ML25100A195
| ML25100A195 | |
| Person / Time | |
|---|---|
| Issue date: | 03/04/2025 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | |
| References | |
| NRC-0240 | |
| Download: ML25100A195 (1) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
Advisory Committee on Reactor Safeguards NuScale Design Centered Review Open Session Docket Number:
(n/a)
Location:
teleconference Date:
Tuesday, March 4, 2025 Work Order No.:
NRC-0240 Pages 1-102 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1716 14th Street, N.W.
Washington, D.C. 20009 (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 COMMISSIONS 7
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 8
9 10 The contents of this transcript of the 11 proceeding of the United States Nuclear Regulatory 12 Commission Advisory Committee on Reactor Safeguards, 13 as reported herein, is a record of the discussions 14 recorded at the meeting.
15 16 This transcript has not been reviewed, 17 corrected, and edited, and it may contain 18 inaccuracies.
19 20 21 22 23
1 UNITED STATES OF AMERICA 1
NUCLEAR REGULATORY COMMISSION 2
+ + + + +
3 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 4
(ACRS) 5
+ + + + +
6 NUSCALE DESIGN-CENTERED REVIEW SUBCOMMITTEE 7
(OPEN) 8
+ + + + +
9 TUESDAY 10 MARCH 4, 2025 11
+ + + + +
12 The Subcommittee met via Video 13 Teleconference, at 9:30 a.m. EST, Walter L. Kirchner, 14 Chair, presiding.
15 16 SUBCOMMITTEE MEMBERS:
17 WALTER L. KIRCHNER, Chair 18 GREGORY H. HALNON, Vice Chair 19 DAVID A. PETTI, Member-at-Large 20 RONALD G. BALLINGER 21 VICKI M. BIER 22 VESNA B. DIMITRIJEVIC 23 CRAIG D. HARRINGTON 24 ROBERT P. MARTIN 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
2 SCOTT P. PALMTAG 1
THOMAS E. ROBERTS 2
MATTHEW W. SUNSERI 3
4 ACRS CONSULTANT:
5 DENNIS BLEY 6
STEVE SHULTZ 7
8 DESIGNATED FEDERAL OFFICIAL:
9 MICHAEL SNODDERLY 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
3 AGENDA 1
I Opening remarks..............
4 2
II Discussion of NuScale Non-Loss-of-3 Coolant-Accident Analysis Methodology 4
Topical Report 9
5 III Staff's Evaluation of NuScale Non-Loss-of-6 Coolant-Accident Analysis Methodology 7
Topical Report
.............. 36 8
IV Discussion of NuScale Extended Passive 9
Cooling and Reactivity Control Methodology 10 Topical Report
.............. 55 11 V
Staff's Evaluation of NuScale Extended 12 Passive Cooling and Reactivity Control 13 Methodology Topical Report
........ 82 14 VI Opportunity for Public Comment 102 15 Adjourn 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
4 P-R-O-C-E-E-D-I-N-G-S 1
9:30 a.m.
2 CHAIR KIRCHNER: Okay, the meeting will 3
now come to order. Good morning. This is the meeting 4
of the NuScale Design Centered Review Subcommittee of 5
the Advisory Committee on Reactor Safeguards. I'm 6
Walt Kirchner, Chairman of today's subcommittee 7
meeting.
8 ACRS members in attendance in person are 9
Ron Ballinger, Vicki Bier, Craig Harrington, Robert 10 Martin, David Petti, Scott Palmtag and Thomas Roberts.
11 ACRS members in attendance virtually via 12 Teams are Vesna Dimitrijevic, Greg Halnon and Matt 13 Sunseri. We also have two of our consultants 14 participating virtually via Teams, Dennis Bley and 15 Steve Shultz. If I missed anyone, either ACRS members 16 or consultants, please speak up now.
17 Michael Snodderly of the ACRS staff is the 18 Designated Federal Officer for this meeting. No 19 member of conflicts of interest were identified and I 20 note that we have a quorum.
21 During today's meeting, the subcommittee 22 will receive a briefing on the staff's evaluation of 23 NuScale Topical Report TR051649416: Proprietary Non-24 Loss-of-Coolant Accident Analysis Methodology and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
5 TR124587: Extended Passive Cooling and Reactivity 1
Control Methodology.
2 We previously reviewed the certified 3
NuScale US600 design as documented in our July 29, 4
2020 letter report on the safety aspects of the 5
NuScale small modular reactor. Like the staff, we are 6
performing a delta review between the two designs 7
including a power uprate from 50 to 77 megawatts 8
electric per module. We are reviewing these chapters 9
and TRs as part of our statutory obligation under 10 Title 10 of the Code of Federal Regulations, Part 52, 11 Subpart E, Section 141, Referrals to the Advisory 12 Committee on Reactor Safeguards.
13 We report on those portions of the 14 application which concern safety. The ACRS was 15 established by statute and is governed by the Federal 16 Advisory Committee Act or FACA. The NRC implements 17 FACA in accordance with its regulations. Per these 18 regulations and the Committee's bylaws, the ACRS 19 speaks only through its published letter report. All 20 member comments therefore should be regarded as only 21 the individual opinion of that member not a Committee 22 position.
23 All relevant information related to ACRS 24 activities, such as letters, rules for meeting 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
6 participation and transcripts, are located on the NRC 1
public website and can easily be found by typing 2
"About us ACRS" in the search field on NRC's home 3
page.
4 The ACRS, consistent with the agency's 5
value of public transparency and regulation of nuclear 6
facilities, provides opportunity for public input and 7
comment during our proceedings. We have received no 8
written statements or requests to make an oral 9
statement from the public, but we have set aside time 10 at the end of the meeting for such public comments.
11 Portions of the meeting may be closed to 12 protect sensitive information as required by FACA and 13 the Government in the Sunshine Act. Attendance during 14 the closed portion of the meeting will be limited to 15 the NRC staff and its consultants. Applicants and 16 those individuals in organizations who have entered 17 into an appropriate confidentiality agreement, we will 18 confirm that only eligible individuals are in the 19 closed portion of the meeting later this afternoon.
20 The ACRS will gather information, analyze 21 relevant issues and facts and formally propose 22 conclusions and recommendation as appropriate for 23 deliberation by the full Committee. A transcript of 24 the meeting is being kept and will be posted on our 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
7 website. When addressing the Subcommittee, the 1
participants should first identify themselves and 2
speak with sufficient clarity and volume so that they 3
may be readily heard. If you are not speaking, please 4
mute your computer on Teams or by pressing *6 if 5
you're on your phone.
6 Please do not use the Teams chat feature 7
to conduct sidebar discussions related to 8
presentations, rather limit the use of the meeting 9
chat function to report IT problems.
10 For everyone in the room, please put your 11 electronic devices in silent mode and mute your laptop 12 microphone and speakers. In addition, please keep 13 sidebar discussions in the room to a minimum because 14 our ceiling microphones are live.
15 For presenters, your table microphones are 16 unidirectional and you'll need to speak into the 17 microphone to be heard. Finally, if you have any 18 feedback for the ACRS about today's meeting, we 19 encourage you to fill out the public meeting feedback 20 form on the NRC's website. With that, we will now 21 proceed with the meeting and I will turn first to the 22 NRC staff and to M.J. for opening comments.
23 MR. JARDANEH: Thank you. Good morning, 24 Chair Kirchner and good morning to the ACRS 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
8 Subcommittee Members, NuScale participants, NRC staff 1
and members of the public.
2 My name is Mahmoud M.J. Jardaneh and I 3
serve as the Branch Chief of the New Reactor Licensing 4
Branch, responsible for the licensing of the NuScale 5
US460 design and the Division of New and Renewed 6
Licenses in NRR. Thank you for the opportunity today 7
for the staff to present their review of the select 8
NuScale US460 Standard Design Approval or SDA, 9
chapters and topical reports.
10 As you are aware, the staff is reviewing 11 all chapters of the SDA concurrently with staggered 12 completion dates based on the complexity of the 13 chapter and the extent of change from the certified 14 NuScale US600 design. Today, the staff will be 15 presenting on their review of the seventh group of the 16 SDA chapter and topical reports, including on the Non-17 Loss-of-Coolant Analysis Methodology Topical Report 18 and the Extended Asset Cooling and Reactivity Control 19 Methodology Topical Report.
20 Previously, the staff presented to the 21 Subcommittee on 16 of the 19 SDA chapters and one of 22 three SDA Topical Reports. The staff is finalizing 23 their review of the remaining three SDA chapters and 24 we will soon share their safety evaluations with the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
9 ACRS.
1 At today's meeting, the staff will focus 2
on the deltas from the design certifications that the 3
NRC approved and the Committee reviewed in the past.
4 The staff will also discuss two remaining open items, 5
one in each of the topical reports to be presented 6
today.
7 Once again, thank you for the opportunity 8
and we look forward to a good discussion. Thank you.
9 CHAIR KIRCHNER: Thank you, M.J. Now, we 10 will turn to NuScale. I believe, Kevin, are you going 11 to kick it off for NuScale?
12 MR. LYNN: Sure, I can do that. Thank 13 you. Good morning, members of the ACRS, NRC staff and 14 thank you for having us here. We appreciate the 15 opportunity.
16 My name is Kevin Lynn. I'm a licensing 17 engineer at NuScale and I've been with NuScale for 18 over three years. Prior to my time at NuScale, I was 19 working in the Nuclear Navy. I also worked in Part 52 20 New Design, New Reactor Design with a different design 21 center and also spent time in an operating plant 22 reactor and also on license renewal for operating 23 plants. I'll allow my colleagues here to introduce 24 themselves as well.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
10 MR. BRISTOL: Good morning, this is Ben 1
Bristol. I'm the manager of the system thermal 2
hydraulics team at NuScale. I've been with NuScale 3
for 13 years now.
4 MS. MCCLOSKEY: Good morning, my name is 5
Meghan McCloskey. I'm a safety analysis engineer with 6
NuScale and I've been with them for about the past 10 7
years and prior to that, I was with Westinghouse, 8
always focused on safety analysis methodology 9
development and application for design basis events.
10 CHAIR KIRCHNER: Thank you all for being 11 here in person. Go ahead.
12 MR. LYNN: Next slide, please. Before we 13 begin, we'd like to acknowledge that our work at 14 NuScale has been supported by the Department of Energy 15 and so we appreciate their support, but also 16 acknowledge that the views expressed during these 17 presentations are not necessarily those of the DOE.
18 Next slide, please.
19 During the open session for non-LOCA 20 topical report, we will start by talking about the 21 history of the non-LOCA topical report, talk about the 22 non-LOCA evaluation model, what the purpose is and the 23 acceptance criteria that's used to analyze. We'll 24 talk about the relevant power uprate and the design 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
11 and operating changes that have the potential to 1
affect the non-LOCA topical report and finish with a 2
summary of the evaluation model applicability 3
assessment and any changes that we've made since the 4
prior revision. Next slide, please.
5 As was alluded by the ACRS, the non-LOCA 6
topical report was previously reviewed by the staff 7
and the ACRS. It was approved by the NRC in 2020 and 8
that approved revision, which was revision three, was 9
used to support safety analyses performed for the 10 US600 design, which utilized the NPM-160 module. That 11 was submitted as part of the review of that.
12 That revision contains certain limitations 13 and conditions which restricted its use to the NMP-160 14 design, so when we began the work on our next design, 15 we realized that we would need to make some 16 modifications to that and so therefore, revision four 17 was submitted in January 2023 and it was submitted at 18 the same time as we submitted our FSAR for the US460 19 design, which utilizes the NMP-20 module.
20 Since the time of the submittal in January 21 2023, we have made some updates and changes to the 22 topical report in response to NRC questions and back 23 and forth with the NRC staff. Revision five will be 24 submitted at some point, which will incorporate all 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
12 those updates, but it has not been submitted at this 1
time. The hope would be that then revision five would 2
become the Dash A approved version for future use. As 3
indicated by the ACRS, due to the nature of the delta 4
review, our focus of the discussion today is on the 5
changes since the NRC's prior approval in revision 6
three. Next slide.
7 This slide provides an overview of the 8
non-LOCA topical report and methodology and how it 9
fits in with other methodology that we utilize as part 10 of the safety analysis. On the left, we start with 11 certain input parameters related to the plant design, 12 core design, fuel design and the SSC design and those 13 all provide input to the NRELAP5 code, which is our 14 system thermal-hydraulic code. NRELAP5 is then used 15 to generate primary and secondary pressures that are 16 used to assess acceptance criteria and it's also used 17 to determine the exit of the safety analysis via 18 confirmation that we have a
- safe, stabilized 19 condition. All of that in that first box is the 20 subject of the non-LOCA topical report.
21 The NRELAP5 output is also used to provide 22 input to the VIPRE-01 code, which is used for our 23 subchannel analysis to determine acceptance criteria 24 for fuel. That's the subject of separate topical 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
13 reports for the subchannel which have both been 1
previously approved by the NRC. Lastly, there is the 2
potential that NRELAP5 is used to provide input to the 3
dose analysis in the form of mass and energy released 4
and that analysis is done separate from this, but is 5
also the subject of an approved top-four port.
6 DR. MARTIN: Question?
7 MR. LYNN: Yeah.
8 DR. MARTIN: It's Member Martin. The 9
NRELAP5 we, of course, have had other meetings and 10 talked about NRELAP5 or the specific application non-11 LOCA. Are there any different packages that are used 12 and so we set that up a little bit more. Some 13 applicants will use the same code but then they are in 14 the process of personalizing it. They'll have an 15 input that says this is for this specific application 16 and then for others, what it does it just creates a 17 different flow through the architecture of the code.
18 For instance, one applicant does both Ps and Bs and 19 they'll have a P or a B in one of the cards up front 20 and it will use a different constituent package.
21 Do you have anything like that in your 22 code?
23 MS. MCCLOSKEY: No.
24 DR. MARTIN: Okay.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
14 MS. MCCLOSKEY: No, we just have the 1
normal, you know, the user options for things like 2
choke flow and --
3 DR. MARTIN: Sure, sure, nothing that 4
you've added specifically that changes the course of 5
events as a consequence of say a different view of the 6
events that you're studying.
7 MS. MCCLOSKEY: No. Nothing like that 8
that fundamentally changes the models or the 9
structures.
10 DR. MARTIN: Right. We've also talked 11 about in the previous meetings that you have changed 12 a version or you've upgraded your version, your 1.7, 13 I believe it's still an open item and I'm sure you're 14 rapidly trying to close, but could you just to the 15 extent that's reasonable in an open meeting like this, 16 just kind of talk about from your perspective what 17 remains to be done to close out any questions related 18 to NRELAP5. Maybe it's just administrative at this 19 point, but --
20 MR. LYNN: So, the only open item at this 21 point is related to a question related to the 22 particular base model that's in use. We have the 23 version, I think we're pretty squared away on the 24 NRELAP version we're using, but as part of that, we 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
15 have a base model that's used essentially as a 1
starting point for all the event-specific analyses and 2
we made some updates to that base model. The staff is 3
still reviewing those updates as a delta compared to 4
the previous base model that we used prior to that 5
point. There's been some questions about that but 6
we're rapidly reaching convergence on that.
7 DR. MARTIN: Oh, so prior to that point 8
are you referring to five years ago or six years ago?
9 MR. LYNN: No, so actually when we 10 submitted in January 2023, we were using a specific 11 version of the NRELAP code 1.6 and the specific 12 version of the base model and since that time, during 13 the course of the review, we made changes both the 14 NRELAP version and to the base model.
15 DR. MARTIN: Okay.
16 MR. LYNN: And so the staff started their 17 review and reviewed the delta essentially from the 18 version we submitted in January 2023 prior to what 19 they approved before and now they are reviewing the 20 delta between what we submitted in January 2023 to the 21 changes that we made during the course of the review.
22 DR. MARTIN: Okay. Are you saying maybe 23 more focus is on really the model and not so much the 24 code?
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
16 MR. LYNN: Correct.
1 (Simultaneous speaking.)
2 DR. MARTIN: Right, so --
3 MR. LYNN: And at this point --
4 DR. MARTIN: Nodalization and some code?
5 MS. MCCLOSKEY: It's not nodalization, 6
it's more on factors of how we've modeled things, like 7
the feedwater pump response, during non-LOCA events.
8 We've modeled that more realistically now.
9 DR. MARTIN: Okay. Okay.
10 MR. LYNN: Yeah, there was an initial 11 condition focused --
12 (Simultaneous speaking.)
13 DR. MARTIN: It's state of the art.
14 MR. LYNN: Some changes to the DHRS, our 15 decay heat removal system, modeling to make it a 16 little bit more realistic. Previously, we'd neglected 17 some portions of the system conservatively. We added 18 those to be more realistic and that was the change 19 then that the staff wanted to --
20 (Simultaneous speaking.)
21 DR. MARTIN: When you say realistic, are 22 you implying that -- and maybe I'm reading too much 23 into it, maybe from testing?
