failures that occur in those systems, 12 and then some discussion.

13 So, in terms of redundancy in components, 14 an example of that are the containment isolation 15 valves on the CVCS piping.

16 Since there are two isolation valves in 17 series, single failure of one isolation valve doesn't 18 change the event progression and so it's not 19 specifically part of a calculation analyzed because it 20 doesn't affect the transient results.

21 CHAIR MARCH-LEUBA: One thing that we've 22 discussed with respect to that in other meetings is 23 what I call analytical redundancy. So, if this 24 particular scram fails, indirectly we will catch it 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 114 with this other one in scram 2.

1 And there's a lot of flows in NuScale that 2 I don't think we're taking proper credit for. So, if 3 the pressure fails and doesn't scram you, you will get 4 a scram at high temperature.

5 MS. McCLOSKEY: The module protection 6 system functions are modeled in the Chapter 15 7 analyses.

8 And I'm not sure if you're getting at 9 considering common-cause failures of instrumentation, 10 and I think as Ben mentioned earlier this morning, 11 there's a summary of those results in Chapter 7.

12 CHAIR MARCH-LEUBA: Yes, and typically we 13 consider failure of one control rod to insert in all 14 Chapter analyses.

15 Is that in addition to this?

16 MS. McCLOSKEY: That's accounted for in 17 the scram worth.

18 CHAIR MARCH-LEUBA: The one rod out is not 19 a single failure, that's an assumption?

20 MS. McCLOSKEY: No.

21 CHAIR MARCH-LEUBA: On top of that you 22 have a single failure.

23 MS. McCLOSKEY: Yes, and on top of that we 24 consider power availability.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 115 CHAIR MARCH-LEUBA: Power is not safety-1 grade. But you have to consider DC power to fail and 2 is that because it was operating before so it should 3 stay there?

4 It would be a failure to make it fail?

5 MS. McCLOSKEY: We consider the 6 availability of DC power because it's not a 7 safety-related Class 1E power supply system.

8 CHAIR MARCH-LEUBA: But in all transients 9 you have the DC power on.

10 MS. McCLOSKEY: For many events that's 11 more limiting for the transient response because the 12 loss of DC power actuates the safety systems.

13 CHAIR MARCH-LEUBA: I didn't see that.

14 MS. McCLOSKEY: In terms of the single 15 failures that are considered in the analyses, in the 16 module protection system single failure of an 17 instrument channel is considered.

18 And that's relevant for asymmetric 19 reactivity events where a censor closer to the power 20 asymmetry could be assumed failed and that would delay 21 the response of the remaining instruments that are 22 operating.

23 In the containment isolation valves we 24 consider failure to close of a main steam isolation 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 116 valve or a feedwater isolation valve. In those cases, 1 we take credit for the non-safety-related back up 2 valves in both of those lines.

3 Similarly, there are check valves in the 4 feedwater that prevent backflow in the case of a 5 postulated large feedwater line breaking inside of 6 containment.

7 And in the case of failure to close those 8 check valves, the non-safety-related back up check 9 valve in the lines is credited.

10 CHAIR MARCH-LEUBA: So, if we state that 11 in plain English, you're taking credit for non-safety-12 grade back up equipment?

13 MS. McCLOSKEY: And that's consistent with 14 NUREG 0138 and the guidance in Reg Guide 1.206 that 15 non-safety-grade equipment can be credited as back up 16 in the case of a single failure to the safety-related 17 component.

18 CHAIR MARCH-LEUBA: As long as the single 19 failure is not the initiating event. So, let's talk 20 about the two check valves. You have an initiating 21 event, Check Valve 1 fails, you can take credit for 2.

22 Now, if Check Valve 1 fails as your 23 initiating event, well, you need to have another one.

24 MS. McCLOSKEY: Well, if Check Valve 1 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 117 fails as the initiating event, that would result in a 1 decrease in the feedwater flow, which is analyzed as 2 an initiating event and doesn't demand response of the 3 check valves.

4 The check valves are used in the case of 5 large feedwater line breaks inside containment where 6 you can get reverse flow from the intact steam 7 generator over to the break if the check valves were 8 not there.

9 CHAIR MARCH-LEUBA: I guess I will ask 10 tomorrow from the Staff about this single failure.

11 The first time I looked at it, it felt to me that 12 we're taking credit for non-safety-grade stuff.

13 MS. McCLOSKEY: And that's consistent with 14 the applicable regulatory guidance and the augmented 15 quality that's applied to these valves. The feedwater 16 reg valve and the backup means isolation valves are 17 seismic Class 1 valves.

18 They're part of the in-service testing 19 program and they're in tech specs with limiting 20 conditions for operability and surveillance 21 requirements.

22 CHAIR MARCH-LEUBA: So, other than not 23 having an N stamp in the outside casing, it's treated 24 as safety-grade?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 118 MS. McCLOSKEY: I think effectively.

1 CHAIR MARCH-LEUBA: The most important 2 thing is whether they're in tech specs in Appendix B.

3 So, whenever one of those equipments goes 4 out to service, if it's safety-grade, you have an LCO 5 and you have to start downgrading power and eventually 6 shutting down.

7 If it's not in tech specs, you won't.

8 MS. McCLOSKEY: The back up main steam 9 isolation valves and the feedwater valve are in tech 10 specs.11 CHAIR MARCH-LEUBA: With an LCO?

12 MS. McCLOSKEY: Mm-hmm. The backup check 13 valve is also seismic Class 1 and part of the in-14 service testing program.

15 CHAIR MARCH-LEUBA: Because check valves 16 in particular have a history of failing a lot and 17 that's why we have --

18 MS. McCLOSKEY: The Chapter 15 analyses, 19 they're only relevant for the postulated accident 20 large feedwater line break.

21 CHAIR MARCH-LEUBA: Okay, we will ask the 22 Staff about their opinion on this.

23 MS. McCLOSKEY: In the emergency core 24 cooling system, we consider failure of one of the ECCS 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 119 valves to open either event valve or a recirc valve.

1 We also consider a module protection 2 system failure to actuate a division of ECCS, in which 3 case one vent valve and one recirc valve would remain 4 closed. 5 The IAB failing to close upon demand is 6 not treated as one of the single failures in the 7 accident analyses. That would occur in the case of a 8 postulated loss of DC power that results in a demand 9 to the ECCS valves.

10 CHAIR MARCH-LEUBA: So, you just told us 11 this morning that you were going to analyze that.

12 MS. McCLOSKEY: We analyze the inadvertent 13 opening of an ECCS valve, yes.

14 CHAIR MARCH-LEUBA: By itself?

15 MS. McCLOSKEY: By itself.

16 CHAIR MARCH-LEUBA: So, you don't want to 17 analyze it in conjunction with another initiating 18 event?19 MS. McCLOSKEY: Correct.

20 CHAIR MARCH-LEUBA: Like loss of DC power?

21 MS. McCLOSKEY: Loss of DC power is part 22 of the loss of power assumptions that are treated.

23 So, loss of DC power is not a specific initiating 24 event. 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 120 But if we go to the next slide on loss of 1 power, we consider loss of AC power at the time of 2 event initiation or at the time of reactor trip. And 3 in the case of loss of AC power, we consider whether 4 the DC power system is available or unavailable.

5 So, postulating a loss of AC power at the 6 time of reactor trip with loss of DC power at the time 7 of reactor trip, if the IAB were not there, then that 8 could postulate a demand on the ECCS system in 9 conditions far outside normal operation.

10 And this is all in the context of the 11 deterministic design basis assumptions for Chapter 15.

12 CHAIR MARCH-LEUBA: But if I understand 13 the system, AC power feeds the batteries and then the 14 batteries feed the instrumentation and so on and on 15 and everything.

16 The AC doesn't bypass. So, if the battery 17 cable out fails, that would be a failure of DC power 18 even though you have AC power.

19 MS. McCLOSKEY: In which case, that would 20 actuate the reactor trip DHRS containment isolation.

21 CHAIR MARCH-LEUBA: I'm not saying it's a 22 bad thing, it's an event that should have been 23 analyzed.

24 MEMBER DIMITRIJEVIC: I thought I was so 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 121 loud. 1 MS. McCLOSKEY: And we consider that range 2 as part of the loss of AC power initiating event, but 3 since the safety systems are actuated, it doesn't 4 progress to more severe condition for the core.

5 CHAIR MARCH-LEUBA: Let me see if I 6 understand. One of the initiating events, 15.6.6, the 7 RRB opens by itself and truly opens.

8 And there are other scenarios that you can 9 imagine where the IAB would prevent that from opening.

10 That's what we have analyzed?

11 MS. McCLOSKEY: The event in 15.6.6 12 postulates some sort of a mechanical failure in the 13 valve. From the perspective of Chapter 15, worked on 14 get into the details of exactly what that postulated 15 failure is.

16 But in other scenarios we assume that the 17 valves operate as designed except in the case of the 18 single failures that we were talking about. Does that 19 answer -- I'm not sure if that gets to your question.

20 CHAIR MARCH-LEUBA: I was trying to figure 21 out the logic of assuming it fails on 15.6.6 and 22 assuming it doesn't fail on everything else.

23 MS. McCLOSKEY: We treat the initiating 24 events separately.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 122 MR. RAD: I can provide some insights 1 within the context of the regulatory framework. This 2 is Zachary Rad, Director of Reg Affairs, NuScale 3 Power. 4 Relative to the single failure criteria, 5 a component treated as passive is assumed to fail as 6 an initiating event but is not assumed as an 7 additional failure.

8 So, following that regulatory framework, 9 we've analyzed the inadvertent opening of the ECCS 10 valve. 11 Continuing on, because it's not considered 12 as an additional failure -- so under a single failure 13 criteria in active components you have to consider the 14 worst single failure of an active component in 15 addition to the initiating event.

16 Because this device is treated as passive 17 in our safety analysis, it is not considered to be an 18 additional failure relative to the initiating event.

19 So, if you have a LOCA you don't assume an 20 additional passive failure, an additional LOCA for 21 instance. In this case, it's a valve that we've 22 treated as passive relative to the single failure 23 criteria. We don't consider that as an additional 24 failure either.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 123 CHAIR MARCH-LEUBA: So, when do you 1 consider additional failures of check valves?

2 MR. RAD: We consider additional failures 3 on active components as we've treated them relative to 4 single failure criteria.

5 CHAIR MARCH-LEUBA: So, check valves is an 6 active component?

7 MR. RAD: Check valve is an active 8 component that is sometimes tre ated as a passive 9 component relative to the single failure criteria.

10 MEMBER CORRADINI: Does that make sense?

11 CHAIR MARCH-LEUBA: No.

12 MR. RAD: So, active in the fact that it 13 actually does move so technically it is active.

14 However, its treatment relative to the 15 single failure criteria is as if it were passive as it 16 relates to the information I just covered before, how 17 it's treated relative to subsequent failures.

18 CHAIR MARCH-LEUBA: IAB is also active?

19 MR. RAD: That's correct, it moves.

20 CHAIR MARCH-LEUBA: It moves.

21 MEMBER CORRADINI: But it would be part of 22 the initial failure under -- I'm looking for all of 23 their -- it's 15.6.6, inadvertent ECCS opening so they 24 assume a failure but then they're claiming that any 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 124 subsequent IAB failures cannot be assumed because 1 they're not an active component.

2 That's what I thought you just said.

3 MR. RAD: That's correct. So, to put it 4 in a different context, how do we assume that was an 5 active component and the initiating event was the 6 inadvertent opening of an ECCS valve for whatever 7 reason? 8 And we have to assume the worst-case 9 single active failure, that evaluation would include 10 the failure of the additional failure of that IAB and 11 the potential opening, additional opening, of a second 12 ECCS valve.

13 Does that make sense? Especially given 14 that our assumptions are loss of AC power and because 15 we don't have safety-related DC power, and correct me 16 if I'm wrong, in our analysis we assume that's lost as 17 well.18 CHAIR MARCH-LEUBA: It might not be lost.

19 MR. RAD: Right, may or may not be lost.

20 MS. McCLOSKEY: Yes.

21 CHAIR MARCH-LEUBA: Okay, I just wanted to 22 make sure it's on the record that it is an assumption 23 that is passive. And the Commission has not agreed on 24 that yet, correct?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 125 There is a request for --

1 (Simultaneous Speaking.)

2 MEMBER CORRADINI: It's still under 3 review. It's an open item also.

4 MEMBER BROWN: But there are a lot of 5 items which appear to be passive, which you might 6 think are active but are referred to as passive.

7 MEMBER CORRADINI: The logic, however 8 unusual, makes sense to me. I can take a passive 9 component and claim a failure but I can't then go on 10 and say other passive components can also be assumed 11 under single failure criteria.

12 That's what he said. I'm sure I said it 13 wrong. 14 (Simultaneous Speaking.)

15 MEMBER BROWN: It's just the rules of 16 doing this sort of thing.

17 MEMBER CORRADINI: Well, let me turn to 18 the Staff, I'll probably muddle it up.

19 MR. NOLAN: Just one point of 20 clarification, this is Ryan Nolan from the Staff.

21 It's agreed that the IAB is an active component, it's 22 whether it's subject to single failure or not.

23 So, I just want to make the clarification 24--25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 126 MEMBER CORRADINI: No, no, you said it 1 better than I did. I apologize.

2 MEMBER BLEY: When you say the loss of DC 3 power can either happen or not, I assume that means 4 you look at it and if that's the worst single failure 5 you can have you use it?

6 Or is there some other criteria?

7 MS. McCLOSKEY: It's in addition to the 8 worst single failure.

9 MEMBER BLEY: In addition to?

10 MS. McCLOSKEY: Yes.

11 MEMBER BLEY: And you still might consider 12 it failed. How do you decide which way you consider 13 it?14 MS. McCLOSKEY: Whichever is more 15 conservative with respect to minimizing margin to the 16 acceptance criteria.

17 MEMBER BLEY: So you go both ways?

18 MS. McCLOSKEY: Yes.

19 MEMBER BLEY: In all of Chapter 15?

20 MS. McCLOSKEY: Yes.

21 MEMBER BLEY: Okay, thank you.

22 MS. McCLOSKEY: So, the next couple of 23 slides go into that loss of power assumption and how 24 it's treated, and what effect it has on the NuScale 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 127 design event progression.

1 Because for non-LOCA events, the power 2 availability affects whether the ECCS valves actuate 3 and then at what time they are postulated to open.

4 For LOCA-type events, the power availability affects 5 the time they actuate and when they open.

6 So, next slide.

7 MEMBER CORRADINI: Can I say it a little 8 bit differently just so...So, the only thing in 9 contention in terms of the assumptions, Staff and you 10 are on the same page in terms of assumptions except 11 for the open item relative to the IAB?

12 In terms of the initiating assumptions you 13 just went through?

14 MS. McCLOSKEY: Yes.

15 MEMBER CORRADINI: Is that a correct 16 statement?

17 MS. McCLOSKEY: Yes, I believe so. We had 18 several RAIs related to the backup --

19 MEMBER CORRADINI: I figured that's why 20 you made it green.

21 MS. McCLOSKEY: -- back up valves but I 22 think that's closed.

23 MEMBER CORRADINI: I just wanted to make 24 sure we summarized it in an appropriate manner, that's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 128 all. Thank you very much.

1 MS. McCLOSKEY: In the case for a non-2 LOCA-type event that the AC power is available and DC 3 power is available, then very early on in the event 4 progression the module protection system will actuate 5 reactor trip and the decay heat removal system if 6 necessary, if normal secondary side cooling is 7 unavailable.

8 And then shortly thereafter, on the order 9 of half an hour to an hour timeframe, stable DHRS 10 cooling is established.

11 If the cooling through the decay heat 12 removal system is very effective and depending on what 13 the initial levels and temperatures in the reactor 14 coolant system are, riser uncovery may also occur in 15 that short timeframe.

16 If the power remains available and there's 17 no credit for any operator actions to restore 18 conditions, that cooling is maintained for the 72-hour 19 duration.

20 If AC power is unavailable, then the 21 beginning of the event progression is the same and the 22 difference comes at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> when the ECCS valves are 23 signaled by the module protection system to open. And 24 then the plant will transition to ECCS cooling.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 129 If both AC power and DC power are assumed 1 unavailable, then the ECCS valves are actuated at the 2 time that the DC power is assumed to be lost.

3 But the event progression is the same 4 because the ECCS valves are held closed by the IAB 5 until the DHRS cooling is sufficient to depressurize 6 the reactor coolant system below the release point, at 7 which point the valves open and it transitions to 8 ECCS-cooled.

9 CHAIR MARCH-LEUBA: And there is no issue 10 with timing? And the IAB set point is going to be 11 different on every valve so if an RV opens before an 12 RVV or an RVV opens before an RV it doesn't make any 13 difference?

14 Because when we lose AC power, we trip 15 everything on a 24-hour timeframe at the same time.

16 When you are now relying on the IAB spring to go 17 clean, each valve will trigger at a different time.

18 Is there any possibility of messing up?

19 Because I would prefer to open the RVVs first and then 20 the RRVs.

21 MS. McCLOSKEY: In the case of the non-22 LOCA event progression, by the time that the RCS is 23 depressurized sufficiently, you've been tripped, for 24 a couple of hours you're at decay heat levels.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 130 And a significant amount of the initial 1 energy in the RCS has been transported to the cool.

2 So, that's not a transition that --

3 (Simultaneous Speaking.)

4 CHAIR MARCH-LEUBA: The DHRS is cooling 5 slowly, the pressure in the vessel is the saturation 6 pressure at that temperature.

7 So, slowly the pressure is -- and there 8 will be one valve that will open first and the others 9 will still be closed.

10 And then there will be a sudden 11 depressurization and all of them will open within a 12 second or two. But does it make a difference, the 13 order?14 MS. McCLOSKEY: With respect to margin to 15 the acceptance criteria, I'd say no and that event is 16 bounded by the initiating event of the valve opening 17 while it power-conditions.

18 CHAIR MARCH-LEUBA: The fact that once you 19 open one, within a couple of seconds everything will 20 open and you are in decay heat?

21 MS. McCLOSKEY: Yes, in decay heat you're 22 depressurizing. All right, the next slide has the 23 LOCA event progressions.

24 CHAIR MARCH-LEUBA: I'm sorry, for all of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 131 these you have assumed CVCS not to be operational 1 because it's not safety-grade.

2 But if you keep it going and maintaining 3 water level and pressure, which it could because it's 4 non-safety grade, would it be a bad thing? IAB will 5 never click?

6 So, you have this same progression event 7 but now the operator didn't look, CVCS continued to 8 maintain the water levels so you are adding water or 9 how you isolate the -- you probably do not isolate.

10 MS. McCLOSKEY: Go ahead.

11 MEMBER CORRADINI: You would have a 12 containment isolation I would think.

13 MR. BRISTOL: If there's no DC power then 14 yes, the modules have been isolated so the reactor is 15 tripped, DHR is actuated and containment is --

16 CHAIR MARCH-LEUBA: There has to be a loss 17 of power.

18 MR. BRISTOL: -- containment isolated, 19 yes. 20 CHAIR MARCH-LEUBA: But if you have a 21 scram without a loss of power?

22 MR. BRISTOL: And we'll get into this in 23 some of the transient results but yes, there are 24 definitely cases where power available and normal 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 132 control systems available is more limiting than not.

1 One specific event is reactivity events.

2 Without pressure control, those trip very quickly on 3 high pressure so it's actually more conservative to 4 assume the spray comes on and maintains pressure 5 control and we eventually progress to a trip condition 6 on overpower over temperature.

7 CHAIR MARCH-LEUBA: Say you have a forced 8 scram for no reason whatsoever, everything else is 9 working.

10 CVCS continues to maintain water level in 11 the pressurizer and DHRS comes on and you isolate the 12 secondary. Will CVCS continue to maintain level and 13 dilute the boron?

14 MR. BRISTOL: With reactor trip, demin 15 water is isolated. So, there's certain conditions in 16 which the demin water supply is available unisolated.

17 CHAIR MARCH-LEUBA: It has to be 18 unisolated only? The reactor trip will isolate clean 19 water? 20 MR. BRISTOL: Mm-hmm.

21 CHAIR MARCH-LEUBA: What I'm coming to 22 hear is there are combinations of things, there are 23 combinations of situations, that work and doesn't 24 work. 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 133 I'm not sure that you have considered all 1 of them in the recommendation.

2 MEMBER CORRADINI: I got the impression 3 they were trying to consider the limiting. They sure 4 haven't considered all combinations. But I thought 5 you were trying to consider the limiting ones.

6 Am I misunderstanding?

7 MR. BRISTOL: The focus is definitely on 8 the limiting ones, particularly for the purposes of 9 Chapter 15. When we get into the topical reports, we 10 can get into some of the sensitivities that led us to 11 conclusions of the limiting events.

12 A lot of sort of the interesting thought 13 exercises get into the progressions for the extended 14 cooling events.

15 And I think when we get into that 16 discussion later this afternoon, we'll kind of discuss 17 how that progresses and why all the events sort of 18 collapse into a pretty consistent trend.

19 But yes, we've given consideration to 20 postulated CVCS malfunction, extended cold water 21 injections, things of that nature.

22 And that's why we have some of these 23 protection systems that are a little bit unique to 24 NuScale, to ensure that we can have that walk-away 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 134 safe story of MPS will isolate things if operators 1 aren't there and paying attention to make sure that we 2 don't just have an unmanaged or unoperated module.

