ML25175A195
| ML25175A195 | |
| Person / Time | |
|---|---|
| Issue date: | 05/06/2025 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | |
| References | |
| NRC-0337 | |
| Download: ML25175A195 (1) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
Advisory Committee on Reactor Safeguards Docket Number:
(n/a)
Location:
teleconference Date:
Tuesday, May 6, 2025 Work Order No.:
NRC-0337 Pages 1-90 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1716 14th Street, N.W.
Washington, D.C. 20009 (202) 234-4433
NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
(202) 234-4433 WASHINGTON, D.C. 20005-3701 www.nealrgross.com 1
1 2
3 DISCLAIMER 4
5 6
UNITED STATES NUCLEAR REGULATORY COMMISSIONS 7
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 8
9 10 The contents of this transcript of the 11 proceeding of the United States Nuclear Regulatory 12 Commission Advisory Committee on Reactor Safeguards, 13 as reported herein, is a record of the discussions 14 recorded at the meeting.
15 16 This transcript has not been reviewed, 17 corrected, and edited, and it may contain 18 inaccuracies.
19 20 21 22 23
1 UNITED STATES OF AMERICA 1
NUCLEAR REGULATORY COMMISSION 2
+ + + + +
3 725TH MEETING 4
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 5
(ACRS) 6
+ + + + +
7 TUESDAY 8
MAY 6, 2025 9
+ + + + +
10 The Advisory Committee met via Video 11 Teleconference, at 1:00 p.m. EDT, Walter L. Kirchner, 12 Chair, presiding.
13 COMMITTEE MEMBERS:
14 WALTER L. KIRCHNER, Chair 15 GREGORY H. HALNON, Vice Chair 16 DAVID A. PETTI, Member-at-Large 17 RONALD G. BALLINGER 18 VICKI M. BIER 19 VESNA B. DIMITRIJEVIC*
20 CRAIG D. HARRINGTON 21 ROBERT P. MARTIN 22 SCOTT P. PALMTAG 23 THOMAS E. ROBERTS 24 MATTHEW W. SUNSERI 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
2 ACRS CONSULTANT:
1 DENNIS BLEY 2
3 DESIGNATED FEDERAL OFFICIAL:
4 MIKE SNODDERLY 5
6 ALSO PRESENT:
7 MAHMOUD "MJ" JARDENEH, NRC 8
STACY JOSEPH, NRC 9
RICKY VIVANCO, NRC 10 LARRY BURKHART, NRC 11 SANDRA WALKER, NRC 12 GETACHEW TESFAYE, NRC 13 14
- Present via telephone 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
3 P-R-O-C-E-E-D-I-N-G-S 1
1:00 p.m.
2 CHAIR KIRCHNER: Okay. The meeting will 3
now come to order. Good afternoon. This is the first 4
day of the 725th meeting of the Advisory Committee on 5
Reactor Safeguards (ACRS). I'm Walt Kirchner, 6
chairman of the ACRS.
7 ACRS members in attendance in person are 8
Ron Balinger, Vicki Bier, Greg Halnon, Robert Martin, 9
Scott Palmtag, Dave Petti, Thomas Roberts, Craig 10 Harrington, and Matt Sunseri. ACRS member in 11 attendance virtually via Teams is Vesna Dimitrijevic.
12 Our consultant participating today virtually is Dennis 13 Bley. If I've missed anyone, please speak up.
14 Mike Snodderly of the ARCS staff is the 15 Designated Federal Officer for this morning's -- this 16 afternoon's Full Committee meeting. No Member 17 conflicts of interest were identified, and I know that 18 we have a quorum.
19 The ACRS was established by statute and is 20 governed by the Federal Advisory Committee Act, or 21 FACA. The NRC implements FACA in accordance with its 22 regulations.
Per these regulations and the 23 Committee's Bylaws, the ACRS speaks only through its 24 published letter reports. Therefore, all Member 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
4 comments should be regarded as only the individual 1
opinion of that Member and not a Committee position.
2 All relevant information related to ACRS 3
activities, such as letters, rules for meeting 4
participation, and transcripts -- pardon me -- are 5
located on the NRC public website and can be easily 6
found by typing "About Us ACRS" in the search field on 7
NRC's home page.
8 The ACRS, consistent with the Agency's 9
value of public transparency and regulation of nuclear 10 facilities, provides opportunity for public input and 11 comment during our proceedings. For this Full 12 Committee Meeting, we have received written statements 13 from an organization called C-10, who are going to 14 make a presentation during the Seabrook session. That 15 would be tomorrow afternoon. Other written statements 16 may be forwarded to today's Designated Federal 17 Officer, and we have also set aside time during this 18 meeting for public comments.
19 A transcript of the meeting is being kept 20 and will be posted on our website. When addressing 21 the Committee, the participants should first identity 22 themselves and speak with sufficient clarity and 23 volume so that they may be readily heard. If you are 24 not speaking, please mute your computer on Teams, and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
5 if you're participating via phone, press *6 to mute 1
your phone and *5 to raise your hand on Teams.
2 The Teams chat feature will not be available for 3
use during the meeting. For everyone in the room, we 4
ask that you please put your electronic devices in 5
silent mode and mute your laptop microphone and 6
speakers.
In
- addition, please keep sidebar 7
discussions in the room to a minimum since the ceiling 8
microphones are "live."
9 For the presenters, your table microphones 10 are very uni-directional, and you'll need to speak 11 directly into the front of the microphone to be heard 12 online and also for the benefit of our court reporter.
13 Finally, if you have any feedback for the ACRS about 14 today's meeting, we encourage you to fill out the 15 Public Meeting Feedback Form on the NRC's website.
16 And during this afternoon's meeting, we 17 are going to take up the NuScale Standard Design 18 Approval Application and related topics. As stated in 19 the agenda, portions of this meeting may be closed to 20 protect sensitive information as required by FACA and 21 the Government in the Sunshine Act. Attendance during 22 the closed portion of the meeting then will be limited 23 to NRC staff and its consultants, NuScale, and those 24 individuals and organizations who have entered into an 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
6 appropriate confidentiality agreement. We will 1
confirm that only eligible individuals are in the 2
closed portion of the meeting.
3 And with that, I actually will turn to 4
myself as the Subcommittee Chair for the NuScale 5
Design-Centered Review. And today we are going to 6
hear from the staff on some updates on the completion 7
of their review and SERs, and then from there, we're 8
going to read in a draft letter report on the SDAA 9
application.
10 So with that, I'm going to turn to 11 Getachew Tesfaye, who is joining us remotely for 12 opening comments. Go ahead, Getachew.
13 MEMBER SUNSERI: He's on mute.
14 CHAIR KIRCHNER: Yeah. You need to unmute 15 yourself. Getachew, your microphone is off.
16 MEMBER ROBERTS: His microphone is open, 17 but we can't hear him.
18 CHAIR KIRCHNER: Getachew, we still cannot 19 hear you. Are you sure your microphone is unmuted?
20 MEMBER HALNON: MJ, you want to --
21 probably need to log off and log back in.
22 MR. JARDENEH: I can go ahead, Chair.
23 CHAIR KIRCHNER: Yes. MJ, could you then 24 take over?
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
7 MR. JARDENEH: Yeah. Good afternoon, 1
Chair Kirchner and subcommittee members.
2 CHAIR KIRCHNER: Identify yourself for the 3
court reporter.
4 MR. JARDENEH: Okay. Good afternoon. My 5
name is Mahmoud Jardeneh, and I am the branch chief 6
for the New Reactor Licensing Branch, responsible for 7
the NuScale Centered Design Approval Review. Thank 8
you, Chair Kirchner and members of the committee for 9
the opportunity to give an update on the NRC staff's 10 review, the staff's safety evaluation with the 11 NuScale's Standard Design Approval Application (SDAA).
12 Since our last presentation to the ACRS 13 subcommittee on April 1st, 2025, NuScale has submitted 14 a revision to the SDAA on April 9th, 2025. This can 15 be found under ADAMS package number ML25099A236. NRC 16 Staff has confirmed that the revision has incorporated 17 all docketed information that were the basis for the 18 staff's safety evaluation presented to the ACRS 19 through April 1, 2025, and identified as confirmatory.
20 As a result of SDAA, chapter safety 21 evaluations have been updated and the final safety 22 evaluation is based on the reading to the SDAA. The 23 only other significant change in those updates, 24 Chapter 15 and Chapter 8 regarding EDAS.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
8 Stacy Joseph and Ricky Vivanco will now 1
summarize those changes. Thank you.
2 CHAIR KIRCHNER: Go ahead, Stacy.
3 MS. JOSEPH: All right. Good afternoon.
4 My name is Stacy Joseph, and I'm a senior project 5
manager in the Office of Nuclear Reactor Regulation, 6
and I'm the PM for Chapter 15 of the NuScale SDAA.
7 As MJ mentioned, Ricky and I are here to 8
inform the ACRS of the material changes to Chapters 15 9
and 18 safety evaluations since the last time we 10 presented these chapters to the members. Chapter 15 11 safety evaluation was updated to explain the basis for 12 why EDAS is not needed to maintain safe shutdown 13 condition prescribed in the definition of 14 safety-related. NuScale classified the EDAS as a 15 non-safety-related system, and the staff assessed 16 whether EDAS meets the definition of safety-related in 17 10 CFR 50.2.
18 The staff notes that while the specified 19 acceptable fuel design limits, or SAFDLs, are not 20 explicitly referenced in the 10 CF 50.2 definition of 21 safety-related SSCs, nor are they a direct indication 22 of fuel clad damage. They are typically used as the 23 measure to demonstrate that the safe shutdown 24 criterion in the definition of safety-related is met 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
9 through sufficient decay heat removal and containment 1
of radioactive materials during and following 2
anticipated operational occurrences, or AOOs.
3 Demonstration of the safe shutdown 4
criterion ensures that the fuel clad damage is 5
unlikely to occur as a result of an AOO and the 6
safety-related SSCs are sufficient to protect this 7
fission product barrier. Accordingly, the staff 8
reviewed and audited engineering documentation to 9
confirm that the fuel fission product barrier would 10 remain intact in the case of EDAS failure during an 11 AOO.
12 NuScale performed minimum critical heat 13 flux ratio and peak clad temperature analysis of a 14 spectrum of state-points for an ECCS blowdown, which 15 is representative of a loss of EDAS at a combination 16 of powers, pressures, and temperatures. The analysis 17 concluded that the clad temperature increase does 18 occur but lasts for less than ten seconds before 19 returning to temperatures less than the initial value.
20 This analysis was presented by NuScale to the ACRS 21 during the Chapter 15 Subcommittee meeting.
22 In
- addition, staff audited NuScale 23 sensitivity calculations of peak containment pressure 24 resulting from various non-LOCA events with subsequent 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
10 loss of EDAS. Limiting results from these studies 1
indicate that peak containment pressure remains below 2
containment design pressure. Therefore, the staff 3
found that EDAS does not meet the definition of 4
safety-related because it is not needed for ensuring 5
a safe shutdown condition of the reactor.
6 Specifically, the staff found that there 7
is reasonable assurance that the reactor will shut 8
down, decay heat will be removed, and fuel and 9
containment integrity will be maintained without 10 reliance on EDAS. The staff conclusion regarding the 11 reliance on EDAS to meet the Chapter 15 safety 12 analysis acceptance criteria of assuming minimal 13 critical heat flux ratio is maintained above critical 14 heat flux limit remains the same.
15 Based on its role to protect the SAFDLs as 16 required by multiple GDCs, the staff considers EDAS to 17 be a non-safety-related SSC that performs an important 18 to safety function. SSCs that are relied on to 19 satisfy the GDCs are subject to the quality assurance 20 requirements of GDC 1, Quality Standards and Records.
21 GDC 1 specifies that programmatic quality standards 22 for SSCs important to safety provide adequate 23 assurance that these SSCs will satisfactorily perform 24 their safety functions specified in the GDCs.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
11 Accordingly, EDAS conforms to consensus 1
standards and augmented quality attributes to ensure 2
the quality of the system is commensurate with the 3
importance of its safety functions. Based on the 4
design augmented standards and controls assigned to 5
the EDAS, as documented in the FSAR, the staff finds 6
that there is reasonable assurance the system will 7
function as designed.
8 I'll now turn it over to Ricky Vivanco, 9
who will discuss the conforming changes made to 10 Chapter 8 related to EDAS.
11 MR. VIVANCO: Good morning. My name is 12 Ricky Vivanco. I'm a project manager in the Office of 13 Nuclear Reactor Regulation and a PM for Chapter 8 of 14 the NuScale SDAA.
15 In alignment with Chapter 15, Chapter 8 16 was updated to refer to the basis and conclusion in 17 Chapter 15 regarding the safety classification of 18 EDAS. The status basis for requesting exemptions to 19 GDC 17 and 18 and the rest of chapter conform to the 20 staff's consideration of EDAS to be a
21 non-safety-related SSC that performs an important 22 safety function. No additional exemptions were 23 generated, and overall, the staff's conclusions in 24 Chapter 8 are unchanged.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
12 CHAIR KIRCHNER: Is that it, Stacy, for 1
your presentation?