24 MR. LYNN: No, so just component wise.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
17 For example, the DHRS is --
1 COURT REPORTER: Excuse me, sorry to 2
interrupt. I'd just like to remind folks to state 3
their name before speaking. I'm having a bit of 4
difficulty determining who is speaking since there is 5
no video feed and everyone is in one room.
6 MR. LYNN: Okay, this is Kevin Lynn. You 7
threw me off. The DHRS receives steam from the steam 8
system and that piping to the DHRS, is a heat 9
exchanger essentially, that piping that carries steam 10 runs and goes through the heart of the refueling coil 11 or the UHS and so there's some condensation that 12 happens as that piping goes through the water before 13 it gets to the heat exchanger.
14 So, on one hand you could conservatively 15 ignore that, but it is actual heat transfer that's 16 occurring, so we've modeled some of those features.
17 DR. MARTIN: Okay.
18 CHAIR KIRCHNER: Maybe you've talked about 19 it before. You're taking credit now and before you 20 hadn't.
21 MR. LYNN: Okay.
22 DR. MARTIN: I remember that conversation 23 previously. All right, thanks. That's all.
24 MR. LYNN: So, to finish this slide just 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
18 to point out that this general picture here and this 1
general scope is consistent with what we had when we 2
were here for prior approval of revision three. Next 3
slide, please.
4 So, now I'll talk about the power uprate 5
and the design changes from the NMP-160 to the NMP-20.
6 The biggest change was an uprate from 160 megawatts 7
hence the name to 250 megawatts thermal, which is our 8
current design, approximately 70-some megawatts 9
electric which was referenced by the ACRS in the 10 opening.
11 For the most part in terms of non-LOCA, 12 the module SSC design is essentially maintained.
13 There were some changes to the operating conditions, 14 so the normal primary pressure, normal operating 15 pressure increased from 1,850 to 2,000 PSI and along 16 with that, we increased the design pressure of the 17 primary side from 2,100 to 2,200 and the secondary 18 side has the same design pressure.
19 With the increase in power, we have a 20 larger delta T across the core because we're natural 21 circulation, but we use a constant T(avg) control and 22 that T(avg) was changed slightly from approximately 23 545 to 540. There was also a reduction in secondary 24 side feedwater temperature and a reduction in the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
19 minimum temperature for criticality during startup.
1 There were some optimizations made to our 2
module protection system for the US460 design. Some 3
of the set points were adjusted to match the changes 4
that we made to the operating conditions. For 5
example, when we increased the pressure, we had to 6
increase the pressure for the trip rated to pressure.
7 There was also a new trip added on high 8
T(avg) and that was added specifically to terminate 9
some of our slower reactivity transients earlier, like 10 a rod withdrawal happening from maybe 75 percent power 11 wasn't hitting the high temperature and high power set 12 points, but the high T(avg) could reach that earlier 13 and cause a trip.
14 Finally, we added some additional DHRS 15 actuations and an isolation of the pressurizer line on 16 low pressurizer pressure. The one thing you won't see 17 on here is some of the discussion of the changes to 18 the ECCS. Those are more pertinent to the LOCA 19 discussion which was held previously, so we're not 20 covering those because they don't come into play in 21 non-LOCA.
22 There was also a change to add an ECCS 23 supplemental boron system. That's not relevant per se 24 to the non-LOCA but it will come up later today when 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
20 we talk about the XPC topical report. Next slide, 1
please.
2 MR. ROBERTS: This is Tom Roberts. Just 3
out of curiosity, why did you pick high T(avg) instead 4
of high T(hot)?
5 MR. LYNN: This is Kevin. We had an 6
existing high T(hot) trip and in this particular case 7
for these particular transients, they weren't reaching 8
the high T(hot) trip as fast as we would like to 9
mitigate them, so in this particular case, they reach 10 high T(avg) sooner than they reach high T(hot), but 11 the high T(hot) is still active.
12 MR. ROBERTS: Okay, thank you.
13 MR. LYNN: Next slide, please. This slide 14 shows a comparison of the US460 to the US600. On the 15 left is the US600 which is our certified design and on 16 the right is US460. This kind of demonstrates the 17 changes that we made to some of the operating 18 conditions. For example, the red line at the top of 19 the box is moved upward because we have that higher 20 operating design pressure and the blue line, which is 21 the normal operating pressure, is moved up as well.
22 You can see the box that we would like to 23 operate in, in which case our safety analysis starts 24 from, is the box with the dotted black lines with 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
21 T(avg) green right in the middle. The size of that 1
box is essentially unchanged between the two designs.
2 Next slide.
3 CHAIR KIRCHNER: Kevin, since you showed 4
it, could I just ask would you just explain you now 5
have a lower acceptable temperature for going 6
critical, what's the design basis behind that?
7 MR. LYNN: So, that's to allow startup 8
sooner essentially. To reach a startup condition, we 9
have to heat up the plant. So, we have a module heat 10 up system which adds heat, non-nuclear heat, into the 11 system and in the previous design it was a 420, so you 12 had to do quite a bit of heat up of non-nuclear heat 13 and this change allows us to essentially go critical 14 earlier and heat up the rest of the way with nuclear 15 heat.
16 CHAIR KIRCHNER: Thank you.
17 MR.
LYNN:
It was essentially an 18 improvement in terms of start up of plant. Next 19 slide.
20 We'll talk about the analytical 21 assumptions used in the non-LOCA analysis. The 22 general approach from the previous revision is 23 maintained. In terms of the scope of the event, we 24 analyzed the design basis events from an event 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
22 initiation until a safe, stable condition is reached.
1 There's kind of two ways that we can reach a safe, 2
stable condition. One is reactor trip and DHRS 3
operation. We have trends that show the temperature 4
is decreasing and pressure is decreasing, so we're on 5
a safe trajectory.
6 The other is potentially there are some 7
events where a reactor trip doesn't occur, a minor 8
decrease in feedwater temperature, a minor decrease in 9
feedwater flow we can essentially reach a new steady 10 state condition. So, that's the end of the event in 11 terms of the scope of the event progression.
12 Obviously, in terms of plant operation, the operators 13 would at some point need to restore themselves back to 14 where they want to be operating, but in terms of 15 operator action, there are no operator actions 16 credited during 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> after initiate event occurs 17 to achieve the safety functions.
18 We do look at different loss of power 19 scenarios, power available, loss of AC power, loss of 20 DC power to see what's more limiting for a particular 21 set of events.
22 We do have non-safety related control 23 systems and those do factor into the non-LOCA 24 analysis, specifically if we have a case where the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
23 normal operation of that control system would tend to 1
make the plant transient less severe, then we neglect 2
or ignore that operation. On the other hand, if we 3
have a normal operating control system that would tend 4
to make the plant more severe, we do then assume that 5
that occurs. So, for an example, in the case of a 6
heat up event or a pressurization event, where 7
pressure is increasing, the normal response of the 8
pressure control system would be to actuate or to turn 9
on spray or increase spray to turn that event around.
10 So, if we credit spray, then it makes the event less 11 limiting, so in those particular cases, we neglect 12 spray which allows the pressurization to continue and 13 eventually reach a trip set point.
14 DR. MARTIN: This is Member Martin. To 15 this question of the role of non-safety systems, when 16 you consider with non-LOCA in particular maybe several 17 figures of merit to look at. Some are going to 18 respond conservatively and some will be non-19 conservative. It really requires a thorough look at 20 these things and not just say attention on maybe the 21 figure of merit with maybe the least amount of margin, 22 right? Because, you know, maybe that one is 23 unaffected or benefits from the role of the non-safety 24 control system, but maybe something else affects the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
24 other metrics. Now, obviously you've been working on 1
this for a really long time and I can only imagine how 2
much analysis you've done.
3 Can you talk a little bit about your 4
approach and this investigation? Is it just kind of 5
brute force, where you kind of evaluated, of course, 6
we kind of know the events, you're more or less a 7
NUREG-0800 you have your own DHRS and all that. But 8
is there a separate kelp file where you just attack 9
this question head-on and identified the events, maybe 10 even a higher level document that, you know, say like 11 a hazards analysis type thing, but one that identifies 12 maybe scenarios from a qualitative standpoint and then 13 those unfortunately seem to matter the most and we go 14 out and determine -- anyway, I'm obviously putting 15 words in your mouth to some extent. Can you briefly 16 go over that about your approach to this sort of thing 17 and how is captured in your QA system or your document 18 control system?
19 MR. LYNN: This is Kevin. One thing that 20 we do is we do, as you mentioned, we do have 21 experience now using this as this is our second 22 design. So, for the experience we had from the US600, 23 we've leveraged that in terms of generally knowing 24 what transients go where and what types of cases that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
25 you need to look at, but certainly as part of the 1
design changes that we made, we looked at wanting to 2
confirm that those behaviors were still true and also 3
see if there were any differences. But for any 4
particular initiating event, we identify first what 5
are the figures of merit for that event, which are 6
most susceptible to that event. For a heat up event, 7
we're not really concerned as much about the fuel 8
response, it's more the pressurization response.
9 For a cool down event, we're both 10 concerned with the fuel response and also potentially 11 the pressurization. In those cases, where there's 12 more than one acceptance criteria that may be 13 relevant, we're looking at different cases within that 14 analysis to potentially maximize or minimize that 15 particular acceptance criteria. One set of conditions 16 may be worse for the RCS pressure, but a different set 17 of conditions may be worse for minimum critical heat 18 flux, for example. So, within a particular event 19 analysis, there's probably on the order of 50 20 individual cases, NRELAP cases, that are run to 21 identify different sensitivities to those things.
22 Even that's potentially in the final documentation of 23 that analysis. In most cases, there is a preliminary 24 analysis that's done that looks at a wider range and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
26 then identifies that hey, this particular set isn't 1
really that important. We can focus in and go to a 2
finer granularity on a particular area of this 3
analysis domain to try and find that limited case.
4 DR. MARTIN: Generally speaking, between 5
the US600 and 460, see any real differences coming out 6
of the design, you know, relatively few design 7
changes? Did you see the trends more or less 8
consistent between the two designs? Any surprises?
9 MR. LYNN: For the most part, things were 10 consistent and I think in our early days, we had some 11 slides in our pre-application meeting comparing the 12 transient progression to show that they were quite 13 similar. One thing that does come to mind is that in 14 terms of the CHF performance, there was a particular 15 nuance of the previous design just the operating 16 domain that we were in that it was sensitive in one 17 direction of biased pressure.
18 So, I believe a high bias pressure was 19 potentially more limiting for CHF which was a little 20 bit counterintuitive. When we changed our design 21 pressure and increased it, it's one of the changes we 22 made, that particular sensitivity disappeared. As 23 part of that, we've changed our biases to look at both 24 high and low pressure to find which one is more 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
27 limiting. That was one change that we did identify 1
and the staff asked a question about that and so we 2
made some changes to the top recorded response.
3 DR. MARTIN: Thank you.
4 MR. LYNN: Next slide, please.
5 MR. ROBERTS: Yeah, Kevin.
6 MR. LYNN: Yes?
7 MR. ROBERTS: Stop there for a minute, 8
this is Tom Roberts. That last line, the credit for 9
non-safety valves. Where it says related valves 10 failed to trip. Can you explain that a little bit 11 more? It seems like that essentially says single 12 pairs don't happen because there's a back up valve 13 that predominantly actuates.
14 MR. LYNN: Yes, so for the main steam 15 isolation valves, there's two valves the safety-16 related valve and the non-safety-related valve. In 17 the event of a single failure of either valve, there's 18 no consequence because the other valve is there to 19 provide that protection. The only noteworthy thing 20 here is instead of two safety-related valves, you have 21 a non-safety and a safety. As part of the review, we 22 did have some questions about that and to demonstrate 23 that it was acceptable to have the second valve be a 24 non-safety-related valve.
In terms of their 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
28 performance, the steam isolation valves are the same.
1 They have the same isolation time and everything. On 2
the feedwater side, the back up, the non-safety-3 related valve, has a slightly slower closing time. In 4
our analyses where we take a single failure, there is 5
a delta there a little bit of additional flow that can 6
happen in that time delta between the two valves, but 7
we do factor that into our analysis.
8 MR. ROBERTS: So, what makes a back up 9
valve non-safety? What compromises are made in the 10 quality or something else to not call them safety-11 related? It sounds like we should just say they're 12 essentially the same valves.
13 MR. LYNN: They are essentially the same 14 valves. It's really just a QA designation of the 15 additional pedigree. I don't know if you have 16 anything to add, Meghan.
17 MS. MCCLOSKEY: The regulating valves are 18 going to be different than the isolation valves, but 19 they also have augmented quality requirements applied 20 to them.
21 MR. LYNN: And the non-safety-related 22 valves are also identified in tech specs and 23 controlled under tech specs and part of the in service 24 testing program, etc., so it's really just a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
29 designation.
1 MR. ROBERTS: Okay, yes, thanks. I guess 2
there was an analogy to the EDAS discussion we've had 3
a couple of meetings ago.
4 So, that kind of leads to my next 5
question, with is the single-failure assumptions.
6 That's not on this slide but it is in the topical 7
report.
8 And, there is a specific statement in the 9
topical report that a inadvertent trip of the ECCS 10 valves is not considered a single-failure.
11 We talked about that in a previous 12 meeting, and I'm just wondering if you've got any more 13 to add on that.
14 Because it seems like if you've got, say, 15 one of those trip valves out of service, and that's 16 allowed by tech specs that you be down to a single 17 trip valve.
18 And so a single-failure in the module 19 protective system, would that presumably trip the 20 remaining trip valve and cause the inadvertent 21 actuation.
22 And, it would seem like that would be a 23 passive electrical failure that you need to consider, 24 which is a, like a trip that's not required or not 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
30 desired.
1 It seems to me that's a kind of definite 2
between pass and failure in an electrical system.
3 And so, I was wondering why you would not 4
include that as a single-failure, or why that would 5
not be rolled up in the single-failure exception that 6
you got previously on the IAB valves. It just seems 7
to me like the same thing.
8 MR. LYNN: So, one thing to point out here 9
is in particular for this topical report, it's a non-10 LOCA topical report methodology.
11 And in our methodology, if we open an ECCS 12 valve, it's no longer a non-LOCA event. So, we don't 13 analyze events with valve openings, with ECCS valve 14 openings, using this methodology.
15 So from that perspective, the non-LOCA 16 topical report doesn't address valve opening.
17 But we have heard the concern though and 18 the question before, and we are prepared to discuss 19 that more in detail in the chapter 15 discussion at 20 the next meeting on April 1.
21 MR. ROBERTS: Okay, thank you.
22 MR. LYNN: So in terms of the non-LOCA 23 evaluation model, the focus is on the design changes 24 since our prior approval.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
31 In this particular case, those design 1
changes don't have a substantial impact on our event 2
progressions, or the important phenomena.
3 From a high/low perspective, primary 4
pressure is still protected by lifting of the RSVs if 5
necessary, during an event.
6 Secondary pressure is protected in two 7
ways. One, the design pressure is equal to the 8
primary pressure, which is unique for our design.
9 And also, the secondary pressure during an 10 event is limited to the saturation pressure at the 11 maximum T-hot at the primary side.
12 For minimum critical heat flux, we are 13 limited typically under a high-power or high-14 temperature condition that might occur during an event 15 like a reactivity insertion event, like a rod 16 withdrawal.
17 As discussed earlier, we do employ NRELAP 18 version 1.7 now. Previously, we had used version 1.4 19 and as I mentioned at the start of the review, we used 20 version 1.6 but we're now currently on version 1.7.
21 We did perform a PIRT previously in the 22 previous revision, in revision 3. And, that PIRT was 23 based on the NPM-160 design.
24 We did a
review and applicability 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
32 assessment, and determined that that PIRT remains 1
applicable, and there are no new phenomena that needed 2
to be added or addressed in this revision.
3 One significant change that we did make is 4
that we performed additional testing for the NRELAP, 5
the validation to specifically on the DHRS 6
performance.
7 And so, that new testing was added to the 8
assessment basis as part of the overall validation of 9
the code.
10 In terms of individual events specific 11 analyses methodology, one of the changes we made is to 12 add a little bit more detail on when we need to do 13 additional sensitivity calculations, with an emphasis 14 on the fact that if margin is low for a particular 15 event, more sensitivity is needed.
16 If you have a lot of margin, you don't 17 need as much sensitivity cases.
18 DR. MARTIN: Member Martin. Just to ask 19 a question about the PIRT.
20 What do you do confirm your PIRT? I would 21 imagine do a lot of sensitivity studies particularly, 22 or I mean how formal is that process when you made 23 your initial PIRT over 10 years ago, correct?
24 And then, subsequent to that do a bunch of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
33 sensitivity studies or what? And then for this 1
design, did you just kind of repeat it all?
2 MS. MCCLOSKEY: For this design, we, so 3
for the, in terms of confirming the PIRT, originally 4
we focused on understanding where the high ranked 5
phenomena had been addressed.