3 And we're trying to make everyone safe.

4 CHAIR MARCH-LEUBA: I'll save it for this 5 afternoon but I'm already thinking of a transient that 6 you haven't done.

7 MR. BRISTOL: Okay.

8 MR. INFANGER: This is Paul Infanger. The 9 inadvertent operation or misoperation of CVCS is an 10 event that's analyzed in 15.5. We looked at all the 11 combinations of what CVCS could --

12 MS. McCLOSKEY: For the increase in 13 inventory event.

14 MR. INFANGER: Increase in inventory and 15 we looked at boron dilution in 15.4.6.

16 MS. McCLOSKEY: The loss of power 17 progressions in a LOCA-type event are typically early 18 in the transient. The module protection system 19 actuates the reactor trip, containment isolation 20 because containment is isolated.

21 The decay heat removal system is also 22 isolated in the design and then ECCS valves are 23 actuated on high containment level in the case of all 24 power available.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 135 And for a realistic event progression, 1 they would be expected to open at that time. And then 2 ECCS cooling is established for the 72-hour duration.

3 If AC power is unavailable, that event 4 progression is basically unchanged. If DC power is 5 assumed to be unavailable as well, then the ECCS 6 valves are actuated by the loss of DC power.

7 And we credit the IAB function to hold 8 them closed until the RCS is sufficiently 9 depressurized, and then the valves will open a little 10 bit earlier to establish ECCS cooling.

11 In terms of the design basis event 12 progressions, the short-term analyses are analyzed 13 from the event initiation until a safe, stabilized 14 condition is reached, by which we mean that the 15 initiating event has been mitigated by the module 16 protection system actuations that are expected to 17 occur. 18 We've demonstrated that margin to our 19 acceptance criteria has been met and system parameters 20 such as inventory levels, temperatures, or pressures 21 are trending in a favorable direction.

22 Either the inventory levels are going up 23 or have stabilized, temperatures and pressures are 24 trending down.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 136 And then after the safe, stabilized 1 condition is reached, we get into the longer-term 2 analyses of ECCS long-term decay and residual heat 3 removal, the return to power analyses, and extended 4 DHRS operation.

5 CHAIR MARCH-LEUBA: I may need your help 6 on this to put this in proper English. But I'm 7 concerned by a little bit of paperwork and we have 8 mode one, mode two, mode three, mode four.

9 Mode two is hot shutdown that requires you 10 to have a temperature greater than 425 and mode three 11 is safe shutdown which can have a temperature lower 12 than 420.

13 But my suspicion is that to go to mode 14 three to safe shutdown, tech specs will require a 15 boron concentration before the operator can go from 16 mode two to mode three.

17 At least Chapter 4 has a table that 18 calculates how much boron you need to have to go into 19 safe shutdown. The table says unless you have 300 PPM 20 you are not in safe shutdown.

21 It's a function of exposure. So, my 22 suspicion is that's going to propagate into tech 23 specs. Now, by going into the passive cooling on 24 DHRS, the operator is initiating a transfer from mode 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 137 two to mode three.

1 You already scrammed, you are in mode two.

2 It initiates a transfer from mode two to mode three 3 without establishing the PPM requirements before he 4 does that. And in Matt's plan that would result in a 5 fine. 6 Is that correct?

7 MEMBER SUNSERI: I understand what you're 8 saying but I'm looking at the table right now and the 9 reactivity conditions are the same for both modes, so 10 less than or equal to 99.

11 So, you don't have to go to the shutdown 12 margin, the cold shutdown margin, if you know what the 13 transition mode looks like.

14 CHAIR MARCH-LEUBA: If you look at the 15 previous table, there is a PPM required to maintain 16 0.99 on Chapter 4. I'm just putting it out there.

17 There's a possibility that by turning 18 passive cooling on, you're actually moving from mode 19 two to mode three. If mode three has some 20 requirements different than mode two, then you are in 21 violation of procedures.

22 And if it does not have different 23 requirements, why have two modes? I'm just putting it 24 out there because if that happens in a control room 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 138 today, you will get a fine.

1 MS. McCLOSKEY: I think I would defer that 2 to Operations and our tech spec folks.

3 CHAIR MARCH-LEUBA: It's on the record, I 4 can read it afterwards. But there is a mode two and 5 a mode three. They're different. There has to be 6 some difference between the two.

7 MR. INFANGER: Without operator action, 8 you will transition to mode three and if all rods are 9 in, you will be subcritical under all conditions.

10 If one rod is not fully inserted, there 11 are some scenarios where you could never return to 12 power and that is analyzed in 15.0.6.

13 CHAIR MARCH-LEUBA: Okay, you guys 14 continue, let me look at the table in Chapter 4.

15 MS. McCLOSKEY: Let's go on to the next 16 slide. 17 So, although the discussion of the topical 18 reports are deferred to later in this qual, we did 19 want to provide a high-level picture of the system's 20 thermal hydraulic methodologies and the links between 21 them, starting with NRELAP5, which is the engine of 22 our system thermal hydraulic analysis for Chapter 15.

23 And NuScale procured the NRELAP5-3D code 24 from INL and modified it to address NuScale-specific 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 139 phenomena in systems. And that's what we call the 1 NRELAP5 code.

2 The code description is provided in the 3 LOCA topical report, along with most of the 4 validation.

5 The LOCA EM was developed following Reg 6 Guide 1.203 and was extended for analysis of other 7 events, such as the valve-opening events and to focus 8 on other acceptance criteria including containment and 9 the long-term cooling analysis.

10 The non-LOCA topical report leverages that 11 code description and validation described in the LOCA 12 topical report based on considering differences 13 between the high-ranked phenomena for the different 14 types of events.

15 And then the containment response 16 technical report is an extension of these evaluation 17 models with focus on the containment pressure and 18 temperature acceptance criteria for both the primary 19 release events and the secondary side pipe-break 20 events. 21 And then we have overcooling, return to 22 power, and event progression from either the decay 23 heat removal system operation or ECCS and long-term 24 cooling with ECCS as an extension from the LOCA EM.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 140 That's, big picture, how this fits 1 together.

2 MEMBER CORRADINI: The way I read the 3 chart, just to repeat it back to you so I'm 4 understanding, NRELAP is being used in all of the 5 various ways but in a different set of assumptions or 6 procedures?

7 NRELAP is the tool but it's used with 8 different assumptions instead of protocols depending 9 upon the application?

10 MS. McCLOSKEY: Primarily, yes, some 11 different protocols. Primarily different biasing of 12 initial and boundary conditions and different 13 requirements to model secondary side breaks, those 14 sorts of --

15 CHAIR MARCH-LEUBA: So, the different 16 boxes identify different conservatisms that you have 17 to input on the input of NRELAP? Like, for example, 18 you have to use Appendix K?

19 MS. McCLOSKEY: Right, that's part of the 20 LOCA topical report. It's not part of the non-LOCA 21 topical report.

22 CHAIR MARCH-LEUBA: But it tells you what 23 input to provide to RELAP? Instead of providing best 24 testing, you provide Appendix K?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 141 MS. McCLOSKEY: Mm-hmm.

1 CHAIR MARCH-LEUBA: And are you going to 2 describe the changes, the new RELAP versus the old 3 RELAP? Are you going to describe those?

4 MS. McCLOSKEY: I think in the closed 5 session this afternoon our subject-matter experts at 6 Corvallis speak to a high-level summary of the 7 changes. 8 CHAIR MARCH-LEUBA: I'm personally more 9 interested in why they were made so late. Did we find 10 an efficiency analysis that triggered the need to do 11 it? 12 MS. McCLOSKEY: No, there were --

13 CHAIR MARCH-LEUBA: It's closed so let's 14 wait. 15 MS. McCLOSKEY: Some of the changes were 16 error corrections that we identified and needed to 17 correct as part of the normal process of development 18 and maintenance.

19 CHAIR MARCH-LEUBA: Typically, when you 20 have an error correction you don't rerun the whole 21 Chapter 15. You have outweighed Chapter 15 against 22 the error which did not affect it.

23 MS. McCLOSKEY: As we're in the middle of 24 the review process, revising the analyses is the path 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 142 that we are taking.

1 CHAIR MARCH-LEUBA: If we start doing 2 this, you'll never finish. We'll never finish.

3 MS. McCLOSKEY: Just one slide on the LOCA 4 EM development, the topical report was developed 5 following the Reg Guide 1.203 evaluation model 6 development and assessment process.

7 We developed PIRT to identify high-ranked 8 phenomena for the LOCA pipe-break events that is also 9 applicable to the valve-opening events, focused on the 10 short-term response.

11 We developed an assessment basis for 12 NRELAP5, including the separate effects test and 13 integral effects test to address these high-ranked 14 phenomena. Unique phenomena were addressed by 15 NuScale-specific tests in items such as the steam 16 generators.

17 The code development, as I said 18 previously, was developed in RELAP5-3D and we 19 performed an applicability evaluation for the EM 20 including bottom-up evaluation of the models and 21 correlations in the code, and a top-down analysis 22 focused on the performance against the IEDs.

23 The non-LOCA EM, we developed that to 24 perform conservative analyses following the attentive 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 143 Reg Guide 1.203 and applying a graded approach, 1 leveraging that code description and much of the 2 validation that was described in the LOCA topical 3 report. 4 We did a PIRT identifying high-ranked 5 phenomena considering all the different types of non-6 LOCA events.

7 And then we did a GAP analysis for those 8 high-ranked phenomena compared to the high-ranked 9 phenomena addressed in the LOCA analyses to identify 10 what had to be addressed in addition for the non-11 LOCA-specific analyses.

12 We did do some additional NRELAP5 code 13 validations, focused primarily on the decay heat 14 removal system and the integral non-LOCA response.

15 MEMBER CORRADINI: Can I take you back?

16 You don't have to go back in the slide but the way 17 you've applied NRELAP is using Appendix K assumptions, 18 not using best estimate assumptions? Am I remembering 19 correctly?

20 MS. McCLOSKEY: Yes, that's correct.

21 MEMBER CORRADINI: Does that influence 22 some of the changes you made between 13 and 14?

23 MS. McCLOSKEY: No.

24 MEMBER CORRADINI: Okay.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 144 MS. McCLOSKEY: All right, and now I'll 1 turn it over to Ben to talk to several of the 2 transient example results that are presented in 3 Chapter 15.

4 MR. BRISTOL: Yes, thanks. So, we have 5 these grouped. I'll try to take this at a little 6 faster pace and just, obviously, you can slow me down 7 when you'd like to.

8 So, analysis results, we have different 9 event types. We'll start with just walking through 10 the sections in 15, how they're categorized.

11 The first type is increase in heat removal 12 by secondary or we call it coolant events. So, 13 there's a variety of them there highlighted. We are 14 going to walk through an example of an increase in 15 feedwater flow event.

16 We've got the limiting analysis results 17 summarized with the acceptance criteria in this table.

18 Are you driving? You're driving.

19 PARTICIPANT: Unless you want to.

20 MR. BRISTOL: I can. There, transition 21 complete. Okay, so for the case that we've presented 22 in the FSAR, this is 100 percent increase in feedwater 23 flow event. So, that's initiated at time zero.

24 In this particular event, that's detected 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 145 by a low-steam super-heat trip so analytical limit is 1 reached. That correlations pretty closely, this is 2 why it's a limiting event, to the high reactor power 3 trip being reached.

4 And we get a reactor trip signal, DHRS 5 actuation, and peak pressure occurs a little bit of a 6 while later.

7 CHAIR MARCH-LEUBA: What initiates DHRS?

8 MR. BRISTOL: Low-steam super heat.

9 CHAIR MARCH-LEUBA: And it's automatic?

10 MR. BRISTOL: That's correct.

11 (Simultaneous Speaking.)

12 CHAIR MARCH-LEUBA: In real life you would 13 expect the operator to take over that reactor and 14 control it? Or would you leave it like that?

15 This is the licensing basis, no hands off, 16 but in real life would you expect the operator to 17 defeat the containment isolation and take it off DHRS?

18 Or just leave it on DHRS?

19 MR. BRISTOL: I think it depends on what 20 the operators are doing but if this is the only module 21 that's being influenced, one of the key things that 22 they try to do is stop the cool-down.

23 And the reason for that is because, very 24 quickly, the CVCS makeup capacity is very low relative 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 146 to the shrinkage that is caused by the cool-down.

1 So, maintaining inventory in the 2 pressurizer is one of the key parameters and the best 3 way to do that is to maintain temperature.

4 CHAIR MARCH-LEUBA: So, you would expect 5 the pressure to go there and defeat DHRS, open up the 6 secondary and start controlling?

7 MR. BRISTOL: If the conditions are 8 correct, they may consider closing the DHRS actuation 9 valves if they can reestablish normal feed, in which 10 case then the primary temperature can be controlled.

11 CHAIR MARCH-LEUBA: But what I'm talking 12 about is, this is the perfect time to tell you on the 13 record, that the table I was talking about before is 14 Table 4.3-2, nuclear parameters for a cycle.

15 And at the bottom of the table it says 16 boron concentration, for safe shutdown you need 1164 17 PPM at the beginning of the cycle, 240 at the end of 18 cycle. 19 It feels to me that somebody when they 20 made these calculations were planning to define all 21 three requirements to have those PPMs. By doing what 22 you just did now, you transfer the core to mode three 23 without achieving those requirements.

24 So, I'm just telling you that it's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 147 perfectly okay to not have those requirements but if 1 you write your tech specs with this PPM for mode 2 three, the transient you just ran now will serve you 3 a fine, will put you in the yellow column of the 4 evaluation of your plant and you'll have to pay 5$50,000.

6 So, somebody has to see the logic of 7 what's the difference between mode two and mode three 8 and is there a requirement for mode three, and is this 9 mode three -- because you're going into mode three.

10 You're going to go below 420 Fahrenheit.

11 MEMBER SUNSERI: I don't know about that, 12 Jose. Just thinking about how the plants I run work, 13 you have a reactor trip. The tech specs are laid out 14 the same, 0.99 K effective or whatever, right?

15 So, you know you're shut down if you 16 verify all your rods are in or if one's stuck or 17 whatever. Now the question becomes what's my shutdown 18 margin and how is xenon affecting that and all that 19 kind of thing?

20 So, you do a shutdown margin calculation.

21 You plug in the 0.99, you plug in your rod 22 configuration, you plug in your temperature and all 23 the reactivity configurations, and you compute what 24 your boron concentration is.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 148 And then you adjust it as necessary over 1 time so you get xenon-free or an equilibrium scenario 2 or whatever it is.

3 CHAIR MARCH-LEUBA: I don't think it's a 4 real problem, I think it's a paperwork problem and 5 somebody that does operations, ask him to read the 6 transcript and see if he understands what I'm saying.

7 Let me repeat it one more, you guys have 8 mode two and three, which are different.

9 They may have different requirements and 10 if you follow what you just described, you jump from 11 mode one to mode three and hands off, didn't touch 12 anything, the possibility exists of you violating your 13 procedures.

14 So it is incumbent on you to write the 15 procedures correctly.

16 MEMBER SUNSERI: But they're going to go 17 from mode one to mode two.

18 CHAIR MARCH-LEUBA: No, they'll go to mode 19 three. 20 MEMBER SUNSERI: No, because mode three 21 has to be less than 420 degrees. You're going to get 22 there in time but you're not going to get there right 23 away. 24 It's just kind of like a PWR, you go from 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 149 mode one to mode three, you skip over two, and you can 1 stay in mode three or you can go to mode four, which 2 is a colder temperature, right?

3 You have to change your boron 4 concentration if you're going to go colder.

5 CHAIR MARCH-LEUBA: The moment you scram 6 you go to mode two. Within an hour to two hours --

7 MEMBER SUNSERI: On this plant.

8 CHAIR MARCH-LEUBA: On this plant, so the 9 one here described. Within a couple of hours, you're 10 going to be in mode three conditions.

11 Depending on how you write, how you define 12 your modes, you might be in violation of something.

13 Look at it.

14 MEMBER CORRADINI: I think we can move on 15 and I think we've got that point.

16 MR. BRISTOL: Okay. All right, so we 17 walked through the event sequence.

18 This figure here, we've got the increase 19 in feedwater flow that the scales aren't the greatest 20 but we go from 80 up to 160, quickly isolate. Here's 21 reactor power as a function of time.

22 Takeaway events detected in the steam 23 generators are isolated before both steam generators 24 are filled, and in this figure DHRS is actuated. This 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 150 is RCS flow, RCS temperature.

1 So we've established stable cooling. This 2 is sort of the truncation criteria for the short-term 3 transient response.

4 CHAIR MARCH-LEUBA: It's important in this 5 transient that you stop -- you turn on DHRS before it 6 overflows.

7 MR. BRISTOL: That's correct.

8 CHAIR MARCH-LEUBA: So, the timing of the 9 scram, not the scram but the transfer to DHRS is 10 important.

11 MR. BRISTOL: That's correct.

12 CHAIR MARCH-LEUBA: Yes.

13 MR. BRISTOL: This figure kind of 14 illustrates that a little bit. We've got secondary 15 pressure which isn't really the point here.

16 The figure is the unimpacted or the steam 17 generator level as the increasing inventory is sort of 18 on this time scale here.

19 This is where we get the low super heat 20 isolation signal and then as DHR drains we have an 21 additional filling of the steam generator, even at a 22 collapsed level of 80 percent, DHR is still effective.

23 CHAIR MARCH-LEUBA: So, the steam 24 generator only fills to about 75 to 80 percent?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 151 MR. BRISTOL: That's correct.

1 CHAIR MARCH-LEUBA: So, that does not 2 impede the DHRS operation?

3 MR. BRISTOL: No.

4 CHAIR MARCH-LEUBA: At that level. What 5 level would it fail DHRS? Pretty high up?

6 MR. BRISTOL:

Yes, I don't have that 7 number immediately offhand.

8 I know in some of the cases we look at, 9 not necessarily the limiting cool-down cases, but this 10 is an event where the feedwater isolation failure is 11 a limiting event from DHR performance perspective.

12 So, one train, if the feedwater isolation 13 valve were to fail, we're waiting on the feedwater reg 14 valve to close in order to mitigate that overfill.

15 That's a much slower timeframe valve so 16 the one generator will end up with a higher level than 17 the other generator and it degrades the performance 18 accordingly.

19 CHAIR MARCH-LEUBA: Do you guys remember 20 that if your steam generator secondary side is full 21 with water, DHRS doesn't work? If the liquid level 22 hits 100, DHRS will be rendered inoperable. And it 23 hits 80 percent.

24 MEMBER CORRADINI: 100 percent of what?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 152 100 percent of the active tube length? Or 100 percent 1 of all the way up to the -- I want to understand what 2 100 percent is.

3 MR. BRISTOL: The tube length.

4 CHAIR MARCH-LEUBA: So there's still 5 plenty of steam volume?

6 MR. BRISTOL: And that's primarily at high 7 RCS temperature conditions.

8 So, if you were looking at this from the 9 sort of minimum or maximum cool-down, as RCS 10 temperature starts to drop, we would quickly see the 11 impact of the increased inventory on performance.

12 CHAIR MARCH-LEUBA: But DHRS isolates 13 everything?

14 MR. BRISTOL: Yes, that's right.

15 CHAIR MARCH-LEUBA: When you close it, 16 whatever inventory you close, that's what you have.

17 MR. BRISTOL: That's right. Okay, so 18 final figures here, here's DHR performance I think.

19 Am I reading that right? And this is the VIPRE figure 20 for the transient.

21 Minimum MCHFR is down here, right at 22 reactor trip. So, the conclusion is DHR is still 23 functionally removing decay heat and MCHFR margin 24 exists.25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 153 Okay, heat-up events, decrease in heat 1 removal events. Again, here's a summary table, you'll 2 see the RCS pressure in all of these is fairly 3 consistent. That's due to the capacity of the reactor 4 safety valve.

5 These cases all have the reactor safety 6 valve lifting. That mitigates the pressurization 7 response. And secondary pressures, the heat-up events 8 tend to be pressurization events as opposed to actual 9 temperature-driven events in most cases.

10 So, the MCHFR is non-limiting for these 11 event types. An example we're walking through I think 12 is loss of AC power and inadvertent actuation of DHR.

13 So, loss of AC, this is an event we 14 simulate where there's a simultaneous loss of 15 feedwater and turbine trip.

16 So, the loss of flow to this steam 17 generator as well as an increase in steam pressure or 18 steam pressurization on the steam side quickly results 19 in high-pressurized pressure.

20 With that big of a transient to the steam 21 generators, the downcomer side actually heats up and 22 swells pretty quickly. That causes a pressurization 23 response that's detected rapidly.

24 We get a reactor trip and DHR actuation 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 154 because of those signals.

1 MEMBER CORRADINI: Which of the various 2 AOOs fills the generator the most? Is it the one we 3 just went through?

4 MR. BRISTOL: Increase in feedwater flow, 5 yes. 6 MEMBER CORRADINI: And if one were to --

7 okay, I'll stop there and I'll come back. Thank you.

8 MR. BRISTOL: So, RCS pressure response 9 over here and secondary side pressure response. So 10 the sharp decline here is the pressure increases 11 rapidly until the safety valve lists and then 12 decreases.

13 As DHR cooling is established, we see sort 14 of this stable cooling trend. One of the things about 15 the way the DHR actuates all of our -- for most of the 16 events, tube failure is an exception, the actual 17 actuation of DHR is what's driving the pressure 18 response.

19 So, as the secondary system is isolated, 20 then it reaches equilibrium saturated condition with 21 the RCS temperature. And so that's really what's 22 driving this pressure response.

23 It will keep pressurizing until it's 24 pretty close to the RCS temperature and so for the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 155 limiting events of that category, RCS temperature is 1 the main driver, actually, of the secondary pressure 2 response.

3 Again, flow, RCS flow, and temperature 4 response with DHR actuation. And I sort of alluded to 5 that in this particular case the slight heat-up 6 pressurization actually creates the limiting MCHFR 7 conditions as the initial condition as opposed to some 8 transient CHF.