2 MS. JOSEPH: Yes, that concludes the 3
staff's presentation.
4 CHAIR KIRCHNER: We'll take a opportunity 5
here to have members ask questions of the staff if 6
they wish.
7 MEMBER ROBERTS: Bob and I may have 8
similar questions. The terminology non-safety-related 9
SSC that's important to safety, what exactly does that 10 mean in terms of the term important to safety, which 11 is its own classification in 10 CFR 50? Are you 12 saying that these SSCs are important to safety, or are 13 they SSCs important to safety function which is 14 somehow different from that?
15 We saw a draft of the Chapter 8 revised 16 chapter. It was a little bit unclear because the 17 first page basically said EDAS was not important to 18 safety, and the second page says important to safety 19 function. So that kind of mystified a couple of us.
20 If you could clarify what the safety is regarding 21 there. Appreciate it.
22 MR. VIVANCO: So the draft that was sent 23 to the Committee was based off of the -- I'm sorry, it 24 was a draft that hadn't been finalized with OGC's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
13 comments yet. And in finalizing that and the results 1
of the NCP process being completed and carried forth, 2
that was just a carryover from a previous revision.
3 So since the NCP was completed and the staff's 4
considerations were finalized, that paragraph did no 5
longer fit the staff's conclusions, so it was removed.
6 MEMBER ROBERTS: Okay. Yeah. Thank you.
7 That was very helpful.
8 Also, the last paragraph of the draft said 9
that the decision on the recommended exemptions the 10 GDCs have attained and a bunch of other GDCs will be 11 deferred to the COL. Can you explain what the logic 12 is to that?
13 MR. VIVANCO: Yes. So exemptions can only 14 be granted as part of licensing actions. With the 15 issuance of the SDAA, there is no license to issue, so 16 the language was chosen carefully to reflect that no 17 exemptions were authorized or granted as part of the 18 safety evaluation. And the COL was referring the SDAA 19 as long as the basis and parameters were the same for 20 each requested exemption is at that point when the COL 21 license is issued that an exemption will be granted.
22 MEMBER ROBERTS: Okay. There were a lot 23 of exemptions. I don't remember how many, but are 24 they all be revised with that kind of language change?
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14 MR. VIVANCO: That's correct.
1 MEMBER ROBERTS: Okay. Thank you.
2 MR. SNODDERLY: Excuse me, Chair Kirchner.
3 This is --
4 CHAIR KIRCHNER: Yes.
5 MR. SNODDERLY: -- Mike Snodderly. For 6
the record and for interested members of the public, 7
the draft markups of Chapter 8 and 15 that the staff 8
shared with the ACRS will be included as part of the 9
transcript.
10 CHAIR KIRCHNER: Thank you.
11 MEMBER MARTIN: As Tom noted, we had 12 identified that inconsistency maybe that sounds like 13 from Ricky you have resolved. That was my main 14 concern, but I had no further question or comment on 15 the EDAS question.
16 CHAIR KIRCHNER: Members? Okay. Well, 17 then thank you very much, Stacy and Ricky. We'll go 18 to letter report.
19 Before I start, I thought I'd just make 20 some general comments. First, going to thank both the 21 applicant and the staff, and again, noting that these 22 are the comments of one member and not a position of 23 the Committee, but as the lead for this review, it was 24 a very complete application that was submitted by the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
15 applicant. Having lead the review of the design 1
certification, they, in my opinion, addressed in the 2
US460 design, they made several improvements.
3 I tried to reflect those in the text of 4
the letter in the background discussion, improvements 5
that addressed concerns that were identified during 6
the design certification review. And I think they did 7
a very complete job in addressing those issues that 8
had been identified now. That was over four years 9
ago.
10 So with that, we tried to capture that for 11 the members. In this write-up, I tried to capture 12 most of the significant changes. I did not capture 13 all the design changes. But those that address 14 concerns and issues from the design certification 15 review and also highlight those changes that they made 16 as they upgraded the power for their small modular 17 reactor design.
18 So with that, I would like to just go 19 ahead and read the letter in the record and go from 20 there. And I'll note that as I do this, there's more 21 in the letter than I think we need to include, and I 22 would hope during our deliberations we could perhaps 23 review and revise this, shorten the length of the 24 letter so that it becomes a record of our review and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
16 advice to the commission and it's -- how should I say 1
it? -- a little more concise and succinct in terms of 2
our conclusions and recommendations.
3 So with that, I'll go ahead and read this 4
in. And I'll note, too, that we have comments, 5
factual corrections that we'll incorporate from 6
NuScale during the line by line, but they do not 7
substantively change the final conclusions and 8
recommendations of the letter report.
9 So with that, "
Subject:
Report on the 10 Safety Aspects of the NuScale US460 Small Modular 11 Reactor Standard Design Approval Application. "Dear 12 Chairman Wright, during the 725th meeting of the 13 Advisory Committee on Reactor Safeguards, May 6 14 through 9, 2025, we completed our review of the 15 NuScale Power, LLC, NuScale, or applicant, NuScale 16 US460 Plant Standard Design Approval Application 17 (SDAA) for its uprated small modular reactor and the 18 NRC staff's associated advanced safety evaluation 19 report with SER with no open items.
20 "This letter report fulfills the 21 requirement of Title 10 of the Code of Federal 22 Regulations, 10 CFR Section 52.141, that the ACRS 23 shall report on those portions of the application 24 which concern safety.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
17 "During our review, had the benefit of 1
interactions with representatives of the NRC staff --"
2 excuse me "-- and the applicant. We also had the 3
benefit of the documents referenced. Appendix I lists 4
the chronology of NuScale Subcommittee and Full 5
Committee meetings and their subjects, and Appendix II 6
contains the list of our memoranda on advanced SER 7
chapter reviews as approved by the committee.
8 "Conclusions and Recommendations. The 9
NuScale small modular reactor described in the SDAA is 10 a natural-circulation pressurized water reactor that 11 incorporates unique design and passive safety features 12 providing enhanced margins of safety and long coping 13 times without operator intervention. There is 14 reasonable assurance that it can be constructed and 15 operated without undue risk to the health and safety 16 of the public.
17 "Two, the NRC staff's SER for the NuScale 18 US460 SDAA should be issued. Three, a standard design 19 approval for the NuScale US460 application should be 20 issued. Four, the NuScale SDAA is a complete 21 well-documented application backed by validated 22 methodologies and extensive experimental testing.
23 With the completion of inspections, tests, analyses, 24 and acceptance criteria (ITAAC), we expect that a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
18 license based on this comprehensively reviewed SDAA 1
should lead to an expedited review.
2 "Background. The NuScale US460 Standard 3
Design Approval Application. The NuScale US460 SDAA 4
is a power uprate of the individual modules of its 5
US600 design certification application, DCA, and 6
consists of up to six NuScale Power Modules, (NPMs),
7 and a single reactor building (RXB).
8 "The NPMs are largely immersed in a large 9
pool of borated water in the RXB, which also serves as 10 the ultimate heat sink (UHS). Each NPM is a small, 11 integrated, natural-circulation pressurized water 12 reactor (PWR) composed of a reactor core and riser, a 13 pressurizer, and two helical-tube steam generators 14 within a reactor pressure vessel, which is housed 15 inside a high-strength, closely fitting containment 16 vessel. This highly integrated design eliminates 17 large-diameter piping to connect to steam generators 18 and the pressurize to the reactor vessel. The 19 modularized system can then be moved within the 20 reactor building and disassembled for refueling.
21 "Reactor core consists of approximately 22 half-length commercial PWR 17 x 17 fuel assemblies, 23 37, and control rod assembly 16, surrounded by a 24 stainless-steel reflector and is cooled by natural 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
19 circulation of borated, light-water primary coolant.
1 Nominal operating conditions, power peaking, and fuel 2
burnup and below those of the current pressurized 3
water reactor operating fleet. Each NPM is rated at 4
250 --" there's a typo there "-- MWt versus 160 MWt 5
for the US600 DCA with an output of approximately 77 6
MWe.
7 "With the power rate uprate, the nominal 8
operating pressure of the reactor was raised to 2000 9
psia, and this led to several other design changes, 10 notably the reactor pressure vessel and containment 11 vessel design pressures and associated materials 12 selection.
13 "Other unique safety features include two 14 independent passively actuated natural-circulation 15 decay heat removal systems (DHRS), each connecting one 16 of the steam generators to the heat exchanger immersed 17 in the reactor pool, and passively actuated emergency 18 core cooling system (ECCS) valves that allow 19 depressurization of a
primary system to the 20 containment and core cooling by recirculation of the 21 primary coolant from containment to the primary 22 system. The sizing of the RPV and the CNV are such 23 that the retained reactor coolant inventory is 24 sufficient to maintain a collapsed liquid level above 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
20 the height of the core fuel rods for postulated 1
accident scenarios.
2 "Both systems provide diverse, passive 3
means of rejecting stored energy and decay heat by 4
means of boiling condensation from the reactor system 5
to the RXB pool. To address boron dilution concerns 6
associated with long-term cooling by DHRS and ECCS 7
operation identified during the DCA review, NuScale 8
added additional holes and slots to the NPM-20 core 9
riser barrel to promote boron mixing. Combined, the 10 DHRS and the ECCRS functional design provides for a 11 long coping time, 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, without the need for 12 safety-related electric power or operator 13 intervention.
14 "Additional US460 design changes from the 15 DCA include manufacturing the lower reactor pressure 16 vessel (RPV) shell of austenitic stainless steel 17 rather than the low alloy steel as planned for the DCA 18 and is used within the legacy pressurized water 19 reactor fleet. This change in material provides 20 technical justification to support exemptions from the 21 requirements in 10 CFR 50.60 on fracture toughness and 22 material surveillance program requirements for a 23 reactor coolant pressure boundary and 10 CFR 50.61, 24 protection against pressurized thermal shock events.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
21 "The NPM design incorporates several 1
notable containment design improvements relative to 2
the DCA. The upper containment vessel and a portion 3
of the lower vessel below the main flange will be 4
manufactured as martensitic stainless steel (F6NM),
5 and the lower section of the CNV of austenitic 6
stainless steel (FKM-19)." There's a mistake there in 7
the nomenclature.
8 "Higher strength allows increased design 9
pressure, 1200 psi, and temperature, 600 degrees 10 Fahrenheit, resulting in improved containment response 11 design margins to the spectrum of primary and 12 secondary mass and energy releases.
13 "Venturis were added to the chemical and 14 volume control system (CVCS) inlet and discharged 15 lines to mitigate inventory loss in event of an 16 unisolable break. The NPM containment isolation valve 17 design configuration has also been modified to include 18 a containment isolation test fixture to better support 19 periodic CIV local leak rate testing. Venturis were 20 also added to the ECCS valves to restrict blowdown 21 flows upon failure or inadvertent opening, reducing 22 pressure and thermal loads upon the containment.
23 "The reactor building pool level band has 24 been lowered in the US460 design to better match the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
22 passive heat transfer rate from the CNV to the pool 1
with the decay heat load and better control the rate 2
of condensation-driven depressurization.
3 Additionally, NuScale added in the US460 design a 4
supplemental boron dispenser system (ESB) and a 5
passive autocatalytic --" catalytic, sorry "--
6 recombiner power system in the containment of each NPM 7
to address safety concerns raised during the DCA 8
review. More details and discussion below.
9 "ACRS Review Approach. Like the NRC 10 staff, we conducted a delta review of the NuScale 11 SDAA, focusing first on safety aspects of the module 12 power uprate and major supporting design changes since 13 the DCA application and review. In particular, we 14 examined design changes that affect the primary safety 15 functions of reactivity control, decay heat removal, 16 and confinement of radionuclides, and changes to 17 structures, systems, and components (SSCs) that 18 implement those safety functions.
19 "We also reviewed key supporting 20 documentation including new, revised, or supplemental 21 topical reports and new technical reports that amended 22 the final safety analysis report (FSAR) chapters. The 23 final document of record was Revision 2, the NuScale 24 US460 Plant SDA AFSAR. To expedite our review, we 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
23 implemented the approach for completing our previous 1
review of the DCA by assigning members to review 2
individual chapters of the FSAR and the associated 3
chapter draft SER, renew safety-significant items, 4
impacts of the power uprate or significant design 5
deltas. Individual members then reported back with 6
summaries for presentation to the Committee as a whole 7
for deliberation and approval.
8 "These chapter reviews included the 9
cross-cutting areas identified from our DCA review, 10 emergency core cooling system (ECCS) and ECCS valve 11 performance, helical-tube steam generator design, 12 density wave oscillations and tube integrity, boron 13 dilution and potential return to criticality, source 14 term (post-accident containment atmosphere sampling) 15 and probabilistic risk assessment (PRA).
16 "The staff implemented a high-impact 17 technical issues approach to working with the 18 applicant to focus completion of their review. This 19 complemented our approach and provided timely 20 information to address outstanding safety-significant 21 technical issues.