6 Because the original PIRT that was done 7
was fairly comprehensive in nature, when we focused on 8
the system thermal hydraulic response.
9 So a number of our phenomena are actually 10 addressed in sub-channel analysis work.
11 So, recognizing where our methodologies 12 landed at the time for the DCA, was the first part of 13 that.
14 And then, building on the understanding of 15 the design response I'd say in terms of what was 16 important, was a factor in how we originally assessed 17 the PIRT.
18 And, we continued that process with the 19 upgraded design and did an applicability assessment 20 that compared the, compared the transient progressions 21 and what was driving our margins to acceptance 22 criteria between the designs, and how that related to 23 the PIRT phenomenon.
24 I think it, our PIRTs, our PIRT was 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
34 initially very detailed I'd say, in terms of the 1
components and the phenomena.
2 And with the body of work that we've done 3
thus far, especially a non-LOCA space, our margins 4
really come down to fairly simple design limits, which 5
Kevin covered at the beginning of this slide.
6 DR. MARTIN: That sounds consistent with 7
my own experience. Generally, the PIRT committee will 8
find many more things they consider important, like --
9 subjectivity to it.
10 And then, when you get into it, you 11 realize yes, there's really a much smaller set but as 12 the consequence of having your PIRT team, your kind of 13 laden with their conclusions.
14 And, that you end up treating maybe things 15 that are not as important as, say, the first guess.
16 So, would you say then that's kind of 17 consistent with what you saw over the last decade?
18 MS. MCCLOSKEY: I think that's reasonably 19 consistent.
20 And the other thing that we've noticed is 21 that the original PIRT work that was done, tended to 22 define out like very, very specific phenomena that 23 particularly when it came to the steam generator and 24 the DHRS heat transfer, it's been more, it's been more 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
35 reasonable for us to treat those things as steam 1
generator heat transfer DHRS heat transfer versus 2
condensation inside.
3 And then, the convention or boiling on the 4
outside of the tubes and the DHRS kind of takes a look 5
at that system a little more holistically.
6 DR. MARTIN: Okay, thank you.
7 MR. LYNN: Again, in terms of methodology 8
changes for event specific analyses, in general we 9
expanded the scope of our analyses to vary parameters, 10 rather than bias in one direction.
11 I gave an example earlier related to 12 initial pressurizing pressure. So, that's one 13 particular example.
14 And then, the last three bullets there is 15 we've made some changes to allow options for certain 16 analyses.
17 So, for the radiological
- analyses, 18 previously we used direct output from the NRELAP 19 analysis as input for those.
20 But we've also added an option for a 21 potential to determine using alternate means to 22 terminate bounding input, so that we don't have to 23 directly translate and wait for that output from 24 NRELAP to use as input.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
36 Similarly, for the control rod drop 1
analysis, we have the potential now, we've identified 2
a method where you can bound that analysis so that you 3
don't have to perform event-specific analysis.
4 Instead, you can bound it by the single rod 5
withdrawal.
6 And then finally for the born dilution 7
event, we have made some changes to allow for the 8
level increase that occurs during that born dilution 9
event, to be used to result in termination of the 10 event, and confirmation of shut down margin.
11 Overall, in terms of the open session our 12 conclusion is that the evaluation model for non-LOCA 13 remains adequate to evaluate an NPM design.
14 Next slide.
15 And, that concludes our open session 16 presentation.
17 CHAIR KIRCHNER: Thank you, Kevin.
18 Members, any questions at this point? I 19 assume you're all waiting for the closed session.
20 Okay, Mike. Do we go next to NRC staff or?
21 MR. SNODDERLY: Yes, please.
22 We had a break scheduled on 10:45, and I 23 think we should stick to that, or around that time.
24 But yes, let's let the staff get started.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
37 CHAIR KIRCHNER: Okay. All right, thank 1
you. So, for those listening in, just a brief pause 2
and we'll have the NRC staff present their evaluation.
3 MR. HAYDEN: Thanks. My name is Tommy 4
Hayden. I'm a project manager in the New Reactor 5
Licensing branch, in the Division of New and Renewed 6
Licenses, in the Office of NRR.
7 I am the PM for the topical report for 8
non-loss of coolant accident analysis methodology.
9 Contributors to the staff's review of this 10 topical report are Zhian Lee, Antonio Barrett, Adam 11 Rau, Peter Lien, Ryan Nolan, Sean Piela, Carl 12 Thurston, Dong Zheng, Joshua Miller, Rosie Sugrue, 13 Upendra Rohagti, Andrew Dyzel, and Marvin Smith.
14 As you'll see, those are from the Methods 15 branch in the Division of Safety Systems, or 16 contractors and consultants to that.
17 My apologies to my colleagues if I've 18 pronounced those horribly. I've done my best.
19 Here's one I can do. Tommy Hayden again.
20 I'm the project manager for this, and then Getachew 21 Tesfaye, is the lead for NuScale.
22 As an overview, NuScale submitted the non-23 loss of coolant accident evaluation model topical 24 report, rev. 4, on January 5, 2023.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
38 The topical report was formally accepted 1
for review on July 31, 2023.
2 The NRC conducted an audit of the topical 3
report from March 2023 to August 31, 2024. Within 4
that audit, 49 audit issues were resolved.
5 And for those not resolved, seven RAIs 6
were generated. One RAI remains open. Kevin and 7
Member Martin discussed that a little bit, and I'll 8
have a slide here shortly.
9 There are two significant differences 10 between the draft SER submitted to ACRS on February 4, 11 2025, and the draft SER published on February 26, 12 2025, to support this meeting.
13 The open item as discussed previously, 14 relates to RAI non-LOCA.LTR 50. In that issue, staff 15 is working to understand changes made to the base 16 model.
17 Those modeling changes revolve around DHRS 18 models, and modeling of core flow distribution.
19 As Kevin alluded to the path forward here, 20 we are converging on an understanding and resolution 21 to this issue.
22 We continue to discuss the modeling 23 changes and have high confidence the issue will be 24 resolved shortly, with minimal impact to the SECI 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
39 evaluation.
1 As noted, the two significant, there were 2
two significant differences from the safety evaluation 3
that we submitted to ACRS early in February, and the 4
SER we submitted just this past week.
5 Those differences are as follows. In 6
section 3537, NIST-2 steam generator decay heat 7
removal system integral effects test.
8 The staff expanded their assessment of the 9
NIST-2 DHRS scalability. And that came as a result of 10 a closure of an open item, RAI non-LOCA LTR 3-9 18, 11 19, 20, 21, and 69.
12 And section 3-9, quality assurance, and 13 section 4-0, limitations and conditions. Again, as a 14 result of the closure of an open item, the removal of 15 the limitation in condition number 10.
16 And then the modification to relay a 17 finding in the 3-9 section of reasonable assurance 18 related to implementation of QA controls, consistent 19 with Reg Guide 1.203 for the non-LOCA --
20 I'll now pass it to Zhian for changes from 21 the LTR rev. 3 to rev. 4.
22 MR. LI: Thank you, Tommy, for the 23 introduction.
24 My name is Zhian Li and it's little bit 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
40 hard to pronounce, Zhian, but yes.
1 Good morning, Mr. Chairman, good morning 2
ECRS members, and good morning colleagues. I'm glad 3
to have this opportunity to present to the committee 4
about our review about the non-LOCA topical report.
5 I'm the team lead. I have a whole bunch 6
of a team -- their education and their support the 7
completion of this review, and I really appreciate you 8
-- see here.
9 The review, we focused on five areas.
10 Number one, the design change of the reactors from 11 NPM-162 to NPM-20.
12 The second, we reviewed the phenomena for 13 the identification and the ranking table. And then, 14 seeing quite a bit work on that.
15 So we try to find to whether there are any 16 design change, or the impact, the PIRT table again.
17 And the then third one is there change in 18 the methodology, the evaluation methodology for non-19 LOCA events.
20 As the NuScale has spoke on that -- go 21 ahead, do you have a question or no?
22 DR. MARTIN: Well, yes, I do.
23 MR. LI: Yes, go ahead.
24 DR. MARTIN: Hide my little green light 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
41 here.
1 Now you were careful with your words, I 2
think. You said you spent a lot of time looking at 3
the PIRT.
4 Now, I'll ask you kind of the same 5
question that I asked Meghan. Did you do a 6
sensitivity studies or were your, that attention on 7
PIRT more qualitative?
8 MR. LI: Well, we did not do sensitivity 9
study. We basically looked through, well not a lot of 10
-- really, yes, take that word back.
11 And we look at detail, put it this way.
12 And that's our first task basically during the review 13 is first to look at yes, what the design change, what 14 the impact, if there are any to the PIRT team.
15 And then, the team spent time on that and 16 we get details, and we try to see whether compare with 17 the previous revision and to the design change, to see 18 if there are any impact.
19 DR. MARTIN: And, maybe just to follow up 20 with the PIRT. I can tell from the gray hair you've 21 done this for a while.
22 MR. LI: Thank you.
23 DR. MARTIN: And, so you've seen other 24 applications and not every, going way back but not 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
42 looking at just reply PIRTs, but PIRTs for non-LOCA 1
have been around for at least as long as PIRTs for the 2
most part.
3 Compared to typical PWRs, does, do those 4
PIRTs more or less cover 80-90 percent of everything 5
that you otherwise see with the NuScale?
6 What stands out uniquely with NuScale?
7 Now, I would say the role of the DSRS, which of course 8
is getting a lot of attention. Yes, that's an obvious 9
one.
10 Anything
- else, and then natural 11 circulation.
12 MR. LI: Based on our understanding of the 13 design, I think the fundamental difference that, so is 14 not, there's in the primary loop, you don't have a 15 pump to drive.
16 DR. MARTIN: Right.
17 MR. LI: Yes, and that the, really the 18 phenomena for the natural circulation, which was also 19 relates to the power density could drive the flow in 20 slightly different way.
21 It's not well-controlled. In the PWR, you 22 have a pump and you know what is a certain --
23 (Simultaneous speaking.)
24 DR. MARTIN: -- are low.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
43 MR. LI: Right, yes, you know exactly what 1
your pump needs, but this one you don't. I think 2
that's more the fundamental difference we see.
3 DR. MARTIN: Thanks.
4 MR. LI: And, that's just to mention that 5
the second, the third part of was you look at the 6
change in the method of evaluation, which the NuScale 7
already discussed that.
8 They have a new methodology for bounding 9
to calculate the bounding radioactive material release 10 if you have a leak in the primary system, more like a 11 CVCS.
12 But broadly, this is beyond the non-LOCA 13 before that's covered in other topical report for the 14 small LOCA, the small break, or small leak that it 15 would, able to use a bounding source.
16 Just a estimate how much I can leak and 17 then, what the timing of the leak. And then, they say 18 okay, I was use the bounding number and then -- into 19 the radiological consequence application.
20 CHAIR KIRCHNER: To that point about 21 bounding assumptions, LOCA and even for NuScale LOCA, 22 you have something like Appendix K.
23 And non-LOCA, there's certainly more 24 latitude.
But historically, they've been 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
44 deterministic-type approaches.
1 Pretty well understood about what 2
uncertainties end up being addressed in a bounding 3
sense.
4 Clear in looking at the evolution of 5
NuScale, that the DHRS has been a particular 6
component, a particular contribution to core cooling 7
that in the earlier version, it was a much more 8
obviously conservative type assumption. They have 9
moved more towards realistic. It's obviously getting 10 plenty of attention.
11 Has there been anything else kind of like 12 that, that has gotten unique attention with how 13 they're addressing uncertainties that you probed?
14 MR. LI: Actually, not really in this 15 particular --
16 (Simultaneous speaking.)
17 CHAIR KIRCHNER: Application.
18 MR. LI: -- case -- application. Because 19 NuScale did not provide a specific method or 20 evaluation for the bounding calculation methodology.
21 So, that's one of the limitation, the condition.
22 Instead, it says the applicant was 23 responding or
- use, referring to this topical 24 methodology in this topical report with having to do 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
45 their analysis to determine what's bounding. And 1
then, what would be the certainty.
2 CHAIR KIRCHNER: Or something like just 3
the uncertainty of a natural circulation itself. You 4
could maybe bound it with low resistance or something.
5 Did they do anything particular to address 6
uncertainties with the natural circulation phenomenon?
7 MR. LI: Not in this methodology. You 8
could be wrong, correct. I don't think they really --
9 (Simultaneous speaking.)
10 CHAIR KIRCHNER: Relying mostly on test 11 data to support what their --
12 MR. LI: Yes, basically mostly on their 13 design they say what are the lines, the size of a 14 line. For example, if you have a CVCS line break or 15 something.
16 But just not, and there was a time you 17 would identify there's a leak, and then their 18 potential was time you --
19 I think that's the idea how they're trying 20 to determine, rather than go to a detailed NRELAP5 21 calculation is okay.
22 With just the estimated total, potential 23 total release, and the maximum time.
24 CHAIR KIRCHNER: Relying a lot more on 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
46 realistic type behaviors, and with some expectation to 1
have margin, reasonable margin.
2 MR. LI: Right.
3 CHAIR KIRCHNER: Maybe not so quantified 4
as a, say --
5 (Simultaneous speaking.)
6 MR. LI: And deterministic --
7 (Simultaneous speaking.)
8 CHAIR KIRCHNER: -- criteria.
9 MR. LI: Yes.
10 CHAIR KIRCHNER: But, okay.
11 MR. BARRETT: This is Antonio Barrett, of 12 the NRC staff. Yes, so like one thing you were asking 13 about the natural circulation.
14 In their model, they actually --- this is 15 stuff that they already did before. It's not new for 16 this, for what they did now.
17 But they biased the loss as higher now so 18 natural circulation.
19 CHAIR KIRCHNER: Okay.
20 That's why -- threw that out there, yes 21 All right, thanks.
22 MR. LI: So we'll move on.
23 The next one actually we're looking into 24 the code updates, and the NuScale during the review, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
1 2
3 4
5 6
7 8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 47 and also in the application they have a 1., I think 1.4.
And then, they move from 1.4 to a new version, 1.7. And then, this is a change during the review. And, we look into the -- the version.
The other one is the change associated with the code bench marking, or we validation. This is all tied to the new tests, and the test result.
Certainly, this one will get into that in the also the update, the CHF correlation for screening the cases sub-channel now.
What NuScale does is they use NRELAP5 to run bunch of cases, identify those steps potential challenge to the system, I think the NCHFR, the minimal critical graphs.
And then, so they identify this case and then throwing into a sub-channel analysis the use of viper code to get a more detailed result, more accurate result.
And, in the previous version, they have a look-up table. I will try to pronounce it. They call it the -- Correlation. It's the look-up table.
And then, they add two more. One is the Correlation. The other one is, yes, well, yes, there's another one. And there are two analytic.
NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
48 I think this with the new correlation will 1
give them more accurate screening and for the next 2
step average.
3 So, and also NuScale updates theirs in 4
response to revision 3, they try to revise some of the 5
limitation, the conditions you see.
6 And, the staff review that limitation 7
condition and with respect the new design. And then, 8
come up with some of the change limitation and 9
condition.
10 And we will get into that during the 11 closing session, the closed section, which I have a 12 much more detailed discussion why we have this 13 limitation condition.
14 But next one.
15 So, we already talk about the revision 16 1.7, the base model change. And, this two tests and 17 the test result, and which we'll get into the review 18 the scaling.
19 Whenever you have to code bench marking on 20 validation, you have to test what you have to address 21 the similarity, scalability, and any distortion.
22 I think that would be discussed more 23 detail in the --
24 Yes, some of the events may get into 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
49 extended, long-time pulling. That would be Howard's 1
in the next topical report, which Antonio and company 2
would present.
3 Next slide, please.
4 Here, the limitation and conditions. The 5
number 1, 7, 9 are the new ones. And, the rest are 6
the, from the previous revision of the topical report.
7 We revised some of the limitation and 8
condition but not major change. But the previous 9
limitation and condition as you clearly see, the first 10 one is really relates to the NPM-20 design, which some 11 unique design features and then you have to address.
12
- And, number 9
is talk about the 13 radiological, using the bounding methodology for 14 radiological analysis.
15 And, number 7 is really about the code 16 version as you all know. The code version is critical 17 for any change. You change the code, try to address 18 certain phenomena, and then so that's our limitation 19 condition.
20 I think that's conclude my presentation.
21 CHAIR KIRCHNER: Yes, thank you, Zhian.
22 So, in conclusion, while there are some 23 differences between the current and previous revision, 24 the staff found the applicant provided sufficient 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
50 information to support the staff's safety finding.
1 The staff found that an applicant that 2
references this topical report with the limitations 3
and conditions, will meet relevant regulatory 4
requirements pending review and approval of that 5
application.
6 Questions? Members?
7 CHAIR KIRCHNER: I have one, Tommy, and 8
Zhian.
9 MR. LI: Yes.
10 MS. PATTON: And, that is why are you 11 limiting it to NPM-20? Why wouldn't it not work for 12 the certified design as well?