9 Inadvertent DHR, so when we're operating 10 at full power conditions the pressure drop across the 11 steam generator is actually a little bit higher than 12 the head, the level head, of the DHR system itself.

13 So, if one of the valves at the top were 14 to open inadvertently, there's actually a little bit 15 of a feedwater bypass that occurs.

16 And so this creates a pretty minor loss of 17 feedwater, a little bit of flow injecting into the 18 steam outlet portion of the steam generator. It 19 reaches an equilibrium condition fairly quickly.

20 In this particular case it takes 400 or 21 500 seconds for the high-temperature trip to be 22 reached, at which point we get, again, reactor trip 23 and DHR actuation. So, here's a little bit slower 24 transient response in terms of the figure.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 156 There's a slight increase in secondary 1 pressure as temperature is increasing, and then DHR 2 actuation. This kind of shows the steam level 3 response.

4 The feedwater bypass creates a little bit 5 of a level loss in the steam generato rs and the 6 difference there in levels is the impact of steam 7 generator versus the non.

8 Again, RCS pressure response, this is a 9 case where we're actually assuming the modular control 10 system is functioning to keep pressure maintained.

11 That creates the limiting temperature response.

12 If this were not assumed, you can see by 13 this progression we would reach the high-pressure trip 14 pretty quickly, much more quickly than the high-15 temperature trip. So, you see the temperature figure 16 over on the spot.

17 So, in summary, the DHR valve opens and 18 diverts some of the feedwater flow around the steam 19 generators but RCS pressures remain within acceptance 20 criteria.

21 Here's our CHF figure in reactor power.

22 So, you see over here there's a slight mismatch 23 between the reactor power and the steam generator 24 power which causes the heat-up event.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 157 Reactivity events, again, here's just a 1 quick summary table. Pressure response, these are 2 primarily evaluated for CHF.

3 The increasing power events generate the 4 limiting category of our CHF-limited events, in 5 particular we'll walk through the single rod 6 withdrawal.

7 That reacts a little bit like an 8 inadvertent bank withdrawal but it has a unique 9 peaking that's applied in the analysis and that's what 10 causes the local heat flex to increase.

11 CHAIR MARCH-LEUBA: This is from low 12 power?

13 MR. BRISTOL: These are from...I think the 14 single rod withdrawal is initiated at 75 percent 15 power. The peaking is just a little bit worse than 16 the 100 percent power.

17 But the bank withdrawal is analyzed for 18 sort of the startup transient that has the power --

19 CHAIR MARCH-LEUBA: But the single rod 20 withdrawal is from 75?

21 MR. BRISTOL: That's right. So, in these 22 cases we actually see that the slower reactivity 23 insertions generate more of a thermal hydraulic 24 transient and that's what generates the limiting 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 158 conditions.

1 So, it's a little bit of a chase between 2 the thermal hydraulic conditions getting to the trip 3 conditions versus the overpower conditions. This 4 particular case, as you can see, we reach high hot leg 5 temperature at about 150 seconds.

6 RCS pressure limit is reached shortly 7 after that, at which point the reactor is tripped and 8 DHR is actuated.

9 So, here's a figure of the reactivity 10 insertion as a function of time and then the power.

11 So, we start at 75 percent power and increase up to 12 just over 100 percent power.

13 The reactivity insertion overall and 14 temperature feedback kind of create that cap there, at 15 which point it would trip the reactor.

16 Pressure and temperature response for the 17 events, there's a slight pressurization the way that 18 the system is modeled. It's actually a simplification 19 that's applied to the spread.

20 This is another one where the pressure 21 control actually makes the event worse and so there is 22 some pressure control applied until that's overcome by 23 the increasing temperature.

24 And we've got RCS flow, MCHFR. So, 1.67 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 159 MCHFR for this event, or is that 62? I can't read 1 that far.

2 Okay, increase in RCS inventory, this is 3 actually a category of events that NuScale doesn't 4 really have very severe transients. We look at the 5 maximum, sort of an inadvertent actuation of the 6 maximum makeup capacity.

7 That's what analyzed here. The 8 consideration really is for a malfunction event where 9 the pressurizer level is increased above the nominal 10 condition to generate a reactor trip, at which point 11 we would take a loss of AC power and a turbine trip.

12 Could we create a pressure response that 13 looks somewhat different than the normal pressure 14 transients that we look at? So, that's basically what 15 is evaluated.

16 It's a pretty slow response, I don't have 17 any of the specific results in this presentation.

18 They're in the SR.

19 So, decrease in inventory events, I'll 20 spend a little bit more time here. We've got a tube 21 failure scenario we'll walk through and then an 22 inadvertent ECCS actuation.

23 I think this is the RRV and then we'll 24 compare that to the limiting LOCA scenario, kind of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 160 set up some of the other topics we'll get into later 1 this afternoon.

2 So, tube failures are detected and 3 mitigated by RCS level. It's a pretty slow event.

4 The first thing that comes in is the low pressurizer 5 level set point. That's actually a protection set 6 point for the pressurizer heaters.

7 So, 35 percent is the pressurizer level at 8 which the pressurizer heaters exist axially. And so 9 once the heater starts to uncover, we want to protect 10 them so there's a pressurizer heater trip and a 11 reactor trip that comes with that.

12 The containment isolation doesn't come 13 further on until 20 percent pressurizer level.

14 CHAIR MARCH-LEUBA: So, the reactor trip 15 gets tripped, it doesn't isolate anything?

16 MR. BRISTOL: That's correct. So, upon 17 reactor trip --

18 MEMBER CORRADINI: How much of it is a 19 change in physical level to go to what you said, 20 20 percent from normal?

21 MR. BRISTOL: Normal is at 60 percent.

22 MEMBER CORRADINI: So what is that?

23 MR. BRISTOL: Pressurizer is ten feet tall 24 I think.25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 161 MEMBER CORRADINI: So, it's almost a foot 1 per...?2 MR. BRISTOL: Yes.

3 MEMBER CORRADINI: Okay, thank you.

4 MR. BRISTOL: So, if the reactor trips and 5 the heater's tripped, it's a bit of a race but we get 6 to low low-pressurizer level and low-pressurizer 7 pressure pretty quickly.

8 In this case, low-pressurizer pressure 9 creates a DHR or containment isolation and DHR 10 actuation. And ultimately, that's what mitigates the 11 event. 12 So, we see here secondary pressure, 13 primary pressure, slight drift down in primary 14 pressure until reactor trip and then we see an 15 increase in DHR actuation.

16 So, with the reactor trip we start to 17 increase the secondary pressure. Here you can really 18 tell the difference between the impacted steam 19 generator and the non-impacted steam generator.

20 So, a scaled-out figure just with the 21 pressures, the impacted steam generator quickly 22 reaches equilibrium pressure with the primary system.

23 The other steam generator is on DHR and providing 24 coolant. 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 162 So, just a figure of pressurizer level, 1 and steam generator level. Again, you can see here 2 upon secondary isolation the level and the impacted 3 steam generator dramatically increasing.

4 So, primary inventory remains well above 5 the top of the core in DHR. The unimpacted train in 6 DHR provides coolant.

7 Here is just a figure of the break flow 8 rate into the integral mass release. We'll get into 9 the radiological results but this is one of the inputs 10 that's provided downstream to the radiological 11 analysis for the dose consequences.

12 Inadvertent RRV opening, this is a very 13 rapid event.

14 MEMBER CORRADINI: Is this the one that 15 maximizes -- maximize is the wrong word. This is the 16 one that is the one that's most severe in terms of 17 depressurization?

18 MR. BRISTOL: No, the inadvertent RVV is 19 a much more rapid pressure transient in terms of the 20 RCS. This is the RRV so this is a liquid space, loss 21 of inventory.

22 It looks a little bit like the discharge 23 line break. This is the event that sets the limiting 24 containment pressure response analysis, and we'll get 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 163 into that later as well.

1 MEMBER CORRADINI: So, this maximizes the 2 peak pressure in containment?

3 MR. BRISTOL: That's correct.

4 MEMBER CORRADINI: Whereas the RVV 5 controls or is l imiting in terms of the 6 depressurization rate?

7 MR. BRISTOL: That's right, yes. Yes, the 8 steam space release is a much faster factor loss than 9 the liquid space release.

10 CHAIR MARCH-LEUBA: But it does not 11 pressurize the containment as much?

12 MR. BRISTOL: That's right. And we'll get 13 into the containment response, but it's a volume 14 transient for the containment.

15 If we're increasing with liquid without 16 de-energizing the RCS, then there's more energy once 17 the ECCS actually actuates overall.

18 Okay, so in this case we get a flow.

19 there is some pressure transient but there is a flow 20 transient in response to the opening of the valve. We 21 get an immediate high containment pressure signal in 22 this case, and that's what causes the reactor trip.

23 This particular scenario actually 24 simulates a loss of AC and DC power at time zero so 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 164 with that, reactor trip comes immediately as well as 1 DHR actuation and containment isolation.

2 And so this is a case we'll kind of see 3 here. This is the case where one RRV is open, the 4 rest go onto IAB immediately with the IAB close 5 function until we reach the IAB release condition, 6 which is the differential pressure.

7 And so that's where we see the rest of 8 ECCS valves opening shortly into the transient. Level 9 figures, I think the nominal level condition in this 10 particular case doesn't look at failure of one of the 11 other valves to open.

12 So, in terms of the top of the active 13 core, the RCS level is right there at about ten feet.

14 The containment level is a couple of feet above that.

15 Here's the flow response I could mention.

16 There's a short flow transient and then 17 with reactor trip we get -- oh, no, sorry, this is the 18 RRV flow rate. So, as the valve opens, containment's 19 pressurizing so the flow drops, and then after ECCS 20 actuation equilibrium is quickly reached.

21 Zoomed in figure on RCS temperature and 22 then this is the temperature response after ECCS 23 actuation.

24 Short-term and longer-term RCS flow 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 165 response. So, the limiting CHF condition occurs to 1 this little transient flow response there, it's 2 actually driving it.

3 So, MCHFR occurs in the first couple of 4 seconds and the margins increase after reactor trip.

5 The technique for calculating this we'll get into 6 further in later follow-up discussions, but we have 7 margins to the acceptance criteria.

8 CHAIR MARCH-LEUBA: So, am I reading this 9 correctly? At time zero the MCHFR is 1.5? Or is 10 there a drop that I don't see? Because I thought it 11 was closer to two.

12 MEMBER CORRADINI: I think it's higher.

13 MR. BRISTOL: So, this gets into the 14 differences in the RELAP calculational approach versus 15 the subchannel calculational approach.

16 MEMBER CORRADINI: -- using your approved 17 NSP...18 MR. BRISTOL: Four.

19 MEMBER CORRADINI: Four, thank you.

20 CHAIR MARCH-LEUBA: So, this RELAP MCHFR 21 is bias low?

22 MR. BRISTOL: Mm-hmm.

23 CHAIR MARCH-LEUBA: Or simply the 24 correlation that you're seeing is bias low?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 166 MEMBER CORRADINI: This is Hench-Levy.

1 MR. BRISTOL: That's correct.

2 MEMBER CORRADINI: And you use that to 3 again be conser vative? I didn't catch that in the 4 chapter. 5 MR. BRISTOL: I think we'll defer that 6 discussion to -- are we getting into that later today?

7 MS. McCLOSKEY: We don't have slides on 8 that later today because that's part of the LOCA 9 topical report.

10 MR. BRISTOL: Yes, we're giving an 11 overview of the LOCA topical in the closed session and 12 that's bordering on the proprietary so we can discuss 13 it --14 CHAIR MARCH-LEUBA: At a high level, CHF 15 correlations are fuel-specific because they depend a 16 lot on the spacers? You're using a generic CHF 17 correlation for the real calculations that do not care 18 what the fuel is?

19 MR. BRISTOL: Not completely. The 20 analytical limit or the exceptions criteria is based 21 on --22 CHAIR MARCH-LEUBA: But that's 23 uncertainties.

24 MR. BRISTOL: But it's benchmarked to our 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 167 fuel-specific CHF --

1 CHAIR MARCH-LEUBA: But the actual value 2 of CHF that you predict, with a fuel-specific CHF 3 correlation versus a generic can be off by 50 percent.

4 The generic ones tend to bound everything 5 because they don't account for the spacer turbulence.

6 And the fuel fabricator has spent a lot of money 7 creating that turbulence.

8 MR. BRISTOL: Certainly.

9 CHAIR MARCH-LEUBA: And are charging you 10 for it. 11 MEMBER CORRADINI: But just keep in mind, 12 when we discussed this a year ago we agreed that the 13 NSP4 had a limited range of applicability in terms of 14 pressure and flow.

15 And they're not under these conditions 16 within that range of applicability to pressure and 17 flow. So, my assumption was this was a conservative 18 application.

19 MR. BRISTOL: I think we are with --

20 MEMBER CORRADINI: Well, you fall out of 21 it. I mean you start off there but you fall out of 22 range. 23 MR. BRISTOL: Sure.

24 MEMBER CORRADINI: Okay, so we're going to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 168 wait until later?

1 MR. BRISTOL: Yes.

2 MEMBER CORRADINI: Okay.

3 CHAIR MARCH-LEUBA: So, now let's get into 4 the recreational complaining again about the IAB.

5 MEMBER CORRADINI: They still have a lot 6 more slides.

7 CHAIR MARCH-LEUBA: Yes, but let's do some 8 recreational complaining. Filling one IAB gives you 9 a 0.1 delta CHF, nothing compared to your margin where 10 you have two to start with.

11 You could superimpose this transient on 12 every other AOO and be perfectly okay and save a lot 13 of hassle with that IAB that is so complicated.

14 That's my ten cents. Keep going.

15 MR. BRISTOL: Thank you.

16 CHAIR MARCH-LEUBA: It's not worth the 17 fight. 0.1 CHF is not worth the fight.

18 MEMBER CORRADINI: I don't think it's that 19 straightforward but I understand what Member March-20 Leuba is saying.

21 It's the same thing I asked yesterday 22 relative to how all these work in concert.

23 CHAIR MARCH-LEUBA: Yes. I thought this 24 transient was a lot worse and that's why you didn't 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 169 want to have it. But it's not bad, it's actually 1 pretty good. Keep going.

2 MR. BRISTOL: Okay, so to contrast, we'll 3 kind of walk through the LOCA scenario.

4 The limiting event from a level 5 perspective as presented in the FSR's ten percent 6 injection line br eak, this is a relatively slow 7 transient although the initial detection's quite 8 quick. 9 Again even very small breaks of high-10 energy lines in containment, containment's small, we 11 quickly get a pressure response. And let's see, so 12 this case also assumes loss of AC power at time zero.

13 We get a reactor trip.

14 So, with the loss of AC power we actually 15 get a pressurization response. The inventory loss is 16 not actually driving the event detection in this 17 particular case.

18 So, with the reactor trip, shortly after 19 that we get the high containment response, containment 20 isolation, and eventually low pressurizer level, low 21 pressurizer pressure response. And this is a case on 22 IAB. 23 So, one of the conservativisms in the LOCA 24 EM is DHR heat removal is not credited so there's a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 170 slight pressurization that occurs.

1 Eventually, the inventory starts to turn 2 the pressure around as inventory is increasing in the 3 containment vessel.

4 That reaches kind of an equilibrium condition 5 and eventually, we're waiting on IAB release out here 6 in the about 6000 second timeframe.

7 That causes a pretty rapid pressure drop 8 which is driving -- if we look over here, this is our 9 level response. It's at the time of ECCS actuation.

10 CHAIR MARCH-LEUBA: So, you barely, barely 11 hit core uncovery right there at 6000 seconds?

12 MR. BRISTOL: Yes, it doesn't actually get 13 to the top of the core from a collapse-level 14 perspective but it's starting to get close to it.

15 CHAIR MARCH-LEUBA: But you're likely to 16 have some flashing so the actual liquid is higher on 17 that?18 MR. BRISTOL: Yes, there's a fair amount 19 of flashing. RCS is at saturated conditions, 20 obviously, at this point and so with this 21 depressurization there's some liquid flashing that 22 occurs. 23 CHAIR MARCH-LEUBA: And we are not 24 publishing here the CHFR because for LOCA that's not 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 171 a concern?

1 MR. BRISTOL: I think we do publish CHFR 2 but it occurs at the initiating event. But CHF is 3 screened as part of the methodology through the entire 4 transient response but not specifically evaluated to 5--6 CHAIR MARCH-LEUBA: But it's not a 7 criteria?8 MR. BRISTOL: That's right.

9 CHAIR MARCH-LEUBA: For LOCA.

10 MR. BRISTOL: It's evaluated. So, one of 11 the mechanisms for the Appendix K evaluation is 12 ensuring that CHF does not occur.

13 CHAIR MARCH-LEUBA: Sure.

14 MR. BRISTOL: As part of the LOCA --

15 (Simultaneous Speaking.)

16-- so within the code there's a model 17 that's built in and it's screened to --

18 CHAIR MARCH-LEUBA: Screened to criteria.

19 If you didn't go over this, you'd have to do more.

20 MR. BRISTOL: That's right.

21 CHAIR MARCH-LEUBA: Before you go on, more 22 recreational complaining. Can you go back to Slide 23 68? And we see the CHFR starts at 1.5, right? Now, 24 go back to Slide 41?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 172 MR. BRISTOL: 31?

1 CHAIR MARCH-LEUBA: 41. Yes, that's the 2 one. CHFR starts at 2.8. What's the difference?

3 MR. BRISTOL: The initial conditions, the 4 models that are applied.

5 CHAIR MARCH-LEUBA: 2.8 versus 1.5?

6 MR. BRISTOL: Well, okay, so let me see if 7 I can do this --

8 CHAIR MARCH-LEUBA: Basically, what I'm 9 saying is make up your mind. Which is it?

10 MR. BRISTOL: 2.8.

11 CHAIR MARCH-LEUBA: Wouldn't this be worse 12 if you just have the 1.5? Indeed, I see an decrease 13 of almost 1.0.

14 MR. BRISTOL: That's right.

15 CHAIR MARCH-LEUBA: If you just have the 16 1.5, it will be bad.

17 MR. BRISTOL: Certainly.

18 CHAIR MARCH-LEUBA: So, why do you have 19 2.8 here and not on the other one?

20 MR. BRISTOL: The conservativisms that go 21 into setting up the channel that's evaluated in the 22 RELAP model are quite conservative and that's really 23 what drives the primary difference in the initial CHF 24 calculation.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 173 CHAIR MARCH-LEUBA: So, the DHRS heat 1 removal event has less conservativisms than the ECCS 2 inadvertent opening?

3 MR. BRISTOL: This calculation is 4 performed using the VIPRE subchannel methodology and, 5 therefore, it's going to calculate different local 6 thermal hydraulic conditions than the RELAP approach.

7 CHAIR MARCH-LEUBA: I hope VIPRE will give 8 you a lower ratio. This is rich, right?

9 MR. BRISTOL: Yes.

10 CHAIR MARCH-LEUBA: VIPRE is more 11 conservative, it will give you a lower number. Maybe 12 it's the other way around.

13 MEMBER CORRADINI: It's the other way 14 around. This is using NSP4.

15 MR. BRISTOL: That's correct.

16 MEMBER CORRADINI: So this, in theory, has 17 been done with their experiments at Stern with their 18 essentially reactor-relevant bundle in difference to 19 what is being used as a default within RELAP. Am I 20 close?21 MR. BRISTOL: That's correct.

22 CHAIR MARCH-LEUBA: So, this is not the 23 RELAP CHFR?

24 MR. BRISTOL: This is not the RELAP CHFR, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 174 this is the VIPRE CHFR.

1 CHAIR MARCH-LEUBA: And the ECCS?

2 MR. BRISTOL: Is the RELAP CHFR.

3 CHAIR MARCH-LEUBA: And you used VIPRE 4 here because otherwise you couldn't survive it?

5 MR. BRISTOL: This event we could use the 6 RELAP approach as well and show a large margin.

7 CHAIR MARCH-LEUBA: It doesn't feel like 8 it. If you start at 1.5 but you lose 1 -- you lose 1.

9 You start at 2.8 and you scram at 1.8 or 1.9. You 10 lose one all in all in CHFR.

11 MR. BRISTOL: Understood.

12 CHAIR MARCH-LEUBA: It would have been 13 nice if Chapter 15 had been consistent or at least 14 properly advertise what you're using. And I assume 15 both methods are acceptable.

16 MEMBER CORRADINI: I think we've got to 17 ask the Staff that separately.

18 CHAIR MARCH-LEUBA: It feels like cheating 19 a little bit.

20 MR. LINGENFELTER: Andy Lingenfelter of 21 NuScale. I think, Jose, to answer your question, part 22 of that is wrapped into the topicals.

23 And while we would have loved to have done 24 the topicals first and Chapter 15 second, it didn't 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 175 work out that way.

1 And so maybe when we get to the 2 proprietary section we can give you a little more 3 color on CHFR --

4 (Simultaneous Speaking.)

5 That might help.

6 CHAIR MARCH-LEUBA: So did you use 7 different evaluation methods --

8 MR. LINGENFELTER: Appendix K for LOCA and 9 we didn't use Appendix K for non-LOCA.

10 CHAIR MARCH-LEUBA: So, the ECCS open 11 valve you used the LOCA methodology?

12 MR. INFANGER: When we did the analysis in 13 RELAP for the non-LOCA, we did calculate an MCHFR and 14 we used that as a scoping for what would be the most 15 limiting events.

16 And then we ran VIPRE on those events to 17 fine-tune it and the VIPRE number is always a lot 18 lower than MCHFR.

19 CHAIR MARCH-LEUBA: So, this is not VIPRE?

20 MR. INFANGER: That is VIPRE. Yes, and 21 just ballpark, you had like two if you use the RELAP 22 calculation. So, the RELAP is much, much higher.

