ML20195B146
| ML20195B146 | |
| Person / Time | |
|---|---|
| Issue date: | 07/08/2020 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | |
| Snodderly, M; Brown, C, ACRS | |
| References | |
| NRC-0962 | |
| Download: ML20195B146 (370) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
675th Meeting, Advisory Committee on Reactor Safeguards (ACRS), Open Session Docket Number: N/A Location: Video Teleconference Date: Wednesday, July 8, 2020 Work Order No.: NRC-0962 Pages 1-280 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1323 Rhode Island Avenue, N.W.
Washington, D.C. 20005 (202) 234-4433
1 1
2 3
4 DISCLAIMER 5
6 7 UNITED STATES NUCLEAR REGULATORY COMMISSIONS 8 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 9
10 11 The contents of this transcript of the 12 proceeding of the United States Nuclear Regulatory 13 Commission Advisory Committee on Reactor Safeguards, 14 as reported herein, is a record of the discussions 15 recorded at the meeting.
16 17 This transcript has not been reviewed, 18 corrected, and edited, and it may contain 19 inaccuracies.
20 21 22 23 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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1 1 UNITED STATES OF AMERICA 2 NUCLEAR REGULATORY COMMISSION 3 + + + + +
4 675TH MEETING 5 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 6 (ACRS) 7 + + + + +
8 OPEN SESSION 9 + + + + +
10 WEDNESDAY 11 JULY 8, 2020 12 + + + + +
13 The Advisory Committee met via Video 14 Teleconference, at 9:31 a.m. EDT, Matthew W. Sunseri, 15 Chairman, presiding.
16 17 COMMITTEE MEMBERS:
18 MATTHEW W. SUNSERI, Chairman 19 JOY L. REMPE, Vice Chairman 20 WALTER L. KIRCHNER, Member-at-Large 21 RONALD G. BALLINGER, Member 22 DENNIS BLEY, Member 23 VESNA B. DIMITRIJEVIC, Member 24 JOSE MARCH-LEUBA, Member 25 DAVID A. PETTI, Member NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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2 1 PETER RICCARDELLA, Member 2
3 ACRS CONSULTANT:
4 MICHAEL CORRADINI 5 STEPHEN SCHULTZ 6
7 DESIGNATED FEDERAL OFFICIAL:
8 CHRISTOPHER BROWN 9 CHRISTIANA LUI 10 QUYNH NGUYEN 11 MICHAEL SNODDERLY 12 13 ALSO PRESENT:
14 ANTONIO BARRETT, NRR 15 BRUCE BAVOL, NRR 16 JOSHUA BORROMEO, NRR 17 ANNA BRADFORD, NRR 18 BEN BRISTOL, NuScale 19 MARK CHITTY, NuScale 20 PAUL DEMKOWICZ, Idaho National Laboratory 21 MICHAEL DUDEK, NRR 22 SARAH FIELDS, Public Participant 23 CRAIG HARBUCK, NRR 24 JORDAN HOELLMAN, NRR 25 PAUL INFANGER, NuScale NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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3 1 MARIELIZ JOHNSON, NRR 2 SHANLAI LU, NRR 3 MICHAEL MELTON, NuScale 4 SCOTT MOORE, Executive Director, ACRS 5 ETIENNE MULLIN, NuScale 6 TONY NAKANISHI, NRR 7 STEVEN NESBIT, EPRI 8 RYAN NOLAN, NRR 9 REBECCA NORRIS, NuScale 10 REBECCA PATTON, NRR 11 TOM SCARBROUGH, NRR 12 JEFFREY SCHMIDT, NRR 13 JOHN SEGALA, NRR 14 ALEXANDRA SIWY, NRR 15 ANDREW SOWDER, EPRI 16 DINESH TANEJA, NRR 17 CARL THURSTON, NRR 18 BOYCE TRAVIS, NRR 19 CHRISTOPHER VAN WERT, NRR 20 YUKEN WONG, NRR 21 PETER YARSKY, RES 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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4 1 AGENDA 2
3 EPRI Topical Report on Uranium Oxycarbide (UCO) 4 Tristructural Isotropic (TRISO) Coated Particle 5 Fuel Performance 6 3.2 Presentations and discussion with representatives 7 from EPRI and NRC staff 8 regarding the subject topic . . . . . . . . . . 5 9 3.3 Preparation of Reports . . . . . . . . . . . 41 10 NuScale Area of Focus: Boron Redistribution 11 4.1 Remarks from the Subcommittee Chairman . . . 45 12 NuScale Power Presentation - Rebecca Norris . . . 7 13 NuScale Power Presentation - Paul Infanger . . . 8 14 NuScale Area of Focus: Boron Redistribution (WK/MS) 15 4.1) Remarks from the Subcommittee Chairman . . 5 16 4.2) Presentations and discussion with 17 representatives from NuScale and the 18 NRC staff regarding subject topic . . . . . 6 19 4.3) Preparation of Reports . . . . . . . . . . .
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5 1 P R O C E E D I N G S 2 (9:31 a.m. EDT) 3 CHAIR SUNSERI: It's 9:31. The meeting 4 will now come to order. This is the first day of the 5 675th Meeting of the Advisory Committee on Reactor 6 Safeguards. I am Matthew Sunseri, Chair of the ACRS.
7 This is a virtual meeting. I will now call the roll, 8 starting with Ron Ballinger.
9 MR. BALLINGER: Here.
10 CHAIR SUNSERI: Dennis Bley.
11 (No audible response.)
12 CHAIR SUNSERI: All right. Hopefully 13 Dennis will be joining us soon. Charles Brown. I had 14 to excuse Charles from this week's deliberations. He 15 has business outside of the ACRS to take care of and 16 will not participate in the full week's briefing.
17 Vesna Dimitrijevic.
18 MS. DIMITRIJEVIC: I'm here.
19 CHAIR SUNSERI: Walt Kirchner.
20 MR. KIRCHNER: Here.
21 CHAIR SUNSERI: Jose March-Leuba.
22 MR. MARCH-LEUBA: Yes, I'm here.
23 CHAIR SUNSERI: Dave Petti.
24 MR. PETTI: Here.
25 CHAIR SUNSERI: Joy Rempe.
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6 1 VICE CHAIR REMPE: Here.
2 CHAIR SUNSERI: Pete Riccardella.
3 MR. RICCARDELLA: Here.
4 CHAIR SUNSERI: And myself, Matt Sunseri.
5 So I'll just reach back and check. Has Dennis Bley 6 joined us yet?
7 (No audible response.)
8 CHAIR SUNSERI: Okay. Well we'll continue 9 on. We have a quorum.
10 The ACRS was established by the Atomic 11 Energy Act as governed by the Federal Advisory 12 Committee Act. The ACRS section of the U.S. NRC 13 public website provides information about the history 14 of the ACRS, and provides documents such as our 15 charter, bylaws, Federal Register Notices for 16 meetings, letter reports, and transcripts of all full 17 and subcommittee meetings, including all slides 18 presented at the meetings.
19 The committee provides its advice on 20 safety matters to the Commission through its publicly-21 available letter reports. The Federal Register Notice 22 announcing this meeting was published on June 15th, 23 2020, and provides an agenda and instructions for 24 interested parties to provide written documents or 25 request opportunities to address the committee.
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7 1 The designated federal official for this 2 meeting is Mr. Christopher Brown. A phone line has 3 been opened to allow members of the public listen in 4 at the presentation and committee discussion. We have 5 received no written comments or requests to make oral 6 statements from the members of the public regarding 7 today's session.
8 There will be an opportunity for public 9 comment, and we have set aside time in the agenda for 10 comments from members of the public attending or 11 listening in. Written comments may be forwarded to 12 Mr. Christopher Brown, the DFO.
13 A transcript of the open portions of the 14 meeting is being kept, and it is requested that the 15 speakers identify themselves and speak with sufficient 16 clarity and volume so that they can be readily heard.
17 Additionally, since this is a virtual meeting, 18 participants should mute themselves while not 19 speaking.
20 During today's committee we will cover the 21 following topics. The first one will be the EPRI 22 Topical Report on Uranium Oxycarbide Tristructural 23 Isotropic Coated Particle Fuel Performance. And we 24 are going to call that TRISO through the remainder of 25 the meeting.
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8 1 We will also discuss NuScale Area of Focus 2 on Boron Redistribution. And that is expected to 3 continue all week. And the rest of the time will be 4 covered preparing reports.
5 We had an agenda item at the first thing 6 of this morning's meeting of Branch Technical Position 7 7-19, Guidance for Diversity and Defense-in-Depth on 8 Digital I&C Systems. This topic has been removed from 9 our agenda at the request of staff.
10 However, I will provide, since we -- this 11 is a last minute change to our agenda, I will provide 12 an opportunity for any members of the public listening 13 in to provide comments on that topic should they have 14 some.
15 One last item of housekeeping here.
16 During the TRISO discussions, Members Petti and Rempe 17 are recusing themselves from the deliberations due to 18 --
19 (Telephonic interference.)
20 VICE CHAIR REMPE: Matt, I've lost sound.
21 Has anyone else lost sound?
22 MR. MOORE: This is Scott. I also have 23 lost sound now.
24 (Off-mic comments.)
25 (Pause.)
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9 1 VICE CHAIR REMPE: Okay, folks. Matt just 2 called me, and his whole system is crashed so he can't 3 even call in. So he gave me a list of things to say, 4 and I will try and finish up for him.
5 In the middle of his announcement about 6 Dave Petti and myself having to recuse ourselves we 7 did want to note that we will be making factual 8 comments. But because of our recusing ourselves we 9 are not allow -- we are not going to be voting on the 10 ultimate letter.
11 Then he also pointed, wanted to note that 12 the discussion on Branch Technical Position is being 13 deferred. So we are going to recess until 1:15 East 14 Coast Time, and we will come back and start the 15 discussion about the TRISO fuel.
16 But he did say if there are any --
17 MEMBER KIRCHNER: Joy.
18 VICE CHAIR REMPE: Yes?
19 MEMBER KIRCHNER: This is Walt. Pardon my 20 interruption. No, I think we are going to recess and 21 then start at the scheduled time later this morning 22 for TRISO. This afternoon is scheduled for NuScale.
23 MR. MOORE: That's correct. This is Scott 24 Moore. Vice Chairman, it's 11:15 that we will be 25 restarting.
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10 1 VICE CHAIR REMPE: Convening for the TRISO.
2 You're right. I'm sorry. I apologize. Thank you, 3 Walt, and thank you, Scott. I don't have the agenda 4 up because I thought --
5 MR. MOORE: Sure.
6 VICE CHAIR REMPE: So anyway, so at 11:15 7 East Coast time we will come back and discuss the 8 TRISO, and have the presentations on that. And then 9 we'll go to NuScale this afternoon.
10 But he did ask that I allow time for 11 public comment on the Branch Technical Position 7-19 12 at this time. I assume the public line is open, 13 Thomas?
14 MR. DASHIELL: The public line is open.
15 VICE CHAIR REMPE: And I assume that there 16 are no comments since I'm not hearing anything.
17 (No audible response.)
18 VICE CHAIR REMPE: Okay. Do any members 19 have any comments?
20 (No audible response.)
21 VICE CHAIR REMPE: Not hearing anything, 22 then I, unless I'm told otherwise, since this is a 23 little unexpected here, I will recess us until 11:15 24 East Coast Time. Does that sound good to everybody?
25 MR. MOORE: Yes.
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11 1 VICE CHAIR REMPE: Thank you. Okay. Talk 2 to you all in a few hours then.
3 (Whereupon, the above-entitled matter went 4 off the record at 9:42 a.m. and resumed at 11:15 a.m.)
5 CHAIR SUNSERI: Okay. This is Matt 6 Sunseri. It is 11:15 and we will reconvene the ACRS 7 meeting. I will begin with a roll call. Ron 8 Ballinger.
9 MR. BALLINGER: Here.
10 CHAIR SUNSERI: Dennis Bley.
11 MR. BLEY: Here.
12 CHAIR SUNSERI: Vesna Dimitrijevic.
13 MS. DIMITRIJEVIC: Here.
14 CHAIR SUNSERI: Walt Kirchner.
15 MR. KIRCHNER: Here.
16 CHAIR SUNSERI: Jose March-Leuba.
17 MR. MARCH-LEUBA: Yes.
18 CHAIR SUNSERI: Dave Petti.
19 MR. PETTI: Here.
20 CHAIR SUNSERI: Joy Rempe.
21 VICE CHAIR REMPE: Here.
22 CHAIR SUNSERI: Pete Riccardella. Let's 23 see, I don't see --
24 MR. RICCARDELLA: I'm here.
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12 1 myself.
2 So we have all present. I will remind the 3 committee that Members Petti and Rempe are recusing 4 themselves. They can participate in factual 5 clarifications, if necessary.
6 And we noted in our opening session I had 7 dropped off, and for some reason my VPN line keeps 8 getting disconnected. Looks like a server problem.
9 It happened at least once during the recess. So I 10 have asked Walt Kirchner to seamlessly take over 11 should I drop off and have to reboot my computer again 12 to get back on. So thank you to Walt for that.
13 And with those opening comments I will now 14 turn to Ron Ballinger, chair of the subcommittee, for 15 the EPRI presentation on TRISO. Ron.
16 MR. BALLINGER: Yes. Thank you, Mr.
17 Chairman. This meeting is -- we'll have presentations 18 by EPRI. I know, I think, as well as the staff 19 related to the Topical Report EPRI-AR1, which is 20 titled Uranium Oxycarbide -- and I'm not even going to 21 use the word Tristructural Isotopic, I'm just going to 22 call it TRISO -- Coated Particle Fuel Performance.
23 It's a TR that we have been asked to write a letter 24 on.
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13 1 the 20 -- May the 6th, excuse me, of this year where 2 we had presentations by EPRI and its consultants and 3 the staff. And so this, this meeting will provide I 4 think abbreviated presentations from those, from those 5 presentations.
6 Our expectation is to provide a letter 7 during this full committee meeting on this topic. And 8 so I'd like to ask John Segala, he's the Chief, 9 Advanced Reactor Policy Branch, Division of Advanced 10 Reactors and Non-Power Production and Utilization 11 Facilities -- we ought to shorten some of these things 12 up I guess -- to make some introductory comments. And 13 then I think the first presenter is Andrew Sowder from 14 EPRI. So John, the floor is yours.
15 MR. SEGALA: Thank you very much. As you 16 said, we are here today to brief the ACRS on the staff 17 safety evaluation for the EPRI TRISO Coated Particle 18 Fuel Performance Topical Report.
19 Since it's been awhile since we briefed 20 the ACRS full committee on our advanced reactor 21 readiness activities, I wanted to take a moment to 22 step back and provide some context for the subject of 23 today's meeting.
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14 1 action plans for enhancing our readiness to 2 effectively and efficiently review and regulate 3 advanced reactors.
4 The near-term implementation action plan 5 activities are divided up into six strategies:
6 Strategy 1 on training; Strategy 2 on computer codes; 7 Strategy 3 on developing guidance; Strategy 4 on 8 industry consensus codes and standards; Strategy 5 on 9 policy issues; and Strategy 6 on communications.
10 At that time, the ACRS recommended that 11 NRC focus its near-term IAP activities on Strategies 12 3 and 5, which the NRC staff has been doing.
13 Supporting Strategy 3, on July 20th we are 14 scheduled to brief the ACRS subcommittee on our plans 15 to develop a new technology-inclusive risk-informed 16 and performance-based regulatory framework for 17 advanced reactors, which is required by the Nuclear 18 Energy Innovation and Modernization Act, or NEIMA.
19 This is a high priority for the NRC. And we are 20 calling this new regulation 10 CFR Part 53.
21 We have a rulemaking plan which in SECY-20-0032 22 up in front of the commission. And we will be 23 briefing the ACRS on an NRC staff white paper 24 outlining specific considerations and questions 25 regarding Part 53.
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15 1 We will also be providing an overview of 2 the final Regulatory Guide 1.233, which endorsed the 3 licensing modernization project described in NEI-1804 4 document, and the NRC's response to the public 5 comments received on the associated draft guide.
6 This TRISO Topical Report which we're 7 discussing today is also a high priority for the NRC.
8 And it also supports Strategy 3 of the near-term 9 implementation action plans for the high temperature 10 reactor designs using TRISO fuel.
11 The data supporting this topical report, 12 as you know, is built off of a long history dating 13 back to 2005 as part of the DOE and NRC's work on the 14 next generation nuclear plant, or NGNP, and DOE's 15 advanced gas reactor fuel development and 16 qualification program, which is still continuing 17 today.
18 Today we will be providing a high-level 19 summary of the findings from the Topical Report and 20 discussing changes the NRC staff made to the 21 limitations and conditions in its safety evaluation as 22 a result of the follow-on items discussed at the 23 subcommittee meeting.
24 We are looking forward to hearing from the 25 ACRS today on this important topic and any insights NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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16 1 and feedback you all may have. And as you stated, we 2 understand that the ACRS is planning to write us a 3 letter. And this completes my opening remarks. Thank 4 you.
5 MR. BALLINGER: Okay. Thank you very much, 6 John. So I guess first up is Andrew, and the floor 7 is yours.
8 MR. SOWDER: Okay. Thank you. I want to 9 thank the ACRS for the opportunity to present today, 10 and the NRC for its ongoing commitment to reviewing 11 this Topical Report, and all the team members who made 12 this report possible.
13 Without further ado, if there's any 14 questions about EPRI or the context for why we were 15 involved in the project, I'd be happy to answer those 16 after the presentation. But time is short, so let's 17 move on to just the general overview of the Topical 18 Report at issue. Next slide.
19 So the Topical Report was generated and 20 submitted to the NRC on May 31st of last year. This 21 was also released as a publicly-available report 22 simultaneously. So everything in the report is 23 intended for the public and is the result of work, 24 publicly-funded work at the Idaho National Laboratory 25 in Oak Ridge as part of the advanced gas reactor fuel NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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17 1 development qualification program, which was initiated 2 almost two decades ago.
3 The overall scope of the Topical Report, 4 it's important to recognize that this explicitly 5 focuses on Programs AGR-1 and AGR-2 only. And these 6 two campaigns were selected as they focus in on fuel 7 performance.
8 The intent was to isolate to the extent 9 possible the results from the influence of specific 10 design, reactor design, and fuel design parameters and 11 influences such as the compacts, recognizing that that 12 cannot be coupled completely. But the fuel 13 performance of the particle fuel itself we felt was a 14 logical subject to focus on and would be as widely and 15 generically applicable for benefitting the most 16 developers and other stakeholders. Next slide.
17 It's important to recognize the long 18 history and the international context in which TRISO 19 fuel was originally developed and has evolved. That 20 international experience is rich with lessons learned, 21 and has demonstrated that high quality fuel can be 22 fabricated in a repeatable consistent manner, and that 23 fuel performance with low inturbid failures is 24 achievable.
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18 1 that this Topical Report, as we state clearly in the 2 report itself, does not rely upon the data or 3 experience from the international and previous work 4 for inclusion in the Topical Report. The Topical 5 Report itself addresses only AGR-1 and AGR-2 results 6 with respect to fuel performance. Next slide.
7 MR. HOELLMAN: This is Slide 4.
8 MR. SOWDER: Yes. So Slide 4 showing the 9 graphics here, mainly just to focus on the fact that 10 this is really the topic at hand. It's the TRISO 11 coated part fuel itself. The figure on the left 12 demonstrates the fuel kernel, which indicates that 13 AGR-1 and AGR in general was -- the focus was on UCO.
14 MR. BALLINGER: Did somebody just get cut 15 out?
16 CHAIR SUNSERI: Apparently. This is Matt, 17 I'm still -- I mean it looks like the connection is 18 still good. We must have lost the presenter.
19 MR. BALLINGER: We lost Andrew.
20 MR. NESBIT: Yeah. This is Steve Nesbit 21 working on behalf of EPRI. I think we can go ahead, 22 and I think Andrew will probably rejoin us shortly.
23 Maybe that was him. Andrew, is that you?
24 (No audible response.)
25 MR. NESBIT: I think we should, given the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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19 1 time, we should probably go ahead with the 2 presentation. And I'll step in and try to do that in 3 Andrew's absence until he rejoins us, if that's okay?
4 MR. BALLINGER: Yes. Thanks for picking up 5 the slack.
6 MR. NESBIT: Not at all. So we are here on 7 Slide 4. And Andrew was talking about the fact that 8 we're focusing on the performance of the coated 9 particles itself. It has a long record 10 internationally. But we're focused on the AGR-1 and 11 AGR-2 tests.
12 So you see the diagrams of the fuels 13 themselves with the kernels, and then surrounded by 14 the carbon buffer layer, the pyrolytic carbon, inner 15 pyrolytic carbon layer, silicon carbide, the outer 16 pyrolytic carbon layer. And that's consistent with 17 basically TRISO fuel throughout.
18 The particles are combined together in the 19 compacts. They can be in cylindrical form, as shown 20 along the top on the right-hand side. They can be in 21 a spherical form, as shown in a pebble bed type 22 configuration as shown below.
23 The diagram shows the relative sizes of 24 the different particles here. Obviously the particles 25 are very, very small. And then the compacts are NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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20 1 larger and manipulated in the reactor itself. Next 2 slide please.
3 So now we're on Slide 5. Want to talk for 4 a minute about the fact that this project was a 5 collaboration between public and private entities. So 6 EPRI is the overall project manager, shown there in 7 the box in the middle, working on the development of 8 the Topical Report and the submission for review. And 9 then working with the NRC on the review process.
10 I know, as the technical lead on the AGR 11 program, they carried out the AGR program. And 12 they're the ones who provided the primary content for 13 the Topical Report itself and spearheaded the response 14 to the request for additional information that came up 15 in the review.
16 Want to mention on the left side of the 17 slide the High Temperature Reactor Technical Working 18 Group. And the entities are listed there: Framatome, 19 X-Energy, StarCore, Kairos Power, BWXT. These are 20 entities that are either developing reactors that rely 21 on TRISO fuel, and/or involved in fabrication of TRISO 22 fuel.
23 So and then, of course, the NRC is the 24 regulatory reviewer. So a couple of things I'll 25 mention. DOE co-funded this along with EPRI. So many NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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21 1 thanks to DOE and their role in this project.
2 Industry provided in-kind support. And the NRC agreed 3 to review this RFP. And so far I think we can say 4 it's been a very successful enterprise.
5 MR. SOWDER: Hey Steve, can you all hear me 6 now? I apologize.
7 MR. NESBIT: You're back, Andrew. Do you 8 want to take over? I was just talking about Slide 5.
9 MR. SOWDER: Sure. Why not. Let's give 10 this a try. So moving on to Slide 6. Sounds like you 11 were right on cue there. Next slide.
12 So I'm not going to go over the content in 13 detail, but this is simply to emphasize the three kind 14 of parts of the report. The first four sections are 15 mainly provided for historical context and background.
16 The last Section 9, and then the appendix, 17 are additional information and references. The 18 emphasis here is that Sections 5 through 8 are really 19 the meat of the report, explicitly presented to the 20 NRC for their review, and support the conclusions that 21 are presented for NRC's approval. Next slide.
22 So paraphrasing the meat of the 23 conclusions, the first conclusion presented to the NRC 24 is that testing of UCO TRISO-coated fuel particles in 25 AGR-1 and AGR-2 provides a foundational basis for use NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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22 1 of these particle designs in the fuel elements of 2 TRISO fueled high temperature reactor design. That 3 is, those designs are pebble or prismatic fuel and 4 helium or salt coolant. Next slide.
5 Second conclusion, paraphrased and 6 summarized, is UCO TRISO-coated fuel particles that 7 satisfy the parameter envelope defined by the measured 8 particle layer properties in Table 5, can be relied on 9 to provide satisfactory performance. Next slide.
10 And the third conclusion: aggregate AGR-1 11 and AGR-2 fission product release data and fuel 12 failure fractions summarized in the Topical Report can 13 be used to support licensing of reactors employing UCO 14 TRISO-coated fuel particles that satisfy the parameter 15 envelope defined by measured particle layer properties 16 in Table 5.5 from AGR-1 and AGR-2.
17 MR. MARCH-LEUBA: Hi. This is -- let me 18 interrupt. This is Jose March-Leuba. Previously the 19 representation during the whole report we say that 20 there is a lot of international data that we didn't 21 use, we focus only to year one and year two. For 22 thermohydraulic correlations, it is considered the way 23 to do it is to divide some of your data points, 24 develop your correlation, and then on a completely 25 different data set verify the correlation.
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23 1 So what you are doing here, you are really 2 developing a correlation for fission product release.
3 Was there any intent or is there any plans to validate 4 these correlations against system data, 5 international data, which will have a much broader 6 range of parameters for publication. It will help on 7 it. Is there any plans for that?
8 MR. SOWDER: Well this is Andrew from EPRI.
9 Speaking as EPRI and in respect to this actual Topical 10 Report, that was not in the scope.
11 What you're suggesting sounds valid, and 12 actually interesting and useful. I suspect that would 13 be left up either to the people who would end up 14 seeing this Topical Report, to the developers, the 15 licensees, as well as maybe even that might be 16 something that INL might take up.
17 I'd turn it over to Paul at INL to respond 18 if that has been considered.
19 MR. DEMKOWICZ: Yeah, this is Paul. I'm 20 not sure that I caught the entire gist of the original 21 comment. We have, of course, compared our data to the 22 international database with the fission product 23 release. But we cannot vouch for the QA of the data 24 from the international community. So that is a 25 potential issue for us.
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24 1 But this is not a -- we're not doing a 2 model validation in this report at all, so.
3 MR. MARCH-LEUBA: But we are developing --
4 I'm calling that correlation because I come from the 5 thermohydraulic side of the house. It is a 6 correlation. And we, the expectation is an applicant 7 that wants to use this fuel will just take it and use 8 it, and will not do anything else with respect to the 9 particle performance.
10 If there are data sets out there which it 11 doesn't fit, it would be -- and it's probably because 12 they collected bad data or they fabricated bad fuel, 13 but it will be interesting to review. I'm just 14 offering.
15 MEMBER PETTI: So Jose.
16 MR. MARCH-LEUBA: Yes?
17 MEMBER PETTI: You're talking about the 18 source term data. This is not what the subject is 19 here. There is a large database that you can find in 20 the IAEA that has the correlations that you're talking 21 about.
22 The program has used those and had it in 23 some of the fuel performance models around the world 24 frankly, and there's been huge benchmarking activities 25 done through the GEN-4 project and the IAEA. The goal NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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25 1 of the program is to develop data for UCO TRISO, and 2 from the source term perspective, to eventually 3 compare to that older data to see, you know, if it 4 just confirm the older data sets, or is there is 5 something different here.
6 Because the older data is U02-based TRISO 7 fuel. The international UCO is a little different.
8 So it's sort of a hybrid answer, but that is in fact 9 the goal of the source term product program. But 10 that's not where we are today. That would be 11 announced in a subsequent Topical Report.
12 MR. MARCH-LEUBA: So it is a process in 13 process that will accomplish this validation, right?
14 That's what you're saying?
15 MR. PETTI: Correct.
16 MR. MARCH-LEUBA: Okay. Thank you.
17 MEMBER KIRCHNER: Paul, this is Walt 18 Kirchner. Just a question on AGR-1 and AGR-2. Was 19 all that fuel produced by BWXT?
20 MR. DEMKOWICZ: No. So we'll --
21 MEMBER KIRCHNER: More correctly, I should 22 say were all the TRISO particles produced by BWXT?
23 MR. DEMKOWICZ: No. So we'll get into that 24 in the next presentation, but --
25 MEMBER KIRCHNER: Okay. All right.
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26 1 MR. DEMKOWICZ: Those particles are for 2 AGR-2.
3 MR. BALLINGER: Can I ask, Paul, just to go 4 forward with Walt's question. But they -- if I can 5 use the terminology, the recipe was the same although 6 other people, more than one source developed it. Is 7 that approximately true?
8 MR. DEMKOWICZ: Yeah. Again, this is --
9 these are all questions that I get into it in the next 10 presentation. But --
11 MR. BALLINGER: Okay, fine. No problem.
12 MR. DEMKOWICZ: Okay, yes.
13 MR. SOWDER: And this is the conclusion of 14 this presentation, so we can actually move on to 15 Paul's if that's okay.
16 MR. BALLINGER: Is this the last slide?
17 Okay, I guess it is.
18 MR. SOWDER: Correct.
19 MR. BALLINGER: So okay. Let's move on 20 then. Thank you.
21 MR. DEMKOWICZ: Okay. Thank you, Dr.
22 Ballinger. My name is Paul Demkowicz. I am the 23 current technical director of the AGR program. And 24 this presentation is a very brief overview of the AGR 25 program and the results of the AGR-1 and 2 experiments NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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27 1 that are presented in the Topical Report.
2 And in addition to that, I will get into 3 a little bit of detail on some of the issues that were 4 raised during the subcommittee meeting on May 6th.
5 Next slide.
6 Okay. So the AGR program, the main 7 objective was to provide data for fuel qualification 8 to support reactor licensing, and to establish a 9 domestic commercial vendor for TRISO fuel. And the 10 motivation of this is to reduce market entry risk for 11 reactor designers.
12 The focus of the program, of course, as 13 we've heard already, is UCO TRISO fuel as opposed to 14 U02 that was developed by the Germans in the 1980s.
15 And there are several different elements of the 16 program.
17 We do fuel fabrication and 18 characterization. We do irradiation testing and ATR 19 under a range of conditions. We perform post-20 radiation examination and high temperature safety 21 testing. There is development of fuel performance 22 models, and also some fission product transport 23 experiments that we just heard a little bit about.
24 Next slide.
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28 1 the program. There were four radiation experiments 2 that the program was built around. And this is where 3 we'll talk a little bit about the nature of the fuel.
4 So the AGR-1 experiment was the first.
5 And it was an early test of lab scale UCO fuel 6 performance, as well as a shakedown of the multi-7 capital instrumented test stream design.
8 So the kernels for all of these 9 experiments were made at BWXT. For AGR-1, the coated 10 particles and the fuel compacts were made at Oak Ridge 11 in lab scale processes.
12 For AGR-2, it represented a step-wide 13 scale-up of the fabrication process. So the coated 14 particles remain at BWXT in a 6-inch coder, and the 15 fuel compacts were still made at Oak Ridge in lab 16 scale process. And this experiment included UCO and 17 U02 fuel.
18 AGR-3/4, as Dave Petti was talking about 19 just a bit ago, is a very different experiment. It 20 was designed to assess fission product transport, to 21 support source term calculations. It included the 22 designed to fail or DTF particles. These are 23 particles with very thin coatings that are designed to 24 fail and release fission products, so we can look at 25 their transport in the post-radiation examination.
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29 1 And then AGR-5/6/7 is our final fuel 2 qualification test and our high temperature 3 performance margin test. And for that experiment, the 4 kernels, the coated particles, and the compacts were 5 all made at BWXT on engineering scale processes.
6 So the time line shows the fuel 7 fabrication, irradiation and PIE campaigns in 8 different colors. And you can see that the AGR-5/6/7 9 irradiation is just about complete. In fact, we have 10 about two weeks left. And we're nearing the 11 completion of the AGR-2 PIE. We're in the middle of 12 the AGR-3/4 PIE. And the AGR-5/6/7 PIE we'll be 13 starting early next year.
14 MR. CORRADINI: So can I ask a question, 15 Paul, here about 3/4 again?
16 MR. DEMKOWICZ: Yes.
17 MR. CORRADINI: 3/4 is not just the 18 kernels, but it's all -- or the TRISO particles, but 19 it's also the compact there within that's your design 20 to fail? Or is it strictly trying to look at 21 retention within the kernels -- particles?
22 MR. DEMKOWICZ: It's everything. So when 23 those DTF particles fail you'll get fission product 24 release. And in the PIE we are expecting to go and 25 look at retention in the kernels, retention in the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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30 1 matrix, and then retention in the parts that are 2 outside of the fuel compacts.
3 MR. CORRADINI: Okay.
4 MR. DEMKOWICZ: Though it's really the 5 whole thing.
6 MR. CORRADINI: So it's -- to put it, it is 7 a function of whether it's a compact or a pebble for 8 3/4? That's kind of what language is for the source 9 term.
10 MR. DEMKOWICZ: The matrix would be 11 important for that. So I mean it is going to have an 12 effect, the amount of matrix that's there, yes.
13 MR. CORRADINI: But you aren't able --
14 you're able to unravel that in the PIE, I'm just 15 trying to understand -- I know 5, 6, and 7 is clearly 16 related to the compact. I wasn't sure about 3/4.
17 That's why I was asking the question.
18 MR. DEMKOWICZ: Yeah. That's right. We 19 are -- in the PIE, we are looking at the transport on 20 all of the components. You could apply that data to 21 any fuel form.
22 MR. CORRADINI: Okay. Thank you.
23 MR. BALLINGER: This is Ron. With regard 24 to 3/4 and pebbles, pebbles are designed much 25 differently than compacts from what I understood. And NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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31 1 so the barrier sequence and things like that in a 2 pebble might be quite different than in a compact. Am 3 I correct?
4 MR. DEMKOWICZ: The difference in a pebble 5 is that it generally is a different packing fraction, 6 so you have a different volume fraction of matrix.
7 And it may be a different matrix formulation. You 8 know, so there are several different matrix 9 formulations. We only use one in AGR-3/4.
10 And so those things are factors. But what 11 we're doing, you know, in the experiment is looking at 12 the important parameters that govern fission product 13 transport in matrix material, so diffusivity and 14 sorptivity and that kind of thing. And those can be 15 applied to a certain extent to other fuel forms.
16 MR. BALLINGER: Got it. Thanks.
17 MR. DEMKOWICZ: Okay. Next slide please.
18 Okay, we are on Slide 4. Just a real quick summary of 19 the AGR-1 and 2 fuel irradiations. These were both 20 done in the advanced test reactor in large B 21 positions.
22 Each experiment has six independent 23 capsules, and they contain 12 fuel compacts each. The 24 AGR-1 experiment had about 300,000 UCO particles, and 25 the AGR-2 has about 114,000 UCO particles.
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32 1 These were approximately two-year 2 irradiation times in terms of reactor days, and that 3 would simulate about a three-year reactor lifetime.
4 The temperature was controlled in the capsules with 5 helium and neon gas mixtures. And we'll talk about 6 that at length in the next five or six slides. The 7 fission gas release for each capsule independently was 8 monitored throughout the experiment to assess the 9 condition of the fuel.
10 The graphic on the right is a four-11 parameter fuel performance envelope in terms of burn-12 up, fast fluids, temperature, and the power density.
13 And AGR-2 Capsule 2 was plotted separately because it 14 intentionally was operated at a significantly higher 15 temperature. And we just wanted to show that while it 16 had a higher temperature, it was in the middle of the 17 range for burn-up and fast fluids. Okay, next slide.
18 Okay. We're on Slide 5. So there was 19 some discussion and a number of questions in the 20 subcommittee meeting on May 6th about the temperature 21 measurement and calculation of temperatures in AGR-1 22 and 2. And so I wanted to go into a bit more detail 23 and explain that in more depth than what we did at the 24 subcommittee meeting.
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33 1 experiments, the AGR-1 experiment had type N 2 thermocouples and high temperature moly niobium 3 thermocouples, about equal numbers of them. And they 4 both experienced about the same in pile failure rates.
5 For AGR-2 it was decided to go with only 6 type N thermocouples, and fewer of them because they 7 were larger diameter than most of the type Ns in AGR-8 1. So there was one observation from AGR-1 that none 9 of the large type Ns failed, even though the smaller 10 type Ns and some of the moly niobiums failed.
11 So they went with the larger type N 12 thermocouples. And because they're larger, you can't 13 get as many in. So --
14 VICE CHAIR REMPE: Paul, factual 15 correction. Did you just say that none of the type Ns 16 failed in AGR-1? That's not true. About half of them 17 failed, just like the moly niobiums ones, right?
18 MR. DEMKOWICZ: Right, I didn't say that 19 they didn't fail, so --
20 VICE CHAIR REMPE: Oh, I thought I heard 21 you say that none of them failed in HTR-1 and that's 22 not true?
23 MR. DEMKOWICZ: It was similar failure 24 rates as stated on the slide there.
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34 1 thought. Thank you.
2 MR. DEMKOWICZ: Yes. So, in HTR-2, all of 3 these TCs had failed by the end of the irradiation.
4 However, while they were functioning, the observation 5 was that they exhibited less drift when compared to 6 the thermocouples in AGR-1, so it was kind of a mixed 7 bag. They didn't last as long, but they had less 8 drift while they were active.
9 In terms of temperature measurement, the 10 approach is to place the TCs in the graphite holders 11 surrounding the compacts. The diagram on the right is 12 one of the capsules from AGR-1 that shows the TCs in 13 the graphite hole through the circles of the location 14 of the fuel compacts.
15 The TC temperatures are calculated with 16 the thermal model and compared to measurements, and 17 this is most important during the early cycles because 18 this is when most of your TCs are still functioning 19 and they haven't experienced any drifts, so you get a 20 validation or a benchmark of your thermal model, and 21 then fuel temperatures are calculated using this 22 benchmarked thermal model.
23 For both experiments, nearly all of the 24 TCs were at temperatures less than 1,000 degrees.
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35 1 in AGR-2 and three in AGR-1 where TCs were in the 2 range up to 1,100 degrees, and there was one 3 thermocouple in AGR-1 that spent a short time up to 4 1,200 degrees.
5 So, the approach was very similar between 6 AGR-1 and 2 in terms of measurement and modeling. The 7 one thing to point out is that for fuel experiments in 8 ATR, a great many of them, including all of the AFC 9 experiments, the ATF-1 experiment that's a test of 10 accident tolerant fuel, and of course the plate field 11 experiments have no thermometry whatsoever.
12 So, the approach for the AGR program in 13 terms of temperature measurement was very rigorous, 14 and most other experiments rely 100 percent on the 15 model to determine fuel temperatures with no feedback.
16 Okay, next?
17 The physics model that we used is an MCMP 18 origin coupled code. It includes the daily depletion 19 of the TRISO fuel in our experiment, the ATR driver 20 fuel, the capsule components in our experiment, and it 21 accounts for the shim cylinder rotation in the ATR 22 reactor.
23 We compare the model with post-irradiation 24 measurements of actinide isotopics in the fuel, the 25 fuel burn up, and there are flux wires in both of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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36 1 these experiments that we compared the total neutron 2 flux to the model.
3 And the model also accounted for the 4 relocation of the AGR-2 experiment that was discussed 5 in the report and it came up in the subcommittee 6 meeting. This had a minimal effect on the overall 7 experiment because it was a low fluence location, and 8 that's the third to left cycle on the plot. You can 9 see that the heat rate was relatively low and it was 10 a very short duration cycle.
11 The thermal model is a 3D finite element 12 model. There are about 350,000 nodes per capsule. If 13 you look at individual compacts, that works out to 14 roughly one node per particle in the compact, so about 15 3,000 to 4,000 nodes in a single compact.
16 And the model considers all of the 17 relevant phenomena, including conduction and 18 radiation, the heat rates in the fuel that come from 19 the physics model, heat rates in the graphite and 20 metallic components, the shrinkage of the graphite, 21 and changes in thermal conductivity with fluence and 22 the thermal conductivity of the compacts. Okay, next 23 slide?
24 So, thermocouple drift is recognized as a 25 very important phenomenon and something that we need NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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37 1 to understand that is going on in the experiment, and 2 so this is evaluated continuously throughout the 3 experiment.
4 And the idea is to compare the TC readings 5 to the calculated temperatures which would capture 6 things like operating condition changes, or shim 7 cylinder rotations, or power changes in the lobe, and 8 also to compare the TC readings to other TCs.
9 And so there was a lot of on drift 10 monitoring like the chart on the right that compares 11 one TC to another and to the model, and the idea is to 12 identify if a control TC, the one that's being used to 13 control the capsule's temperature, is drifting or 14 failed, and then control is shifted to an alternate TC 15 that's functioning.
16 If there are no more functioning TCs in 17 the capsule, then control is based entirely on the 18 model predictions. Okay, next slide?
19 Temperature uncertainty of the model was 20 determined for both AGR-1 and 2, and these considered 21 the contribution in uncertainty in all of the fuel 22 temperature calculation input parameters.
23 So, it looked at things like the fuel, 24 uncertainty in the fuel heat rate, the gap width 25 between the graphite and the capsule shell, the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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38 1 graphite thermal conductivity, the fuel compact 2 conductivity, the gas fraction of neon in the capsule, 3 the shell and graphite emissivities, and the non-fuel 4 component heat rates, and those come from the physics 5 simulations.
6 So, for all of these input parameters, 7 sensitivity studies were performed, and that looks at 8 identifying the relative impact of that parameter on 9 temperature, and then the uncertainty in these 10 individual temperatures or for these individual 11 parameters were estimated, and then a total 12 uncertainty in the calculated fuel temperature is 13 determined.
14 The volume average and time average 15 temperature uncertainties at 1 sigma for AGR-1 and 2.
16 The range for the different capsules is shown in the 17 bullets there. The figure on the right is the 18 instantaneous volume average and peak temperatures in 19 the AGR-2 Capsule 2 as an example.
20 And one observation is that the 21 instantaneous -- the uncertainty on the instantaneous 22 temperatures tends to be higher than what it is on the 23 time and average temperatures because when you 24 propagate the uncertainty, it's a root mean squared 25 process, and so you get a slightly smaller uncertainty NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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39 1 on the time averages, but you can see that the 1 sigma 2 uncertainties in general on both the volume average 3 and the peak temperatures there, it's about 100 4 degrees. Next slide?
5 Oh, one thing I wanted to address on that 6 last slide is there was a question as to why the AGR-2 7 uncertainties here are less than AGR-1, and the reason 8 is that it is mainly because uncertainties on most of 9 these parameters were the exact same between the two 10 experiments in terms of conductivities, fuel heat 11 rates and things like that, but the gap width for AGR-12 2 that controls your temperature was larger than AGR-13 1, and therefore when you have changes in the gap, the 14 relative change is smaller, so the relative 15 uncertainty is smaller for AGR-2. Okay, next?
16 Another important issue is temperature 17 bias. If you are -- often you're modeled relative to 18 what's actually going on, so we look at this as well 19 continuously throughout the irradiations.
20 And it's assessed by looking at what we 21 call the TC residuals, and this is the measured 22 temperature of the TC minus what it is calculated to 23 be in the model.
24 And in particular, we focus on the early 25 cycles when the TC drift was, in most cases, was NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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40 1 negligible. And the plot shows all of the TC 2 residuals for AGR-2 Capsule 2.
3 You can see essentially when TCs failed by 4 when those traces end, and as I mentioned earlier, all 5 of the TCs had failed in Capsule 2 by the end.
6 The green trace at the top is TC 3 from 7 Capsule 6. It was determined to be unreliable from 8 the beginning. It was offset and it was drifting 9 badly, so if we exclude that one, for Capsules 2, 3, 10 and 6, the overall bias was close to zero.
11 And if you look at the plots, what that is 12 saying is that if we look at the mean of those 13 residuals, it is averaging close to zero.