13 MR. BARRETT: I can --
14 MR. LI: Antonio, I can speak too and you 15 can supplement. Becky, go ahead.
16 MS. PATTON: Yes, this is Becky Patton, 17 I'm the supervisor from Reactive Systems.
18 Yes, so the staff looked at that early on 19 and the way I think that it was requested, it wasn't 20 just backward looking to the NPM-160, but it was also 21 forward looking to other module designs that would 22 have certain features.
23 And, when we approve a topical report 24 methodology, we don't do the forward looking like if 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
51 other applicants, other technologies, BWRs and PWRs 1
when they come in.
2 You have to look at the sort of the 3
technology I want to say family, but that specific 4
design like for BWRs. You'd have BWR 3s, 4s, 5s, 5
right?
6 And, you come in with the topical report 7
and you say I want to cover these types of designs, 8
but we don't do a forward looking because that would 9
require the staff to look at all kinds of other things 10 that you can do with that design.
11 So, we looked at that early on and the 12 forward looking thing was sort of off the table, as 13 something that the staff could entertain.
14 The backward looking was really a
15 practicality of it for the 160, that that would have 16 required all of the RAI responses, all of the 17 considerations and everything to have also considered 18 the 160.
19 And so, there were some early on 20 engagements at the management level to, the decision 21 was made to take that off the table as well.
22 It doesn't mean that they couldn't come in 23 at some future time for an applicability. There's 24 certainly that allowance within the limitation and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
52 conditions.
But it was mostly a
practical 1
determination.
2 CHAIR KIRCHNER: Yes, I wasn't thinking of 3
forward looking, I was just thinking backward to the 4
DCA, and overall I think the methodologies enhanced 5
and obviously using an improved and updated version of 6
NRELAP.
7 So, my thinking was well, it would work as 8
well for the former design at this point. But I think 9
this is a trend in all your TRs on methodologies, to 10 kind of restrict it to the application at hand.
11 But it just strikes me that they made some 12 significant improvements in their modeling capability, 13 and that it would be a if they wanted to revisit the 14 previous design that was considered for the DCA, the 15 methodology would be applicable, as well.
16 So, I guess this is just at this juncture, 17 standard practice to somewhat limit the TRs to the 18 actual application at hand, and --
19 MS. PATTON: Yes, I wouldn't say that. I 20 wouldn't say it's -- standard.
21 MR. LI: Definitely it's not.
22 MS. PATTON: Oh, I'm sorry.
23 CHAIR KIRCHNER: Yes, go ahead, Becky.
24 MS. PATTON: Yes, Becky Patton again.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
53 Yes, I wouldn't say it's necessarily 1
standard practice. Like I said, it was a practicality 2
of getting through this review on a predictable 3
timeframe. And not having to do a backward look as 4
well.
5 Like I said, the condition and limit is 6
written in such a way that you can do a fairly 7
straightforward applicability-type review in the 8
future.
9 If the backwards look to the 160's 10 designer also for any forward look for a future 11 design, that's also written in there.
12 So, I wouldn't say that it's our process 13 going forward. We certainly do topical report reviews 14 for the obsolete too, that are sort of stand alone 15 where you're looking at multiple technologies.
16 This was really a practicality --
17 (Simultaneous speaking.)
18 CHAIR KIRCHNER: Okay.
19 MS. PATTON: -- of this review. That's 20 the effect the decision that was made.
21 CHAIR KIRCHNER: All right, thank you.
22 Questions?
23 So, at this point, is this a good juncture 24 to take a quick break?
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
54 MR. SNODDERLY: Perfect, you're right on 1
time.
2 CHAIR KIRCHNER: Okay.
3 MR. SNODDERLY: It's 10:40 and we had a 4
break scheduled for 10:45 so -- with you.
5 CHAIR KIRCHNER: Let's go to 10:55. We'll 6
reconvene at 10:55 Eastern Time and we'll take up an 7
extended, I have a feeling, TR.
8 Thank you.
9 (Whereupon, the above-entitled matter went 10 off the record at 10:38 a.m. and resumed at 10:55 11 a.m.)
12 CHAIR KIRCHNER: Okay, we are back in 13 session and we are going to turn back to NuScale, and 14 we are taking up now the Extended Passive Cooling 15 Topical Report, and I will turn to Ben Bristol.
16 MR. BRISTOL: Good morning. This is Ben 17 Bristol. I'm the manager of the System Thermal 18 Hydraulics Group.
We'll go through quick 19 introductions and then Tom is going to kick us off.
20 MR. CASE: Good morning. My name is Tom 21 Case. I'm a licensed engineer with NuScale. I've 22 been with NuScale for about two years and in the 23 nuclear industry for about 14 years, and I'm a 24 licensed professional engineer.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
55 MR. CODDINGTON: Taylor Coddington, Safety 1
Analysis. I've been with NuScale about seven years.
2 CHAIR KIRCHNER: Just speak up a little 3
more, Taylor.
4 MR. CODDINGTON: Taylor Coddington. I've 5
been with NuScale about seven years in safety 6
analysis.
7 CHAIR KIRCHNER: Thank you.
8 MR. CASE: So, this is the open portion of 9
NuScale's presentation of the Extended Passive Cooling 10 and Reactivity Control Methodology Topical Report.
11 Next slide?
12 This portion will cover the evaluation 13 model scope, regulations, and acceptance criteria, the 14 NPM design features related to the methodology, 15 phenomena identification and ranking table or PIRT 16 evolution, and the evaluation model structure, 17 validation
- basis, and adequacy assessment and 18 conclusions. Next slide?
19 This is a new topical report that was 20 developed to support the 250 MWt NPM design and SDAA 21 submittal, but is applicable to NPMs that meet the 22 design requirements and conditions specified in the 23 topical report.
24 The scope of the methodology covers 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
56 analysis of long-term cooling and reactivity control 1
following the short-term response to required design 2
basis LOCA and non-LOCA events.
3 The regulations applicable to the topical 4
report include 10 CFR 50.46(b)(4) and (5), and NuScale 5
principal design criterion 35 for long-term ECCS 6
cooling and maintaining a coolable geometry, NuScale 7
PDC 34 for extended DHRS cooling, and GDC 26 and 27 8
for reactivity control.
9 The methodology also supports an exemption 10 to GDC 33 for a safety-related system to provide 11 makeup in response to reactor coolant leakage. Next 12 slide?
13 So, the applicable regulatory requirements 14 translate into three safety objectives, decay and 15 residual heat removal, reactivity control, and 16 maintaining coolable geometry. The methodology uses 17 the following acceptance criteria corresponded to 18 those safety objectives.
19 The acceptance criteria are collapsed 20 liquid level remains above the top of the core, the 21 reactor core remains subcritical, and boron 22 concentration remains below precipitation limits, and 23 these acceptance criteria need to be met for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 24 after event initiation and the subcriticality analysis 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
57 assumes the highest worth control rod remains 1
withdrawn from the core. Next slide?
2 DR. PALMTAG: I just have a question on 3
the k effective equals one, plus one. For normal 4
shutdown margin calculations, you usually see 5
something like shutdown margin with one percent, so it 6
might be a 0.99 factor plus uncertainties. Can you 7
tell me why it's one here?
8 MR. CASE: Yeah, so for the long-term 9
cooling analysis and reactivity control, we're looking 10 at post-event initiation subcriticality as an 11 acceptance criteria, and so that's different than 12 shutdown margin as defined by tech specs, which would 13 basically establish initial conditions or ensure 14 initial conditions are maintained during normal 15 operation.
16 And so, the shutdown margin calculation 17 controlled by tech spec is different than what the 18 long-term cooling analysis is analyzing, and so the k 19 effective less than one is an appropriate acceptance 20 criteria for the long-term reactivity control given 21 the assumptions and conservatisms that are applied to 22 the methodology, and those conservatisms will be 23 discussed in the closed session.
24 DR. PALMTAG: Okay, so there's no margin 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
58 per se on the shutdown. You're assuming all of the 1
conservatism is built into the modeling, I guess?
2 MR. CASE: Correct, and that shutdown 3
margin calculation in tech specs does include a margin 4
prior to event initiation, whereas the acceptance 5
criteria we're looking at here during the long-term 6
cooling is just k effective less than one. Next 7
slide? And I'll turn it over to Ben Bristol for 8
design features.
9 MR. BRISTOL: Good morning. This is Ben.
10 So, we wanted to take a minute to just kind of talk 11 through some of the passive cooling features. These 12 have been described to the ACRS previously in other 13 presentations, but specifically with respect to the 14 long-term cooling conditions. So, just as a quick 15 orientation, after a LOCA event or some event where 16 ECCS is required, the function is all about 17 depressurizing the systems.
18 So, what happens is we have water 19 redistribution from the RCS into containment, a level 20 is established in containment, and the vent valves and 21 the condensation on the containment wall is used to 22 depressurize the system.
23 Once pressure equilibrium occurs, then 24 recirculation is passively provided based on a level 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
59 head difference between the liquid inside the 1
containment compared to the liquid level inside the 2
RPV.
3 Under these conditions, the HRS is also 4
active. However, mostly the steam generator tubes are 5
uncovered. So, inside the RCS, condensation is 6
occurring on the tube, the outer tube walls in 7
addition to the condensation that's occurring in 8
containment itself.
9 So, the distribution of the reactor 10 coolants is really established based on the pressure 11 drop, the vapor pressure drop, the pressure drop 12 across the vent valves. We've described previously 13 some optimization and the differences between the NPM-14 160 design and the NPM-20 design.
15 That included a key feature change, which 16 is the reduction of one of the vent valves, so three 17 vent valves to two vent valves. It's this long-term 18 cooling analysis and behavior that demonstrates the 19 appropriateness of that sizing change and it's really 20 driven by the containment wall heat transfer rates, 21 which we will present on the next slide if you go to 22 that, Wendy?
23 In the XPC LTR, we consider a variety of 24 different exceptions criteria. One of those looks at 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
60 biases and conservatisms that maximize the containment 1
heat removal, and another analysis looks at conditions 2
where we minimize the containment heat removal in 3
order to demonstrate that depressurization functions 4
still occur.
5 Specifically, we look at sensitivities on 6
pool temperature, one of the main drivers, and what we 7
wanted to point out in this slide is the difference 8
between these two figures, so the equilibrium level 9
under the minimum pressure or maximum heat removal 10 conditions.
11 The equilibrium level is about five feet 12 of margin above the top active fuel, so that's the 13 liquid level inside the RPV compared to the top of the 14 core. In contrast, the figure on the right shows 15 under the maximum temperature conditions and minimum 16 heat removal conditions the overall system pressure 17 remains higher.
18 The vent valve capacity is not tested as 19 severely and that results in a much higher equilibrium 20 level. So, we reach an equilibrium state of about ten 21 feet or about twice the margin under those conditions.
22 CHAIR KIRCHNER: Ben, could you go back to 23 your previous picture? Just I wanted to ask you to 24 address the change. One of the changes is your 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
61 ultimate heat sink pool level.
1 I don't know if that previous picture, one 2
slide back, if that's to scale, but I don't think 3
that's the level that we're going to see actually in 4
the NPM-20 design.
I think your level is 5
significantly lower on the containment vessel.
6 MR. BRISTOL: Yeah, that's correct. This 7
is a non-scale --
8 CHAIR KIRCHNER: Schematic.
9 MR. BRISTOL: -- schematic.
10 CHAIR KIRCHNER: Yeah.
11 MR. BRISTOL: The equilibrium level and 12 the DHRs aren't quite scaled here either, but roughly 13 the pool level is around in the pressurizer band I 14 guess I would say.
15 CHAIR KIRCHNER: Several feet above the 16 DHRS heat exchanger.
17 MR. BRISTOL: That's correct.
18 CHAIR KIRCHNER: And that's reflected now 19 going forward to what you were presenting in the 20 maximum temperature conditions because that pool level 21 would have an impact on where you wind up in the long-22 term.
23 MR. BRISTOL: Yeah, that's correct. So, 24 if you can consider the condensate, the containment 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
62 condensing surface area, it's directly proportional to 1
the pool level. The space above the pool has very 2
little heat transfer rate.
3 It heats up essentially to the steam 4
temperature and it does very little heat transfer 5
work, so reducing the pool level allows us to optimize 6
the thermal hydraulic response under the maximum 7
cooling conditions. Thanks, Wendy.
8 Okay, so switching gears here a little 9
bit, one of the other topics that we spent a fair 10 amount of review time with in the DCA or NPM-160 11 design was under the conditions where we were 12 condensing either on the containment wall or on the 13 steam generator walls, tube walls inside the RCS.
14 The characteristics of boron transport, 15 generally, boron is left behind when the water boils, 16 and therefore, the condensed water is of a deborated 17 state or a zero boron state, pure water in that 18 regard. So, the core can create a little bit of a 19 distilling effect, and the areas where condensate 20 accumulates are therefore diluted relative to the 21 average.
22 So, one of the concerns was downcomer 23 dilution, whether it be from the recirculation from 24 containment or direct contribution of condensate from 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
63 the steam generator tube walls. In order to mitigate 1
that more thoroughly in this design, we've included 2
some passive features.
3 They're simply flow paths, liquid flow 4
paths in the figure here. We have the four sets of 5
holes in the upper riser. Those are there under 6
conditions where we have extended DHR. DHRS cooling 7
can shrink the RCS, and that results in the level 8
dropping out of the pressurizer and up to and 9
including uncovering the riser.
10 Under these conditions, the four sets of 11 holes allow for continued circulation of the RCS loop 12 to ensure that any condensing that's occurring in the 13 steam generator tubes is overcome by the natural 14 circulation flow paths in order to keep a relatively 15 uniform concentration in the RCS.
16 Similarly, under ECCS conditions where the 17 upper four sets of holes uncover, you have another set 18 of holes in the lower riser, and these provide the 19 same effect of allowing transport of more highly 20 borated RCS liquid in the core and upper riser region 21 to mix with the condensate that's recirculating, 22 whether it be from the recirc valves in the 23 containment or from the steam generator tube 24 condensation itself. I'll pause for any questions on 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
64 this. We're going to switch gears again on the next 1
slide. Thanks, Wendy.
2 Okay, the last design feature that I have 3
to present here is the supplemental boron components 4
that we've added as part of ECCS. So, there's two 5
sets of components here on the diagram. We have --
6 the way this system works is we've got a dissolver 7
basket or container where we have boric oxide pellets, 8
and those are maintained in containment throughout the 9
core cycle.
10 In the event of the need for an ECCS, this 11 system passively works to collect condensate, the 12 condensate that's collecting on the containment wall, 13 redirect it through the basket and create liquid boric 14 acid that mixes with the liquid in the containment, 15 which then is recirculated through the recirc valves 16 into the RCS to provide the additional reactivity 17 control and hold down to support the long-term cooling 18 acceptance criteria that Tom described.
19 So, the features primarily associated with 20 the dissolver basket are those in the upper portion of 21 containment. In addition to that, we have what we 22 call the mixing tubes in containment, and what that 23 does is it redirects pure condensate, so deborated 24 water, from the condensing walls down to the bottom of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
65 containment.
1 What this allows for is any borated 2
accumulation that occurs in the lower containment 3
region to eventually be transported back upward 4
through the combination of convective effects, as well 5
as simple mass turnover that's provided by the tubes 6
that deposit the lower borated water to the bottom of 7
containment, the lower mixing tubes. If there's on 8
questions on that, we'll --
9 DR. PETTI: Ben?
10 MR. BRISTOL: Yeah?
11 DR. PETTI: This is Dave. Just during 12 normal operation, what's the atmosphere in 13 containment? It's evacuated, right?
14 MR. BRISTOL: Yes, it's evacuated normally 15 around one PSIA.
16 DR. PETTI: I'm just wondering what 17 happens to the lower boron oxide just sitting there, 18 you know, for a long time, whether there's any 19 potential degradation. The passive pressure of water 20 vapor would be pretty low, I guess, in PSI, okay.
21 MR. BRISTOL: Yeah, generally, the RPV is 22 quite high under the conditions, so there's some 23 radiative heat transfer that's occurring. Depending 24 on where the components are located, they can be quite 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
66 hot under normal operating conditions.
1 Most things attached to the containment 2
wall tend to stay closer to the pool temperature, but 3
there is a heat balance there between the heat loss 4
through the conductive effects and the heat addition 5
through the radiative heat transfer.
6 DR. PETTI: You check, at least on the 7
first part, every so often.
8 MR. BRISTOL: Yeah, the qualification of 9
the boron pellets is part of the program.
10 DR. PETTI: Okay.
11 DR. BALLINGER: Yeah, this is Ron 12 Ballinger. What's the packing fraction in there? In 13 other words, you've got, I'm assuming, spherical 14 pellets of some kind.
15 So, you dump them in here, and if the 16 packing fraction is above a certain number, you don't 17 have a continuous flow path through the bed, but if 18 it's low enough, you do have a flow path, a continuous 19 flow path, excuse me, through the bed, and that would 20 avoid this issue that we're sort of dreaming up, I 21 guess, of reconsolidation of these pellets to make a 22 solid mass as opposed to so that fluid can't get 23 through.