22 "Discussion. The following sections 23 discuss safety and technical issues, observations, and 24 results from our review.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
24 "ECCS and ECCS valve performance. The 1
passive ECCS system includes four valves with 2
independent hydraulic actuation systems. When 3
actuated, ECCS vents steam through two reactor vent 4
valves (RVVs) mounted on the top of the reactor 5
pressure vessel to the containment immersed in the 6
reactor pool. The steam condenses and accumulates in 7
the lower CNV and is then returned through the two 8
reactor recirculation valves (RRVs) to the downcomer 9
region of the reactor pressure vessel.
10 "The ECCS does not provide additional 11 coolant to this system, but instead the vessel sizes, 12 RPV, reactor vessel and containment vessel, are 13 designed to retain sufficient inventory in the reactor 14 vessel to keep the core covered during all postulated 15 events.
16 "Notably, the DCA design included three 17 RVVs and two RRVs with an inadvertent actuation block 18 valve in the hydraulic control system for each ECCS 19 valve. The NPM-20 design employs only two RVVS and 20 the IAB valves have been removed from their control 21 system. The setpoint for a timer actuation of the 22 ECCS after loss of all site power or reactor trip was 23 changed to eight hours from 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The applicant's 24 accident analyses appropriately reflect the changes 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
25 made to the ECCS for the US460 design, including the 1
removal of the RVV IAB valves, a lower differential 2
pressure-based actuation, and changed setpoint logic 3
based on riser level sensors.
4 "These changes simplify the ECCS actuation 5
scheme, improve reliability, and result in more rapid 6
system response following a LOCA initiation. The 7
NuScale evaluation model uses conservative initial 8
conditions to bound primary system depressurization 9
and inventory retention and the staff's confirmatory 10 TRACE analyses verified that the applicant's models 11 conservatively predict the timing of ECCS valve 12 opening reactor vessel level and containment pressure 13 response.
14 "The Committee finds that the analytical 15 treatment of the ECCS performance including bounding 16 assumptions on valve stroke times and initial RCS 17 inventory supports the conclusion that the system will 18 perform its safety functions to support its licensing 19 basis.
20 "Eliminating these IABs has been 21 beneficial overall, but it does increase the potential 22 for inadvertent operation of an RVV. The safety 23 analysis address inadvertent initiation of ECCS by 24 opening both RVVs and hence bound actuation of one RVV 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
26 from steady-state plant conditions.
1 "The applicant assumes inadvertent RVV 2
actuation during an unrelated transient is 3
sufficiently unlikely that it does not need to be 4
considered in the safety analysis. Nevertheless, the 5
applicant identified a scenario where if an RVV were 6
to actuate during an unrelated transient that 7
increases temperature and power, minimal critical heat 8
flux ratio (MCHFR), thermal limits would be exceeded 9
by a small amount for a short period of time.
10 "The applicant's analyses demonstrate that 11 despite the MCHFR limit exceedance, steel clad 12 temperatures would be significantly below limits 13 because the collapsed liquid level remains above the 14 fuel height, and the consequences of such a highly 15 unlikely event would be acceptable.
16 "One potential cause for inadvertent 17 actuation of an RVV is the failure of the non-safety 18 augmented direct current power system (EDAS) removing 19 power to the solenoid trip valves for both RVVs.
20 While this system is designated as non-safety-related, 21 it has significant redundancy and includes quality 22 augmentations that approach those included in the 23 safety-related system. The NRC staff evaluated this 24 system and deemed it sufficiently reliable to support 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
27 NuScale's analysis assumptions."
1 And the next section, I think -- let me 2
read it. I think we'll wind up eliminating this. "At 3
the time this letter report was written, NRC staff 4
management was evaluating a staff non-concurrence that 5
disagreed with the approach used to document 6
acceptance of this system. We take no position on the 7
non-concurrence. We agree with both the NRC staff 8
management and the non-concurring staff that the EDAS 9
design combined with the applicant's assessment that 10 the consequence of the untimely loss of EDAS would be 11 acceptable, even if it were to occur, is sufficiently 12 reliable to support approval of the SDAA.
13 "In the final design certification 14 application letter, the Committee also noted that the 15 performance of the unique ECCS valve systems as an 16 important risk contributor to the DRA. The Committee 17 letter stated NuScale will perform extensive 18 qualification testing to provide confidence in the 19 ability of the valves to maintain their required 20 performance after extended periods in an operational 21 environment and concluded these additional actions 22 should address the underlying safety concerns. For 23 the SDAA review, residual committee concerns regarding 24 reliable valve operation opening on demand are 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
28 considered resolved.
1 "Helical-tube steam generator design.
2 NuScale has continued to evolve their understanding of 3
density wave oscillation (DWO) and its potential 4
impact on the operation of the helical-tube steam 5
generators.
6 "Testing and analysis. Making two 7
adjustments reflected in the US460 design. The DCA 8
steam generator inlet flow restrictors (IFR) design 9
has been simplified with an IFR installed directly at 10 each steam generator tube inlet instead of a support 11 plate with individual IFRs for each tube attached.
12 "These will impose a suitable pressure 13 drop for avoiding DWO within a normal operational 14 power range. DWO conditions may still be encountered 15 during startup, low power, and other transient 16 operations resulting in a slow accumulation of steam 17 generator tube damage. Rather than demonstrate the 18 attesting that DWO conditions challenging to system 19 components and operations could be avoided, a DWO 20 management strategy has been adopted for the US460 21 design. NuScale defines an approach temperature as 22 the difference between the reactor coolant system 23 T-hot and the main steam outlet temperature, which is 24 directly correlated to DWO margin and established an 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
29 approach temperature limit curve below with which DWO 1
onset could occur.
2 "Under the DWO management strategy, a 3
cumulative time in conditions favorable to DWO is 4
tracked against the technical specific limit in 5
combination with steam generator tube inspections to 6
ensure that the steam generator remains well-removed 7
from unacceptable DWO-related damage accumulation.
8 "The applicant's accident analyses further 9
address low stability concerns associated with the 10 helical-tube steam generators, particularly under 11 natural-circulation conditions following transients or 12 during long-term cooling. NuScale's evaluation model 13 incorporates a conservative bias on DHRS heat transfer 14 performance and applies operational limits to identify 15 and minimize operation near conditions where DWOs 16 might occur.
17 "The staff's review confirmed that the 18 modeling approach includes appropriate conservatism 19 and that operational constraints, including approached 20 temperature limits, provide further margin against 21 instability. The Committee knows that the evaluation 22 model supported by confirmatory analyses demonstrates 23 that the system's stability is maintained under design 24 basis conditions and that the steam generator design 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
30 supports reliable passive heat removal throughout the 1
event spectrum evaluated in Chapter 15.
2 "Boron dilution and return to critically.
3 To deal with the potential criticality issues 4
identified in the DCA associated with boron 5
redistribution dilution and stratification, NuScale 6
incorporated additional features in the NPM-20 design, 7
including lower, midplane, and near-top riser hols and 8
slots and ESB boron baskets within the containment.
9 By enhancing, mixing, and mitigating stratification 10 that could otherwise lead to localized deboration, the 11 design changes maintain the core in a subcritical 12 state in event of a small break LOCA DHRS actuation 13 and after ECCS actuation and into extended passive 14 cooling.
15 "The Committee reviewed NuScale's 16 methodology to evaluate ECCS and the DHRS extended 17 passive cooling function and the effectiveness of 18 these measures in its accident analyses as presented 19 in Chapter 15 of the FSAR. In its methodology, 20 NuScale used the following figures of merit (FOM) to 21 assess performance: subcriticality, coolable 22 geometry (boron concentration below the solubility 23 limit for precipitation) and collapsed liquid level 24 above the top of the active fuel.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
31 "The extended passive cooling GR and 1
analyzed it and showed that coolable geometry is 2
retained and the collapsed liquid level remains above 3
the active fuel pipe. And the Committee agrees with 4
these conclusions."
5 "However, the ability to remain 6
subcritical after ECCS actuation depends on the 7
behavior of several core parameters of core 8
reactivity. These include the following: initial 9
concentration of boron present in the RCS coolant, 10 which increases in the core region due to constant 11 boiling; uncertainty in boron concentration return 12 through the RRVs from containment due to concentration 13 stratification that boron added from the ESB dissolver 14 baskets; core cooling down substantially over a 15 72-hour period, which adds positive reactivity; xenon 16 peaking, then decay until 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The xenon is 17 almost gone while samarium is increasing over the same 18 period, and all control rods except the highest worth 19 rod are considered inserted.
20 "It should be noted that some of these 21 parameters that are considered beneficial to core 22 cooling, such as lowered decay heat and lowered 23 coolant temperatures, make it more difficult to remain 24 subcritical.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
32 "For the
- NPM, the most limiting 1
criticality conditions occur at the end of cycle 2
(EOC). It's when the RCS boron concentration at the 3
core is near zero. NuScale's evaluation model 4
conservatively applies cold water temperatures, 5
worst-case control rod configurations, and low initial 6
boron concentration to bound the minimum shutdown 7
margin throughout this period.
8 "From all the cases analyzed, the core 9
remains subcritical, but the margin to criticality can 10 be relatively small. The smallest margin to 11 criticality shown was 28 parts per million boron.
12 This margin to criticality is within the predicted 13 boron concentration uncertainty usually presumed in 14 pressurized water reactors, which is typically 50 to 15 100 ppm.
16 "Cold, off-nominal conditions usually 17 increase the amount of uncertainty. NuScale has 18 indicated that there are many conservatisms built into 19 their methodology that increase the margin to 20 criticality, such as the use of conservative 21 temperatures in the analysis.
22 "The NRC staff also ran computational 23 fluid dynamic (CFD) calculations that show there is 24 additional conservatism in the NuScale boron tracking 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
33 model. In their analyses, the CFD calculations added 1
approximately 180 ppm to the shutdown margin. With 2
these conservatisms, it is shown that the core remains 3
subcritical after an ECCS actuation.
4 "The Committee finds that the modeling 5
assumptions are appropriately conservative. At our 6
request, the staff indicated that future technical 7
specifications would ensure that the boron 8
concentration requirements necessary to preserve this 9
margin are maintained across below cores.
10 "Source term, post-accident combustible 11 gas monitoring. In our DCA review, we were concerned 12 that the proposed post-accident combustible gas 13 monitoring system would risk bypass of containment by 14 opening a substantial sized line, yet not provide a 15 representative sample of the containment atmosphere.
16 Therefore, we agree that it should not receive 17 finality and NuScale design certification.
18 "This issue has been addressed in the 19 NuScale SDAA design by including a
passive 20 autocatalytic recombiner in each NPM to control 21 combustible gas concentrations as per 10 CFR 50.44.
22 The part is designed to keep the oxygen levels below 23 four percent, preventing combustion and ensuring an 24 inert containment atmosphere. This change supports an 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
34 NPM-20 exemption request from 10 CFR 1
50.34(f)(2)(xvii)(C) for combustible gas monitoring.
2 Additionally, the applicant has proposed GDC 41 to 3
meet the combustible gas control intent of GDC 41.
4 The draft SER approves these exemptions.
5 "Probabilistic risk assessment (PRA) and 6
anticipated transients without scram (ATWS). The 7
NuScale US460 design-specific PRA has been 8
comprehensive in scope and in the level of detail.
9 The scope includes Level 1 and Level 2 PRA for 10 internal and external initiating events for both full 11 power and lower power shutdown conditions. PRA was 12 performed was performed for a single module and used 13 to develop quantitative or qualitative risk insights 14 for multiple modules.
15 "Self-assessment of the PRA was performed 16 to evaluate components with industry standards. The 17 Committee review focused on the design changes and 18 their impact on the differences in the risk profile 19 between US600 DCA and the US460 SDAA. Design changes 20 most relevant to the core damage frequency or changes 21 to ECCS, including reducing the number of RVVs from 22 three to two, the addition of an eight-hour actuation 23 timer, and the addition of redundant solenoid trip 24 valves on RRVs and RVVS.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
35 "These changes result in a small reduction 1
in ECCS reliability and consequently in a small 2
increase in the CDF. The most noticeable difference 3
between the US600 DCA and US460 SDAA risk profile is 4
the significant reduction in the large release 5
frequency (LRF). Design changes most relevant to the 6
LRF are removal of the inadvertent actuation blocks on 7
the reactor vent valves, addition of low reactor 8
pressure vessel riser level ECCS actuation signal, and 9
the addition of Venturi flow restrictors to CVCS 10 injection and discharge lines to limit maximum brake 11 flow.
12 "By a fast reduction in system pressure to 13 atmosphere, these changes limit coolant loss from 14 brakes outside of containment with failed containment 15 isolation and allow the event mitigation without a 16 need for operator action or inventory makeup. This 17 eliminates the main contributors to the DCA LRF and 18 results in the SDAA LRF to be practically negligible.
19 "Another design change with possible 20 impact on the PRA results is the addition of a digital 21 reactor building crane control system, which would 22 reduce the potential for operator errors during crane 23 operation. Due to the lack of final design details 24 and shutdown plans and procedures, it's premature to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
36 analyze impacts of this design change.
1 "The Committee is in full agreement with 2
the staff findings that the PRA is of sufficient 3
technical adequacy to support the SDAA and that the 4
Commission's CDF and LRF goals have been met with high 5
margin. This being said, in order to facilitate 6
realism in the PRA inputs to plant operational 7
requirements and programs, we believe that a few 8
improvements should be considered for future PRA 9
developments. Some of these are summarized below.