14 For Capsule 5 on the other hand, it's the 15 second from the top. I know that text is small.
16 There were two TCs and they both were reading, or the 17 residuals were low and the average was about minus 60, 18 and that indicates about a 60-degree over-prediction 19 in fuel temperature.
20 So, as a result of the known uncertainty 21 in temperature and the potential for bias that I just 22 talked about, I would note that higher temperature 23 capsules were included in the experiment plan.
24 That includes AGR-2 Capsule 2 and the AGR-25 7 irradiation, which is Capsule 3 of the current NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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41 1 irradiation, and these were included to address this 2 risk of potential temperature bias and uncertainty.
3 Okay, next slide?
4 So, we did a survey of some of the data 5 that we have for PIE in terms of fission product 6 release to see what it could tell us about the 7 potential for uncertainty or bias in our uncalculated 8 fuel temperatures, and there's two examples here.
9 And in general, the fission product 10 release data that we have, it supports the magnitude 11 of the uncertainties and biases that I just talked 12 about.
13 So, one example on the left is the level 14 of release of silver 110-M from individual compacts.
15 All of those data points is the -- it's essentially 16 the fraction that is retained in the compact as a 17 function of temperature, and it includes the AGR-1 and 18 the AGR-2, and I've also thrown in the AGR-3/4 19 irradiation for comparison.
20 And while there's a good deal of scatter 21 in the data and there are some reasons for that that 22 we don't really have time to get into, but it's 23 interesting that if you fit all of those datasets with 24 an inverse logistic function, that the inflection 25 points are all within about 30 degrees.
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42 1 On the right is data for the strontium and 2 europium release from AGR-2, AGR-1 and 2 capsules, and 3 it's the average capsule release, so there is a data 4 point for each capsule.
5 And the main observation here is that the 6 Capsules 6 and 5 in AGR-2 which were at similar 7 temperatures as the AGR-1 had very similar release of 8 strontium and europium, whereas Capsule 2 which ran 9 about 200 degrees hotter had a notably higher release 10 of both of those, so it's confirmation that AGR-2 11 capsule fuel was indeed a much hotter capsule.
12 And again, what these are showing is not 13 a real fine determination of the uncertainty in 14 temperature. It is looking at or it's confirming that 15 our uncertainty is on the order of 100 degrees and not 16 on the order of 200 or 300 degrees. Okay, next slide?
17 And I just wanted to point out that there 18 are a pretty large number of publications relevant to 19 AGR-1 and 2 temperature measurement calculation and 20 uncertainty.
21 The references in the green and blue were 22 referenced in the topical report. I've thrown in the 23 yellow, which is the data qualification reports and 24 the thermocouple data analysis reports for both 25 experiments.
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43 1 And then also there are over a dozen peer-2 reviewed technical journal articles and conference 3 papers and those can be reviewed at your leisure to 4 understand more about what was done to measure 5 temperature, to evaluate TC response, to calculate 6 fuel temperatures, and to quantify the uncertainty.
7 Okay, next slide?
8 So, I've condensed the result summary into 9 one slide here and I'll just run through this real 10 quick. The fission gas release during AGR-1 indicated 11 that we had zero failures of TRISO particles.
12 In AGR-2, as discussed in the report, 13 there were some issues with how the R over B, the 14 fission gas data was measured in the latter half of 15 that experiment, so PIE has indicated that we have 16 less than or equal to four failures.
17 The kernels and coatings generally held up 18 very well in all of the irradiation conditions. That 19 includes Capsule 2 from AGR-2 that was at very high 20 temperature.
21 The PIE has helped to elucidate the 22 mechanism of failure of the SIC layer, which is very 23 important, and that's discussed in more detail in the 24 report.
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44 1 fuel has been very exceptional, with low coating 2 failure rates between 1,600 and 1,800 degrees C in 3 pure helium, and the fission product release data has 4 been obtained on some of the key isotopes like silver, 5 cesium, europium, strontium, and krypton.
6 And finally, if we look at our failure 7 fraction calculations, and these are all the upper 8 limit in the plot there at 95 percent confidence for 9 sodium carbide failure, which is a less severe mode of 10 failure where the SIC layer fails, but a carbon layer 11 has stayed intact, and full TRISO failures, which is 12 in red, and that's where all three of the layers have 13 failed and the particle can release gas.
14 There is significant margin between our 15 measured failure rates and the historic performance 16 specs for modular high temperature gas-cooled reactors 17 by about a factor of ten. Next slide?
18 MEMBER KIRCHNER: Paul, this is Walt 19 Kirchner again.
20 MR. DEMKOWICZ: Yes?
21 MEMBER KIRCHNER: Just a quick 22 clarification question. On your previous plots of 23 experimental data, that was the capsule temperature, 24 not the estimated particle temperature, is that 25 correct? Because those temperatures are much lower NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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45 1 than these temperatures.
2 MR. DEMKOWICZ: Right, so that was all for 3 irradiation, so that would all be taking place during 4 irradiation. These temperatures, the 16, 17, and 5 1,800, that data is collected during --
6 MEMBER KIRCHNER: These results are 7 driving the fuel to failure at higher temperatures 8 under PIE conditions?
9 MR. DEMKOWICZ: That's correct.
10 MEMBER KIRCHNER: Thank you.
11 MR. CORRADINI: So, Paul, Walt gets it, 12 but I guess I don't. The first two plots or the first 13 two points that are titled irradiation are the data, 14 and then the ones at 16, 17, and 18 are what again?
15 Can you just say it again, please?
16 MR. DEMKOWICZ: Yes, so there are two 17 different types of failures that are included here, 18 and this is really an advance in our program in even 19 being able to measure the blue data points. We can go 20 in and find particles where the SIC layer only has 21 failed.
22 This is a less severe mode of failure 23 where the SIC layer has failed, but the OPyC, the 24 outer carbon layer, is intact, and so that particle 25 doesn't release fission gas. The red is a TRISO NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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46 1 failure, we call it, because all of those dense layers 2 have failed and the particle is releasing gas.
3 So, it's basically, it's two modes of 4 failures that we've quantified, during the 5 irradiation, that's what the irradiation column is 6 for, and during our post-irradiation safety testing at 7 16, 17, and 1,800. So, this is all experimental data.
8 MR. CORRADINI: Okay, so it's a separate 9 test after the irradiation?
10 MR. DEMKOWICZ: Right.
11 MR. CORRADINI: But the knowing that it's 12 16, 17, and 18 is calculated or calculated and 13 measured? That's maybe where I was going with this.
14 MR. DEMKOWICZ: Yeah, it's not calculated.
15 These are furnace tests where you've got much more 16 fine control of temperatures and --
17 MR. CORRADINI: Oh, okay.
18 MR. DEMKOWICZ: Yeah.
19 MR. CORRADINI: Okay, thank you. Sorry, 20 I forgot. Thank you.
21 MR. DEMKOWICZ: Any other questions on 22 that slide? Okay, next slide, which is the final, I 23 just wanted to mention about the RAIs. The staff 24 submitted four technical RAIs and the topics are 25 there. We discussed these in the subcommittee meeting NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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47 1 a bit.
2 I'll just reiterate that we felt that the 3 RAIs reflected a pretty careful reading of the report 4 and a good grasp of the key issues by the staff, and 5 as a result of these RAIs, we have provided responses, 6 and that includes additional information and some more 7 extended technical discussion, and some revisions to 8 the topical report.
9 That is the end of my presentation. I'd 10 be happy to take any additional questions.
11 MEMBER BLEY: Paul, this is Dennis Bley.
12 I've gone back through our transcript from the last 13 meeting and I think you addressed most of the things 14 people brought up during that meeting.
15 Dr. Rempe brought up a couple of times 16 asking you why in the tests you had done, peak 17 temperature instrumentation, the very accurate ones 18 weren't used, but I think she was really pointing 19 forward. Are you planning to do anything like that in 20 the future tests?
21 MR. DEMKOWICZ: So, the AGR-5/6/7 22 experiment that's in the reactor now is, I would 23 consider it the state of the art for where we are now 24 in terms of thermometry and these in-pile experiments.
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48 1 thermocouples and the moly/niobium.
2 So, there were some identified issues with 3 both, and there were some identified issues with the 4 moly/niobium thermocouples from the AGR-1 experiment 5 in that the annealing schedule, it resulted in excess 6 drift I think I would say in those thermocouples.
7 What they have done at the lab in the last 8 few years is to understand better the annealing 9 schedule. You have to anneal it at a sufficiently 10 high temperature over the entire length of the TC, and 11 the result in AGR-5/6/7 was much better or a much more 12 stable response from both the moly/niobium and from 13 the Type Ns.
14 The Type Ns that we did, we worked with 15 several different entities. One of them was the 16 University of Cambridge that came up with, you know, 17 essentially a Type N TC that was optimized for in-pile 18 use, and both of those have worked a lot better.
19 But I would note that we still have the 20 same problem in that all of the TCs in our bottom 21 capsule, Capsule 1, and there was a lot of them in 22 AGR-5/6/7, have failed, so you still have this problem 23 of the longevity of TCs, but the stability of them was 24 improved in 5/6/7.
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49 1 all of these experiments and tried to improve the 2 subsequent experiments, and I'm sure that there's 3 going to be a lot of lessons learned from 5/6/7 in 4 this regard as well that can be applied in future 5 irradiation experiments.
6 MEMBER BLEY: Okay, thanks, but it sounds 7 like you're not thinking of going to any simple peak 8 temperature measurements in the future?
9 MR. DEMKOWICZ: I'm not sure what you 10 mean, a direct measurement of the fuel you mean?
11 MEMBER BLEY: No, melt wires or things 12 like that are what Joy had brought up that last time 13 around.
14 MR. DEMKOWICZ: Right, so we actually did 15 not use melt wires for the first time in 5/6/7 because 16 the observations from AGR-1 and 2 were that they were 17 actually of pretty limited usefulness.
18 One problem is, you know, it's complex to 19 fabricate and you have to insert them, and then the 20 PIE is fairly involved and you lose about half of them 21 in the process.
22 And it turns out that the higher the 23 temperature of the melt wire, the more likely it is 24 for it to have reacted with the graphite and you lose 25 it, and we just didn't get a lot of use out of them, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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50 1 and so we didn't even use them in 5/6/7.
2 I actually just had a conversation about 3 this with our experiment designer and we were agreeing 4 that it probably calls for some more advanced melt 5 wire designs essentially than what's been used in the 6 past.
7 MEMBER BLEY: Okay.
8 VICE CHAIR REMPE: So, Paul, first, there 9 were no melt wires is my understanding in AGR-2. They 10 were only used in AGR-1 and they were purchased from 11 another source, not INL, and they were encapsulated in 12 metal as opposed to something that you could see 13 through, which in more recent years, has been used 14 successfully by encapsulating them in quartz and then 15 you just look at it, and we actually did quite a bit 16 of that.
17 Again, I'm trying to stay factual here, 18 but again, you learn from experience, and it seems 19 like -- and there are, you know, certain things you 20 have to consider, but it has been used successfully at 21 ATR, and I think it was in EPRI tests.
22 MR. DEMKOWICZ: So, that's incorrect 23 though. We did use melt wires in AGR-2.
24 VICE CHAIR REMPE: Oh, okay, so it was my 25 understanding you didn't, but I don't think you got NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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51 1 them with quartz encapsulation. I thought it was just 2 for, you know, a niobium tube is what I thought they 3 had put the ones for AGR-1 in, and I did not know 4 about AGR-2. What about AGR-3? What was the use in 5 the capsules for AGR-3?
6 MR. DEMKOWICZ: The approach was similar 7 to AGR-1 and 2. They were in vanadium. The capsules 8 were vanadium.
9 VICE CHAIR REMPE: Oh, vanadium, thank 10 you. I'm sorry. I couldn't remember what they used.
11 (Simultaneous speaking.)
12 VICE CHAIR REMPE: What about 13 thermocouples in the capsules for AGR-3/4?
14 MR. DEMKOWICZ: So, AGR-3/4 had the added 15 benefit of these exterior rings, and so you could put 16 thermocouples much further outboard from the fuel than 17 you could for AGR-1 and 2.
18 You know, AGR-1 and 2, I showed the cross 19 section. There is no place in that graphite where 20 you're going to put a thermocouple that's not really 21 close to a compact.
22 In AGR-3/4, you could put them further 23 outboard, and I don't recall off the top of my head 24 what types or what the distribution was, but all of 25 them survived for the entire experiment.
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52 1 VICE CHAIR REMPE: Were there any in or 2 they were just outboard? Clarify, please.
3 MR. DEMKOWICZ: In? What do you mean in?
4 VICE CHAIR REMPE: Well, I can show this 5 picture from AGR-1 earlier in your slide, the 6 thermocouples, and do they have similar thermocouple 7 positions in AGR-3/4, which of course we've not 8 reviewed, but were there anything within the capsule?
9 MR. DEMKOWICZ: Yeah, all of the 10 thermocouples were in the capsule. What I mean is if 11 -- yeah, we didn't have time to go into AGR-3/4 and 12 that's not the subject here, but --
13 VICE CHAIR REMPE: Right.
14 MR. DEMKOWICZ: -- it was a very different 15 capsule design. It didn't look like this at all.
16 What you had is a stack of compacts in the 17 middle and then three different rings of graphite, and 18 so you could put thermocouples a good distance away 19 from the fuel compacts where they weren't as hot, and 20 their survivability, not surprisingly, was a lot 21 better.
22 VICE CHAIR REMPE: So, they had then in as 23 well as out is what you're telling us on the record?
24 MR. DEMKOWICZ: All of the thermocouples 25 were inside the capsule. It's a question of where NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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53 1 inside that capsule cross section they were, and they 2 were further away from the fuel compacts --
3 VICE CHAIR REMPE: That's what I was 4 trying to get to. Thank you.
5 MR. DEMKOWICZ: Yeah.
6 MEMBER KIRCHNER: Paul, this is Walt 7 Kirchner. Can you go back to your last slide, please?
8 Would you elaborate, under the RAIs, sub-bullet number 9 two? So, where I'm going, it's a leading question.
10 My sense is that the Table 5.5 is 11 necessary, but not sufficient, so what other important 12 fuel properties or coating process parameters need to 13 be added to Table 5.5 to use your results of the 14 topical report?
15 MR. DEMKOWICZ: So, some of the specific 16 items that the staff brought up and have now been 17 added in that discussion, and it's in that section 18 where Table 5.5 resides, I forget the number, but are 19 things about essentially particle design, so the 20 buffer to volume, or the kernel to buffer volume ratio 21 relative to peak burn up. That's been discussed.
22 The kernel stoichiometry in terms of the 23 oxide carbide mixture was added. In terms of coating 24 process parameters, the fact that it's an 25 uninterrupted coating process --
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54 1 MEMBER KIRCHNER: Okay.
2 MR. DEMKOWICZ: -- had been added more 3 prominently basically as a requirement to get the 4 right types of coating properties. So, these weren't 5 added to Table 5.5 per se. They were added to the 6 discussion in that section and noted as necessary to 7 get the right performance.
8 MEMBER KIRCHNER: All right, thank you.
9 MEMBER BALLINGER: Okay, this is Ron. Are 10 there any other questions on this presentation?
11 Hearing none, we thank you again, Paul. I think we 12 should just now transition to the staff presentation.
13 Is -- Travis, are you ready to go?
14 MR. TRAVIS: Yeah, give me just a moment 15 to set up the presenter status and all of that.
16 MR. HOELLMAN: Hey, Boyce, do you want to 17 share or do you want me to continue?
18 MR. TRAVIS: If you have it up, go ahead 19 and continue. I'll have it up as a backup if it 20 doesn't work, but --
21 MR. HOELLMAN: Okay.
22 MR. TRAVIS: Is everyone able to see it 23 okay?
24 MR. HOELLMAN: It looks okay to me.
25 MR. TRAVIS: Okay.
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55 1 MR. HOELLMAN: Go ahead, Boyce.
2 MR. TRAVIS: Okay, good afternoon, 3 everyone. I will try to keep this brief in terms of 4 my comments so that there's time to address questions 5 and whatnot. You can move onto slide two.
6 So, at a high level, the purpose of the 7 topical report and stated goal was to provide a 8 foundational basis for establishing fuel performance 9 for TRISO particles.
10 And I guess I'll note here that as we 11 noted in our limitations and conditions, the scope was 12 confined to the particles themselves. Factors outside 13 of the particle would be addressed by a vendor or 14 subsequent licensee or applicant referencing this 15 topical report.
16 The topical report lays out a set of 17 performance criteria. They are noted in Table 5.5, 18 and as Dr. Kirchner noted, or Member Kirchner noted, 19 there is some other discussion in the topical report 20 that also confines what constitutes an acceptable 21 particle.
22 For the most part, these are identified 23 either explicitly in the topical report or alluded to 24 in the staff's limitations and conditions in the 25 safety evaluation on the topical report.
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56 1 These performance criteria are based on 2 empirical data from the AGR-1 and 2 tests in 3 irradiation and the performance is outlined within the 4 topical report.
5 And so as part of this presentation, I'll 6 start by providing a high level summary of the 7 findings in the topical report, and then I'll step 8 through some new discussion, the changes to the 9 staff's safety evaluation, and some follow-up items 10 from the subcommittee meeting. So, if you move onto 11 slide three?
12 So, the technical review team for this 13 project, Jordan Hoellman, who is moving the slides for 14 me, is the project manager. My name is Boyce Travis.
15 I'm a reactor systems engineer and the lead reviewer 16 for this topical presenting on behalf of the staff.
17 Other members of the review team from my 18 branch were Jeff Schmidt, Chris Van Wert, and Antonio 19 Barrett, who I believe are all on the line in this 20 presentation as well. So, if we move onto the next 21 slide, slide four?
22 Yeah, so this is a reused slide from the 23 previous presentation, but I've included it here 24 because I think it does a good job of filling in what 25 the role of this topical report constitutes.
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57 1 So, as part of a license application for 2 a TRISO fuel design, there's going to be a lot of 3 other factors that go into it. A large part of that 4 license application is going to be the safety 5 demonstration. And for a TRISO fuel reactor design, 6 we expect the fuel qualification to perform a large 7 part of that safety demonstration.
8 This topical report makes up a reasonable-9 sized portion, but not all of what would constitute 10 fuel qualification for a vendor that's using a TRISO-11 fueled reactor design, and so there are other factors 12 outside of the particle itself and/or conditions that 13 this topical report does not confine.
14 So, for instance, very high temperatures 15 or specific transient ramp power or temperature ramps 16 that don't fall within the scope of this topical 17 report would have to be the subject of future 18 licensing submittals.
19 And so this topical report is, as noted, 20 a foundational basis for a future TRISO license 21 application and makes up a large part, but not all of 22 what we would expect to see for a fuel qualification 23 for a TRISO fuel design.
24 Next slide, slide five? So, I'm not going 25 to read these conclusions. I'll just kind of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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58 1 paraphrase what's here. EPRI has already gone over 2 this.
3 Ultimately, the topical report concludes 4 that the testing in AGR-1 and 2 constitutes a valid 5 performance demonstration over a range of operating 6 conditions, which is outlined in the report.
7 The kernels were manufactured in a variety 8 of different ways and exhibited some property 9 variations, but within the specifications that are 10 outlined in the report, no matter the manufacturing 11 process, they exhibited similar irradiation and 12 accident safety, or accident performance as defined by 13 the performance that's described in the topical.
14 And then the aggregate data from these two 15 tests, as summarized in the report, again, all of this 16 is part of the data that's referenced in the report, 17 can be used to support licensing of reactors that are 18 going to use UCO TRISO purely from the perspective of 19 the particle itself for this report.
20 Other forms, or other impacts of the fuel 21 outside of the particle would be the responsibility of 22 anyone that's referencing this report as part of a 23 future submittal.
24 So, if you'll move onto slide six? Slide 25 six kind of provides a high-level review background of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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59 1 what the staff went through in this topical report.
2 In effect, the information presented here 3 would allow applicants or licensees who reference this 4 report to use the AGR data based on adhering to the 5 manufacturing specifications in Table 5.5 and the 6 discussions in the topical report, and subject to the 7 operational and performance ranges that are detailed 8 in the TR.
9 And so that's the other piece going back 10 to the discussion we had earlier of Table 5.5 doesn't 11 perform everything.
12 It's kind of the, as Dr. Corradini 13 mentioned, the recipe, but there are other aspects of 14 what you put the final particle in, the conditions you 15 subject it to related to burn up, and time average 16 temperature that this report has boundaries on.
17 And if you went beyond those boundaries, 18 including uncertainty as we'll discuss later, then you 19 would need to justify that, going beyond those 20 boundaries, either through additional testing data, 21 another reference, or work that's done outside of the 22 scope of this topical report as a licensee or vendor.
23 Staff conducted an audit and asked five 24 RAIs. The responses are noted on the ADAMS ML numbers 25 on the slide. I'll note that staff found the audit NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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60 1 extremely useful.
2 It was a huge efficiency boost to be able 3 to go out to Idaho and speak with the experts who did 4 some of this testing and gain a better and more 5 focused look at what some of the background there, and 6 develop a small number of RAIs that allowed us to, you 7 know, really hone the review in on the safety 8 evaluation that resulted as a part of this project.
9 And then as a result of our review and the 10 subject of the RAIs, the scope of the topical report 11 was narrowed somewhat to the tested particle ranges 12 that are now in Table 5.5 of the report, and some 13 additional performance parameters that we noted 14 earlier were identified as limits that the particles 15 are subject to in order to reference the report.
16 So, if you'll move onto slide seven? I'll 17 be starting on the new information discussion here.
18 So, as a result of the previous ACRS meeting, staff 19 decided to revise limitation one and condition two.
20 If you'll remember, there are a total of 21 five limitations and conditions that were the subject 22 of this topical report. We felt that upon reflection, 23 a couple of these could use some further refinement.
24 And so the yellow highlighted portion here 25 in limitation one, we added some discussion to this NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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61 1 limitation to say that it's any performance beyond the 2 particle of the fuel form, including other influences 3 of a specific reactor design beyond that fuel form to 4 account for some discussions as we expect there to be 5 a fairly broad spectrum of applicants and licensees 6 that may use a TRISO fuel design using various 7 different coolants, different fuel forms.
8 As we've already noted, there are compacts 9 and pebbles that we are 100 percent aware of that 10 exist as fuel forms. There may be others, and so we 11 just wanted to emphasize that impacts of your reactor 12 design's typing on these particles need to be assessed 13 by you, the reactor designer.
14 This report governs only what happens 15 inside and up to the particle boundary, and so, again, 16 those would be the subject of a future submittal and 17 not under the scope of this review. If you'll move on 18 --
19 MEMBER KIRCHNER: So --
20 MR. TRAVIS: Go ahead, sorry.
21 MEMBER KIRCHNER: So, Boyce, this is --
22 may I interrupt? This is Walt Kirchner speaking.
23 MR. TRAVIS: Yeah, of course.
24 MEMBER KIRCHNER: So, I understand the 25 limitation here and confining it to the TRISO NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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62 1 particle. Now, you have an applicant come in. They 2 have to put the particle into some fuel form, usually 3 with a binder. The binders vary.
4 The packing density varies for different 5 shapes like the compacts and for the pebbles, and 6 there may be other fuel forms that are used. Would 7 this require then in-pile testing?
8 MR. TRAVIS: So, I'm going to hedge a 9 little when I respond to that. I don't think it 10 necessitates in-pile testing necessarily if there is 11 a -- so, I guess, let me step back.
12 It would require in-pile testing in some 13 form or fashion. There has been a lot of in-pile 14 testing conducting, including what's been done in 15 these AGR experiments.
16 And so if a vendor or licensee could 17 justify that their packing fraction, their binder 18 method looks or is sufficiently similar to what's 19 already been tested in a reactor design, I think the 20 staff would be receptive to exploring that.
21 I don't think that every individual -- I 22 don't necessarily think that every individual designer 23 would have to do additional in-pile testing for their 24 own fuel form if that makes sense.
25 MEMBER KIRCHNER: Yeah, fair enough.
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63 1 Thank you.
2 MR. TRAVIS: Yeah, of course.
3 MEMBER BLEY: This is Dennis Bley.
4 MEMBER KIRCHNER: So, so --
5 MEMBER BLEY: Oh, I'm sorry. Go ahead, 6 Walt.
7 MR. CORRADINI: This is Corradini.
8 Travis, I guess I wanted to make sure I understood the 9 additional words of what you're covering. Are the 10 additional words in yellow basically things that we 11 haven't thought of, but may come about?
12 MR. TRAVIS: In some sense, yes. In other 13 senses, it's more in the -- so, this was, I think, 14 directly to address a concern.
15 For instance, if a reactor design were to 16 use a non-helium coolant and it had some impact that 17 propagated through the fuel form to the particle, that 18 is also -- like if there is a particle interaction 19 other than the binder or the fuel form, that also is 20 the subject of that vendor designer.
21 MR. CORRADINI: Okay.
22 MR. TRAVIS: So, I mean, yes to your 23 question, but also the specific concern we were 24 looking at here is we are aware of other things that 25 might theoretically impact the particle, and we want NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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64 1 to make sure that it's clear that those are -- that 2 particle interactions with other reactor effects, not 3 just the fuel form, are the subject of this.
4 MEMBER KIRCHNER: Yeah, other coolants --
5 (Simultaneous speaking.)
6 MEMBER KIRCHNER: -- are going to be a 7 challenge. Almost all of the database experiences 8 helium or whatever was used in the in-pile capsules, 9 but usually it's, you know, it's a noble gas, but it's 10 usually helium there as well.
11 So, once one goes to a different coolant, 12 then that raises a number of questions about the 13 potential for attack of the particle fuel by the 14 actual coolant. Thank you.
15 MR. TRAVIS: I heard a couple more 16 questions and I don't know if Dr. Corradini got to 17 finish.
18 MR. CORRADINI: No, Walt's faster than I 19 am, but he caught what I was trying to get at. Thank 20 you very much.
21 MR. TRAVIS: Yep, any further questions?
22 MR. SCHULTZ: Boyce, this is Steve 23 Schultz.
24 MR. TRAVIS: Sure.
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65 1 information coming from AGR-5 to 7 tests that are 2 going to be incorporated into future evaluations 3 either related to the fuel form or to additional 4 information related to the particle?
5 MR. TRAVIS: So, I'm going to say yes, but 6 very tentatively. I think that in most cases, 7 especially related to source term considerations, 8 vendors are going to cite other data from the AGR 9 program in order to fully flesh out what their fuel 10 qualification looks like, but at this point, I don't 11 know exactly what portion of that they're going to 12 cite, and so it would kind of be speculation.
13 So, I will say that I do expect other data 14 sources to be needed for most of the reactor designs 15 that come in.
16 MR. SCHULTZ: That helps. Thank you.
17 MR. TRAVIS: If there's no other 18 questions, I will move onto slide eight. Okay, so 19 slide eight includes the other revision to the topical 20 we made as a result of the previous ACRS discussions, 21 and this relates to the discussion of uncertainty, and 22 so we've added the text highlighted in yellow here in 23 condition two.
24 I guess I'll note that the expectation of 25 how this condition is applied has not changed based on NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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66 1 that added text, but as the ACRS noted, some of that 2 was based on an implicit understanding of what was 3 going to be done regarding uncertainty and going 4 forward on how this topical is being referenced.
5 This text was an effort to more explicitly 6 lay out what the expectation is regarding uncertainty 7 in the analytical justification that's used when 8 referencing this topical report.
9 And so with that, I'll move onto slide 10 nine, and I have two slides here that will talk 11 briefly about items from the subcommittee meeting that 12 resulted, or that were questions kind of directed more 13 at the staff safety evaluation.
14 There was a question at the subcommittee 15 regarding how burn up and depletion were 16 characterized, both somewhat in the topical report, 17 but more in how the staff described the information in 18 the safety evaluation regarding these.
19 Burn up and depletion were resolved fully 20 via calculation in MCMP and Origin. The staff's 21 information is derived from these references that are 22 documented in the topical report.
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67 1 that was discussed in the subcommittee meeting.
2 And so we didn't feel that it was 3 necessary to change the description in the safety 4 evaluation based on the information that's provided 5 both in the topical report, but more importantly, in 6 the references that are identified on this slide and 7 referenced in the topical report.
8 And so moving onto slide ten, this is 9 regarding uncertainty for a little more discussion on 10 what we discussed, why, and the result of the changes 11 that we made to condition two.
12 Again, we brought up uncertainty a number 13 of times during the subcommittee meeting. The 14 uncertainty for these experiments is comprised of a 15 number of different experimental inputs, all of which 16 played a role, and Paul went into much greater detail 17 during his presentation.
18 I guess we would just note here that the 19 gap width in particular accounts for a number of 20 effects, including things like expansion or 21 contraction, that change during the course of the 22 experiment, and so can act as a large driver on 23 uncertainty.
24 The data that was measured on the 25 uncertainty is summarized in Section 6.5. As Paul NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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68 1 mentioned, the references that were on the slide, some 2 of which are references 78 through 80 in the topical 3 report, go into further detail.
4 The staff did, we looked into those 5 references in some greater detail, and I think we're 6 comfortable with how it's characterized in the report.
7 It is an average value, but the band is characterized 8 appropriately based on the data.
9 And we expect that an applicant 10 referencing the report will have considered those 11 uncertainties as part of when they reference that data 12 as part of their analytical, whatever analytical 13 product they're using to finish qualifying their fuel 14 form.
15 And so I have one more slide in 16 conclusion, slide 11. Ultimately, the conclusion in 17 the report is that the experiments were conducted 18 under an adequate quality assurance program that 19 produced the data.
20 The TRISO particles, if they're 21 manufactured in accordance with the specifications in 22 the topical report, including table 5.5, will perform 23 adequately to the level as described in the topical 24 report, up to temperature, burn up, values that are 25 explicitly identified in the topical report and are NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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69 1 based on that data that is valid and can be referenced 2 by someone coming in with a TRISO particle design that 3 meets the specifications that are outlined in the TR.
4 And so based on the review of the TR and 5 the information provided in the RAI responses and the 6 updates to the topical report, staff agrees with the 7 conclusions that have been requested subject to the 8 limitations and conditions that are identified in the 9 safety evaluation were previously discussed.
10 So, that concludes my presentation. I'd 11 be happy to take any further questions.
12 MEMBER BALLINGER: Well, this is Ron. It 13 looks like there are no further questions. Thank you 14 very much for the presentation, and actually thank 15 everybody for their presentations. But we now, I 16 think, need to go and ask for public comments, and I'm 17 assuming, Thomas, is the line open?
18 MR. DASHIELL: The bridge line is open for 19 comments.
20 MEMBER BALLINGER: Thank you. So, are 21 there any members of the public that would like to 22 make a comment? Please identify yourself and make 23 your comment. We've got to give them a few seconds to 24 unmute their microphone. I think we're done. I think 25 hearing no comments, I think we're done with the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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70 1 presentations.
2 Once again, thank you very much for the 3 presentations. Once again, we will be producing a 4 letter for this topical report for the SE, and so with 5 that, I'll turn it back to you, Matt. Thank you.
6 CHAIR SUNSERI: Thank you, Ron, and thank 7 you to the staff and all of the other presenters that 8 presented today. So, my question for you, Ron, is you 9 have a report prepared, a draft report prepared for 10 this. It's about 250 lines. How long would it take 11 for you to read that in?
12 MEMBER BALLINGER: If you would like me to 13 make a prediction, I don't want to.
14 CHAIR SUNSERI: Well, let me say it 15 differently. Do you think you could have that read in 16 by 1:00? That would give you 25 minutes, 20 minutes.
17 MEMBER BALLINGER: Yes, I think so.
18 CHAIR SUNSERI: Okay, so that's going to 19 cut into our lunch break a little bit, but I think 20 it's the best use of our time to do that, so can we 21 get that letter up?
22 And while that letter is coming up, if 23 anybody needs to take a bathroom break, please go 24 ahead and do so right now, but we're going to continue 25 through with the reading of the staff letter.
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71 1 MEMBER BALLINGER: Yeah, I should -- no, 2 I don't -- I sent -- I made some minor changes to the 3 letter actually early this morning and sent them to 4 Chris, so I'm reading from the one that I have. I'm 5 not exactly sure whether Chris had a chance to address 6 the, to input those changes. So, Chris, are you --
7 did you get the thing this morning?
8 MR. BROWN: Yeah, I'll give you a call on 9 your cell phone.
10 MEMBER BALLINGER: Okay, all right, so in 11 any case, I'll read from the latest version that I 12 have.
13 CHAIR SUNSERI: Well, so, are we going to 14 have it on the screen? Is Sandra prepared to put this 15 up or did we get ahead of her?
16 MR. BROWN: If not, I'll run it, 17 absolutely.
18 MR. MOORE: Sandra, this is Scott. Are 19 you on and are you hearing this?
20 PARTICIPANT: Yes, I'm on.
21 MR. MOORE: Okay, so -- go ahead.
22 PARTICIPANT: I was going to say what 23 letter do I need to pull up?
24 MR. BROWN: Sandra, I'll handle it. Don't 25 worry about it.
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72 1 MEMBER BALLINGER: Yeah, the title of the 2 revision would be Revision 1.1.
3 MR. BROWN: Thank you.
4 MR. HOELLMAN: Okay, Chris, I'm going to 5 stop sharing so you can do it, okay?
6 MR. BROWN: Thank you.
7 MR. MOORE: Chris, this is Scott. So, 8 you're going to show it on the screen or you're going 9 to give it to Sandra?
10 MR. BROWN: Scott, I'm talking to Sandra 11 now and we're pulling it up shortly.
12 MR. MOORE: Okay.
13 VICE CHAIR REMPE: Someone, the court 14 reporter is asking a question about being off the 15 record. I think the answer is yes, but I'm not the 16 person to answer that question. Matt, can you answer, 17 or are you there, that you can answer the court 18 reporter's question?
19 CHAIR SUNSERI: Yeah, yeah, so we --
20 that's correct. So, for the court reporter, we will 21 go off the transcript from now, from this point, and 22 we will resume at 1:45 p.m. We'll be back on the 23 transcript at 1:45 p.m.
24 (Whereupon, the above-entitled matter went 25 off the record at 12:38 p.m. and resumed at 1:46 p.m.)
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73 1 CHAIR SUNSERI: So, welcome back. It's 2 1:45, 1:46 now. We are going back into session for 3 the ACRS presentation on the NuScale Area of Focus:
4 Boron Redistribution, and I will begin with a roll 5 call. Members, please acknowledge your attendance.
6 Ron Ballinger?
7 MEMBER BALLINGER: Here.
8 CHAIR SUNSERI: Dennis Bley?
9 MEMBER BLEY: Here.
10 CHAIR SUNSERI: Vesna Dimitrijevic?
11 MEMBER DIMITRIJEVIC: Here.
12 CHAIR SUNSERI: Walt Kirchner?
13 MEMBER KIRCHNER: Here.
14 CHAIR SUNSERI: Jose March-Leuba?
15 MEMBER MARCH-LEUBA: Yes.
16 CHAIR SUNSERI: Dave Petti?
17 MEMBER PETTI: Here.
18 CHAIR SUNSERI: Joy Rempe?
19 VICE CHAIR REMPE: Here.
20 CHAIR SUNSERI: Pete Riccardella?
21 MEMBER RICCARDELLA: I'm here.
22 CHAIR SUNSERI: And myself, so we have 23 full attendance with the exception of Charlie who is 24 excused, and we're going to start with the NuScale 25 boron dilution discussion.
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74 1 We will begin in open session, and at some 2 point, there will be a transition to a closed session.
3 You should have a separate email for that closed 4 session invitation.
5 I would remind everybody do not share that 6 with anybody that doesn't need it, and don't post it 7 on the message bar because then it becomes no longer 8 privately held information.
9 So, with that, I will now turn over to 10 Walt for us kicking off this session. Walt?
11 MEMBER KIRCHNER: Thank you, Mr. Chairman.
12 Today, we're going to hear from both the applicant and 13 the staff on what we had previously called boron 14 redistribution focus area, but our real attention 15 today and interest is in the area of boron dilution 16 events that would occur after uncovery of the riser in 17 the nuclear power module.
18 So, we are going to hear first from 19 NuScale and then from the staff in open session as the 20 Chairman has indicated. We will then move to a closed 21 session later this afternoon. We'll have a different 22 link for that, and again, tomorrow morning, we'll be 23 in closed session to hear further from the staff.
24 We are also going to provide time needed 25 to hear a differing view from the staff, a staff NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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75 1 member specifically, and that will be part of the 2 closed session.
3 And for the public, the reason that it 4 will be part of the closed session is we're dealing 5 with both export control and proprietary information.
6 I'm sure at some point that material will be available 7 to the public.
8 Normally I don't do this, but this time, 9 we're on the last leg of our review of the NuScale 10 design certification application and the staff's SER, 11 and we're at a rather important juncture with a 12 significant technical issue.
13 So, to frame the meeting and express at 14 least my interest as the subcommittee chair, and 15 hopefully on behalf of the full committee, I am most 16 interested to hear from both the applicant and the 17 staff about their analyses and evaluations of these 18 boron dilution events which are both AOO category and 19 design-basis events such as a DHRS cool down event, 20 that would be an AOO, or a small break LOCA design-21 basis accident-like event.
22 We would like to hear bounding analyses 23 that give us high confidence that we can assess the 24 boron dilution problem, know what the concentrations 25 are in the primary system and in cases up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
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76 1 Also, we are much interested to know what 2 happens at ECCS actuation. There are new set points, 3 for example, and/or if the 24-hour timer actuates the 4 system.
5 And finally, and we're interested in that, 6 by the way, because depressurization of the system 7 could lead to a number of event sequences of concern, 8 perhaps such a manometer oscillation in the primary 9 system with power feedback, so further just to focus 10 things.
11 And finally, we need to see that there is 12 a path to recovery that does not result in a potential 13 reactivity insertion accident and possible subsequent 14 core damage.
15 The nuclear power module cannot be left in 16 a cliff state. That would not complete the Chapter 15 17 evaluations, and so we're looking for that. To 18 qualify that, we're not looking for operating 19 procedures. We're looking for a physical description 20 or basis for recovery from such a boron dilution 21 event.
22 So, with that, I am going to turn to our 23 lead in this focus area, Jose March-Leuba, for any 24 comments before we go to the applicant.
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77 1 I do have comments and they're going to be very 2 negative because I'm extremely dissatisfied with both 3 the SER and the FSAR.
4 Back in February, we reached the consensus 5 that, an item I had been highly pushing for several 6 months, that the boration of the downcomer was a 7 serious condition, and we stopped the specification 8 and we went to work on it, and came up with a good 9 solution for some of the events by drilling these 10 bypass orifices in the high upper part of the 11 downcomer, but it only solved it halfway because after 12 you have an ECCS actuation, you will drop the level 13 below those orifices and you continue to de-borate.
14 So, for any ECCS actuation, which is an 15 AOO, many, many transients lead to it, you will start 16 to de-borate the downcomer. Will it take an hour, ten 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br />, 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />? I don't know because the analysis 18 hasn't been performed. It's been ignored.
19 So, if you allow it, if you let it go, and 20 I've said it many times, if you have an ECCS 21 actuation, you have weeks to work with this because 22 there is no way the operator is going to start 23 recovering within hours. That operator is going to 24 need approvals from committee upon committee.
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78 1 from the Vatican before they can recover, so there 2 will be plenty of time to de-borate, which means that 3 you park right at the core inlet in the lower plane 4 de-borated water.
5 And the worst-case scenario, which is end 6 of cycle, that may be worth $20, $25 worth of positive 7 reactivity, and you're just waiting for a provocation 8 to put that positive reactivity into the core. Those 9 provocations exist.
10 My favorite one is the initiation of one 11 of the non-safety grade systems like CFDS which we 12 would push it into the core. At low reactivity, we 13 push it in.
14 The applicant has chosen to completely 15 ignore this extremely dangerous condition. Let me say 16 it again, dangerous, that condition. I have reviewed 17 many power reactors. I haven't seen a condition in 18 the power reactor that is more dangerous than having 19 $20 worth of reactivity waiting to get into the core, 20 and the applicant has chosen to ignore it.
21 There is a lot of lip service going around 22 to risk-informed issues. However, the applicant has 23 chosen not to evaluate the risk of this condition and 24 the risk of operator actions on either of the 25 actuations or any of these conditions that can put NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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79 1 those $20, $25 of reactivity into the core.
2 They just don't want to do it. There is 3 a lot of lip service to risks, but they don't want to 4 complete the risk of the most risky condition we have 5 in this reactor. I find that unsustainable. You 6 cannot support it.
7 MEMBER KIRCHNER: Okay, Jose, and for 8 everyone on the line, this is Walt Kirchner again.
9 You've heard one member's opinions. Remember we speak 10 as a committee. I'm hopeful that today and tomorrow 11 perhaps, Jose, both the applicant and the staff 12 disprove your contentions.
13 Again, I would go back and just assert one 14 more time we're interested up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, and the 15 reasons are several, but we will work with the staff 16 on that particular point as a cut off.
17 It is my opinion, and now you're listening 18 to yet another member's opinion, that this system will 19 not be left for weeks while there are conference calls 20 with the NRC, that this will be addressed through 21 either tech specs or EOPs, and operator intervention 22 will take place at 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, if not sooner.
23 But let's hear from both the applicant and 24 the staff on these issues, but as a courtesy, let me 25 turn -- any other members wish to make an opening NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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80 1 comment?
2 CHAIR SUNSERI: Walt, this is Matt. I 3 just want to emphasize a point you made, being a 4 former operator myself. I think it's very important 5 for everyone to understand that the control room of 6 this plant will be run by a senior licensed operator 7 licensed by the Nuclear Regulatory Commission.
8 And that person is the sole decision maker 9 on what happens with this reactor. They will have 10 their procedures. They will march through those 11 procedures at the pace necessary independent of time 12 pressures, but reacting to physical plant parameters, 13 to take, to address the conditions of the core.
14 So you know, I heard you say that there 15 won't be conference calls and all that stuff.
16 Notwithstanding the fact that there will be a 17 technical support center advising that licensed 18 operator, notwithstanding the fact that there will be 19 an emergency operating center thinking about offsite 20 risk and advising that person.
21 But I just wanted to emphasize that the 22 decision making is retained by the licensed SRO. And 23 they'll be making those decisions in real time and in 24 accordance with their approved procedures.
25 That's all I have to add. Thanks.
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81 1 MEMBER MARCH-LEUBA: Matt, I don't want to 2 start an argument. But what the FSAR says, is that 3 once you reach the ECCS operations, the RRB opens.
4 You are in a safe and a stable condition.
5 And your operator is finished with his job. He 6 doesn't have to do anything else. That's what the 7 FSAR says today.
8 MEMBER KIRCHNER: So may I -- Jose, let's 9 then save that and explore it with both the Applicant 10 and the staff. Because now, we're getting into a 11 discussion mode.
12 So with that, I'll be a little peremptory.
13 And I'm going to turn first to NuScale. Is Paul 14 Infanger going to be the first presenter?
15 MS. NORRIS: This is Rebecca Norris. I'm 16 actually doing the introduction. And Paul will be the 17 primary.
18 MEMBER KIRCHNER: Okay. Well please 19 Rebecca. Sorry, my apologies. Go ahead, Rebecca.
20 MS. NORRIS: Oh, no problem. So thank 21 you, Member Kirchner and Member March-Leuba. So first 22 of all, good morning or afternoon, depending on what 23 coast you're on. I am Rebecca Norris with NuScale 24 Power. I am the supervisor for the boron 25 redistribution audit that just closed. And also the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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82 1 associated design changes.