23 CHAIR MARCH-LEUBA: So RELAP would give 24 you 4.8?25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 176 MR. INFANGER: Yes. No, the minimum would 1 be like 3.8.

2 MS. McCLOSKEY: And just to clarify, that 3 screening technique that's applied as part of the non-4 LOCA EM is different than the CHF evaluation that's 5 performed for the valve opening events using RELAP.

6 So, that's a little bit of a difference 7 there. 8 MEMBER CORRADINI: We've got to go to 9 closed session so we can talk this out.

10 CHAIR MARCH-LEUBA: Right, and I'll make 11 a note to ask the question when we revisit and keep 12 talking, because how come we have factors of two on 13 CHFRs for different methodologies? It would be nice 14 to be semi-consistent.

15 MR. BRISTOL: Okay.

16 MEMBER BLEY: I apologize, I was out for 17 some of the time. I don't think you have any slides 18 on that. 15A, you're not going to talk about that, 19 right? Or are you?

20 MEMBER CORRADINI: It's exempt out. We 21 haven't gotten there yet though.

22 MEMBER BLEY: But I'm going to leave 23 early, and I apologize for that as well and I'd like 24 to --25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 177 MEMBER CORRADINI: But I think similar to 1--2 MEMBER BLEY: There are no slides on it.

3 MEMBER CORRADINI: Right, and similar to 4 APR1400 it essentially is exempt for a Chapter 15 5 analysis.

6 MR. BRISTOL: It is beyond design basis.

7 MEMBER BLEY: There's an argument in 8 Chapter 15 that is part of the submittal.

9 MEMBER CORRADINI: Right, but I think this 10 is consistent with past DCs.

11 MEMBER BLEY: They had an argument in 12 Chapter 15 about it? I don't remember that.

13 MEMBER CORRADINI: I've got the slides.

14 MEMBER BLEY: So, you're telling me to 15 shut up?16 MEMBER CORRADINI: I didn't say that. I 17 didn't say that at all, I'm just simply saying it's 18 consistent, that's all I said.

19 MEMBER BLEY: I want to make a comment and 20 ask a couple short questions and then I'll be done 21 with it. The argument at the end in here is that ATWS 22 is covered by the PRA and it calculates a very low 23 frequency of ATWS, which I believe for the electronics 24 getting a signal.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 178 But most of the likelihood of failure to 1 scram in other systems is due to problems with the 2 rods going in. And I don't know that that was 3 covered. So, I'm suspicious of the 1.7-5 per year.

4 We're not going to argue the PRA here.

5 You begin with the discussion that links back to the 6 anticipatory turbine trip that you don't have, and I'm 7 thinking back 40 years to when that came into play for 8 PWRs with U-tube steam generators.

9 And the original ATWS calculations at 10 least for some of those saw a very -- well, before it 11 failed to scram, it kept running and used up the 12 inventory for certain transients, the inventory in the 13 steam generators.

14 Then all of the sudden the pressure goes 15 up faster than the relief and safety valves can 16 relieve and you were going to break something in the 17 system, so they came up with this anticipatory turbine 18 trip to prevent that.

19 In a design such as this where you don't 20 have any real inventory in the steam generators, I 21 don't think that would apply.

22 But should you have an ATWS -- and are we 23 going to cover that somewhere else? Maybe -- in your 24 design and the pressure starts taking off inside, you 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 179 have a couple nice big vent valves.

1 Does that take the edge off of the ATWS if 2 you actually have one? I'll go back at this in the 3 PRA the next time they come around but if you can say 4 anything about it --

5 MEMBER CORRADINI: So, can I help you a 6 little bit?

7 MEMBER BLEY: -- I'd appreciate it. I 8 don't know if you can or not.

9 MEMBER CORRADINI: There's two things 10 happening.

11 One, we did have a Staff audit calculation 12 that was presented last month by Dr. Yarsky that went 13 over this and I think the answer to the vent valve, 14 the pressure in the vent valve, is it does open, it 15 does have that.

16 (Simultaneous Speaking.)

17 MEMBER BLEY: -- the top off the pressure, 18 okay. I didn't remember that.

19 MEMBER CORRADINI: I also think there's 20 now -- I'm going to look at the Staff -- a completed 21 report by the Staff, a large report, very interesting, 22 on ATWS which we can get.

23 MEMBER BLEY: I wouldn't mind getting 24 that. 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 180 MEMBER CORRADINI: In fact, I thought 1 Chris Brown sent us an email that that was available.

2 MEMBER BLEY: I don't know.

3 MEMBER CORRADINI: I can find the email 4 and send it out to you. He basically sent us a 5 download site --

6 MEMBER BLEY: For the ATWS?

7 MEMBER CORRADINI: For the proprietary, 8 for what Staff has done in terms of a whole range of 9--10 MEMBER BLEY: You have helped me, I 11 assume, as long as I can go through it.

12 (Simultaneous Speaking.)

13 MR. SCHMIDT: This is Jeff Schmidt from 14 reactor systems. So, that was done under Chapter 19 15 and Dr. Yarsky did that, that confirmatory. So, 16 reactor systems may have it or don't have it.

17 MEMBER CORRADINI: But I think we 18 requested it. Some time between last month and this 19 month, Chris sent an email out with a location. I can 20 resend the email.

21 MEMBER BLEY: I missed that if that came 22 out. That probably covers my --

23 MEMBER CORRADINI: It has a complete --

24 (Simultaneous Speaking.)

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 181 MEMBER BLEY: -- except for the PRA stuff 1 which I'm a little nervous about.

2 MEMBER CORRADINI: Okay.

3 MEMBER BLEY: Thank you.

4 MEMBER CORRADINI: I'll send the email.

5 I'll make sure that Mike or I send the email to the 6 Committee again.

7 MEMBER BLEY: I appreciate it.

8 CHAIR MARCH-LEUBA: With an ML number 9 preferably?

10 MEMBER CORRADINI: Yes, there is an ML 11 number. 12 CHAIR MARCH-LEUBA: And it points to the 13 right place?

14 MEMBER CORRADINI: I was able to download 15 the report.

16 MEMBER BLEY: So, you've seen it?

17 MEMBER CORRADINI: I 've seen it. I 18 haven't read it, I had other homework.

19 CHAIR MARCH-LEUBA: All I know is the last 20 time I saw it, I saw the cover page and they told me 21 they couldn't give it to me.

22 MEMBER CORRADINI: We've got it.

23 MR. BRISTOL: Okay, I think that concludes 24 the transient portion of the presentation. We're 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 182 going to go into the radiological doses next.

1 MR. INFANGER: This is Paul Infanger.

2 CHAIR MARCH-LEUBA: Before you start, is 3 this going to be similar to what we've done with the 4 LOCA and non-LOCA methodology?

5 Because there is a source term methodology 6 topical report that hasn't been reviewed yet.

7 MR. INFANGER: Right, and we're not going 8 to get into the topical report.

9 CHAIR MARCH-LEUBA: You're using the 10 results of that report assuming it gets approved?

11 MR. INFANGER: That's correct.

12 CHAIR MARCH-LEUBA: Is that what you're 13 doing now?

14 MR. INFANGER: That's correct. Okay, so 15 the radiological analysis, we used the standard 16 radiological dose consequences that are used in the 17 industry. We used Reg Guide 1.183 and we used that 18 for the acceptance criteria.

19 And if you look at the events, this is 20 right out of the guidance, and they talk about lost 21 coolant, accidents, fuel-handling accidents, rod 22 ejection accident. But the acceptance criteria is due 23 to damaged fuel.

24 However, in our events only fuel-handling 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 183 accidents resulted in damaged fuel. We don't have 1 fuel damage in any of our other accidents.

2 The first three reactor loss of coolants, 3 fuel-handling accidents and rod ejection accident, 4 they talk about the radiation source being damaged 5 fuel. That's for the acceptance criteria.

6 But if it's a NuScale reactor, we don't 7 have any accidents of damaged fuel except the fuel-8 handling accident where it's assumed. And all of our 9 other events we use coolant activity, RCS activity 10 with iodine spiking as the source term.

11 DR. SCHULTZ: Paul, for the pre-incident 12 spike, what do you assume for the coolant activity?

13 What percentage of fuel failure do you have?

14 I've seen a couple of different numbers 15 related to that.

16 MEMBER CORRADINI: You're looking at a 17 fraction of fuel damage?

18 DR. SCHULTZ: It's the pre-incident spike, 19 yes. I presume that it's related to your technical 20 specification?

21 MR. INFANGER: We used the tech spec limit 22 for the initial coolant but then you have an iodine 23 spike on top of that, on top of the RCS allowable 24 load. 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 184 DR. SCHULTZ: Okay, thank you.

1 MR. INFANGER: Okay, so for the 2 radiological consequences analysis using the 3 alternative source terms, we used essentially the same 4 recommendations in Reg Guide 1.183 to evaluate the 5 consequences of our design basis event, which is the 6 iodine spiking event, and also, a beyond-design-basis 7 core damage event.

8 And that's described in detail in the 9 accident source term topical report. For feedwater 10 line break, we reviewed it and found that the steam 11 line break had more limiting consequences so we used 12 that as a bounding event and didn't do a separate 13 feedwater line break dose analysis.

14 We also looked at the reactor pool 15 boiling, a very large reactor pool, and so Staff had 16 requested us to look at what happens if you had an 17 event where you had long-term boil off of that?

18 And we found that there's a small amount 19 of tritium in that water from refueling and things 20 like that, and we found that the dose was 21 insignificant.

22 We looked at potential shine to the 23 control room operators so if you're having an event in 24 the reactor building, there is potential for some 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 185 reactivity shine into the control room.

1 And that was found also to have no impact 2 on total dose, or very small.

3 DR. SCHULTZ:

Is that because of the 4 shielding that you have around the control room?

5 (Simultaneous Speaking.)

6 MR. INFANGER: Yes, the wall's very thick, 7 a lot of concrete between the reactor building and the 8 control room.

9 DR. SCHULTZ: And the control room dose is 10 the higher evaluation that you've got in the dose 11 evaluation.

12 What did you assume for in-leakage to the 13 control room, either from egress or from unfiltered 14 in-leaking to the control room?

15 MR. INFANGER: I believe it was 10 cfm.

16 I'll have to check on that. Does anyone back in 17 Corvallis have the in-leakage used in the control room 18 dose? 19 I think that's actually in Chapter 6.4 but 20 Corvallis, are you on the line? I don't know if we 21 have anybody. There's another meeting right now, 22 unfortunately. Our rad protection guys are at another 23 meeting --

24 MEMBER CORRADINI: You can come back to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 186 us. 1 MR. INFANGER: We'll get back to you.

2 MEMBER CORRADINI: I would appreciate 3 that. 4 PARTICIPANT: Paul, we can have that in a 5 minute. 6 MR. INFANGER: Thank you. Okay, and of 7 course, the conclusion is that the doses are 8 acceptable for all the events. We used fairly 9 standard industry computer codes to calculate the dose 10 consequences.

11 We used SCALE, TRITON, and ORIGEN for the 12 types and quantities of radioactive isotopes. We used 13 NRELAP to define the thermal hydraulic conditions for 14 the events and the steam line break.

15 For beyond-design-basis events, we used 16 MELCOR to calculate a core damage event. The one 17 thing they did a little different than in other sites 18 is we used ARCON96 to calculate the dose for the EPZ 19 and site boundary.

20 And we did that because the site is so 21 much smaller than other sites, so the industry 22 standard code is put on and that works well for longer 23 distances.

24 But the ARCON is better utilized for short 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 187 distances. And so since our site is so small, ARCON96 1 is used frequently for control room dose and we use it 2 also for our safe boundary dose.

3 We used RADTRAD to calculate the 4 radionuclide transports. STARNAUA was used for 5 aerosol removal in containment.

6 We also used a NuScale-specific code, pHT, 7 to calculate the containment pH, which is important 8 for iodine, the evolution. And then we used MCNP for 9 valuing the shine potential.

10 CHAIR MARCH-LEUBA: You said containment 11 pH?12 MR. INFANGER: Yes.

13 CHAIR MARCH-LEUBA: What is that a 14 function of?

15 MR. INFANGER: Just the chemistry of the 16 RCS, boron and --

17 CHAIR MARCH-LEUBA: I would assume that 18 you have that -- were controlling the RCS before you 19 start so how does it evolve? Unless you start to make 20 a lot of hydrogen and things like that.

21 Never mind, I'm just curious.

22 MR. INFANGER: This is about NuScale pHT?

23 CHAIR MARCH-LEUBA: Yes, why is the pH 24 varying during the event? I'm just curious.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 188 MEMBER CORRADINI: He'll satisfy your 1 curiosity later.

2 MR. INFANGER: Yes, we'll skip that and 3 return to it shortly.

4 CHAIR MARCH-LEUBA: Don't change the 5 slides, I still have another question. Another 6 curiosity, in SCALE 6.1 TRITON, your design cross-7 sections are CASMO-5.

8 So, did you actually run a whole depletion 9 calculation for your fuel with TRITON? I mean, it's 10 a lot of work when you already have it done with 11 CASMO. 12 Is that because ORIGEN is incompatible 13 with CASMO cross-section? Are you going to convert 14 them, or you don't know?

15 MR. INFANGER: No, I'm not aware.

16 CHAIR MARCH-LEUBA: I know people are not 17 using TRITON anymore because it's a big amount of 18 work. You need the whole depletion for so many fuel 19 segments.

20 So, if you truly did that, you did a lot 21 of work that you didn't need to do because you already 22 have the CASMO cross-sections. So, you can find out?

23 MR. INFANGER: Yes.

24 CHAIR MARCH-LEUBA: It's not a minor 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 189 activity.

1 MR. INFANGER: Okay, the accident source 2 term topical report, the number is listed there. It 3 talks about the various sample calculations for each 4 of the events.

5 The FSAR has the actual events that we 6 analyze for DCA, with our sample calculations in the 7 topical report. As far as using Reg Guide 1.183, we 8 deviated from it and in most cases it was for Appendix 9 C and D are related to BWRs and Appendix G is locked 10 rotor. 11 Since we don't have reactor coolant pumps 12 there is no such event. So, we didn't use those 13 sections because they're not applicable to our design.

14 We used Reg Guide 1.183's iodine spiking assumptions 15 and decontamination factors for fuel-handling 16 accidents.

17 We only credited it 23 feet of water even 18 though the pool was much deeper than that. We did 19 iodine removal in the secondary piping or the 20 condenser.

21 Thermal hydraulic response due to the rod 22 ejection accident shows that there was no fuel damage 23 so we did not calculate a dose from the fuel-handling 24 accident. It would just be handled just with the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 190 generic evaluation of RCS --

1 DR. SCHULTZ: Bounded by the other events.

2 MR. INFANGER: We used ARCON96 atmospheric 3 dispersion methodology for the short distances to the 4 EAB and LPZ. And we used RADTRAD and modeling 5 techniques consistent with the Reg Guide.

6 So, again, the AST topical accident source 7 term topical report has the methodology. There was an 8 NEI position paper for small modular reactors, 9 investigating some of the uniqueness of the small 10 cores and information on that related to that.

11 I'll use B, spectrum of accidents from 12 MELCOR, surrogate accident scenarios. So, we used 13 MELCOR to simulate the core damage event and that was 14 used a lot also for the PRA.

15 ARCON96 dispersion methodology was used, 16 RADTRAD modeling techniques. And they're now used 17 for the aerosols and pHT.

18 We showed this slide before and this is a 19 summary of the doses. And if you look at the iodine 20 spike design basis source term, the offsite dose is 21 very, very low, less than 0.01.

22 The core damage event, again, is a beyond 23 design basis event since none of our accidents 24 involved core damage. But even those are well within 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 191 the limits.

1 CHAIR MARCH-LEUBA: Paul, may I ask if the 2 CR means control room?

3 MR. INFANGER: Yes.

4 CHAIR MARCH-LEUBA: So, this calculation, 5 does it assume the compressed air system doesn't work?

6 MR. INFANGER: No, this assumes the 7 compressed air system functions.

8 CHAIR MARCH-LEUBA: And how does the 9 radioactivity get into the control room?

10 MR. INFANGER: In-leakage.

11 CHAIR MARCH-LEUBA: Even though it's high 12 pressure?13 MEMBER CORRADINI: That's what I assumed.

14 CHAIR MARCH-LEUBA: How does it physically 15 happen?16 MEMBER CORRADINI: I don't want to answer.

17 I guessed the answer but I don't know.

18 MR. INFANGER: We'll get the number but I 19 think there's a small a mount of in-leakage from 20 ingress and egress.

21 CHAIR MARCH-LEUBA: Every time you open 22 the door?23 MR. INFANGER: Yes.

24 CHAIR MARCH-LEUBA: So, it's an assumption 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 192 of how many times you open the window?

1 MEMBER CORRADINI: It's an assumed number.

2 MR. INFANGER: It's an assumed number.

3 CHAIR MARCH-LEUBA: So, it has a large 4 uncertainty, very large uncertainty?

5 DR. SCHULTZ: That's included in that. It 6 also depends on whether you're filtering intake air.

7 MR. INFANGER: Initially, we use air 8 bottles to pressurize the control room and after 72 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> we would go to filtered air.

10 DR. SCHULTZ: And then you have to take 11 consideration of the filters?

12 MR. INFANGER: Right, and the dose 13 analysis is done for 30 days for the control room.

14 CHAIR MARCH-LEUBA: So this is for 30 15 days?16 MR. INFANGER: 30 days.

17 CHAIR MARCH-LEUBA: Okay, so the --

18 (Simultaneous Speaking.)

19 MR. INFANGER: The bottles run out after 20 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.

21 CHAIR MARCH-LEUBA: Okay, so this is the 22 effectiveness of your HEPA filters?

23 MR. INFANGER: Yes.

24 MR. PRESSON: And I would like to bring in 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 193 Kenny Anderson from Corvallis to answer a couple of 1 these questions, specifically TRITON.

2 MEMBER CORRADINI: Is he going to be 3 online or are you going to tell us?

4 MR. PRESSON: Online.

5 MR. ANDERSON: This is Kenny.

6 MEMBER CORRADINI: Go ahead.

7 MR. ANDERSON: This is Kenny Anderson with 8 Corvallis.

9 In regards to the question what is TRITON 10 used for, it calculates the microscopic cross-section, 11 that's been said, it calculates macroscopic cross-12 sections similar to the ORIGEN tool and the SCALE 13 package.

14 And then that sets the initial inventory 15 for the core and then that inventory is used with the 16 right processing to get the initial inventory into the 17 RADTRAD models or the other models to eventually 18 calculate the dose or the pH.

19 CHAIR MARCH-LEUBA: My comment was that 20 you already had validated design cross-section sets 21 generated by CASMO-5. And by running TRITON you're 22 reproducing the same numbers that you already have.

23 And my experience, because I used to sit 24 across from the guy that used to do the work, it's a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 194 lot of work to do a cycle depletion with TRITON. So, 1 when did you do the work and who did it?

2 MR. ANDERSON: Each time we do an FSAR 3 revision we redo it.

4 CHAIR MARCH-LEUBA: So you do it in house?

5 MR. ANDERSON: Yes, we commercially grade 6 dedicated the components of the SCALE package that we 7 use and I agree, you could use CASMO-5 to simulate the 8 calculation but there are pros and cons associated 9 with that.

10 We thought SCALE is the right tool for the 11 right job.

12 CHAIR MARCH-LEUBA: Well, it gives you a 13 direct plug-in to ORIGEN so I understand it. But my 14 comment was I was surprised because it's a lot of 15 work. But if you know what you're talking about, I'm 16 happy. 17 Thank you very much.

18 MR. INFANGER: And Ken, could you talk a 19 little bit about what we use the pHT program for?

20 MR. ANDERSON: Yes, that takes in the 21 total acids and bases and shows generally a basic 22 solution which as long as you're above a certain 23 threshold, you can prove that there will be no iodine 24 re-evolution.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 195 The iodine that's in the water won't come 1 from out of solution into the air space, which would 2 then be eligible to be released. If there was iodine, 3 we have to assume you'd have higher doses.

4 CHAIR MARCH-LEUBA: Yes, I understand that 5 but what would change the pH inside the vessel after 6 an accident? What are the input parameters you put to 7 give to the code?

8 MR. ANDERSON: The initial acid that is 9 released from the fuel and the fuel's damage, that's 10 postulated and then as radiolysis occurs, that's going 11 to be an acid contribution.

12 And then you take credit for the bases 13 that are appropriate and you do the chemistry balance 14 and get the final pH.

15 CHAIR MARCH-LEUBA: Okay, so mostly it 16 releases from the fuel, which are chemical components, 17 and radiolysis. Thank you very much.

18 DR. SCHULTZ: Kenny, we talked about this 19 a little earlier, the shine dose, the way it's 20 presented in a couple of documents is there just isn't 21 any shine dose.

22 And I'm surprised with regards to the LOCA 23 event and the fuel-handling accident that there's no 24 shine dose to the control room. Can you describe why 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 196 that would be?

1 Is there just sufficient shielding so that 2 you don't calculate a shine dose?

3 MR. ANDERSON: We do have generic shine 4 doses. We take the worst event and we calculate shine 5 doses to the control room.

6 There's a few different mechanisms where 7 the shine can reach the control room, and then we just 8 apply that to each event. So, that's real 9 conservative.

10 DR. SCHULTZ: Okay, that's more of what I 11 would have expected. So, there is some but it doesn't 12 increase the calculated dose from the other components 13 of release to an extent that it really makes much 14 difference.