10 "The additional SSCs for human actions 11 could be discovered relative as measured to the 12 plant-specific CDF/LRF. Risk importance measures are 13 also used, and other importance-related questions are 14 considered. For example, an SSC failure would 15 increase CDF two orders of magnitude should be 16 considered in the importance ranking, even though an 17 underlying absolute delta CDF is less than a selected 18 value.
19 Second bullet: "To evaluate realistic 20 uncertainty in the results, the underlying mean values 21 for the risk measures, the ECCS with high risk 22 importances should receive a detailed evaluation on 23 certainties and the applied data common cause 24 assumptions and passive heat transfer failure 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
37 likelihood. In order to justify that point estimate 1
and mean values are identical, correlated SSCs and 2
factors like common cause factors treated as dependent 3
should be evaluated to assure their completeness.
4 Third bullet: "Sensitivities are mostly 5
calculated for single factors. The combination of 6
sensitivities are not considered. The overall results 7
could be very sensitive to underestimating multiple 8
factors. For example, it could provide a valuable 9
insight to combine sensitivity to the steam generator 10 tube
- rupture, initiating frequency with the 11 sensitivity to assumptions of single tube rupture on 12 the single steam generator.
13 "As opposite to above, a few sensitivities 14 are calculated as big lumps by sensitivities, all 15 common cause
- failures, or all human error 16 probabilities (HEPs). It would be more valuable to 17 know sensitivities to different common cause groups, 18 like ECCS or DHRS, or to specific HEPs. The current 19 SDAA PRA model does not include sequences related to 20 concerns about the potential for boron dilution and 21 return to criticality during ECCS operation, 22 particularly following a LOCA or other events 23 involving RCS depressurization and inventory 24 redistribution.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
38 Finally, this is an insert. "While in 1
change from the previous US600 design, one aspect of 2
the approach used to meet the intent of the ATWS 3
requirements is worthy of note. Specifically, the 4
ATWS discussions in the FSAR do not cite the analyses 5
that the applicant performed which demonstrate that 6
the consequences of an ATWS event would be acceptable.
7 Instead, the FSAR states that the diversity within the 8
module protection system (MPS) is sufficient to meet 9
the intent of the ATWS requirements.
10 "It is unclear to us whether the diversity 11 within the MPS would be sufficient if the consequences 12 of an ATWS event had been more severe. For example, 13 the assessment and diversity within the system covers 14 only the digital portions of the MPS and does not 15 address other aspects of design or operation, such as 16 use of a common supply chain, potential maintenance 17 errors, potential effects of a common environment, et 18 cetera.
19 "We agree that the applicant continues to 20 meet the intent of the ATWS regulations based on a 21 combination of acceptable consequences and significant 22 diversity within the digital portions of the system.
23 However, for future applications citing NuScale as a 24 precedent, we use caution accepting diversity within 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
39 the MPS is sufficient to meet the intent of the ATWS 1
requirements if the consequences of an ATWS event are 2
more severe.
3 "As stated in our design certification 4
letter, the PRA should be updated at the COL stage to 5
appropriately reflect the risk of boron dilution 6
events, including associated operator actions. Risk 7
insights would be better supported when the design is 8
completed and the COL items are addressed, ITAAC items 9
are closed, and the plant-specific PRA are completed 10 before fuel load, including a human reliability 11 analysis based on natural plant procedures and 12 experience gained during operator training and plant 13 simulator exercises.
14 "Subject to the above notes, we conclude 15 that the results of NuScale's full-scope PRA for the 16 internal and external events indicate that the NuScale 17 US460 design will meet the Commission's goals for CDF 18 and LRF with significant margin.
19 "Summary. The NuScale's small modulator 20 reactor described in the SDAA is a natural-circulation 21 pressurized water reactor that incorporates the unique 22 design and passive safety features, providing enhanced 23 margins of safety and long coping times without 24 operator intervention. There is reasonable assurance 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
40 that in can be constructed and operated without undue 1
risk to the health and safety of the public. The NRC 2
staff's final SER for the NuScale US460 SDAA should be 3
issued. A standard design approval for NuScale US460 4
application should be issued.
5 "NuScale SDAA is a
- complete, 6
well-documented application backed by validated 7
methodologies and extensive experimental testing.
8 With the completion of ITAAC, we expect that a license 9
application based on this comprehensively reviewed 10 SDAA should be to an expedited review. And we are not 11 requesting a formal response from the staff to this 12 letter. Sincerely."
13 Thank you.
14 MEMBER HALNON: So take a break?
15 CHAIR KIRCHNER: Take a break.
16 (Laughter.)
17 CHAIR KIRCHNER: Or a drink of water.
18 Just an observation, and it's at least painfully 19 apparent to me reading the letter, it's too long and, 20 in my opinion, can be significantly condensed and 21 still transmit the message, at least in this member's 22 opinion. I can be incorporated in the conclusions and 23 recommendations.
24 I thank those who gave me input, and with 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
41 that, I think we should take high-level comments from 1
members first and proceed from there.
2 MEMBER PETTI: Well, I have one or two.
3 I have about five or six.
4 CHAIR KIRCHNER: And I note one thing, 5
too, also. We have input from NuScale, and we can 6
capture that in the line by line, number of 7
corrections.
8 MEMBER PETTI: The first yellow section on 9
EDAS, I think we have to shorten it based on what we 10 heard today, something that I think we could do before 11 we get to line by line. We have the sentences in 12 there from the previous review about testing, that 13 they have completed the testing and we don't have to 14
-- I don't want to throw it all away. I want to keep 15 that because I think --
16 CHAIR KIRCHNER: Right.
17 MEMBER PETTI: -- that that's important.
18 In the source term, there's a sentence in 19 there about the exemption has been approved, but I 20 gather it really hasn't.
21 CHAIR KIRCHNER: It hasn't.
22 MEMBER PETTI: Can't do that, so we got to 23 get rid of that. I thought I saw some edits from Tom 24 that really reduced the whole ATWS section, so I think 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
42 that is worthwhile considering.
1 And the PRA section, it seems like we 2
picked up stuff from the previous letter that you have 3
it highlighted in yellow. I think it --
4 (Simultaneous speaking.)
5 MEMBER ROBERTS: Yeah. That was actually 6
a placeholder.
7 MEMBER PETTI: -- be consistent with where 8
we are today. Finally, the last sentence before the 9
end of the letter is that they meet CDF and LRF with 10 sufficient margin. I think sufficient is the wrong 11 word. I would say extensive, ample, but it's large 12 margin.
13 CHAIR KIRCHNER: Yeah. I may not have 14 read it correctly. Significant margin.
15 MEMBER PETTI: Significant. I think if we 16 attack those brief things, we'll be in better position 17 for going at it line by line. I just note that you 18 used font 14. If you used our font 16 standard, we'd 19 be at over 500 lines. This is a lot.
20 MEMBER HALNON: You took my last comment.
21 (Laughter.)
22 MEMBER HALNON: I agree with Dave. For 23 the court reporter, this is Greg. I don't think that 24 I was in this morning's meeting.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
43 The PRA
- stuff, it seems like we 1
intertwined some of the generic stuff that we're 2
looking at in a couple weeks or a couple meetings from 3
now. And I think it felt like we were saying that PRA 4
is not quite good enough because we have these generic 5
issues. I think we can mention and draw down and say 6
that we're still looking at some generic issues that 7
may impact the next PRA but not necessarily make it 8
sound like it's not out there, especially since with 9
we kind of embedded a recommendation to better or to 10 make it include other items during operating 11 licensing.
12 I came away from that listening to the 13 reading of it, and I had not digested it, but reading 14 it made it sound like it was. We've had a couple of 15 licensees or applicants come in with stuff like that.
16 (Audio interference.)
17 MEMBER HALNON: We could mention it 18 without going to too much detail. I don't know we 19 could. It probably came from you and Vesna.
20 MEMBER BIER: Well, it may have come from 21 Vesna. I don't think the wording came from me. I 22 think --
23 CHAIR KIRCHNER: It came from Vesna.
24 MEMBER BIER: Okay, thanks. I think 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
44 there's two separate issues. The thing about, well, 1
if this thing causes a two order of magnitude 2
increase, it should be considered significant, that 3
one, we may want to table and say, you know, the 4
Committee is looking at how to treat these and may 5
have a recommendation generically in future or 6
something.
7 The part about, like, mean value versus 8
point estimate and make sure you have the correlations 9
accounted for, that's just a fact. I mean, that's not 10 a Committee opinion really, so I don't mind keeping 11 that in, that the PRA should be careful about 12 addressing this.
13 MEMBER HALNON: Okay. Yeah, I thought 14 that you were going to talk about those other issues 15 in much more detail.
16 MEMBER BIER: Yeah.
17 MEMBER HALNON: -- coming up.
18 MEMBER SUNSERI: This is Matt. I have a 19 couple of thoughts. They probably aren't all that 20 helpful, but I'm going to say them anyway. I think 21 the letter is too long. I agree with that but maybe 22 for a different reason. There's so much technical 23 detail in it, it reads to me like a safety evaluation 24 report, like the SER that the staff does. Got a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
45 section by section breakdown.
1 And to me, while it's technically 2
accurate, it seems to me it dilutes our kind of review 3
that is supposed to be at the key issues, like ample 4
margin on a PRA. Minimal operator actions, good use 5
of passive features to maintain safety, these are the 6
things that make NuScale different from the other 7
things we use. And to me, it just gets all lost in 8
all the technical breakdown.
9 To me, it's not a matter of just going 10 into each one of these paragraphs and condensing them 11 and taking out half of the technical detail, but --
12 MEMBER PETTI: You're basically arguing 13 whether we need the subsections at all.
14 MEMBER HARRINGTON: You might be able to 15 take that whole discussion section, make it an 16 appendix or something, and just have a five-page 17 letter just going over the, you know, passive safety 18 features, minimal operator actions, big PRA margin, 19 you know, the four or five key things. I don't know.
20 MEMBER PETTI: One of the design choices 21 they made that you now see, as safety analysis 22 reflects, and that's what you're kind of saying is you 23 missed that. And we'll work it into the introduction 24 and background, but I appreciate your perspective.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
46 MEMBER SUNSERI:
It's just one 1
perspective.
2 MEMBER BIER: Yeah. I kind of agree with 3
Matt. I mean, I wouldn't even describe it as a 4
high-level comment, maybe a zeroth order comment. As 5
I was listening, when we got to the discussion, I 6
thought the discussion was going to be a reflection of 7
what had come before. And instead, the discussion 8
went kind of on and on and launched into all these 9
topics that had not really been highlighted earlier in 10 the letter.
11 And so I don't know whether it makes sense 12 to move the whole discussion to an appendix or whether 13 we have to kind of be selective and maybe pick a few 14 parts that we think are important enough to keep in 15 the body of the letter.
16 MEMBER PETTI: So I think the real 17 question is we all wanted to tie it back to the 18 previous review and show how each of our previous 19 issues had been closed out, and that's why I think it 20 is what it is. Should that be the objective of the 21 letter, I guess, is really what I'm hearing.
22 MEMBER HARRINGTON: Well, I mean, you 23 won't get me arguing against closing the loop. I like 24 closing the loop. We're on the record, and so we got 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
47 to close the loop.
1 I mean, this is like a new design, 2
though, right? We want to say for this reactor as is 3
being designed, these are the key reasons why we think 4
it's safe or that we see as safe, whatever. And the 5
rest of it is just technical detail. That's a 6
superficial comment. The technical detail is 7
important. That's why we're here, right? But, you 8
know, it's not key, the essential points that we want 9
to make. We can close the loop whether patching it or 10 appendix. I don't know how to do it. I'm just kind 11 of thinking out loud here.
12 MEMBER HALNON: This is Greg. When you 13 say closing a loop, it sounded like we had some 14 unfinished safety questions from the DCA. The DCA is 15 issued. We concluded it was safe to issue.
16 Therefore, there shouldn't be any loop closure. It 17 should be --
18 CHAIR KIRCHNER: The staff had carveouts 19 and we identified, I would say, just concerns is maybe 20 a better way to put it. Just, you know, for 21 background, it's probably useful because we have so 22 many news members to just revisit what happened.
23 We were proceeding almost at lockstep with 24 the staff as it went through its first review of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
48 DC application, and that was chapter by chapter, and 1
we were kind of locked in to SER chapter by chapter.
2 And we made a decision after that first pass through.
3 The staff was issuing SER chapters with open items, 4
and then the process they were using, they were going 5
to revisit each chapter and close out the open items 6
to get a finished product.
7 We decided not to do that. That's when we 8
adopted the approach of saying, "What are the 9
safety-significant issues in this review that the 10 Committee should concern itself with and devote time 11 to?" And those were items identified with EECS valve 12 performance, steam generator tube integrity, boron 13 dilution, this matter of how in the DCA they were 14 proposing to do post-accident containment atmosphere 15 sampling. And then the overall PRA results.