2 So first I would like to say that we do 3 disagree that the -- with Member March-Leuba that the 4 reactor will be placed in a dangerous position.
5 However, we want to leave that to the NRC's 6 presentation, because we have defended that position 7 with them. And they will be presenting their SER 8 conclusions.
9 And if we need to provide input at that 10 time, we can. This presentation that we are about to 11 give you, is just describing a high level overview.
12 No further design changes were implemented since the 13 June 3rd to 4th ACRS meeting, where we gave the 14 initial presentation of design changes.
15 And additionally I want to thank the staff 16 for their thorough review of the safety and 17 completeness of our design solution. Safety has been 18 and will continue to be NuScale's top priority. And 19 we appreciate the staff's flexible response when the 20 need for a late breaking design change became apparent 21 a few months ago.
22 So with that, I will turn over to Paul 23 Infanger for the body of the presentation.
24 MEMBER KIRCHNER: Paul, do you have your 25 mic unmuted?
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83 1 MS. NORRIS: This is Rebecca again. It 2 seems we're having a little technical difficulty. If 3 you can give us a moment or two to try to address it.
4 MEMBER KIRCHNER: Surely.
5 MR. INFANGER: I think I was muted there 6 by the program. Hello, can you hear me now?
7 CHAIR SUNSERI: Yes, Paul. We can hear 8 you. Go ahead please.
9 MR. INFANGER: All right. Thank you.
10 Good day and welcome, this is our presentation of kind 11 of an update for what we have done last month.
12 And we're going to be updating what we 13 have provided to the staff as part of our boron 14 redistribution issue. We have provided some 15 information about the boron redistribution audit.
16 And we will provide a summary of our final 17 design changes. And also discuss what information we 18 added to the design certification, Revision 4.1 on the 19 boron redistribution.
20 We also made some changes to the local 21 topical report for the boron redistribution. And also 22 there was a separate issue that came up during the 23 boron redistribution audit, related to GDC-33. And we 24 had mentioned that in the June 3rd and 4th meeting.
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84 1 decisional. And we didn't know exactly what the 2 resolution would be. And that process is complete.
3 And that information was submitted in the DCA Revision 4 4.1. And we'll go through a little bit about what we 5 did for that. And then we'll talk a little bit our 6 conclusions.
7 So just as a recap, we made two 8 presentations on June 3rd and 4th. We provided an 9 overview in the public meeting. And then we had a 10 separate session for a closed meeting, where we 11 provided a lot of technical detail into how we 12 calculated the flow through the new riser holes. And 13 answered some questions that came up during the open 14 in the first closed session.
15 So the basic -- the basic issue was that, 16 you know, under certain conditions ECCS actuation or 17 respiration of the natural circulation with BHRS, 18 could transport polluted coolants to the reactor core 19 from a downcomer that has lower boron concentration.
20 And we presented the design solutions that we 21 developed to prevent or mitigate the boron 22 distribution.
23 MEMBER MARCH-LEUBA: Let me stop you right 24 there. Because this sentence is a little misleading.
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85 1 open, will the coolant design with holes, the 2 downcomer continues to de-borate, or continues to be 3 boron redistribution?
4 MR. INFANGER: Yeah. Once you've actuated 5 ECCS, the level will be below the holes. And at that 6 point, you will, the downcomer will dilute. Yes.
7 MEMBER MARCH-LEUBA: And we don't know how 8 long you have to stay there. It can be an hour, or it 9 can be 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />. It can be 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />. So you decided 10 not to analyze that position.
11 MR. INFANGER: Yes. So check the 15 and 12 scope is 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Beyond that case is in Chapter 19 13 and in Operations.
14 MEMBER MARCH-LEUBA: So how long does it 15 take for the downcomer to de-borate after the ARB is 16 open?
17 MR. INFANGER: I don't have the time --
18 MEMBER MARCH-LEUBA: So it could be less 19 than 32 hours3.703704e-4 days <br />0.00889 hours <br />5.291005e-5 weeks <br />1.2176e-5 months <br />, right?
20 MR. INFANGER: I --
21 MEMBER MARCH-LEUBA: Remember, this is 22 working full steam. All of the steam generated is 23 exposed to this environment. And all of the upper 24 parts of the containment is open to the steam 25 environment and condensing on the wall with a very NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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86 1 cold UHS.
2 So whatever calculation you did for the 3 new calculation, you wouldn't be bounding for this 4 condition. So you -- is it true that you did not 5 calculate this condition? For this occurrence here?
6 MR. INFANGER: Yes. When you -- once you 7 actually ECCS the pressures between the reactor 8 pressure vessel and the containment equalize. And 9 initially, the initial flow is out into the 10 containment. And then the flow that starts when ECCS 11 starts its natural circulation process, the flow is 12 very slow.
13 And it's just the condensate level 14 difference from it condensing in the containment. So 15 there's no unusual --
16 MEMBER MARCH-LEUBA: But I just got that 17 same thing -- on a humongously large surface, just the 18 outer shell of the containment, which is in contact 19 with the pool, which should be at 70 or 80 degrees.
20 So you are -- I mean whatever steam makes it there is 21 condensing.
22 But we have established -- we're not going 23 to argue about the physics. We have established that 24 NuScale does not know how long it takes for this 25 condition to de-borate.
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87 1 MR. INFANGER: We do. I don't -- I didn't 2 prepare that information for this presentation. So --
3 MEMBER MARCH-LEUBA: You do. You have a 4 document, a documentary calculation for that?
5 MR. INFANGER: We have calculations. And 6 they have been audited by the staff.
7 MEMBER MARCH-LEUBA: Can I see them?
8 MR. INFANGER: We submitted that 9 information on the docket in RAI-8930 response we 10 updated.
11 MEMBER MARCH-LEUBA: Well so how long does 12 it take to de-borate?
13 MR. INFANGER: As I said, I didn't prepare 14 that information.
15 MEMBER MARCH-LEUBA: You don't know.
16 MR. INFANGER: Well --
17 MEMBER MARCH-LEUBA: But you --
18 MR. INFANGER: NuScale knows. I didn't 19 bring that information to this presentation.
20 MEMBER MARCH-LEUBA: Okay. I'm talking to 21 the staff now --
22 MR. INFANGER: You can probably look back 23 at some --
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88 1 apparently exists, you obviously have reviewed it 2 during the audit. And you will be able to tell me 3 what this time is. I mean nowhere in the FSAR says 4 that the chamber de-borates after RRB is open.
5 VICE CHAIR REMPE: Could I ask what tool 6 NuScale used to do these detailed calculations to 7 determine when it de-borates? Because I saw some 8 information in the SER indicating they'd reviewed the 9 NuScale calculations. But I'm just curious about the 10 level of detail and what the analytical tool was used?
11 CHAIR SUNSERI: And while you're thinking 12 about that question, this is Matt. I have one, maybe 13 a similar, but slightly different.
14 Once the ECCS valves open up and you flood 15 the containment, or you establish the level in 16 containment and you couple the core through the core 17 barrel to the water in the containment, through the 18 containment liner, to the ultimate heat sink, when 19 does that conduction rate of cooling diminish the --
20 be equal to decay heat removal such that you're not 21 steaming the reactor anymore? I guess, or does it 22 ever get to that condition?
23 MR. INFANGER: This type of information 24 would have to be presented in a closed session. We 25 did not prepare a closed presentation for this NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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89 1 meeting. Staff is going to be addressing these in 2 their review of the ACR. And at that time, if there's 3 questions, we could -- we could chime in.
4 MEMBER MARCH-LEUBA: Yeah. Well let's --
5 in the open session, what do you claim? Your claim is 6 that the -- after the level drops below the orifices, 7 the downcomer does not de-borate, or it does de-8 borate? If your claim that the one goes slowly --
9 MR. INFANGER: There's no mechanism --
10 MEMBER MARCH-LEUBA: Go ahead.
11 MR. INFANGER: There's no mechanism to get 12 the un-borated water from the downcomer into the 13 reactor.
14 MEMBER MARCH-LEUBA: So it will eventually 15 de-borate. We might be arguing about how long it 16 takes.
17 MR. INFANGER: Yeah. And at that point 18 then it becomes an operational concern. And we've got 19 -- we have CO items to develop procedures that will --
20 that are required to look at low boron concentration 21 in the containment and the downcomer. So those 22 procedures --
23 MEMBER MARCH-LEUBA: Have you ever rated 24 -- since we are doing a risk informed evaluation, have 25 you calculated the risk that this dangerous condition NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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90 1 poses to the reactor by, you know, by what the 2 calculation claims? Or things that we don't know like 3 oscillations, sensibilities, depressurization? Have 4 you ever rated that risk?
5 MR. INFANGER: The physical phenomena that 6 we're addressing in design basis space are due to 7 analytical simplifications that make the condition 8 difficult to calculating mixing in the actual 9 condition. And that's why we did, we did 10 modifications that are, prevent the condition from 11 happening in the 72 hour time frame that we're 12 required to evaluate for Chapter 15.
13 MEMBER MARCH-LEUBA: Well you're just 14 speaking on the record.
15 MR. INFANGER: It definite -- it one --
16 but once it --
17 MEMBER MARCH-LEUBA: You are speaking on 18 the record.
19 MR. INFANGER: But once you've gone to 20 Chapter 19, if you use the Chapter 19 methodology, we 21 don't believe that there is a mechanism that would 22 lead to this, the operation of that.
23 MEMBER MARCH-LEUBA: Is it a model for 24 relief? Is it a religious belief? Or do we have a 25 documentation that you have analyzed every possible NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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91 1 actuation error? Have you agreement? I mean it's --
2 does that document exist that we can look at it?
3 CHAIR SUNSERI: Hey --
4 MEMBER MARCH-LEUBA: Am I supposed to 5 believe you?
6 CHAIR SUNSERI: So let me ask a question 7 here and jump in here. I think we're all anxious for 8 the answers to these questions. And I think we may be 9 just getting a little ahead of ourselves. Why don't 10 we let the Applicant go through the information they 11 want to present.
12 Listen to what they have to say. And 13 then, you know, before this is all over, we'll have 14 the chance to ask our questions either in open session 15 or closed session, depending on where it's appropriate 16 to do so.
17 We're kind of stuck -- I think we're stuck 18 right here at this point in time, to be honest. And 19 I think we can -- we would do ourselves better to move 20 forward, hear what they have to say, and then --
21 MR. MELTON: Hello, Matt? Matt, this is 22 Mike Melton with NuScale. Can you hear me?
23 CHAIR SUNSERI: Yes. Yes, Mike.
24 MR. MELTON: Yeah. So I would appreciate 25 it if we could stay on the purpose of the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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92 1 presentation. We would be happy to address some of 2 the comments in the closed session. But that really 3 is the staff's presentation and their time to talk 4 about the FSARs.
5 So if Paul could stay on track, we'd 6 appreciate it. We absolutely disagree with the 7 wording dangerous. And I think at the end of the 8 slides and the discussions, we should get to that 9 point. We do not see any core damage period, after 10 all the work we've done.
11 And we'll be happy to bring the ACRS and 12 Dr. Leuba up to speed as necessary as we go through 13 this process. But for now, I was thinking --
14 MEMBER DIMITRIJEVIC: May I also --
15 MR. MELTON: If we could stay on track 16 with our presentation and go forward.
17 MEMBER DIMITRIJEVIC: Yes. But in your 18 presentation, you should really define to us what 19 scenarios you have looked. Because so far we have a 20 very general discussion. But not really the 21 definition of all initiated three to that state.
22 And water that's receiving this scenario 23 and sequences leading to this state. Any in what time 24 we will get in the situation we have to worry about 25 something? So far, we have a general discussion. But NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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93 1 it's not translated to, at least in my opinion, it's 2 not translated to Chapter 19 scenarios.
3 MR. MELTON I appreciate that. I think we 4 will get there. We are presenting the differences 5 from the June 3rd and 4th meeting where we had 6 extensive discussions with the ACRS, and the final 7 changes that we made in that time period.
8 And during that time, we have been 9 involved in detailed and challenging conversations 10 through the audit with the staff. They will present 11 their findings as is pretty much the bulk of this 12 meeting. So what we want to do is bring the ACRS up 13 to date on our status and our changes that got us to 14 this point.
15 MEMBER MARCH-LEUBA: But I need to 16 intervene here a little while. Sorry to not get 17 along. But this is going to be a long meeting. In 18 the June meeting, we were told that when you turned 19 CFDS after the breaking downcomer, after activating 20 the ECCS. It would not possibly cause any core 21 damage, because there was some time constant thing.
22 And you confessed that that was just an 23 opinion. And there was no calculation behind it. So 24 have you done a -- am I to understand what you're 25 saying now that you have calculated what happens when NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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94 1 you turn CFDS after downcomer regulation?
2 Is that being documented? And is there a 3 document you can give me the number so I can go into 4 the reading room and read it? Or you have not? This 5 could be --
6 MR. INFANGER: Yeah. I've got --
7 MEMBER MARCH-LEUBA: Exactly what we're 8 doing for this presentation. What has been done since 9 June to now?
10 MR. INFANGER: Yeah. We did a 11 calculation. And if Ken Amone (phonetic) is on the 12 line, he was the engineer for CRA that just did that 13 evaluation. If you could just, Ken if you could just 14 give a brief summary of what we did. This is a --
15 again, this is a public call, so we cannot get into 16 the proprietary details.
17 MEMBER MARCH-LEUBA: I'm willing to wait 18 until the closed session as long as you tell me the 19 document information now exists, and has been 20 documented. Because in June, it had not.
21 MR. MELTON: We -- this is Mike. We have 22 completed the calculations.
23 MEMBER MARCH-LEUBA: Okay. So where --
24 MEMBER KIRCHNER: Jose, this is Walt. I'm 25 sorry everyone, I was dropped off the Skype there for NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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95 1 quite a bit. So thank you, Mr. Chairman for 2 intervening. Let's let the Applicant go through the 3 slides they have to present, and then ask our 4 questions.
5 I think, Jose, you've got your point on 6 the table. And let's hear from them at this point.
7 And then either we'll take it up in closed session or 8 at the end of their presentation. So Paul, please go 9 forward.
10 MR. INFANGER: Can you hear me? I think 11 I've had some microphone problems here.
12 MEMBER KIRCHNER: Your audio is a little 13 garbled for some reason.
14 MR. INFANGER: Okay. It was -- okay, is 15 that any better?
16 MEMBER KIRCHNER: Somewhat. Okay, go 17 ahead.
18 MR. INFANGER: Okay. The purpose of this 19 presentation is to inform of additional work since the 20 June 3rd and 4th meeting of ACRS. And implement some 21 design changes to the topic reports and the staff 22 changes.
23 MEMBER MARCH-LEUBA: Sorry Paul, you are 24 really garbled. I can barely understand it. But it's 25 really bad.
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96 1 MR. INFANGER: I'm going to hang up and 2 call back in. It will just take a minute.
3 MEMBER MARCH-LEUBA: Okay.
4 MS. NORRIS: This is Rebecca Norris.
5 While he's reconnecting, just so everyone knows, we 6 are on slide four, about to go to slide five.
7 (Pause.)
8 MR. INFANGER: Okay. I've called back in.
9 Is there -- am I any clearer?
10 MEMBER KIRCHNER: That's much better. Yes.
11 The Court Reporter could not work with the previous 12 audio. So go ahead Paul.
13 MR. INFANGER: All right. One more time.
14 Okay, so again, this is just an update to the June 3 15 and 4. There is new technical information as we'll 16 talk about shortly. The -- in this time period since 17 the last meeting, we've continued on with the boron 18 distribution audit.
19 That audit had initiated on March 9th.
20 And we've had daily meetings between NuScale and the 21 staff. In the mornings we would basically meet with 22 the staff, tell them what information we put in the 23 electronic reading room, or we would take requests 24 from the staff for additional documentation. And 25 schedule any technical calls that were needed. We had NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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97 1 numerous technical calls, often three or four a week 2 that lasted several hours a day.
3 We documented 21 submittals that described 4 design change information, provided analysis, and the 5 DCA changes. And on June 19th we submitted final DCA 6 changes for this boron redistribution issue. It was 7 a complete submittal with all parts of the DCA. And 8 then we exited the audit on June 26th, just a couple 9 of weeks ago.
10 So this is very similar to what we 11 presented on June 3rd and 4th. The design changes, 12 everyone is pretty well aware of it. We implemented 13 these design changes to prevent the possible boron 14 solution sequences. And the --
15 MEMBER MARCH-LEUBA: Sorry. Let me stop 16 you right there. Because this is another misleading 17 slide. You introduced some design changes to prevent 18 a subset of the postulated boron distribution 19 sequences. Is that correct?
20 MR. INFANGER: I think we --
21 MEMBER MARCH-LEUBA: I mean we still have 22 -- we still have sequences.
23 MR. INFANGER: We believe the --
24 MEMBER MARCH-LEUBA: You believe in what?
25 MR. INFANGER: We believe all of the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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98 1 sequences we were required to evaluate for Chapter 15.
2 MEMBER MARCH-LEUBA: Okay. So you did not 3 include any ECCS, forced ECCS actuation de-boration?
4 Correct?
5 MR. INFANGER: The design changes we 6 implemented we believe prevent those situations.
7 MEMBER MARCH-LEUBA: But how can you say 8 that? The moment you actuate the ECCS, the water 9 level drops below the orifices, and it's past de-10 boration. So it does not prevent boron dilution.
11 Both, it prevents some of it.
12 MR. INFANGER: Well we'll have to get into 13 it in the closed session. But there's no mechanism to 14 get the water from the downcomer into the core. So 15 the --
16 MEMBER MARCH-LEUBA: And there is a 17 thorough and exhaustive search for all possible 18 scenarios. And you have recommended that?
19 MR. INFANGER: Those were evaluated in 20 our, by our engineers and by the staff. So we'll go 21 -- they will -- at this point, we're just giving a 22 status. And the staff will explain how we met the 23 criteria for the SER. And then if we have additional 24 questions, we'll address them at that time.
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99 1 point out that this slide -- this slide says the 2 design changes prevent these boron solution sequences.
3 All of them on this slide. But if the sequences --
4 MEMBER KIRCHNER: But Jose -- Jose, this 5 is their position. And we will have an opportunity to 6 challenge it. So let's continue on at this point and 7 not quibble over the wording of the view graphs. I 8 think your point is well taken.
9 And I'm certainly prepared to ask that 10 question when we get to the right juncture about 11 whether this prevents all possible boron dilution 12 sequences. So let's continue on. Go ahead Paul.
13 MR. INFANGER: Okay. The -- in addition 14 to the four three-quarter inch riser holes, we added 15 an ECCS actuation on low RCS pressure. And we lowered 16 the set point for the ECCS actuation on containment 17 level.
18 For the DCA, we provided additional 19 information for the staff to support their development 20 of their safety evaluation. And some of that 21 information that was needed, the staff wanted more 22 information related to the ECCS actuation signal 23 interlocks.
24 They wanted that referenced in the ECCS 25 actuation table in Chapter 6. And also in the Chapter NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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100 1 15 analytical limits table. So those now reference 2 the table in Chapter 7, which goes into detailed 3 information about all of the permissives and 4 interlocks associated with the ECCS system.
5 Probably the single largest change we 6 made, is we added a section in the long term cooling 7 section of 1505 of Chapter 15. We added a description 8 of the riser hole flow path evaluation.
9 We -- the downcomer boron concentration 10 remains above the critical boron concentration during 11 DHCS cool down for beginning cycle and middle cycle 12 events. And there's minimal impact at the end of 13 cycle due to the low boron concentration in the 14 reactor.
15 VICE CHAIR REMPE: So it doesn't matter 16 because we have copies of your slide Paul, but I think 17 what's on my screen is slide six. And I think you're 18 getting ready to go to slide eight. Have we lost 19 whoever is running the slides connection?
20 MR. INFANGER: I just finished slide 21 seven.
22 MS. NORRIS: This is Rebecca. I am 23 presenting. Mine shows slide eight. Are other people 24 having the same problem? I can cycle the 25 presentation.
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101 1 MEMBER PETTI: I see slide six.
2 VICE CHAIR REMPE: That's what I see too.
3 I think you need to reset.
4 MS. NORRIS: I'm sorry.
5 VICE CHAIR REMPE: It's not a big deal.
6 We've got our own copies. Just keep telling us what 7 slide you're on, Paul.
8 MR. SNODDERLY: Yeah. Just -- this is 9 Mike Snodderly. Just quickly, if you don't activate 10 your screen once in a while, it will go to sleep.
11 And that's, I think, the problems that 12 Paul and Rebecca are having. So please, just once in 13 a while, move a slide, or -- to keep your system 14 active. Thank you.
15 MS. NORRIS: Understood. Hopefully you 16 can see it again now.
17 MR. SNODDERLY: Not yet. It's loading.
18 We can see it. Please proceed. You're on slide 19 eight.
20 MR. INFANGER: Okay. Okay --
21 MEMBER KIRCHNER: Paul, was there 22 something you wanted to cover on slide seven? What we 23 see in front of us right now is slide eight.
24 MR. INFANGER: Oh, well slide seven was 25 the DCA changes. And the -- where we added ECCS NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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102 1 actuation information on the interlocks to the Tables 2 in Chapter 6 and Chapter 15. This was information the 3 staff wanted for, related to the instrumentation. And 4 we added a section 1505, added information to that 5 section that describes the -- more details about the 6 riser hole flow path and how we performed that 7 evaluation.
8 And that presented the information that 9 the boron concentration in the downcomer remains above 10 the critical boron concentration for beginning and 11 middle of life scenarios. And at end of life, there's 12 very little impact because the boron concentration is 13 very low.
14 MEMBER KIRCHNER: And Paul, for the 15 record, all these -- this is Walt Kirchner. For the 16 record, these calculations of boron concentration were 17 performed how? Were these just the next balance 18 calculations? Or were they RELAP? Or were they 19 computational fluid dynamics calculations?
20 What was the tool that was used to 21 estimate boron distribution concentration gradients 22 and mixing in the downcomer and lower plenum?
23 MR. INFANGER: Okay. Ben Bristol is from 24 our -- a supervisor in our engineering for safety 25 analysis.
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103 1 MEMBER KIRCHNER: I'm not asking for the 2 details now, just the methodology that was used for 3 the public record.
4 MR. INFANGER: Yeah. I was going to ask 5 Ben to give a brief, nonproprietary description of the 6 -- of how we calculated the downcomer boron.
7 MR. BRISTOL: Hi. Sure. This is Ben 8 Bristol with NuScale. The -- at the ACRS that -- we 9 would present to the ACRS in June, we performed a 10 simple mass volume-based distribution calculation 11 based on inlet and outlet flow conditions.
12 MEMBER KIRCHNER: Then a question I will 13 ask in the closed session is: what kind of granularity 14 was used to do those estimates? In other words, what 15 axial noding was employed?
16 MR. BRISTOL: Well we can go through that.
17 (Pause.)
18 MEMBER KIRCHNER: Keep going Paul.
19 MR. INFANGER: And --
20 VICE CHAIR REMPE: Another question for --
21 you can wait until the closed session if you want to, 22 but today we're going to hear about the staff and how 23 they evaluated this issue.
24 And you've mentioned you're going to be 25 developing some procedures. Are you planning to use NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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104 1 a more sophisticated tool in the future to support 2 development of these procedures? And you can answer 3 later if you want to.
4 MR. INFANGER: Those are going to be in 5 the COL Applicant's -- the design certification does 6 not develop procedures. That will be the Applicant 7 for the combined license.
8 VICE CHAIR REMPE: So the staff will be 9 needing to evaluate what the Applicant does, and 10 hopefully with more detailed evaluations.
11 MR. INFANGER: Right. We have a COL item 12 that -- we have a COL item that requires the Applicant 13 to develop procedures, which includes covering this 14 scenario.
15 VICE CHAIR REMPE: And does it say using 16 more sophisticated tools? I've forgotten what the 17 exact wording of the COL item was.
18 MR. INFANGER: No. It's not that 19 prescriptive.
20 VICE CHAIR REMPE: Thank you.
21 MEMBER MARCH-LEUBA: Okay. While we're 22 talking procedures and tech specs, can you tell me how 23 you measured the boron concentration? What 24 instrumentation is used? That is part of the 25 specification, specifying instrumentation.
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105 1 MR. INFANGER: We have a -- there is a 2 boron measurement that comes off of the CDCS discharge 3 line. But the detail on the instrumentation is part 4 of the design.
5 MEMBER MARCH-LEUBA: So it is the PSS, 6 right? Prime something system. And the only thing 7 that was in the drawings.
8 MR. INFANGER: It's a balanced plant 9 system. It's not interlaced.
10 MEMBER MARCH-LEUBA: Yes. Correct. Now 11 if that boron concentration, first, when you have a 12 tech spec that says your boron concentration has to 13 be, say, 2,000 for Mode 5. What do you mean?
14 Do you mean the boron concentration in the 15 core or the downcomer? What does a tech spec mean 16 when it says your boron concentration must be 2,000?
17 MR. INFANGER: Okay. Well --
18 MEMBER MARCH-LEUBA: Okay, while you think 19 about that, you obviously cannot mention the boron 20 solution. This boron system, the boron instrument 21 samples off the CDCS let down line. At what elevation 22 does that let down line come into the vessel? And 23 specifically, is it above or below the water level?
24 MR. INFANGER: It would depend on the, on 25 the level --
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106 1 MEMBER MARCH-LEUBA: If you get there and 2 your goal --
3 MR. INFANGER: All right. Well --
4 MEMBER MARCH-LEUBA: Your arteries are 5 open and you're cold. What I'm going to is, I don't 6 believe the design you're sending for certification 7 has a boron measurement system that you can rely on 8 under these conditions, or at least I haven't seen an 9 analysis that shows it. And that's not efficiency.
10 MR. INFANGER: Right.
11 MEMBER MARCH-LEUBA: I mean we are 12 certifying that instrumentation. And we will want to, 13 so but I think we've established that whenever we take 14 readings for operator procedures, set points, tech 15 specs, if the instrumentation doesn't work, you 16 haven't thought very carefully how to do it. However, 17 I'm out.
18 MR. INFANGER: Okay. Thank you. We will 19 --
20 MR. MELTON: This is Mike Melton. We will 21 defer those questions. We have thought carefully 22 about everything. And we should be able to address 23 that later after the staff makes their presentations.
24 MEMBER MARCH-LEUBA: Eagerly await them.
25 MR. MELTON: Okay.
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107 1 MR. INFANGER: The next slide is slide 2 eight. Finishing up on the LOCA topical report, the 3 staff had requested additional information about the 4 ECCS actuation on low pressure. The LOCA topical was, 5 the sample calculations were completed before we added 6 the low RCS pressure ECCS actuation. And so we added 7 information to state that the existing calculations 8 were still conservative.
9 That the -- there would be some scenarios 10 where you would get an earlier ECCS actuation than was 11 done in these LOCA calculations. But the results have 12 been conservative results, because used for MCHFRN for 13 the last liquid level above the top of that fuel.
14 Most steam spaced breaks will go on the 15 new RCS pressure, low pressure ECCS actuation. And 16 some liquid space breaks. So we added that 17 information to the topical report to -- and stated 18 that it would be information in the topical report, 19 still demonstrated that the methodology was 20 conservative and balanced.
21 We also added descriptions of the ECCS 22 actuation signal interlocks. The -- again, since the 23 topical report was developed before the new signal, no 24 RCS pressure was added, that is new information. But 25 we also added the interlocks associated with the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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108 1 existing containment level of ECCS actuation for 2 consistency.
3 And a description of what the interlocks 4 are there for. And those are to prevent ECCS 5 actuation for non-LOCA events and expected operational 6 conditions. So you don't want ECCS going off on --
7 for non-LOCA events or during other planned reactor 8 operational scenarios.
9 We also added a discussion of the function 10 and impact of the riser holes too this topical. And 11 the main conclusion on that was that the analyzed flow 12 range remained the same, the minimum and maximum 13 remained the same even with the riser holes.
14 And slide nine. So that's -- up to slide 15 eight, that describes what we changed since our -- the 16 submittal we had. Right before June, I believe it was 17 on May 20th, we had submitted an update to the DCA and 18 topical reports.
19 And then since then, the changes that 20 we've made were the ones I just described. So those 21 were new since the last presentation we made to the 22 ACRS. So the other topic we wanted to address in this 23 public presentation was an issue that came up that was 24 still in development when we are making the last 25 presentation. So we didn't have the information to NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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109 1 present.
2 And that was on the General Design 3 Criteria 33. And what GDC-33 does is it has a 4 requirement that the rev coolant makeup system is 5 available to mitigate small RCS breaks with or without 6 AC power.
7 And NuScale had already submitted with the 8 initial application, an exemption to GDC-33. And 9 primarily because the MPM design does not require 10 additional coolant to maintain adequate core cooling 11 for the duration of design basis events. So we didn't 12 need a makeup system to handle leaks. Because leaks 13 go into the containment and the containment, fluid in 14 the containment is available during ECCS actuation.
15 So you don't actually lose the coolant, so 16 there was no need for makeup. So as such, the 17 chemical and volume control system, make up system, 18 the system itself and the backup power are not safety 19 related. It's not required. But one of the things 20 that was missing from the initial application really 21 is we did have just some description of the exemption.
22 But we didn't discuss now we actually met the intent 23 of GDC-33, and that's with the ECCS system.
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110 1 as any leak greater than the makeup system capacity.
2 And it also actuates for most smaller leaks. And then 3 depending on pool temperature down to, you know, 4 almost single digit amounts of leaks.
5 And then we did an analysis that was for 6 smaller leaks, we still meet staff goals without 7 needing to provide any makeup.
8 So slide ten. We've enhanced the basis 9 for our GDC-33 exemption. As said, the original 10 revision four of the DCA only had information in 11 Section 9 of the DCA, which is -- because that's where 12 the acceptance criteria for most plants on the makeup 13 system would be, in Section 9.3.
14 And since we didn't have -- since we 15 didn't have -- since we just, in that section we just 16 said that we didn't need a make up system to meet the 17 GDC, it was not applicable to the MPM design. And 18 then we didn't credit CVCS. But we didn't have 19 information to support how we did meet the GDC, or at 20 least the intent of the GDC, because we did request an 21 exemption from it, because the wording does 22 specifically call out make up systems.
23 So we added information to the SR 4.3 24 basically saying that small leaks with now ECCS, the 25 boron mixturing is maintained by riser holes until the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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111 1 holes are uncovered. And the core concentration 2 remains above the initial boron concentration for 72 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.
4 So that information is in with the core 5 description in SR 4.3. And then in Section 6.3 for 6 ECCS, we added information that the ECCS actuation on 7 the set points, or on the 24-hour timer prevents that 8 lose AC power, mitigates most leaks.
9 And then we evaluated and showed that 10 smaller leaks, that with really cold pool temperatures 11 down around the low tech spec limit, they won't get 12 automatic actuation of ECCS in 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. But that 13 they don't challenge SAFDLs, and no credit is needed 14 for the CDCS make up system.
15 MEMBER MARCH-LEUBA: Paul, when we're 16 talking about Chapter 6, I don't have it in front of 17 me right now, but I'll paraphrase it. The main thing 18 that it says, on boron and downcomer degradation is 19 prevented after ECCS actuates. And it appears several 20 times, the after ECCS actuates.
21 What you mean is that you have 22 demonstrated that it doesn't de-borate up to the point 23 of ECCS actuation. But we have established that after 24 ECCS actuation, it will de-borate.
25 So if we are going to issue a final NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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112 1 version, it would be nice to fix that section says 2 what you really mean. Which is instead of after ECCS 3 actuation, you mean up to the point of ECCS actuation, 4 because that's what you demonstrate.
5 MR. INFANGER: I think we need to address 6 that in the closed session.
7 MEMBER MARCH-LEUBA: This is just that.
8 Okay. We will, but I'll bring it up again.
9 MR. INFANGER: All right.
10 MEMBER KIRCHNER: Yeah, Paul. This is 11 Walt Kirchner again. Yeah, on your second major 12 bullet, there's two sub-bullets. This is of much 13 interest for us. So we expect that we'll get to hear 14 the calculational evidence to support the two 15 statements there.
16 I would just note that yes, of course the 17 core concentration remains above the initial 18 concentration. That's not the issue. The issue is, 19 what is the downcomer and lower plenum concentration?
20 Because any perturbation would then allow the 21 possibility of that lower boron concentration to enter 22 the core.
23 And that is the main concern. Not that 24 the core concentration remains above the initial 25 concentration. That's not a good metric. That's not NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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113 1 a good figure of merit in this case. That's not the 2 concern.
3 So what it says there is good and correct.
4 But there should be a third sub-bullet that says and 5 the, the dilution of the downcomer and lower plenum 6 does not raise the possibility of a reactive, 7 insertion of reactivity on any upset.
8 And the upset could be any kind of 9 perturbation on the system. Again, you've got two 10 free surfaces here once you've got these conditions.
11 And there are, you know, the operator could turn on 12 the CVCS system to extract water; that's a 13 perturbation. He could, or she could initiate spray.
14 There are a number of things that could 15 perturb the status quo. So what is of most concern 16 is: what's the concentration profile on the downcomer 17 and the lower plenum in terms of boron?
18 Not just that the core remains. Probably 19 the core, if there's no perturbations, the core will 20 just have higher and higher boron concentration. End 21 of statement. But we would like to explore that in 22 the closed session. Maybe that's a hint to the staff.
23 MR. INFANGER: Okay. And that was 24 evaluated by the staff. So we will direct to that.
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114 1 the end of the information about the GDC-33. So the 2 next slide is just, slide 11 is just the summary and 3 conclusions. And that the statement of the design 4 changes preclude boron redistribution for possible 5 design basis and beyond design basis events.
6 ECCS actuation and low RCS pressure are 7 high containment level. It shows the initial flow was 8 out of the reactor pressure vessel into containment.
9 And it precludes the influx of un-borated water from 10 containment or downcomer. So your initial flow is 11 going to be out. You're going to get mixing. And 12 then the flow is going to be slowly back in.
13 The riser holes that show boron mixing in 14 the downcomer and core region and for DHRS events, as 15 it cools and shrinks, the RCS level above the riser 16 does not shrink down below where the riser holes are.
17 And the holes remain, the mixing of boron 18 concentration are like a little mini flow between the 19 riser and the downcomer and core.
20 For the smaller LOCAs and RCS leaks, while 21 the holes continue to be mixing, while the RCS level 22 is above the holes. And they ensure that the core 23 concentration remains above the initial concentration.
24 And then we provided additional basis in 25 Chapter 4 and Chapter 6 for our justification for our NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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115 1 exemption to GDC-33. And explained how we met the 2 intent of GDC-33 using the ECCS system.
3 And that the riser holes support the boron 4 mixing. And there was no reliance on CDCS make up or 5 operator action. And that SAFDLs continue to be met 6 for all RCS leaks.
7 MEMBER MARCH-LEUBA: I need to say 8 something, because this slide shows a clear bias or 9 lack of attention to detail. Okay. First bullet, 10 design changes preclude boron released solution for 11 postulating design basis and beyond design basis 12 events. Okay.
13 If you have an ECCS actuation, is that a 14 design basis event? Because of a small LOCA for 15 example?
16 MR. INFANGER: No.
17 MEMBER MARCH-LEUBA: Okay. Does the 18 design change preclude boron redistribution in that 19 case? Does the downcomer go into de-borate after you 20 open the ECCS pump? So that statement is false.
21 MR. INFANGER: The analysis we've done 22 shows that we do not have unacceptable reactivity 23 events from those scenarios.
24 MEMBER MARCH-LEUBA: But you don't have to 25 do an analysis. Once you open the ECCS valves, you NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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116 1 are draining on the downcomer and the containment 2 either from the water containment or from the steam 3 generators. You're draining the steam water.
4 As I say, I don't know if it's going to 5 take 10, 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />, 1,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />. But it -- the boron 6 redistributing is beyond a shadow of a doubt. There 7 is nothing you can do that will convince me that you 8 don't release steam water. And admit you will end up 9 with a completely de-borated containment and 10 downcomer.
11 So that statement flies --
12 MR. INFANGER: No. But that water cannot 13 get into the core. There just is no mechanism. And 14 that's what our analysis shows.
15 MEMBER MARCH-LEUBA: That's not what you 16 say. That -- that number one, that's not what you say 17 in this slide. Number two, I have seen no evidence to 18 support your statement yet. Provide me with some.
19 MR. INFANGER: We provided that 20 information -- we provided that information to the 21 staff. And they will be discussing --
22 MEMBER MARCH-LEUBA: I haven't seen it.
23 MR. INFANGER: -- how that's met. And 24 then we will answer questions at that time in the 25 closed session.
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117 1 MEMBER MARCH-LEUBA: All right. Now on 2 the other bullet, which says riser holes assure boron 3 mixing in downcomer and core region and then go to the 4 first bullet. To assure core concentration remains 5 above initial concentration, if anything the presence 6 of riser holes will reduce the core concentration, 7 because some boron will leak to the downcomer.
8 So it has nothing to do with --
9 MR. INFANGER: You're talking about the 10 concentration that when you're operating the power 11 plant, you have a certain boron concentration. From 12 that point on, the ECCS will concentrate boron in the 13 core. And then you will -- even if these events --
14 MEMBER MARCH-LEUBA: ECCS won't 15 concentrate boron in the core. The boron in the core 16 will be concentrated by boiling.
17 MEMBER KIRCHNER: It's boiling is the 18 phenomena that concentrates the core.
19 MEMBER MARCH-LEUBA: That is right.
20 MEMBER KIRCHNER: I think that --
21 MR. INFANGER: Right. It evaporates.
22 MEMBER MARCH-LEUBA: Okay. I'm just 23 really -- but it looks a lot like there is lack of 24 attention or detail. It's as if you don't understand 25 the process.
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118 1 I mean it doesn't seem like it. And I'm 2 sorry to say that, but when I see these statements 3 that are false on the face, it shows that you guys 4 don't understand the problem. That is what the 5 impression I get. Because you're making incorrect 6 statements that are false on the face. I mean they're 7 not.
8 So let's go on now.
9 MEMBER KIRCHNER: Paul, maybe I can help.
10 I think the word here that is troublesome for Jose and 11 me, is design changes preclude. I think they 12 mitigate. But they don't preclude boron 13 redistribution. The boron is going to redistribute 14 when you have a LOCA event, any of these events.
15 You're going to get concentration in the 16 hot part of the reactor pressure vessel, i.e., the 17 core, probably the riser. Hopefully it's also mixing 18 down in the lower plenum. I haven't heard anything 19 about that.
20 The holes don't do it. The holes realize, 21 as Jose actually points out, will diminish the 22 concentration. But this is a good thing, because what 23 you want is to prevent an accumulation of distilled 24 water in the downcomer. That's why the holes are 25 there.
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119 1 So to support Jose's point, I think the 2 choice of words here are perhaps not what you intend.
3 I think the design changes mitigate the boron dilution 4 like events.
5 But the boron is going to redistribute in 6 the system. That will be a -- as soon as you're in 7 the down -- as soon as the riser is uncovered, it's 8 going to then result in boron concentration gradients.
9 That's not in and of itself a bad thing.
10 It's the extended dilution of the downcomer that has 11 -- is of most concern. So your holes there aren't 12 precluding boron redistribution. They're actually 13 doing a positive contribution to minimizing the 14 dilution of the downcomer.
15 And it begs the question about the 16 elevation of the holes. And we can explore that in 17 the closed session for some of the transients which 18 you already indicate there are transients where the 19 holes are uncovered.
20 MR. INFANGER: Yeah. Boron redistribution 21 will occur. But it precludes an unacceptable boron 22 redistribution. And that was the intent.
23 MEMBER KIRCHNER: Yeah, okay.
24 MEMBER BLEY: Walt, this is Dennis.
25 MEMBER KIRCHNER: Yes, Dennis?
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120 1 MEMBER BLEY: I'd like to get a comment on 2 the table before we leave --
3 MEMBER KIRCHNER: Go ahead.
4 MEMBER BLEY: -- this session. And it's 5 in support of Jose and a little bit Matt, I want to 6 challenge what you said earlier.
7 Although operators will follow their 8 procedures most likely, there's a whole host of 9 operating events however that point out there are 10 conditions under which it's difficult for the 11 operators to do what we would hope they'd do.
12 As Jose points out, we don't have anywhere 13 right now in the FSAR or in the operational chapters 14 that point out there could be a long term boron 15 dilution problem in the downcomer under certain 16 conditions.
17 Without such a condition being identified 18 here, some years from now, when the procedures are 19 actually written, or we actually have operators, they 20 don't have a low boron distribution in the downcomer 21 alarm, or even an obvious measurement at this time.
22 And I think for me to be happy with this 23 design cert at this point on this issue, there needs 24 to be a condition or something added into the FSAR 25 that clearly points out that this has to be considered NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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121 1 very carefully when developing the procedures.
2 And this could drop off the table by that 3 time. And operators aren't real good in responding to 4 things that they haven't really thought about or 5 worked on, and have to diagnose on the fly, sometimes 6 without much help.
7 They might be sitting here and looking at, 8 my God, how did this happen? Uh oh, now we figure it 9 out. So I think without some form of --
10 MR. INFANGER: We did -- so we did enter 11 that -- we did add that information into the FSAR.
12 Chapter 4 and Chapter 15 both have detailed 13 descriptions about the potential to have un-borated 14 water in the containment and the downcomer.
15 And Chapter 13 requires procedures that 16 will address all of those operating conditions. So 17 all of that information is in there.
18 MEMBER MARCH-LEUBA: Oh come on. Come on.
19 It's a phrase opinion at the bottom of a paragraph.
20 At the bottom of a section.
21 MEMBER BLEY: I certainly agree on that, 22 Jose.
23 MR. INFANGER: If it's required that -- so 24 for Reg Guide 1.126 that you -- all procedures 25 described in the FSAR are implemented into plant NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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122 1 operating procedures. So it's -- there is, you know, 2 a regulatory flow path there that requires all of this 3 information to be in the plant procedures.
4 MEMBER MARCH-LEUBA: I've waited for you 5 guys to show me the first --
6 MR. INFANGER: It's only in the --
7 MEMBER BLEY: How did you not -- and how 8 did that slip through the process? We had a rule that 9 said you ought to catch it.
10 MEMBER MARCH-LEUBA: Yeah. Yeah, but I 11 got away from the decision. You guys can show me the 12 calculations.
13 MR. INFANGER: So I'd like to remind the 14 ACRS that we --
15 MEMBER KIRCHNER: May I intervene here for 16 a moment? Thank you, Dennis. I think Rebecca Norris 17 is pointing to me that Ben would like to make a 18 comment. Let's let Ben, if we can unmute his mic. Go 19 ahead Ben.