24 PARTICIPANT: That is something that is 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
67 addressed in the XPC LTR itself. There's correlations 1
that we found for pellets being dropped, and what 2
configuration they form, and the path factor that they 3
would result in, and demonstrating the environmental 4
qualification of the pellets is something that is 5
being considered.
6 MR. BRISTOL: Yeah, and specifically, I 7
think we've got some more details in the closed 8
session.
9 DR. BALLINGER: Okay.
10 MR. BRISTOL: We can get into that and 11 some of the testing that we did as part of that.
12 CHAIR KIRCHNER: Ben, what happens during 13 the refueling operation? You don't -- you know, you 14 keep -- that upper part of the containment remains 15 dry, so to speak, or I think --
16 MR. BRISTOL: Yes.
17 CHAIR KIRCHNER: -- or it floods and you 18 replace them.
19 MR. BRISTOL: Yeah, so where those are 20 located is below the level of the pool. Obviously, we 21 needed the condensing surface area above over where 22 the basket, the dissolver basket is located, so that 23 was one of the challenges in trying to figure out the 24 design.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
68 So, if part of refueling floods the 1
reactor module up to the pool level before it's 2
unbolted, so the bed will get flooded, it will 3
dissolve from there, and then as part of operations, 4
the upper module goes for inspections in the dry dock, 5
comes back, returns flooded as part of the restart 6
operations, then containment flood and drains are used 7
to drain containment --
8 CHAIR KIRCHNER: Right.
9 MR. BRISTOL: -- at which point there's an 10 operation where the pellets are installed and 11 confirmed to be relocated back in the basket, and from 12 that point on, then the containment atmospheric 13 conditions are controlled such that the boron doesn't 14 dissolve from there until ECCS operations is required 15 for some transient.
16 DR. PALMTAG: Scott Palmtag. Just to 17 confirm though, the way you've installed the dry 18 pellets, they're not flooded.
19 MR. BRISTOL: That's correct.
20 DR. PALMTAG: They remain dry --
21 MR. BRISTOL: Yeah.
22 DR. PALMTAG: -- until the next refueling.
23 MR. BRISTOL: That's correct. Okay, 24 Wendy, next slide?
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
69 MS. McCLOSKEY: Okay, this is Meghan and 1
I'll pick up here to talk about, first about the PIRT 2
evolution for this topical report. NuScale had 3
previously developed PIRTs for extended ECCS cooling 4
or extended DHRS cooling for the NPM-160 design, but 5
we took that work and reassessed it holistically 6
because we now had different acceptance criteria as 7
well as design changes to consider.
8 So, we started right back at the beginning 9
in considering what phases and figures of merit were 10 relevant for the phenomenon and that's what's shown on 11 the table at the bottom here for the NPM-160 design on 12 the left and then the updated, the 250 megawatt design 13 that's part of the SDAA on the right. For LOCA, phase 14 two is the same. That's really no different here.
15 For non-LOCA and extended DHRS operation, 16 with the previous design, we had a couple different 17 extended DHRS phases depending on whether the riser 18 level was above the top of the riser or whether the 19 DHRS cooling had shrunk it to below the top of the 20 riser and you had intermittent or perhaps interrupted 21 natural circulation there.
22 With the upper riser flow paths that Ben 23 pointed out with the four different levels there that 24 are sized to maintain liquid flow over top of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
70 steam generator during extended DHRS operation, we're 1
really more focused now on phase three and stable 2
natural circulation.
3 And then with respect to figures of merit, 4
the NPM-160 design, we established different design 5
criteria, particularly in the US PDC 27, where I'm 6
going to get this mixed up with 26, in that 27, the 7
long-term subcriticality was demonstrated with other 8
cold conditions with all rods in, and with the worst 9
rod stuck out condition, we evaluated that low power 10 recriticality and demonstrated that the fuel cladding 11 remained intact by demonstrating margin to the correct 12 heat flux
- ratios, low
- pressure, low power 13 recriticality conditions.
14 So, now with the design criteria to remain 15 subcritical considering worst rod stuck out, our decay 16 heat source long-term is, or our core heat source 17 long-term is decay heat levels, and under that 18 condition, demonstrating core cooling is met by 19 demonstrating that our collapsed liquid level remains 20 above the top of the core and we maintain a coolable 21 geometry, and then subcriticality remains a figure of 22 merit as well as an acceptance criteria here.
23 So, that really shifted how we were 24 looking at the PIRT and some things became differently 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
71 important as we went through that process. Next 1
slide?
2 In terms of the structure, we've got a 3
couple of key pieces. We're continuing to use NRELAP5 4
as the thermal hydraulic engine that's driving the 5
methodology, and we used the results from the code 6
calculations to demonstrate that the collapsed liquid 7
level is maintained above the top of the fuel and to 8
evaluate the containment response.
9 That's basically the same as the scope 10 that we had performed for the DCA and essentially the 11 same methodology there, and then NRELAP5 also provides 12 the thermal hydraulic input boundary conditions for 13 the transport analysis.
14 We used SIMULATE5 for the core reactivity 15 analyses, and that determines the critical boron 16 concentrations as well as the initial starting boron 17 concentrations because we're evaluating a range of 18 operating cycle exposures and operating histories, 19 different shutdown times, and evaluating conditions 20 for a range of thermal hydraulic conditions that could 21 potentially occur during long-term cooling.
22 And then the boron transport calculations 23 really bring all of the pieces together. We have this 24 currently implemented in MATLAB scripts, but it could 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
72 be done in other applicable computational tools.
1 So, the topical report provides the 2
methodology requirements for the transport analysis, 3
and this is where we map the NRELAP5 thermal hydraulic 4
conditions in the context of the different boron 5
transport regions that we're evaluating and the boron 6
loss terms or addition terms from the ESB, and we 7
compare those concentrations to the critical boron 8
concentrations calculated by SIMULATE5 for those 9
thermal hydraulic conditions in order to demonstrate 10 subcriticality.
11 And the boron transport analysis for 12 precipitation is similar except that we are treating 13 the loss terms differently because it's the opposite 14 directions of conservatism and we're comparing against 15 solubility limits rather than critical boron 16 concentrations.
17 DR. PETTI: Meghan, just a question on the 18 precipitation. We know the solubility of boric acid, 19 but sometimes in some systems, radiation fields can 20 cause boric precipitation and then, you know, you're 21 a chemical beaker, so it's important to make sure 22 there's good margin. Is there always, you know, good 23 margin relative to --
24 MS. McCLOSKEY: Yes, yeah, we don't need 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
73 a lot of additional boron to maintain subcriticality, 1
and so that's 25 to 30 kilograms, I think, per 2
dissolver inside of containment. So, our source term 3
for boron addition is much smaller than what we 4
typically see in like operating PWRs.
5 DR. PETTI: Okay.
6 MS. McCLOSKEY: And so, our concentrations 7
remain commensurately lower.
8 DR. PETTI: Okay, great.
9 DR. MARTIN: This is Member Martin.
10 RELAP, the way it models reactivity is not at all 11 like, say, any other reactor physics code, right. You 12 just wouldn't give it a boron concentration and expect 13 it to reflect reality. It's really about the delta, 14 and I expect that you're using a point kinetics model 15 on --
16 MS. McCLOSKEY: We're not using RELAP's 17 reactivity models at all in the long-term cooling.
18 DR. MARTIN: Right, okay, so you're not 19 even doing like a delta reactivity --
20 MS. McCLOSKEY: No, we're --
21 DR. MARTIN: You track boron.
22 MS. McCLOSKEY: No, we're not tracking --
23 we're tracking boron through the MATLAB script.
24 DR. MARTIN: So, you don't model boron in 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
74 NRELAP5?
1 MS. McCLOSKEY: Correct.
2 DR. MARTIN: Okay, so this is all outside?
3 MS. McCLOSKEY: Yes.
4 DR. MARTIN: All right, I need to think 5
harder about that.
6 (Laughter.)
7 DR. MARTIN: All right, thanks.
8 MS. McCLOSKEY: All right, next slide?
9 So, in terms of the validation basis for the method, 10 our NRELAP5 validation basis is probably pretty 11 familiar to folks at this point. We are continuing to 12 build on the basis established for the LOCA and the 13 non-LOCA EMs, and then we have additional specific 14 long-term cooling testing that was performed at the 15 NIST-2 facility.
16 Taylor briefly mentioned the boron 17 dissolution testing that was done. That was separate 18 effects testing that we performed to assess the 19 methods for slow-biased or fast-biased dissolution in 20 the dissolver baskets against that test data and 21 confirmed that our methods would bound the measured 22 data in whichever direction is conservative for a 23 particular transient evolution.
24 SIMULATE5 has an extensive validation 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
75 basis and use cases developed for a wide range of 1
other applications, and what we've done particular to 2
this evaluation model is develop a nuclear reliability 3
factor or NRF specifically considering the extended 4
passive cooling conditions, and that is included in 5
the critical boron concentration to account for 6
uncertainties associated with the reactivity balance 7
there.
8 And then in terms of the boron transport 9
methods and the adequacy basis, a lot of this relies 10 on the thermal hydraulic input, and it also relies on 11 ensuring that we have conservative treatment of the 12 phenomena that are specific to the boron transport of 13 how that boron is being transported within the module.
14 Next slide?
15 Overall, in the adequacy assessment from 16 the bottom-up perspective, we focused on correlations 17 that are in NRELAP5 and the correlations that we used 18 in the boron dissolution analysis, and we identified 19 some limitations of those correlations there. The 20 top-down assessment also considered what was the 21 numerical features within NRELAP5 and its fundamental 22 governing equations and how it assessed against the 23 NIST-2 tests.
24 So, we identified some limitations in the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
76 models and correlations, particularly as related to 1
NRELAP5 under these types of conditions, and we have 2
identified conservative treatments within the 3
evaluation model in order to address those limitations 4
or we have implemented alternate approaches to confirm 5
that what we're getting from the method is 6
conservative.
7 And so, we have evaluated the limitations 8
under these types of low pressure conditions 9
predominantly where the code really wasn't originally 10 developed to operate, and we've ensured that we have 11 conservative treatment required by the evaluation 12 model to address those.
13 So, overall, our conclusion is that for an 14 NPM with design features that are specified in the 15 topical
- report, the methodology provides a
16 conservative method to demonstrate adequate core 17 cooling and decay heat removal, that the module 18 remains subcritical following design basis events, and 19 that coolable geometry is maintained. Any questions?
20 CHAIR KIRCHNER: Members? I have a lot of 21 questions, but I think probably I'll hold most of them 22 for the closed session, but just for the public 23 session, it seems to me that in a simple way on this 24 boron issue, you could look at your system and say 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
77 that, with the assumptions you used, the most were the 1
rod bank stuck out, what the --
2 And it's probably more a beginning of 3
cycle problem than end of cycle problem. What's the 4
critical boron concentration to be sufficiently below 5
k effective of one? As a figure of merit, is that 6
possible to do? Do you use that in your thinking to 7
kind of do an overall assessment?
8 You've looked at the boron redistribution 9
and such, and then you look at the effect of your 10 riser holes and so on, and look at how the boron is 11 transported, but you then have a goal, if you will, as 12 the function of burnup for where you are in the cycle.
13 This is how much we can't let the concentration of 14 boron get below this amount. I'm trying to remember 15 what your steady state normal start of the cycle PPM 16 is. It's about 1,000 or something, something in that 17 order without getting into --
18 MR. CODDINGTON: Yeah, 1,000 is about 19 right for --
20 CHAIR KIRCHNER: Yeah.
21 MR. CODDINGTON: -- equilibrium end of 22 cycle.
23 CHAIR KIRCHNER: So, if you're in the 24 beginning of cycle and you go through these transients 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
78 and either the extended cool down or the ECCS 1
functions, and you're looking at a figure of merit 2
target for what you don't want the boron concentration 3
to go below X. Is that how you look at your mass 4
balance, so to speak, of how effective your boron 5
dispensers are for the ECCS system and so on? Is that 6
basically your approach?
7 MR. CODDINGTON: Yeah, yeah, so, you know, 8
depending on what the initial exposure is, you have a 9
different initial boron concentration, and then we do 10 track the boron as it moves throughout the system and 11 compare it back to critical boron concentration that 12 is specifically tied to not only a cycle exposure, but 13 also a specific operating history.
14 CHAIR KIRCHNER: Right.
15 MR. CODDINGTON: So, yeah, that, the 16 critical boron concentration floats with time, with 17 the specific transient being evaluated, with the time 18 since reactor scram, so it's a large number of 19 simulated cases effectively.
20 CHAIR KIRCHNER: And then to deal with 21 uncertainty, because you have no way really to measure 22 local boron concentrations in this system, how do you 23
-- what's the conservatism that you build in to have 24 confidence that, you know, plus or minus 25 PPM or 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
1 2
3 4
5 6
7 8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 79 what, you know, what kind of design targets do you have for the functionality of the riser pools doing their job as well as the, in the case of ECCS, the boron dispensers functioning?
MR. CODDINGTON: Yeah, so we do have a fair number of conservatisms in the method. You know, we don't assume that. We do assume the rod is stuck out and it's worth a lot. There are others that go into the analysis methodology, and then we do develop a specific XPC that gets applied at the critical boron concentration, and I don't know exactly how public those numbers are, so I'd probably prefer to save them for closed session.
CHAIR KIRCHNER: Okay, well, I can pursue this in the closed session, but I just wanted to get a sense in the open session how you, you know, you have identified some rather, I don't want to call them gross because that's the wrong word, but some overall figures of
- merit, like collapsed liquid level obviously is an obvious one.
But the tracking of what the different boron concentrations are in the system is a much more complicated problem and I'm just looking for, you know, what's your designer's figure of merit on boron NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
80 concentration or do you just condense that with the 1
changes you've made in the design? You've kind of 2
overwhelmed the problem and you will not have a 3
significant inventory of unborated water anywhere in 4
the system?
5 MS.
McCLOSKEY:
We won't have a
6 significant inventory of unborated water near the 7
core, which is where we care about it being unborated.
8 I think the other thing is when we're considering a 9
normal operating history, it's only as we get towards 10 the end of the cycle conditions.
11 You know, if your plant has been operating 12 along at these load conditions for a cycle, it's 13 getting towards the end of cycle conditions where the 14 worth of the highest worth control rod remaining stuck 15 out can be offset by the amount of reactivity feedback 16 that comes along with up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of very effective 17 passive cooling conditions and the assumption that the 18 operators aren't doing anything at all to resolve the 19 system, to resolve the issue.
20 You know, the plant is always going to be 21 initially shutdown, and then it's the later cooling 22 from the ECCS and the slow burnout of xenon worth that 23 rides the critical boron concentration back up, and 24 you can see some of those effects in some of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
81 closed session work.
1 CHAIR KIRCHNER: Okay, so you also have 2
included the xenon?
3 MS. McCLOSKEY: Yes, and we --
4 MR. CASE: Particularly the downcomer 5
resolution is something that we look at more 6
specifically, and the method doesn't require us to 7
stay above the critical concentration, but it's a part 8
of the consideration.
9 I think it is important that, and this 10 will be evident in the curves, that the end state of 11 the transient is very safe in terms of margin 12 perspective to the critical concentration, so there's 13 really an inflection point.
14 Meghan was kind of describing the dynamics 15 of the transport behavior and then the xenon and the 16 temperature effects, right? So, all of those create 17 a
bit of a
pinch point that we look at 18 deterministically, right, to apply margin, but overall 19 in the context of where the transient ends up, it's in 20 a good spot.
21 The dilution of the containment was not 22 something that we set out to resolve. I think that's 23 a consideration. In the event that we have modules 24 under those conditions, there's certain procedures, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
82 and we still have some of that language in the SRs as 1
to the consideration of that during recovery efforts.
2 MR. CODDINGTON: And I guess I would just 3
add that in this sizing of the ESB, some of our 4
transients that we do evaluate don't result in a 5
diluted downcomer. There's a flow path that is 6
maintained from the core and riser to the downcomer --
7 CHAIR KIRCHNER: Right.
8 MR. CODDINGTON: -- if you assume an 9
injection uprate, for instance. Some of the sizing of 10 the ESB and how much boron it needs to hold, you know, 11 the minimum value there is effectively enough to make 12 sure that it would remain shut down even for that type 13 of event where you don't actually concentrate boron in 14 the core very much.
15 CHAIR KIRCHNER: Okay, well, we can pursue 16 it further in the closed session, okay. Members? And 17 that concludes your presentation, Ben, yes?
18 MR. BRISTOL: Yes.
19 CHAIR KIRCHNER: Okay, so for those 20 listening in, we're going to pause for a moment and 21 change out to NRC staff.
22 MR. DRUCKER: Well, I just want to do a 23 slide check here. Are you guys seeing the full 24 slides?
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
83 CHAIR KIRCHNER: Not yet. We're seeing --
1 can you go to the slide show?