15 Is that what you're saying? That's why 16 you use a generic value or a maximum value?

17 MR. ANDERSON: Yes.

18 DR. SCHULTZ: Okay, thank you.

19 MR. PRESSON: And Table 15.0-15 contains 20 some of the information on in-leakage. It looks like 21 around 150 cfm.

22 CHAIR MARCH-LEUBA: I misunderstood. I 23 thought that was not for 30 days but for 3 days.

24 MR. INFANGER: Okay, and with that, the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 197 next section is on the containment response analysis.

1 Megan's going to address that.

2 MS. McCLOSKEY: Okay, so as was discussed 3 yesterday afternoon in the overview of Chapter 6, the 4 containment is designed to withstand the full spectrum 5 of primary and secondary system, mass and energy 6 releases, accounting for the worst-case single failure 7 and considering loss of power scenarios.

8 And the NuScale methodology for analyzing 9 the containment response is based on NRELAP5 and it's 10 described in our technical report. We are --

11 CHAIR MARCH-LEUBA: For those of us that 12 memorize numbers, is that the LOCA report?

13 MS. McCLOSKEY: No, that's the containment 14 response technical report.

15 CHAIR MARCH-LEUBA: It's a different, 16 third report?

17 MS. McCLOSKEY: Yes.

18 CHAIR MARCH-LEUBA: Thank you. Have we 19 seen that one?

20 MEMBER CORRADINI: It's with Chapter 6.

21 MS. McCLOSKEY: It's with Chapter 6, it's 22 referenced in Chapter 6.

23 MEMBER CORRADINI: The results are in 24 Chapter 6.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 198 MS. McCLOSKEY: The results are summarized 1 in a table in Chapter 6.

2 MEMBER CORRADINI: Right.

3 MS. McCLOSKEY: And then they're presented 4 and discussed in more detail along with the 5 methodology for biasing the initial in-boundary 6 conditions in the technical report.

7 And so due to the design of the module 8 with the small high-pressure containment and the ECCS 9 valve opening, we are using NRELAP5 for calculating 10 the mass and energy releases from the RPV and the 11 containment pressurization response as an integrated 12 model. 13 The limiting event scenarios that are 14 addressed, on the primary side we are examining LOCA 15 pipe-breaks in the CVCS discharge and injection lines 16 and the pressurizer high-point vent line. So, two 17 liquid space cases and then the vapor space break.

18 We also are considering the valve opening 19 events for an inadvertent recirc valve opening or vent 20 valve opening.

21 On the secondary side, we look at the main 22 steam line breaks and the feedwater line breaks in 23 site containment.

24 The qualification of the NRELAP5 code for 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 199 these analyses is based on the qualification and the 1 plant modeling approach that's described in the LOCA 2 and the non-LOCA topical reports for the primary and 3 the secondary-side events respectively.

4 And this report was used because the 5 containment pressure response was considered as a 6 figure of merit from the PIRT development in both of 7 these Ems.

8 And in particular, since the primary-side 9 release events are limiting, the LOCA EM identified 10 high-ranked phenomena that are important for 11 predicting the containment response.

12 So, again, the response is based on the 13 models from those -- developed from the methodologies 14 from those topical reports.

15 But we are biasing the initial and the 16 boundary conditions used in the models in order to 17 bias the mass and energy release and maximize the 18 containment pressure and temperature response as 19 opposed to addressing the critical heat flux or level 20 acceptance criteria that are addressed in the LOCA 21 topical report.

22 For the event analyses, we're applying the 23 maximum break sizes or valve sizes in order to 24 maximize the mass and energy release to the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 200 containment.

1 In the limiting-condition cases, the peak 2 pressure occurs after ECCS valve opening and so, as 3 was alluded to earlier, the peak pressure is a little 4 bit of a balance between how much volume you have 5 remaining in containment versus the energy still in 6 the RCS at the time the ECCS valves open.

7 This slide summarizes the results of the 8 containment analysis result. In the black or the 9 orange font are the limiting case for each of the 10 break or valve opening cases considered.

11 Grey are the base cases from the 12 containment pressure analysis. So, the difference 13 between the two considers effects of single failures, 14 primarily the effects of single failures and power 15 availability.

16 The initial conditions are biased 17 consistently and then the containment acceptance 18 criteria are shown at the bottom.

19 Our limiting event is the inadvertent RRV 20 opening event with a maximum pressure of 986 psia.

21 Compared to the base case, there's about a 45 PSI 22 delta to the base case in that scenario.

23 That's our largest liquid space discharge 24 event so you get an ECCS valve opening relatively 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 201 early in the transient.

1 And that can be distinguished against the 2 RCS discharge line break scenario that's up at the top 3 here, where the base case assumes all power is 4 available so ECCS actuates on high containment level.

5 And therefore, it's more than 1000 seconds 6 into the event before the ECCS valves open. And that 7 allows some cooling through the containment wall 8 before the valves open and the peak pressure occurs.

9 CHAIR MARCH-LEUBA: Remind me, what's the 10 limit for the CMV pressure?

11 MS. McCLOSKEY: It's 1050 PSI here.

12 CHAIR MARCH-LEUBA: That's what I thought.

13 So this is close.

14 MEMBER CORRADINI: There was a change to 15 that. You went from some value to 1050. Has that 16 been reviewed and accepted by Staff?

17 MS. McCLOSKEY: We went from 1000 PSI to 18 1050 PSI and that was submitted to the Staff towards 19 the end of last year.

20 MEMBER CORRADINI: So, that's under review 21 and has been accepted?

22 MS. McCLOSKEY: Sorry?

23 MEMBER CORRADINI: It's been reviewed and 24 accepted?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 202 MS. McCLOSKEY: Yes, for the SER.

1 CHAIR MARCH-LEUBA: There are calculations 2 that you satisfy the ASME code at the extra 50 PSI, 3 correct?4 MS. McCLOSKEY: Mm-hmm.

5 CHAIR MARCH-LEUBA: And you will have to 6 do the hydraulic pressure and everything at this 7 pressure? All the testing?

8 MS. McCLOSKEY: Yes.

9 CHAIR MARCH-LEUBA: You didn't have to 10 make a change on this side? You're convinced that you 11 have sufficient margin?

12 MS. McCLOSKEY: No, it was an analysis 13 change. 14 CHAIR MARCH-LEUBA: I'm always worried 15 when I see a result that is that close to the limit 16 and every single plant has it on other pressure 17 events. So, I will wait until two slides from now to 18 ask you the question.

19 MS. McCLOSKEY: Okay.

20 MEMBER CORRADINI: Can I ask a different 21 question? I know we're now creeping into another time 22 window, but the peak pressure at 986 versus 941, are 23 the conservatisms that were assumed to go to limiting 24 case, is there one particular one or are there a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 203 series of --

1 MS. McCLOSKEY: The primary change there 2 is the loss of power assumption, which affects the 3 timing of the ECCS valve opening.

4 MEMBER CORRADINI: Okay.

5 MS. McCLOSKEY: And then the limiting wall 6 temperature case is the injection line break case that 7 is a break from the hot leg condition.

8 The next several slides have results of 9 the limiting pressure case for the inadvertent opening 10 of the RRV. We assume loss of AC and EDSS DC power at 11 the event initiation.

12 We assume a single failure of the 13 remaining RRV to open, which forces all of the -- when 14 the ECCS valves open, it all has to vent through one 15 RRV or the vent valves, which maximizes the energy 16 release to containment with the ECCS valve opening.

17 The low bias IAB opening is assumed. We 18 accounted for a fast release of non-condensable gas 19 into containment to account for non-condensable gas 20 that might be present as dissolved in the RCS fluid or 21 in the pressurizer.

22 Per the methodology, there's no credit for 23 DHRS operation so with the loss of DC power you get a 24 relatively early opening of the ECCS valves about a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 204 minute after the event.

1 And then the peak containment pressure 2 occurs shortly thereafter, but it's rapidly decreased 3 to below 50 percent.

4 CHAIR MARCH-LEUBA: Here is where I want 5 to ask the questions.

6 MS. McCLOSKEY: Okay.

7 CHAIR MARCH-LEUBA: If you look at the top 8 left, which is the pressure, and you concentrate on 9 the high times, you see an ISDK which, to me, that's 10 the condensation of the steam on the vessel wall, 11 containment wall.

12 Is that your understanding too?

13 MS. McCLOSKEY: Yes, and what you see in 14 the plot on the lower right are several of the energy 15 balance terms and it's a little hard to read in here.

16 But I want to clarify here that the 17 containment heat removal shown on this plot is the 18 heat removal to the reactor pool, and that's this red 19 line here. That's when the energy gets all the way 20 out to the reactor pool.

21 The total energy transfer from the break 22 from the ECCS valves is this pink line that's coming 23 down here. So, it does take 200 seconds before heat 24 removal to the reactor pool is established, and it's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 205 well after the peak occurs.

1 That peak is turned around by the 2 condensation on the inside of the wall and the 3 absorption into the metal.

4 CHAIR MARCH-LEUBA: And there is on the 5 top left a very nice inflection point at 100 seconds.

6 MS. McCLOSKEY: That's the ECCS valve 7 opening. 8 CHAIR MARCH-LEUBA: And there is another 9 inflection point around 400 PSI. My suspicion is the 10 first decreased rate is one ECCS valve dumping steam, 11 then right where you have your mouse, all the ECCS 12 valves start dumping.

13 And at that point you've run out of 14 inventory. You're dump everything you can dump and 15 now you start cooling.

16 MS. McCLOSKEY: You dump everything you 17 can dump and you can see the RCS pressure comes down 18 accordingly.

19 CHAIR MARCH-LEUBA: There's only steam 20 inside the vessel.

21 MS. McCLOSKEY: Yes. So, we don't lose 22 all of the inventory from the RCS, there's a 23 significant amount of inventory that remains --

24 CHAIR MARCH-LEUBA: You start boiling it 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 206 off. 1 MS. McCLOSKEY: It flashes, it becomes 2 saturated, and you establish recirculation through the 3 recirculation valves.

4 CHAIR MARCH-LEUBA: Roughly at 200 5 seconds, if you look at the bottom left, you have a 6 net, not loss. And what comes in equals what comes 7 out because this is the sum of the break plus the --

8 (Simultaneous Speaking.)

9 Now, if you had had higher inventory in 10 the pressurizer, would that peak inflection point on 11 the top one, would it be a little higher? If you had 12 more inventory to lose?

13 MS. McCLOSKEY: We've biased the inventory 14 high to the high-end of the normal operating --

15 CHAIR MARCH-LEUBA: This is already --

16 (Simultaneous Speaking.)

17 MS. McCLOSKEY: Yes.

18 CHAIR MARCH-LEUBA: This is fully closed.

19 Okay, good enough.

20 MS. McCLOSKEY: I think that covers the 21 points on that slide.

22 MEMBER CORRADINI: Maybe I don't remember.

23 The one thing was the biased high pressurizer level.

24 Are you starting with a vacuum?

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 207 MS. McCLOSKEY: Yes, at three psia --

1 (Simultaneous Speaking.)

2 MEMBER CORRADINI: There was a discussion 3 between you and the Staff about 65 lost pounds of air.

4 I want to understand where that was. There were non-5 condensables that were asked about, do you know what 6 I'm talking about?

7 MS. McCLOSKEY: Yes, we account for the 8 non-condensables both initially present in containment 9 to give you that 3 psia and that are maybe present in 10 the pressurizer vapor space or dissolved in the RCS.

11 MEMBER CORRADINI: So, is this a corrected 12 calculation with the additional 65 pounds?

13 MS. McCLOSKEY: Yes.

14 MEMBER CORRADINI: And the source of the 15 65 pounds was internal to the RCS or external inside 16 the containment? That's what I couldn't understand.

17 MS. McCLOSKEY: Internal to the RCS.

18 MEMBER CORRADINI: And what came out, a 19 solution?20 MS. McCLOSKEY: Yes.

21 PARTICIPANT: And what's in the 22 pressurizer?

23 MS. McCLOSKEY: Yes.

24 MEMBER CORRADINI: Okay, thank you.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 208 CHAIR MARCH-LEUBA: Because if it was in 1 containment it wouldn't be operating. It would be --

2 MEMBER CORRADINI: 65 pounds is not a lot.

3 I'm not sure, one PSI is how many pounds in your 4 containment? I was going to calculate that but --

5 (Simultaneous speaking.)

6 MS. McCLOSKEY: The 3 PSI is on the order 7 of 60 to 65 pounds. So, it happens to be about equal 8 to what we get from the RCS as well.

9 CHAIR MARCH-LEUBA: Well, my brain is 10 telling me is that somebody designed the size of the 11 containment five years ago and we are really lucky 12 because he was right in the know.

13 Or we've been losing margins since then.

14 I'm sure you don't design your containment that close 15 to limits. Probably you'll be losing margin.

16 MEMBER CORRADINI: I don't know, there's 17 an awful lot of dries that are awful close.

18 MS. McCLOSKEY: And I've got two slides 19 where we look at some of the other margins that aren't 20 accounted for in that 986 number.

21 CHAIR MARCH-LEUBA: This is not unusual.

22 You look at all the hours of pressure and every single 23 BWR, they have less margin than you do.

24 Because if they hit the limit, they 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 209 sharpen the pencil and do a new calculation which is 1 more accurate until he goes under.

2 MS. McCLOSKEY: The containment is very 3 effective at removing energy after the initial blow-4 down. 5 So, in this case, by about half an hour 6 into the event, we've reduced the pressure to below 50 7 percent of the design limit that's well within the 24 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> expected to support the radiological analyses.

9 And in terms of the long-term cooling, 10 we'd refer to the long-term cooling technical report 11 to demonstrate continued effective decay and residual 12 heat removal.

13 And finally, in terms of the margin 14 assessments, the maximum pressure has less than ten 15 percent margin to the acceptance criteria, which is 16 guidance from the DSRS.

17 Additional factors that are not accounted 18 for in that 986 number that would provide additional 19 margin are both accounting for the external pressures 20 in the assessment and crediting some degree of heat 21 removal from the DHRS.

22 This maximum pressure is taken at the 23 bottom of the containment and it's conservatively 24 evaluated assuming an external pressure of 0 psia that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 210 doesn't account for atmospheric pressure or the pool 1 hydrostatic head.

2 It would provide about 22 PSI additional 3 margin. The evaluation model also doesn't credit the 4 single- failure-proof safety-related decay heat 5 removal system that would be actuated.

6 We have some sensitivity calculations 7 indicating about 37 PSI additional margin could be 8 obtained but we've not pursued that due to the 9 additional validations of NRELAP5 that would be 10 required under these scenarios.

11 So, overall, our conclusion is that our 12 analysis provides assurance that we provide sufficient 13 margins to satisfy the requirements of GDC16 and 50.

14 MEMBER CORRADINI: Can I suggest a break?

15 MS. McCLOSKEY: Yes.

16 MEMBER CORRADINI: Please? Can we take a 17 break until about 3:35 p.m.?

18 (Whereupon, the above-entitled matter 19 went off the record at 3:23 p.m. and 20 resumed at 3:35 p.m.)

21 MEMBER CORRADINI: So let's get back into 22 session. So, Ben, we'll turn it back to you.

23 MR. BRISTOL: Okay, thank you. So the 24 next topic we're going to cover here is long-term 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 211 cooling. And just to sort of set the expectation, 1 what we're trying to cover here is the scope that was 2 defined in the long-term coolant technical report. So 3 this isn't a full, comprehensive list of all of the 4 issues related to the extended ECCS operation or even 5 the HR operation, but we'll get into those a little 6 bit later. I think we're prepared to address most of 7 them.8 So as I mentioned, specifically we're 9 looking at demonstrating that post-LOCA ECCS kind of 10 performance acceptance criteria maintaining coolable 11 geometry and demonstrating ample cooling via ECCS. In 12 addition, a couple other DSRS-specific considerations.

13 So in terms of acceptance criteria, 14 there's primarily two that we're looking at in term s 15 of this analysis scope, one being that core cooling is 16 maintained and that is evaluated via acceptance 17 criteria of collapsed liquid level, keeping the core 18 covered.19 In addition, cladding temperature is 20 evaluated as part of the analysis. And then 21 specifically, something a little different is that 22 coolable geometry is maintained, and that's evaluated 23 through demonstrating boron precipitation limits are 24 not exceeded.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 212 So in terms of the technical reports, 1 RELAP is used to evaluate the integral response to 2 decay heat removal paths from ECCS and containment 3 heat transfer to the pool.

4 A point of, again, scope: recriticality 5 is not analyzed as part of this analysis, so design 6 basis decay heat or the design base is shut down 7 condition is assumed, that overcooling analysis we'll 8 actually get into in the next presentation. It's 9 otherwise presented in the SR.

10 CHAIR MARCH-LEUBA: So you mean long 11 cooling under decay heat conditions?

12 MR. BRISTOL: Under decay heat conditions, 13 that's right.

14 So in terms of development of the 15 evaluation approach, PIRT was used, addressing ECCS 16 cooling conditions and within evaluation of long-term 17 cooling PIRT phenomena. The LOCA EM is used as a sort 18 of initial validation source. Much of the phenomena 19 is addressed as part of that analysis.

20 In other places, bounding analytical 21 techniques via inputs or methodology are assumed.

22 We'll address a couple of those.

23 In addition, there were a couple of 24 assessments that were specifically set up using the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 213 NIST facility --

1 MEMBER CORRADINI: We'll talk about those 2 in closed session. This kind of goes back to my 3 question about something out of 15.02, and RELAP's 4 ability to model these tests versus what I'd see at 5 full scale.

6 So are we going to discuss these -- we're 7 not going to discuss these now, I would assume.

8 MS. MCCLOSKEY: No, we're not going to 9 discuss them now, and --

10 MEMBER CORRADINI: Otherwise I'll just 11 wait and ask the staff tomorrow. I want to get to --

12 because staff had some comments about RELAP's ability 13 to calculate what they saw in these relative to 14 consistency in calculation for the full scale, and I 15 want to address it. I just don't know where to do it.

16 MS. MCCLOSKEY: I think we'll hear the 17 questions in closed session, and then --

18 MEMBER CORRADINI: Okay. Fine.

19 MS. MCCLOSKEY: -- try to get that one 20 too.21 MEMBER CORRADINI: All right.

22 MS. MCCLOSKEY: That's the way to respond 23 to this.24 MEMBER CORRADINI: Okay.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 214 MR. BRISTOL: So just finally in terms of 1 qualification, the qualification inclusions from LOCA 2 EM are used for evaluating the LOCA-type initiating 3 events, and then the non-LOCA EM is leverage for the 4 non-LOCA DHRS events that then transition.

5 All of the event types are considered as 6 part of the LTC technical report. All of the events 7 that end up in ECCS mode in terms of what's presented 8 in the technical report.

9 Okay. So just a couple of details on the 10 precipitation analysis. It's a simple volume mixing 11 approach. There's no time dependence; what we mean by 12 that is that the boron redistributes as part of ECCS 13 actuation.

14 That way, that redistribution and any of 15 the boron that goes into containment provides would be 16 non-conservative, so it's assumed that essentially the 17 thermohydraulic transient is evaluated assuming that 18 the core and lower riser region contain all of the 19 initial boron mass from the start of the event.

20 In fact, the actual mass that's used is 21 the bounding sort of startup condition. So for 22 conservatism, the precipitation temperatures are 23 evaluated against the maximum allowable boron mass 24 with no credit for any of the redistribution 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 215 mechanisms or potential loss mechanisms.

1 So in terms of the analysis scope, we look 2 at a spectrum of the LOCA Break spectrum, including, 3 in addition to the inadvertent opening of the RRV or 4 RVV. Those are evaluated out through the longer term.

5 As part of the way the analyses are 6 performed, there's a simplified model; I'm going to 7 get into that in the next slide, but the calculations 8 are set up from the start of the event, and then to 9 ensure that the boundary conditions are effectively 10 transferred.

11 So instead of transferring them, we 12 actually do comparisons of the full EM models versus 13 the simplified model to demonstrate that we're 14 capturing the transient correctly such that the point 15 that we distinguish the onset of long-term cooling is 16 starting from the correct initial conditions.

17 As part of the transient scope, we look 18 for -- it's about a 12-and-a-half-hour period that the 19 transient calculations are performed. Beyond that, a 20 state point method is used, and we'll discuss the 21 basis for that.

22 Simply put, the transient phase or 23 transient progression has recovered within the 12-hour 24 window such that what we're looking for beyond the 12-25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 216 hour0.0025 days <br />0.06 hours <br />3.571429e-4 weeks <br />8.2188e-5 months <br /> time frame is simply just limiting temperature 1 conditions. That's where the state point analysis can 2 give us a conservative result.

3 MEMBER CORRADINI: So maybe this is 4 getting ahead, but do these include the results in 5 terms of your response in RA8930, or is this prior to 6 this?7 MR. BRISTOL: No. We'll get into the 8930 8 topic in the closed session.

9 MEMBER CORRADINI: Okay. Fine.

10 MR. BRISTOL: So we essentially have three 11 cases that we're kind of looking for in terms of the 12 way the models are biased. The biases for minimum 13 level are a little about different than minimum 14 temperature. And then a more traditional sort of ECCS 15 performance analysis, looking at maximum temperature 16 is also evaluated.

17 It turns out maximum temperature cases are 18 non-limiting or minimum cool-down cases are non-19 limiting for either the precipitation analysis or the 20 minimum-level analysis, and that has to do with the 21 vapor pressures that are reached and their effect on 22 ECCS performance.

23 So just a summary of the results here:

24 minimum level analysis confirms that the core remains 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 217 covered, and the minimum temperature analysis confirms 1 that precipitation limits are not reached.

2 The maximum temperature analysis just 3 shows that we have a trend that's successful from a 4 cladding perspective.

5 So what we've got in the figure here is 6 100 percent injection line break as compared to the 7 more limiting LOCA SAL break. The five percent and 8 sort of slower break. We see here that the definition 9 of the onset of long-term cooling for the larger break 10 is after the equilibrium conditions are reached, which 11 is right about here for the larger break.