20 MR. BRISTOL: Yeah. Can you hear me?
21 MEMBER KIRCHNER: A little louder, please.
22 MR. BRISTOL: This is Ben Bristol with 23 NuScale engineering. Can you hear me?
24 MEMBER KIRCHNER: Yes. Go ahead Ben.
25 MEMBER MARCH-LEUBA: Yes.
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123 1 MR. BRISTOL: Okay. Yeah, I would like to 2 remind the Committee that we spent quite a bit of time 3 in March explicitly discussing the analysis that went 4 into ECCS mode cooling, boron redistribution issues, 5 and their potential for a safety concern from a 6 Chapter 15 perspective.
7 And we included some discussion of what 8 potential recovery actions could occur, to demonstrate 9 that the systems were -- that we have in the design 10 were sufficient to allow for safe recovery from those 11 conditions.
12 What was brought up in the June meeting 13 was the specific concern about an inadvertent ECCS 14 actuation. And as Paul mentioned, we have -- we 15 spent some time discussing that. We went back and 16 spent and have done analysis of it. And if it would 17 be useful, after the staff has finished their 18 presentation tomorrow, we can certainly get into the 19 details of our analysis of that.
20 But I've been a little confused with the 21 conversation, the way the conversation has gone. And 22 the assertion that NuScale hasn't provided analysis 23 and hasn't performed analysis.
24 We've spent two years working with the 25 staff on the analysis of boron redistribution during NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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124 1 ECCS cooling. And have acknowledged that boron 2 accumulation in the core is good for reactivity and 3 hold down.
4 We understand that boron solution in the 5 downcomer, if it could sink to the core, would be of 6 concern. And that, we've spent a lot of time looking 7 at and evaluating and ensuring that doesn't exist.
8 MEMBER MARCH-LEUBA: Yes. But you spent 9 two years studying the boron redistribution and did 10 all the beautiful calculations with moving from the 11 reds to blue and all that. And failed to define the 12 uncontrolled cooling in passive mode. Which turned 13 out to be an air hole.
14 And it had likely done core damage with a 15 very high frequency is what I understood from NRC. So 16 you just, you spent two years working on it. But you 17 failed to identify the most important event that could 18 happen in NuScale, and we have fixed it now.
19 So when you tell me that we've been 20 looking at it, and I'm telling you, well, where did 21 you, you can see here is what happens. I would like 22 to see those analyses. Because if you spent two years 23 doing it, then define it.
24 MR. BRISTOL: Okay. So just to clarify, 25 we spent -- we understood that ECCS phenomenologically NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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125 1 and that the way the boiling and condensing works, is 2 a method for boron redistribution.
3 The NRC asked us about that several years 4 ago. And we've spent a great deal of time quantifying 5 what occurs when boron could be, and there are some 6 simplifications that go into that analysis.
7 What we -- what we identified back in 8 March was the specific concern prior to ECCS actuation 9 that boron redistribution in the riser and downcomer, 10 if the riser were to uncover, could result in core and 11 surge events that need to be precluded.
12 And we spent some time in June explaining 13 to the ACRS how the design changes have fixed that 14 issue. But the issue of boron transport and 15 redistribution and the analysis of it had already been 16 presented to the ACRS back in March.
17 And we spent some -- a great deal of time 18 reviewing that with the staff to ensure that there is 19 no safety concerns, no safety issues for ECCS cooling 20 mode.
21 MEMBER KIRCHNER: Ben, this is Walt. Yes, 22 we acknowledge we heard and received the presentations 23 on boron redistribution. The issue here is the boron 24 dilution set of events that is of concern.
25 And you have correctly stated that after NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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126 1 your corrective action, I may not be using the right 2 terminology, that you looked at this and made the 3 design changes. That's the holes in the risers, you 4 changed set points, and so on.
5 So I think what we're looking for in the 6 closed session, is again, the confirmation that in the 7 event where we get shrinkage and/or redistribution 8 such that we're now below the riser holes, within as 9 I said in my opening comments, within a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 10 envelope, do you de-borate the downcomer such that you 11 could have the possibility or potential for a 12 reactivity insertion event and consequences? And 13 that, I think, right now, is what we're looking for.
14 And second, we can't leave the --
15 notwithstanding that you're going to develop operating 16 procedures and such, we have to be convinced of, based 17 on physics, that for example, reactivation of the CVCS 18 system doesn't -- you're not sitting at a cliff, and 19 then all of the sudden the operator operates one of 20 these systems, either in a letdown mode, or a makeup 21 mode, or a spray mode, or a containment drain and fill 22 system, that it doesn't trigger an upset in the system 23 that inserts diluted water into the core.
24 And the analysis to back that up. That's, 25 I think, as succinctly as I can state it. And then NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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127 1 again, you can't have a design where it's at a cliff 2 state. So I would expect that you would put in tech 3 specs at 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, or whatever time, based on your 4 analysis, that the operator intervenes and does such 5 and such.
6 Because you haven't gotten to the end of 7 the Chapter 15 analysis if the downcomer is sitting 8 there with a de-borated condition.
9 MR. BRISTOL: I'll repeat. That analysis 10 was provided to the ACRS and presented in March. The 11 accumulation of the boron redistribution presentation 12 that we presented in March includes the calculation of 13 the rate at which the core accumulates boron and the 14 downcomer dilutes boron.
15 And we evaluated the safety concerns of 16 that condition. And presented that analysis in March.
17 And the staff presented their findings in March.
18 MEMBER KIRCHNER: Okay. We will explore 19 this with the staff. Members, are there other 20 questions of NuScale at this point?
21 (No audible response.)
22 MEMBER KIRCHNER: Using the 15 second rule 23 at this point then, Mike Snodderly just help me here.
24 MR. SNODDERLY: Yes. Yes, sir.
25 MEMBER KIRCHNER: Are we going to have --
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128 1 MR. SNODDERLY: Yes.
2 MEMBER KIRCHNER: We're going to have a 3 public presentation from the staff. Is that correct?
4 MR. SNODDERLY: That is correct. And I 5 would like to request that Marieliz Johnson share her 6 screen.
7 She will be the presenter for the staff.
8 And if we can get started. Thank you.
9 CHAIR SUNSERI: Walt, this is Matt. While 10 we're doing this transition, I want to take a 10 11 minute break.
12 We've been at this for an hour and 15 13 minutes. It's after lunch. We need to take a 10 14 minute break.
15 MEMBER KIRCHNER: Thank you, Matt. Well 16 let's say we'll re --
17 CHAIR SUNSERI: Let's make it -- we'll 18 reconvene at a quarter after the hour. 3:15 we'll 19 reconvene.
20 MEMBER KIRCHNER: Okay. Thank you.
21 MR. SNODDERLY: And thank you, Marieliz.
22 And we'll yes, see you guys at 3:15. And we'll start 23 with Marieliz Johnson from the staff. And also I 24 believe Anna was going to make an opening statement 25 for the staff, Chairman Sunseri.
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129 1 CHAIR SUNSERI: Understood.
2 (Whereupon, the above-entitled matter 3 went off the record at 3:04 p.m. and resumed at 3:15 4 p.m.)
5 CHAIR SUNSERI: Okay, this is Matt 6 Sunseri, I have 3:15. We will reconvene with a roll 7 call of the Members. Ron Ballinger?
8 MEMBER BALLINGER: Here.
9 CHAIR SUNSERI: Dennis Bley?
10 MEMBER BLEY: Here.
11 CHAIR SUNSERI: Vesna Dimitrijevic? Walt 12 Kirchner?
13 MEMBER KIRCHNER: Here.
14 MEMBER DIMITRIJEVIC: Yes, I'm here sorry.
15 I did not mute the button. I'm here.
16 CHAIR SUNSERI: Yes no, that's okay. I 17 have that problem myself. Jose March-Leuba?
18 MEMBER MARCH-LEUBA: Yes, I'm here.
19 CHAIR SUNSERI: Dave Petti? Dave Petti, 20 are you trying to -- Joy Rempe?
21 VICE CHAIR REMPE: Here.
22 CHAIR SUNSERI: Pete Riccardella?
23 MEMBER RICCARDELLA: Here.
24 CHAIR SUNSERI: And myself. So we're just 25 missing Dave. It sounds like he might be having a mic NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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130 1 problem.
2 So we have a quorum, we can continue.
3 Walt, I think the Staff had some introductory remarks 4 they wanted to --
5 MEMBER KIRCHNER: Yes, I believe so.
6 Would this be Anna Bradford? Who from the Staff is 7 going to start?
8 MS. BRADFORD: Yes, thank you. This is 9 Anna Bradford.
10 MEMBER KIRCHNER: Thank you. Go ahead, 11 Anna.
12 MS. BRADFORD: Good afternoon. As 13 mentioned, my name is Anna Bradford. I'm the director 14 of the Division of New and Renewed Licenses in the 15 Office of Nuclear Reactor Regulation.
16 I'd like to thank the Committee, as well 17 as the ACRS Staff, for the opportunity to come before 18 you today. And I'd also like to thank our technical 19 project staff that have worked very diligently on the 20 issues that will be discussed. And that have already 21 had some interesting discussions.
22 In February 2020, NuScale identified a 23 design issue associated with its boron redistribution 24 analysis that required substantive design changes in 25 order to demonstrate that the regulations were met.
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131 1 And as result, we initiated an audit on March 4th.
2 NuScale submitted their final design changes on May 3 20th and the Staff completed our audit on June 26th.
4 Over the course of the last several months 5 the Staff has reviewed some very complex NuScale 6 related design changes, which affected 11 design 7 certification application chapters, five technical 8 reports and two topical reports.
9 Today we're prepared to present our 10 findings to the Committee. I believe that the Staff's 11 presentational highlight our continuous focus on 12 safety significance and supporting the NRC's mission 13 to protect public health, safety and the environment.
14 And as you heard earlier, I would also 15 like to note that we have recently received a 16 differing view from a staff member that will be 17 discussed during the closed session.
18 So thank you again for this opportunity, 19 we look forward to the interaction with all of you 20 today. And with that, I'll turn it back over to 21 Marieliz.
22 MS. JOHNSON: Good afternoon. Marieliz 23 Johnson. Today we're going to present a focused area, 24 boron redistribution and the applicable design changes 25 of the NuScale design application.
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132 1 For the agenda we're going to present the 2 NRC Staff review team, background, design changes, 3 discussion by review team and the conclusions. In the 4 next several slides you'll see the Staff, the review 5 team.
6 A quick background. As Anna mentioned, in 7 February NuScale modified NRC Staff about, of an error 8 of the boron redistribution analysis and informed that 9 they are following the corrective action program.
10 The Staff started an audit in March 4th 11 with a scheduled letter on May 1st. On May 20 NuScale 12 submitted their final design changes document. On 13 June 3rd the Staff presented the audit status to the 14 ACRS Members. And on June 26th we exited the audit.
15 The three design changes are the ECCS 16 actuation on high containment water levels at point 17 change, new ECCS actuation on low RCS pressure signal 18 and addition of the riser holes.
19 Here you see the 11 chapters that were 20 affected by the change. And the technical and topical 21 reports.
22 Mike, do you have anything to add? Mike 23 Dudek?
24 MR. DUDEK: I do. Can you hear me?
25 MS. JOHNSON: Yes.
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133 1 MR. DUDEK: Okay. So --
2 MEMBER KIRCHNER: Yes, Mike, we can hear 3 you.
4 MR. DUDEK: OGC has reviewed and approved 5 seven of the ten chapters that experienced the design 6 change. We are still working towards three chapters 7 going through OGC. Those three chapters would be 8 Chapter 6, Chapter 15 and Chapter 19.
9 We hope to have those OGC concurrences and 10 legal, non-legal objections soon. And assuredly we 11 aim to have them by the next ACRS date of July 21st.
12 Thanks.
13 MS. JOHNSON: Now I'm going to turn it 14 over to Yuken Wong so we can start the Staff 15 presentation.
16 MR. WONG: Can you hear me?
17 MEMBER KIRCHNER: Yes. Go ahead, Yuken.
18 MR. WONG: Okay. My name is Yuken Wong 19 from the mechanical engineering and in-serve testing 20 branch. The NRC Staff, with the assistance from Dr.
21 Stephen Hambric revealed the structural integrity and 22 flow induced vibration effects related to the new 23 riser holes.
24 The four riser holes are small compared to 25 the riser. And the structure properties of the riser NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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134 1 are not affected significantly.
2 The alternating stress due to the 3 turbulent baffling is very slow. Even with a stress 4 concentration due to the riser holes. The alternating 5 stress will not approach the material critic limit.
6 NuScale calculated the discharging jet 7 loads from the riser holes. And these loads are more 8 than an order of magnitude, lower than the lows 9 already considered in the steam generator tube 10 analysis.
11 So the jet loads from the rider holes will 12 not significantly affect the steam generator tubes.
13 The riser holes will not cause state 14 residences. There is constant flow through the riser 15 holes. And the flow eliminates the possibility of a 16 shear layer flow instabilities.
17 In case the flow cannot suppress the flow 18 instabilities, NuScale calculated the flow instability 19 frequencies and the riser acoustic frequencies. These 20 frequencies are well separated.
21 The Staff ordered the NuScale calculations 22 and found that NuScale adequately addressed the riser 23 structure integrity and potential flow induced by 24 bringing the gaps of the riser holes.
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135 1 interrupt you for a moment?
2 When you say flow instability, you mean a 3 density wave instability in the current riser?
4 MR. WONG: No. This is the shield layer 5 instability.
6 MEMBER MARCH-LEUBA: Okay. So it's a LOCA 7 instability, okay.
8 MR. WONG: Correct. Okay, I'm going to 9 turn over the presentation to Tom Scarborough.
10 MR. SCARBOROUGH: It tells me now I'm no 11 longer muted, so I don't know if you've heard anything 12 I've said so far.
13 So, let me start over. So --
14 MEMBER KIRCHNER: Could you start from the 15 beginning please?
16 MR. SCARBOROUGH: I sure will. Thank you.
17 Sorry about that. I don't know why it took so long to 18 unmute me.
19 Okay. Okay, this slide has to do with the 20 main valve itself opening.
21 MEMBER KIRCHNER: Hold on. Stop. Would 22 you just identify yourself for the court reporter?
23 MR. SCARBOROUGH: Oh, I'm sorry. This is 24 Tom Scarborough in the mechanical engineering branch.
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136 1 apologies. Go ahead.
2 MR. SCARBOROUGH: No problem. No problem.
3 Okay, so early in the audit process NuScale indicated 4 that they might rely on the ECCS main valve self-5 opening at low differential pressure.
6 So we looked at that as part of the audit 7 process. So, the self-opening of the emergency core 8 cooling system main valve was part of the initial 9 group of concept testing of the valve system at the 10 Target Rock Facility with pressurized ambient water in 11 2015.
12 There were several tests at that time that 13 demonstrated that the main valve spring could open the 14 ECCS main valve under a narrow range of very low 15 differential pressure conditions. Now, the specific 16 differential pressure conditions is proprietary, and 17 we can get into more of that in the closed session if 18 you like.
19 So the Staff looked at that. And in 10 20 CFR 50.43(e), that requires that the new reactor 21 design features be demonstrated by testing or a test 22 based analysis.
23 So, the Staff reviewed that Target Rock 24 test report and determined that based on the 25 repeatability of the test that the report provided a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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137 1 reasonable demonstration that the ECCS main valve 2 spring will reliably open the main valve at very low 3 differential pressure conditions would satisfy 10 CFR 4 50.43(e). So, that's where we go with that.
5 Now, we did look at the main valve spring 6 itself. Now, the main valve spring is designed 7 manufactured safety related component, but the 8 function itself is not considered by NuScale to be 9 safety related.
10 However, the Staff considers it to be 11 important to safety because of its assumed performance 12 to open the main valve at low differential pressure 13 conditions.
14 So we looked at the design specifications.
15 They specify the function of the main valve spring for 16 low differential pressure operation, so therefore that 17 function will be tested as part of the qualification 18 program under ASME Standard QME-1-2007. As accepted 19 in Revision 3, Reg Guide 1.100. So it will be covered 20 by the design specifications.
21 Now also in the NuScale FAR in Section 22 3.9.6, it does specify that the performance assessment 23 testing of the ECCS valve system will include testing 24 to verify that the main valve will open at low 25 differential pressure as either part of the shutdown NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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138 1 process or a specific testing activity.
2 So based on that the Staff was comfortable 3 with the self-opening capability of the main valve 4 with that spring that's installed in the main valve.
5 And that --
6 MEMBER BLEY: Tom?
7 MR. SCARBOROUGH: -- completes my 8 presentation. Yes, sir.
9 MEMBER BLEY: This is Dennis Bley. My 10 understanding from previous meetings was that function 11 has already been tested. Is this further testing 12 you're talking about?
13 MR. SCARBOROUGH: Yes, actually, the ECCS 14 valve system testing that was conducted at Target Rock 15 after the initial testing, we did look at the initial 16 testing back in the 2018 time frame.
17 And the testing of the whole system 18 itself, under the initial proof of contact testing, we 19 did not consider that to be sufficient to satisfy 20 50.43(e). Because it focused on ambient water 21 pressurized, it did not have high temperature water 22 condition.
23 So from an overall performance of the ECCS 24 valve system, that initial proof concept testing was 25 not sufficient for a 50.43(e) demonstration. Because NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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139 1 you didn't have any flashing, you didn't have the 2 sharp changes in differential pressure that would 3 occur under the operation of the ECCS valve system.
4 So NuScale conducted additional testing, 5 in response to our questions, to demonstrate that 6 50.43(e) was satisfied using high pressure, high 7 temperature water, and borated water, to show that it 8 would operate properly.
9 Now, this goes back, the 2015 testing goes 10 back to the ambient pressurized water, where here it's 11 a much more simpler operation. You're just showing 12 that under the conditions of the main valve itself 13 that the small spring installed in the main valve 14 would open the main valve at very low differential 15 pressures. And do a repeatability.
16 And that's what they showed in that 17 initial proof of concept testing back in 2015. So 18 based on that we went back in time, like they had done 19 initially. And that initial testing we considered to 20 be sufficient to satisfy 50.43(e) for design 21 certification.
22 Now of course, they still have to conduct 23 design specification qualification testing, which is 24 much more detailed, as part of QME-1. And they still 25 need to do that.
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140 1 But from a design certification 2 perspective, we considered that initial testing to be 3 sufficient.
4 MEMBER KIRCHNER: Tom, a question of 5 clarification. This is Walt Kirchner.
6 Since you point out in your third bullet 7 that the spring is important to safety, I am assuming 8 that the ECCS valves are safety related components.
9 MR. SCARBOROUGH: Yes, sir. They are 10 completely all safety related. And all the components 11 --
12 MEMBER KIRCHNER: So what is the 13 distinction you're trying to draw there?
14 MR. SCARBOROUGH: Oh. Because the 15 function of the spring, the function of that little 16 spring was not considered to be safety related by 17 NuScale. The function of that small spring.
18 But everything is designed and 19 manufactured, including the small spring, as safety 20 related components under Appendix B. They're all 21 qualified that way.
22 It was the function. We had this 23 distinction that NuScale had that the function of that 24 small spring was not considered to be safety related.
25 But the staff noted that it is called out in the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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141 1 designed specifications, therefore it will be tested 2 under QME-1 by the requirements of QME-1.
3 If it's in the design spec it is required 4 by QME-1 to be tested to be qualified. And so they 5 will be required to qualify that function of the 6 spring.
7 So we're making the distinction that we're 8 calling the function of that small spring to be 9 important to safety under Appendix A to Part 50. And 10 they still will need to be able to test it and quality 11 per QME-1.
12 MEMBER KIRCHNER: Okay, that may be a 13 conversation for the future but thank you. That 14 helps.
15 MR. SCARBOROUGH: Okay, thank you. Okay, 16 Marieliz, you can move on if there's no more 17 questions.
18 MR. TANEJA: So, Slide 12. This is Dinesh 19 Taneja from the I&C engineering branch.
20 The lowering of the set point for ECCS 21 actuation on the high containment water level, 22 affected Chapter 7 and the set point methodology 23 topical report.
24 This design change did not require any 25 changes to the containment vessel water level sensors.
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142 1 The revised analytical range of 240 inches to 264 2 inches is within the calibrated span of 100 inches.
3 That is from 220 inches to 320 inches.
4 The calculated total loop uncertainty is 5 bounded by the plus and minus 12 inch nominal set 6 point allowance that is assumed in all applicable 7 analyses. Changes made in Chapter 7 are consistent 8 with the assumption made in our applicable analyses.
9 Next slide please. So for the new ECCS 10 actuation and low RCS pressure signal, existing wide-11 end RCS pressure sensors are used.
12 The safety classification for the sensor 13 is being upgraded to A1. They used to be A2.
14 Changes made in Chapter 7 and Tier I 15 tables 2.5-2 and 2.5-4 are consistent with the 16 assumptions made in the applicable analyses.
17 Interlocks are provided to automatically 18 bypass ECCS actuation when T hot is less than 475 19 degrees Fahrenheit or when containment vessel pressure 20 is less than one psia.
21 Next slide please. Now I'm Slide 14. The 22 set point methodology technical report is revised to 23 demonstrate that the calculated total loop uncertainty 24 is bounded by the plus and minus 100 psia allowance 25 assumed in applicable analysis.
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143 1 The advanced sensor technical report has 2 also been revised to include the SFAS actuation 3 function for the wide-end RCS pressure sensors and the 4 related interlock functions.
5 Next slide please. Slide 15. Digital 6 based sensors are used for the wide-end RCS pressure 7 signals. Therefore, most could perform digital common 8 cause failure assessment to demonstrate coping with 9 the potential failure, potential failure mode of these 10 sensors.
11 The best estimate D3 coping analysis, 12 defense-in depth and diversity coping analysis, that 13 credits xenon reactivity and all rods end condition, 14 concluded that an earlier ECCS actuation, low RCS 15 pressure, would not be required for any break size or 16 location or LOCA break spectrum.
17 In these cases, ECCS actuation occurs due 18 to high containment level or low DP across the ECCS 19 valves. The Staff finds that sufficient diversity 20 exists such that ECCS is available to mitigate these 21 small break LOCA events.
22 This concludes my presentation. Any 23 questions?
24 MEMBER MARCH-LEUBA: Yes, Dinesh. I 25 apologize, this is Jose. I apologize in advance NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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144 1 because I know you don't know the answer to this 2 question, but I need to place the question because 3 you're the I&C guy.
4 MR. TANEJA: Okay.
5 MEMBER MARCH-LEUBA: For boron, de-6 boronization of the downcomer, especially after ECCS 7 actuation, carry has been taken at least orally, 8 because I cannot find much documentation on this, 9 carry has been taken from the boron concentration 10 instrumentation, the boron concentration 11 instrumentation, which will be used by the operator to 12 enforce tech specs and to perform whatever those magic 13 procedures the COL will come up with.
14 Now, this instrumentation we now know that 15 is samples from the CVCS recirculation line. So CVCS 16 must be running. It must be sucking water from the 17 letdown line. And then that water will be sampled by 18 the PSS and it will provide a concentration for the 19 boron. Which will work very well during normal 20 operation.
21 But what confidence does the I&C branch 22 have that this instrumentation will work for the 23 intended conditions?
24 And let me point you out that the CVCS 25 letdown line, I cannot find the saturation, but this NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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145 1 drawing show it 224 feet of the RB. So it's likely in 2 the steam space.
3 Even if it's not in the steam space, for 4 the recirculation to work CVCS has a centrifugal pump 5 that is rated 50 gpm and is rated for more than 2,000 6 psi of operation. But in these conditions you will 7 probably likely be super prosthetic and that pump will 8 likely cavitate.
9 So you can tell me, no, I don't know, but 10 my question is, what confidence does the NRC Staff has 11 that the instrumentation that is being created to 12 perform this operator action safely actually works?
13 MR. TANEJA: Okay. So in Chapter 7 space 14 we evaluated all the pulse accident monitoring 15 instrument, PAM instrumentation in accordance with --
16 MEMBER MARCH-LEUBA: No, this is the PSS.
17 The PSS, plant sampling system.
18 MR. TANEJA: Right, right. So, you know, 19 if the action, the credited operator action, it was 20 credited in Chapter 15 space to --
21 MEMBER MARCH-LEUBA: It's probably in the 22 Chapter 19 space.
23 MR. TANEJA: Okay. So if it's credited in 24 the Chapter 19 space then we did not evaluate it in 25 Chapter 7, we evaluate any potential operator action NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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146 1 that is credited in Chapter 15 space as part of the 2 PAM variables. Post action monitoring variables.
3 MEMBER MARCH-LEUBA: Yes.
4 MR. TANEJA: Which are documented in 5 Chapter 7. So for mitigating or dealing with any of 6 the events that are in Chapter 15 space, there are no 7 manual credited operator actions.
8 MEMBER MARCH-LEUBA: Right.
9 MR. TANEJA: So therefore the sensors are 10 the parameters that we evaluated. You know, this did 11 not fall into that category --
12 MEMBER MARCH-LEUBA: Yes, but if --
13 MR. TANEJA: -- so therefor we did not 14 need it to credit --
15 MEMBER KIRCHNER: Jose and Dinesh, this is 16 Walt Kirchner. If it's a LOCA, and NuScale can 17 correct me if I'm wrong, you'll get an isolation 18 signal for the containment. This will isolate the 19 CVCS line. You have no sample.
20 MEMBER MARCH-LEUBA: Yes, but you can 21 always exceed it to get it. I mean, even one more 22 reason why this doesn't work.
23 But even if the operator went to defeat 24 the isolation and establish recirculation, you can 25 because this is in the steam space.
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147 1 MR. TANEJA: Well, you know, so the design 2 basis event, you are correct that you are going to get 3 an automatic containment isolation, which will isolate 4 the sampling system.
5 And if you do need to take a sample, you 6 would have to procedurally, and override the isolation 7 signal to be able to access the sampling system to 8 take a sample. So it really did fall outside of the 9 DCA review in a boundary.
10 MEMBER MARCH-LEUBA: Now, is this is a 11 wholly now review process? Maybe we need to think 12 about it because if Chapter 19 takes credit for this 13 instrumentation, 19, there has to be some 14 specification that it works.
15 MEMBER DIMITRIJEVIC: Jose, this Chapter 16 19 doesn't take credit for this instrumentation. This 17 operator action is not in Chapter 19.
18 Operator action, about staffing CVS and 19 CVCS, which we've discussed before, they are totally 20 unconcerned about the bottom in this moment. So this 21 sequence, these actions are not put into the PRA. And 22 we will bring that up as soon as we come to the 23 Chapter 19.
24 MEMBER MARCH-LEUBA: Right. My point is, 25 to my knowledge, by reviewing all of the available, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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148 1 the limited available documentation that is limited, 2 that's available to me, I don't see any evaluation of 3 the risk imposed by this de-boronization. I don't 4 know --
5 MEMBER DIMITRIJEVIC: No, there is no.
6 there I no scenario, there is no sequence, there is 7 not any even discussion in Chapter 19 of this.
8 MEMBER MARCH-LEUBA: Right. Right. And 9 in my humble opinion it should. Because we found out, 10 we found out that the thing that the holes now solve, 11 which is the small break, this lower being, small 12 break LOCA, was the limiting core damage frequency by 13 many others among it.
14 So, I just --
15 MEMBER DIMITRIJEVIC: The Chapter 19 is 16 coming in the end of this presentation --
17 MEMBER MARCH-LEUBA: All right.
18 MEMBER DIMITRIJEVIC: -- so let's bring 19 this up again then.
20 MEMBER MARCH-LEUBA: All right. But this 21 was I&C. The I&C has, the Staff has not evaluated 22 whether the boron concentration instrumentation works.
23 It's available to the operator if they want to take 24 credit for it whenever they want to take credit for 25 it.
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149 1 Now --
2 MEMBER KIRCHNER: Jose? Jose, this is 3 Walt. In the current Chapter 15 scenarios they don't 4 take credit and they don't un-isolate to look at boron 5 concentration.
6 They have designed and analyzed and feel 7 that they, as Paul has presented, prevent this event.
8 In Chapter 15 space. So therefore there is no need 9 for an instrumentation and sampling line.
10 MEMBER MARCH-LEUBA: Being Chapter 15 11 space because you are --
12 MEMBER KIRCHNER: They're assuming that 13 there is no operator intervention --
14 MEMBER MARCH-LEUBA: Right.
15 MEMBER KIRCHNER: -- and that the design 16 of the system and the systems, like ECCS that they 17 rely on, actuation, are sufficient for their Chapter 18 15 scenarios.
19 MEMBER MARCH-LEUBA: Because customarily 20 in other reactors we stop that Chapter 15 analysis 21 when one reaches a safe and stable condition. Which 22 for most AOOs is one minute or less. Okay.
23 And you never ride certain quality, you're 24 on it for the first minute when you reach a safe and 25 stable condition, you stop. My argument is that a de-NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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150 1 borated lower plenum with 24 less or 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br />' worth 2 of positive activity, ready to get into the core at 3 the minimum perturbation, is not a safe and stable 4 condition.
5 MEMBER KIRCHNER: Yes. And you've stated 6 that. I think they have the point and we will, let's 7 explore that with the Staff when we get to Chapter 15.
8 MEMBER MARCH-LEUBA: Right. But we have 9 built a foundation to have significant doubts that 10 whenever NuScale wants to take credit for operator 11 actions, the operator will be blind. He won't know 12 where the boron is. Because the boron instrumentation 13 doesn't work.
14 And this is part of the CVA.
15 Instrumentation is part of the 75 design. Over and 16 out.
17 MR. TANEJA: Thank you.
18 MEMBER KIRCHNER: Dinesh, please continue.
19 MR. TANEJA: I'm done, unless there are 20 any additional questions. No other questions than 21 Slide 16 starts with Chapter 16.
22 MR. HARBUCK: Good afternoon, this is 23 Craig Harbuck of the technical specifications branch.
24 And I'll be presenting the effects on the technical 25 specifications by these design changes.
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151 1 The first one, regarding the lowering of 2 the set point for the high containment water level, 3 ECCS actuation, had no effect on the tech specs as the 4 set point for it is not explicitly stated being given 5 as required by the set point program in the set point 6 methodology.
7 And then for the new ECCS actuation on low 8 RCS pressure, we added a new function and renumbered 9 the subsequent functions. And in Table 331-1.
10 And for this new function we required four 11 operable channels, as for the other functions in the 12 table, for the most part, that are required to be 13 operable in Mode 1 and Mode 2 when RCS temperature, 14 hot temperature, is above 475 degrees Fahrenheit. And 15 that is the new T6 interlock.
16 And then we added a condition to go along 17 with this applicability so that if you were in default 18 actions you would exit that applicability.
19 The other interlock, P1, ensures that 20 unless the pressure, the containment goes above one 21 psia, this function would be blocked.
22 The existing surveillances for the MPS 23 instrumentation also apply to this function. And all 24 references for these functions and tech specs and 25 bases and additional explanatory information was added NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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152 1 to the bases to conform to these changes.
2 Regarding the addition of the riser hole 3 modification there was added material in the bases for 4 tech spec subsections 331 and 351. And this concludes 5 all the changes that are effective with technical 6 specifications and the bases.
7 MEMBER KIRCHNER: Members, any questions?
8 MS. JOHNSON: Alex Siwy?
9 MS. SIWY: Yeah, I was just waiting.
10 Fifteen second rule, right? This is Alex Siwy, and 11 I'm a technical reviewer in the reactor systems 12 branch. As described on Slide 17, one of the many 13 areas the reactor systems staff reviewed with respect 14 to the design changes is how the rise holes might 15 impact steady state RCS characteristics and DHRS 16 performance as described in Chapter 5.
17 Now the riser holes are relatively small, 18 so we initially suspected that any effects would also 19 be small. But to confirm that, the staff audited 20 NuScale sensitivity calculations for five non-LOCA 21 events that showed that the rise holes had an 22 insignificant impact on steady state RCS and secondary 23 parameters of interest as well as non-LOCA event 24 progressions and figures of merit. In addition, the 25 staff performed confirmatory calculations of a DHRS NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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153 1 cooldown and observed that there were minimal 2 differences when the riser holes were modeled.
3 MR. CORRADINI: Alex?
4 MS. SIWY: Yes.
5 MR. CORRADINI: You used just -- you used 6 the applicant's RELAP calculation and did 7 sensitivities with it, or you did a separate 8 calculation with another tool within the NRC staff?
9 MS. SIWY: We used -- I believe it was the 10 applicant's NRELAP 5 model.
11 MR. CORRADINI: And did additional 12 calculations or had them do additional calculations?
13 MS. SIWY: Yeah, we performed additional 14 calculations ourselves.
15 MR. CORRADINI: Okay. All right. Thank 16 you.
17 MS. SIWY: So as a result of --
18 VICE CHAIR REMPE: Could you verify --
19 this is Joy. I'm sorry to interrupt you. But in both 20 cases we've asked earlier today, what was the 21 applicant's tools, and verify that they did indeed 22 have RELAP 5 calculations.
23 MS. SIWY: Yeah. For these analyses, the 24 applicant used NRELAP 5 consistent with their non-LOCA 25 methodology.
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154 1 VICE CHAIR REMPE: Okay. Thank you.
2 MS. SIWY: Sure. So as a result of this, 3 the staff finds that the steady state RCS parameters 4 and DHRS performance, as described in DCA Part 2, Tier 5 2, Chapter 5, would not change substantially if the 6 riser holes were to be added. And therefore, changes 7 to Chapter 5, other than a basic description of the 8 riser holes, are not necessary. Are there any other 9 questions on this slide?
10 MEMBER MARCH-LEUBA: Yes, Alex. And I 11 apologize because I don't know if this proprietary or 12 not. So I may put you on the spot. But I agree with 13 you because I have seen those numbers, that the impact 14 on the flow -- pressure and flow on these orifices is 15 negligible. Can we say what the number is? Well, it 16 doesn't matter. It is very small. Do you agree that 17 the change in flow is very small?
18 MS. SIWY: I agree it's very small.
19 MEMBER MARCH-LEUBA: Yeah, and 20 insignificant, right? Because what I'm going to is --
21 and we're not supposed to be designing the reactor for 22 them. But if they had also drilled another set of 23 holes at the RRV level, all of this problem would have 24 went away because then we would not be deliberating 25 the lower number. And the impact on operation is NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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155 1 minimal. But I'm not designing the reactors for them.
2 Over and out.
3 MS. SIWY: Okay.
4 MEMBER RICCARDELLA: I'm sorry, Jose.
5 What level did you say that was in?
6 MEMBER MARCH-LEUBA: RRV, below the lowest 7 water level that you can reach --
8 MEMBER RICCARDELLA: Okay.
9 MEMBER MARCH-LEUBA: -- you have a second 10 set of holes.
11 MEMBER RICCARDELLA: All right. Thank 12 you. That's all.
13 MEMBER MARCH-LEUBA: And then you never 14 uncover them.
15 MS. SIWY: Are there any other questions 16 or comments on this slide?
17 (No audible response.)
18 MS. SIWY: Okay. Can we please move to 19 Slide 18? Thank you. The reactor system staff also 20 reviewed several aspects of Chapters 6 and 15 with 21 respect to the design changes and provides this brief 22 summary of areas not substantially affected by the 23 design changes. The first area is DCA Part 2, Tier 2, 24 Section 6.2.1.1 related to containment analyses and 25 the containment response analysis methodology NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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156 1 technical report.
2 This area was not substantially affected 3 because the limiting design basis events and resulting 4 values for peak containment pressure of 994 PSIA and 5 peak containment wall temperature of 526 degrees 6 Fahrenheit were unaffected by the design changes based 7 on NuScale sensitivity study results. In addition, 8 the previously non-limiting cases remaining non-9 limiting with the design changes considered.
10 MEMBER KIRCHNER: Alex, this is Walt 11 Kirchner. So your first bullet refers to actually the 12 containment limiting design case, and I believe that 13 is the reactor recirculation valve discharge 14 inadvertent opening. What kind of loads did you see?
15 Or I know we heard earlier from your colleague about 16 structural loads.
17 Do you see because of these holes any kind 18 of loading -- additional loading as the primary system 19 goes down, in particular, impingement on the steam 20 generator tube bank? I would expect the downcomer to 21 void first, closest to the RRV, and then the pressure 22 wave would kind of back up the downcomer and into the 23 riser core area. So are there any concerns about 24 loads because of the flow through the holes that have 25 been introduced or impingement on the steam generator NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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157 1 tubes?
2 MS. SIWY: I personally have not looked at 3 that, and I'm wondering if any Chapter 3 reviewers 4 might have.
5 MR. WONG: This is Yuken Wong. NuScale 6 did evaluate the impingement loads, and those loads is 7 about an order of magnitude lower than the loads from 8 fitting and thermal expansion. So those are loads 9 from the riser holes. It will have an insignificant 10 effect on the adjacent steam generator tubes.
11 MEMBER KIRCHNER: Okay. Thank you.
12 MS. SIWY: Thanks, Yuken. So the second 13 major area not substantially affected by the design 14 changes is the LOCA and non-LOCA topical reports. The 15 staff audited related NuScale calculations like I had 16 discussed on the previous slide and confirmed that 17 only conforming changes were needed such as the ones 18 that NuScale mentioned already related to updating the 19 LOCA topical report to acknowledge that there is a new 20 ECCS actuation signal on low RCS pressure.
21 The third major area not substantially 22 affected is basically all Chapter 15 non-LOCA events.
23 As discussed on the previous slide, the riser holes 24 have an insignificant impact on steady state 25 conditions, transient progressions, and non-LOCA NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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158 1 figures of merit. In addition, the changed high 2 containment level ECCS actuation set point is not 3 relevant to non-LOCAs because non-LOCA events simply 4 don't accumulate sufficient level in containment to 5 reach the set point. And finally, non-LOCA events are 6 unlikely to actuate ECCS on the new low RCS pressure 7 signal because of the associated interlocks that 8 Dinesh mentioned earlier.
9 And the final area not substantially 10 affected is the Chapter 15 inadvertent ECCS actuation 11 events. For this event, the staff audited NuScale's 12 qualitative assessment and agrees that the design 13 changes would have an insignificant impact on steady 14 state conditions, the transient progression, and 15 figures of merit, in part, because of the current 16 analysis for this event considers the immediate loss 17 of DC power which results in the earliest possible 18 ECCS actuation when the IAB release pressure is 19 reached. Are there any questions on Slide 18?
20 (No audible response.)
21 MS. SIWY: Thanks. I believe the next 22 presenter is Carl Thurston.
23 MR. THURSTON: Yes, this is Carl Thurston 24 from the reactor systems branch. So I'm going to talk 25 about the effects on the LOCA transient. Primarily, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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159 1 that would be 15.6.5, the loss of coolant accident.
2 So for the loss of coolant accidents, 3 these are primarily affected by the low pressure 4 signal. Because the low pressure activated a lot --
5 allowed the ECCS to activate a lot earlier. So steam 6 space and larger liquid space breaks, they also 7 activate a lot earlier on low pressure.
8 The earlier ECCS actuation and the lowered 9 CNV level setting kind of minimizes condensation and 10 improves boron distribution. And lastly, the minimum 11 collapsed liquid level and CHFR figures of merit are 12 not changed because the limiting case is based on loss 13 of AC power. So those cases are not affected by the 14 new RCS pressure set point.
15 MEMBER MARCH-LEUBA: Carl, Jose here 16 again.
17 MR. THURSTON: Yes.
18 MEMBER MARCH-LEUBA: Your last bullet, 19 what that means is that the -- (Telephonic 20 interference.) -- operation on the CNV high level 21 actuation setting does not change the medium collapse 22 level on TAF. So I --
23 MR. THURSTON: So --
24 MEMBER MARCH-LEUBA: -- find that 25 inconsistent because if you open it with the level two NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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160 1 feet above TAF, for example, then containment is 15 2 feet higher than that.
3 MR. THURSTON: Well, so the limiting case 4 for the top of active fuel is a very small 5 percent 5 injection line break. And the reason that it's 6 limiting is because you can fill up. So even if you 7 have a case and this case does not assume DHRS, so the 8 RCS pressure lags high.
9 So the level will fill up and then go 10 beyond the new level set point and you have to wait 11 for the IAB. So that way, you discharged the maximum 12 amount from the reactor vessel into containment. And 13 that's how you achieve your minimum level of active 14 fuel.
15 MEMBER MARCH-LEUBA: Same as it was before 16 the modification. But --
17 MR. THURSTON: That's correct.
18 MEMBER MARCH-LEUBA: -- if your level is 19 only literally two feet above TAF, then the 20 containment level is 15, 20 feet higher. When you 21 open the RRV, you're going to have a very large flow 22 going into the downcomer and the downcomer will flush 23 into the core. So you have to ensure that the 24 downcomer is not de-borated below the critical boron 25 concentration.
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161 1 MR. THURSTON: Right. So for this 2 particular scenario, so DHRS is not on. So you don't 3 have the cold surface for condensing on the steam 4 generator tubes, right?
5 MEMBER MARCH-LEUBA: Right. But you're 6 condensing on the -
7 MR. THURSTON: You're condensing in 8 containment. That's right.
9 MEMBER MARCH-LEUBA: No, no, no. The 10 containment is you have 15 feet higher on containment 11 of cold water. So you have 15 feet of vessel --
12 primary vessel wall condensing.
13 MR. THURSTON: That's right. That's 14 right.
15 MEMBER MARCH-LEUBA: So are we sure that 16 we've done all the analysis to ensure that the CBC, 17 the critical boron concentration, is not reached?
18 Because when your level in the vessel is very low, the 19 volume of downcomer is lower so it doesn't as long 20 time.
21 MR. THURSTON: That's right. That's 22 right.
23 MEMBER MARCH-LEUBA: You have run all 24 these cases?
25 MR. THURSTON: Right. So these cases were NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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162 1 evaluated under 8930. And so the limiting case was 2 the RRV break for the 8930 boron distribution 3 analyses. So this did not rise to the level of review 4 for those boron-related calculations.
5 MEMBER MARCH-LEUBA: This is -- I mean, 6 under this particular -- so it's a 5 percent break of 7 the charging line.
8 MR. THURSTON: Correct.
9 MEMBER MARCH-LEUBA: You are going to have 10 a rush of flow coming from containment downcomer.
11 It's going to push whatever is in the downcomer into 12 the core. So we -- has NuScale analyzed this and made 13 sure --
14 MR. THURSTON: Right. So --
15 MEMBER MARCH-LEUBA: -- they're not below 16 the CBC?
17 MR. THURSTON: Right. So I'm saying that 18 this is not the limiting case for boron distribution.
19 So I guess, I mean, we can --
20 MEMBER MARCH-LEUBA: Seems to me that it 21 may be.
22 MR. THURSTON: -- probably get back and 23 confirm that. But that is the staff's understanding 24 that this is not the limiting case regarding boron 25 distribution.
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163 1 MEMBER MARCH-LEUBA: The protocol is I'm 2 relying on your eyes because I don't like to see 3 anything. I mean, I know you very well. We're good 4 friends, and I trust you. And I'm relying on you to 5 look at these things.
6 MR. THURSTON: Yes.
7 MEMBER MARCH-LEUBA: This looks to me like 8 it could be the limiting case, and you're telling me 9 you didn't look at it.