16 So those were the five focus areas we 17 identified, and when we did our second pass, we did 18 look at the chapters for closing out of open items, 19 but we focused most of our attention on those five 20 technical areas, so to speak. And some of them were 21
-- open is not the right way to describe it, but from 22 the DCA, there were concerns identified.
23 So there was the mention of carveouts, so 24 there were a few areas, including the steam generator 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
49 and its integrity, that were carveouts in the DCA 1
review by the staff where the staff and the applicant 2
agreed that further effort was needed. For example, 3
one was ECCS valve testing. So by and large, that's 4
been completed. There were some changes in the valve 5
designs. You heard about the IABs being taken off to 6
the valves.
7 So they've done that testing. They've 8
done further testing on the steam generator since the 9
DCA, and then they obviously made several important 10 design changes to address the issue of boron 11 distribution and potential dilution in a number of the 12 transient scenarios, small break and cooldown ECCS 13 actuation.
14 So the message I was trying to convey was 15 that significant important design changes were made by 16 the applicant, not by us, but the applicant deserves 17 the credit for taking initiative and completing those 18 testing programs that they had committed to, as well 19 as making a number of design changes that improved the 20 performance and took questions off the table, if you 21 will, from the DCA review to where we are now.
22 So I tried to approach the letter from 23 that perspective and address in the background -- and 24 the reason I put most of the design changes in the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
50 background, again, is these are changes that the 1
applicant made, improvements and design choices. They 2
were not the Committee's choices. The applicant 3
deserves the credit for implementing those and 4
completing the testing and such. They changed their 5
approach on the steam generator. They changed the 6
design as well on the inlet flow restrictors and such.
7 So I was trying in the letter to capture 8
the significant deltas in the design changes from the 9
DCA, credit the applicant where due, and then try and 10 close the loop in terms of what does this mean in 11 terms of improving the safety of the design? And I 12 think these, putting aside the PRA results changing, 13 their changing, we're up there with vary significant 14 margin to the Commission's safety goals as far as the 15 PRA results.
16 So we can get into the weeds on the PRA, 17 but the bottom line is that they have demonstrated 18 significant margin to the safety goals. I was putting 19 more of my thought and attention and words -- too many 20 words, I think -- into how they implemented design 21 changes and how that improved the overall design of 22 the plant.
23 So in that sense, I was closing the loop 24 on where we had left off on the DCA where there were 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
51 1
MEMBER PETTI: Walt, it's only 150 lines 2
before you get to discussion.
3 CHAIR KIRCHNER: Yeah.
4 MEMBER PETTI: So I don't think that 5
background -- that's all right where you talk about 6
it. It's really, I think, the discussion is what is 7
almost 300 lines. Twice as long as the background.
8 And maybe the answer is moving it to an 9
appendix, but it has a lot of --
10 (Simultaneous speaking.)
11 CHAIR KIRCHNER: Well, most of this 12 material came from our chapter memos.
13 MEMBER PETTI: Memos.
14 CHAIR KIRCHNER: So it's there, and some 15 of them might have additional information that we've 16 received in the last week. Might warrant being 17 revised and updated to capture that information.
18 My own sense is, again, I took your input, 19 so each of these sections under discussion could be, 20 perhaps, condensed if not made much more succinct.
21 This is what changed, and this is the impact primarily 22 in terms of the safety analysis results.
23 MEMBER HALNON: Sorry. Sandra, if you 24 just go up to 163 real quick, and I'll just give you 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
52 an example of what at least I perceive as being able 1
to do.
2 So 163 starts the ECCS valve performance.
3 That first gives you background, what it is, how it 4
works, what it does. That second paragraph -- go up 5
to 174 -- that paragraph is really all that's 6
required. I don't even know if you need to go as far 7
down as TRACE and all that stuff. When you get down 8
to that point where it said, "The applicant's accident 9
analyses appropriately this is
- 180, 10 appropriately reflect the changes made to the ECCS 460 11 design," what more do we need to say?
12 In my mind, it could be --
13 CHAIR KIRCHNER: You could collapse it.
14 MEMBER HALNON: You could collapse it down 15 and start with the end of line conclusion of what do 16 you need to make that conclusion clearer. And then 17 the rest of the stuff, if you want to put it -- that 18 probably in the DCA application. I just don't know if 19 we need to do a tutorial on how the systems work in 20 order to be able to say the conclusion. I'm not 21 suggesting we edit it right now. It was just an 22 example.
23 The portion of the tube steam generator 24 tube design, we have flow restrictors were installed.
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53 I mean, what's the delta? The flow restrictors being 1
pushed the temperature curve, whatever you call that.
2 And then the accident analysis further addresses the 3
stability.
4 MEMBER PETTI: The boron section is very 5
long. There is a lot going on.
6 MEMBER HALNON: Yeah. So I think there's 7
a lot of information that's -- I don't want to say 8
redundant, but maybe is --
9 CHAIR KIRCHNER: Extracurricular.
10 MEMBER HALNON: -- low-level of detail not 11 necessary to support the conclusion.
12 CHAIR KIRCHNER: Let me go around the 13 table and get input. I'll start with Craig. Craig, 14 you looked at the ECCS containment, their systems.
15 The ECCS valve performance, what would you consider 16 the key takeaway or message that we want to convey 17 here?
18 MEMBER HARRINGTON: To me, the big piece 19 there is the closing the loop part to the DCA.
20 There's a connection from that to PRA issues as well.
21 To Greg's point, when we started talking about this, 22 I looked at that section, and the first paragraph is 23 just something that, yeah, it explains how the system 24 works, but we really didn't do that in this letter.
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54 I don't think we do.
1 So kind of agree with Greg's comment about 2
that, that much of the rest of this could go away. We 3
might want to keep some form or fashion something 4
about the greater likelihood of an RVV actuation with 5
the removal of the IABs and how that ties in with PRA, 6
but that may not be all that critical, and it 7
certainly doesn't go with closing the loop to the DCA.
8 Yeah, a lot of that could come out.
9 Same with the steam generator part. Maybe 10 we can just succinctly state that these were made to 11 better manage that issue, the DWO issue, and --
12 MEMBER BALLINGER: Yep.
13 CHAIR KIRCHNER: What do you think, Ron, 14 on the steam generator?
15 MEMBER BALLINGER: I was wondering that 16 there are two sets of things that happened between the 17 DCA and the SDAA, and that is issues related to 18 safety, the boron dilution, da-da-da, those resulted 19 in changes of the design. But there's another set of 20 changes to the design that were simply made to go from 21 X power to Y power.
22 MEMBER HARRINGTON: Yeah.
23 MEMBER BALLINGER: And I don't think we 24 need to say anything about that. I would focus on the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
55 first set.
1 MEMBER HARRINGTON: Maybe a statement that 2
that was done.
3 MEMBER BALLINGER: Yeah, yeah. But you 4
could shorten it up. And that should be reflected in 5
the conclusions and recommendations, which they're 6
not. I mean, they're way general. It's a great 7
thing, we should do it, and all that stuff, but we 8
really went round and round and round, and the staff 9
went round and round and round on some of the issues 10 with the DCA.
11 I don't know. I just wondering whether we 12 can shorten it up quite a bit by focusing on the 13 issues that were brought out in the original design, 14 which they addressed.
15 MEMBER BIER: Yeah. I think I would agree 16 with that. I mean, certain things like including the 17 Venturis, it gives a very concrete idea of that the 18 changes to improve safety were significant, they were 19 just causing it occur, you know, pencil whipping or 20 whatever, and the power issue is not really directly 21 related to safety other than, yes, they appear to have 22 done it correctly or whatever.
23 MEMBER BALLINGER: I mean, the materials 24 changes were because they needed to go from one power 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
56 to another.
1 MEMBER ROBERTS: The EDAS issue was 2
documented in two relatively long paragraphs because 3
it took months to get to a conclusion, which I think 4
we heard a conclusion this afternoon. I'm not 5
entirely sure that the non-concurrence has been fully 6
resolved, but it sounds like there's a resolution 7
that, at least to me, makes perfect sense. For us to 8
spend a lot of time on something that's not really a 9
safety issue, it took us a better part of a year to 10 get to that conclusion, it maybe doesn't warrant any 11 mention in the letter at all.
12 MEMBER BALLINGER: That discussion might 13 result in a precedent being set.
14 (Simultaneous speaking.)
15 MEMBER ROBERTS: Yeah. I don't know. The 16 non-safety with important safety --
17 (Simultaneous speaking.)
18 MEMBER BALLINGER: Yeah.
19 MEMBER ROBERTS: -- or whatever. I don't 20 know if that's something that's a precedent or just 21 part of engineering.
22 MEMBER PETTI: May I ask on a question on 23 the PRA? Is this the first application that we've 24 seen, the PRA was quote, used, in the design process.
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57 Did AP1000 use a PRA in the design process?
1 MEMBER DIMITRIJEVIC: Well, everyone did.
2 MEMBER PETTI: No. I mean the legacy 3
fleet. The legacy fleet doesn't. I'm talking about 4
the new ones. They have to do. Is this the first 5
one? I'm not --
6 MEMBER DIMITRIJEVIC: I don't know in the 7
new process, Dave, but everybody uses PRA to extend 8
advanced reactors in the design. I would not any say 9
this was extensively the other issues, the things 10 which brought some of those changes, because those 11 scenarios didn't exist in PRA and they still don't, 12 you know, boron dilution and that. And in general, 13 issues did not come from PRA, so I mean, you know.
14 But on that perspective, there is nothing 15 really, you know, special here compared with, you 16 know, my other experience with advanced reactors. My 17 main goal in the PRA, so they have low numbers, right?
18 We should always be uncomfortable with low numbers 19 because they cannot be realistic. They are often not 20 realistic. I don't want to say they cannot be 21 realistic. There is a lot of things that I'm not 22 really totally 100 percent comfortable, and that's 23 because I have not looked in thermal hydraulic 24 analysis behind that.
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58 The thing is, like, for example, this 1
plant cannot have LOCA site containment, which is, you 2
know, unheard in the industry because it depressurize 3
fast enough. What does it mean fast enough? What has 4
to be done to that to be succeed? The things like 5
that stay in the air, but for example, steam generator 6
tube rupture is not suddenly -- I apologize for 7
NuScale. I know it's a failure. But it's I'm so used 8
to the steam generator tube rupture.
9 So in general, the tube failure is not 10 really important so much because it does not lead to, 11 you know, the loss of coolant outside of containment 12 because it depressurize fast enough, it basically is 13 no event.
14 So there is a lot of assumptions made 15 here. My main point in the PRA was this is very big 16 PRA, a lot of details, but somehow, in the end all of 17 these should fit together. They miss a lot of points 18 that will leave anybody who reviews that PRA, who has 19 a lot of experience, slightly uncomfortable.
20 What made me uncomfortable is that, for 21 example, you know, ECCS valves, those are like the 22 most dominant thing in the risk. Those are new 23 valves. We have to assume their failure rates because 24 there is no industry data on them, and we can still 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
59 assume common cause factors for them.
1 So now we assume -- I don't really know 2
because that's a multi-factor, and I did not look in 3
details, but I have a feeling approximately seven out 4
of 100 failures between those valves will be from 5
common cause. And I have a feeling that that's really 6
optimistic. If these valves fail, there is a high 7
chance that they will fail from common cause. These 8
make them fail in these situations.
9 So there is a lot of assumptions we should 10 make because it's a new plant and we have so many new 11 design features, which should be kept in mind. With 12 data sensitivity, they say all common cause factors 13 increase to 95, so we don't really know is it from 14 failure, is it from common cause factors, is it decay 15 heat removal system?
16 I am very interested in importance of 17 decay heat removal system, which through all this 18 discussion I could not really figure out, because 19 obviously, decay heat removal system was very 20 important to prevent a LOCA outside containment. And 21 I had a feeling was important also to prevent these 22 boron events, but that prevented that, you know, that 23 things like the looking at this make us thinking that 24 this thing said okay.
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60 But if you just change a little in the 1
sensitive places, you just take a little bit, 2
suddenly, you can be ten to minus seven. And then 3
suddenly not everybody will say, "No, that's still 4
good. It means the goal." But they will not say, 5
"Oh, okay. Now we don't have to worry about 6
anything," because it's not true. You should have 7
important assumptions. You cannot say, "Oh, you know, 8
in ten to minus nine, nothing is important." That's 9
not the good engineering.
10 You should really look in detail. So when 11 I was writing, and I wrote only two pages, I really 12 didn't really, you know -- I tried to keep that as 13 small as possible. I wasn't writing to the -- I don't 14 even know who we writing. I was writing for the 15 future people when they completing these things, 16 saying, "Hey, look at the sensitivity combinations."
17 Don't say something is sensitive to something and then 18 don't have that considering the uncertainty approach, 19 and make sure that this is true that no human actions 20 are important and not any other system are important 21 even they are providing certain defense.
22 My letter was for the future NuScale 23 analysts. It wasn't just for Commission to say that 24 we agree with this SER because I don't think there is 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
61 the doubts we are here. We are going to prove it in 1
this meeting.