12 For the smaller break, it's actually this 13 scope all the way up to the -- this dip is due to the 14 ECCS actuation itself. In three of the recovery 15 phase, this is what we consider in the LOCA 16 methodology, and so the long-term cooling then picks 17 up from there.

18 And so from kind of a phenomena 19 perspective, we have two different things going on.

20 There's depressurization-driven ECCS kind of capacity 21 minimum level that we get through here. You see a 22 little bit of it in this response here as well.

23 That's driven by the maximizing 24 containment cooling, which minimizes the vapor 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 218 pressure and containment and maximizing the stored 1 energy and decay heat in the RCS, which maximizes the 2 pressure in the RCS to maximize the differential 3 pressure across the vent valve. And that's what 4 really drives our long-term cooling minimum levels 5 phenomenon.

6 MEMBER CORRADINI: Say that again slow.

7 MR. BRISTOL: So because it's a manometer 8 problem --

9 MEMBER CORRADINI: Sure.

10 MR. BRISTOL: -- we want to maximize the 11 deep heat in the vent space, and that's going to 12 establish the actual equilibrium condition in the 13 liquid space. Does that make sense?

14 So the deep heat across the vent valve, 15 that's the flow-driven DP. The flow through the reset 16 valve is very, very, very small, very low DP. So head 17 is what's driving flow backward.

18 If my DP across my vent valve, my steam 19 flow rate is too small, I'll continue to accumulate 20 level in the containment, but now allow it to 21 recirculate back into the RPB.

22 So what we want to maximize is the 23 containment heat removal, which draws the vapor 24 pressure down on the containment side, but the vapor 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 219 generation rate on the RCS side. And that maximizes 1 the flow capacity that's required for the vent valves.

2 And these are all evaluated with one train 3 of ECCS assumed failed, which is really the only way 4 we ever see this thermohydraulic transient response.

5 So in conclusion, I think I covered that 6 in these couple of bullets here. The summary is that 7 once decay heat begins to drop, and it's a combination 8 of decay heat and the stored energy in the system, the 9 level starts to recover the DP, the demand across the 10 vent valves continues to drop, and we see a level 11 recovery. That gives us the confidence that we can 12 kind of switch analytical techniques; we don't need to 13 continue running RELAP through these really kind of 14 slow transient progressions or calculations.

15 So here's just a couple more figures 16 describing the difference in the two events. Unless 17 there's specific questions, I don't need to cover them 18 in much more detail.

19 Okay. Minimum temperature case: so this 20 would be a case where all of ECCS is assumed to 21 function. I don't have the level figure in this 22 particular case, but it's one the quickly reaches an 23 equilibrium condition. So minimizing the temperature 24 just by itself, including 100 percent actuation if 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 220 ECCS doesn't drive that same level of response, which 1 is why we distinguished those two cases.

2 So in this case, we're primarily looking 3 at ensuring that as temperature continues to drop, we 4 don't reach the precipitation limits for boron.

5 MEMBER CORRADINI: Remind -- you're going 6 to go to the next slide?

7 MR. BRISTOL: Yes.

8 MEMBER CORRADINI: So again, is the red 9 line five percent break?

10 MR. BRISTOL: Yes.

11 MEMBER CORRADINI: So what is going on 12 that I almost come up with the same behavior? I guess 13 I'm a little confused. I'm sorry. I'm looking at the 14 water level again.

15 MR. BRISTOL: Okay. So in this case, I 16 believe it's an IAB blocked-out case, and so what we 17 have is, without DHR cooling available, so we have a 18 pressurized RCS with a very small --

19 MEMBER CORRADINI: So both trains of DHRS 20 are blocked?

21 MR. BRISTOL: Yes, they're not credited.

22 That's correct. So it's a very slow system 23 depressurization, because they're mostly losing liquid 24 inventory out the break, so that's a pretty low-energy 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 221 release.1 Eventually this level begins to accumulate 2 in containment. I get more and more energy released 3 through the RPV wall itself. Eventually, I 4 depressurize to the IAB release pressure window, at 5 which point ECCS actuates and then I continue the 6 transient progression.

7 So this slide we're just looking at the 8 maximum temperature case for both the two break 9 scenarios. Again, this case would be where the pool 10 temperature is biased to sort of the high condition, 11 assuming we're practically at pool boiling conditions 12 to ensure that even if the pool boiled and we 13 initiated transient from there, we still would provide 14 adequate ECCS performance.

15 So that's one of the cases where we sort 16 of take an analytical conservatism that's outside the 17 initial conditions of tech specs per se, in order to 18 just sort of deterministically addressing pool heat up 19 effects.20 None of the long-term cooling specifically 21 address transient pool temperature, but we do address 22 it from a minimum condition in terms of the constant 23 minimum or a constant maximum.

24 So long-term cooling conclusions: maximum 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 222 temperature cases show adequate core cooling. Minimum 1 temperature cases show margin to precipitation, and 2 the minimum level cases show the core stays covered.

3 Of note, the limiting 100 percent 4 injection line case had the minimum level of about 2.8 5 feet above the core. That minimum occurred about 6 three and a half hours.

7 MEMBER SKILLMAN: Ben, are you assuming 8 your minimum temperature for precipitation as 65 9 degrees Fahrenheit? Was that your marker for 10 precipitation?

11 MR. BRISTOL: No. We're using, we're 12 evaluating precipitation, so there's some calculations 13 that are performed within the analysis that actually 14 look at the volume, the mixing volume that's assumed, 15 relative to the temperature in the core as a function 16 of time.17 MEMBER SKILLMAN: What was the maximum 18 boron concentration you had on that track?

19 MR. BRISTOL: So I don't have --

20 MEMBER SKILLMAN: Yes, it isn't in any of 21 your images here.

22 MR. BRISTOL: I believe it's in -- there's 23 a table of results in the technical report that 24 actually describe the precipitation conditions and the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 223 way that calculation's performed. I don't have a 1 slide on that, no.

2 MS. MCCLOSKEY: And we look at it in terms 3 of margin to the solubility temperature, since we 4 calculate the solubility temperature as a function of 5 the mixing volume, which is the liquid in the core and 6 riser region.

7 And my recollection from the technical 8 report results is that there's at least 30 degrees 9 Fahrenheit margin to the solubility temperature in all 10 cases.11 MEMBER SKILLMAN: Thank you.

12 MEMBER CORRADINI: Is this the -- I guess 13 maybe I should have asked this earlier. Is this the 14 two-volume calculation where you've got the riser and 15 the core in one volume, and all what's outside of in 16 containment as the second volume?

17 MR. BRISTOL: No. This is an even more 18 simplified conservative analysis. We'll get into 19 that; I have a presentation --

20 MEMBER CORRADINI: I don't want to ask 21 much more, but I thought it was --

I wanted to ask 22 when it was -- we'll wait to closed session.

23 MR. BRISTOL: Yes. And we can circle back 24 to how it relates to these results --

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 224 MEMBER CORRADINI: Okay.

1 MR. BRISTOL: -- when we get to that 2 session.3 MEMBER CORRADINI: Okay. Thank you.

4 MR. BRISTOL: Okay. Are we ready to move 5 on?6 MEMBER CORRADINI: Can't wait.

7 MR. BRISTOL: Loss of shutdown margin.

8 This is the analysis of our postulated return to power 9 event. A couple of elements of licensing vices, I 10 suppose. The NuSCALE DCA includes an exemption 11 request from GDC 27. I think the ACRS has been 12 briefed on that before.

13 The reason for that: ECCS design does not 14 include boron addition as part of the design, and 15 therefore there's almost no way to meet the as-written 16 definition of GDC 27.

17 As an alternative, NuSCALE has proposed --

18 and this is in review with the staff -- the principal 19 design criteria 27. What we're trying to capture is 20 the intent of the GDC as applied to past designs that 21 wouldn't have necessarily active poison addition 22 capabilities.

23 And so the demonstration of the 24 acceptability of that variant from GDC is highly 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 225 dependent on showing acceptable results from both an 1 overcooling event with a stuck rod, and the one key, 2 I think, for us in terms of the design criteria is the 3 safety-related reactivity control system is designed 4 and is required to always ensure the core stays sub-5 critical through cold-check conditions without boron 6 addition.7 So it's all rods in on a reload basis, we 8 will demonstrate that the core can go Re critical and 9 stay Re critical out cold conditions.

10 So compliance immediate shutdown margin is 11 sufficient to turn the events around that we analyzed 12 in Chapter 15 and ensure that the SAFDLs are met.

13 Again, cold shutdown is ach ieved with all rods 14 inserted, and the loss of shutdown margin consequences 15 are sufficiently benign.

16 We've defined that to be a SAFDLs 17 evaluation of a limiting return to power condition and 18 that the overall heat removal capacities of ECCS and 19 DHRS are not challenged by the event.

20 It turns out that heat removal 21 capabilities above those systems are actually what 22 drive the event.

23 And then on top of that, the overall 24 probability of the combination of events that lead to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 226 a loss of shutdown margin is sufficiently small.

1 So just the reactivity kind of physics 2 overview: there's two main drivers, or three, I 3 guess, that one could postulate. Primarily one is 4 moderator cooling that drives an insertion of 5 reactivity as the systems decrease RCS temperature.

6 Under the limiting kind of cold pool conditions with 7 either DHRC or ECCS, the temperature decrease can 8 happen fairly rapidly on the order of a few hours. We 9 just looked at a couple of those figures already.

10 Another primary driver is the immediate or 11 the time-dependent fission product decay. Core 12 poisons, and so xenon being the primary one there. It 13 actually inserts negative reactivity for the first few 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> post-event, and then gradually decays over the 15 course of 12 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, about that time frame.

16 So in that sort of after six to 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> 17 is really when it starts inserting a fair amount of 18 reactivity.

19 MEMBER CORRADINI: In your analysis, you 20 neglect this, so you conservatively come potentially 21 under some conditions to return to power soon. Am I 22 misunderstanding?

23 MR. BRISTOL: No, that's correct. That's 24 correct.25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 227 MEMBER CORRADINI: And that was something 1 that was required by staff, or is that something you 2 chose to --

3 MR. BRISTOL: No, that was a conservatism 4 that we discretionarily applied.

5 MEMBER CORRADINI: Okay. Have you done a 6 calculation to see how much later you actually then 7 delay return to power?

8 MR. BRISTOL: Yes. The next couple of 9 slides, I'm going to get into that characterization 10 and circle it back to what we've actually presented in 11 15.6 to try to give that a little more context.

12 One of the other open items, and again, 13 we've got a presentation on this, but I just wanted to 14 address from a return to power perspective is, boron 15 redistribution.

16 Overall in ECCS mode, the core is boiling, 17 so that tends to be a concentrator of boron. The 18 containment is the condenser. The vapor leaves with 19 a very low fraction of the boron, as opposed to the 20 inlet conditions.

21 So we sort of know if the system starts 22 with boron in it, then it's going to tend to 23 accumulate in the core, leading to a lower boron 24 condition probably being more limiting for the return 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 228 to power analysis. That's one of the things we're 1 working with the staff in reviewing of.

2 I think for us, the conclusion is, as long 3 as the main loss mechanism of concern would be, could 4 there be some solidification mechanism that then just 5 leads to a loss of soluble boron from the system even 6 after it starts to concentrate, because of the 7 extended period of time that we're talking about.

8 And so that's a big part of the 9 presentation that we'll get into. Our conclusion is 10 that there's not.

11 CHAIR MARCH-LEUBA: The other concern is 12 that you're accumulating lower rate in the 13 containment, and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> later when you open the 14 ECCS, the low ratio goes into the lower plane and gets 15 into the core.

16 MR. BRISTOL: Sure.

17 CHAIR MARCH-LEUBA: You can get the slag 18 into the water. I just have difficult problem to 19 monitor.20 MR. BRISTOL: Right, and that's something 21 I think we have addressed with the staff. Just the 22 way that the ECCS actuation occurs and the way the 23 circulation rates are, there's no mechanism to get a 24 large slug actually through the system. So we've got 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 229 some analysis of that.

1 Okay. So I think I covered this. Oh, so 2 this is what I was alluding to. We're working through 3 a better characterization, I think, of the transient 4 nature of the event, using the physics a little more.

5 Initially, the OCRP event that we presented as part of 6 the SR was set up to be analyzed a little bit more 7 like kind of a stylistic AOO analysis where we're 8 using core design limits in trying to approximate 9 these defects.

10 So the overall reactivity balance was 11 mischaracterized a fair amount from a tiny 12 perspective. The point really was to show that even 13 through a pretty severe return to power kind of 14 analysis, we were a long way from CHF limits and were 15 well bounded by other event analyses.

16 So the purpose of this work is really a 17 little bit more detailed characterization of the three 18 things I talked about before: specifically that the 19 cooldown rates of both ECCS and DHRS, relative to the 20 xenon-driven reactivity insertion. So I kind of 21 alluded to that before.

22 Over the 12- to 72-hour range, the 23 reactivity insertion rate is really, really slow. So 24 in sort of looking at this, worst rod stuck out Re 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 230 criticality is achieved in RCS temperatures below 200 1 degrees, around 200 degrees, such that we used the 2 state point analysis that we developed for the long-3 term cooling approach to then do a state point 4 reactivity calculation --

5 CHAIR MARCH-LEUBA: Using what tool?

6 MR. BRISTOL: SIMULATE-5 for the --

7 CHAIR MARCH-LEUBA: Does the SIMULATE 8 effectively calculate -- calculation?

9 MR. BRISTOL:

That's right.

So we 10 actually iterated to critical power levels based on 11 thermohydraulic conditions from equilibrium either 12 ECCS or DHR cooling conditions.

13 CHAIR MARCH-LEUBA: That's good, because 14 you're reaching a calculation with a constant MTC as 15 you're going through the whole transient, which is 16 crazy. SIMULATE is when the regulate operations, 17 correct? You get a 200 degrees Fahrenheit if you have 18 depressed rise, which you open to see if you are 19 boiling.20 MR. BRISTOL: That's right.

21 CHAIR MARCH-LEUBA: So with decay heat, 22 does this calculation come from boiling, or is it not 23 boiling?24 MR. BRISTOL: It does not. We 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 231 conservatively assumed sub-cooled conditions for the 1 boundary conditions to simulate. So that gives us a 2 much more conservative critical power level.

3 The power levels are low enough; I'll get 4 to them my next slide. But I think we've got overall 5 confidence in the characterization of the event, even 6 with the conservativisms that are applied.

7 We have looked at the influence of density 8 with SIMULATE and demonstrated that very little 9 voiding in the core would suppress the power, 10 obviously. And so that's an important conclusion, but 11 there is some concern if the low void fraction rates, 12 where we would justify one, two, three percent boiling 13 rates.14 And as any ECCS mode, as we get to lower 15 and lower vapor pressure conditions, the level head in 16 the riser starts to drive a saturated kind of 17 temperature curve, and we could postulate that the 18 boiling could, or some of the two-phase exchange heat 19 removal could be a current closer to the level of 20 interface, and with convective mixing driving the 21 cooling of the core region.

22 CHAIR MARCH-LEUBA: Considerable.

23 MR. BRISTOL: Yes. So like I said, we did 24 a steady-state characterization of RCS as a function 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 232 of the decay heat for both DHR and ECCS heat removal.

1 There's a big spectrum calculation that was done; that 2 was using a read-out model.

3 And then like I said, the worst rod stuck-4 out critical power level is iterated to using SIMULATE 5 as a function of RCS temperature.

6 Conclusions that a loss of shutdown margin 7 can be achieved on kind of the time frame of 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> 8 or so with zero boron in the system after xenon's 9 decay. Temperatures are below 200 degrees.

10 ECCS cooling is a little bit more 11 effective, so it drives a little higher temperature 12 conditions. Again, that's with the sub-cooling 13 assumption is part of that.

14 Pool temperatures: so one of the things 15 that I thought was important to characterize is that 16 any pool heat of effect that could occur would 17 actually mitigate the event as the pool gets above 140 18 degrees. It's going to shut -- the RCS temperature 19 just climbs with it, and it's going to shut everything 20 back off.21 And then simple CHF analysis; I don't have 22 any of the results, but the pool in the CHF analysis 23 demonstrates large margin.

24 MEMBER CORRADINI: What do you use for the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 233 CHF analysis?

1 MR. BRISTOL: That particular case is 2 Zuber.3 MEMBER CORRADINI: Foster-Zuber?

4 MR. BRISTOL: Zuber-Griffith.

5 MEMBER CORRADINI: Oh, okay.

6 MR. BRISTOL: So up here we've got the 7 riser uncovered, so one of the things we'll also get 8 to in the closed session, but we've addressed somewhat 9 is riser uncovery nominally adds resistance to the 10 cooling capability. So we looked at a comparison of, 11 if inventory is maintained in the RCS, DHR is going to 12 be more effective than if the riser uncovers, so 13 that's kind of a quantification of the difference 14 there.15 Down here this is ECCS cooling or kind of 16 the equilibrium temperature as a function of continual 17 decreasing decay heat.

18 MEMBER CORRADINI: I don't understand this 19 graph. I looked at it a few times, and I'm lost. Can 20 you help us, please?

21 MR. BRISTOL: Okay. So each of these 22 points represents a RELAP calculation that we did that 23 set a constant heat input; constant decay heat, 24 constant core power level, using our system model.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 234 MEMBER CORRADINI: Oh, so you basically 1 did a series of parametrics.

2 MR. BRISTOL: That's right.

3 MEMBER CORRADINI: Where you set some 4 decay heat level.

5 MR. BRISTOL: Yes. And the equilibrium 6 temperature condition in the core then is a function 7 of the actual decay heat level.

8 MEMBER CORRADINI: Right.

9 MR. BRISTOL: So that's what we're doing 10 there. If we were to assume that there's no residual 11 heat removing, we're at a pure steady-state condition.

12 This would be the temperature solution for that power 13 level. This upper graph, like I said, is with the 14 riser uncovered.

15 CHAIR MARCH-LEUBA: Only DHRS is working, 16 right?17 MR. BRISTOL: And only DHRS working.

18 CHAIR MARCH-LEUBA: Both of them or only 19 one?20 MR. BRISTOL: Two.

21 MEMBER CORRADINI: Okay. Which maximizes 22 cooling.23 MR. BRISTOL: That maximizes the heat 24 removal. This is with the riser covered, so at any 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 235 given heat level we're going to get quite a bit lower 1 temperature condition, and this is the same 2 calculation performed in ECCS mode.

3 MEMBER CORRADINI: And the black line?

4 MR. BRISTOL: This is the SIMULATE 5 results. So --

6 MEMBER CORRADINI: So you're looking for 7 the intersection of the little dots and the black 8 line?9 MR. BRISTOL:

That's right. So the 10 critical power level in ECCS mode would be evaluated 11 to be about one percent reactor power --

12 CHAIR MARCH-LEUBA: Again, how do you do 13 the SIMULATE?

14 MR. BRISTOL: So the SIMULATE calculation 15 is performed taking the thermohydraulic boundary 16 conditions --

17 CHAIR MARCH-LEUBA: From?

18 MR. BRISTOL:

From -- well, it's a 19 spectral analysis as well, so we just define --

20 iterate to a critical power level assuming a core 21 inlet temperature of 100 degrees, 120 degrees, 130 22 degrees, et cetera. And so --

23 CHAIR MARCH-LEUBA: In SIMULATE you have 24 to specify the power and the core inlet temperature 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 236 and the flow?

1 MR. BRISTOL: In this case we're iterating 2 to critical power level.

3 CHAIR MARCH-LEUBA: Critical power level?

4 MR. BRISTOL: That's right.

5 CHAIR MARCH-LEUBA: But even -- you have 6 to specify a temperature and a flow?

7 MR. BRISTOL: A temperature and a flow, 8 that's correct. So what we ended up doing is mapping 9 the flow, the DHR flow, correlating to the riser cover 10 condition as the flow condition. What the flow does 11 is essentially just sets the delta T across the core 12 to a given power level.

13 CHAIR MARCH-LEUBA: But what I'm going to 14 is the black line is a function of core power and 15 flow, and you've brought in the function of decay 16 heat, which is power.

17 MEMBER CORRADINI: Yes, I don't think 18 that's what he -- that isn't how I understood the 19 curve. The black line is basically, for a set of 20 thermohydraulic conditions of density and temperature, 21 what's the power I achieve? And he's just simply 22 plotting out the excess as if it were an equivalent 23 decay heat.

24 MR. BRISTOL: That's right.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 237 MEMBER CORRADINI: And so he's basically 1 saying that at the worst set of conditions was the --

2 now I think I get it. The ECCS little dots, I have 3 one percent plus 0.35 percent as the total power that 4 I'd be producing. It's the red line plus the black 5 line. Am I understanding --

6 MR. BRISTOL: No, the intersection, we're 7 saying is that --

8 MEMBER CORRADINI: Oh, you're adding the 9 two together?

10 MR. BRISTOL: Yes. That would be the 11 equivalent critical power level for the --

12 MEMBER CORRADINI: But the conservatism 13 that I'm seeing here, unless I misunderstood, is the 14 black line is assuming zero void.

15 MR. BRISTOL: That's correct.

16 MEMBER CORRADINI: So I'm way to the 17 right.18 MR. BRISTOL: So it's pretty 19 characteristic of the DHR conditions where we're sub-20 cooled. So that's about the real answer for DHR, and 21 again, in ECCS conditions we do see under the extreme 22 cooldown conditions that we can actually move the 23 boiling up out of the core region itself and into the 24 lower riser as a flashing type phenomena with an 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 238 amount of convective --

1 MEMBER CORRADINI: Okay. Fine. But the 2 black line right now is zero void?

3 MR. BRISTOL: Is zero void.

4 MEMBER CORRADINI: So I think it's like a 5 reactor static calculation. The black line is a 6 reactor static calculation overlaying and intersecting 7 essentially a thermohydraulic parametric on power.