10 MR. THURSTON: No, no. I'm saying that 11 it's not the limiting case. I'm saying that --
12 MEMBER MARCH-LEUBA: But it looks to me --
13 my judgment tells me it could be.
14 MEMBER KIRCHNER: Well, Jose, this is Walt 15 Kirchner. Depending on the rate -- Carl, how long 16 does this blowdown take?
17 MR. THURSTON: Oh, this is a very long 18 blowdown. So it might --
19 MEMBER KIRCHNER: It's a long blowdown.
20 MR. THURSTON: -- take a couple hours.
21 It's a 5 percent break.
22 MEMBER KIRCHNER: But it's a big enough 23 break that the boron is carried over with the flashing 24 --
25 MR. THURSTON: So --
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164 1 MEMBER KIRCHNER: -- of the primary 2 system. But I think the concern that Jose may have 3 voiced is while this water is accumulating, is it 4 still at saturated conditions in the containment 5 vessel? Or has it been cooled --
6 (Simultaneous speaking.)
7 MR. THURSTON: Well, it's going to be 8 cooled -- significantly cooler in water in the 9 containment, right, because you're condensing on those 10 walls and those walls are going to be quite cold. And 11 that will be -- as Jose pointed out, it will be 12 raining in the containment.
13 MEMBER KIRCHNER: Yeah, but now we have a 14 large --
15 MR. THURSTON: And that level will build 16 up.
17 MEMBER KIRCHNER: -- a large level of cold 18 fluid. And the cold fluid with the opening of the 19 ECCS valves then goes into the downcomer and into the 20 core. So --
21 MR. THURSTON: That's right.
22 MEMBER KIRCHNER: -- have you looked at 23 the moderator temperature feedback effect on the core?
24 MR. THURSTON: I mean, I don't think we 25 have looked specifically at this -- well, it has been NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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165 1 evaluated. So it was evaluated in 8930. And I guess 2 -- I don't know if Becky or Jeff can chime in here to 3 help me out. But this case was not found to be 4 limiting in any of the 8930 analysis we did because 5 for Chapter 15.6.5, we're pretty much only looking at 6 the LOCA figure of merit --
7 (Simultaneous speaking.)
8 MR. THURSTON: -- and the other emphasis 9 were done in a different calculation.
10 MEMBER KIRCHNER: Again, the concern would 11 be an injection of cold moderator into the core.
12 MR. THURSTON: Yeah, I understand.
13 MR. SCHMIDT: So this is Jeff Schmidt from 14 the reactor systems branch. So we have looked at 15 that. So we've looked at ECCS actuation, basically 16 keeping it -- and end of cycles are a good example.
17 There's not much boron to redistribute between the 18 core and the downcomer, right?
19 So when the ECCS actuates, that downcomer 20 water will -- and lower plenum water will enter the 21 core. And that reactivity effect has been looked at 22 as part of, like, the EOC return to power case. Does 23 that answer your question?
24 MEMBER KIRCHNER: Thank you, Jeff. Yes, 25 as long as you looked at it and analyzed it. And the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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166 1 follow through obviously is that if there's a 2 significant level in the containment, then you'll have 3 a traveling wave, so to speak, of colder and colder 4 water coming through the core until the system 5 equilibrates at equal levels, downcomer and --
6 (Simultaneous speaking.)
7 MR. SCHMIDT: Yeah, so we have looked at, 8 I guess, the transient effect of ECCS, and we've also 9 looked at the quasi-static state where you're just in 10 boil up and you have zero ppm coming into the core.
11 I don't know if you recall from the March 12 presentations, I gave a presentation on an NCNTMP 13 (phonetic) -- case. That was run where you had zero 14 ppm coming into the core. And we looked at one 15 saturated --
16 MEMBER MARCH-LEUBA: Watch out, Jeff.
17 That might be proprietary.
18 MR. SCHMIDT: Oh, okay. All right. So 19 there was an analysis done of this of zero ppm --
20 thank you, Jose -- where --
21 MEMBER MARCH-LEUBA: Jeff, my answer to 22 your previous question is no. We're way past the GDC 23 27 return to power which is an end of cycle problem.
24 We are now on the de-boration problem which is a 25 beginning of cycle problem. And --
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167 1 MR. SCHMIDT: Yes, yes. I was trying --
2 MEMBER MARCH-LEUBA: -- another --
3 MR. SCHMIDT: -- to answer the moderator 4 temperature effect --
5 MEMBER MARCH-LEUBA: Yeah.
6 MR. SCHMIDT: -- not the boration effect, 7 Jose.
8 MEMBER MARCH-LEUBA: Right, right. But if 9 you remember the presentation we got in June by 10 NuScale where they presented the critical boron 11 concentration, it's not -- doesn't take 100 percent 12 de-boration to get critical. I don't remember if the 13 number is provided. It probably is, but it's not 100 14 percent. It's much, much lower than that.
15 So if any rain -- distilled water rain is 16 coming into the downcomer, then with a lower level, 17 it's coming from the vessel wall because the vessel 18 has to be 10, 20 foot of cold water in the containment 19 on the other side. And it doesn't take that much de-20 boration. Of course, that CBC is a very conservative 21 number, and it assumes that once the worst stack crawl 22 out, which is a very conservative assumption. But 23 everything else is not conservative. This doesn't 24 look good, guys.
25 MR. SCHMIDT: I guess we can discuss more.
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168 1 So NuScale, are you referring to just, like, a LOCA 2 transient in the dilution? So they did 1,900 cases 3 where they looked at the new set point. And their 4 figure of merit was downcomer concentration versus 5 critical boron concentration. So that --
6 MEMBER MARCH-LEUBA: So they have looked 7 at this particular run and say that it's not above the 8 -- below the CBC?
9 MR. SCHMIDT: That's right.
10 PARTICIPANT: That's correct.
11 MR. SCHMIDT: That's correct.
12 PARTICIPANT: That's correct.
13 MR. BRISTOL: This is Ben Bristol with 14 NuScale.
15 MEMBER MARCH-LEUBA: Okay. You have --
16 (Simultaneous speaking.)
17 MR. SCHMIDT: Yeah, that's right. Go 18 ahead, Ben.
19 MEMBER MARCH-LEUBA: It sounds --
20 (Simultaneous speaking.)
21 MR. BRISTOL: So there's a unique nuance 22 in the assumptions that are made that the LOCA model 23 was developed very specifically for -- with special 24 conservatisms for calculating minimum level. Carl was 25 kind of alluding to that. The key one here is the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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169 1 treatment of DHR.
2 For our analysis of boron distribution, we 3 did not apply that same conservative assumption 4 because the DHR system would be actuated and would be 5 expected to be actuated. So there's a unique 6 phenomena where under the LOCA conditions where the 7 IAB will block it and hold out longer than the ECCS 8 signal would be expected to come in. That does not 9 occur under conditions where the DHR is operable.
10 MEMBER MARCH-LEUBA: Correct. And --
11 MR. BRISTOL: So the analysis Jeff was --
12 go ahead.
13 MEMBER MARCH-LEUBA: And your statement 14 that you have looked at this 5 percent charging line 15 break, you have looked at it assuming DHRS is on?
16 MR. BRISTOL: Correct.
17 MEMBER MARCH-LEUBA: Therefore, IAB 18 doesn't block, and everything is fine?
19 MR. BRISTOL: That's right. And the level 20 --
21 (Simultaneous speaking.)
22 MR. BRISTOL: -- still comes in when we 23 expect it to.
24 MR. CORRADINI: So this is Corradini. I 25 want to make sure since Ben jumped in, wasn't this the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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170 1 March presentation we heard in detail in closed 2 session?
3 MEMBER MARCH-LEUBA: No.
4 MR. CORRADINI: I'm asking Ben.
5 MR. BRISTOL: No, this was analysis that 6 we performed in June -- in support of the June 7 meetings.
8 MR. CORRADINI: But then I'm going back to 9 the March presentations. I thought those focused on 10 boron distribution under ECCS actuation conditions.
11 Am I misremembering?
12 MR. THURSTON: No, we did present this 13 case in the March meetings.
14 MR. CORRADINI: Okay. I thought so.
15 Thank you.
16 MEMBER MARCH-LEUBA: Well, I mean, I'm 17 sorry to be the bad guy, I don't get that warm feeling 18 about what is it that we've done. And I, myself, 19 haven't seen any of this. I don't want to see it 20 again, but I'd like to see a summary before you're 21 asking me to decide what you've done is acceptable.
22 At least summarize what you plan.
23 MR. THURSTON: Yeah. So I think the staff 24 can take action, Jose, to give back to the ACRS.
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171 1 take an action to confirm. So this case was evaluated 2 by NuScale, and it's a part of the recent audit that 3 we completed. And we can take an action to get back 4 to the ACRS with confirmation.
5 MEMBER MARCH-LEUBA: Tonight? We're 6 running out of time.
7 MS. PATTON: This is Becky Patton. I 8 mean, yeah, we can, Carl. I mean, I think we've 9 documented a lot of this within the SER. But if -- we 10 have a closed session tomorrow. So if you want to 11 provide more embellishment, I think we certainly 12 could.
13 MEMBER MARCH-LEUBA: What I would like is 14 that you give me sufficient reason to believe that you 15 have covered all -- you cross all the t's, dot all the 16 i's, or at least most of them. I mean, right now, 17 with what I have, the SER is orders of magnitude 18 better than the SAR. The SAR has absolutely no 19 information. It just says, trust us. We looked at 20 it. It looks good.
21 The SER at least contains some 22 information, but it still doesn't have all the 23 details. And this is very delicate, these 24 calculations. Whether you reach the CBC, the critical 25 boron concentration, or not, depends on minutes. If NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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172 1 DHR is running or not running or you're condensing on 2 the wall or you're not condensing on the wall, the 3 details matter. Okay. I said enough. Thank you.
4 MEMBER KIRCHNER: Carl, please go on.
5 MR. THURSTON: Yes, so this is actually my 6 last slide.
7 VICE CHAIR REMPE: Can I interrupt for 8 just a minute too? When you talk about you've 9 documented it and I don't have the specific location, 10 but Chapter 6, there were occurrences by the staff 11 that you did the calculations and after ECCS actuation 12 and you had confidence that the SAFDLs were fine -
13 (Telephonic interference.) And then you kind of -- and 14 I don't remember now whether it was Chapter 15 or 6.
15 But you said you extrapolated that to 16 seven days or used it to infer to seven days. What 17 would be good to know is exactly what type of 18 calculations were the basis for those kind of 19 statements in Chapter 6 -- (Telephonic interference.)
20 -- what I'm saying?
21 MEMBER KIRCHNER: Joy, your signal audio 22 is cutting in and out. You might want to just quickly 23 restate what you're requesting.
24 VICE CHAIR REMPE: Okay. I can see red 25 bars which is a bad thing. Can you hear at all?
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173 1 MEMBER KIRCHNER: I can hear you, but 2 you're breaking in and out.
3 VICE CHAIR REMPE: I'm in the mountains of 4 Sun Valley, and this is -- (Telephonic interference.)
5 -- because it's been fine today and I can hear you 6 all. What I'm trying to get to is -- I'll say it 7 again. If it doesn't work, I'll try later, send an 8 email.
9 But in Chapter 6, staff has said in the 10 safety evaluation -- the draft safety evaluation 11 report, the staff says, we audited calculations that 12 looked at the plant response after ECCS actuation and 13 things were great. The SAFDLs weren't exceeded, et 14 cetera. And somewhere I recall also seeing about it 15 was evaluated out to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. And then the staff 16 inferred out to seven days. Can you hear enough of 17 what I said? Or did it -- (Telephonic interference.)
18 -- now. So is it getting better and you can 19 understand me? Or do I need to repeat myself?
20 MR. SCHMIDT: So this is Jeff Schmidt from 21 reactor systems here. I think I heard you. I think 22 the extrapolation out to seven days was more of the 23 decay heat removal system that I recall.
24 VICE CHAIR REMPE: Okay. So what about 25 the fact that you looked at the calculations? After NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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174 1 ECCS actuation, things were great and the SAFDLs 2 weren't exceeded.
3 MR. SCHMIDT: That only goes --
4 VICE CHAIR REMPE: What type of 5 calculations --
6 MR. SCHMIDT: -- I think, to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> that 7 I recall.
8 VICE CHAIR REMPE: Okay. And what type of 9 calculations did you look at, NRELAP calculations or 10 hand calculations, because it was just --
11 MR. SCHMIDT: Yeah, so those were RELAP 12 calculations.
13 VICE CHAIR REMPE: -- I couldn't figure 14 out what you're looking at. We were talking at the 15 same time. Please say it again.
16 MR. SCHMIDT: I'm sorry. It was the 17 leakage cases I think that you're referring to in 6.3 18 were NRELAP. The hand calculation determines the 19 riser hole flow under DHRS operation. But it does --
20 part of that is used to determine the riser hole flows 21 in that NRELAP calculation.
22 As we'll discuss in the closed portion, 23 the NRELAP calculation has a slightly higher hole flow 24 rate. So what NuScale did is they kind of 25 renormalized it. So it's a combination really of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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175 1 NRELAP -- it's primarily NRELAP with a renormalization 2 for a riser hole flow.
3 VICE CHAIR REMPE: Okay. Thank you. It 4 would be good to see something like this documented 5 with a little more detail because I'm struggling with 6 the fact that the staff -- the additional calculations 7 you have are very detailed that we saw, the official 8 ones. I've not really got a good feel for what 9 NuScale did. But now we've got differences of 10 opinions on staff calculations, and it's kind of 11 puzzling. Usually, the staff reviews what NuScale 12 does. We're not struggling with differences just on 13 staff calculations.
14 MR. SCHMIDT: I'm not sure I understood 15 that, but I think I -- like I said, it's the 16 applicant's NRELAP that was audited. But they used 17 some information for their -- so some of the time 18 period during these LOCAs, right, especially the small 19 break LOCAs, the riser holes remain covered. So that 20 hole flow rate during when they are covered still 21 comes from the hand calculation of the extended DHRS.
22 I don't know if that's any clearer, but --
23 VICE CHAIR REMPE: Well, I thought --
24 (Telephonic interference.) -- looked at, and I think 25 some of this was in the actual SER where they said, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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176 1 after ECCS actuation, there's cases that have the 2 riser holes becoming covered. But you did some audit 3 reviews and you decided it -- (Telephonic 4 interference.) And Jose -- (Telephonic 5 interference.) -- that's what really the staff looked 6 at.
7 They don't have any NuScale calculations 8 -- (Telephonic interference.) -- particular quote 9 because Section 6.3 and I highlighted it. And it's 10 going to take me a while to find the exact words. But 11 if there were some calculations after, that NuScale 12 did -- (Telephonic interference.) -- after the riser 13 holes were covered. And they determined that the 14 SAFDLs weren't -- (Telephonic interference.) -- see 15 the specific calculation results. And I don't think 16 -- (Telephonic interference.) -- before because why 17 would have done -- (Telephonic interference.) --
18 riser holes uncovered?
19 MR. SCHMIDT: I guess I didn't catch all 20 of that. I'm sorry. You were cutting in and out 21 again.
22 MEMBER MARCH-LEUBA: Joy, this is Jose.
23 The court reporter is saying he cannot transcribe you.
24 You really are cutting off. Would you mind if we 25 continue and you reboot or restart the Skype -
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177 1 VICE CHAIR REMPE: I don't think that --
2 MEMBER MARCH-LEUBA: -- because the court 3 reporter cannot hear you.
4 VICE CHAIR REMPE: Okay. I don't think 5 that'll help. It's the internet connection, Jose.
6 But I can try.
7 (Simultaneous speaking.)
8 MR. SCHMIDT: The staff does cover this in 9 a later slide. We might be able to get to it then.
10 MEMBER KIRCHNER: Joy --
11 VICE CHAIR REMPE: The other thing is, 12 Jose --
13 (Simultaneous speaking.)
14 MEMBER KIRCHNER: -- phone line.
15 VICE CHAIR REMPE: Pardon? Oh, call in on 16 the phone line. Okay.
17 MEMBER KIRCHNER: You might not cut out so 18 much.
19 VICE CHAIR REMPE: Okay. Thanks. Go 20 ahead.
21 MR. THURSTON: Yes. So that's the 22 conclusion of staff's review for Slide 19.
23 MR. SCHMIDT: Okay. This is Jeff Schmidt 24 from the reactor systems. I got the next couple 25 slides. Again, as we've talked, the applicant added NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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178 1 riser holes to limit the downcomer dilution during 2 decay heat removal cooldown.
3 The RCS water level may drop below the 4 riser following reactor trip depending on the initial 5 RCS conditions. Those are mostly hot full power when 6 you have towards the lower end of the pressurizer 7 range. NRELAP and the staff's TRACE model showed 8 riser uncovery between five and six hours under 9 nominal conditions assuming no operator action.
10 The concern was that the ECCS valves could 11 open either on the loss of AC power at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or the 12 main valve like Tom talked about on the low 13 differential pressure, that spring he was referring to 14 earlier, causing a potential in-surge of diluted water 15 into the downcomer. And this is DHRS operation, and 16 there are times when ECC -- (Telephonic interference.)
17 MEMBER KIRCHNER: Jeff, I think we lost 18 your audio.
19 MR. SCHMIDT: Yeah, somebody muted it.
20 I'm sorry. I don't know what happened there. I 21 didn't touch anything. Okay. So I'm not sure where 22 I left off. The second bullet? Can anybody hear me?
23 MEMBER BLEY: I can hear you, Jeff.
24 MEMBER KIRCHNER: Yeah, Jeff, we can hear 25 you. Start with you mentioned the riser uncovery and NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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179 1 under DHRS operation under nominal conditions, no 2 action by the operators, takes five to six hours. And 3 then you were transitioning into it.
4 MR. SCHMIDT: So again, the issue is under 5 DHRS cooldown, the ECCS valves could open either a 6 loss of AC power at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or on the main valve low 7 differential pressure causing a potential in-surge of 8 diluted downcomer water into the core. So the 9 applicant performed a series of hand calculations to 10 determine the riser hole size and elevation to 11 maintain the downcomer boron concentration. Above the 12 critical boron concentration for times and cycle, when 13 significant, downcomer dilution is possible. Next 14 slide.
15 The applicant performed -- evaluated two 16 different primary to secondary side heat transfer 17 modes, depending on the relationship of primary to 18 secondary side. This kind of bound the problem. The 19 conductive cooling as it was referred to is where the 20 secondary side is below the primary side level. And 21 heat is transferred primarily through the riser wall.
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180 1 side level. Each transfer mode has different 2 condensation rates and thermohydraulic phenomena that 3 determine the riser hole flow rates. The staff 4 audited the applicant's hand calculations to ensure 5 the conservative condensation and riser hole flow 6 rates were sufficient to prevent significant downcomer 7 dilution. Next slide.
8 CHAIR SUNSERI: Hey, this is Matt. I 9 noticed that there's quite a few guests that have 10 their microphones open. So that may be causing a 11 bogging down of our system. If you're not talking, 12 please mute your microphone, please. Thank you.
13 MR. SCHMIDT: And let me ask. I can't see 14 the bottom corner of my slides because there is a 15 showing of people that are muted. Does anybody know 16 how to get rid of that?
17 MEMBER KIRCHNER: Jeff, just for your 18 information, we're seeing you blocking your slide.
19 But don't worry about it. Just talk through it if you 20 think --
21 CHAIR SUNSERI: But you can do that by 22 going up to the top right-hand corner of your screen, 23 the little arrow with the guy in it and click, content 24 view.
25 MR. SCHMIDT: Okay. Because I'm not NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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181 1 controlling my slides, so I -- all right. So I think 2 it's resolved. I can see my slides now. The NRELAP 3 and TRACE models show pressure and temperature 4 decreasing during cooldown consistent with convective 5 heat transfer.
6 Both NRELAP and TRACE show a liquid 7 discharge over the riser for approximately one and a 8 half to two hours after riser uncovery. The 9 applicant's hand calculation conservatively assumes no 10 boron containing liquid discharge over the riser 11 during that time frame. The applicant assumes state 12 point values for the decay heat, RCS pressure, steam 13 generator pressure, and for the convective case, a 14 riser to downcomer temperature difference as a 15 function of time.
16 This was all part of their hand 17 calculation to determine condensation rates and the 18 hole flow rates. Staff compared the assumed state 19 point values and found them either reasonable or 20 conservative compared to the applicant's NRELAP 5 and 21 the staff's NRELAP 5 and the TRACE confirmatory cases.
22 Staff audited the applicant's hand calculated 23 condensation rate both the convective and boiling heat 24 transfer mode and found them to be conservative. Next 25 slide, please.
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182 1 For the convective heat transfer mode, the 2 staff confirmed the applicant's hand calculation of 3 through-wall heat transfer was conservative. Staff 4 compared the riser to downcomer temperature difference 5 after the liquid discharge over the riser and found 6 that temperatures were consistent with the staff's 7 NRELAP 5 and TRACE confirmatory runs. When decay heat 8 is high, again, liquid discharge prevents a direct 9 comparison to the assumed state point calculations, at 10 least for the riser to downcomer temperature 11 differential I should say. Staff reviewed the 12 methodology associated with the riser and downcomer 13 level determination and found it to be reasonable.
14 VICE CHAIR REMPE: So Jeff, this is Joy.
15 MR. SCHMIDT: Yeah.
16 VICE CHAIR REMPE: Is it still cutting in 17 and out or is it --
18 MR. SCHMIDT: Oh, I can hear you now.
19 VICE CHAIR REMPE: Good, okay. What I was 20 trying to ask earlier was that in Chapter 6, there are 21 places where the staff indicates -- and I think it's 22 Section 6.3 -- that after ECCS actuation, there are 23 some cases they looked at where the riser holes became 24 uncovered. But the ECCS was adequate to ensure that 25 the SAFDLs weren't exceeded or there weren't any NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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183 1 problems. Were those calculations NRELAP 2 calculations, or were they the combined hand 3 calculations, NRELAP baseline type of thing? And has 4 ACRS really seen those calculations?
5 MR. SCHMIDT: I don't think -- so the 6 staff audited those calculations and a NuScale 7 calculation. I don't -- I mean, when you say, has 8 ACRS seen those calculations, no. They're probably in 9 the audit report.
10 VICE CHAIR REMPE: Which I'm not sure we 11 had. But they were NRELAP calculations. They weren't 12 hand calculations. What can you --
13 MR. SCHMIDT: They were NRELAP 14 calculations. They were just informed by the riser 15 hole flow rate hand calculation. But they were 16 predominately -- think of them as NRELAP calculations.
17 VICE CHAIR REMPE: Okay. Yeah, I think 18 that right now, as you said in the open session 19 earlier, we're to discern between something the staff 20 has produced versus a difference of opinion. If we 21 could see more of what NuScale did, maybe it would --
22 (Telephonic interference.) -- inform us on what to 23 believe.
24 MR. SCHMIDT: Right. So yeah, I 25 understand, and that's probably -- would have to NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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184 1 probably come out in the audit report of what we 2 looked at. Or we'd have to go back and modify RSE.
3 VICE CHAIR REMPE: Yeah, I'd be interested 4 to see a little more detail of what -- (Telephonic 5 interference.) But anyway, that's just my --
6 (Telephonic interference.)
7 MR. SCHMIDT: Okay. Yeah, so I guess I 8 just want to leave you with was that I think -- I 9 don't remember the exact number. I want to say 60 10 NRELAP cases. And NuScale can probably correct me on 11 the number. There's a table in their calculation that 12 has a whole list of a variety of conditions that they 13 ran.
14 VICE CHAIR REMPE: More information would 15 be helpful. Thank you.
16 MR. SCHMIDT: Okay. And I think we can 17 get probably into some of those details in the closed 18 session if you want.
19 VICE CHAIR REMPE: More information today 20 would be helpful.
21 MR. SCHMIDT: Okay, sure. Let's see.
22 Staff -- let's see. I think I covered that. I think 23 we're on the next slide. Next slide, please. Is 24 anybody hearing me? All right. This is the 25 connective heat transfer mode continued.
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185 1 Staff reviewed the loss form factor and 2 found the values and the hand calculations to be 3 conservative. This was obviously to determine the 4 pressure across the holes. Staff audited the 5 applicant's energy balance verification as part of 6 their hand calc check and agrees within the framework 7 of the hand calculation a conservative riser hole mass 8 flow rate was determined.
9 In other words, the total of the energy 10 loss from condensation through-wall and riser hole 11 flow rate energy was less than the assumed decay heat 12 energy. Staff compared the applicant's hand 13 calculated riser hole mass flow rate with the 14 applicant's NRELAP cases that was part of the audit 15 and the staff's TRACE confirmatory cases and found the 16 applicant's hand calculated values to be reasonable.
17 Next slide.
18 So the other bound of the heat transfer 19 mode is the boiling condensing heat transfer mode. In 20 this case, it's two phase level swell on the riser 21 that determines the pressure differential and the flow 22 across the holes. The applicant performed analysis 23 through 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> using a quasi-steady state analysis 24 method, very similar to the conductive case for a 25 generic event progression.
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186 1 Calculation included conservatisms 2 intended to underestimate riser void fraction and 3 overestimate the condensation rate. And during the 4 closed session, we'll get into the details of that, 5 including the staff's hand calculations. NRC staff 6 reviewed the applicant's methodology, audited 7 supporting calculations, and performed confirmatory 8 calculations.
9 A review of draft scenarios with no 10 reactor coolant leakage, i.e., no LOCA cases or I 11 should say leakage cases, not LOCA cases, below the 12 definition of LOCA. Staff found the applicant's 13 method and results acceptable for the conditions 14 reviewed in the application. Next slide.
15 So the idea, as we've talked about during 16 this, is to maintain the downcomer concentration above 17 the critical concentration. So the last part of this 18 exercise is to determine the downcomer concentration.
19 So as part of this, it's assumed to be in a quasi-20 steady state with the core and net flow as equal to 21 the riser hole flow and the condensation rate.
22 The applicant uses a wave front model to 23 transport boron from the riser to the downcomer and 24 back to the core. Staff finds the wave front model 25 conservative as the model maximizes boron transfer out NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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187 1 of and minimizes boron transport into the downcomer 2 and effectively ignoring any potential recirculation 3 mixing. The staff's riser hole design acceptance 4 criteria is to maintain downcomer concentration 5 greater than at critical, including the effects of 6 xenon with the highest worth control rod remaining out 7 of the core at BOC and MOC conditions for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
8 The staff grades the applicant's 9 acceptance criteria as conservative as maintaining a 10 downcomer concentration above the critical value, 11 ensures shutdown should occur when the ECCS valves 12 open at times in life when significant, downcomer 13 dilution is possible. At EOC, as I was referring to 14 a little earlier, there's a negligible downcomer 15 dilution between the core and the riser. Obviously, 16 as you go to zero, there's zero differential between 17 the riser and the downcomer.
18 And the staff looked at the downcomer with 19 a surge in between if you were to open up on the timer 20 at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and after 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> didn't cause a return 21 to power greater than that evaluated already in the 22 return to power analysis at 15.0.6. And that really 23 is the -- we found that the ECCS cooldown is already 24 in DCA 15.0.6 was still the limiting case. Next 25 slide. Turning this over to Josh.
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188 1 MR. BORROMEO: Yeah, so this is Josh 2 Borromeo from the nuclear systems performance branch.
3 I'm going to be talking about GDC 33. So NuScale 4 evaluated boron redistribution and the design changes 5 with respect to the exemption for GDC 33. And GDC 33 6 requires a system to supply RCS makeup for protection 7 against RCS leaks and small breaks.
8 So specifically, NuScale evaluated the RCS 9 leaks below the 50.46 LOCA spectrum which is within 10 the capacity of their CVCS. However, to justify the 11 exemption, NuScale assumed only using safety-related 12 systems, so not using CVCS and no operator actions.
13 So the approach that NuScale took was very similar to 14 the extended DHRS.
15 So this kind of gets back to the 16 discussion that we were having before. So the way I 17 like to think about these RCS leakage cases -- and 18 this is the analysis in 6.3 that I think was discussed 19 previously. These are essentially extended DHRS cases 20 and specifically the boiling condensing heat transfer 21 mode that Jeff just talked about but with the addition 22 of an RCS leak.
23 So it's a combination of -- so what 24 NuScale did was a combination of RELAP calcs and hand 25 calcs to figure out the two phase level in the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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189 1 reactor. So does that clear up kind of what NuScale 2 did whenever they analyze these cases, like, what 3 codes they used, what method they used?
4 MEMBER MARCH-LEUBA: Yeah, I have no 5 problem with this GDC 33 evaluation.
6 MR. BORROMEO: Okay. So the staff 7 evaluated the approach in two ways. So they took a 8 look in cases where ECCS actuates while holes are 9 covered and then when ECCS actuates after the holes 10 are uncovered. And I think in the SE, I think there's 11 some confusion similar to what we were talking about 12 during the NuScale presentation about there was an 13 evaluation after ECCS actuates. Well, really it was, 14 what happens at the time of ECCS actuation? So there 15 wasn't a calculation beyond ECCS actuation, right? It 16 essentially stopped there.
17 VICE CHAIR REMPE: So there was no -- just 18 say it again -- NRELAP calculation beyond the time 19 when ECCS actuation occurred?
20 MR. BORROMEO: Correct.
21 VICE CHAIR REMPE: So --
22 MEMBER MARCH-LEUBA: Sorry, Joy. Go 23 ahead.
24 VICE CHAIR REMPE: No, you go ahead.
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190 1 been emailing on this topic for the last week. I kept 2 telling her that the intent of the SER was to say that 3 there will not be any boron issue at the time of ECCS 4 actuation which could be a very big problem because 5 then you have the rush of water coming in. But the 6 SER says after ECCS actuation which means for two 7 weeks after ECCS actuation. If you guys are still 8 changing the SER, I would recommend that you look at 9 the language and replace after ECCS actuation without 10 the time of actuation.
11 MR. BORROMEO: Understood.
12 VICE CHAIR REMPE: And I agree with that.
13 That's what I was trying to ask because I still had 14 hope that there were some calculations you looked at 15 beyond, and there were none. And that's what I'm 16 trying to get to.
17 MR. BORROMEO: Right. There was no 18 calculations completed for RELAP beyond, right? But 19 there was -- NuScale did evaluate what would happen if 20 you lost the riser hole.
21 VICE CHAIR REMPE: So then -- and they did 22 that with hand -- a simple analytical model, right?
23 MR. BORROMEO: Well, I mean, I'll 24 characterize it as they took a look at the results at 25 the time of ECCS actuation and then made a conclusion NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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191 1 off of that. And then I think probably tomorrow we 2 can get in the details of what the staff observed with 3 respect to their calculations as well as what we 4 observed in our own confirmatory calcs using RELAP and 5 TRACE.
6 VICE CHAIR REMPE: So that's where I was 7 -- the point I was trying to make -- been trying to 8 make all day today is here we are where the staff has 9 done a lot of calculations that are more detailed than 10 the applicant. And there's some questions amongst the 11 staff on what's been done. Jeepers, it would've been 12 nice if the -- (Telephonic interference.) -- had done 13 some more detailed calculations.
14 MR. BORROMEO: Well, I mean, I don't know 15 if I would totally agree that they just didn't look at 16 this at all. I mean, they did a lot of cases at 17 various initial conditions, right? And we took some 18 of the limiting ones, and we're trying to find other 19 cases where it could be worse. So I think we took 20 what NuScale did and kind of extrapolated on a few 21 cases where we thought there might be some issues.
22 But what I think the applicant did wasn't 23 insufficient, I'll say.
24 VICE CHAIR REMPE: Because of the 25 calculations the staff did, you have confidence. Then NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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192 1 we're trying to decide on whether we have confidence.
2 And usually, the applicant would have to take the 3 lead, and then the staff does confirmatory analysis.
4 But anyway, I think I tried to make the point as best 5 I could.
6 MR. BORROMEO: Understood, understood. So 7 the other points I want to emphasize is the majority 8 of cases that we saw and what the staff expects is 9 that ECCS is going to go off prior to these holes 10 being uncovered, right? So they're going to hit the 11 ECCS RCS low pressure set point, or they're going to 12 come open on the ECCS valve design feature that Tom 13 talked about earlier that open below EP, right? So 14 that's what we -- for the majority of cases, that's 15 what we expect to happen.
16 Now there was some uncertainty about the 17 calculations that NuScale did with respect to, for 18 example, a two phase level. And because the ECCS 19 valves are this -- this dP function for them to open 20 is not safety-related, there was some uncertainty 21 there. So we took a look at scenarios where if you 22 lost the riser hole, what would happen if ECCS would 23 actuate after that?
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193 1 failures for this to occur. So it's not likely that 2 you would get to a situation where you lost the riser 3 hole before ECCS actuates. But the NuScale evaluation 4 showed that core boron concentration would remain 5 above the initial RCS boron concentration and the 6 staff performed confirmatory studies to help us to 7 come to a regulatory determination on that. So 8 overall, the staff has reasonable assurance that the 9 underlying purpose of GDC 33 is met without reliance 10 on non-safety-related systems or operator actions.
11 MEMBER PETTI: I have a question or a 12 request because I'm losing the thread here a little 13 bit. This idea that NuScale didn't do any 14 calculations after ECCS actuation, if you go back and 15 pull the March 2020 subcommittee slides, there's a 16 whole bunch of analysis of what's going on with boron 17 after ECCS actuation. So I just need to have the 18 whole picture painted because we're jumping around so 19 much, and I don't know if that's NuScale or Ben can do 20 that when we get into closed session either today or 21 tomorrow or the staff. But to kind of lay out here's 22 the phase space and this is covered here and this was 23 covered here so that we get a sense of completeness 24 because I think some of us are forgetting stuff that 25 was presented in the past.
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194 1 MR. BORROMEO: Sure. So I was speaking 2 related to the evaluation that NuScale did with 3 respect to GDC 33. So maybe Jeff or someone else can 4 speak to what they did for 8930.
5 MR. SCHMIDT: Yes, this is Jeff Schmidt 6 from reactor systems again. Yeah, so the March, I 7 guess, ACRS presentation covered what the -- when you 8 had significant boron -- well, it covered a couple 9 things, and one was that EOC return to power. And the 10 other was when you have significant boron 11 concentration, what would happen to the core and 12 downcomer concentrations out to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and there was 13 an evaluation out to seven days?
14 So that is correct is that, that was 15 covered in March. What we're trying to cover in these 16 slides here today is relative to the design changes, 17 right? We didn't go back -- all the way back to March 18 and redo all this --
19 MR. CORRADINI: So Jeff --
20 MR. BORROMEO: -- as far as the 21 presentation goes. So --
22 MR. CORRADINI: Jeff, this is Corradini.
23 I'm kind of with Member Petti on this. The March 24 analysis is not affected by the riser hole because 25 upon actuation, the riser holes are uncovered. So all NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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195 1 the March analysis still is applicable.
2 MR. SCHMIDT: That's right. That's right.
3 MR. CORRADINI: So that's, I think, part 4 of the big --
5 MR. SCHMIDT: So what this --
6 MR. CORRADINI: -- picture that was lost 7 in all the back and forth that we've been going 8 through all this afternoon. And it's my understanding 9 at least in the closed session -- so that's all I'll 10 say -- is that NuScale and staff went through this in 11 great detail and we're satisfied with how ECCS 12 performs out to a few days. I'll just use the word, 13 a few days, because your next slide is where I have 14 some major questions.
15 MR. SCHMIDT: Okay. All right. Well, 16 let's get to the next slide then if we're done with 17 this one.
18 MR. NOLAN: Hi, this is Ryan Nolan, and 19 I'm going to close out the reactor systems 20 presentation for the open session and briefly discuss 21 operator recovery actions and their role within the 22 NuScale design basis review. Clearly, boron 23 distribution within the core must be carefully 24 considered when exiting extended DHRS and ECCS cooling 25 modes. The NuScale Chapter 15 safety analysis does NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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196 1 not rely on operator actions to satisfy the pertinent 2 regulatory criteria.
3 So consideration of operation actions to 4 recover a module following an event is outside the 5 scope of the staff's design basis review. Multiple 6 operator errors of commission for -- or common caused 7 failures are considered beyond design basis and they 8 are addressed as part of Chapter 19. This is sort of 9 laid out in -- this is laid out in 15.0, sort of the 10 ground rules of how we do the Chapter 16 reviews for 11 passive designs. Is there a question?
12 MEMBER BLEY: Yeah, there is. This is 13 Dennis Bley. That makes sense from the usual point of 14 view which is that after this initial period, things 15 have reached a stable condition, and recovery means 16 putting the plant back together again. If you leave 17 hands off this one, you can eventually get into some 18 trouble. And I think you're extending the normal 19 rules into a case where 50 years ago when we were 20 setting all this up, it wouldn't have applied because 21 you weren't really stable yet. That's all.
22 MR. SCHMIDT: So this is Jeff Schmidt from 23 the reactor systems. So I'm not sure I understood the 24 statement because we get to this core concentration 25 downcomer dilution state. And I guess we consider NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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197 1 that a safe, stable state.
2 MR. CORRADINI: But I think, Jeff -- this 3 is Corradini. I'm kind of with Member Bley. You're 4 getting to a point now where at some point, you're 5 going to have to recover. And there's got to be some 6 sort of point at which the design and the operator has 7 to start recovering. And this would seem to be the 8 appropriate point.
9 And just from a precedent standpoint, 10 AP1000-ESBWR also at three days had to take on actions 11 to essentially get back to a safe and stable state.
12 Even though they were safe and stable at high 13 pressure, they still then went through a cooldown 14 discussion that staff required.
15 MR. NOLAN: Right, right. But that 16 analysis was within the scope of Chapter 19. That was 17 not within the Chapter 19 safety analysis.
18 MR. CORRADINI: That's not my memory, but 19 -- unless I misunderstood Member Bley's point. This 20 is the point where you essentially extend out how 21 things evolve, and you've got to find at least a path 22 back to recovery. And it seems to me this would be 23 the point to identify it. To say that it's outside 24 the scope of the design certification strikes me as 25 kind of not -- well, at least personally, that doesn't NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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198 1 seem acceptable. You want to technically show there's 2 a way to get back to essentially a recovered condition 3 because you don't want to keep this condition going on 4 for extended periods of time.
5 MR. NOLAN: These are -- I guess I'm not 6 familiar with ESBWR. But these are low 7 temperature/pressure conditions, right? I think we've 8 all assumed we're on ECCS here, right?
9 MR. CORRADINI: Right.
10 MR. NOLAN: Right. So you can sit on ECCS 11 for quite a period of time.
12 MEMBER MARCH-LEUBA: Yeah, I probably 13 should let Mike and Dennis make my point. But if you 14 have 20 to 25 dollars' worth of positive activity 15 parked in the lower plenum waiting for any 16 perturbation to put it inside the core, that's not a 17 safe and stable condition. It's not.
18 MR. SCHMIDT: I understand your concern.
19 MR. CORRADINI: But let me just -- let me 20 say my concern a little bit differently. I don't 21 particularly buy into a lot of what we've been 22 discussing here. But it just strikes me from good 23 engineering practice there's got to be a point with 24 which you require the owner operator, once they've 25 come to a safe and stable state to get to a recovered NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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199 1 condition.
2 And I don't think letting ECCS go on 3 interminably is an acceptable condition. You've got 4 to come back to it, and it's got to be at some defined 5 time. I'm picking three days because -- and I'll use 6 AP1000 as the example is they were safe and stable, 7 but that at a high pressure, low temperature condition 8 with their containment. And staff basically said, 9 that's good.
10 But what's better is to come back to 11 essentially a lower pressure. So in their case, 12 pressure was the thing that was required to 13 essentially be mitigated. In this case, it strikes me 14 it's concentration of boron in different locations at 15 different values. And if you continue to do this, it 16 just exacerbates the situation.
17 MR. SCHMIDT: Yeah, and I think that they 18 do have to recover at some point. I'm not sure what 19 that point is. I mean, it could be beyond obviously 20 the 72-hour coping period of Chapter 15, right?
21 MR. CORRADINI: But to me, again, I'm just 22 speaking for myself as an individual consultant to the 23 committee. It just strikes me that this is the 24 appropriate time to put in a tech spec requirement 25 that there ought to be operating procedures in places, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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200 1 that at three days into a DBA event or something 2 similar to the DBA event there should be recovery 3 actions identified.
4 MR. SCHMIDT: Yeah, I think at the design 5 certification state, and maybe other people can jump 6 in here, is that those procedures and demonstration 7 that those procedures can recover you are just at a 8 COL or a later stage than the DCA. I can understand 9 why others would think differently.
10 MEMBER MARCH-LEUBA: I have thought about 11 this a lot. You guys know I've been thinking about 12 this a lot. If you have a non-repairable break of the 13 CVCS charging line, I just don't see how you're going 14 to recover. The --
15 (Simultaneous speaking.)
16 MEMBER MARCH-LEUBA: -- to get out of this 17 is to put borated water inside the core and riser.
18 Every other source of water into the core and 19 containment is in the downcomer which will create a 20 reactivity event. So it is mandatory. I think it's 21 absolutely mandatory to tell me there is one recovery 22 procedure that may work. If there is two or three or 23 four, the COL can choose the one they want. But show 24 me there is one. And when you have a non-repairable 25 break of the charging line of the CVCS, I don't see NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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201 1 how you do it.
2 MR. SCHMIDT: Yeah, I understand your 3 concern, and I think some of that will be addressed a 4 little bit in the Chapter 19 where I think they looked 5 at more of the recovery -- possible recovery aspects.
6 MEMBER MARCH-LEUBA: Let's not wait. Tell 7 me if you're charging line for CVCS is not working, 8 how are you going to take that core into Mode 4 so you 9 can support it to the refueling station and fix it?
10 Tell me.
11 MR. SCHMIDT: I honestly can't answer that 12 question because I was not involved in any of the 13 recovery aspect.
14 MEMBER MARCH-LEUBA: I've been thinking 15 very hard about it. I don't see a way to do it other 16 than, I mean --
17 MR. SCHMIDT: I guess my response was if 18 you can't do it, then the COL -- if they can't come up 19 with a procedure to do this, then the COL will have to 20 take a departure from the DCA.
21 MEMBER MARCH-LEUBA: What do you mean 22 departure? You should not buy this reactor because it 23 doesn't work.
24 MR. SCHMIDT: I'm not the purchaser of it, 25 but --
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202 1 MEMBER MARCH-LEUBA: Yeah, but it is -- I 2 think it's so clear. Show me. Number one, evaluate 3 what all the possible states of your reactor are.
4 This is a DCA condition. Evaluate what all the 5 possible errors are, and evaluate the risk that this 6 reactor poses to the public -
7 (Simultaneous speaking.)
8 MR. SCHMIDT: And I think that is 9 addressed somewhat in Chapter 19, the 19 slides. So 10 maybe we should come back to this after the Chapter 19 11 slides.
12 MEMBER KIRCHNER: This is Walt Kirchner.
13 My Skype has dropped me multiple times now. So I 14 missed your discussion on this, but I did want to loop 15 back to this as well. I just want to concur with 16 Jose.
17 I also wanted to ask you, Jeff, what's the 18 figure of merit with how much margin on this? For 19 example, in -- (Telephonic interference.) -- it was 20 stated that the critical -- the boron concentration in 21 the downcomer is above the critical boron 22 concentration for the core. How much? How much 23 margin?