2 Also, when come on the length of the 3
letter, okay, we decide in some moment in one thing 4
the shorter letters are better because they get to the 5
end or that it's easier for us to write them or 6
something, you know. If we have to say something, I 7
think that the letter limits should be the issue. If 8
we are repeating some things which are known, we 9
definitely should cut on those. That's my --
10 MEMBER HALNON: The issue was not the 11 length; it was the dilution of the important points, 12 not necessarily the length. It could be a 13 thousand-page letter as long as the important points 14 are hit, not put in with a bunch of other stuff.
15 MEMBER DIMITRIJEVIC: All right.
16 MEMBER HALNON: I agree with you, though.
17 You don't strive for shortness. That's not the way.
18 It's clarity and completeness is the goal.
19 MEMBER DIMITRIJEVIC: All right. Maybe 20 then we should in this big picture decide what are our 21 important points and make that those are made.
22 MEMBER HALNON: Yeah. I think we're 23 probably dancing around that exact point. I did have 24 one question though for you. Help me understand the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
62 difference between a very important portion of the PRA 1
and very important to safety when we're dealing with 2
very low numbers. Is there a difference there?
3 I realize you cut the grass, there's 4
always going to be one blade that's higher than the 5
rest. That's the most important. You got to go back 6
and get that. But when it's way far from the safety 7
goal or whatever threshold you want to call it, is 8
there a difference between very important versus very 9
important to safety?
10 MEMBER BIER: Let me try and respond to 11 that, and it may not be the same as Vesna's response.
12 MEMBER HALNON: She'll correct you.
13 (Laughter.)
14 MEMBER BIER: Yeah. She'll say. Yeah.
15 But I mean, I think part of it is it kind of relates 16 in a way to what Vesna was talking about of what's 17 good engineering practice, because if the total risk 18 is extremely small, it may be that those few tallest 19 blades of grass are not significant from a public 20 health and safety point of view.
21 But I think as a risk manager or a plant 22 manager or whatever, you still want to know which 23 things should I be the most concerned about, which 24 things should I be looking out for or tracking over 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
63 time or investing in. And it kind of answers that 1
question of, yeah, your plant looks very safe from 2
what we can see now, but that doesn't mean, like, 3
okay, you're done. Hands off, walk away, and don't 4
look at it again.
5 So that would be part of my answer, but 6
Vesna, I'm curious to hear what you would say.
7 MEMBER DIMITRIJEVIC: I mean, you know, 8
the reason, you know, safety and non-safety and 9
important, not important, I don't really know that 10 safety was. I was listening carefully to many things 11 through my Committee meeting to figure out exactly how 12 the safety versus non-safety is determined. That's 13 not PRA. PRA is an important, not important because 14 that safety, you know, you don't write. Either you 15 satisfy whatever deterministic requirements to be 16 categorized as safety or non-safety.
17 Now, important for safety, it comes from 18 how much it contributes to the risk. And so it could 19 be, you know, like for example. I'm not sure how this 20 works in the practice, but we don't really have too 21 many safety system. That mean this plant can operate 22 without all of those system for very long time because 23 work with the tech specs, you know, charging on the 24 other parts which are non-safety, you know, the DC 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
64 power or something like that.
1 So it basically, this plant will be 2
totally fine without non-safety system. When it comes 3
to the --
4 MEMBER HALNON: I wasn't talking about 5
classification. I was staying strictly in PRA space.
6 Important versus important --
7 MEMBER DIMITRIJEVIC: All right. Well, 8
the report tells you including plants if it 9
contributes to the half of the percent to the risk, 10 then it's important, and if it is remove, it will 11 increase risk twice is important. Here, those things 12 are changed, so if it contributes 50 percent to this, 13 it's important.
14 And it is dependent on how much 15 contributes to the risk and how much will risk 16 increase if it fails or if it's not in operate.
17 MEMBER HALNON: I guess the question was 18 more if you start with a threshold like this and 19 adequate safety sign, and you're decades and decades 20 below that in your numbers, why can't we let it stay 21 decades and decades below that, say, that's okay 22 space, as long as --
23 MEMBER DIMITRIJEVIC: You know, Greg, 24 nobody uses these things. I mean, it's not really 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
65 that the design plant. This 10 CFR 50.59, it's, you 1
know, forbidden and unfortunately not used. This 2
plant has nothing important other than ECCS and, you 3
know, ultimate heat sinks and reactor vessel and 4
containment which every plant is important.
5 So it's not that this importance has any 6
meaning in the plan design. I mean, you know.
7 (Simultaneous speaking.)
8 MEMBER HALNON: Yeah. I understand good 9
engineering practice, at least judgment and looking at 10 things like that, knowing what's the most important.
11 But you connect that up with having to put words on a 12 paper that translate into a supply chain, a cost, and 13 a program, and everything else down the road, and you 14 have to assess, at least in my mind, the cost of that 15 versus the ability to say you're way below the line 16 from the standpoint.
17 And we shouldn't have to worry about it 18 because we designed this plant with such safety margin 19 that it did that so we don't have to worry. We design 20 everything such that we worry about everything. We're 21 never going to get there.
22 I guess that's the discussion down the 23 road, I guess, when you got to get to the PRA 24 discussion. You know, mathematically, I get it.
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66 Conceptually, I get it. Practically, it doesn't work.
1 So it's just me.
2 MEMBER DIMITRIJEVIC: Okay. Well, there's 3
one other thing which I just want to tell you that you 4
should keep in mind. Safety, non-safety, this is 5
where your price gets it. Important and not 6
important, that doesn't really put price to the level 7
safety but the sort of dedicated application which 8
nobody really is used so far in this industry, and 9
nobody really knows what price of that is.
10 So I don't think the PRA in this plant 11 definitely didn't contribute for anything because 12 anything is important. Anything is not important, but 13 eventually will contribute to something which will be 14 between safety classification and non-safety 15 classification sort of dedicated probably tasks to 16 show the reliability and things like that.
17 MEMBER HALNON: Well, I get the insights 18 from PRAs are important, but we're either going to use 19 them or we're not. And in this situation, I would say 20 that I didn't even need a PRA. I could have told you 21 the ECCS is probably the most important piece. I 22 could have told you from a deterministic perspective 23 that EDAS is an important system, but it doesn't have 24 to be safety-related. I could have told you all that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
67 stuff, and we don't even need to spend the money on a 1
PRA. Well, to just do the PRA, then suddenly say it 2
doesn't matter what it says, I think this is 3
important. Main insights.
4 MEMBER DIMITRIJEVIC: I did not hear you, 5
Greg. What system you were talking about?
6 MEMBER HALNON: Well, I could have told 7
you without the PRA that the ECCS system is in just 8
about every nuclear plant, if not all of them, are one 9
of the most important systems. So I --
10 (Simultaneous speaking.)
11 MEMBER DIMITRIJEVIC: Well, PRA must have 12 done --
13 MEMBER HALNON: I didn't need the PRA to 14 tell me.
15 MEMBER DIMITRIJEVIC: Yeah. Very good.
16 So let's cancel Chapter 19. I mean, if PRA was done 17 to tell you what system is important, I mean, Chapter 18 19 is a part of FSER. What in the 53 to be done 19 without PRA?
20 MEMBER HALNON: Without PRA? I don't know 21 if I'd need Chapter 19 if we did the PRA. Oh, never 22 mind. Let's move on. Again, we're philosophically 23 talking at this point. Trying to get through this.
24 Trying to give Walt time to read and make decisions.
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68 (Laughter.)
1 MEMBER ROBERTS: And Greg, I have maybe a 2
slightly different answer to what you asked and Vicki 3
or Vesna. So when I look at the ATWS risk, they have 4
covered it with a reliable protective system and a 5
plant that can withstand the loss and scram. Each of 6
those is robust. How robust are each of those?
7 If you look at the design of the 8
protective system, it's a single platform, which is 9
very well designed by a single designer subject to 10 whatever common cause failures you can dream up for a 11 common platform. Not all of those have been covered 12 by the design because it's probably also covered by 13 the design.
14 So you have an estimate of what the 15 failure rate might be. You might estimate ten to the 16 minus eight and that wouldn't be a believable number.
17 You might estimate ten to the minus five. That might 18 be a believable number. I don't know. But there's 19 some scenarios that are going to cause a common cause 20 failure of a single platform, whereas the NRC table 21 but the conclusion 40 years ago that you can't ever 22 count on a common platform. You have to have a second 23 platform unless the plant could withstand the event.
24 Well, in this case, the plant could 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
69 withstand the event, so the fact that there is a 1
highly reliable platform is, you know, basically 2
gravy. So you could do the analysis and say, well, if 3
I'm wrong there, no big deal, that the plant is a 4
plant. Great, good performance.
5 If you had a different plant where you had 6
your ten to the minus eight model protective system, 7
but the plant, if it failed, you would go to a 8
catastrophic state so now you have ten to the minus 9
eight as your CDF or your LRF, whatever parameter, you 10 might think that's great. That's well under the 11 goals. But if you're wrong about the protective 12 system reliability, you know, that caused quite a 13 different area.
14 So that's where if you were looking at 15 these relative statistics, then that will give you 16 some insights. And yeah, if I'm wrong, you know, I'm 17 in a place I don't want to be, so maybe I'll go 18 redesign something else in the plant.
19 MR. HANLON: It sounds all great until you 20 start actually drawing out what ten to the minus eight 21 looks like, ten to the minus five. I mean, there's 22 lots of zeros there.
23 MEMBER ROBERTS: Yep.
24 MR. HANLON: And if you can't believe that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
70 there's seven zeros, that's too many, I can't believe 1
that. Five zeros, I can believe. I don't get it.
2 From an operator perspective, my mind doesn't go 3
there. Mathematically, I get it, but practically, it 4
doesn't make any difference.
5 MEMBER ROBERTS: Right. And historically, 6
the deterministic requirement is you have a protective 7
system that's diverse in totality, a diverse system, 8
or a plant that can withstand it. Here there's kind 9
of a middle ground.
10 MEMBER HALNON: Well, I just have to --
11 MEMBER ROBERTS: And a middle ground may 12 be perfectly reasonable, particularly since this 13 middle ground is a pretty strong case.
14 MEMBER HALNON: I'm just asking if 15 something comes out ten to the minus eight, just leave 16 it and move on. If it's ten to the minus five, let's 17 leave it and move on. But don't sit there and say 18 it's ten to the minus five in this case, and I believe 19 it, and ten to the minus eight, but I don't believe 20 it, so do it anyway. It doesn't make any sense to me.
21 Either we're going to do it and believe the PRA. It's 22 low-risk, lots of margin, let's move on. Or we're 23 going to --
24 (Simultaneous speaking.)
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71 MEMBER DIMITRIJEVIC: Okay. I not feeling 1
great, so I shouldn't defend the PRA, but, you know, 2
this is a very specific plant. It's a passive plant, 3
and it has features which we are not familiar with.
4 I can give you many an examples in the current fleet 5
where there is no way that people could predict what 6
is the safe system, you know, most important system, 7
you know. Like, nobody will say the Seabrook most 8
important system is service motor or component 9
cooling, which are not even safety systems.
10 So the thing is that PRA brought some new 11 insights discovering these
- hidden, you
- know, 12 dependencies. Everybody says these generators are 13 important, but nobody says service motor is important 14 because it cools them or the service motor cools the 15 ECCS in Seabrook, which is important for the still 16 LOCAs. Things like that are discovered in the complex 17 system through the PRA models. I just saying they're 18 not really used as much in risk informed application, 19 and that's a pity.
20 Here this is very specific plant relying 21 on the passive features, and there is, you know, not 22 too much to say. However, those passive features are 23 new. We don't have experience. We don't have a 24 failure data. We have to learn about that.
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72 MEMBER MARTIN: I can't help but think, 1
you know, our jobs should be easier than what we're 2
talking about because we're beginning with a design 3
that was already approved. Now, some of the things 4
that we're critiquing, you know, really go back before 5
that, correct?
6 And then maybe to your point in the 7
letter, our methodology, the delta, if we just kind of 8
proceed through the deltas and, like, for PRA, are we 9
more reliable? You know, those kind of questions that 10 were before us as what NuScale has shown us the last 11 two years was just, you know, farther away from, you 12 know, the threshold they had before in a good sense, 13 you know. When it comes to a common A, the power 14 uprate, you know, Ron, like I said, we don't need to 15 have a lot of that stuff in there.
16 They provided more evidence on, you know, 17 at least in Chapter 15, in deterministic sense that, 18 you know, we can say, well, that wasn't there before, 19 but now it's now there. And, you know, we like that.
20 I think focusing on the deltas gets us through the 21 letter, and maybe in that sense, we could filter out 22 that it wasn't as important and bring it down by 30 23 percent, 25, 30 percent. I think our target is a 24 specific number of lines.
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73 MEMBER PETTI: But again, to what end?
1 MEMBER SUNSERI: I think the delta review 2
is a good way to get through the material. But from 3
our perspective, making a safety statement about this 4
particular plant, I think it has to be comprehensive.
5 I think, you know, Dave or Greg or whoever is saying, 6
we should come out strong on the four or five things, 7
whatever they are, three, and make this plant safe, 8
passive designs and all that stuff.