2 MR. SNODDERLY: Patrick, give us some 3
time. We won't start until we can see the slides, all 4
of us can see the slides, but thank you for asking.
5 Any other comments, Patrick, or things we can do to 6
help with the transcript?
7 (Pause.)
8 MR. SNODDERLY: Okay, thank you for the 9
feedback.
10 MR. TESFAYE: This is Tesfaye. David, can 11 you hear me?
12 MR. DRUCKER: Yes, I can hear you. We got 13 you.
14 Am I okay to start?
15 CHAIR KIRCHNER:
- Yes, please, but 16 introduce yourself.
17 MR. DRUCKER: Good day. My name is David 18 Drucker and I'm a Senior Project Manager in the New 19 Reactor Licensing Branch in NRR and the Lead Project 20 Manager for the XPC topical report review.
21 This slide shows the contributors to the 22 review of the XPC topical report, and I will present 23 a few introductory slides, and Antonio Barrett, the 24 lead reviewer, will present the remainder of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
84 slides.
1 During the staff's review of the topical 2
report, 25 audit issues were identified and resolved, 3
and eight RAIs were issued. The second to last bullet 4
on this slide says two RAIs remain open. However, 5
since these slides were submitted to ACRS last week, 6
one of the RAIs was closed, so there's only one open 7
RAI.
8 The significant changes between the draft 9
safety evaluation provided to ACRS on February 4 and 10 the safety evaluation published on February 26 will be 11 discussed in slide 16.
12 As I mentioned earlier, only one RAI 13 remains open. RAI XPC-6 was recently closed. NRC 14 staff is reviewing a revised response to RAI XPC-21 15 that was submitted by NuScale on February 27.
16 A significant change between the draft 17 safety evaluation provided to ACRS on February 4 and 18 the safety evaluation published on February 26 is the 19 addition of limitation and condition number 10 and 20 number 11, which will be discussed in more detail 21 later in this briefing. Next, Antonio Barrett will 22 discuss the staff's review of this topical report in 23 detail.
24 MR. BARRETT: Thank you, David. My name 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
85 is Antonio Barrett of the NRC staff. I work in the 1
new reactor, excuse me, the Nuclear Methods Systems 2
and New Reactors Branch, excuse me. Anyway, so let's 3
-- all right, we're on the first slide.
4 So, relevant changes from the DCA to the 5
SDAA, in the DCA, they had a long-term tooling and 6
technical report and SR evaluations, and now for the 7
SDAA, we have a new XPC topical report methodology and 8
new design features.
9 With respect to the criticality 10 evaluations, there were some for the DCA. There were 11 some conditions and events where you could return to 12 power, and now with the new SDAA and using at least 13 the new methodology and the design features now can 14 return to power. Go to the next slide?
15 Additionally, some of the additional 16 changes are increasing the riser holes which were 17 there to help promote mixing. For the DCA, the RVVs 18 contained in IAB, which would prevent a blowdown on 19 the ECCS signal, now for the SDAA, the RVVs do not 20 contain these IABs, so when you get a valid ECCS 21 signal it won't blowdown. Some of the boron addition 22 that we're going to talk about eventually.
23 And for the long-term cooling 24 enhancements, there is the new ECCS supplemental boron 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
86 system, so the combination of the riser holes, this 1
containment boron addition, the containment mixing 2
tubes, they all contribute to the boron transport and 3
redistribution around the system during DHRS and ECCS 4
cooling. Next slide?
5 And this is just a figure kind of 6
depicting some of the stuff that we already described 7
and I think you've already seen a lot of this stuff 8
already talked about during the NuScale slides. Over 9
here, you see the RVVs that no longer contain the 10 IABs, the containment mixing tubes which promote 11 mixing towards the bottom of the CNV, the riser holes, 12 the upper and lower riser holes which promote mixing 13 between the downcomer and the riser core section, as 14 well as the boron addition source. Next slide?
15 So, for some of the review highlights, 16 we're going to cover those on the next two slides.
17 So, the XPC topical report is an extension of the 18 short-term LOCA and non-LOCA topical reports. It was 19 built off of those particular evaluation models and 20 the staff reviewed it as such, and the staff used the 21 guidance in Reg Guide 1.203 to perform this review.
22 And the staff performed their own 23 independent PIRT, Phenomenon Identification and 24 Ranking Table, evaluation, and compared it to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
87 NuScale's that they had performed.
1 The staff also reviewed the computational 2
tools used. NRELAP5 was used for the thermal 3
hydraulic response only. SIMULATE was used for their 4
neutronics calculations, and then a MATLAB script was 5
used to input all of the calculational framework for 6
their transport methodology, and that's how they 7
transport boron throughout the system.
8 The staff reviewed the NRELAP5 test 9
assessment basis. This included reinterval effects 10 tests, a long-term cooling test, and LOCA ECCS tests, 11 and then a non-LOCA test which was mainly a DHRS test 12 at the NIST-2 facility, and the staff reviewed the 13 validation and the associated uncertainties as shown 14 through those test comparisons between the NRELAP 15 predicted predictions versus the test data.
16 So, and the staff also reviewed the 17 construction and development of the long-term cooling 18 thermo-hydraulic model, and that model was based off 19 of the short-term LOCA base model, and then with some 20 adjustments to make it into the long-term cooling 21 model, some things to make it run a little bit 22 smoother, and the validation basis for that comparison 23 that staff review was about.
24 In the XPC topical report, there's a lower 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
88 riser hole flow assessment that's required to ensure 1
that you get adequate lower, that you're actually 2
calculating adequate lower riser hole modeling, and 3
the staff reported an evaluation of that as well.
4 And the staff also reviewed particular 5
events that were considered for collapsed liquid 6
level, heat removal capability, and the boron 7
transport for subcriticality and precipitation.
8 DR. MARTIN: This is Member Martin. We'll 9
talk about this more in the closed session. The 10 MATLAB model is obviously something a bit different 11 than NRELAP5 and SIMULATE5 because, you know, a lot of 12 history with those other codes. Once you just kind of 13 describe your approach to reviewing that, it's going 14 to require maybe a little bit more intention than the 15 other two.
16 MR. BARRETT: Yeah, as far as the review, 17 the staff requested disks that contained the RELAP 18 models, as well as the MATLAB scripts that were used, 19 so we got those in-house and we exercised them in 20 detail from the various sensitivity studies.
21 DR. MARTIN: So, it wasn't just a 22 qualitative review?
23 MR. BARRETT: Correct.
24 DR. MARTIN: There was some quantitative, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
89 okay.
1 MR. BARRETT: So, we can actually check to 2
see that they actually implemented what they were.
3 DR. MARTIN: Okay, appreciate that.
4 MR. BARRETT: Can we go to the next slide?
5 We kind of discussed it already a little bit. We 6
reviewed the boron transport subcriticality 7
methodology concentrating on the thermal hydraulic 8
conditions as well as the mixing model assumptions for 9
assuming.
10 We also did the critical boron equation, 11 and it's going to operate less than the critical boron 12 concentration which obviously tells you your margin to 13 recriticality.
14 And similarly, we provided the same sort 15 of review for the boron transport and precipitation 16 methodology analysis, which is very similar to the 17 transport subcriticality methodology except for 18 getting the boron basically in one particular area.
19 MR. BLEY: Excuse me, this is Dennis Bley.
20 Could you speak a little slower? Coming over Teams, 21 it's blurring a little and it's hard to understand.
22 CHAIR KIRCHNER: Just pull it closer to 23 you.
24 MR. BARRETT: Okay, does that sound a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
90 little bit better?
1 MR. BLEY: It does.
2 MR. BARRETT: Okay, so the boron transport 3
precipitation methodology was reviewed similarly to 4
how the boron transport subcriticality methodology was 5
reviewed, and some of the similar comments I made 6
earlier to Member Martin, except for the boron 7
precipitation methodology was geared towards 8
collecting all of the boron in one particular 9
location, and so you can compare it back to the 10 solubility limit for precipitation. Can we go to the 11 next slide?
12 So, Dave mentioned earlier that there were 13 some differences in the safety evaluation between what 14 you saw before and what you were just presented with, 15 one of which was the updated nuclear reliability 16 factor review portion, which is we just got the 17 response.
18 As Dave stated, we were still under 19 review, and then there were two limitations and 20 conditions added. One was requiring enough boron to 21 account for the integral down powers and pre-transient 22 operational histories to include xenon impacts as well 23 as low decay heats.
24 And in
- addition, there is another 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
91 limitation and condition that was added, and this one 1
was with respect to boron precipitation, and this was 2
to require that the zero power maximum operational 3
limit for boron concentration will be used as the 4
initial condition in the RPV to help account for some 5
uncertainties. Go to the next slide, Dave?
6 So, for the limitations and conditions, 7
for limitation and condition one, changes to the 8
short-term LOCA or non-LOCA topical reports will 9
require changes to the XPC topical report, so that 10 would have to be looked at.
11 For limitation and condition number two, 12 it's applicable only to the US460 and NPM-20 based off 13 of how the review was performed and how the PIRT was 14 performed.
15 Number three, you have to maintain 16 insignificant non-condensable gas in containment for 17 evaluate the amount of non-condensable gases in 18 containment in your subcriticality methodology.
19 Number five, the methodology was limited 20 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and does not include post-event recovery 21 actions. Limitation and condition number six, the RVV 22 compressible flow qualification is going to have to be 23 a part of the ASME QME-1 qualification in the 24 application.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
92 Limitation and condition number seven, 1
there must be an initial test program, first module 2
only, for dissolution testing so that you can account 3
for the different boron dissolution
- rates, 4
condensation rates, et cetera.
5 CHAIR KIRCHNER: Antonio, if I could 6
interrupt there just in the open session, what's your 7
expectation? How will they measure in that initial 8
test program the boron dissolution to your 9
satisfaction?
10 MR. BARRETT: Yeah, so --
11 CHAIR KIRCHNER: What are you looking for, 12 for metrics?
13 MR. BARRETT: Yeah, so it's going to be 14 consistent with the evaluation model. So, they make 15 certain assumptions or predictions about what happens 16 with condensation and condensation flow rates, and 17 they have the different mechanical designs set up to 18 get the condensate, have it go certain places.
19 So, I would imagine like a steam test over 20 varying conditions that would then validate how much 21 you collect, where it collects, how it's able to 22 dissolve a certain amount of boron, does it or does it 23 not, versus what was assumed in the analysis and then 24 overall, the mixing portion in terms of the vault 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
93 water container.
1 CHAIR KIRCHNER: You're seeing these as 2
nuclear driven tests, by which I mean you have nuclear 3
heating tested?
4 MR. BARRETT: I do not. I think it's --
5 as long as you get the steam, I think that would be 6
the most important part of the test.
7 CHAIR KIRCHNER: Okay, so they already 8
would use an auxiliary boiler kind of setup to bring 9
the module up to some temperature where they can 10 safely pull rods, but okay, how are you going to 11 measure this?
12 MR. BARRETT: Yeah, so it should be just, 13 in my opinion, my view, it would be just a dissolution 14 rate. So, if your collection is setup appropriately, 15 you would collect the amount of condensate per 16 whatever steam rate that you have, and then it would 17 dissolve the boron at a certain rate. And if you're 18 assuming, for example, in the analysis, that you're 19 not getting that dissolution rate, then there would be 20 a mismatch there.
21 CHAIR KIRCHNER: But the easy part is the 22 dissolution of the actual boron, I shouldn't use the 23 word pellets, whatever their geometric form is in the 24 basket. That's the easy part. Where does the boron 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
94 go? Is that what you're looking for?
1 MR. BARRETT: No, so the easy part is 2
definitely, I guess, a main portion of it. The second 3
part would be you have your mixing tubes, and whether 4
or not --
5 CHAIR KIRCHNER: Right.
6 MR. BARRETT: -- you're actually getting 7
that sort of mixing. So, what we would think you 8
would do is something similar to like a gradient, 9
concentration gradient. Does it actually -- are you 10 getting that sort of mixing flow through the tubes 11 that you expected?
12 CHAIR KIRCHNER: So, they would have to 13 design a probe that would be in the downcomer region 14 and/or the containment downcomer region to --
15 MR. BARRETT: That would be one way. I 16 think that you could do some sampling at different 17 elevations potentially over time, but I think there's 18 a lot of different ways that you can do it, but I 19 don't see it as being overly complex.
20 CHAIR KIRCHNER: So, let me take it one 21 step further. Would this eventually show up as an 22 ITAC then in a COL application?
23 MR. BARRETT: Yeah, so right now, I think 24 we asked this question as part of the SDAA design and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
95 now it's part of their initial test program.
1 CHAIR KIRCHNER: Okay.
2 DR. PALMTAG: This is Scott Palmtag. Just 3
to follow up on that, I'm kind of curious, how would 4
they get steam into the containment vessel? Is that 5
something you imagine doing offline at some facility 6
or doing it actually when they build the first, 7
install the first module?
8 MR. BARRETT: Yeah, I imagine it's when 9
they actually install the first module, but yeah, like 10 I think Dr. Kirchner was saying, like you could either 11 use the ox boiler if it was able to give you the steam 12 levels that you want. I think probably maybe you 13 might be a little bit more interested in the lower 14 steam levels, but as long as you can get the steam in 15 there somehow, I think that would be good enough.
16 DR. PALMTAG: How would you do that? I'm 17 just trying to figure out the piping. I mean, I don't 18 know all of the piping, but you have your reactor 19 pressure vessel. You'd have to open those valves to 20 let the steam into the containment or in the --
21 MR. BARRETT: No, I don't think you 22 actually -- I think that's one way you could do it, 23 but a different way would be you can just put the 24 steam directly in. We're not talking about nuclear 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
96 heating.
1 We don't even necessarily need you to 2
simulate an ECCS blow valve per se. You don't 3
necessarily have to, but if you're going to have a way 4
to just put the steam in, I think that that would be 5
one, and so it doesn't have to be overly --
6 DR. PALMTAG: Just when you have -- we're 7
not talking a special test facility. We're actually 8
talking about the real containment vessel.
9 MR. BARRETT: Yes.
10 DR. PALMTAG: Is there -- maybe this is 11 something I can ask NuScale, but is there available 12 piping that they could dump the steam into the 13 containment vessel?
14 CHAIR KIRCHNER: They have a containment 15 fill and drain system, so my sense would be that would 16 be used. Go ahead.
17 MR. NOLAN: This is Ryan Nolan from the 18 staff. And so, the staff wasn't too focused on how 19 you get the steam into containment, but our 20 understanding is right now that there's a module heat-21 up system that they would use to bring the RCS up to 22 pressure and temperature, right.
23 And so, you would use that system and then 24 you could open the vent valves, which would then 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
97 create steam inside the containment, or they could 1
scope out a temporary system. We weren't really 2
overly concerned with how you get steam into 3
containment, but as of right now, I believe that's the 4
structure that was proposed with the initial testing.
5 DR. PALMTAG: Yeah, I understand it's easy 6
to define this, but I'm curious when the NuScale 7
people come back up, I'm kind of curious how they're 8
actually doing this because if you're -- I mean, 9
you're limited by your piping that's in there.
10 MR. NOLAN: Right, so as of right now, 11 this is part of the initial test program, so Chapter 12 14 does include Revision 2 of the FSAR will include a 13 test that describes how to perform this.
14 MR. BARRETT: So, limitation and condition 15 eight is approved for the NRELAP5 Version 1.7 in 16 conjunction with Basemodel Rev. 5 with allowable, you 17 know, change processes, allowable change processes.
18 Limitation and condition nine, you've got 19 to have a separate approval required for single 20 failures, electric power assumptions, and operator 21 actions, which would be a part of the downstream 22 application. Dave, can you go to the next slide?
23 And the last two, as we discussed earlier, 24 a limitation and condition to account for integral 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
98 down powers and xenon low decay heat for 1
subcriticality analyses, and limitation and condition 2
number 11, where you have zero power maximum 3
operational limit, no xenon, at the beginning of cycle 4
where initial conditions warrant more precipitation 5
analyses.
6 DR. PALMTAG: This is Scott Palmtag again.
7 So, I have some questions about ten and 11. So, in a 8
lot of calculations, your core calculation where you 9
have to do your cycle limits, you have to show that 10 you have shutdown capability for all kinds of other 11 limits. Is this meant to be more of a bounding 12 analysis that you're going to set some limit for the, 13 I guess, minimum boron concentration that's going to 14 handle all cycles or is it something that's going to 15 have to be shown on a cycle by cycle basis?
16 MR. BARRETT: Yeah, so I think we can get 17 into it a little bit more in the closed session, but 18 I think there will be -- what we envision is there's 19 something that's done -- well, I think it's already --
20 in response to XPC-6, NuScale already put in like a 21 curve, if you will, that will then be placed into the 22 cooler that will probably generally cover most cycles, 23 but can be updated if you wanted to get more margin 24 like, you know, that considers like your power 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
99 ascension rate and things of that nature.