24 MR. SCHMIDT: So --
25 (Simultaneous speaking.)
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203 1 MR. SCHMIDT: -- nuclear reliability 2 factors --
3 MEMBER KIRCHNER: Right.
4 MR. SCHMIDT: -- as part of that. I don't 5 think there's -- so there is some margin, and I think 6 either NuScale or us can provide it in the closed 7 session of what the margin is.
8 MEMBER KIRCHNER: Okay. I would like to 9 explore that. Some margin doesn't mean a very 10 sanguine situation.
11 MR. SCHMIDT: Yeah, we can go through the 12 specifics.
13 MEMBER KIRCHNER: In two hours, you don't 14 want to find out that it's 73 hours8.449074e-4 days <br />0.0203 hours <br />1.207011e-4 weeks <br />2.77765e-5 months <br /> the thing actually 15 can go critical.
16 MR. SCHMIDT: Oh, no. So if you compare, 17 like, the -- I think if we're talking -- I guess let's 18 make sure what we're talking about. Are you talking 19 about the extended decay heat removal cooldown and the 20 riser hole function?
21 MEMBER KIRCHNER: I don't care what 22 scenario it is. Whatever the concentration is in the 23 downcomer versus the critical boron concentration for 24 the core is the figure of merit that I have in mind, 25 plus significant margin to account for significant NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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204 1 uncertainties.
2 MR. SCHMIDT: So there is margin. And 3 like I said, we can go through those. I probably 4 can't say the values --
5 MEMBER KIRCHNER: Okay. Well --
6 (Simultaneous speaking.)
7 MR. SCHMIDT: -- in the open discussion.
8 But there are --
9 (Simultaneous speaking.)
10 MR. SCHMIDT: -- 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
11 There is margin between the critical boron 12 concentration and the downcomer diluted concentration.
13 And those are values -- I guess you got to put it in 14 context, and we'll get into that more in the --
15 (Telephonic interference.) -- slides. But that's with 16 conservative riser holes. That's what conservative.
17 MEMBER KIRCHNER: I know that.
18 MR. SCHMIDT: Condensation --
19 MEMBER KIRCHNER: Assumptions on mixing, 20 et cetera. So yes, we can do that. But I also want 21 to go back to Member Bley's comment and then our 22 consultant, Mike Corradini. It just seems to me that 23 you're not completing Chapter 15 analyses if you can't 24 show that with a hands off this reactor under an 25 extended, for example, cooldown condensation mode that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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205 1 does not return to critical.
2 MR. SCHMIDT: Well, okay, so for boron --
3 with significant boron concentrations, as we went 4 through in March, it shows it doesn't return to 5 critical, that the final concentration in 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> is 6 greater than the initial. Hence, you're not critical.
7 This riser hole design, for example, shows that you 8 have margin to criticality.
9 And again, the point was if you're on 10 decay heat removal system and you actuate ECCS either 11 at the 24-hour time or at the low dP that you don't 12 introduce a de-borated slug into the core. And that's 13 a function of assuming conservative condensation 14 rates, low riser hole flow rates, and margin between 15 the critical and the de-borated state. So I think we 16 have shown in all these modes that you have, 17 basically, either a subcritical core or you return to 18 power at end of cycle as we discussed in March. And 19 that return to power is benign and your SAFDLs are 20 met.
21 MEMBER BLEY: This is Dennis again. I 22 just want to throw in a few last little things here.
23 I still think we don't have many other accidents that 24 end in a state that where a simple operator action 25 along the way could throw you in to something much NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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206 1 worse than you're in already. That's why I think it 2 ought to be addressed at this stage.
3 I don't find anything anywhere I can look 4 in the SAR or the SER, I think, that's as explicit as 5 your two big bullets. NuScale told us earlier that 6 Chapter 4 has a statement about it and Chapter 13. I 7 don't find anything in 13. The notes in Chapter 4 are 8 really benign. You'd have to have been through all 9 this discussion to know what they were talking about.
10 MR. SCHMIDT: Yeah, and I think a very 11 similar note is in 15.04 about the post-recovery 12 actions and --
13 MEMBER BLEY: Since you refer --
14 (Simultaneous speaking.)
15 MR. SCHMIDT: -- potential for a diluted 16 situation.
17 MEMBER BLEY: Since you refer often to 18 Chapter 19 as covering this, maybe you'll stay around 19 when we get to Chapter 19 because --
20 MEMBER DIMITRIJEVIC: That's not covered 21 in Chapter 19. That is not -- any of those recovery 22 actions are not mentioned in Chapter 19.
23 MR. SCHMIDT: Well, I think some of the 24 consequences were evaluated by research and a white 25 paper with regard to action by PRA.
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207 1 MEMBER DIMITRIJEVIC: Okay. But that 2 white paper is not FSAR, so --
3 (Simultaneous speaking.)
4 MEMBER MARCH-LEUBA: We got the white 5 paper yesterday. We got a copy of that white paper 6 yesterday, and I glanced at it. It's a good white 7 paper. I wish we had it a little earlier because I 8 haven't been able to read it in detail.
9 MEMBER PETTI: So the note came up on my 10 machine. Ben Bristol would like to say something.
11 MR. BRISTOL: Can you hear me?
12 MEMBER PETTI: We can.
13 MR. BRISTOL: Yeah, this is Ben Bristol 14 with NuScale. So a couple of points. Unfortunately 15 at this point in the design, it's not responsible for 16 us to start speculating on what potential recovery 17 actions would be. We do have some high level 18 descriptions of the system capabilities that we can 19 provide in the closed session that will help address 20 the concern that have been stated about the ability to 21 recover, particularly with certain failure modes. So 22 we can get into that in a little bit more detail 23 tomorrow.
24 I think the other point that's important 25 is that I think all of the thermohydraulic members NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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208 1 understand that the idea that a gradient -- a 2 significant gradient between the lower plenum of the 3 core could be sustained. It's just not physically 4 possible. It's a simplification that we use in 5 Chapter 15 to address uncertainties, right?
6 It's not a realistic condition.
7 Identification of the facts themselves would cause the 8 lower plenum and the downcomer with the convective 9 currents that exist under extended ECCS conditions 10 that have much better mixing than we would postulate 11 or try to defend in Chapter 15. So there's 12 differences -- important differences in the 13 assumptions that we use in Chapter 15 and the actual 14 plant conditions.
15 MEMBER MARCH-LEUBA: Ben, for the record, 16 whenever I've talked about this, you might look on the 17 record and say I've always said if all the planets 18 align, you can have a terrifying event. But unless --
19 as a reviewer, I'm asked by Congress actually to judge 20 the quality of your submittal. Unless I have a 21 calculation that shows me otherwise, I have to assume 22 all the planets align because that's what could 23 possibly happen.
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209 1 make it go boom. Okay? In a reactor, it's 2 impossible. But unless we have some calculations, 3 hand calculations, bounding calculations, preferably 4 detailed calculations, we cannot say what will happen.
5 What position do you put me in?
6 I don't think all these terrible events 7 that I keep describing are possible or likely.
8 They're possible. They're not likely. But unless you 9 give me some calculations, some arguments, what do you 10 want me to do? Okay. Over and out.
11 MR. BRISTOL: I appreciate that.
12 CHAIR SUNSERI: This is Matt. I'm going 13 to intervene here. Walt just dropped off again. He's 14 asked me to chair while he's getting back on. I think 15 the issue has been discussed. We're at a transition 16 slide. If I'm looking ahead a little bit, we're going 17 into Chapter 19 is the next slide, right? Am I 18 correct on this?
19 MR. SCHMIDT: Yes, that's correct.
20 CHAIR SUNSERI: Okay. So what I'd like to 21 do at this point, we've been at this over an hour or 22 so now. Maybe it's been two hours. So I think we 23 need to take a 15 or 20-minute break here, get ready 24 for Chapter 19, and come back into session on Chapter 25 19. And then we can have -- if this is where the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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210 1 recovery is discussed, the white paper, all that 2 stuff, we can pick up the discussion there. So let's 3 take a recess here until 5:20. We'll resume at 5:20.
4 (Whereupon, the above-entitled matter went 5 off the record at 5:05 p.m. and resumed at 5:21 p.m.)
6 CHAIR SUNSERI: Okay, so 5:21, let's go 7 ahead with the roll call. Ron Ballinger?
8 MEMBER BALLINGER: Here.
9 CHAIR SUNSERI: Dennis Bley?
10 MEMBER BLEY: Yes.
11 CHAIR SUNSERI: Whoa, everybody, please, 12 if you're not speaking, please put your microphones on 13 mute. Vesna Dimitrijevic?
14 MEMBER DIMITRIJEVIC: I'm here.
15 CHAIR SUNSERI: Walt Kirchner?
16 MEMBER KIRCHNER: Here.
17 CHAIR SUNSERI: Jose March-Leuba?
18 MEMBER MARCH-LEUBA: Present.
19 CHAIR SUNSERI: David Petti?
20 MEMBER PETTI: Here.
21 CHAIR SUNSERI: Joy Rempe?
22 VICE CHAIR REMPE: Here.
23 CHAIR SUNSERI: Pete Riccardella?
24 MEMBER RICCARDELLA: I'm here.
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211 1 we're all back from break. And I guess, we were 2 strategizing how the rest of today's going to go and 3 I'm going to take a second here, Walt, if you don't 4 mind, just outline what I think the rest of the week 5 looks like. Because I think it's important for 6 people's planning on this.
7 So, as you know, we have a couple of 8 sessions here where we're having presentations on, 9 open and closed presentations. We have two topics for 10 the week, one is the EPRI report on TRISO, and the 11 other is the NuScale series. NuScale is the most 12 important thing we have on our agenda right now but we 13 can't ignore the other work that we have as well.
14 So, we obviously want to get the level of 15 information that the Committee needs to make an 16 informed decision on its outcomes of this DCA.
17 I'm just surmising from the level of 18 detail that we're getting into in the discussion of 19 these things that we may not have enough time 20 allocated as far as the briefings go. So, I would say 21 that we had time also allocated for report preparation 22 this week with the idea that we would work on the 23 boron dilution letter and try to advance it, and work 24 on our final letter and try to advance that.
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212 1 complete either one of those letters this week and, 2 therefore, that would be the goal of our follow-on 3 week, the week of July 21st. So, I anticipate what's 4 going to happen is as we go finish our formal 5 presentations and we go into report preparation, we 6 will be discussing in high-level detail and fine 7 detail all the information that we're hearing this 8 week.
9 Normally staff, and normally the 10 Applicant, observes during our report preparation and 11 we occasionally ask factual comments or questions of 12 them, or clarifying remarks. So, I anticipate there 13 may be a lot more of that kind of open discussion to 14 help us as we deliberate on our reports. And so 15 therefore, I'm asking Staff and the Applicant to look 16 carefully at our schedule where we have time allocated 17 for report preparation. And I'm going to make a bold 18 request here and ask that you make yourselves 19 available during those timeframes to support our 20 deliberations and any questions we might have as we 21 contemplate what's going to be in our letters.
22 So, that's the request. At this time, for 23 today, we're going to work through the open session 24 presentation and then we will take a recess after 25 that. We'll ask for public comments on the open NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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213 1 session and then we will resume tomorrow morning by 2 starting with an open session, just to open the record 3 and let everybody know where we are and where we're 4 going. And then we will quickly close this session 5 and pick it up where we're leaving off today. Walt, 6 are you comfortable with that?
7 MEMBER KIRCHNER: Yes, Matt. Maybe one 8 clarification so we don't tie up too many people. I'm 9 thinking of NuScale in particular and also the Staff, 10 who are working on the NuScale SER. And that is, I 11 thought we agreed that we would do the TRISO letter 12 tomorrow afternoon?
13 CHAIR SUNSERI: Yes, that's good 14 clarification. So, at 2:30 p.m. I believe it is --
15 let me check the agenda here -- yes, 2:30 p.m.
16 tomorrow afternoon we start our report preparation.
17 And we will lead that off with the TRISO letter, so 18 we'll do the TRISO letter report tomorrow afternoon 19 starting at 2:30 p.m. And that will probably take I'm 20 guessing two hours maybe.
21 MEMBER PETTI: How long is this P&P going 22 to be?
23 CHAIR SUNSERI: I'm sorry, Dave, you're 24 really muffled, I couldn't understand that.
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214 1 to take on Friday?
2 CHAIR SUNSERI: Two hours.
3 MEMBER PETTI: The rest of the time we'll 4 devote to NuScale?
5 CHAIR SUNSERI: Yes, so after we finish 6 with TRISO and with the exception of the P&P on Friday 7 morning, we have all the rest of time, half the day on 8 Saturday, to devote to NuScale.
9 MR. DUDEK: Mr. Sunseri, this is Michael 10 Dudek, Branch Chief. Can you maybe get the times to 11 Mike Snodderly so that we can distribute those via 12 email to us so we know exactly who needs to tie in and 13 when?
14 MR. SNODDERLY: I will, I have it, I'll do 15 it.
16 CHAIR SUNSERI: Yes, that's a fair request 17 and to the extent that we can predict where we will 18 be, we can give that information to you.
19 MEMBER RICCARDELLA: Matt, would it maybe 20 be advisable to postpone TRISO to a Friday and have 21 the whole day tomorrow for NuScale?
22 CHAIR SUNSERI: I'm thinking. I don't 23 know how long -- I guess the problem is it's hard to 24 predict where we're going to be on what the end state 25 on NuScale looks like. So, I guess my thinking on NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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215 1 this was we'll get all the barriers out of the way, if 2 I can use that terminology, and I don't mean that 3 TRISO is a barrier but it's an activity that needs to 4 get done.
5 So, I'm thinking if we get that up and 6 down tomorrow, then that just leaves us to run all out 7 on NuScale. And I think we also may need to take a 8 little break from NuScale after we get through all the 9 presentations tomorrow anyway, just to think about 10 what we heard.
11 MEMBER RICCARDELLA: Okay, just a 12 suggestion.
13 CHAIR SUNSERI: But it's a good one. So, 14 let me turn it around on the membership, what is the 15 membership's preference? I'm just trying to lead us 16 through it here.
17 MEMBER BALLINGER: This is Ron.
18 With respect to TRISO, the discussion that 19 we've been having so far, at least that I've been 20 listening to, is very intense and requires -- you 21 would have to have some serious concentration on 22 what's going on. And I'm wondering whether the TRISO 23 discussion is simply, for lack of a better word, a 24 nuisance in the continuity of the discussion.
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216 1 need sort of a break, if you will -- sorry about my 2 bell. But on the other hand, there may just not be a 3 logical point to have the break.
4 MEMBER KIRCHNER: This is Walt. Ron and 5 Pete and Matt, when we, working with Mike Snodderly 6 earlier this week, strategized on schedule. We do 7 have a preliminary, for lack of the right word, draft 8 of a boron dilution letter that is not ready to be 9 shown at this point to go into a public letter-writing 10 session. And our thinking was that both Jose and 11 myself, and perhaps we can conscript one other Member, 12 could work on that offline to have a majority to do 13 the TRISO. We need a break to do that is what I'm 14 saying.
15 And so giving us at least the earlier part 16 of Thursday evening, because our presence is needed 17 for a quorum for the TRISO work letter report, we 18 could reflect on the presentations and the 19 discussions. And then modify that letter accordingly, 20 perhaps even, with the Chairman's permission, during 21 the recuse from P&P and have something, then, that we 22 could actually use for the purposes of the letter 23 writing activity, which would probably then be Friday.
24 Anyway, that was the reason we thought 25 that we needed the break, so that we could work on NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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217 1 that letter draft for the Committee.
2 CHAIR SUNSERI: I'm trying to look at the 3 roster here and figure out what the quorum looks like.
4 Can you restate what that sequence would look like in 5 your mind? Because we have two Members that are going 6 to be recused from TRISO, that puts us down to seven, 7 of which we would need four to carry on business to 8 get through the TRISO report.
9 MEMBER KIRCHNER: Not to be too much of a 10 parliamentarian, but the bylaws, there's some 11 ambiguity. But in general, I think major decisions, 12 and certainly a letter report from the Committee I 13 think falls in that category, should have a majority, 14 and that suggests six.
15 So, I think you need Jose and myself.
16 CHAIR SUNSERI: The bylaws allow, the 17 bylaws specifically say that Members that are recused 18 are removed from the majority for the purpose of 19 forming a quorum. So, legally, I mean --
20 MEMBER KIRCHNER: Yes, that's the quorum 21 part and not the major decision, but okay.
22 CHAIR SUNSERI: It's the major decision 23 part.
24 VICE CHAIR REMPE: Matt?
25 CHAIR SUNSERI: Yes?
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218 1 VICE CHAIR REMPE: At the beginning of 2 this discussion, I could swear you said you didn't 3 expect to get either the NuScale full letter or this 4 boron dilution letter done during this meeting.
5 Is that what I thought I heard or did I 6 just mishear part of it?
7 CHAIR SUNSERI: No, you heard that.
8 There's only two parts to the thing. Really, if you 9 think about our normal course of business, we would be 10 having a Subcommittee meeting right now to get this 11 new information. And then 30 days from now we would 12 be writing a letter based on reflection and the 13 Subcommittee Chair putting together a draft. So, 14 we're trying to put together a letter at the same time 15 we're getting the initial information.
16 So, with that, unless the information was 17 just perfect and we understood everything quite well, 18 it might have been possible to get a letter out but I 19 did not have that expectation.
20 VICE CHAIR REMPE: So, might I suggest in 21 light of that comment that whatever Walt and Jose 22 have, and they have looked at the draft, go ahead and 23 read it after we finish the presentations. Then go to 24 the TRISO file and update it. But we may not be able 25 to finish this meeting and that's why I'm kind of --
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219 1 what you can get done this week done, and then let's 2 progress as far as we can with TRISO.
3 But getting the Member discussion after 4 the draft is read might be a worthwhile thing and it 5 might influence -- since this is happening so real 6 time, perhaps the Staff at NuScale may -- let's just 7 see where the chips fall.
8 MEMBER KIRCHNER: Joy, this is Walt. I 9 just do not feel that we should use the current draft 10 letter that we have at this point. I think Jose and 11 I need an opportunity to go through it one more time 12 before we put it in front and do that in an open 13 public session.
14 MEMBER MARCH-LEUBA: My thought was an 15 adjustment because I wrote a very negative letter 16 based on the available information at the time. I'm 17 hoping to get some good information tomorrow and I can 18 change it. But you have to see my letter.
19 VICE CHAIR REMPE: So, then, okay, we do 20 the presentations, then we do the TRISO and you guys 21 tinker with it tomorrow night. And then you want to 22 read it after P&P. Is that the schedule that you 23 would prefer?
24 MEMBER MARCH-LEUBA: My goal is for Walt, 25 me, and maybe Dave, or somebody, Mike, write the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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220 1 conclusions tomorrow night. So, the Committee has a 2 buy-in of what the conclusions are and then we can 3 write the pros on the letter afterwards. But the 4 Committee has to have a bylaw of conclusions.
5 Right now --
6 (Simultaneous speaking.)
7 CHAIR SUNSERI: Yes, so that's what we 8 talked about. When we finish with presentations, we 9 ask Members for what are the main points and that's 10 essentially what you're talking about. So, it just 11 sounds like to me the logical sequence is we'll just 12 continue on like we're doing today, we'll get into the 13 closed session today. We will end with the open 14 session today, we will pick up the closed sessions 15 tomorrow, we will get through the closed sessions and 16 then do the TRISO letter tomorrow afternoon.
17 And then whatever break you guys need, if 18 you need to miss P&P or whatever, as long as we have 19 a quorum with the P&P, we can then pick up the letter-20 reading Friday after P&P. Does that sound reasonable?
21 MEMBER KIRCHNER: That works for me, Mr.
22 Chairman, thank you.
23 MEMBER PETTI: And I'm definitely willing 24 to help on the NuScale letter.
25 CHAIR SUNSERI: Yes.
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221 1 VICE CHAIR REMPE: So, if we're not going 2 to finish it, we still are planning to go through 3 Saturday even though we aren't going to try and finish 4 the letter is what I'm still trying to understand?
5 CHAIR SUNSERI: Right. It is absolutely 6 critical. Let me back up. While my expectation 7 wasn't that we would produce a letter, my expectation 8 is that this Committee would be as some kind of 9 consensus point on what the content of these letters, 10 what the conclusion of these letters, are going to be 11 so that we could have any chance of finishing them on 12 the week of the 21st.
13 MEMBER KIRCHNER: It seems to me the way 14 we have it scheduled, we're going to end up with a 15 dead space tomorrow afternoon. We have 2:30 p.m.
16 until 6:00 p.m. and for letter-writing, that's not 17 going to take us that long to do the TRISO letter.
18 And I'm hearing that we won't be ready to even start 19 looking at the boron dilution letter tomorrow 20 afternoon.
21 CHAIR SUNSERI: So, from 2:30 p.m. you 22 want to start until however long it takes to finish 23 the TRISO letter. If we finish in two hours, that 24 would be 4:30 p.m. and so, you're right, that would 25 actually work to our benefit because we could recess NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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222 1 at that time while whoever could go off and start 2 working on the draft letter and be ready for Friday.
3 MEMBER RICCARDELLA: Okay, and there's a 4 chance we might not get finished with all the 5 presentations by before lunch.
6 CHAIR SUNSERI: We have about six hours 7 tomorrow.
8 MEMBER RICCARDELLA: Okay.
9 VICE CHAIR REMPE: Anna Bradford's going 10 to need Civil Staff support on Saturday.
11 (Simultaneous speaking.)
12 CHAIR SUNSERI: I can't hear you, there's 13 some ringing noise going on.
14 VICE CHAIR REMPE: There's a note in 15 messaging from Anna Bradford wanting to know if the 16 Committee needs Staff support on Saturday.
17 CHAIR SUNSERI: Oh, let's put it this way, 18 right now I'm asking our Staff to be able to support 19 us on Saturday. I don't know where we will be but if 20 we all want to be successful on this, we need to be 21 lining it up. If we end up cancel it on Friday 22 afternoon to meet for it, then so be it but I found it 23 easier -- at least my judgment is it's easier to turn 24 it off than it is to turn it on, and we may need it.
25 MR. MOORE: So, this is Scott. The ACRS NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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223 1 Staff is prepared to support Saturday. I think Anna's 2 asking will the NRC Staff need to support Saturday?
3 And I think, Anna, in answer to your 4 question, you heard Chairman Sunseri say that for the 5 letter-writing, this will be slightly different than 6 normal letter-writing. There may be more interaction 7 between the Committee Members and the Staff and the 8 Applicant. So, I think that's about as much as I can 9 answer at this point.
10 CHAIR SUNSERI: That's a good summary of 11 what I was saying. Well said, better than me.
12 MS. BRADFORD: Thank you, this is Anna 13 Bradford. I just want to confirm what I thought I was 14 hearing, which was that the letter-writing may 15 continue into Saturday. It might be kind of an 16 interactive letter-writing session. There might be 17 some questions that we might want to be wanting to 18 answer.
19 MR. MOORE: That's correct.
20 VICE CHAIR REMPE: Thank you.
21 MEMBER MARCH-LEUBA: Hey Matt, since I'm 22 the troublemaker, let me make a statement here so 23 everybody knows what's involves. To date, including 24 today, I've seen no evidence whatsoever that after the 25 down-come of de-borates, when you go into ECCS cooling NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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224 1 mode, restarting CFDS or reversing flow on the led-2 down line on CVCS will not cause a reactivity event.
3 Unless you guys provide some information 4 tomorrow that I am wrong, I don't see how we get out 5 of this. So, you have all night? You have 18, 16 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> to work on it? But tomorrow, please convince me 7 that when the downcomer and lower plenum is completely 8 de-borated and you restart CFDS, or reverse floor on 9 the let-down line of the CVCS does not bring those $25 10 worth of reactivity into the core.
11 Okay? This is important. I mean, the 12 scheduling is important but taking it apart is more 13 important. To date, I have not seen any evidence 14 whatsoever that is the case. Over and out.
15 CHAIR SUNSERI: Thank you. Any further 16 comments?
17 VICE CHAIR REMPE: Is this a good time to 18 ask my question? Dave, I think you need to mute 19 unless you have a question.
20 CHAIR SUNSERI: It's hard to tell if 21 there's five or six people who have their mics on.
22 VICE CHAIR REMPE: Anyhow, before we broke 23 I had a question that's pertinent to Jose's comment 24 but it's a question for Ben Bristol. Because I still 25 get the feeling that different impressions from what NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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225 1 I hear from NuScale when I keep asking this question.
2 Ben just told us we have several upper-level candidate 3 actions that we believe will avoid this surge of 4 undiluted water.
5 What's the basis for those high-level decisions?
6 Could Ben elaborate? Do they have calculations that 7 support this? I thought I heard earlier today NuScale 8 saying, no, that's the COL Applicant's job. Does 9 NuScale have anything in house and what is it? Is it 10 hand calculation or some NRELAP calculations?
11 Do they do a CFD analysis?
12 MR. BRISTOL: This is Ben Bristol. Can 13 you hear me?
14 VICE CHAIR REMPE: Yes.
15 MR. BRISTOL: Okay, sure. I think we can 16 bring some more details on that tomorrow. I think 17 maybe an important characterization is coming into 18 this meeting, NuScale was in a support role of the 19 Staff and their SER, and so that's why we were not 20 planning on presenting any new technical information.
21 However, I think we've heard the feedback 22 and we understand the concern, and I think we can 23 characterize the design's capabilities better.
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226 1 on safety systems, some of the details need to be 2 pretty high level because we don't have all of the 3 final design systems mapped out yet.
4 But, yes, we have done several, we have 5 been working nonstop on this situation since the 6 February timeframe when the issue was initially 7 identified. And we have quantified it and 8 characterized it all number of different ways, up to 9 an including descriptions of the operators 10 capabilities, what they would have, what they would 11 see for different event progressions, different event 12 scenarios.
13 And I think it is important to consider 14 that what we feel is the combining of deterministic 15 one-directional mixing assumptions that we use in 16 Chapter 15 and the actual realistic conditions, where 17 we know that the lower plenum will not be at zero 18 boron connection, and in all likelihood, the downcomer 19 will not be in the unsafe position that has been 20 characterized throughout the day. But we can 21 certainly follow up tomorrow with some more details on 22 the plant capabilities and what operators could do in 23 the very unlikely event that we ended up in this 24 condition for an extended period of time.
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227 1 question. With all this additional information that 2 you say you have, is that what the Staff reviewed 3 during their audit?
4 MR. BRISTOL: We do not believe that 5 information is relevant for the DCA --
6 (Simultaneous speaking.)
7 VICE CHAIR REMPE: Did the Staff do an 8 audit --
9 (Simultaneous speaking.)
10 MR. BRISTOL: Pull up the DCA.
11 VICE CHAIR REMPE: So you said you have 12 information but the Staff's never reviewed it?
13 MR. BRISTOL: Again, as we've discussed at 14 the ACRS several times over the course of this 15 discussion, the specifics of procedures related to 16 bringing a module out of post-transient, where we've 17 established safe and stable conditions is not 18 developed at the DCA stage. So, no, the Staff has not 19 reviewed the credentials that we have with the design.
20 VICE CHAIR REMPE: Thank you.
21 CHAIR SUNSERI: This is Matt. I'm not 22 trying to be provocative or anything with this 23 comment, but I just think we're talking past each 24 other and let me just say this. We're not interested 25 in the procedures. We understand the process, the COA NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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228 1 application, the procedure, details step by step, we 2 understand the design. What we're talking about is a 3 strategy.
4 What strategy would the people use to 5 develop the procedures that provides a fail-safe way 6 of getting out of the situation? So, we're not asking 7 for you to tell us the step-by-step procedure. I 8 don't know if that helps or not but I think we just 9 keep stirring the water up here when we say procedures 10 and outside of scope. That's not what we're asking 11 for. We're asking for the how, not the details. Does 12 that make any sense?
13 MR. BRISTOL: Yes, I understand, and I 14 think if you get a chance to review some of the 15 information that was provided in March, we did 16 actually spend a little bit of time describing some of 17 the plant capabilities from that perspective.
18 CHAIR SUNSERI: And that's good. We get 19 a ton of information and as Dave Petti said, it 20 doesn't always come together in the right sequence.
21 And so it will be helpful when you talk about this 22 tomorrow just laying out a substantial step-by-step 23 holistic way of bringing this along, bringing us along 24 so that we understand better. Thank you.
25 MR. BRISTOL: Understood.
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229 1 CHAIR SUNSERI: So, anything else? Let's 2 go on with Chapter 19 then. Walt, you back on?
3 MEMBER KIRCHNER: Yes, I'm back on. So, 4 let's go ahead to Chapter 19, please. Who's up from 5 the Staff for this one?
6 MR. NAKANISHI: Good afternoon, this is 7 Tony Nakanishi with PRA licensing. So, I'd like to 8 discuss the Staff review associated with the boron --
9 (Simultaneous speaking.)
10 Can you hear me?
11 MEMBER KIRCHNER: Once again, we have to 12 ask people who are not speakers or presenters to turn 13 off your mic, please. Go ahead, Tony.
14 MR. NAKANISHI: Okay, good afternoon. So, 15 I'd like to spend the next few slides discussing the 16 Staff review associated with the boron redistribution 17 issues. From a Chapter 19 PRA perspective, I think 18 it's important to note that since we've been talking 19 about this --
20 OPERATOR: The presenter has allowed 21 participants to unmute themselves. You can now unmute 22 yourself by pressing Star-6.
23 MR. NAKANISHI: I hope you can hear me now 24 but what I was saying was that it's important to shift 25 the mindset from a design basis perspective to how we NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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230 1 look at things in the Chapter 19 perspective. We look 2 at scenarios from a realistic standpoint and the 3 figure of merit we're looking at is core damage.
4 So, with that, I also wanted to 5 acknowledge Marie Pohida and Alissa Neuhausen from the 6 DRA Staff that's integral to this part of the review, 7 as well as the Office of Research provided substantial 8 support. Dr. Peter Yarsky --
9 I keep getting muted for some reason. Can 10 you hear me?
11 MEMBER KIRCHNER: Yes, we can hear you.
12 VICE CHAIR REMPE: After Peter's last name 13 you cut out.
14 MR. NAKANISHI: Okay, yes, so I just want 15 to acknowledge Research's support that provided a lot 16 of confidence in our review. I would expect that Pete 17 and others may be chiming in to contribute to this 18 discussion.
19 So, just at the outset, I just want to 20 review the objective of the Chapter 19 review, which 21 is to ensure that the design is properly reflected in 22 the PRA and the boron redistribution issues are 23 properly addressed, such as that any risk-significant 24 scenarios are properly captured.
25 So, next slide, please. So, as was NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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231 1 mentioned before, we had significant interactions with 2 the Applicant through the audit process to look at the 3 underlying calculations, analyses, that support the 4 PRA. And clearly, the thermohydraulic analyses were 5 a key focus for the Staff. In particular, we wanted 6 to make sure we understood that the sequence 7 progression with the new design change such that the 8 potential for increased ECCS actuation and subsequent 9 incomplete ECCS actuations are addressed. We also 10 looked at the interlock conditions.
11 We wanted to make sure that certain 12 scenarios that relied upon the interlock to bypass 13 ECCS actuation, we looked at that to make sure that if 14 an interlock were to fail, for example, the potential 15 for, again, incomplete ECCS actuations are addressed.
16 And I also want to emphasize the Staff's 17 review focused on the reactivity insertion aspects in 18 light of the boron redistribution and the design 19 changes associated with those phenomena.
20 Next slide, please. So, what I'd like to 21 do is go through some specific scenarios that the 22 Staff focused on that we thought were relevant to the 23 boron redistribution issues and the design changes.
24 And so the Applicant found and the Staff agrees that 25 with the new design changes, certain non-LOCA NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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232 1 scenarios now result in ECCS actuation on the new low 2 RCS pressure signal.
3 So, whenever there's significant coolant 4 introduced into the containment and whenever the 5 reactor coolant system temperature remains high, close 6 to saturation, that leads to an ECCS actuation. So, 7 we're looking at RSV cycling scenarios as well as non-8 LOCA ATWS scenarios. And so those specific sequences 9 appear in a lot of these entries so there is some 10 impact with respect to how the PRA was modeled. And 11 the Staff did confirm that those event trees were 12 properly updated.
13 Next slide, please. So, in the previous 14 slide, I mentioned that the non-LOCA ATWS scenarios 15 now are assumed to actuate ECCS. And so, essentially, 16 non-LOCA ATWS scenarios become a LOCA ATWS, if you 17 will, and so with that comes the potential for 18 incomplete ECCS actuation. And one of the potential 19 actions taken to mitigate the inventory loss from ECCS 20 failure is a manual actuation of CVCS. So, we wanted 21 to make sure that the CVCS injection does not 22 introduce reactivity insertion.
23 And so the Applicant responded to our 24 question with some assessment that the scenario is 25 likely not going to collapse enough voids in the riser NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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233 1 to introduce core flow from the downcomer. But the 2 Staff wanted to do a little more independent 3 assessment and we were able to confirm the Applicant's 4 conclusion that it's probably unlikely that there 5 would be sufficient void collapse to introduce a large 6 amount of reactivity.
7 Essentially, if the injection rate is 8 significantly larger than the vapor generation rate, 9 you may get into the potential of flow incursion. But 10 the Staff assessment, and this is where we received 11 significant support and insights from the Office of 12 Research, that the CVCS injection flow is likely not 13 sufficient to cause a flow incursion.
14 Next slide, please. So, another area we 15 focused on is --
16 MEMBER BLEY: I'm sorry, can I press you 17 on that a little bit?
18 MR. NAKANISHI: Sure.
19 MEMBER BLEY: It's relatively unlikely 20 that a pump's going to fail but we model pumps and 21 look at that small chance of failure. When you say 22 relatively unlikely, what does that mean?
23 MR. NAKANISHI: So, this is getting into 24 specific reactor coolant system conditions that would 25 require or lead to that kind of scenario. So, it's NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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234 1 more of a phenomenological condition and since we're 2 talking about ATWS conditions, basically, you would be 3 at a fairly high heat generation condition. And in 4 those situations, it's really unlikely to have those 5 kinds of conditions, basically during an ATWS 6 condition. So, I'm not sure if that addresses the 7 question.
8 MEMBER BLEY: I think what you're telling 9 me is they left all of this stuff out of the PRA model 10 because it's relatively unlikely but we have a lot of 11 other things in the PRA model that are relatively 12 unlikely to me. And we run them through the analysis 13 to see which ones show up. Here, you can get rid of 14 most of the PRA by saying things are relatively 15 unlikely and, therefore, we aren't going to model 16 them.
17 MEMBER DIMITRIJEVIC: What they're trying 18 to say, this failure is in PRA. For example, if you 19 look in the general transient event tree, you will see 20 that even the ATWS, so favorite two trip, they model 21 success, if ECCS fails and the CVS success leads to 22 success, okay. There is a couple of those different 23 scenarios.
24 I'm trying to find the sequence numbers, 25 which supposedly have the thermohydraulic support for NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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235 1 them, as identified in the table in 0.16. So, I 2 assume that this thermohydraulic support after this 3 update actually considers the bottom situation. Is 4 that a true statement or not in order to credit 5 success?
6 MR. NAKANISHI: Yes, that's correct. So, 7 previous to this discussion of boron redistribution, 8 we really focused on more of the inventory loss aspect 9 that could lead to core damage. And now we're sort of 10 revisiting the success criteria analyses to look at 11 the reactivity aspects.
12 But to get back to Dr. Bley's point that 13 basically, the assessment, we believe, supports, 14 essentially, the condition, again, for an ATWS 15 condition. It's the vapor generation rate would be 16 too high relative to the injection rate. And so based 17 on analysis, and you know, maybe Pete, if you're 18 around, you might be able to elaborate on that.
19 MR. YARSKY: Yes, this is Peter Yarsky 20 from the Research Staff, and what we mean by highly 21 unlikely here is a constellation of thermohydraulic 22 conditions that would have to exist in the reactor 23 cooling system that are somewhat self-inconsistent.
24 So, as Tony's mentioning, you have to 25 postulate that you had an ATWS event and a failure of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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236 1 ECCS and a LOCA. But somehow you get into a condition 2 of very low vapor generation rate and low pressure.
3 And so we see that and under that specific set of 4 thermohydraulic conditions, you have an unknotted core 5 that somehow with ECCS failure gets to very low 6 pressure and low steaming rate, if those stars align 7 and you have that particular constellation, then 8 injection of CVCS at both CVCS pumps running can 9 produce enough condensation in the riser that you 10 would have a flow incursion that could have the 11 potential reactivity consequence.
12 But getting to a condition where you have 13 ECCS failure plus ATWS plus low pressure plus low 14 steaming rate, we don't really see a clear path for 15 how you develop and evolve to that specific condition.
16 MEMBER BLEY: So, these are much less 17 likely than, at least, what relatively unlikely means 18 to me? These are --
19 MR. YARSKY: Yes, we're going to do an 20 exhaustive calculation of every possible plant 21 evolution but you do have this inconsistency in your 22 assumptions, that you have all rods on so you have 23 power if ECCS fails here at high pressure. But if you 24 can somehow get to low pressure and low power from 25 there; we did some hand calculations to show that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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237 1 specific set of thermohydraulic conditions, this might 2 present a problem.
3 But it's not clear how you get to that set 4 of thermohydraulic conditions because it's kind of 5 inconsistent with the assumptions that are built into 6 the event sequence.
7 MEMBER BLEY: It is, and using the event 8 sequence to show these inconsistencies is a pretty 9 reasonable way to say they're --
10 (Simultaneous speaking.)
11 MR. YARSKY: Right, and so we just say 12 it's highly unlikely.
13 (Simultaneous speaking.)
14 MEMBER DIMITRIJEVIC: I want to point out 15 again that there is nothing in event tree presenting 16 this event and nothing is discussed even in analyses.
17 There is a sequence which leads to success. There is 18 nothing there talking that this injection is small and 19 this is a boron injection, there is nothing even 20 mentioning boron. Boron is not even brought in the 21 discussion on the sequences.
22 So, if the PRA is extensive now, there is 23 absolutely not anything which points to what you are 24 telling us in the discussion. Currently, we have this 25 event tree which leads to success, period. Nothing NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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238 1 impacts, nothing in the event tree, nothing in 2 sequences, nothing either points to that except that 3 there is this TH number, which I don't know that is 4 documented and where it was discussed.
5 But instead of reviewing the PRA, they 6 will have to assume that this is a very unlikely event 7 because there is not any event to begin, unlikely or 8 not unlikely with high lucidity or small incentive is 9 not present in the PRA.
10 MR. NAKANISHI: So, NuScale's PRA 11 estimates a fairly low core damage frequency. So, we 12 wanted to make sure was that there aren't any 13 sequences out there that can all of the sudden become 14 a core damage. And so some of these sequences you 15 might think as fairly low likelihood and it may be, 16 but relative to the NuScale risk profile, we wanted to 17 make sure we cover these scenarios.
18 And so, really, that was the focus of this 19 review, was to look at these scenarios and see if they 20 are indeed a success. And what we attempted to do was 21 NuScale did update their FSAR. Now, there's always 22 some judgment as to how much we would want in the 23 FSAR, but there are some key assumptions that were 24 updated, additional design features, associated with 25 the holes and things like that, had been updated, the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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239 1 event trees had been updated.
2 The Staff FSAR attempts to talk to some of 3 these scenarios. So, there could always be more but 4 we think it's adequate.
5 MEMBER DIMITRIJEVIC: You mean more than 6 nothing? Because there is absolutely nothing, 7 everything about this assumption which is discussed.
8 MR. NAKANISHI: So, the particular CVCS 9 aspect, yes, I don't think is in the FSAR. I believe 10 we touch on it in the Staff safety evaluation and the 11 audit report, I believe, hasn't been provided to the 12 Committee but we expect to provide additional 13 information in the audit report.
14 MR. SNODDERLY: This is Mike Snodderly 15 from the ACRS Staff. The Committee has not been given 16 the audit report, it has not been finalized by the 17 Staff.
18 MR. NAKANISHI: That's right. We're 19 moving in parallel with a lot of things.
20 MEMBER BLEY: Expect to see that before 21 our meeting in two weeks.
22 MR. NAKANISHI: Pardon?
23 MEMBER BLEY: We'd like to see that audit 24 report in two weeks from now.
25 MR. NAKANISHI: I guess, yes, maybe DNRL NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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240 1 could provide some feedback on that.
2 MS. JOHNSON: We're working to have that 3 before that. We'll try our best.
4 MEMBER BLEY: Okay.
5 MR. NAKANISHI: Okay, so, if I could move 6 on to the LOCA ATWS scenarios, and then again, this is 7 another example where previously, LOCAs assumed a 8 doubled-ended guillotine break because that's the most 9 challenging from an inventory perspective. But, as we 10 have been discussing, the smaller breaks and liquid 11 line breaks can lead to a more challenging scenario or 12 consequence from a boron redistribution standpoint.
13 So, we asked the question about what 14 happens if you have a LOCA with the ATWS and ECCS 15 actuates. So, the Applicant provided a comprehensive 16 analysis of break spectrums, break locations, and if 17 we could go to the next slide, Marie?
18 So, what the Applicant did was they ran 19 NRELAP 5 with a 1D kinetics option as well as the 20 NRELAP boron tracking model. They've updated some 21 modelizations to provide some additional information 22 on how the plant would respond.
23 Now, we noted that while the analysis 24 provided reasonable results, we also recognize that we 25 really haven't done the code review that we would NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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241 1 typically do for Chapter 15, for example. And so we 2 wanted to have additional assurance with respect to 3 the conclusions that are being reached that there's no 4 core damage.
5 So, NuScale provided a more integrated 6 analysis, supplemented the NRELAP calculations with a 7 hand calculation using the Fuchs Norheim method. We 8 believe it's a conservative approach, assuming 9 instantaneous reactivity insertion of the boron 10 reactivity or boron dilution. And we found that 11 looking at the energy deposition in the fuel, there's 12 reasonable margin to the core coolability criteria.
13 So, we are confident that the LOCA ATWS scenarios with 14 boron dilution will not lead to core damage.
15 MEMBER KIRCHNER: Tony, this is Walt 16 Kirchner. Did you use RG1236 as the criteria for 17 determining core coolability? So, Draft Guide 1327.
18 (Simultaneous speaking.)
19 MR. NAKANISHI: So, what we used was the 20 SRP 4.2 as a 230 calorie per gram limit. There's 21 significant margin, we believe, to that but that was 22 the criteria we used.
23 MEMBER DIMITRIJEVIC: In the sensitivity 24 analysis, what type of sensitivity analyses were 25 those? Based on the size of LOCA actuation of ECCS?
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242 1 Or what type of sensitivity?
2 MR. NAKANISHI: Yes, so I believe it was 3 varying the amount of dilution. In this case I don't 4 know exactly what they did but we think it provides 5 confidence to the uncertainty, the potential 6 uncertainty, due to the fact that we didn't do a 7 detailed KILD review.
8 MEMBER DIMITRIJEVIC: This is also just 9 depending on the time of ECCS actuation, right? You 10 didn't analyze anything after ECCS actuation?