9 Sure, the passive cooling only works if 10 the ECCS valves couple the system, so that's something 11 that needs to happen, but, you know, the fact that we 12 learned that through a delta review doesn't take away 13 from the fact that that is part of the big picture, 14 right?
15 I go back to my original statement. I 16 just lose the big picture the way the letter is 17 constructed. We had something up front that said, 18 "Here's why this plant is safe," and then the rest of 19 the letter supported those four things and then 20 there's technical detail that's important to have but 21 not directly related, put it an appendix or knock out 22 it or whatever we want to do. But, you know, I feel 23 strongly that our letter has to have a big impact on 24 why this is safe for all the right reasons, and then 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
74 the supporting stuff comes in.
1 MEMBER PETTI: I would just note I was 2
struck, now having looked at TerraPower, little bit of 3
Terrestrial, knowing what the gas reactor guys are 4
going to do, looking at this, there's a lot of 5
commonality in design space to reduce risk. It's 6
passive, no operator action. You're going to see a 7
lot of them coming. No need for power for safety 8
functions to be actuated.
9 We're going to see this over and again, so 10 we shouldn't be surprised when the PRA says numbers 11 that are really low. They are designing using the PRA 12 to make sure the number stays, in their mind, very 13 low, whatever you want to quantify it. But that's 14 what they're doing, and coupling it with the inherent 15 characteristics of each technology, which can be a 16 little bit different in passive design.
17 MEMBER HALNON: And my point, Dave, is 18 that we just got to believe it and move on. If we 19 don't believe it and move on, I mean maybe we find 20 stuff that's --
21 MEMBER PETTI: Yeah. NuScale spent two 22 billion dollars to get here from what I'm told. If 23 that ain't enough, we ought to go home.
24 (Laughter.)
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75 MEMBER PETTI: You know? Because, A, I 1
don't think any of the others are going to spend that 2
type of money, you know. It's about as good as you 3
can do from the engineering perspective, if not a 4
little bit more than maybe is good enough.
5 And my go is this didn't all happen by 6
accident. They made design choices. Design is 7
everything here in terms of the leverage, and that's 8
what you want to highlight, I think, is to say, look, 9
there are important things that were done, whether it 10 be the SDAA or not, that in part the safety attributes 11 that Matt says we want on.
12 You can take out the paragraph on the 13 source term and the post-accident monitoring because 14 I don't think it even needs to rise to our letter.
15 It's a design change they made. I don't think it gets 16 there.
17 CHAIR KIRCHNER: It's a very good design 18 change.
19 MEMBER PETTI: It is. I mean, it is, but 20 in terms of the ones that -- if we're going to talk 21 about any specific things.
22 CHAIR KIRCHNER: I don't want to harp on 23 it, but I will because it's an excellent design change 24 because prior to, they would have opened up 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
76 containment and risk, not only bypassing containment, 1
but exposing operators in the course of trying to take 2
a sample for post-accident atmosphere assessment. By 3
putting the combiner in, you don't open it up. I 4
mean, really, it's a major. And it's passive.
5 MEMBER HALNON: In that kind of situation, 6
there's probably a couple of those.
7 (Simultaneous speaking.)
8 MEMBER PETTI: But then everybody has to 9
go back and write their section in seven lines.
10 MEMBER HALNON: Yeah. Well, no, you just 11 go at the end and say --
12 MEMBER PETTI: You know, it's short and 13 sweet.
14 MEMBER HALNON: -- "In other notable 15 improvements in a design for risk reduction are --"
16 bullet, bullet, bullet, bullet. You don't have to 17 explain what they all are. I mean, I realize these 18 letters got to stand on their own, but they don't.
19 MEMBER PETTI: Never. You have to go back 20 and you have to --
21 (Simultaneous speaking.)
22 CHAIR KIRCHNER: And we're going to have 23 the chapter memos in the --
24 MEMBER PETTI: Absolutely.
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77 CHAIR KIRCHNER: -- back, so we could put 1
those bullets in --
2 MEMBER PETTI: And say, "See chapter --"
3 Yes.
4 I'm the only who sound like a contrarian, 5
because I tend to agree with you, but we do not know 6
anything about the SCDA, the certifying design? We 7
wouldn't even talking about this thing because it was 8
just another -- I mean, this was the only plant we 9
saw. We wouldn't even be writing about this.
10 CHAIR KIRCHNER: No, I hear you. If we 11 didn't see the DCA, we just saw this, then --
12 (Simultaneous speaking.)
13 MEMBER SUNSERI: Some of the DCA was --
14 the carveout of the part is -- I don't want to get too 15 nuanced here -- but, you know, some of it was because 16 they weren't complete with their design yet. Some of 17 it was they weren't complete enough to know that there 18 were problems with their design. So I mean, you know, 19 not all carveouts were equally made, I guess.
20 And so, you know, whether or not one needs 21 to be referenced back in this letter to say they've 22 addressed the point or not, now I'm talking myself out 23 of it. There's some tying back to the original 24 letter, but anyway.
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78 MEMBER MARTIN: Several of the carveouts, 1
I mean, they really were truly for the COLA, right?
2 I mean, they tended to get resolved this second 3
go-round. So to focus on carveouts, per se, 4
obviously, would be appropriate by just going back to 5
the safety questions and the DWOs probably should be 6
on the list and the boron dilution, sure criticality 7
on the list.
8 You know, if you don't keep on talking 9
about PRA and maybe move into the PRA discussion 10 really focused on design improvements that were made 11 with insights from PRA, that might knock out ECC 12 performance and ATWS and maybe even the source term 13 section. They could have bullets or something like 14 that that kind of condense the content there all under 15 the heading of, you know, reliability improvements 16 gained by PRA insights. I don't know. I'm obviously 17 spitballing.
18 And then, you know, retain most of the 19 sections on DWO. And ATWS can be condensed as kind of 20 Tom had mentioned earlier. What else do we have in 21 there?
22 CHAIR KIRCHNER: So the boron dilution one 23 definitely --
24 (Simultaneous speaking.)
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79 MEMBER MARTIN: Of course, yeah. That can 1
probably more or less stay like it is. It's not going 2
to get through our line by lines unscathed, of course, 3
but --
4 MEMBER PETTI: It really needs to be 5
condensed. The problem is that some of it just to set 6
it up takes a lot of time because these are subtleties 7
here from a hydraulic space to get you to understand 8
it.
9 MR. SNODDERLY: Well, and as, of course, 10 we've all noted, we have the memos. The challenge for 11 the final letter is you obviously don't want to repeat 12 what's in the memos, but there are certainly some 13 cross-cutting issues that the final letter can kind of 14 pull all together and integrate.
15 And I think that's what I kind of see you 16 did, Walt, for both the issues try to bring in where, 17 you know, Chapter 8, 15, and 19, you know, that always 18 tries to get in there. Or 5 and 15 with DWO, you 19 know, those sort of things. I think when you 20 originally outlined the letter, you identified not 21 just one person necessarily for sections, sometimes 22 you had teams that were contributing from their 23 perspectives of their particular chapters.
24 MEMBER SUNSERI: So in order to move 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
80 forward, can we maybe take like five minutes to go 1
around and just list from each member's perspective 2
what are the key safety things that they see at this 3
plant, use of passive designs, no need for off-site 4
electrical power. I mean, everybody has probably got 5
their one thing or something that they like. And then 6
we can agree on the list of back out from -- or, you 7
know, make sure that the letter supports that. I 8
don't know.
9 MEMBER PETTI: We've already said that in 10 the previous letter.
11 MEMBER SUNSERI: This is like starting 12 over. This is a SDAA of a new plant, okay? Nobody is 13 going to say when they build this plant, "Oh, by the 14 way, there's a certified design out there." They're 15 going to reference this one. Has to stand alone, 16 stand on its own.
17 MEMBER PETTI: So Matt, I had eight design 18 and operational features. NuScale ensures its safety 19 through several key design and operational features:
20 passive heat removal, passive ECCS, reduced stored 21 energy, low source term, supplemental boron system, 22 containment bypass minimization, no operator actions 23 required, and no safety-related --
24 (Audio interference.)
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81 CHAIR KIRCHNER: Great list. Well, 1
obviously I had the list in front of me, and I thank 2
you, Dave. Yeah. And I tried to make sure in the 3
background section that I kept each bullet rather than 4
just putting them in as a list.
5 MEMBER PETTI: And then I put a sentence 6
after each one to explain what it is.
7 MEMBER DIMITRIJEVIC: Dave, why did you 8
identify this boron thing as a safety part?
9 Supplemental boron.
10 MEMBER PETTI: Minimized the potential for 11 return to power through the emergency boron system.
12 MEMBER DIMITRIJEVIC: I mean, that's in 13 every plant, you know. And the other thing, did you 14 put the pool?
15 MEMBER PETTI: Yes. That's in one of the 16 others. Yeah, it's in the passive heat removal.
17 CHAIR KIRCHNER: Passive heat removal.
18 MEMBER PETTI: "Utilized a large pool as 19 its ultimate heat sink for passive heat removal 20 through redundant decay heat removal systems."
21 "ECCS," I said, "uses highly reliable independent 22 hydraulic actuation systems on four valves to condense 23 steam on the containment vessel surface, maintain 24 sufficient inventory to keep the core covered during 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
82 all postulated events."
1 I was just trying to think at a high level 2
what are the takeaways. Restored energy was really to 3
address ATWS.
4 MEMBER HALNON: If he started a discussion 5
with that paragraph on those, whatever, and then 6
finished with some notable deltas between DCA and 7
SDAA, and then ended it with -- that's really long at 8
that point -- to support the safety. It's all in 9
here.
10 MEMBER SUNSERI: Yeah. You could look at, 11 you know, salvaging a lot of stuff where you need to.
12 Is there some place very prominent what we feel the 13 safety case is and what we agree?
14 CHAIR KIRCHNER: Anyone else? Well, then 15 16 MEMBER BALLINGER: You know, I think 17 Dave's got a great -- that's a great list. We could 18 probably make this letter very short, putting that 19 list in their right up front, adding a few words in 20 the discussion about each topic, and then include a 21 discussion that address the issues that were brought 22 up in the earlier design that we brought up in a 23 previous letter.
24 And that satisfies both the safety that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
83 you're talking about, and it suggests or demonstrates 1
that the issues that were brought up for the earlier 2
design have been addressed. Those are the key things, 3
are they not?
4 CHAIR KIRCHNER: Probably, but I would 5
modify that a little bit. I don't think we have to go 6
back and look at everything in the previous letter, 7
only the things that would be relevant to this 8
particular design.
9 MEMBER BALLINGER: Right. Yeah. Yeah.
10 MEMBER SUNSERI: So, you know, the steam 11 generator flow vibration, that's a big deal, all 12 right. That was a --
13 MEMBER BALLINGER: But they had flow 14 restrictors in the original design.
15 MEMBER SUNSERI: Yeah.
16 MEMBER PETTI: It's different though.
17 MEMBER SUNSERI: That was --
18 MEMBER BALLINGER:
But they were 19 different, but they were still flow restrictors.
20 MEMBER PETTI: Yes.
21 MEMBER HARRINGTON: The difference is 22 interesting and it's
- useful, but it's not 23 determinative for this design. It's just different.
24 MEMBER BALLINGER: Well, it is to the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
84 extent that they understand the DWO much better, and 1
the flow restrictors in that design was to deal with 2
the DWO, right?
3 CHAIR KIRCHNER: On both designs, the --
4 (Simultaneous speaking.)
5 MEMBER BALLINGER: Yeah, both of them, but 6
I think they did more analysis.
7 CHAIR KIRCHNER: Well, this is a much 8
simplified and improved design because -- well, we 9
don't have to rehash the old design, but that had 10 significant --
11 (Simultaneous speaking.)
12 MR. BALLINGTON: But the DWO, well, the 13 sentence in there about the restrictors new design or 14 whatever that addresses DWO, that's one of your -- on 15 the list of things.
16 CHAIR KIRCHNER: Okay. Well, I think it's 17 coming up to break time, and I would propose that take 18 a break. I will reach out to a few individuals 19 offline, and I'll go away and take what I've heard and 20 reformat the letter accordingly, and probably shorten 21 it considerably at the same time, and try and turn 22 something around and provide it for your 23 consideration, if not this evening, tomorrow.
24 Let's look ahead to the rest of our agenda 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
85 and just discuss how we use our time accordingly. We 1
had budgeted this afternoon for the NuScale letter 2
report. Bear with me and I'll get the agenda. We are 3
scheduled to take up first thing tomorrow the 4
TerraPower Topical Report on source term. Dave has 5
cautioned me that that's a long letter also. And 6
we've got the morning budgeted for that.
7 We have the afternoon for the Seabrook.
8 I sense from looking at the source term draft letter 9
report that we will take that whole time and then 10 some.
11 What's your sense, Greg -- Looking ahead 12 to tomorrow afternoon, we have the Seabrook and the 13 ASR topic on our agenda. What's your sense of agenda 14 timing schedule?
15 MEMBER HALNON: I think that we'll be done 16 well before 3:00 o'clock. I think it'll be more maybe 17 a couple hours, given the fact that we have a 18 presentation by C-10 and there's no presentations 19 after that. It's just us discussing what our next 20 steps would be based on the information we received.