1 DR. PALMTAG: I'm just a little concerned 2
about having some bounding analysis because everything 3
has been done on an equilibrium core, right, so as you 4
know, cycle one is going to be completely different 5
and you never quite get to the equilibrium core.
6 There might be fuel changes and everything that goes 7
along the way.
8 I'm not sure that there's been enough 9
analysis. The equilibrium core analysis can really 10 cover cores. I would think this would have to be 11 something that would have to be shown for each core 12 design.
13 MR. BARRETT: Yeah, so currently, it's in 14 the cooler right now, so I assume that it will be done 15 for every core design, but that's a part of their tech 16 spec that they currently presented to us. We can show 17 it maybe later, but, so.
18 DR. PALMTAG: Yeah, and you probably will 19 not be able to answer this, but you have an 20 operational minimum boron concentration is the way I 21 understand this. Won't this -- maybe it's a small 22 amount, but won't this significantly affect core 23 operations and cycle length?
24 MR. BARRETT: No, this is just so that you 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
100 can do your precipitation analysis with additional 1
boron. That's it. So, this is not an actual -- if 2
you're talking about 11, there is not an actual limit 3
on operation or anything of that nature.
4 We're just saying when you're at zero 5
power, no xenon, boron concentration, you're at a very 6
high boron concentration, you have to deborate to kind 7
of go through your cycle, right? So, we're just 8
saying if you use it as your initial condition just 9
when you do the analysis to add some conservatism, and 10 this is how they already currently do the analysis, 11 then you must have this additional boron to account 12 for uncertainties.
13 DR. PALMTAG: I guess I'm not really --
14 I'm not sure I understand that. So, as you deplete 15 your cycle, at the end of the cycle, you're going to 16 be at zero boron, and then, but that won't be sort of 17 sufficient? There's going to have to be an additional 18 boron concentration above that zero boron?
19 MR. BARRETT: No, so I think maybe I, when 20 I was talking about ten and the limits and whatnot, 21 that's kind of a different thing. So, going down to 22 L&C number 11, only when you perform your boron 23 precipitation analyses, which means that the more 24 boron you have, the worse off you are, the worse, you 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
101 know, the closer you are to your solubility limit.
1 DR. PALMTAG: Okay.
2 MR. BARRETT: So, forgetting about 3
everything else and just putting some boron --
4 DR. PALMTAG: Okay, this is specifically 5
precipitation?
6 MR. BARRETT: Correct, yeah.
7 DR. PALMTAG: All right, thank you.
8 MR.
CODDINGTON:
This is Taylor 9
Coddington. So, it's effectively, for the boron 10 precipitation analysis, use a conservative method is 11 effectively finished or the limitation is trying to be 12 established.
13 DR. PALMTAG: Right, I misunderstood. I 14 didn't realize it was for precipitation. I thought 15 there would be a minimum boron limit in the core for 16 criticality purposes, but we can get into that in the 17 closed session.
18 MR. BARRETT: All right, Dave, can you go 19 to the next slide? I think that's the end. So, the 20 staff believes the applicant has provided sufficient 21 information to support this safety finding.
22 The staff found what the applicant 23 represents in this topical report satisfies the 24 limitations and conditions and will meet relevant 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
102 regulatory requirements pending review and approval of 1
the application. Thank you very much for your time.
2 If there's any more questions, I'll take those.
3 CHAIR KIRCHNER: Members, questions or 4
you're just saving everything for this afternoon?
5 Okay, all right, with that then, if there are no 6
further questions, let me take this opportunity to see 7
if we have any comments from the public either here in 8
our room or online. Just if you're online, unmute 9
your microphone, state your name and affiliation as 10 appropriate, and make your comment.
11 In the room here, I think we have all 12 staff and applicant with us, so I am not hearing 13 anyone wishing to make a public comment. We're going 14 to adjourn, not adjourn, but we're going to close the 15 open session and we will return at 1:00 Eastern Time 16 for the closed sessions, and those of you who are 17 authorized will have the Teams link to join us. So, 18 we are recessed until 1:00.
19 (Whereupon, the above-entitled matter went 20 off the record at 12:03 p.m.)
21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
LO-179859 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com February 26, 2025 Docket No. 052-050 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738
SUBJECT:
NuScale Power, LLC Submittal of Presentation Material Entitled ACRS Subcommittee Meeting (Open Session) Non-Loss-of-Coolant Accident Topical Report and Extended Passive Cooling and Reactivity Control Methodology Topical Report, PM-179845, Revision 0 The purpose of this submittal is to provide presentation materials for use during the upcoming Advisory Committee on Reactor Safeguards (ACRS) NuScale Subcommittee Meeting on March 4th, 2025. The materials support NuScales presentation of the subject topical reports for the US460 Standard Design Approval Application.
The enclosure to this letter is the nonproprietary presentation entitled ACRS Subcommittee Meeting (Open Session) Non-Loss-of-Coolant Accident Topical Report and Extended Passive Cooling and Reactivity Control Methodology Topical Report, PM-179845, Revision 0.
This letter makes no regulatory commitments and no revisions to any existing regulatory commitments.
If you have any questions, please contact Amanda Bode at 541-452-7971 or at abode@nuscalepower.com.
Sincerely, Mark W. Shaver Director, Regulatory Affairs NuScale Power, LLC Distribution:
Mahmoud Jardaneh, Chief New Reactor Licensing Branch, NRC Getachew Tesfaye, Senior Project Manager, NRC Michael Snodderly, Senior Staff Engineer, Advisory Committee on Reactor Safeguards, NRC Thomas Hayden, Project Manager, NRC David Drucker, Senior Project Manager, NRC
LO-179859 Page 2 of 2 02/26/2025 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com
- ACRS Subcommittee Meeting (Open Session) Non-Loss-of-Coolant Accident Topical Report and Extended Passive Cooling and Reactivity Control Methodology Topical Report, PM-179845, Revision 0, Nonproprietary
LO-179859 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com ACRS Subcommittee Meeting (Open Session) Non-Loss-of-Coolant Accident Topical Report and Extended Passive Cooling and Reactivity Control Methodology Topical Report, PM-179845, Revision 0, Nonproprietary
1 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 ACRS Subcommittee Meeting (Open Session)
March 4, 2025 Non-Loss-of-Coolant Accident Topical Report and Extended Passive Cooling and Reactivity Control Methodology Topical Report
2 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 ACRS Subcommittee Meeting (Open Session)
March 4, 2025 Non-Loss-of-Coolant Accident Topical Report Presenters: Kevin Lynn, Meghan McCloskey, Ben Bristol
3 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Acknowledgement and Disclaimer This material is based upon work supported by the Department of Energy under Award Number DE-NE0008928.
This presentation was prepared as an account of work sponsored by an agency of the United States (U.S.)
Government. Neither the U.S. Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S. Government or any agency thereof.
4 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Agenda Non-loss-of-coolant accident (non-LOCA) topical report history Non-LOCA evaluation model (EM) analysis purpose, transient class, acceptance criteria Relevant power uprate design and operating changes Summary of EM applicability assessment and updates
5 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Non-LOCA Topical Report History Non-LOCA topical report Revision 3 was approved by NRC in 2020 Approved Revision 3 was used in Final Safety Analysis Report (FSAR) analyses for US600 (with NPM-160) design that has been certified Approved Revision 3 contained limitations and conditions (L&Cs) restricting use to NPM-160 design Revision 4 was submitted in January 2023 along with FSAR for US460 (with NPM-20)
Updates to Revision 4 have been made since January 2023 in response to NRC questions Revision 5 will incorporate these updates, but has not been submitted at this time Focus of discussion today is changes since prior NRC approval of Revision 3
6 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Non-LOCA EM: Analysis Purpose, Transient Class, Acceptance Criteria Scope consistent with the NRC-approved Revision 3 Plant design, core design, fuel rod design, plant initial conditions, structures, systems, and components (SSC) performance Primary
- pressure, secondary
- pressure, safe stabilized condition Fuel cladding integrity Radiological dose acceptance criteria Mass & energy release input Non-LOCA topical report TR-0516-49416-P Subchannel topical reports TR-0915-17564-P-A TR-108601-P-A Accident source term topical report TR-0915-17565-P-A
7 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Power Uprate and Design Changes Summary NPM-160 to NPM-20 Power uprate from 160 MWt to 250 MWt Module SSC design essentially maintained Operating conditions o Increased primary pressure from 1850 psia to 2000 psia o Primary and secondary side design pressures increased from 2100 psia to 2200 psia o Use Tavg control instead of Thot control (Tavg changed from ~545°F to 540°F) o Decreased secondary side feedwater temperature at 100% power from 300°F to 250°F o Reduced minimum temperature for criticality from 420°F to 345°F Module protection system (MPS) actuations optimized for US460 design o Adjusted to accommodate modified operating conditions o Added reactor trip on high Tavg to terminate slower reactivity transients earlier (e.g., reactivity transient initiated from lower power) o Additional decay heat removal system (DHRS) actuations - for any containment vessel (CNV) isolation signal during power operation o Pressurizer line isolation on low pressurizer pressure
8 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Pressure/Temperature Operation and Limit Changes US600 (Certified Design)
US460 (Design currently under review)
9 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Analytical Assumptions for Non-LOCA Analysis Approach from NRC-approved Revision 3 methodology maintained:
Scope of event progression Safety analyses of design-basis events are performed from event initiation until a safe, stabilized condition is reached Operator action No operator actions required to achieve 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 event occurs Loss of power Evaluate whether power available, loss of alternating current (AC) power, or loss of AC and direct current (DC) power is more limiting Nonsafety-related module or plant control systems Operation of nonsafety-related control system that leads to a less severe plant response is not credited Operation of nonsafety-related control system that leads to a more severe plant response is assumed Nonsafety-related SSC credited Nonsafety-related secondary main steam isolation valves (MSIVs) and feedwater (FW) regulating valves serve as backup for safety-related valve single failure Nonsafety-related check valves in FW piping serve as backup for safety-related check valve failure
10 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Non-LOCA EM Updates Design changes have no substantial change in non-LOCA event progressions or important phenomena o Reactor pressure vessel (RPV) pressure protected by reactor safety valve (RSV) lift o Secondary pressure protected by design pressure equal to RPV design pressure, physically limited to saturation pressure at maximum primary hot side temperature o Minimum critical heat flux ratio (MCHFR) limited under high power, high temperature conditions (e.g., reactivity insertion events)
Non-LOCA phenomena identification and ranking table (PIRT) from NPM-160 remains applicable Current EM employs NRELAP5 v1.7 (NRC-approved Revision 3 used NRELAP5 v1.4)
NRELAP5 assessment basis expanded with NIST-2 steam generator (SG)-DHRS tests Methodology changes for event-specific analyses o Provided additional detail on when more extensive sensitivity calculations performed
Dependent on margin to acceptance criteria - more sensitivity studies needed where margin is smaller o Generally expanded scope to vary parameters rather than bias in only one direction o Option for radiological analyses to use bounding input rather than transient-specific input o Option to demonstrate control rod drop analyses bounded by single rod withdrawal or steady-state conditions o Option to use increase in level during boron dilution events to determine shutdown margin at event termination
==
Conclusion:==
EM remains adequate to evaluate an NPM design
11 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 11 Questions?
12 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Acronyms AC Alternating current CNV Containment vessel DC Direct current DHRS Decay heat removal system EM Evaluation model FSAR Final safety analysis report FW Feedwater L&C Limitation and condition LOCA Loss-of-coolant accident MCHFR Minimum critical heat flux ratio MPS Module protection system MSIV Main steam isolation valve NIST NuScale Integral System Test Facility Non-LOCA Non-loss-of-coolant accident NPM NuScale Power Module PIRT Phenomena identification and ranking table RPV Reactor pressure vessel RSV Reactor safety valve SG Steam generator SSC Structures, systems, and components Tavg Average temperature Thot Hot temperature
13 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 ACRS Subcommittee Meeting (Open Session)
March 4, 2025 Extended Passive Cooling and Reactivity Control Methodology Topical Report Presenters: Thomas Case, Meghan McCloskey, Ben Bristol
14 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Agenda Evaluation model (EM) scope, regulations, acceptance criteria NuScale Power Module (NPM) design features Phenomena identification and ranking table (PIRT) evolution EM structure EM validation basis EM adequacy assessment and conclusions
15 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 NPM Extended Passive Cooling and Reactivity Control Scope InitiatingEvent NonLOCAevent DHRSactuation Inadv.ECCSor Valveopening event PipebreakLOCA insideCNV NonLOCAevent Rxtriponly NoDHRSactuation Controlrod ejection ShorttermDHRS operation ShorttermECCS operation ShorttermECCS operation Normalshutdown ExtendedDHRS cooling EDAScapacity ECCSactuation at24hrs ECCSvalve opening ECCSvalvepassive opening InsufficientSDM ECCSactuation ext.DHRStimer Longterm ECCScooling ARIorWRSO anypoweravailability ARIorWRSO anypoweravailability ARIorWRSO AC,DCpoweravailable ACpoweravailable ARI ACpowerlost EDASlost ARIorWRSO ACpoweravailable WRSO Veryeffective DHRScooling ACpowerlost EDASavailable ARI Shortterm toLongterm ECCS Transition ExtendedDHRS toECCS Shortterm toLongterm ECCS Extended passive cooling Shortterm nonLOCA Shortterm nonLOCA Shortterm LOCA Rodejection Leakage DHRStoECCS RTNSS7days ELAP14days 72hours Postevent returntoservice designcapability LeakageECCS actutation New topical report to support 250 MWt NPM design and US460 submittal Regulations:
o 10 CFR 50.46(b)(4) and (5) o Principal design criterion (PDC) 35 -
emergency core cooling o PDC 34 - residual heat removal o General design criterion (GDC) 26, GDC 27 - reactivity control and subcriticality, normal operation or following anticipated operation occurrences (AOOs) or accidents o Supports application exemptions to GDC 33 for system with safety function to provide makeup in response to reactor coolant pressure boundary leakage
16 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Extended Passive Cooling (XPC) Figures of Merit Safety Objective Acceptance Criteria Provide decay and residual heat removal Collapsed liquid level remains above top of core Reactivity control Core remains subcritical Maintain coolable geometry Boron concentration remains below precipitation limits Key assumptions/requirements:
Demonstrate subcriticality (keff<1) with highest worth control rod withdrawn from core Demonstrate acceptance criteria met for at least 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />
17 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 NPM Design - Long-term ECCS Collapsed Level After emergency core cooling system (ECCS) actuation, decay and residual heat generate vapor and energy transferred to reactor pool ultimate heat sink:
o ECCS recirculation and condensation on containment wall, heat transfer through vessel wall o Steam generator (SG)-decay heat removal system (DHRS) operation with condensation on outside of SG tubes During ECCS long-term cooling, reactor coolant distributes between reactor pressure vessel (RPV) and containment vessel (CNV)
Distribution of reactor coolant depends on o ECCS venting capacity and demand o Containment heat transfer capacity reactor pool reactor recirculation valves containment vessel reactor vent valves
18 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 NPM Design - Long-term ECCS Collapsed Level Minimum Level Conditions High CNV wall heat transfer Maximum Temperature Conditions Low CNV wall heat transfer 4-24 hours: module pressure
~ 100 psia - ~ 50 psia 2-24 hours: module pressure
~ 100 psia - ~ 5 psia
19 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 NPM Design Features - Boron Transport Method Applicability ECCS actuation designed for core cooling and reactivity control Upper riser flow paths between riser and downcomer o Sustain liquid flow over the SG for decay heat removal after riser uncovery o Maintain boron transport during DHRS operation Lower riser flow paths between riser and downcomer o Maintain boron transport during ECCS operation Low RCS level Low-low RCS level Upper riser flow paths Lower riser flow paths
20 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 NPM Design Features - Boron Transport Method Applicability (continued)
ECCS supplemental boron (ESB) feature o Passive design feature to maintain subcriticality during design basis extended passive cooling o Boron oxide (B2O3) pellets in dissolver basket(s) o Mixing tube(s) in containment o Condensate collection channels to dissolver basket(s) and mixing tube(s)
21 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 PIRT Evolution for XPC Design Certification Application (DCA) NPM-160 Design Standard Design Approval Application (SDAA) CORE250B/NPM-20 Design Phase Figure of Merit (FOM)
Phase FOM Loss-of-coolant accident (LOCA) long-term cooling (LTC) Phase 2 Period beginning after reactor recirculation valve (RRV) flow direction reverses and flows from CNV to RPV Critical heat flux ratio (CHFR);
Collapsed liquid level (CLL);
Subcriticality ECCS Phase 2 Period beginning after RRV flow direction reverses and flows from CNV to RPV CLL; Subcriticality; Coolable geometry Non-LOCA Phase 3 Stable natural circulation CHFR; Mixture level (phase 3, 4);
Subcriticality DHRS Phase 3 Stable natural circulation Non-LOCA Phase 4 Intermittent natural circulation n/a n/a Non-LOCA Phase 5 Interrupted natural circulation n/a n/a Previously developed PIRTs for NPM-160 long-term ECCS or DHRS cooling were re-assessed holistically, expanded as needed due to ESB design changes Requirement to maintain subcriticality
22 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 EM Structure NRELAP5 thermal-hydraulic analysis o Evaluate collapsed liquid level above top of fuel and containment response
Minimum level conditions
Maximum temperature conditions o Provide boundary conditions for boron transport SIMULATE5 core reactivity analysis o Provide critical boron concentrations o Evaluate range of operating cycle exposures, operating histories, thermal-hydraulic conditions Boron transport analysis o Implemented in MATLAB scripts or other appropriate computational script o Map NRELAP5 conditions to critical boron concentration from SIMULATE5 to demonstrate subcriticality o Evaluate maximum concentration to demonstrate margin to precipitation concentrations
23 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 EM Validation Basis NRELAP5 validation o Builds on validation basis for LOCA and non-LOCA EMs o Additional validation against NIST-2 LTC and LOCA tests Boron dissolution validation o Separate effects tests performed o Methods for slow or fast-biased dissolution assessed against test data SIMULATE5 o Extensive validation basis developed for other applications o Nuclear reliability factor (NRF) for XPC conditions evaluated and included in critical boron concentration Boron transport o Relies on thermal-hydraulic input o Conservative treatment of phenomena specific to boron transport
24 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 EM Adequacy Assessment and Conclusions Adequacy assessment evaluated from bottom-up and top-down perspectives o Models and correlations in NRELAP5 or phenomena treatment in boron transport considered o Top-down assessments considered NIST-2 integral tests and overall approach/conservatism in the EM Adequacy assessment discusses limitations in the models and correlations EM requires conservative or bounding approaches to address limitations in models and correlations
==
Conclusion:==
EM provides conservative method to demonstrate that an NPM, with specified design features, provides adequate core cooling and decay heat removal, remains subcritical following design basis events, and maintains coolable geometry.