11 MR. NAKANISHI: Right, so this is up to 12 the ECCS actuation. So, the ECCS actuation will 13 trigger, basically, an influx of downcomer liquid 14 right into the core. So, that was the issue that we 15 looked at here, but relative to your question about 16 post, we're going to have a slide on that. We'll talk 17 about that a little more too.
18 MEMBER KIRCHNER: Tony, again for 19 clarification, this is Walt Kirchner. On your first 20 bullet, the boron tracking model, which has not been 21 reviewed and approved by the Staff -- actually, I 22 guess this is a question I should have asked earlier.
23 For the Chapter 15 analysis, was the boron 24 tracking model reviewed and approved by the Staff? Or 25 is that part of the audit report? I'd assume you NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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243 1 would use the same tracking model, that's why I'm 2 asking this.
3 MR. NAKANISHI: So, we're not using the 4 same tracking model. And Reactor Systems, Jeff or 5 somebody, can correct me but for Chapter 15, they had 6 a different method for addressing boron 7 redistribution, including hand calculation.
8 For Chapter 19, they basically used the 9 NRELAP calculation. They've updated the nodalization 10 in the downcomer and the riser to be able to address 11 some two-dimensional effects. And we think it's a 12 good approach, although, from a Staff standpoint, we 13 didn't do a detailed review. We really didn't have 14 time to do a detailed review and because of that, we 15 asked NuScale to supplement that potential modeling 16 uncertainty with additional technical basis.
17 MEMBER KIRCHNER: What I'm drawing from 18 this is, kind of the wave-front conservative approach 19 for Chapter 15, this is more a best-estimate approach?
20 It sounds like they went to more nodalization as well.
21 MR. NAKANISHI: That's correct.
22 MEMBER KIRCHNER: Is that a fair 23 characterization?
24 MR. NAKANISHI: Yes.
25 MEMBER KIRCHNER: Thank you.
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244 1 MEMBER PETTI: Was the nodalization done 2 to try to capture some multi-dimensionality that 3 wasn't in the Chapter 15 analysis?
4 MR. NAKANISHI: The nodalization, 5 essentially, created a two-dimensional component in 6 the riser and the downcomer.
7 MEMBER PETTI: Okay, great, thanks.
8 MR. NAKANISHI: Okay, next slide, please?
9 MEMBER DIMITRIJEVIC: Let me actually stop 10 you because this may not be a bad place to actually 11 how see how much of those actual scenarios we look in.
12 Because LOCA is very simple, it only has four 13 scenarios to look in, right? The event tree has only 14 four sequences leading to success and those sequences 15 activate the reactor trip and the successful, ECCS 16 successful, that's the first one. Or the other two 17 trips successful, ECCS fails, CVCS successful. Right?
18 MR. NAKANISHI: That's right.
19 MEMBER DIMITRIJEVIC: So, we assume every 20 reactor trip is successful and we don't have to worry 21 about reactivity, right? That's what you said?
22 Then if we have reactor trip fail, we 23 again have ECCS successful and that's the sequence 24 which was analyzed. That's Sequence Number 4, right?
25 Reactor trip fail, ECCS successful.
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245 1 MR. NAKANISHI: Right, so --
2 MEMBER DIMITRIJEVIC: And then there is 3 another sequence which is if ECCS fails, CVCS 4 successful, but you said the CVCS can never add 5 reactivity to worry about for boron in LOCA.
6 MR. NAKANISHI: I think that's correct, 7 yes.
8 MEMBER DIMITRIJEVIC: Okay, so the only 9 sequence you guys are concentrating on is the reactor 10 trip fail, ECCS successful, right?
11 However, is this ever mentioned in Chapter 12 19? Is anything about this, what you have on those 13 two slides, can this be found anywhere in Chapter 19?
14 MR. NAKANISHI: So, the issue here, we 15 wanted to make sure that the break spectrum was 16 addressed. Smaller breaks are more likely than the 17 double-ended guillotine, and also, the smaller breaks 18 can lead to increased dilution.
19 So, we wanted to cover that and I believe 20 Chapter 19, the FSAR, has some additional information 21 to indicate, and I believe it's in the success 22 criteria table, this topic.
23 MEMBER DIMITRIJEVIC: No, I'm at the six-24 criteria table, its only change is related to the 25 number of sequences. The thermohydraulic simulation NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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246 1 number, but nothing else.
2 There is no discussion. If you can point 3 to me the spectrum of the break, the sensitivity 4 analyses, whatever you told us is in Chapter 19, I 5 will appreciate that.
6 MR. NAKANISHI: Yes, so there isn't going 7 to be that level of detail in the FSAR. So, we do 8 discuss this to some extent in the FSER and again, we 9 plan to provide additional information in the audit 10 report.
11 MEMBER DIMITRIJEVIC: I pointed this out 12 in our June meeting that issue was never addressed in 13 Chapter 19.
14 It was never discussed, and therefore, any 15 recoveries or any uncertainties or any sensitivities 16 are not present there?
17 MR. NAKANISHI: Right, so a lot of this is 18 reviewing what the Staff did during the audit and some 19 information will have to be in the audit report as 20 opposed to the FSAR.
21 Okay, next slide, please.
22 MR. CORRADINI: This is Corradini, I think 23 what Vesna's asking, though, in the original PRA 24 calculations and analysis was were these events 25 considered?
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247 1 Or, essentially, considered too unlikely 2 to even analyze?
3 MR. NAKANISHI: So, these events were 4 considered but they were looking at it more from the 5 inventory loss perspective.
6 So, the reactivity aspect wasn't explicit 7 before.
8 MEMBER DIMITRIJEVIC: Was boron dilution 9 events not considered an original?
10 And the only thing that has changed 11 between the original PRA and this PRA is that we have 12 a change in the actuation of ECCS system and we have 13 it as a whole. So, they didn't rely on that but it's 14 still just inventory loss, not boron dilution.
15 So, boron dilution I can say it's not 16 considered in Chapter 19. It may be considered in 17 your audit or the simulation but we cannot see that 18 from Chapter 19.
19 MR. NAKANISHI: Right, so where we're 20 headed with this is, basically, boron redistribution 21 is not going to be a risk-significant scenario.
22 That's the conclusion that we're trying to 23 support through these discussions.
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248 1 mechanisms that Research assisted us with, we believe 2 we have reasonable assurance that boron distribution 3 and dilution will not lead to a risk-significant 4 scenario.
5 In other words, not a core damage event.
6 MEMBER MARCH-LEUBA: Tony, this is Jose.
7 I know that we will fix it and I know that one of my 8 heroes, Peter, is the one that wrote the report.
9 I am still waiting to get some details 10 about why Peter thinks that a $1 per minute reactivity 11 ramp that goes all the way to $29 of insertion 12 activity is acceptable in the core.
13 How come anybody can say that if you put 14 $29 worth of positive reactivity into the core, even 15 if the ramp is very slow, that you don't melt that 16 core?
17 I'm hoping to get the answers tomorrow.
18 MR. YARSKY: I could maybe take a stab at 19 giving a short answer to the question.
20 MEMBER MARCH-LEUBA: Okay.
21 MR. YARSKY: So, when we developed the 22 white paper, we wanted to have a better 23 phenomenological understanding of the processes that 24 could potentially move diluted water into the core.
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249 1 that because the riser wall will have a conduction 2 heat transfer pathway to the downcomer, what will 3 occur inside the portion of the vessel that's inside 4 the riser wall itself, there will be an internal 5 recirculation flow pattern that will develop.
6 And that internal recirculation flow 7 pattern is going to mix the core inventory with the 8 upper riser.
9 So, you have a mixing --
10 MEMBER MARCH-LEUBA: Peter, you are 11 repeating my theory to me.
12 You probably have read my white paper 13 where it explains that, I just have not seen that 14 theory validated with any analysis, hand calculations, 15 or even place of paper.
16 MR. YARSKY: So, what we did, Jose, was we 17 calculated what that mixing time is using TRACE 18 results and that mixing time is about 40 seconds.
19 MEMBER MARCH-LEUBA: Fantastic. Where is 20 that calculation?
21 MR. YARSKY: The flow calculation should 22 be in the white paper that you received this week.
23 So, you can take a look at it in there.
24 MEMBER MARCH-LEUBA: By this week you mean 25 yesterday afternoon?
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250 1 MR. YARSKY: If you got it, you would have 2 gotten it this week so it's been very recent.
3 MEMBER MARCH-LEUBA: Yes, it was yesterday 4 afternoon and I had all these things to look at.
5 MR. YARSKY: Of course, I'm sure. So, the 6 short answer is we looked at a lot of different 7 possible phenomena or mechanisms that could move the 8 diluted water into the core.
9 But when we looked at that, if the process 10 is slow, and by slow we mean relative to that mixing 11 time, what would happen is if you're putting in the 12 water -- whatever the mixing time is, if it's slow 13 relative to that mixing time, that positive reactivity 14 that's being inserted because the water's diluted, 15 even if you're ramping it up, it starts to be erased 16 by the process of mixing in the high concentration of 17 boron from the top of the riser.
18 (Simultaneous speaking.)
19 -- sustainable if you have mixing.
20 MEMBER MARCH-LEUBA: Let's stipulate that 21 I agree with you.
22 But number one, I have not seen a single 23 place for written information -- indeed, all the ACRS 24 Members are falling asleep now because they don't know 25 what we're talking about.
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251 1 And the only place I've seen it written is 2 when I wrote --
3 (Simultaneous speaking.)
4 MEMBER KIRCHNER: We actually are very 5 attentive and I know exactly what you're talking 6 about, and I have questions.
7 VICE CHAIR REMPE: I also have questions.
8 (Simultaneous speaking.)
9 -- certainty in a calculation like that, 10 Peter, and TRACE and the validation basis but we can 11 talk about that tomorrow.
12 MEMBER MARCH-LEUBA: TRACE cannot possibly 13 calculate that.
14 What Pete is saying is that the front of 15 light water that's coming in the bottom of the core 16 miraculously gets transferred to the upper plenum 17 without creating heating in the core.
18 And then it mixes with the upper plenum 19 and, therefore, the core never dilutes. And I agree 20 with him, I wrote that on my paper to the Staff but I 21 haven't seen it anywhere.
22 The front of diluted water comes into to 23 bottom of the core and gets transferred to the upper 24 plenum without going through the core.
25 MEMBER KIRCHNER: That's not likely.
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252 1 (Simultaneous speaking.)
2 -- analyses and there's substantial mixing 3 at the lower entrance to the core, and we should take 4 that up tomorrow because --
5 (Simultaneous speaking.)
6 -- great technical detail.
7 MEMBER MARCH-LEUBA: I think we should 8 wait for tomorrow, I agree 100 percent, and I believe 9 that Pete, as usual, is right but you cannot rely on 10 that. And especially if it's a function of the power 11 level.
12 If you have high power, you will have a 13 lot of convective currents. If you have very low 14 power, three, four, five weeks after shutdown, how 15 many convective powers do you have?
16 I don't know, let's talk about it tomorrow 17 in detail.
18 MEMBER PETTI: Can I ask a question and 19 comment? I think it would help if all of the Members 20 go back and look at the last 20 Subcommittee slides, 21 where ECCS actuation and boron redistribution was 22 discussed.
23 If people have questions tonight, it would 24 be worth reading Peter's white paper again because a 25 lot of information is in there. I think it'll just NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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253 1 mean more to today's discussion, as it does to me.
2 And third, I am not an expert but if this 3 is Chapter 19, not Chapter 15, then the burden of 4 proof is different.
5 It's a best estimate calculation, not a 6 Chapter 15 calculation, because it seems like that 7 should play into other things in the discussion.
8 MEMBER KIRCHNER: David, that was my 9 earlier point when I drew out Tony about this. This 10 is a best estimate now calculation that's being used.
11 MR. NAKANISHI: Should I move on?
12 MEMBER KIRCHNER: Yes, Tony, please 13 proceed.
14 MR. NAKANISHI: So, another scenario we 15 looked at was an isolated CVCS injection line break 16 outside of containment and this is a potential risk-17 significant scenario because it's a bypass scenario if 18 there is core damage.
19 And because of the new ECCS actuation 20 design, basically, the ECCS actuates earlier than 21 before, which could lead to greater inventory loss.
22 And so if we revise thermal hydraulic analysis showed 23 that additional -- so, previously, DHRS wasn't needed 24 for this scenario.
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254 1 of DHRS is required to essentially reduce the RPV 2 pressure to reduce the rate of coolant loss from the 3 RPV. And that will allow the operator reaction to 4 inject containment flooding and drain system to 5 prevent core damage.
6 So, here, we wanted to make sure that the 7 DHRS effectiveness is appropriate for the scenario of 8 concern. DHRS by design is really intended for non-9 LOCA conditions, but this is a LOCA condition and the 10 steam generator would be uncovered.
11 So, the Staff went back and we wanted to 12 make sure there's enough -- so, the experimental basis 13 is sort of sparse but we discussed this with the 14 cognizant NRELAP experts in house and with 15 contractors.
16 And we believe that there's enough physics 17 to be able to credit DHRS in this condition. So, this 18 was a scenario that we focused on. Next --
19 MEMBER DIMITRIJEVIC: Your concern here is 20 core uncovering, not the boron? Where you concentrate 21 it, do you have enough time to prevent the core 22 uncovering, is that your statement?
23 MR. NAKANISHI: That's correct. So, this 24 has nothing to do with boron redistribution, it's a 25 function of the ECCS design change.
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255 1 MEMBER KIRCHNER: These are just the 2 thermohydraulic figures of merit, not boron?
3 MR. NAKANISHI: Correct.
4 MEMBER DIMITRIJEVIC: Right, but you did 5 not consider the consent broadly the couple times that 6 you may have extended the ECCS operation.
7 Here, with operator for the small break 8 operator starting, does CFDS later after that to make 9 up for losses? Would that be the issue at the bottom?
10 MR. NAKANISHI: Right, so we'll touch on 11 that I believe in the next I think two more slides.
12 But this action, initiate containment 13 flooding and drain system, is a very short-term 14 response to an un-isolated CVCS line break outside of 15 containment.
16 So, this action here is really not the 17 same. It's really to address the inventory loss 18 issue.
19 Next slide, please.
20 So, the other scenario we looked at, and 21 again, this is a pure thermohydraulic issue, but the 22 NuScale design is such that if you have a LOCA inside 23 a containment but say you failed to isolate the 24 containment, if you succeed with ECCS actuation, the 25 inventory loss will be sufficiently low that you'll NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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256 1 achieve success.
2 In other words, no core damage. So, in 3 light of earlier ECCS actuation, we wanted to make 4 sure that assumption is still valid. And so we asked 5 for additional information relative to how much 6 coolant mass loss do you get.
7 And the Applicant did additional 8 sensitivity studies during the timings and we agree 9 that the ECCS actuation, or the new ECCS actuation 10 still prevents core damage for this scenario.
11 Next slide, please. So, this is getting 12 to, and we talked about this a little bit already, but 13 this is post-event recovery scenario and we have ATWS 14 indicated here.
15 But really, the assessment we've done 16 applies to whether the reactor failed to scram or 17 whether the reactor was successful in tripping. So, 18 first of all, I think it's very reasonable to assume 19 that any adverse maneuvers would be properly governed 20 by plant-specific procedures.
21 But here we wanted to focus on the 22 consequence and so suppose that either a CVCS is used 23 or a CFDS is used, after some time, after ECCS 24 actuates and the operator would initiate containment 25 flooding and drain system, or CVCS.
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257 1 And basically, based on Research's 2 assessment of the reactivity insertion rate, and 3 comparing that to -- we have here a thermal time 4 constant and that's probably on the order of a few 5 seconds.
6 But it was also mentioned that there's 7 also the mixing time. Basically, the time to add a 8 dollar of reactivity based on the geometry of the 9 module and the amount of initial reactivity in the 10 downcomer.
11 So, where we're ending up with this is we 12 don't think it's a fast enough event to cause core 13 damage.
14 MEMBER MARCH-LEUBA: I'm sorry, this is 15 exactly what I was trying to get to, and hopefully, 16 we'll get into the proprietary information tomorrow 17 with more details.
18 But there is, by any estimate, at least 19 $20, maybe $29, of positive reactivity in the lower 20 plenum.
21 I don't care how much load you put it in 22 or how thermal exhibiting you are with the core, if 23 you put $29 worth of positive reactivity into the 24 core, there is no way that core doesn't melt.
25 MR. NAKANISHI: So, the other NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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258 1 consideration here is the pressure. The low pressure 2 conditions that we're in here would affect the density 3 feedback.
4 MEMBER MARCH-LEUBA: I was going to ask 5 you what void, reactivity, or density feedback you 6 used on your estimation?
7 Because my estimation in my brain -- it's 8 not even hand calculations, I'm just thinking -- come 9 out to be positive. Have you calculated the void 10 reactivity feedback under these conditions?
11 MR. NAKANISHI: So, maybe Pete could 12 expand? Yes, how about it, Pete, would you like chime 13 in on that?
14 MR. YARSKY: This is Dr. Peter Yarsky from 15 the Research Staff. The first item I think I'd like 16 to address is the idea of ramping in all of the 17 reactivity from the downcomer.
18 And while, Jose, I absolutely agree with 19 you, if you could put all of the $29 into the reactor 20 core, surely it would lead to core damage.
21 But the idea is inside the core you have 22 a reservoir of highly, highly concentrated boric acid 23 that's contributing a huge amount of negative 24 reactivity.
25 So, if you add the water from the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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259 1 downcomer very slowly and it mixes with the highly 2 concentrated boric acid water in the core, it kind of 3 erases that reactivity insertion as you're going.
4 So, it doesn't ramp up, there's sort of 5 this mixing phenomena that as you're adding that 6 reactivity, it's kind of removing it by restoring the 7 high concentration of boron to that liquid as it's 8 being inserted.
9 So, there's kind of like the insertion 10 ramp that you're describing, but there's also a 11 process where that reactivity is being removed by 12 putting the boron back into the core.
13 MEMBER MARCH-LEUBA: Okay, so what you're 14 saying --
15 MR. YARSKY: There's one mechanism above 16 the ramping and then if that makes sense, I can move 17 on to talk about the void feedback?
18 MEMBER MARCH-LEUBA: First, let's talk 19 about the mixing.
20 I 99 percent agree with you that if 21 especially the core is hot, surely after shutdown 22 there will be significant convective coolants in the 23 core that will mix it.
24 But I have not seen any single calculation 25 that tells me how does it mix or whether does it mix.
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260 1 In the absence of those calculations, I have to assume 2 it moves as a front, which is what everybody else had 3 been assuming until five minutes ago.
4 So, you say it doesn't move as a front --
5 MR. CORRADINI: Jose, I think the wave-6 front model was for Chapter 15 calculations, not for 7 PRA calculations, if I remember how the Applicant 8 presented it.
9 Maybe I'm misremembering.
10 MEMBER MARCH-LEUBA: Michael, have you 11 ever seen a calculation of convective currents in the 12 core that mix the diluted water with the highly 13 borated water?
14 Do you have any idea?
15 MR. CORRADINI: I've read Pete's white 16 paper, if that's what you mean.
17 MEMBER MARCH-LEUBA: So, yesterday he 18 postulated there might be some mixing and let me --
19 (Simultaneous speaking.)
20 -- I agree 100 percent, I agree with Pete 21 100 percent. And indeed, I wrote a white paper for 22 the Staff saying that, that that's what probably 23 happens, but I have no idea if it happens.
24 Just because I believe it happens, it's 25 not what happens.
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261 1 MEMBER PETTI: Jose, I thought there was 2 some calculations behind the discussion in the white 3 paper, but it is a 40-page white paper and I could be 4 wrong as I remember other areas.
5 MEMBER MARCH-LEUBA: Let's ask Pete, what 6 calculations are behind it?
7 MR. YARSKY: So, the Research Staff, to 8 support I forget which Chapter of the review but it's 9 part of the NuScale Reactor Systems Research Plan, 10 performed a number of LOCA calculations.
11 And we were able to farm those long-term 12 calculations to look up the internal recirculation 13 flow patterns.
14 MEMBER MARCH-LEUBA: And those were 15 calculated using what?
16 MR. YARSKY: TRACE, TRACE calculations.
17 MEMBER MARCH-LEUBA: There is TRACE 18 calculations? You were using the three-vessel 19 component?
20 MR. YARSKY: Yes, it's actually, I'm 21 fairly certain, a vessel in vessel in vessel model, 22 where we have a vessel representing the containment 23 vessel representing most of the RCS, and then another 24 vessel representing just the riser.
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262 1 stipulate.
2 I agree with you that this is the likely 3 thing to happen but if this was an Applicant or a 4 Licensee sending into to you for review, would you 5 accept this calculation?
6 MR. YARSKY: I think it's important to 7 recognize the difference between the Chapter 15 8 acceptance criteria for methodology and what is used 9 for the beyond design basis events, where you rely on 10 much more heavily on just best estimate without 11 considerations of the uncertainties.
12 Here, I think the physical process of the 13 internal recirculation is so key to the progression of 14 the event. I think it's overly conservative to ignore 15 it.
16 MEMBER MARCH-LEUBA: I agree with you 100 17 percent, I just don't see any definitive calculation 18 I can put my hand on heart and say, yes, this is 19 right.
20 I think there will be internal 21 calculations, I think it will mix, and yet, I think 22 the likelihood that the water will be transferred to 23 the upper core, the upper riser, and mixed there.
24 It won't mix in the core, it'll mix in the 25 riser. But we need more than my gut feeling.
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263 1 MR. YARSKY: Well, the other thing I would 2 mention is that we're looking at an ATWS case here.
3 So, if you're inserting reactivity less than a dollar 4 you are going to have a power increase, right?
5 We don't see this as being something that 6 will challenge core coolability, so long as you stay 7 covered and you're not in a prompt critical excursion.
8 But that is going to further promote mixing.
9 So, the thing that's driving your event to 10 where you would be worried about the reactivity 11 insertion, that exact same thing, if it's slow, is 12 going to promote that mixing.
13 MEMBER MARCH-LEUBA: And we go back to the 14 boron reactivity coefficient. I've been working it in 15 my head and I'm convinced the boron reactivity 16 coefficient is positive.
17 MR. YARSKY: so, this is the other item I 18 think is worth spending at least a couple minutes to 19 discuss.
20 So, while under the highly borated 21 conditions that you would have in the core, if the 22 physical process of the feedback was thermal 23 expansion, like it is when you're at high pressure, 24 then, Jose, it certainly does look like the moderator 25 feedback would be positive.
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264 1 But under these conditions, you have to 2 look at a post-ECCS actuation, right? Because if you 3 don't have a LOCA with ECCS actuation, it's not really 4 a mechanism to move the de-borated water --
5 MEMBER MARCH-LEUBA: You're likely 6 depressurized.
7 MR. YARSKY: So, you're at low pressure?
8 (Simultaneous speaking.)
9 So, now that you're at low pressure 10 though, the physical mechanism of density feedback 11 changes.
12 It's no longer really being driven at all 13 by thermal expansion, it's being driven by void 14 formation.
15 MEMBER KIRCHNER: And I believe now it 16 will turn negative.
17 MR. YARSKY: Yes, so when you're in this 18 void formation regime, what will happen is as you heat 19 up the coolant, you'll form bubbles and what happens 20 is, essentially, the hydrogen leaves the core and all 21 the boron stays where it is.
22 MEMBER MARCH-LEUBA: No. As you form 23 voids, you push the boron out of the core and keep the 24 hydrogen.
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265 1 you're flashing but so long as the average flow rate 2 is still upwards, you're not reversing --
3 (Simultaneous speaking.)
4 -- the boron doesn't leave.
5 MEMBER MARCH-LEUBA: There isn't a flow 6 rate of risers and coolers. Is all the easy flow just 7 sufficient to compensate for the --
8 MR. YARSKY: Some kind of preservation 9 that was like a flashing event, then the void 10 formation would push inventory out of the core. You'd 11 have the reverse flow.
12 MEMBER MARCH-LEUBA: No, there won't be 13 any reverse flow, it will be all --
14 (Simultaneous speaking.)
15 MR. YARSKY: -- any reverse flow. And so 16 because there's no reverse flow, the boron doesn't 17 leave.
18 MEMBER KIRCHNER: Might I interject here?
19 I suspect that this discussion could go on well beyond 20 7:00 p.m. Eastern Time.
21 I would propose that we hold that in-depth 22 discussion for the presentation of, I believe, Peter, 23 you are going to present your white paper in closed 24 session tomorrow, is that correct?
25 MR. YARSKY: No, I don't believe there's NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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266 1 anything in the --
2 MEMBER KIRCHNER: We'll have the 3 opportunity to question you on the white paper? Let 4 me turn the tables. Is that correct?
5 Is that part of the Staff's closed 6 presentation?
7 MEMBER MARCH-LEUBA: No, it's not.
8 MR. NAKANISHI: So, yes, there was no 9 prepared presentations on the white paper by Dr.
10 Yarsky, but hopefully, he can answer --
11 MEMBER KIRCHNER: We can question him on 12 the content and the assumptions.
13 MEMBER PETTI: We can get a PowerPoint 14 from Mike Snodderly.
15 MEMBER MARCH-LEUBA: Before we close the 16 record, we just had a spirited physics argument 17 between two bright minds, one much brighter than mine.
18 And there is a disagreement, there is a 19 difference of opinion, and there is no document, there 20 is no record that we can review from the Applicant or 21 the Staff that positions it.
22 If there is a difference of opinion 23 between two bright minds, then it's a difference of 24 opinion. We have a problem.
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267 1 been made, Jose. May I go back and just ask Tony, 2 Tony, on the last two bullets, I will just make a 3 statement. You don't have to answer it in real time.
4 We could also defer this for tomorrow.
5 Quite frankly, the fuel thermal time constant is not 6 an issue, it's the rate of reactivity insertion that 7 is the governing factor.
8 So, that's not a good figure of merit on 9 the first sub-bullet.
10 Second one, once again, a fellow Member 11 asked, found very unlikely, I just don't know what to 12 do with something that's been found very unlikely.
13 So, in tomorrow's discussion in closed session, can we 14 address both of these?
15 Actually, address probably this whole 16 topic?
17 MEMBER DIMITRIJEVIC: I want to add 18 something also here.
19 MEMBER KIRCHNER: Go ahead.
20 MEMBER DIMITRIJEVIC: Okay, I want to make 21 this point very clear. Sometimes I babble and maybe 22 it's not clear. Here it says PRH updating and there 23 it says post-event recovery.
24 There is no post-event recovery in Chapter 25 19. There is nothing about boron dilution in the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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268 1 Chapter 19, only one sentence in the assumption under 2 success criteria which says the host and the exchange 3 of actuation have addressed concerns of the boron 4 redistribution.
5 That's all, I just want you to know when 6 I say, oh, this is not the Chapter 15, should be in 7 Chapter 19, there is nothing in Chapter 19 on those 8 issue. And therefore, the PRA Chapter 19 is name of 9 the slides but this thing was not discussed.
10 There is not any possible recovery or 11 anything. So, if we think the dose evaluation should 12 be discussed everywhere in the FSAR, then maybe the 13 Chapter 19 is the place.
14 We should also discuss that because 15 currently they are not there. That's all I want to 16 point. Saying Chapter 19 has some post-event 17 recovery, that's not true.
18 MR. NAKANISHI: Right, so what we're 19 trying to do here is to review with the Committee what 20 we've done as part of the audit to look at these 21 scenarios to make sure that these are not core damage 22 events.
23 And so I guess, again, there's a judgment 24 as to how much we want in the FSAR. We certainly 25 would. I believe we have some discussion, again, in NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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269 1 the FSER, or safety evaluation, and we certainly would 2 elaborate on these in the audit report.
3 And then the other point, Dr. Kirchner's 4 comment about the reactivity insertion rate, what we 5 tried to convey with that bullet is, essentially, if 6 the reactivity insertion time, the time it takes to 7 add a dollar is significantly greater than the fuel 8 thermal time constant, then there would be a feedback 9 mechanism that would curve the reactivity insertion.
10 And then the second point, what we're 11 really saying there is that we've considered this 12 phenomenon and we think that it's, as Dr. Yarsky 13 pointed out, thermohydraulically, the starts have to 14 align for this to be a concern.
15 So, essentially, we think there's a basis 16 to screen it out from the risk assessment.
17 MEMBER MARCH-LEUBA: Tony, I'm sorry to 18 say this but there are so many things wrong with what 19 you just said. If you have $20, $25, $30 worth of 20 positive activity going into the core, I don't care 21 what void activity you calculated, your core is going 22 to melt.
23 And my evaluation in my head, not even on 24 paper, is that the void reactivity coefficient is 25 positive, which is even worse. It will have a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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270 1 positive excursion.
2 So, unless you can provide me a 3 calculation that says the void reactivity coefficient 4 is negative, I cannot accept your statement that as 5 long as the $29 worth of activity commences slowly, we 6 will survive it.
7 There is no way on heaven or earth that a 8 reactor can survive $29 worth of negative reactivity, 9 especially one that has a positive coefficient.
10 Maybe we can get into the details 11 tomorrow, but this is --
12 MEMBER KIRCHNER: Jose, let's take that 13 for a note for tomorrow because I could go on to 14 scenarios like such insertion will induce flow 15 oscillations and maybe flow oscillations are good 16 because you have perfect mixing by the time you're 17 done oscillating a few cycles.
18 But let's take that for tomorrow and where 19 are we, Tony, in your presentation? Are there more 20 slides?
21 MR. NAKANISHI: We just have one more, 22 which is a conclusion slide.
23 MEMBER KIRCHNER: Please go onto your 24 conclusion.
25 MR. NAKANISHI: So, basically, through the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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271 1 interactions with the Applicant, we've looked at 2 potential scenarios that we thought might be important 3 to consider in the PRA.
4 And we're basically concluding that 5 there's no known risk-significant contributors that 6 are unaccounted for in the PRA, and that we're able to 7 make the safety findings as described in the SRP.
8 And that concludes my presentation.
9 MEMBER KIRCHNER: Questions?
10 At this point, thank you. We have to 11 remember that we have to turn to the public for any 12 comments, so Mike Snodderly, I see we have a sidebar 13 that someone from NuScale wants to make a comment?
14 Mike Melton, would you go ahead and make 15 your comment and then we'll turn to the public.
16 MR. MELTON: Yes, sir. Can you hear me 17 well?
18 MEMBER KIRCHNER: Yes, I can hear you, 19 Mike.
20 MR. MELTON: Okay, I had to mute and then 21 I get a message that I'm no longer muted and I miss 22 conversation. So, I believe we can talk about this 23 more tomorrow in the closed session.
24 We haven't spoken up about the $29 of 25 reactivity. We definitely do not agree with that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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272 1 number and we'd be happy to talk about that even more 2 tomorrow.
3 So, I think there's been a little bit of 4 excitement on that but we actually do not agree with 5 that based on reactivity, and we'll address that 6 tomorrow. The point about post-accident recovery 7 procedures is not within the scope of the DCA.
8 They are not within the scope of the DCA 9 and I think the NRC has pointed that out as well. So, 10 that part we definitely agree is not within the scope 11 of the DCA.
12 So, I think in closed session we will have 13 an opportunity to get some of these real details. I 14 just want to be able to say we can have a much more 15 positive spin on this but we're going to need to 16 provide the details to Dr. Leuba to satisfy those 17 concerns.
18 That's all, and thank you.
19 MEMBER KIRCHNER: Thank you, Mike. Mike 20 Snodderly, can we turn next for public comments if 21 there are any and ask to see -- I assume right now the 22 public line is open?
23 MR. DASHIELL: The public line is open for 24 comment.
25 MEMBER KIRCHNER: Thank you, sir. Okay, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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273 1 members of the public, if there is anyone out there 2 who wishes to make a comment, please state your name 3 and make your comment.
4 MS. FIELDS: This is Sarah Fields --
5 MEMBER KIRCHNER: Go ahead, Sarah.
6 MS. FIELDS: -- from Utah and I have a few 7 comments to make. I know this is very difficult and 8 complex and time-consuming and tiring for you all, so 9 I do appreciate everyone's efforts.
10 I had two comments. One has to do with 11 NuScale and their development of a control room 12 staffing topical report, which will accompany their 13 standard design approval.
14 And they had a meeting with the NRC on May 15 28th and they had slide presentations. And what 16 NuScale would like to do is have a pathway for any 17 NuScale COL Applicant to reduce the control room 18 staffing to one control room operator and two senior 19 operators.
20 So, when you're considering the issues 21 having to do with what happens to recovery in case of 22 a boron dilution situation, you might also think about 23 having one operator for all 12 modules and two senior 24 operators in the control room.
25 I think this topical report does bring up NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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274 1 some very serious issues in light of NuScale DCA 2 discussion today.
3 Also, the NRC with the support of the 4 nuclear industry and the Department of Energy has 5 proposed changes to emergency preparedness rules 6 applicable to small modular reactions and other new 7 reactor technology.
8 This proposed rule would make it possible 9 to reduce the size of the plume exposure pathway, 10 emergency planning zone to the site boundary, rather 11 than the usual ten-mile zone.
12 The draft rule is currently open for 13 public comment and the docket number is NRC-2015-0225.
14 I've asked for an extension of the 15 comment period, which ends July 27th, because I feel 16 that a lot of the discussion related to the NuScale 17 design SMR is relevant to this NRC proposed rule that 18 states that new emergency planning requirements and 19 guidance would adopt a performance-based, technology-20 inclusive, risk-informed, and consequence-oriented 21 approach.
22 So, I think that all of the information 23 that is being presented to the ACRS, the ACR 24 discussion, the rulemaking procedure, is relevant to 25 this proposed rulemaking as it affects the risk NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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275 1 associated with the NuScale design and others designs.
2 I'm not quite sure why the NRC, and this 3 is another Department within the NRC, why they are 4 moving forward with this when there are so many 5 unknowns regarding the NuScale design and they're 6 talking about performance-based reactor approach and 7 consequence-oriented approach when at this time we 8 really have no performance to consider and there are 9 many risks and consequences that have yet to be 10 explored.
11 Oh, also, I'd like to know what the 12 NuScale schedule would be for tomorrow and how a 13 member of the public would be able to access the 14 sessions that are not closed when it comes to the 15 NuScale design, and how a member of the public can 16 find out at what time an open session for the ACR risk 17 review will be started.
18 Hello?
19 MEMBER BLEY: Matt, are you going to 20 address that?
21 CHAIR SUNSERI: Yes, we take the comments, 22 I heard the comments. We're going to talk about our 23 schedule at the end of this session today.
24 MRS. FIELDS: Yes, but you're going to 25 close the session. Are you going to talk about it NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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276 1 now?
2 CHAIR SUNSERI: Yes, ma'am. I will 3 address the schedule for tomorrow before we leave 4 today, if you can just hang on for a little.
5 MRS. FIELDS: Before you close the open 6 portion?
7 CHAIR SUNSERI: Correct.
8 MRS. FIELDS: Thank you.
9 MEMBER KIRCHNER: Thank you, Sarah. I 10 apologize, I was disconnected for a bit there. So, 11 was Sarah provided an answer about when the public 12 sessions would reconvene?
13 CHAIR SUNSERI: Not yet, Walt, I'm going 14 to do that when we get to that point.
15 MEMBER KIRCHNER: I think, Sarah, if you 16 would hold on, I think the Chairman is going to make 17 an announcement about schedule once we conclude our 18 NuScale discussion this afternoon.
19 Are there any other comments from members 20 of the public?
21 CHAIR SUNSERI: Not yet, Walt. I think we 22 might have lost Walt again. Are you there, Walt?
23 Okay, we lost him.
24 Any other members of the public wishing to 25 make a statement? Okay, hearing none, Mike, can you NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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277 1 close the public line?
2 MR. DASHIELL: The public line is now 3 closed.
4 CHAIR SUNSERI: Okay, so let me extend my 5 appreciation to everyone during the very long meeting 6 today, in particular members of the public for their 7 patience and endurance to be at this late hour of the 8 afternoon.
9 And thanks for all the presentations from 10 Staff and NuScale. As you can tell, it's very 11 detailed. We are looking for information to help 12 inform our decision and there's a lot of details 13 necessary to do that.
14 As far as tomorrow goes, we're going to go 15 into recess now. We're not going to have any more 16 discussions today. Tomorrow morning at 9:30 a.m. we 17 will reconvene in an open session.
18 We will address any comments or questions 19 from the ACRS Members that can be dealt with in the 20 open session. I anticipate that being a short session 21 and then we will ask for any public comments at that 22 time, and then we will go into closed session.
23 So, throughout the day, though, there will 24 be the opportunity that we might go back into open 25 session. So, in order to let the public know what NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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278 1 we're going to do, our Staff is prepared to go onto 2 the public line and make periodic announcements.
3 And so, Scott, I don't know if you had a 4 chance to think about that but I would suggest 5 something like every hour on the hour, somebody make 6 an announcement of where we are and if we are going to 7 be anticipating coming back into open session.
8 MR. MOORE: Yes, Chairman Sunseri, we can 9 do that.
10 CHAIR SUNSERI: Okay, and then as far as 11 what we know, we know we will go back to open session 12 at 2:30 p.m. tomorrow afternoon with the primary goal 13 of starting the TRISO -- I'm looking at my schedule, 14 hold on a second.
15 Yes, 2:30 p.m. tomorrow afternoon and we 16 will pick up the letter report on the EPRI TRISO time.
17 And then however long that takes, I don't know, it may 18 take an hour, it may take three, or whatever.
19 We will then decide at the end of that 20 session what we want to do, if we were going to 21 continue on with NuScale after that or if we are just 22 going to recess for the rest of that day while people 23 go off and think about what they heard from the closed 24 sessions, prepare a draft report that we may be able 25 to put up in a public session should it be developed NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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279 1 far enough along to do that.
2 But that would not be until Friday some 3 time, at the earliest. It would be Friday 11:30 a.m.
4 Friday morning. So, I hope that helps a little bit 5 with the big-picture and I'm sorry that we can't be 6 more detailed in what we're doing.
7 We're kind of picking our way through this 8 and doing the best job we can of keeping everybody 9 informed. So, let me ask if anyone has any questions 10 about the schedule?
11 Can everybody still hear me?
12 MR. MOORE: Yes.
13 MEMBER KIRCHNER: Yes, Matt, thank you.
14 CHAIR SUNSERI: Okay, so just in recap 15 then, we will open tomorrow morning at 9:30 a.m. in 16 open session just to reorient ourselves and address 17 any questions that the Members may have after they've 18 slept on the information they've heard today.
19 We will then have an opportunity for 20 public comment prior to closing that open session, and 21 we will close that open session and go into closed 22 session for approximately four hours.
23 We'll have a lunch break towards the end 24 of that and then we will go back into open session at 25 2:30 p.m., unless something changes during the closed NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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280 1 session which allows us to go back in open session.
2 So, then, the Staff is going to be on the 3 public line making hourly announcements on our 4 progress.
5 Okay, I think I got that out and so any 6 last-minute comments before we close and adjourn for 7 today?
8 MEMBER KIRCHNER: Yes, Mr. Chairman, this 9 is Walt Kirchner. I just want to thank the NuScale 10 and the NRR Staff and research for their participation 11 today and presentations.
12 CHAIR SUNSERI: Good, thank you, Walt, and 13 I certainly agree with that. Everybody did a good 14 job. So, at this point in time, we are recessed until 15 9:30 a.m. Eastern tomorrow morning. Thank you.
16 (Whereupon, the above-entitled matter went 17 off the record at 7:16 p.m.)
18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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LO-0720-70826 July 1, 2020 Docket No.52-048 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738
SUBJECT:
NuScale Power, LLC Submittal of Presentation Materials Entitled ACRS Full Committee Presentation: NuScale Topic - Boron Redistribution and General Design Criterion 33, PM-0720-70785, Revision 0 The purpose of this submittal is to provide presentation materials to the NRC for use during the upcoming Advisory Committee on Reactor Safeguards (ACRS) NuScale Full Committee Meeting on July 8, 2020. The materials support NuScales presentation of boron redistribution and General Design Criterion 33.
The enclosure to this letter is the nonproprietary presentation entitled ACRS Full Committee Presentation: NuScale Topic - Boron Redistribution and General Design Criterion 33, PM-0720-70785, Revision 0.
This letter makes no regulatory commitments and no revisions to any existing regulatory commitments.
If you have any questions, please contact John Fields at 541-452-7425 or at JFields@nuscalepower.com.
Sincerely, y,
Zackary W. Rad
- Director, Di t R Regulatory l t Affairs Aff i NuScale Power, LLC Distribution: Robert Taylor, NRC
$QQD%UDGIRUG15&
Michael Snodderly, NRC Christopher Brown, NRC Gregory Cranston,NRC
Michael Dudek, NRC
Enclosure:
ACRS Full Committee Presentation: NuScale Topic - Boron Redistribution and General Design Criterion 33, PM-0720-70785, Revision 0 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com
LO-0720-70826
Enclosure:
ACRS Full Committee Presentation: NuScale Topic - Boron Redistribution and General Design Criterion 33, PM-0720-70785, Revision 0 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360-0500 Fax 541.207.3928 www.nuscalepower.com
NuScale Nonproprietary ACRS Full Committee Presentation NuScale Topic Boron Redistribution and General Design Criterion 33 July 8, 2020 1
PM-0720-70785 Revision: 0 Copyright 2020 by NuScale Power, LLC.