8 MR. BRISTOL: That's correct.

9 MEMBER CORRADINI: I got it, finally.

10 CHAIR MARCH-LEUBA: I ain't got it, but 11 that's okay.

12 MR. BRISTOL: Okay.

13 MEMBER CORRADINI: Just so you guys have 14 seen this before, the shine application for the 15 construction permit when they were doing their annular 16 thing, showed exactly the same sets of calculations 17 about how they would essentially achieve criticality 18 or sub-criticality under the shine medical technology.

19 Same sort of parametric calculation; 20 that's why --

21 CHAIR MARCH-LEUBA: I just don't know 22 where the decay heat power comes into the SIMULATE 23 calculation if you specify what the temperature is.

24 MR. BRISTOL: So decay heat is -- maybe 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 239 decay heat is the confusing parameter here. RELAP is 1 just given a point, basically, of a constant power 2 level, and that generates four ECCS conditions at 3 given temperature condition for DHR conditions at a 4 different temperature condition.

5 And then we're recorrelating the SIMULATE 6 results, which we specify flow and temperature, so we 7 run a spectrum of temperatures. We assume just a 8 constant flow for all of these analyses that's on the 9 conservative high end. It correlates to the DHR 10 covered conditions.

11 So for ECCS mode it's really pretty high.

12 The internal flow isn't something we would necessarily 13--14 CHAIR MARCH-LEUBA: In a realistic 15 condition the flow would be essentially zero, but you 16 will be uncovered.

17 MR. BRISTOL: Right.

18 CHAIR MARCH-LEUBA: And -- anyway --

19 MR. BRISTOL: Sure.

20 CHAIR MARCH-LEUBA: I think two reasonable 21 people can come up with five different answers.

22 MR. BRISTOL: I suspect we'll see some 23 more tomorrow. So on the topic of different answers, 24 going back to what we've actually got in 15.06; so 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 240 again, the purpose is, when we submitted the DCA was 1 to do a pretty bounding analysis.

2 So the way that's performed is, a DHR 3 cooldown is more productively performed. There's a 4 couple of key conservatisms; on is that there's no 5 xenon applied as a poison in terms of the overall 6 reactivity balance. The minimum kind of core design 7 limit shutdown margin is assumed. There's a constant 8 MTC applied, and really all that's doing is setting 9 the overall defect that gives us essentially the point 10 at which we go Re critical.

11 When we do the CHS evaluation, we actually 12 transition and use a density-based curve, so that's 13 sort of a state point difference that's applied. And 14 again, the calculation was actually updated to just 15 apply the density curve through the entire transient.

16 So with DHR we actually use the 17 temperature transient; generate a power overshoot, and 18 that's used in core physics codes to calculate LOCA 19 peaking factors. They are then applied in the CHF 20 analysis, and then CHF techniques similar to what's 21 used in the LOCA models is applied in terms of 22 evaluating the CHF.

23 And so these are, I think, the updated 24 figures in the SR. Again, we have the DHR-driven 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 241 power overshoot. This particular case doesn't actuate 1 ECCS at the peak; that's only performed through the 2 CHF case, so this is the equilibrium DHR condition, 3 and this is was the type of analysis that was used 4 with the stability that Dr. Yarsky was talking about 5 earlier today.

6 So we take these, apply them in a way in 7 PIM and evaluate the decay ratio that results. Here's 8 a figure of the temperature conditions.

9 So this is where we take the same scenario 10 and actually open the valves at the point of the power 11 peak. That drives the density-driven feedback. We 12 reach sub-criticality. I don't have the extended 13 figures in this analysis.

14 There's an RER response that shows if you 15 were to extend this model, which really wasn't the 16 purpose; the purpose was really to make the argument 17 that actuating ECCS up here is more limiting than 18 anything that would be kind of self-limited 19 oscillations down in this regime.

20 But because the reactivity balance is so 21 far from what's more characteristic of the core, it 22 does show extended oscillations out this way.

23 And the CHS results: the conclusion in 24 the SR, it's the conclusion still that this is --

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 242 either way you model it, it's non-limiting from a CHF 1 or SAFDLs perspective in terms of transience. We're 2 still under review on some of the finer points that 3 I'm sure Jeff will cover more. And that's all I have 4 on that topic.

5 MEMBER CORRADINI: Just, can we go back?

6 MR. BRISTOL: Yes.

7 MEMBER CORRADINI: But these, what you 8 view as bounding analyses with a point kinetics in 9 dynamic, in difference to the previous plot that we 10 were asking about, which essentially is a what-if in 11 terms of power, right?

12 MR. BRISTOL: That's right.

13 MEMBER CORRADINI: Okay.

14 MR. BRISTOL: That's right.

15 MEMBER CORRADINI: So these are steady-16 state calculations of a series of what-ifs, whereas 17 the other two are considered to be your bounding 18 calculations for dynamic?

19 MR. BRISTOL: Yes. So we don't actually 20 believe there would be the dynamic response that we've 21 got presented. And just to kind of contextualize that 22 a little bit, again the purpose of that calculation 23 was to do it kind of generically enough that it would 24 be obvious that it was conservative.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 243 The downside of that is that it paints it 1 maybe a slightly variant picture as to the actual 2 conditions that we would reach in long-term cooling 3 phase.4 MEMBER BROWN: Go back to 107. How far 5 out does the line go?

6 MEMBER CORRADINI: That's 266 minutes.

7 MR. BRISTOL: That's line -- yes, that's 8 where we truncated -- what we see extending this line 9 is --10 MEMBER BROWN: How long do you stay at 11 power?12 MR. BRISTOL: Pretty flat response.

13 MEMBER BROWN: What is it, three percent 14 or two and a half? Something like that?

15 CHAIR MARCH-LEUBA: No, that's megawatts.

16 MEMBER BROWN: Oh, megawatts; that's fine.

17 Whatever the power is, how long does it stay there?

18 MR. BRISTOL: So if we had no temperature 19 increasing in the pool it would stay at that solution 20 until an operator came and did something about it.

21 Again, this is the --

22 MEMBER BROWN: What would he do?

23 MR. BRISTOL: Insert the rod, add boron:

24 any number of things.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 244 MEMBER BROWN: But the rod's stuck.

1 MR. BRISTOL: Shut off the DHR and stop 2 the cooldown.

3 (Simultaneous speaking.)

4 MEMBER DIMITRIJEVIC: -- on-site power --

5 MR. BRISTOL: Actuate ECCS initiates the 6 same --7 CHAIR MARCH-LEUBA: I thought the obvious 8 action in the ECCS would be to flood containment with 9 borated water from the pool.

10 MR. BRISTOL: Yes, that would be --

11 CHAIR MARCH-LEUBA: And open ECCS.

12 MR. BRISTOL: Right, right. Again, this 13 isn't really characteristic of the timing of the 14 event. The purpose of this analysis is to show that 15 we can conservatively evaluate.

16 CHAIR MARCH-LEUBA: Yes, I just feel that 17 a 100 percent realistic analysis will show that this 18 doesn't happen. I mean, it would have been nice that 19 this didn't happen, and we didn't need GDC 27 20 exception, because look at Charlie. Every time he 21 talks about it, he gets upset, and he is pro-nuclear.

22 (Laughter.)

23 CHAIR MARCH-LEUBA: All members of the 24 public will hear this, they say, Oh, what are you 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 245 building in my neighborhood? I think it's just an 1 issue of the conservatisms that we had it. I don't 2 think this happens.

3 MEMBER BROWN: It's not a matter of 4 principle. Reactors should shut down under some 5 particular design condition. The ones I'm familiar 6 with that I've worked with over 35 years, when the rod 7 stuck out, we shut down.

8 MR. BRISTOL: Sure.

9 MEMBER BROWN: We had to work at it. It 10 wasn't easy, okay? We had to work at it, but that's 11 what you did.

12 MR. BRISTOL: And I think, to that point, 13 because of the unique aspects of our reactor design, 14 that one stuck-out rod, which is traditionally applied 15 to a big core, is a ton of margin, and --

16 CHAIR MARCH-LEUBA: His reactors are this 17 size.18 MR. BRISTOL: Fair enough. It's a lot of 19 margin for our design, and so in demonstrating passive 20 cooling for a coping period that outlives your poison, 21 that's a lot of temperature defect to try to 22 accommodate in deterministic analysis phase.

23 Certainly, maybe there's an answer. If 24 one could address all the uncertainties appropriately, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 246 that would show, yes, we can squeak by without a 1 critical configuration.

2 CHAIR MARCH-LEUBA: Can you go back to the 3 dotted line? The one with -- that one. So if I read 4 this correctly, all the red points have a K effective 5 less than one.

6 MR. BRISTOL: Yes.

7 CHAIR MARCH-LEUBA: All the blue points 8 that are above the line are K effective less than one, 9 and same with the this. Anything that is under the 10 line has a K effective greater than one and it boils 11 to maintain criticality.

12 MR. BRISTOL: Or would respond back up to 13 that temperature equilibrium condition.

14 MEMBER CORRADINI: They'd move up. It 15 would move up.

16 MR. BRISTOL: So if the coolant were to 17 drive you to here, you'd bump back up to here and --

18 CHAIR MARCH-LEUBA: You're grossly 19 overcooling.

Yes, okay. So if -- you could do it 20 with sub-cooling or with voids.

21 MR. BRISTOL: Right.

22 CHAIR MARCH-LEUBA: Correct. So the 23 nominal case for this is the ECCS, which is purple.

24 And what this calculation is saying is, it happens, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 247 yes? Anything less than one percent decay heat.

1 MEMBER BROWN: You stay critical.

2 CHAIR MARCH-LEUBA: When do you get one 3 percent decay heat for 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />?

4 MEMBER BROWN: No, it's below.

5 MR. BRISTOL: That's a good question. I 6 would have to follow up on --

7 MEMBER CORRADINI: What do you mean?

8 CHAIR MARCH-LEUBA: You get one percent 9 heat is 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />?

10 MEMBER CORRADINI: Three hours.

11 CHAIR MARCH-LEUBA: Three hours?

12 MR. BRISTOL: Three hours.

13 MEMBER CORRADINI: Based on the ANS 14 standard. Rule of thumb is 10,000 seconds-ish.

15 DR. SCHULTZ: Did you put a team on this 16 to do what Jose suggested? Look at the best estimate?

17 Forget about the uncertainties for a moment and do the 18 evaluation approach with the best code you've got and 19 the best assumptions you can make and worry about 20 applying uncertainty and evaluation later?

21 MEMBER BROWN: Steve's got a reasonable 22 suggestion. The point is, this is a conservative 23 analysis, and you do a best-estimate analysis under 24 the particular circumstances. If you've done it 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 248 right, it doesn't go critical.

1 (Simultaneous speaking.)

2 MEMBER CORRADINI: I think there's -- I 3 guess maybe I'm different than the rest --

4 (Simultaneous speaking.)

5 MEMBER BROWN: -- get up critical and stay 6 critical.7 MEMBER CORRADINI: Yes, but I think 8 there's a bounding calculation. That's the way I look 9 at it. There's a set of bounding calculations under 10 two initiators. If I start doing best estimates, I 11 don't have two initiators; I've got a plethora of 12 these, so I've got a plethora of best estimates. And 13 as long as they stay under this, then --

14 CHAIR MARCH-LEUBA: No, because they all 15 end up in the same place. They'll end up losing DC 16 power after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or pull a timer and open the ECCS 17 valve and going into the ECCS cooling through the 18 vessel. It continues through; any initiator in 19 transient will end up there, in that position.

20 MEMBER DIMITRIJEVIC: Well, you have loss 21 of power and stack roll.

22 CHAIR MARCH-LEUBA: You have stack roll --

23 MEMBER DIMITRIJEVIC: And loss of power.

24 CHAIR MARCH-LEUBA: And you have lost 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 249 power for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, plus.

1 MEMBER DIMITRIJEVIC: Well, I mean, I 2 think -- it's 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> because, I mean, if you can get 3 that, you can get boron after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, you will not 4 get --5 CHAIR MARCH-LEUBA: Yes. And you don't 6 take credit for any of the on-site AC power in these 7 times.8 MR. BRISTOL: So I think to answer that 9 question, yes, there was a whole lot of consideration 10 that went into any ways that we could, in Chapter 15 11 space with Chapter 15 rules, and it starts -- you 12 know, you start pulling the thread, and it starts 13 breaking down because again, when deterministically 14 taking that stuck rod is driving the problem, and so 15 if I start trying to pull in, Well, my pull is really 16 going to be 100 degrees. Yes, that totally changes 17 the dynamic response; it improves it quite a bit.

18 Am I going to operate a plant with a tech 19 spec of 100 degrees? No. So that's not a thread that 20 I can pull.

21 CHAIR MARCH-LEUBA: Yes, but that's still 22-- presume these results: say it is considerable that 23 you can have these, but under nominal conditions, when 24 my pool is going to be at 90 degrees or maybe 78 --

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 250 MR. BRISTOL: Certainly.

1 CHAIR MARCH-LEUBA: -- under nominal 2 conditions, it will have it. Because if you could put 3 75 percent decay heat, you have enough heat up, it 4 boils or heat up that pool will move up.

5 MR. BRISTOL: Yes.

6 CHAIR MARCH-LEUBA: So you're just killing 7 yourself and ourselves with you by being too 8 conservative. I would rather not have to give you an 9 exception for anything, because you're satisfied.

10 It's a marketing decision.

11 MEMBER BROWN: It's a principles decision.

12 MEMBER CORRADINI: We're shooting for 13 about an hour late. Do we want to continue, or do you 14 want to go into closed session?

15 MEMBER BROWN: I'm finished here.

16 MEMBER CORRADINI: I think we have to hear 17 from the public.

18 MS. MCCLOSKEY: I have one correction to 19 make. When we were discussing the margin to the boron 20 precipitation and the solubility limits, in most of 21 the long-term cooling cases that we have, there's 30 22 degrees margin of solubility limit or more. The 23 limiting case for an injection line break at low power 24 conditions, and therefore low decay heat has about 16 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 251 degrees margins of solubility temperature. I needed 1 to get that correction in.

2 MEMBER CORRADINI: Thank you.

3 MEMBER DIMITRIJEVIC: I have a question.

4 Because of the 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> loss, when you did this 5 analysis, did you just assume the loss of power is not 6 favorable? It doesn't matter how long, right?

7 MR. BRISTOL: That's correct.

8 MEMBER DIMITRIJEVIC: Because if you said 9 that this occurred in three hours, and you analyzed 10 this, if you get loss of power only before three 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br />, 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is irrelevant. It's just that you 12 lost on-site power?

13 CHAIR MARCH-LEUBA: You need to open the 14 ECCS valve so you would have additional cooling to the 15 vessel to get here.

16 MEMBER DIMITRIJEVIC: I know, but that's 17 okay. I mean, 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />; why do you -- you don't have 18 on-site power. That's what I'm --

19 CHAIR MARCH-LEUBA: You have batteries for 20 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. That's what the assumption is. The 21 batteries last for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, and then the ECCS open, 22 and --23 MEMBER DIMITRIJEVIC: So there is no on-24 site power, and you will have your batteries deplete.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 252 CHAIR MARCH-LEUBA: You have a timer that 1 you should log.

2 MS. MCCLOSKEY: There's a timer.

3 MEMBER DIMITRIJEVIC: Yes. How do you 4 open the ECCS in this case? I mean, what happens?

5 MEMBER CORRADINI: It just fail --

6 MR. BRISTOL: So the transient -- if we go 7 to this case, the event progression would be starting 8 at hot zero power conditions in terms of RCS 9 temperature and inventory, and then a simultaneous 10 loss of AC and DC such that we go to IAB.

11 And right around the time that we're 12 starting to deterministically applying an IAB release 13 condition at this particular point.

14 MEMBER DIMITRIJEVIC: So you lost AC and 15 DC simultaneously?

16 MR. BRISTOL: In this particular case, 17 yes, because there would be no -- Dr. Yoo was saying 18 that there wouldn't be an actuation of ECCS until the 19 24-hour point, except that ECCS was already actuated.

20 So we're just riding the pressure down to the IAB 21 release point and then sort of deterministically 22 applying it as a release conservatism at the time of 23 the power peak. So that's how we get the ECCS 24 actuation.

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 253 CHAIR MARCH-LEUBA: This one you assume a 1 DC failure of type zero?

2 MR. BRISTOL: Mm-hmm.

3 CHAIR MARCH-LEUBA: So as they cool down 4 is the one that triggers the --

5 MEMBER CORRADINI: Right.

6 MR. BRISTOL: Right.

7 CHAIR MARCH-LEUBA: Yes. That's even less 8 probable.9 MR. BRISTOL: Right.

10 MEMBER CORRADINI: But that's why -- I 11 think we're circling here. That's why I guess my 12 personal view is, these are bounding. We have to make 13 sure the range of potentials are bounded by them, but 14 to try to hit a best estimate, I see that to be a very 15 difficult assignment.

16 CHAIR MARCH-LEUBA: Oh, this is bounding, 17 but that's two hours after shutdown, and the xenon is 18 sufficient to keep you way down.

19 (Simultaneous speaking.)

20 CHAIR MARCH-LEUBA: In the 24-hour --

21 (Simultaneous speaking.)

22 CHAIR MARCH-LEUBA: -- because xenon is 23 getting out. Unless you started from a xenon-free 24 startup and you have this crammed right in -- well, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 254 anyway, we have to live with it.

1 MEMBER CORRADINI: Should we go to the 2 public line? It's open? So does anybody in the room 3 want to make a statement?

4 And on the public line, do we have anybody 5 on the public line? Can you please acknowledge that 6 you're out there?

7 Okay. Why don't we close the public line, 8 please? And then can I ask NuSCALE and staff to make 9 sure that -- we're going to close the line. We'll 10 keep the NuSCALE staff line open, and we'll go into 11 closed session. We'll just verify the public line is 12 closed. Thank you, Mike. You guys going to stay 13 where you are, and we'll get another set of slides?

14 I can't wait.

15 CHAIR MARCH-LEUBA: He can misspell your 16 name.17 MEMBER CORRADINI: Since we're kind of 18 quasi-open, quasi-closed, if I were to do a best 19 estimate, I would rather just take your steady-state 20 set of calculations and look and see the range of 21 uncertainty on those. I wouldn't go through a 22 dynamic. The dynamic to me just strikes me like a 23 dead end, but at least your steady-state ones were 24 looking for a cross point between a reactor static 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 255 calculation and a thermohydraulic parametrics.

1 That, at least, would show you the range 2 of what these things are as I make some assumptions of 3 what's realistic and what's not realistic.

4 DR. SCHULTZ: You have to set that base 5 case in some fashion and then do parametrics.

6 MEMBER CORRADINI: Because if you look at 7 their steady state one on slide whatever, it's 8 slightly more than the dynamic, because we're talking 9 about 15 megawatts, where you're predicting in the 10 dynamic of about 10 megawatts under those two bounded 11 conditions.

12 So I'd rather, if I were an analyst, I'd 13 rather try to noodle with this, which is a whole lot 14 easier to do to try to see what the uncertainties 15 might be, or what the range of uncertainties are, or 16 the assumptions. Because you neglected a whole bunch 17 of things to get to this already.

18 MR. BRISTOL: Is actually close to two.

19 MEMBER CORRADINI: Oh, I thought it was 20 one percent of decay heat. Oh, one percent of decay 21 heat.22 MR. BRISTOL: One percent of reactor 23 power.24 (Simultaneous speaking.)

25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 256 MEMBER CORRADINI: That's 15 megawatts.

1 CHAIR MARCH-LEUBA: No, 1.6.

2 MEMBER CORRADINI: Oh, one percent; 1.6?

3 I'm sorry.

4 MR. BRISTOL: Yes, so the dynamic response 5 is supposed to be at 10 percent.

6 MEMBER CORRADINI: Okay. Sorry. But this 7 would be --- well, no, I guess I'm -- this would be --

8 I wouldn't look at that as the dynamic. I'd look at 9 that at the long term -- the one that Charlie was 10 asking about, where I set a limit.

11 MEMBER BROWN: The 104?

12 MEMBER CORRADINI: It's the one over long 13 periods of time, yes? It's not the peak; it's --

14 MEMBER BROWN: It's 104, not 108 --

15 MEMBER CORRADINI: Yes. That's what I 16 would --17 (Simultaneous speaking.)

18 CHAIR MARCH-LEUBA: Yes. But that's a 19 calculation based on a constant MTC using point 20 kinetics. That's crazy. I mean, that has nothing to 21 do with reality.

22 Since we're offering advice, what I would 23 do is, I would take and pull up five. I would input 24 the power one percent decay heat, 1.6 megawatts, and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 257 let it settle to whatever it wants to settle, on the 1 flow, on the void, or the temperatures. Then take 2 that void and temperature and put in SIMULATE.

3 It's going to factor into the one or not.

4 That's a DC calculation. I think you complicated it 5 too much by doing the critical search. And each of 6 those purple points, you're -- it's -- but then on a 7 closed-loop calculation, I recalculate what the flow 8 is, I recalculate what the voids are, and put that 9 into SIMULATE. That's what I would do.

10 MEMBER CORRADINI: Okay. So you had two 11 pieces of advice, and they're worth about as much as 12 the people that gave them to you, since there's no 13 money involved. So we're closed.

14 (Whereupon, the above-entitled matter went 15 off the record at 4:31 p.m.)