25 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 25 Questions?
26 PM-179845 Rev. 0 Copyright © 2025 NuScale Power, LLC.
NuScale Nonproprietary Template #: 0000-21727-F01 R10 Acronyms AOO Anticipated operational occurrence CHFR Critical heat flux ratio CLL Collapsed liquid level CNV Containment vessel DCA Design certification application DHRS Decay heat removal system ECCS Emergency core cooling system EM Evaluation model ESB ECCS supplemental boron FOM Figure of merit GDC General design criterion/criteria LOCA Loss-of-coolant accident LTC Long-term cooling NIST NuScale Integral System Test Facility Non-LOCA Non-loss-of-coolant accident NPM NuScale Power Module NRF Nuclear reliability factor PDC Principal design criterion/criteria PIRT Phenomena identification and ranking table RCS Reactor coolant system RPV Reactor pressure vessel RRV Reactor recirculation valve RVV Reactor vent valve SDAA Standard design approval application SG Steam generator XPC Extended passive cooling
Non-Proprietary 1
Presentation to the ACRS Subcommittee Staff Review of NuScale Licensing Topical Reports TR-0516-49416, Rev. 4, Non-LOCA Analysis Methodology TR-124587, Rev. 0, XPC Methodology March 4, 2025 (Open Session)
Non-Proprietary 2
Presentation to the ACRS Subcommittee of the Staffs Review of NuScale Non-Loss-of-Coolant Accident Analysis Methodology, TR-0516-49416, Rev 4.
March 4, 2025 (Open Session)
Non-Proprietary 3
NuScale Non-LOCA LTR Review Technical Reviewers
- *Zhian Li, NRR/DSS/SNRB
- Antonio Barrett, NRR/DSS/SNRB
- Adam Rau, NRR/DSS/SNRB
- Peter Lien, NRR/DSS/SNRB
- Ryan Nolan, NRR/DSS/SNRB
- Sean Piela, NRR/DSS/SNRB
- Carl Thurston, NRR/DSS/SNRB
- Dong Zheng, NRR/DSS/SNRB
- Joshua Miller, NRR/DSS/SNRB
- Rosie Sugrue, NRR/DSS/SNRB
- Upendra Rohatgi, RES consultant
- Andrew Dyszel, SNRB contractor
- Marvin Smith, SNRB contractor Project Managers
- Thomas Hayden, NRR/DNRL/NRLB
- Getachew Tesfaye, Lead, NRR/DNRL/NRLB Contributors
Non-Proprietary 4
NuScale Non-LOCA LTR Review NuScale submitted the Non-Loss-of-Coolant Accident (Non-LOCA)
Evaluation Model Topical Report (TR-0516-49416-P), Rev. 4 on January 5, 2023. The topical report was formally accepted for review on July 31, 2023.
NRC conducted an audit of the topical report from March 2023 to August 31, 2024.
49 audit issues were resolved in the audit For items not resolved during the audit, 7 RAIs were generated 1 RAI remains Open There are 2 significant differences between the draft SER submitted to ACRS on February 4, 2025, and the draft SER published on February 26, 2025 Overview
Non-Proprietary 5
NuScale Non-LOCA LTR Review 1 Open Item remaining RAI Non-LOCA.LTR - 50
- Issue description:
- Staff is working to understand changes made to NRELAP5 (v1.7) and the NPM basemodel:
- Modeling changes to DHRS models
- Modeling of core flow distribution
- Path forward:
- NRC and NuScale continue to discuss these modeling changes and have high confidence the issue will be resolved shortly, with minimal impact to the SE Open Item(s)
Non-Proprietary 6
NuScale Non-LOCA LTR Review 2 significant differences
- Section 3.5.3.7, NIST-2 Steam Generator - Decay Heat Removal System (DHRS) Integral Effects Test
- Expanded explanation of NIST-2 DHRS scalability
- Due to closure of Open item RAI NonLOCA.LTR-3,9,18,19,20,21,69
- Section 3.9, Quality Assurance and Section 4.0, Limitations and Conditions
- Removed Limitation and Condition No. 10
- Inserted finding of reasonable assurance related to the implementation of Quality Assurance controls consistent with RG 1.203 for the Non-LOCA EM Significant differences between previously submitted SER
Non-Proprietary 7
NuScale Non-LOCA LTR Review Considered design changes from NPM-160 to NPM-20 Applicability of Phenomenon Identification and Ranking to NPM-20 Use of bounding assumptions for primary coolant release in the radiological analysis instead of calculating primary side mass release Updated critical heat flux (CHF) screening for subchannel analyses Updated initial conditions and biasing scheme for each Non-LOCA event Changes from LTR Rev. 3 (NPM-160) to LTR Rev. 4 (NPM-20)
Non-Proprietary 8
NuScale Non-LOCA LTR Review NRELAP5 revised to version 1.7 NRELAP5 basemodel updated for NPM-20, some system models updated Updated DHRS information with new tests (used in Non-LOCA, LOCA, XPC LTRs)
NIST-2 tests for validation of NRELAP5 for DHRS performance Test results and code predictions of oscillation Reviewed scaling and distortion Long-term progression of non-LOCA events is covered in the XPC LTR Changes from LTR Rev. 3 (NPM-160) to LTR Rev. 4 (NPM-20)
Non-Proprietary 9
NuScale Non-LOCA LTR Review 1)
Applicable to NPM-20 only 2)
Changes to LOCA LTR may require changes to Non-LOCA LTR 3)
Types of analyses approved for Non-LOCA EM 4)
DHRS heat transfer uncertainty 5)
Credit for Non-Safety MSIVs 6)
Separate approval required for single failures, electric power assumptions and operator actions 7)
Approved for NRELAP5v1.7 in conjunction with NPM-20 basemodel Rev. 5 8)
Separate approval required for analytical limits and actuation delays; Applicant must assess for changes to event-specific bias directions 9)
Separate approval required for inputs to radiological consequence analysis not derived from transient analyses Limitations and Conditions
Non-Proprietary 10 NuScale Non-LOCA LTR Review While there are some differences between the current and previous revision, the staff found that the applicant provided sufficient information to support the staffs safety finding.
The staff found that an applicant that references this topical report with the limitations and conditions will meet relevant regulatory requirements pending review and approval of the application.
Conclusions
Non-Proprietary 11 NuScale Non-LOCA LTR Review Questions?
Non-Proprietary 12 Presentation to the ACRS Subcommittee of the Staffs Review of NuScales Extended Passive Cooling and Reactivity Control Methodology (XPC) Topical Report, TR-124587, Revision 0 March 4, 2025 (Open Session)
Non-Proprietary 13 NuScale XPC LTR Review Technical Reviewers
- *Antonio Barrett, NRR/DSS/SNRB
- Dr Rosie Sugrue, NRR/DSS/SNRB
- Dr John Lehning, NRR/DSS/SNRB
- Dr Adam Rau, NRR/DSS/SNRB
- Dr Peter Lien, NRR/DSS/SNRB
- Carl Thurston, NRR/DSS/SNRB
- Dr Len Ward, SNRB contractor
- Marvin Smith, SNRB contractor
- Chis Boyd, RES/DSA
- Jason Thompson, RES/DSA/CRAB II
- Justin Coury, RES/DSA/CRAB II
- Dr Andrew Bielen, RES/DSA/FSCB Project Managers
- David Drucker, PM, NRR/DNRL/NRLB
- Getachew Tesfaye, Lead PM, NRR/DNRL/NRLB Contributors
Non-Proprietary 14 NuScale XPC LTR Review NuScale submitted the Extended Passive Cooling and Reactivity Control Methodology (XPC) Topical Report, TR-124587, Revision 0 on January 5, 2023. The topical report was formally accepted for review on July 31, 2023.
NRC conducted an audit of the topical report from March 2023 to August 31, 2024.
25 audit issues were resolved in the audit For items not resolved during the audit, 8 RAIs were generated 2 RAIs remain open Significant differences between the draft SER submitted to ACRS on February 4, 2025, and the draft SER published on February 26, 2025, are discussed in Slide 16 Overview
Non-Proprietary 15 NuScale XPC LTR Review 2 Open Items remaining RAI XPC.LTR - 6
- Issue description:
- Staff is working to resolve issues with subcriticality considering downpowers and low decay heat RAI XPC.LTR - 21
- Issue description:
- Staff is working to resolve issues related to the incorporation of Nuclear Reliability Factors Path forward:
- NRC and NuScale continue to discuss both of these issues and have high confidence they will be resolved shortly, with minimal impact to the SE Open Items
Non-Proprietary 16 NuScale XPC LTR Review Significant difference
- Sections 4.8.4, Critical Boron Concentration Evaluation and 4.8.7, Boron Precipitation Methodology Assessment, explain why Limitation and Condition No. 10 and No. 11 respectively were added
- Section 5, Limitations and Conditions
- Limitation and Condition No. 10 added to require an applicant to provide technical specification controls to ensure adequate boron concentration is maintained
- Limitation and Condition No. 11 added to require an applicant use a specific initial boron concentration Significant differences between previously submitted SER
Non-Proprietary 17 NuScale XPC LTR Review Long Term Cooling and Reactivity Control
- DCA LTC Technical Report and FSAR Evaluations
- SDAA New XPC Topical Report Methodology and new design features Criticality Evaluations
- DCA has return to power under some conditions with evaluations
- SDAA precludes return to power with use of XPC methodology and design features Relevant Changes from NPM-160 (DCA) to NPM-20 (SDAA)
Non-Proprietary 18 NuScale XPC LTR Review Revised Reactor Design
- Increased number of riser holes to promote mixing between the downcomer and riser to help address potential for recriticality
- Revised Reactor Vent Valve design
- NPM-160 RVV with IAB
- NPM-20 RVV without IAB
- Long Term Cooling enhancements
- Riser holes, containment boron addition and containment mixing tubes contribute to boron redistribution and transport during DHRS and ECCS cooling Relevant Changes from NPM-160 (DCA) to NPM-20 (SDAA)
Non-Proprietary 19 NuScale XPC LTR Review Relevant Design Changes from NPM-160 to NPM-20 Riser Holes ESB RVV Mixing Tubes
Non-Proprietary 20 NuScale XPC LTR Review XPC TR reviewed as an extension of the LOCA and non-LOCA TRs Independent Phenomenon Identification and Ranking Table evaluation Reviewed computational tools used - NRELAP5, SIMULATE5 and MATLAB Reviewed NRELAP5 Test Assessment Basis
- NIST-2 LTC, LOCA ECCS, Non-LOCA Tests
- Reviewed validation and uncertainties Reviewed NRELAP5 LTC model used for thermal-hydraulic response
- Reviewed LTC NRELAP5 model validation vs LOCA base model Review and evaluation of lower riser hole flow assessment Review of evaluated events for collapsed liquid level, DHRS and ECCS heat removal capabilities and boron transport Review Highlights
Non-Proprietary 21 NuScale XPC LTR Review Review of boron transport subcriticality methodology
- Thermal hydraulic conditions
- Boron transport and mixing model assumptions
- Critical boron concentration and Nuclear Reliability Factors Review of boron transport precipitation methodology
- Thermal hydraulic conditions
- Boron transport and mixing model assumptions Review Highlights
Non-Proprietary 22 NuScale XPC LTR Review Updated Nuclear Reliability Factor review portion Add limitation/condition for requiring enough boron to account for integral down powers and xenon impacts for subcriticality analysis applications Add limitation/condition to require the zero power maximum operational limit boron concentration (no xenon) at the beginning of cycle is used as an initial condition for precipitation analysis applications Safety Evaluation Report Differences
Non-Proprietary 23 NuScale XPC LTR Review 1)
Changes to LOCA or Non-LOCA LTR may require changes to XPC LTR 2)
Applicable US460/NPM-20 only 3)
Maintain insignificant non-condensable gas in containment 4)
Consider the density difference between the borated and unborated liquid 5)
Methodology limited to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 6)
RVV compressible flow qualification 7)
Initial test program (first module only) for dissolution testing 8)
Approved for NRELAP5v1.7 in conjunction w/NPM-20 Basemodel Rev. 5 9)
Separate approval required for single failures, electric power assumptions and operator actions Limitations and Conditions
Non-Proprietary 24 NuScale XPC LTR Review
- 10) Account for integral down powers and xenon for subcriticality
- 11) Zero power maximum operational limit boron concentration (no xenon) at the beginning of cycle is used as an initial condition for precipitation Limitations and Conditions
Non-Proprietary 25 NuScale XPC LTR Review The staff found that the applicant provided sufficient information to support the staffs safety finding.
The staff found that an applicant that references this topical report, and satisfies the limitations and conditions, will meet relevant regulatory requirements pending review and approval of the application.
Conclusion
Non-Proprietary 26 NuScale XPC LTR Review Questions?
Meeting Title Open Session NuScale Subcommittee on Staff's Evaluation of NuScale Non LOCA and Extended Passive Cooling Topical Reports Attendee Michael Snodderly ACRS DFO Stephen Schultz ACRS Larry Burkhart ACRS Thomas Dashiell ACRS Andrea Torres ACRS Patrick King Court Reporter Christina Antonescu ACRS Tammy Skov ACRS Shandeth Walton ACRS Sandra Walker ACRS Erin Whiting NuScale Karl Gross NuScale Ron Ballinger ACRS Kyle Hoover NuScale Amanda Bode NuScale Kenny Anderson NuScale Wendy Reid NuScale Derek Widmayer ACRS Nathanael Hudson RES Matt Sunseri ACRS Dennis Bley ACRS Hossein Nourbakhsh ACRS Getachew Tesfaye NRR Greg Halnon ACRS Sarah Turmero NuScale Lucas Kyriazidis RES Stewart Bailey NRR Mahmoud -MJ-Jardaneh NRR Gene Eckholt NuScale Freeda Ahmed NuScale Allyson Callaway NuScale David Drucker NRR Brian Wolf NuScale Adam Rau NRR Jason Thompson RES Gary Becker NuScale Tyler Beck NuScale Timothy Polich RoPower Ben Bristol NuScale Stacy Joseph NRR River Rohrman NRR Stephanie Garland ACRS Vesna Dimitrijevic ACRS
Peter Lien NRR Thomas Hayden NRR Adam Brigantic NuScale Christopher Boyd RES Ken Rooks NuScale Rick Rosenstein NuScale Dan Lassiter NuScale Taha Abdelnaeem Framatome Hiroaki Sonoyama Marvin Smith Eric Baker NuScale Andrew Deszel Numark Kevin Lynn NuScale Thomas Case NuScale Ben Bristol NuScale Taylor Coddington NuScale Thomas Griffith NuScale Meghan McCloskey NuScale Rebecca Patton NRC Antonio Barrett NRC Len Ward Consultant Kris Cummings NuScale Zhian Li NRR Adam Rau NRR Warren Erling NRR Sean Piela NRR Rosemary Sugrue NRR Andrew Bielen RES Justin Coury RES Carl Thurston NRR Joshua Miller NRR Dong Zheng NRR