Template #: 0000-21727-F01 R6
Presenters Rebecca Norris Licensing Supervisor Paul Infanger Licensing Specialist 2
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Agenda
- Boron Redistribution Update
- Boron Redistribution Audit
- Summary of Final Design Changes
- General Design Criterion 33 DCA Changes
- Conclusions 3
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Boron Redistribution Update
- During ACRS Full Committee meeting June 3 and 4, 2020, scenarios were discussed that could lead to dilution of fluid in reactor pressure vessel (RPV) downcomer
- under certain conditions, ECCS actuation or restoration of natural circulation flow could transport diluted coolant to the reactor core
- presented design solutions to prevent or mitigate boron redistribution
- The purpose of this presentation is to inform the ACRS of additional work, since the June 3 and 4, 2020 meeting, required to complete design changes, changes to associated Topical Reports, and FSAR changes 4
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Boron Redistribution Audit
- Audit initiated March 9, 2020
- Daily update meetings between NuScale and NRC staff
- Numerous technical calls
- Docketed twenty-one submittals with design change information, analyses and DCA changes
- DCA Revision 4.1 (complete submittal all Parts) June 19, 2020
- Public Audit Exit Meeting on Boron Redistribution held June 26, 2020 5
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Summary of Final Design Changes
- Addition of four 3/4-inch holes Actuation on RCS in riser at midpoint of steam Pressure generator (SG)
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DCA Revision 4.1 Boron Redistribution Changes
- Table 6.3-1 ECCS Actuation and Table 15.0-7 Analytical Limits
- Added reference to ECCS actuation signal interlocks in Table 7.1-5
- Section 15.0.5 Long Term Cooling
- Added description of riser hole flow path evaluation
- Downcomer boron concentration remains above critical boron concentration during DHRS Cooldown for beginning of cycle (BOC) and middle of cycle (MOC)
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LOCA Topical Report Boron Redistribution Changes
- LOCA Topical Report changes (submitted June 19, 2020)
- Added description of ECCS actuation on low RCS pressure
- Steam space LOCAs and inadvertent RVV opening and some liquid space LOCAs actuate ECCS on low RCS pressure
- Most liquid space breaks and inadvertent RRV actuate ECCS on CNV Level
- Earlier ECCS actuation on RCS pressure less limiting for MCHFR and collapsed liquid level above the top of active fuel (TAF)
- Existing results remain conservative and bounding
- Added descriptions of ECCS actuation signal interlocks
- Interlocks prevent ECCS actuation for non-LOCA events and expected operational conditions
- Discussed function and impact of riser holes
- Minimum and maximum RCS flow unchanged 8
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- General Design Criterion (GDC) 33 requires that a reactor coolant makeup system be available to mitigate small RCS breaks with or without power available
- NPM design does not require additional coolant to maintain adequate core cooling for duration of design basis events (DBEs)
- chemical and volume control system (CVCS) makeup system and backup power are not safety-related
- ECCS and containment isolation systems credited to meet intent of GDC 33
- ECCS actuates automatically for LOCA spectrum (greater than makeup system capacity and most smaller leaks)
- Analysis demonstrates that specified acceptable fuel design limits (SAFDLs) met for small RCS leaks 9
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- Basis for GDC 33 Exemption enhanced
- DCA Revision 4 only included statement in Section 9.3.4 that GDC 33 was not applicable to NPM design and that makeup from CVCS is not credited
- Small leaks with no ECCS, boron mixing maintained by riser holes until holes uncovered
- Core concentration remains above initial concentration for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />
- ECCS actuation on setpoints (or by 24-hour timer for events with a loss of AC) mitigates most leaks
- Evaluation shows smaller leaks with cold pool temperature do not challenge SAFDLs
- No credit for CVCS makeup 10 PM-0720-70785 Revision: 0 Copyright 2020 by NuScale Power, LLC.
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Summary and Conclusions
- Design changes preclude boron redistribution for postulated design basis and beyond design basis events
- ECCS actuation on low RCS pressure or high CNV level
- assures initial flow out of RPV to preclude influx of unborated water from CNV or downcomer
- Riser holes assure boron mixing in downcomer and core region
- when DHRS cools and shrinks RCS level below the riser
- To assure core concentration remains above initial concentration
- Basis for GDC 33 added to Chapter 4 and Chapter 6
- No reliance on CVCS makeup or operator action
- SAFDLs met for all RCS leaks 11 PM-0720-70785 Revision: 0 Copyright 2020 by NuScale Power, LLC.
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Acronyms AC - alternating current RRV - reactor recirculation valve ACRS - Advisory Committee on Reactor RVV - reactor vent valve Safeguards SAFDL - specified acceptable fuel design limits BOC - beginning of cycle SG - steam generator CNV - containment vessel TAF - top of active fuel CVCS - chemical and volume control system DCA - Design Certification Application DHRS - decay heat removal system ECCS - emergency core cooling system EOC - end of cycle FSAR - Final Safety Analysis Report GDC - General Design Criteria LOCA - loss-of-coolant accident MCHFR - minimum critical heat flux ratio MOC - middle of cycle NPM - NuScale Power Module RCS - reactor coolant system RPV - reactor pressure vessel 12 PM-0720-70785 Revision: 0 Copyright 2020 by NuScale Power, LLC.
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Portland Office Richland Office 6650 SW Redwood Lane, 1933 Jadwin Ave., Suite 130 Suite 210 Richland, WA 99354 Portland, OR 97224 541.360.0500 971.371.1592 Charlotte Office Corvallis Office 2815 Coliseum Centre Drive, 1100 NE Circle Blvd., Suite 200 Suite 230 Corvallis, OR 97330 Charlotte, NC 28217 541.360.0500 980.349.4804 Rockville Office 11333 Woodglen Ave., Suite 205 Rockville, MD 20852 301.770.0472 http://www.nuscalepower.com Twitter: @NuScale_Power 13 PM-0720-70785 Revision: 0 Copyright 2020 by NuScale Power, LLC.
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Focus Area: Boron Redistribution/Applicable Design Changes NuScale Design Certification Application ACRS Full Committee Meeting July 8, 2020 Non-Proprietary
Agenda
- NRC Staff Review Team
- Background
- Design Changes
- Discussion by Review Team (Chapter &
Design Change)
- Conclusion Non-Proprietary 2
NRC Staff Review Team DEX/EMIB Division of Engineering and External Hazards/Mechanical Engineering and Inservice Testing Branch:
Angela Buford Thomas Scarbrough Yuken Wong Steve Hambric (consultant)
DSS/SNRB Division of Safety Systems/Nuclear Methods, Systems, and New Reactors Branch:
Becky Patton Carl Thurston Shanlai Lu Ryan Nolan Joshua Borromeo (NRR/DSS/SNSB)
Jeffrey Schmidt (NRR/DANU/UART)
Alex Siwy John Lehning (NRR/DSS/SFNB)
Leonard Ward (consultant)
RES/DSA/CRAB Research/Division of Systems Analysis/Codes and Reactor Analysis Branch:
Andrew Ireland Peter Yarsky Non-Proprietary 3
NRC Staff Review Team DNRL/NCSG Division of New and Renewed Licenses/Corrosion and Steam Generator Branch:
Steve Bloom Greg Makar Leslie Terry DSS/SNSB Division of Safety Systems/Nuclear Systems Performance:
Scott Krepel Syed Haider DEX/EICA Division of Engineering and External Hazards/Instrumentation and Controls A:
Jeanne Johnston Booma Venkataramen Dinesh Taneja Joe Ashcraft Dawnmathews Kalathiveettil DSS/STSB Division of Safety Systems/Technical Specifications Branch:
Vic Cusumano Craig Harbuck Non-Proprietary 4
NRC Staff Review Team DRO/IOLB Division of Reactor Oversight/Operator Licensing and Human Factors Branch:
Christian Cowdrey Lauren Nist Maurin Scheetz DRA/APLC Division of Risk Assessment/PRA Licensing Branch C:
Stacy Rosenberg Anne-Marie Grady Pohida, Marie Tony Nakanishi Alissa Neuhausen DNRL/NRLB Division of New and Renewed Licenses/New Reactor Licensing Branch:
Michael Dudek Marieliz Johnson Prosanta Chowdhury Getachew Tesfaye Omid Tabatabai Greg Cranston Bruce Bavol Non-Proprietary 5
Background
- On February 27, 2020, NuScale notified NRC staff of an error in their boron redistribution analysis and informed that they are following their corrective action program.
- Staff started an audit on March 4, 2020
- On May 1, 2020, staff sent a schedule letter (ML20112F455) to NuScale. The purpose of this letter was to communicate the status of the NRC staffs review of the NuScale design certification application given the current schedule and the need for additional design changes.
- On May 20, 2020, NuScale submitted Second Updates to DCA Rev 4, that includes final design change documents for NRC review (ML20141L787).
- On June 3, 2020, staff presented audit status to ACRS members.
Non-Proprietary 6
Design Changes
- ECCS actuation on high containment water level setpoint change
- Addition of riser holes Non-Proprietary 7
Background -
Impacted Chapter SERs
- Chapter 3 - Design of Structures, Components, Equipment, and Systems
- Chapter 4 - Reactor
- Chapter 5 - Reactor Coolant System and Connecting Systems
- Chapter 6 - Engineered Safety Features
- Chapter 7 - Instrumentation and Controls
- Chapter 9 - Auxiliary Systems
- Chapter 13 - Conduct of Operations
- Chapter 15 - Transient and Accident Analyses
- Chapter 16 - Technical Specifications
- Chapter 19 - Probabilistic Risk Assessment and Severe Accident Evaluation Non-Proprietary 8
Background -
Impacted Topical &
Technical Reports Impact - 5 Technical Reports (support various chapters/SERs):
- TR-0616-49121, Setpoint Methodology
- TR-0316-22048, Advanced Sensor
- TR-0516-49084, Containment Response (CRAM)
- TR-0916-51299, Long Term Cooling
- TR-1116-52011, Technical Specifications Regulatory Conformance and Development Impact - 2 Topical Reports:
- TR-0516-49416, Non-LOCA (Non-Loss-of-Coolant Accident Analysis Methodology)
- TR-0516-49422, LOCA (Loss-of-Coolant Accident Evaluation Model)
Non-Proprietary 9
Mechanical-Chapter 3 NRR/DEX/EMIB
- 3 - Addition of Riser Holes
- NRC staff reviewed structural integrity and flow-induced vibration (FIV) effects related to the new riser holes.
- Stress concentration due to the riser holes will not significantly affect the alternating stress margin due to turbulent buffeting
- Jet loads from riser holes will not significantly affect the steam generator (SG) tubes
- Riser holes will not cause acoustic resonances
- Flow through the riser holes eliminates the possibility of shear layer flow instabilities
- Should an instability occur, flow instability frequencies and upper riser acoustic frequencies are well separated
- Staff determined that NuScale adequately assessed the riser structural integrity and potential FIV effects of the four riser holes.
Non-Proprietary 10
Mechanical-Chapter 3 NRR/DEX/EMIB ECCS main valve self-opening
- Target Rock 2015 report describes testing that demonstrates main valve spring will open main valve at low differential pressure.
- Test report provides reasonable demonstration that ECCS main valve spring satisfies 10 CFR 50.43(e).
- ECCS main valve spring is important to safety because of assumed performance of spring function.
- Design specifications will include ASME Standard QME-1 qualification.
Non-Proprietary 11
I&C-Chapter 3 & 7 NRR/DEX/EICA
- 1 - ECCS actuation on high containment water level setpoint change
- Change to CNV water level sensors is not required
- Changes made in Chapter 7 are consistent with assumptions made for Chapter 15 safety analysis:
- CNV water level analytical limit range (240 - 264)
- High CNV level nominal setpoint (252)
- +/-12 allowance from nominal setpoint
- Setpoint methodology technical report revised to demonstrate:
- Revised analytical limit range is within the 100 calibrated span (220 - 320)
- Calculated total loop uncertainty is bounded by +/-12 nominal setpoint allowance Note: All levels are in terms of module elevation with the global zero elevation at the bottom of the reactor pool Non-Proprietary 12
I&C-Chapter 3 & 7 NRR/DEX/EICA
- FSAR Table 3.2-1 revised accordingly
- Changes made in Chapter 7 and Tier 1 Tables 2.5-2 and 2.5-4 are consistent with assumptions made for Chapter 15 safety analysis:
- Low WR RCS pressure analytical limit of 800 psia
- Low WR RCS pressure signal actuation delay time of 2.0 seconds
- ECCS actuation automatically bypassed when Thot < 475F (T-6 interlock) or CNV pressure < 1psia (P-1 interlock)
Non-Proprietary 13
I&C-Chapter 3 & 7 NRR/DEX/EICA
- Setpoint methodology technical report revised to:
- Add setpoint calculation for low WR RCS pressure protective function
- Demonstrate that calculated total loop uncertainty is bounded by
+/-100 psia allowance for nominal setpoint of 900 psia assumed in safety analysis
- Advanced sensor technical report revised to:
- Add T-6 interlock function for NR RCS hot temperature sensors
- Add ESFAS actuation function for WR RCS pressure sensors
- Change safety and risk classification for WR RCS pressure sensors to A1 (was A2)
- Add P-1 interlock function for NR containment pressure sensors Non-Proprietary 14
I&C-Chapter 3 & 7 NRR/DEX/EICA
- Digital-based sensors CCF assessment
- Digital-based sensors are used for low RCS pressure signal
- Low RCS pressure ECCS actuation signal is implemented primarily to mitigate the possibility of a boron dilution scenario as a result of a small-break LOCA
- Actuation signal has interlocks T-6 and P-1 to prevent unnecessary ECCS actuation for non-LOCA events
- Limiting case analyzed for LOCA boron dilution is a smaller break in the LOCA break spectrum that has an ECCS actuation on low RCS pressure
- This conservative analysis assumes highest worth control rod assembly not inserted and neglects negative reactivity insertion from xenon
- Best-estimate D3 coping analysis, which credits xenon reactivity and an all-rods-in condition concluded that an earlier ECCS actuation on low RCS pressure would not be required for any break size or location in the LOCA break spectrum
- In these cases, ECCS actuation occurs due to high CNV level or low DP across the ECCS valves
- Sufficient diversity exists such that ECCS is available to mitigate these small-break LOCA events Non-Proprietary 15
Tech Spec-Chapter 16 NRR/DSS/STSB
- 1 - ECCS actuation on high containment water level setpoint change
- No changes to Function 22.a of MPS instrumentation list in TS Table 3.3.1-1; setpoint not stated in LCO 3.3.1; conforming changes to Bases not needed
- Function 23.a added to MPS instrumentation list in TS Table 3.3.1-1 (relabeled Functions 23, 24, and 25 as 24, 25, and 26)
- Requires 4 operable channels in MODE 1 and MODE 2 with RCS Hot Temperature above 475 degrees F (new T-6 interlock);
- Condition N added to provide default required actions to exit applicability
- ECCS actuation at 800 psia RCS pressure is blocked unless containment pressure exceeds 1 psia (new P-1 interlock)
- Existing Surveillances apply
- Updated references to relabeled MPS Functions; conforming changes and additions to Bases
- 3 - Addition of riser holes
- Conforming changes and additions to Bases for TS Subsections 3.3.1 and 3.5.1 Non-Proprietary 16
Rx Systems-Chapter 5 NRR/DSS/SNRB
- 3 - Addition of riser holes
- Staff reviewed the effect of riser holes on steady-state RCS characteristics and DHRS performance
- Staff audited NuScale sensitivity calculations for five non-LOCA events that showed the riser holes had an insignificant impact on:
- Steady-state RCS and secondary parameters of interest
- Non-LOCA event progressions and figures of merit
- Staff performed confirmatory calculations of a DHRS cooldown and observed minimal differences with riser holes
- Staff finds that steady-state RCS parameters and DHRS performance described in DCA Part 2, Tier 2, Chapter 5, would not change substantially if riser holes were added
- Therefore, changes to DCA Part 2, Tier 2, Chapter 5, other than a description of the riser holes are not necessary Non-Proprietary 17
Rx Systems-Chapter 6 & 15 NRR/DSS/SNRB Areas Not Substantially Affected by the Design Changes
- DCA Part 2, Tier 2, Section 6.2.1.1, and CRAM technical report
- Limiting DBEs and resulting values for peak CNV pressure (994 psia) and peak CNV wall temperature (526 °F) unaffected
- Previously non-limiting cases remain non-limiting with design changes
- LOCA and non-LOCA topical reports
- Staff audited related NuScale calculations and confirmed only conforming changes needed
- Chapter 15 non-LOCA events
- As previously discussed, riser holes have an insignificant impact on steady-state, transient progression, and figures of merit
- Changed high CNV level ECCS actuation setpoint is not relevant to non-LOCAs
- Unlikely to actuate ECCS on new low RCS pressure signal
- Chapter 15 inadvertent ECCS actuation event (15.6.6)
- Staff audited NuScales qualitative assessment and agrees that the design changes would have an insignificant impact on steady-state, transient progression, and figures of merit Non-Proprietary 18
Rx Systems-Chapter 6 & 15 NRR/DSS/SNRB Areas Affected by Design Changes
- These are primarily affected by new low pressure signal and revised (lowered) CNV high level actuation setting
- Steam space and larger liquid space breaks now actuate earlier on low pressure
- Earlier ECCS and lowered CNV level setting improves boron redistribution
- Min Collapsed Level above TAF and Min CHFR figures of merit were unchanged Non-Proprietary 19
Rx Systems - Chapter 6 &15 NRR/DSS/SNRB
- The applicant added riser holes to limit downcomer dilution during a DHRS cooldown
- RCS water level may drop below the riser following a reactor trip depending on initial RCS conditions
- NRELAP5 and the staffs TRACE model show riser uncovery between 5-6 hours under nominal conditions assuming no operator action
- ECCS valves could open on either a loss of ac power for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (24-hour timer) or on main valve low differential pressure causing a potential in surge of diluted downcomer water into the core
- The applicant performed a series of hand calculations to determine the riser hole size and elevation to maintain downcomer boron concentration above the critical concentration for times in cycle when significant downcomer dilution is possible Non-Proprietary 20
Rx Systems - Chapter 6 &15 NRR/DSS/SNRB
- The applicant evaluated two different primary to secondary side heat transfer modes depending on the relationship of primary to secondary side level
- Convective cooling where the secondary side level is below the primary side level and heat is primarily transferred through the riser wall
- Boiling/condensing where heat is primary removed from condensing steam on exposed steam generator tubes when secondary side level is above the primary side level
- Each heat transfer mode has different condensation rates and thermal-hydraulic phenomenon that determine the riser hole flow rates
- The staff audited the applicants hand calculation to ensure condensation and riser hole flow rates were sufficient to prevent significant downcomer dilution Non-Proprietary 21
Rx Systems - Chapter 6 &15 NRR/DSS/SNRB
- NRELAP5 and TRACE models show pressure and temperature decreasing during a cooldown consistent with convective heat transfer mode
- Both NRELAP5 and TRACE show liquid discharge over the riser for approximately one and half to two hours after riser uncovery
- The applicants hand calculation conservatively assumes no boron containing liquid discharge over the riser
- The applicant assumed state point values for the decay heat, RCS pressure, steam generator pressure and, for the convective case, a riser to downcomer temperature difference as a function of time
- Staff compared the assumed state point values and found them either reasonable or conservative compared to the applicants NRELAP5 and the staffs NRELAP5 and TRACE confirmatory cases.
- Staff audited the applicants hand calculated condensation rate for both the convective and boiling/condensing heat transfer mode and found them to be conservative Non-Proprietary 22
Rx Systems - Chapter 6 &15 NRR/DSS/SNRB Convective Heat Transfer Mode
- For the convective case, the staff confirmed the applicants hand calculation of through wall heat transfer was conservative
- The staff compared the riser to downcomer temperature difference, after liquid discharge over the riser, and found the temperatures consistent with staffs NRELAP5 and TRACE confirmatory runs
- When decay heat is high, liquid discharge prevents a direct comparison of the hand calculated and NRELAP5 and TRACE riser to downcomer temperature difference
- Staff reviewed the methodology associated with the riser and downcomer level determination and found it to be reasonable Non-Proprietary 23
Rx Systems - Chapter 6 &15 NRR/DSS/SNRB Convective Heat Transfer Mode - contd
- Staff reviewed the form loss factor and found the value used in the hand calculation to be conservative
- Staff audited the applicants energy balance verification and agrees, within the framework of the hand calculation, a conservative riser hole mass flow rate
- The total of condensation, through wall and riser hole flow energy is less than the decay heat
- Staff compared the applicant's hand calculated riser hole mass flow rate with the applicants NRELAP5 cases and the staffs TRACE confirmatory cases and found the applicants hand calculated values reasonable Non-Proprietary 24
Rx Systems - Chapter 6 &15 NRR/DSS/SNRB Boiling/Condensing Heat Transfer Mode
- Two-phase level swell in riser during extended decay heat removal system operation would create differential pressure at riser flow holes, driving flow from riser to downcomer
- Applicant performed analysis through 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> using a quasi-steady statepoint analysis for a generic event progression
- Calculation included conservatisms intended to underestimate riser void fraction and overestimate condensation rate
- NRC staff reviewed applicants methodology, audited supporting calculations, and performed confirmatory calculations
- Review addressed scenarios with no reactor coolant system leakage
- NRC staff found applicants method and results acceptable for the conditions reviewed in the application Non-Proprietary 25
Rx Systems - Chapter 6 &15 NRR/DSS/SNRB Boron Concentration
- The core/riser and downcomer/low plenum is assumed to be quasi-steady state where core inlet flow is equal to riser hole flow and condensation rates
- The applicant uses a wave front model to transport boron from the riser to downcomer and back to the core
- The staff finds the wave front model conservative as the model maximizes boron transfer out of and minimizes boron transport into the downcomer affectively ignoring any potential recirculation mixing
- The applicants riser hole design acceptance criterion is to maintain a downcomer boron concentration greater than the critical concentration, including the effects of Xenon, with the highest worth control rod remaining out of the core, at BOC and MOC conditions for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />
- The staff agrees the applicants acceptance criterion is conservative as maintaining a downcomer boron concentration above the critical value ensures shutdown should the ECCS valves open at times in life when significant downcomer dilution is possible Non-Proprietary 26
Rx Systems - Chapter 6 &15 NRR/DSS/SNRB Boron Concentration - contd
- At EOC negligible downcomer dilution exists such that a downcomer in surge between 24 and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> will not cause a return to power greater than that evaluated in DCA 15.0.6
- As noted in the staffs safety evaluation Section 15.0.6, a return to power under riser uncovered conditions is not expected for EOC nominal conditions and is bounded by the ECCS cooldown return to power Non-Proprietary 27
Rx Systems - Chapter 6 &15 NRR/DSS/SNRB
- NuScale requested exemption from GDC 33
- GDC 33 requires a system to supply RCS makeup for protection against RCS leaks and small breaks
- NuScale analyzed the design changes following a similar approach as extended DHRS to ensure underlying purpose of GDC 33 was met
- Staff evaluated the analysis with focus on boron dilution and determined the design continues to meet the underlying purpose of the criterion Non-Proprietary 28
Rx Systems- Chapter 4 &15 (Recovery)
NRR/DSS/SNRB
- Post-event recovery actions are important to capture in the development of operating procedures
- outside the scope of the design certification review
- procedures will be developed by the COL applicant or holder at a future licensing stage (COL item 13.5-2)
Non-Proprietary 29
PRA-Chapter 19 NRR/DRA New ECCS actuation on low RCS pressure signal
New riser bypass holes
- Bypass holes provide a flow path from the riser through the downcomer to prolong boron mixing if level drops below top of riser.
- NRELAP PRA model was updated with new design features.
Non-Proprietary 30
PRA-Chapter 19 PRA audit overview Staff audited assumptions and/or results of revised T/H analysis for all initiators evaluated in the Level 1 internal events PRA.
Low pressure ECCS interlocks prevent ECCS actuation for Non-LOCA events
- RCS is subcooled in DHRS cooldown events (< 475
ºF) and have no increase in CNV pressure.
Non-Proprietary 31
PRA-Chapter 19 Non LOCA scenarios Certain non LOCA scenarios now result in ECCS actuation on the low RCS pressure signal:
- Continuous RSV cycling (e.g. DHRS failure)
The staff confirmed impacts of additional ECCS challenges with potential for incomplete ECCS actuation are incorporated in the PRA event trees.
Non-Proprietary 32
PRA-Chapter 19 Non LOCA ATWS scenarios CVCS credited to prevent core damage given ATWS with ECCS failure.
Staff questioned whether CVCS injection following ECCS failure could cause core damage due to a reactivity insertion.
Comparing the total liquid mass in the core versus the small CVCS coolant injection rate, coolant injection in the riser will not:
- rapidly reduce liquid temperatures in the core region,
- rapidly condense and collapse voids.
- The two redundant safety-related demineralized supply isolation valves would automatically transfer to the highly borated water source (DCA Section 9.3.4.1).
Staff performed an independent evaluation to confirm NuScale's response that core damage does not result from CVCS injection.
Non-Proprietary 33
PRA-Chapter 19 LOCA ATWS scenarios Based on TH insights, the PRA assumes that LOCA ATWS does not result in core damage upon ECCS actuation.
Breaks on the smaller end of the LOCA spectrum result in:
- later ECCS actuation
Applicant evaluated the following for various break sizes:
- high point vent LOCA (steam space)
Non-Proprietary 34
PRA-Chapter 19 LOCA ATWS scenarios (continued)
- Applicant used N-RELAP5 with 1-D neutron kinetics option and the boron tracking model which has not been reviewed and approved by the staff.
- Due to code uncertainty, NuScale provided sensitivity analyses to show the effect of additional dilution in the downcomer prior to ECCS actuation.
- NuScale also provided a hand calculation using the Fuchs-Nordheim method to support the conclusion that LOCA ATWS does not result in core damage due to reactivity insertion.
Non-Proprietary 35
PRA-Chapter 19 Unisolated CVCS Injection Line Break Outside Containment ECCS actuation may occur when the level in the RPV is well below the RRV elevation.
One train of DHRS is now required to:
- allow the operator to initiate CFDS injection to recover level before core damage Non-Proprietary 36
PRA-Chapter 19 LOCA Inside CNV with failure of containment isolation Given an earlier ECCS actuation, the system will reach atmospheric pressure earlier and lose less coolant from the module.
Staff audited documents describing the integrated coolant mass flow out of the containment and sensitivity studies to evaluate the effects of the ECCS actuation timing Non-Proprietary 37
PRA-Chapter 19 Post Event Recovery from SBLOCA ATWS An operator attempting to inappropriately restore water level using either the CVCS or the CFDS could challenge the reactor by adding positive reactivity if diluted water is present in the downcomer.
Either action to inject would likely be precluded by the plant-specific emergency operating procedures (EOPs).
Staff independently calculated the reactivity insertion rate for CFDS and net void shrinkage rates for CVCS riser injection and concluded:
- CFDS slow rate of core refill, time to add 1$ reactivity >> fuel thermal time constant - no core damage.
- Core damage from rapid void collapse following CVCS riser injection evaluated for ATWS with small leak and found very unlikely (must be at very low decay heat without rod insertion, very low pressure with high CVCS flow rates)
Non-Proprietary 38
PRA-Chapter 19 Conclusions The staff confirmed that NuScale appropriately updated:
- DCA event trees
- DCA Table 19.1-7 on success criteria
- DCA Table 19.1-21: Key Assumptions for the Level 1 Full Power Internal Events Regarding boron redistribution, the staff confirmed
- There are no known significant risk contributors that are unaccounted for in the PRA.
- DCA Chapter 19 risk results and insights were appropriately updated so that staff could finalize their safety findings consistent with SRP 19.0 Non-Proprietary 39
Questions?
Non-Proprietary 40
Topical Report EPRI-AR-1 Uranium Oxycarbide (UCO) Tristructural Isotropic (TRISO) Coated Particle Fuel Performance Andrew Sowder, Ph.D., CHP Senior Technical Executive Advisory Committee on Reactor Safeguards July 8, 2020 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
TRISO Fuel Topical Report Objective:
Support commercialization of mature advanced nuclear designs to maintain nuclear as a future energy generation option Scope:
- U.S. Department of Energy (DOE)-sponsored AGR-1 and AGR-2 fuel campaigns
- Global context, history, and experience
- Performance demonstration of TRISO-coated particle fuel with uranium oxycarbide (UCO) kernels
- Irradiation, post-irradiation examination (PIE), and available post-irradiation safety testing data Publicly available report:
- Uranium Oxycarbide (UCO) Tristructural Isotropic (TRISO) Coated Particle Fuel Performance: Topical Report EPRI-AR-1(NP).
EPRI, Palo Alto, CA: May 2019. 3002015750 https://www.epri.com/#/pages/product/3002015750/
2 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
U.S. and International Experience International experience:
- High-quality TRISO fuel can be fabricated in a repeatable, consistent manner
- Fuel performance with very low in-service failures is achievable under anticipated HTGR conditions U.S. DOE AGR program:
- Fabrication of high-quality low-defect fuel is achievable at industrial scale via stable, repeatable processes
- Demonstration of excellent irradiation performance of a large population of UCO TRISO fuel particles under high-burnup, high-temperature HTGR conditions 3 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
TRISO Coated Particles and Fuel Forms
- International development and use of TRISO fuel has occurred over 60 years
- U.S. DOE Advanced Gas Reactor Fuel Development and Qualification (AGR)
Program launched in 2002 Figures courtesy of Idaho National Laboratory 4 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
A Model Collaboration and Public-Private Partnership DOE and EPRI co-funding Industry in-kind support NRC off-fee review 5 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
Topical Report Contents (sections for NRC review in blue)
Section 1 - report scope, purpose, content, and structure Section 2 - TRISO fuel in the context of past Nuclear Regulatory Commission (NRC) regulatory activities and current regulatory framework Section 3 - non-AGR experience base for coated particle fuel technology in the United States and internationally Section 4 - basis for the particle design and test conditions used in the AGR program Section 5 - brief overview of the AGR program, including the different program elements and the four fuel irradiation campaigns around which the program is structured Section 6 - irradiation response of fuel particles in the AGR-1 and AGR-2 campaigns Section 7 - follow-on safety test performance and post-irradiation examination data for AGR-1 and AGR-2 Section 8 - summary of the report, including conclusions for NRC approval Section 9 - references Appendix A - more detail on the U.S. regulatory history related to TRISO fuel Appendix B - more detail on the international coated particle fuel experience base Appendix C - information from the AGR-1 and AGR-2 fuel specifications 6 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
Conclusion 1 Testing of UCO TRISO-coated fuel particles in AGR1 and AGR2 constitutes a performance demonstration of these particle designs over a range of normal operating and off-normal accident conditions. Therefore, the testing provides a foundational basis for use of these particle designs in the fuel elements of TRISO-fueled HTR designs (that is, designs with pebble or prismatic fuel and helium or salt coolant).
7 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
Conclusion 2 The kernels and coatings of the UCO TRISO-coated fuel particles tested in AGR1 and AGR2 exhibited property variations and were fabricated under different conditions and at different scales, with remarkably similar excellent irradiation and accident safety performance results. The ranges of those variations in key characteristics of the kernels and coatings are reflected in measured particle layer properties provided in Table 5-5 from AGR1 and AGR2. UCO TRISO-coated fuel particles that satisfy the parameter envelope defined by these measured particle layer properties in Table 5-5 can be relied on to provide satisfactory performance.
8 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
Conclusion 3 Aggregate AGR1 and AGR2 fission product release data and fuel failure fractions, as summarized in this report, can be used to support licensing of reactors employing UCO TRISO-coated fuel particles that satisfy the parameter envelope defined by measured particle layer properties in Table 5-5 from AGR1 and AGR2.
9 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
TogetherShaping the Future of Electricity 10 www.epri.com © 2020 Electric Power Research Institute, Inc. All rights reserved.
Advanced Gas Reactor Fuel Development and Qualification Program: Overview and AGR-1 and AGR-2 Results Summary Advisory Committee on Reactor Paul Demkowicz, Ph.D.
Safeguards Idaho National Laboratory July 8, 2020 AGR Program Technical Director
Advanced Gas Reactor Fuel Development and Qualification Program Objectives and motivation
- Provide data for fuel qualification in support of reactor licensing Reduce market
- Establish a domestic commercial vendor for TRISO fuel entry risk Approach
- Focus is on developing and testing UCO TRISO fuel
- Develop fuel fabrication and quality control measurement methods, first at lab scale and then at industrial scale
- Perform irradiation testing over a range of conditions (burnup, temperature, fast neutron fluence)
- Perform post-irradiation examination and safety testing to demonstrate and understand performance during irradiation and during accident conditions
- Develop fuel performance models to better predict fuel behavior
- Perform fission product transport experiments to improve understanding and refine models 2 energy.gov/ne
AGR Program Timeline Early test of lab-scale UCO fuel Designed-to-fail (DTF) fuel to assess Program performance; shakedown of fission product retention and transport participants:
test train design. in reactor graphite and fuel matrix. INL ORNL Engineering-scale particles in Fuel qualification test. BWXT lab-scale compacts. Includes Engineering-scale UCO UCO and UO2 fuel. particles and compacts.
Fuel AGR-1 AGR-2 AGR-3/4* AGR-5/6/7 Fabrication Irradiation AGR-3/4 (in ATR)
AGR-1 AGR-2 AGR-5/6/7 AGR-1 AGR-5/6/7 PIE *Includes fabrication of AGR-2 DTF particles; driver fuel taken from AGR-1 fabrication campaign AGR-3/4 3 energy.gov/ne
AGR-1 and AGR-2 Fuel Irradiations
- Advanced Test Reactor - Large B positions
- Six independent capsules; 12 fuel compacts per capsule
- AGR-1: ~300,000 UCO particles
- AGR-2: ~114,000 UCO particles
- Approx. 2-year irradiation time to simulate 3-year reactor lifetime
- Temperature controlled with He/Ne Key AGR-1 and gas mixtures AGR-2 irradiation
- Fission gas release conditions monitored throughout experiment to assess fuel condition 4 energy.gov/ne
AGR-1 and AGR-2 Temperature Measurement and Control
- Thermocouple (TC) types:
- AGR-1: Type N (9) and Mo/Nb (10)
- Similar in-pile failure rates
- AGR-2: Type N (11); larger diameter than AGR-1
- All failed by end of irradiation, but less drift compared to AGR-1
- Temperature measurement
- TCs placed in graphite holder surrounding compacts
- Calculated TC temperatures compared to measurements
- Early cycles most important, because TCs were still functioning and had experienced no drift
- Fuel temperatures calculated using the benchmarked thermal model
- Most TCs <1000ºC in both experiments (a few exceptions T<1100ºC)
- Similar approach for AGR-1 and AGR-2 5 energy.gov/ne
Physics and Thermal Models AGR-2 Capsule-average Compact Heat Rate
- Physics Average compact heat rate (W/cm3)
- MCNP-ORIGEN coupled code
- Included daily depletion of TRISO fuel, ATR driver fuel, and capsule components, and shim cylinder rotation
- Post-irradiation comparison to (a) actinide isotopics, (b) fuel burnup, (c) flux wire measurements
- Accounted for relocation of experiment (AGR-2)
- Thermal model D finite element model
- ~350,000 nodes per capsule
- Roughly 1 node per particle in the compacts
- Considered all relevant phenomena:
- Conduction; radiation; heat rates in fuel, graphite and metallic components; graphite shrinkage and changes in thermal conductivity with fluence; thermal conductivity of compacts 6 energy.gov/ne
Thermocouple Drift
- Thermocouple drift evaluated AGR-1 Capsule 5 TC1 and TC3 Drift Monitoring continuously throughout irradiation using control charting
- Compared TC readings to calculated temperatures (captures operating condition changes) and to other TCs in same capsule (indicates differences in TC behavior under similar conditions)
- If no functioning TCs remained, control was based on the model predictions Source: B.T. Pham and J.J. Einerson, AGR-1 Thermocouple Data Analysis, INL/EXT-12-24761 (2012) 7 energy.gov/ne
Temperature Uncertainty
- Temperature uncertainty analyses were performed for AGR-1 and AGR-2
- Considered contribution from uncertainty in all fuel temperature calculation input parameters:
- Fuel heat rate (from physics simulations)
- Ne gas fraction
- Thermal conductance gap width (graphite and
- Capsule shell emissivity fuel compact dimensional change; data from PIE)
- Graphite emissivity
- Graphite thermal conductivity
- Non-fuel component heat rates (from physics
- Fuel compact conductivity simulations)
- Sensitivity studies performed to determine parameters with highest impact on temperature uncertainties
- Uncertainty in individual parameters estimated and total uncertainty in calculated fuel temperatures determined
- Capsule volume-average, time-average temperature uncertainties (T):
AGR-2 Capsule 2 volume-avg and peak
- AGR-1: 33 - 55ºC temperatures and single standard deviation
- AGR-2: 28 - 39ºC uncertainties
- Uncertainty on instantaneous (daily) temperatures higher than time-averaged values 8 energy.gov/ne
AGR-2 Temperature Bias AGR-2 TC residuals
- Temperature bias between measurements and model was assessed by examining TC residuals (Tmeasured - Tcalculated) during early cycles when TC drift was negligible
- TC 6-3 determined to be drifting and unreliable
- For Capsules 2, 3, and 6 the overall bias was close to zero
- For Capsule 5, the bias was assessed as -60ºC (60ºC overprediction in fuel temperature)
- Higher-temperature capsules (AGR-2 Capsule 2, AGR-7) were included in the program plan to address risk of potential temperature bias 9 energy.gov/ne
Fission Product Release from Fuel Compacts vs. Temperature Fission product release data support the temperature uncertainties and biases determined by analyses
- Ag retention in fuel compacts from AGR-1,
- Sr and Eu retention in AGR-2 Capsules 6 and 5 AGR-2, and AGR-3/4 follow a very similar very similar to AGR-1 at same temperature range.
dependence on temperature Notably higher release from AGR-2 Capsule 2 (150
- Inflection points all within ~30ºC to 250ºC higher time-avg vol-avg temperatures).
1.2 1.0E-01 1.0E-01 AGR-3/4 AGR-2 AGR-1 Eu AGR-1 Sr 1.0 AGR-1 1.0E-02 AGR-2 Eu 1.0E-02 AGR-2 Sr 0.8 1.0E-03 1.0E-03 Ag-110m M/C Released fraction Released fraction 0.6 1.0E-04 1.0E-04 0.4 1.0E-05 1.0E-05 0.2 Individual compact 1.0E-06 1.0E-06 110mAg retention 0.0 1.0E-07 1.0E-07 950 1050 1150 1250 950 1050 1150 1250 800 900 1000 1100 1200 1300 1400 Capsule average TAVA Temperature (°C) Capsule average TAVA Temperature (°C)
TAVA Temperature (oC) Eu and Sr release from compacts for each capsule 10 energy.gov/ne
Publications Relevant to AGR-1 and AGR-2 Temperature Measurement, Calculation, and Uncertainty
- B.T. Pham and J.J. Einerson, AGR-1 Thermocouple Data Analysis, INL/EXT-12-24761 (2012)
- B.T. Pham and J.J. Einerson, AGR-2 Final Data Qualification Report for U.S. Capsules -
ATR Cycles 147A through 154B, INL/EXT-14-32376 (2014)
- G.L. Hawkes, AGR-1 Daily As-Run Thermal Analyses, ECAR-968 Rev. 4 (2014)
- G.L. Hawkes, AGR-2 Daily As-Run Thermal Analyses, ECAR-2476 Rev. 1 (2014)
- B.T. Pham, J.J. Einerson, and G.L. Hawkes, Uncertainty Quantification of Calculated Temperatures for the AGR-1 Experiment, INL/EXT-12-25169, Rev. 1 (2013)
- B.T. Pham, J.J. Einerson, and G.L. Hawkes, Uncertainty Quantification of Calculated Temperatures for the U.S. Capsules in the AGR-2 Experiment, INL/EXT-15-34587 (2015)
- Over a dozen peer-reviewed technical journal articles and conference papers 11 energy.gov/ne
Results Summary
- Fission gas release during experiment indicated zero failures in AGR-1; PIE 1.0E-02 indicated 4 failures in AGR-2 SiC failures Failure fraction (Upper limit @ 95% confidence)
- Kernels and coatings generally held up very TRISO failures MHTGR performance well in all irradiation conditions specs for TRISO failure
- PIE has helped to elucidate SiC layer failure 1.0E-03 mechanisms
- High-temperature performance is exceptional, with low coating failure rates at 1600 - 1800ºC in pure helium 1.0E-04
- Fission product release data obtained (e.g.,
Ag, Cs, Eu, Sr, Kr)
- Significant margin exists between observed coating failure rates and historic design 1.0E-05 Irradiation 1600°C 1700°C 1800°C specs for allowable failures 12 energy.gov/ne
Request for Additional Information (RAI) Response Overview
- NRC submitted four technical RAIs
- Important operating conditions beyond temperature and burnup
- Other important fuel properties or coating process parameters
- Acceptable particle parameter ranges (Table 5-5)
- Limitations on fission product release data
- RAIs reflected a careful reading of the report and good grasp of key issues impacting the conclusions
- Applicant provided NRC staff with responses to RAIs
- Additional information and technical discussion
- Revisions to the topical report 13 energy.gov/ne
Extra Slides 14 energy.gov/ne
Fission Gas Release AGR-1 Capsule 6 Comparison of 85mKr R/B
- R/B ratios during AGR-1 remained <2x10-7, for TRISO fuel irradiations indicating no failures out of 300,000 particles
- AGR-2 R/B indicated no failures through three cycles; R/B data for remainder of irradiation not qualified because of hardware problems
- Current PIE estimate indicates 4 particle failures during AGR-2 irradiation
- R/B data compare favorably to historic German values, but at ~20% FIMA (AGR-1) 15 energy.gov/ne
Fission Product Release from AGR-1 and AGR-2 Fuel Compacts Fission product release from AGR-1 and AGR-2 UCO fuel compacts AGR-2 Capsule 2
- Cs release is very low through intact SiC; Time-average peak irradiation temperature 1360°C higher releases are associated with a limited number of particles with failed SiC
- Sr and Eu can exhibit modest release; release is much higher with high in-pile temperatures (AGR-2 Capsule 2 time-average peak temperatures 1360C)
- High Ag release, consistent with historic TRISO fuel observations 16 energy.gov/ne
Safety Testing Results AGR-1 safety test results
- Cs release fraction very dependent on SiC layer failure; not released through intact SiC
- Frequency of SiC layer failure increases with increasing test temperature but remains relatively low even at 1800C for 300 h (~10-3)
- Eu and Sr release increases with test temperature; dominated by release from inventory in the matrix at 1600-1700C
- Ag release is from inventory stored in the matrix
- Kr release is directly related to TRISO failures (failure only observed in 1800C tests) 17 energy.gov/ne
Studying failed particles greatly improves understanding of fuel performance 72 fuel X-ray tomography to compacts Capsule locate failures containing disassembly 300,000 particles in Identify particles with failed coatings Study particles with failed coatings AGR-1 Identify compacts with leakers irradiation X-ray Fuel Compacts Gamma count to Materialography to expose find particles with defective region for analysis Plenum low cesium Optical between retention Capsules SEM Gamma scan to identify cesium hot TEM spots and compact Advanced location microscopy to study Deconsolidation to obtain
~4,000 particles from coating layers in AGR-1 Test Train detail compact Vertical Section 50 nm 18 energy.gov/ne
Particle Failure Statistics
- Use binomial statistics to determine 1.0E-02 upper bound on failure fractions at 95% SiC failures Failure fraction (Upper limit @ 95% confidence) confidence based on (1) observed TRISO failures failures and (2) number of particles in MHTGR performance specs for TRISO failure sample 1.0E-03
- Historic design specifications and empirical failure fractions only concerned with TRISO failure
- AGR program has been successful at 1.0E-04 quantifying discrete failure of the SiC layer of UCO fuel as well
- AGR-1 and -2 TRISO failure fractions are 1.0E-05
~10x lower than historic MHTGR design Irradiation 1600°C 1700°C 1800°C specs at 95% confidence 19 energy.gov/ne
Significant Topical Report Changes Related to RAIs
- Added fast neutron fluence and power density to key irradiation conditions
- Added data on silicon carbide (SiC) stress metric (relates to acceptable kernel-to-buffer volume ratio)
- Added standard for silicon carbide microstructure grain size
- Clarified that uninterrupted coating is considered a process requirement when applying the results of this topical report
- Refocused Table 5-5 on as-irradiated property ranges and addressed comparison of a fuel particle population to the AGR-1 and AGR-2 fuel
- Revised text of Conclusion 3 to state that fission product release data can be used to support licensing of reactors and clarified that Conclusion 3 only applies to fission products specifically referenced in the report 20 energy.gov/ne
ScreenShots - Attendees: July 7, 2020; Metallurgy and Reactor Fuels SC Meeting