16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.(202) 234-4433WASHINGTON, D.C. 20005-3701(202) 234-4433 LO-0619-65988 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360

-0500 Fax 541.207.3928 www.nuscalepower.com June 17, 2017 Docket No. PROJ0769 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 "ACRS Subcommittee Presentation: NuScale Topical Report - Evaluation Methodology for Stability Analysis of the NuScale Power Module,"

PM-0619-65962, Revision 0 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 June 19, 2019. The materials support NuScale's presentation of the "Evaluation Methodology for Stability Analysis of the NuScale Power Module" topical report.

The enclosure to this letter contains the nonproprietary version of the presentation entitled "ACRS Subcommittee Presentation: NuScale Topical Report - Evaluation Methodology for Stability Analysis of the NuScale Power Module." If you have any questions, please contact Matthew Presson at 541-452-7531 or at mpresson@nuscalepower.com. Sincerely, Zackar y W. Rad Director, Regulatory Affairs NuScal e Power, LLC Distribution:

, NRC, OWFN-

Gregory Cranston, NRC, OWFN-8 H12 Bruc e Bavol, NRC, OWFN-8 H12

Enclosure:

"ACRS Subcommittee Presentation: NuScale Topical Report - Evaluation Methodology for Stability Analysis of t he NuScal e Power Module ," PM-0 619-6 596, Revision 0 LO-0619-65988 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360

-0500 Fax 541.207.3928 www.nuscalepower.com

Enclosure:

"A CRS Subcommitt ee Presentation:

NuScal e Topical Report - Evaluati on Methodology for Stability Analysis of th e NuScal e Power Module ," PM-0 619-6 596, Revisi on 0 PM-0619-65962 1Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5ACRS SubcommitteePresentationJune 19, 2019NuScale Topical ReportEvaluation Methodology for Stability Analysis of the NuScale Power Module PM-0619-65962 2Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5PresentersDr. Yousef FarwilaSystem Thermal HydraulicsBen BristolSupervisor, System Thermal HydraulicsMatthew PressonLicensing Specialist PM-0619-65962 3Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Agenda*Introduction

• Stability Solution Type

• Stability Investigation Description

-Theoretical

-Numerical Using New C ode PIM-Experimental Benchmark

• Procedure and Methodology

• Summary*Questions and Discussions PM-0619-65962 4Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5The Main Message

• The NuScale Power Module (NPM) design was found to be stable in the entire range of normal operation

• Outside of normal operation, the reactor is destabilized

when the riser flow is voided, however

-Unstable flow oscillation amplitude is limited by nonlinear effects and the critical heat flux ratio actually improves

• The stability threshold is protected by scram upon loss of riser inlet subcooling

-Conceptually equivalent to a "region exclusion" not a "detect and suppress" solution type

-No action required to implement a stability solution hardware

• These conclusions are based on extensive first principles, experimental, and computational studies.

PM-0619-65962 5Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Stability Evaluation

• Natural circulation instabilities were reported

-See for example D.S. Pilkhwalet al., "Analysis of the unstable behaviourof a single-phase natural circulation loop with one

-dimensional and computational fluid

-dynamic models," Annals of Nuclear Energy 34 (2007) 339

-355.a)HHHC: horizontal heater and horizontal cooler (the only unstable configuration);

b)HHVC: horizontal heater and vertical cooler; c)VHHC: vertical heater and horizontal cooler; d)VHVC: vertical heater and vertical cooler (qualitatively like NuScale module)

• I nvestigation of the NuScale module stability commenced to demonstrate stability, identify threshold conditions, and license stability protection methodology(a)HHHC(b)HHVC(c)VHHC(d)VHVC PM-0619-65962 6Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Independent Models Reduced Order Model (RADYA)Stability Investigation ElementsModule Design and Operational DomainFirst Principles Theory

--Experience

--PIRTExperimental Data and Benchmarking(NIST-1)Construct Models and Main Code (PIM)Comprehensive Analysis & Results

• SteadyStatePerturbations

• StabilityduringTransientsConclusions

• StablewithinOperatingDomain

• Threshold isRiserVoidingStability Solution:

• Protectrisersubcoolingwithmargin*HardwarealreadypartofMPS PM-0619-65962 7Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Theoretical Investigation

• Kick off with an expert committee to generate a first PIRT

• Scoping review of thermalhydraulic instability modes and contrasting with the NPM design features

• Identification of the possible instability mechanism

• Analysis from first principles

-Riser-only mode (separate from cold leg)

-Stability trend with power using a simple SG model

-Inform design of stability experiments

• All medium ranked phenomena treated as highly ranked PM-0619-65962 8Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Theoretical and First Principles

• A system with feedback processes may undergo oscillatory instability if the feedback is:

-Negative (positive feedback is unconditionally unstable)

-Delayed -Sufficiently strong

• NuScale natural circulation mode is examined

-Feedback is negative. A perturbation increasing core flow decreases exit temperature thus decreases riser density head

-Feedback is delayed. Transport delay for core exit condition to fill

the riser and reach maximum density head effect.

-Feedback strength is related to liquid thermal expansion and

possibility of phase change, riser length, SG characteristics, reactivity feedback- Requires detailed modeling PM-0619-65962 9Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Main Stability Analysis Tool: PIM

• Transient 1

-D 2-phase non-equilibrium primary loop flowCoreCoolingHeat ExchangerFeedwaterSuperheated SteamPressurizer PM-0619-65962 10Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Model Equations of the PIM code

• Thermalhydraulic conservation equations

-Liquid and vapor mass balance

-Mixture momentum conservation with drift flux (integrated momentum)

-Energy conservation (assume saturated vapor)

,,1, lnlnlnn dMmm dt,,1, gngngnn dM mm dtgravfrictionlocalresid dIPPPP dt,,,1,1,,lnlnlnlnlnlnnfgn dMhmhmhhQ dttimeliquid massvapormassliquid mass flow ratevapor mass flow raterate of evaporationintegrated momentumgravitational press. dropfriction pressure drop local pressure l g l ggravfrictionlocal t M M m m I P P

P

dropresidual pressure dropliquid enthalpy latent heatpowercontrol volume index1upstream indexresid lfg P h h Q n n

PM-0619-65962 11Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Model Equations of the PIM code

• Point Nuclear Kinetics

-Thermalhydraulic model provides reactivity input

• Moderator density reactivity feedback model (equivalent to moderator temperature reactivity under single

-phase flow)

• Doppler fuel temperature reactivity feedback

-Heat source from neutron kinetics feeds back to thermalhydraulics

• Energy deposited in fuel pellets (proportional to neutron flux)

• Fraction of fission energy deposited directly in coolant

• Decay heat: input by the user as fraction of initial power1 d C dtdC C dtConcentration of the delayed neutron precursorsDecay constant of the delayed neutron precursorsNeutron flux amplitudeDelayed neutron fractionPrompt neutron lifetimeReactivity C

PM-0619-65962 12Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Model Equations of the PIM code

• Heat conduction in fuel rods

-Pellet conductivity is function of temperature and burnup

-Driven by energy deposited in fuel pellets

-Heat flux at outer rod surface as power source to coolant

-Pellet temperature needed for Doppler reactivity

• Heat transfer models for heat sink (steam generator)

-Secondary side flow is driven by user

-provided inlet forcing function

-Secondary flow is subcooled, 2

-phase equilibrium, and superheated

-Primary flow parameters calculated from transient conservation equations

-Heat transfer between primary and secondary flow

• Heat transfer correlations

• Transient heat conduction in tube walls PM-0619-65962 13Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Model Equations of the PIM code

• Closing Relations and Correlations

-Frictional pressure drop (single

-and two-phase friction and local losses)

-Drift flux parameters

-Non-equilibrium evaporation and condensation model

-Thermodynamic properties for water

-Physical material properties (pellets, cladding, SG tubes)

-Pellet-clad gap conductance

-Reactivity coefficients as functions of exposure and moderator density

• What is not modeled

-Pressurizer; pressure is input provided constant or forcing function

-Heat transfer through riser wall, adiabatic riser is default option

-Heat capacity of structures; only ambient heat losses through vessel PM-0619-65962 14Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5PIM Results of Perturbing SS

• Purpose is to calculate stability parameters of decay ratio and period at different conditions of power and exposure

-Following a user

-applied small perturbation flow will oscillate-Oscillations will grow with time if system is unstable

-Oscillations will decay eventually returning to the pre-perturbation state if the system is stable

• Stability parameters, decay ratio and period, are extracted from the transient output. Observations:

-Unconditional stability in the entire operational range

-DR decreases with power and exposure

-Period also decreases with p ower-Observations agree with the independent Reduced Order Model PM-0619-65962 15Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5PIM Application Methodology

• For perturbations of steady state to get DR

-Vary power within 5

-100% of rated

-BOC and EOC, and any point in between if warranted

-Conservative assumptions for MTC and decay heat fraction

• For a depressurization transient (scram not credited)

-Verify that unstable oscillations limit cycle without CHFR decrease

• Stability conclusion is generic, but confirmation is needed

-For plant upgrades such as power uprates

-Plant operation changes such as operating temperatures and maximum boron concentration

-Changes in fuel design that would change natural circulation flow PM-0619-65962 16Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Long Term Stability Solution

• Region Exclusion for NuScale

-Unstable region defined by a single parameter (core exit subcooling)

-Monitor and protect margin to riser exit subcooling (with temperature margin below saturation point at pressurizer pressure)

-Operator alarm when subcooling margin is approached

-Riser exit subcooling will be controlled by the reactor protection system as part of normal operating limits

-not only for preventing instabilities

-Generic solution: there are no fuel or cycle design elements PM-0619-65962 17Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Summary and Conclusions

• Stability of the NuScale module was evaluated using a dedicated code (PIM) and supported by first principles analysis and experimental data benchmarking

• The module was found unconditionally stable within

normal operation domain using conservative criterion

• Stability boundary identified as associated with riser

voiding (loss of riser inlet subcooling)

• Stability protection methodology protects riser inlet

subcooling with a margin to define the exclusion region enforced by the module protection system with scram PM-0619-65962 18Copyright 2019 by NuScale Power, LLC.Revision: 0 Template #: 0000

-21727-F01 R5Portland Office6650 SW Redwood Lane, Suite 210 Portland, OR 97224 971.371.1592Corvallis Office1100 NE Circle Blvd., Suite 200 Corvallis, OR 97330 541.360.0500Rockville Office11333 WoodglenAve., Suite 205Rockville, MD 20852 301.770.0472Charlotte Office2815 Coliseum Centre Drive, Suite 230 Charlotte, NC 28217 980.349.4804Richland Office

1933 JadwinAve., Suite 130Richland, WA 99354 541.360.0500Arlington Office2300 Clarendon Blvd., Suite 1110 Arlington, VA 22201London Office 1 stFloor Portland HouseBressendenPlaceLondon SW1E 5BH United Kingdom

+44 (0) 2079 321700http://www.nuscalepower.comTwitter: @NuScale_Power Presentation to the ACRS Subcommittee Staff Review of NuScale Topical Report TR-0516-49417-P, REVISION 0"EVALUATION METHODOLOGY FOR STABILITY ANALYSIS OF THE NUSCALE POWER MODULE"Presenters: Ray Skarda, Ph.D.-Reactor Systems Engineer, RESPeter Yarsky, Ph.D.

-Senior Reactor Systems Engineer, RESBruce Bavol

-Project Manager, Office of New ReactorsJune 19, 2019(Open Session)Non-Proprietary 1

NRC Technical Review Areas/Contributors 2Non-Proprietary

• Ray Skarda

-RES/Division of Systems Analysis (DSA)/Code and Reactor Analysis Branch (CRAB)

• Peter Yarsky

-RES/DSA/CRAB

• Rebecca Karas (BC) -NRO/Division of Engineering, Safety Systems and Risk Assessment (DESR)/Reactor Systems, Nuclear Performance, and Code Review Branch (SRSB)

Staff Review Timeline

• NuScale submitted the Topical Report (TR) TR

-0516-49417-P, "Evaluation Methodology for Stability Analysis of the NuScale Power Module," on July 31, 2016, (Agencywide Documents Access and Management System (ADAMS) Accession No.

ML16250A851). Applicant provided supplemental information by letter dated December 3, 2016 (ADAMS Accession No.

ML16340A756).

• Staff issued 62 requests for additional information (RAIs) with

NuScale providing responses

-all responses were resolved/closed.

• Staff plans to brief advisory committee on reactor safeguards (ACRS) fullcommittee on July 10, 2019

• Staff plans to issue its final SER in late August 2019.

• Staff plans to publish the "

-A" (approved) version of the TR in late November 2019.

3Non-Proprietary OutlinePrimary Review Areas

• Regulatory Criteria

• Long Term Stability Solution

• Instability Modes and Phenomenology

• PIM Evaluation Model

• Uncertainty and Acceptance Criteria

• Stability with Worst

-Rod-Stuck-Out (WRSO)

• Stability Topical Report Conclusions

• Design Certification Document (DCD) 15.9 Stability 4Non-Proprietary Regulatory CriteriaGeneral Design Criteria (GDCs) from Design

-specific Review Standard 15.9.A

• GDC 10, "Reactor Design," requires that specified acceptable fuel design limits (SAFDL) not be exceeded during any condition of normal operation, including conditions that result in unstable power oscillations with the reactor trip system available.

• GDC 12, "Suppression of Reactor Power Oscillations," requires that oscillations

be either not possible or reliably and readily detected and suppressed.

• GDC 13, "Instrumentation and Control," includes requirements for the hardware

implementation of long term stability (LTS) solution.

• GDC 20, "Protection System Functions," requires the reactor protection system to

initiate automatic action so unstable power oscillations are avoided.

• GDC 29, "Protection against Anticipated Operational Occurrences," requires

stability LTS solution design for an extremely high probability of accomplishing safety functions.

5Non-Proprietary Long Term Stability Solution (LTSS) Exclusion Region Based Solution 6Non-Proprietary

• The NuScaleLTSS is based on an exclusion region principle. GDC 12 and GDC 10 are met by preventing instabilities that could challenge specified acceptable fuel design limits (SAFDLs).

• The Module Protection System (MPS) precludes instability by enforcing riser subcoolingmargin and tripping the reactor. GDC 13, GDC 20, and GDC 29 are met by operation of the MPS to sense adverse conditions and trip the reactor.

Instability Modes

• Dynamic and static instability modes were considered.

• Applicant identified and evaluated many modes.

• The applicant's findings in terms of modes are consistent with staff findings from an independent Phenomena Identification and Ranking Table development process.

7Non-Proprietary PIM Evaluation ModelThe PIM Evaluation Model is Simple but Acceptable

• The PIM evaluation model includes simple models for thermal

-hydraulics, reactor kinetics, fuel thermal

-mechanical response, and steam generator tube heat conduction and heat transfer.

• Integral validation provided against NIST

-1 stability tests.

8Non-Proprietary Decay Ratio (DR) Acceptance Criterion

• DR is insensitive to variations in most of the important phenomena over the PIM application range.

• DR Acceptance Criterion affords sufficient margin to account for bias and

uncertainty.*Numerical effects were considered as part of the DR bias.

9Non-Proprietary Stability with WRSONuScale is stable at intermediate pressures

• Applicant conservatively analyzed stability for intermediate pressures (i.e, before emergency

-core-cooling-system (ECCS) actuation).

• Strong moderator feedback increases likelihood of recriticality with

WRSO, but strong moderator feedback is stabilizing.

• Applicant's analysis demonstrates stability margin at intermediate

pressures.10Non-Proprietary Stability with WRSONuScale will experience mild flow oscillation at low pressure*After ECCS actuation, level drops below the riser, natural circulation flow pattern is broken and flow oscillations occur where core flow is driven by density head differences provided by void formation in the core region.

• Analyses performed by the applicant demonstrate flow oscillations that

are not safety significant.

11Non-Proprietary Stability Topical Report ConclusionsPIM-based Stability Analysis Method is Acceptable

• PIM is a simple model, but its models are anchored to upstream, high

-fidelity models to improve accuracy.

• The DR is highly insensitive to variations in important phenomena and

their models, leading to relatively small uncertainty in the DR.

• PIM predictions in steady

-state and transients have been confirmed by the staff with independent TRACE confirmatory calculations.

• PIM is acceptable for performing stability analysis for the NuScale power

module.12Non-Proprietary Stability Topical Report ConclusionsLTS Solution is Acceptable

• Primary instability mechanism properly identified by the applicant and confirmed by independent staff TRACE analysis.

• During normal, at power operation, the NuScale power module is very

stable.*The exclusion region based LTS solution is effective in preventing the

reactor from becoming unstable during normal operation including the effects of AOOs.

• Potential instability during return to power with WRSO is not a safety

concern.*GDCs 10, 12, 13, 20, and 29 are met.

13Non-Proprietary DCD 15.9 Stability ReviewStability Performance during Steady State Conditions is Acceptable

• Stable under steady

-state conditions

-Analyses demonstrate at all power levels > 5 percent of rated that the DR remains well below the acceptance criterion.

• Transients analyzed

-Certain events result in new stable, steady state conditions.

-Certain events result in reactor trip due to MPS enforcement of the

exclusion region prior to the onset of instability.

14Non-Proprietary DCD 15.9 Stability ReviewStability Performance during Transients is Acceptable

• All AOO classes considered in the applicant's analysis.

-Increase in heat removal by the secondary system

-Decrease in heat removal by the secondary system

-Decrease in reactor coolant system flow rate

-Increase in reactor coolant inventory

-Reactivity and power distribution anomalies

-Decrease in reactor coolant inventory

• LTS Solution is effective in preventing the occurrence of instability.

• Therefore GDCs 10, 12, 13, 20, and 29 are met.

15Non-Proprietary Questions/comments before the closed session starts?

16Non-Proprietary 17Non-ProprietaryBackup Slides 18Non-ProprietaryDCD 15.9 Stability ReviewIncrease in Heat Removal by the Secondary System*Analysis consistent with the stability analysis methodology topical report.

• Applicant analyzed maximum feed flow increase that does not produce an automatic, prompt MPS trip.

• PIM calculations confirm that the reactor remains stable 19Non-ProprietaryDCD 15.9 Stability ReviewDecrease in Heat Removal by the Secondary System*The staff reviewed the feedwater (FW) flow reduction event analyzed in the DCA. *The DCA demonstrates that even mild FW flow events will progress in similar manners, eventually leading to a MPS trip based on hot

-leg temperature (i.e., the LTSS).

• Therefore, the staff finds that the LTSS is effective in preventing the reactor from reaching an unstable condition.

• The staff review of the DCA analysis does not impact the staff review of the Stability TR.

20Non-ProprietaryDCD 15.9 Stability ReviewDecrease in Reactor Coolant System Flow Rate

• CVCS pump over

-speed would be considered an AOO.

• The staff found that a CVCS flow reduction or a reduction in secondary side heat removal event would bound this class of events.

• Analysis of CVCS pump over

-speed is not required to demonstrate compliance with GDC 12.

21Non-ProprietaryDCD 15.9 Stability ReviewIncrease in Reactor Coolant Inventory

• Events that increase inventory but also increase reactor coolant system pressure are non

-limiting because higher pressure increases stability margin.*Staff considered events such as CVCS or spray malfunction that could increase inventory but maintain pressure, and these would be bounded by events that increase or decrease secondary side heat removal.

• Analysis of this class of event is not required to demonstrate compliance with GDC 12.

22Non-ProprietaryDCD 15.9 Stability ReviewReactivity and Power Distribution Anomalies

• A bounding event is analyzed based on a maximum control rod withdrawal that does not produce an automatic, prompt MPS trip based on high flux or high flux rate.

• PIM calculations confirm that the reactor remains stable.

23Non-ProprietaryDCD 15.9 Stability ReviewDecrease in Reactor Coolant Inventory

• The limiting event is a slow depressurization where the low pressure trip is not credited.

• PIM calculations show that, eventually, the reduction in pressure leads to low riser subcooling, which initiated the LTS solution MPS trip to enforce the exclusion region.

• PIM calculations demonstrate that the onset of instability would occur well after the reactor is shutdown by control rods.

24DCD 15.9 Stability ReviewLTS Solution MPS Trip TimingNon-Proprietary 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com

1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com

June 19, 2019

June 19, 2019

Decrease in RCS flow rate (n/a to NPM design)

RCS pressure, secondary pressure, Safe stabilized condition Fuel cladding integrity Radiological dose acceptance criteria

MCHFR, Water level above top of fuelWater level above top of fuel, Cladding temp, Boron precipitation Containment peak pressure, temperature

June 19, 2019

June 19, 2019

June 19, 2019

June 19, 2019

'Steam generator tube rupture events shall also be reviewed as part of the LOCA break

spectrum analysis. The

reviewer shall review the

potential coolant inventory

loss from reactor vessel to the secondary side.'

June 19, 2019

The reactivity control systems shall be designed to have a combined capability of reliably controlling reactivity changes to as sure that under postulated accident conditions and with appropriate margin for stuck rods the capability to cool the core is maintai ned.Following a postulated accident, the control rods shall be capable of holding the reactor core subcritical under cold condition s, without margin for stuck rods.

Portland Office6650 SW Redwood Lane, Suite 210 Portland, OR 97224

971.371.1592Corvallis Office1100 NE Circle Blvd., Suite 200 Corvallis, OR 97330

541.360.0500Rockville Office11333 WoodglenAve., Suite 205 Rockville, MD 20852

301.770.0472Charlotte Office2815 Coliseum Centre Drive, Suite 230 Charlotte, NC 28217

980.349.4804Richland Office 1933 JadwinAve., Suite 130 Richland, WA 99354

541.360.0500Arlington Office2300 Clarendon Blvd., Suite 1110 Arlington, VA 22201London Office 1 st Floor Portland HouseBressendenPlace London SW1E 5BH

United Kingdom

+44 (0) 2079 321700http://www.nuscalepower.comTwitter: @NuScale_Power