21 So I think we'll be done by the first break.
22 CHAIR KIRCHNER: Okay. So then we could 23 come back, if we're ready, to either continue the 24 source term letter -- that might be the right thing to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
86 do.
1 And Thursday morning, we have P and P for 2
starting off the morning. Let me turn to Larry 3
Burkhart who leads this. Larry, what's your sense for 4
the agenda --
5 (Simultaneous speaking.)
6 MR. BURKHART: It's fairly short, so I 7
would be surprised if we went more than two hours for 8
the P and P. Probably less.
9 CHAIR KIRCHNER: Okay. So that leaves us 10 Thursday morning and the latter of Thursday morning if 11 we're efficient on P and P, and then Thursday 12 afternoon and Friday is set aside right now for letter 13 reports.
14 MEMBER PETTI: So Walt, do we have all the 15 NuScale letters done? So we don't have to review any?
16 CHAIR KIRCHNER: No. One, four, eight, 17
- 15. They're all in the P and P folder and NuScale 18 letter.
19 MEMBER PETTI: You're saying that probably 20 is Thursday.
21 CHAIR KIRCHNER: That's Thursday. But 22 we're not going to go -- oh, we could do it now.
23 MR. BURKHART: Depends when you want to do 24 them. If you wanted to do them now, we could.
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87 MEMBER PETTI: After break.
1 CHAIR KIRCHNER: We could do them now.
2 MR. SNODDERLY: 8 and 15 are ready. One 3
hasn't been reviewed by NuScale, but I'm pretty 4
confident there's not proprietary information and 5
NuScale could, you know, if they see something, they 6
can let us know. We should have NuScale's comments on 7
four tomorrow, so I think four would be better off 8
done Thursday. Fifteen and eight are ready to go.
9 You could knock out one of those two.
10 CHAIR KIRCHNER: Come and --
11 MR. BURKHART: Four didn't even have a 12 proprietary version.
13 MEMBER MARTIN: I'm happy to read them in.
14 I mean everyone's going to fall asleep by the time we 15 get to the end if I read it in.
16 MEMBER PETTI: I'm just trying to take 17 stuff off.
18 MEMBER MARTIN: Absolutely.
19 (Simultaneous speaking.)
20 MEMBER PALMTAG: You have a lot of good 21 stuff in there that was in the XPC topical report, and 22 there were some questions about where that goes. It 23 wasn't quite in 15, and if we take it out of the final 24 letter, where could we put that? I mean, it was kind 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
88 of a last minute.
1 MEMBER MARTIN: Nothing says we can't put 2
it in 15.
3 CHAIR KIRCHNER: We could put it in 15.
4 MEMBER PALMTAG: I wanted to capture that 5
somewhere because it was a last minute thing. We 6
didn't really know where to put it. I'm kind of 7
worried that if we take it out of here, we're losing 8
it.
9 (Simultaneous speaking.)
10 MEMBER HALNON: Take a break. You come 11 back. Might as well just make it longer. I mean, 12 it's not going to get shorter.
13 MEMBER SUNSERI: These memos don't have to 14 be to the same level of scrutiny either.
15 MEMBER HALNON: Exactly.
16 MEMBER SUNSERI: Just cut the paragraph 17 and paste it in there.
18 MEMBER BIER: I liked Greg's idea about 19 that instead of rewriting everything that was already 20 in the chapter memos, maybe we should just make the 21 appendix be the chapter memos and then highlight key 22 points from each. Yeah.
23 CHAIR KIRCHNER: We will do that. They 24 are all referenced in this letter.
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89 MEMBER BIER: Yeah, because then it 1
significantly reduces the amount of editing we have to 2
do, I think.
3 CHAIR KIRCHNER: Okay. So 15 and 8 after 4
the break? All right. Can we be ready to do that, 5
Mike?
6 MR. SNODDERLY: Yeah. Yeah.
7 CHAIR KIRCHNER: Yeah. That's do that, 8
then. All right. I think it --
9 (Simultaneous speaking.)
10 MEMBER PALMTAG: Four is very short, and 11 there was no proprietary version of Chapter 4, right?
12 MR. SNODDERLY: I agree with Scott. I 13 still think we start with 15 and 8, we get those done, 14 and then do four.
15 MEMBER HALNON: You could read the Chapter 16 4 memo right now.
17 MR. CUMMINGS: I will check to see if 18 we've reviewed that for proprietary information.
19 MR. HANLON: We're just worried about 20 proprietary information and accuracy.
21 MR. CUMMINGS: Yeah. We're reviewing it 22 now for proprietary information. This is Kris 23 Cummings, NuScale.
24 CHAIR KIRCHNER: Yes. We can always do 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
90 our part just to --
1 (Simultaneous speaking.)
2 MEMBER HALNON: By the end of the 3
afternoon, I think we'll have it.
4 MR. BIER: Yeah.
5 MR. SNODDERLY: They said tomorrow. Why 6
don't we get through 15 and 8, see where we're at.
7 But I'm with Scott. I'm pretty comfortable that 8
there's not anything proprietary --
9 (Simultaneous speaking.)
10 MEMBER PALMTAG: It's already 3:15, so 11 there's not a whole lot of time.
12 CHAIR KIRCHNER: So what time is it now?
13 (Simultaneous speaking.)
14 MR. BURKHART: So Chairman --
15 MEMBER ROBERTS: It's 3:15.
16 MR. BURKHART: -- before you break -- this 17 is Larry Burkhart from the ACRS staff -- we have had 18 the court reporter on, so yes, I recommended we leave 19 him go, and he can come back tomorrow morning at 8:30.
20 CHAIR KIRCHNER: Okay. Did you get that?
21 We'll let the court reporter go, and please be back 22 with us tomorrow morning at 8:30.
23 (Whereupon, the above-entitled matter went 24 off the record at 3:14 p.m.)
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
From Section 8.1.2:
NuScale stated, in SDAA Part 7, Exemptions, Section 4, that it requests an exemption from GDC 17 because the design contains no safety-related functions that rely on electric power.
NuScale stated that the design of the NuScale Power Plant provides passive safety systems and features to accomplish plant safety-related functions without reliance on electric power, and that the design, therefore, meets the underlying intent of GDC 17 without the need for the electric power systems specified in GDC 17. NuScale further stated that it requests an exemption from the GDC 18 requirements for inspection and testing of electric power systems and the electric power provisions of GDC 33, 34, 35, 38, 41, and 44 to address conforming changes and that the underlying intent of these requirements, to ensure sufficient electric power is available to accomplish the safety functions of the respective systems, is met without reliance on electric power.
In its request for an exemption, NuScale stated that it seeks an exemption because its design does not rely on safety-related SSCs. However, the GDCs at issue (GDCs 17, 18, 33, 34, 38, 41, and 44) pertain to SSCs that are important to safety, not safety-related SSCs.
Nonetheless, notwithstanding NuScales focus on safety-related SSCs, the NRC staff finds that the request need not address SSCs that are important to safety, in that there are no important to safety electrical systems in NuScales design (i.e. all electrical systems are non-safety related and are not important to safety) because they are not needed to provide reasonable assurance that the facility can be operated without undue risk to the health and safety of the public. NuScale and the NRC staff considered all power systems for the NuScale design, both onsite and offsite. NuScale designated all onsite and offsite electrical systems as non-safety related and determined that there are no other electrical systems that should be classified as important to safety. The NRC staff conducted an audit of the electrical systems in NuScales design. Based on its review and audit, the staff concurs that none of the electrical systems in NuScales design are important to safety.
For offsite power, FSAR Section 8.2 states that the passive design of the plant does not rely on AC power and does not require an offsite power system to perform safety-related or risk-significant functions. SER Section 8.2 contains the staffs evaluation of offsite power. SER Section 15.0.0.6.2 states that offsite power is not credited to mitigate Chapter 15 events.
Therefore, the staff finds that offsite power is not needed for accident mitigation or safe shutdown and thereby is nonsafety related.
For the onsite AC systems, FSAR Section 8.3 states that the onsite power systems include AC power systems, and the plant safety-related functions are achieved and maintained without reliance on onsite AC electric power. Further, the applicant stated that the onsite power systems do not perform any risk-significant functions. SER Section 8.3.1 contains the staffs evaluation of the onsite AC systems. SER Section 15.0.0.6.2 states that the normal AC power systems are not safety related and are not credited to mitigate Chapter 15 events. Therefore, the staff finds that the onsite AC systems are not needed for accident mitigation or safe shutdown and thereby are nonsafety related.
For the onsite DC systems, in SER Section 8.3.2, the staff used a risk-informed, graded approach to evaluate the quality aspects of the augmented DC power system (EDAS). In SER Section 8.3.2, the staff finds that the EDAS is nonsafety related with augmented quality and is acceptable. Chapter 19 discusses the availability controls related to the EDAS. The staff finds that the augmented quality and availability controls for the DC systems are acceptable. EDAS, with the augmented quality and availability controls, supports a finding that the SDA provides
reasonable assurance of adequate protection of public health and safety. The staff considers EDAS to be a non-safety-related or non-Class 1E SSC that performs an important to safety function, based on its role to protect specified acceptable fuel design limits, as discussed in SER Section 15.0.0.6.2, and there is reasonable assurance the system will function as designed. Therefore, using risk-informed decision-making and a graded approach, the staff finds the onsite DC systems, including the EDAS, are not safety related and have augmented provisions.
Therefore, the staff finds that the NuScale US460 design meets the underlying intent of GDC
- 17. NuScale further requested an exemption from the GDC 18 requirements for inspection and testing of electric power systems and the electric power provisions of GDC 33, 34, 35, 38, 41, and 44, to address conforming changes. It also noted that the underlying intent of these requirements, to ensure sufficient electric power is available to accomplish the safety functions of the respective systems, is met without reliance on electric power.
Based on the non-Class 1E classification of the onsite and offsite electric power systems, and on the analysis described in Section 8.1.3 to support the staffs findings regarding the criteria in 10 CFR 50.12, Specific exemptions, the staff finds that the application of these regulations to the NuScale SMR design would not serve the underlying purpose of the rule from which an exemption is being sought or would not be necessary to achieve the underlying purpose of the rule. Accordingly, the staff finds that the requested exemption from GDC 17, GDC 18, and the electric power provisions of GDC 33, 34, 35, 38, 41, and 44, if shown to be applicable and properly supported in a request for exemption by a COL applicant that references the SDA, would be justified and could be issued to the COL applicant for the reasons provided in NuScales SDAA, provided there are no changes to the design that are material to the bases for the exemption. Where there are changes to the design material to the bases for the exemption, the COL applicant that references the SDA would be required to provide an adequate basis for the exemption.
15.0.0.6.2 Availability of Power Normal alternating current (AC) power systems are not safety-related and not credited to mitigate Chapter 15 events. The normal AC power systems consist of the following:
EHVS (high-voltage (13.8-kilovolt (kV)) AC electrical system and switchyard)
EMVS (medium-voltage (4.16-kV) AC electrical distribution system)
ELVS (low-voltage (480-volt (V) and 120-V) AC electrical distribution system)
The onsite DC power systems are not safety-related and are stated to not be credited to mitigate Chapter 15 events in most cases, as described further below. The DC power systems consist of the following:
EDAS (augmented DC power system to supply essential loads) and EDNS (normal DC power system to supply nonessential loads).
The loss of normal AC power causes the MPS to initiate a reactor trip, actuate the DHRS, and close the containment isolation valves (CIVs). The loss of normal AC power also causes the loss of the EDAS chargers causing the EDAS to rely on backup batteries. If the augmented DC power system (EDAS) supply to the MPS or the ECCS and DHRS valves is lost, the ECCS valves open. Alternatively, at 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> after a loss of normal AC power to the EDAS battery chargers, the MPS actuates the ECCS valves causing them to open. If the 8-hour ECCS actuation is manually bypassed during the first 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, the MPS load sheds the ECCS valves at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, causing them to open. When the EDAS supply is lost or shed or ECCS is actuated, RCS coolant is immediately discharged into containment through the RVVs, and subsequently through the RRVs when the IAB valve operating pressure threshold is reached.
As no power systems in the design are designated as safety-related, several loss of power scenarios are evaluated to ensure that the FSAR Chapter 15 acceptance criteria are met. The applicant evaluated the following loss of power scenarios:
Loss of normal AC either at the time of the initiating event or at the time of the turbine trip (TT). After 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the ECCS valves move to their fail-safe open position.
Loss of normal DC power (EDNS) and normal AC. Power to the reactor trip breakers is provided via the EDNS, so this scenario is the same as a loss of normal AC with the addition of reactor trip at the time power is lost.
Loss of the augmented DC power system (EDAS), EDNS, and normal AC at the time of the initiating event. This scenario results in a reactor trip, actuation of DHRS, and closure of CIVs. The RVVs move to their fail-safe open position when power is lost, and the RRVs move to their fail-safe open position when RCS pressure drops below the IAB valve operating pressure threshold.
Also evaluated are the scenarios in which power, AC or DC, remains, if the consequences of the event are more limiting.
The FSAR does not evaluate scenarios where EDAS is lost subsequent to an initiating event (after time zero) during the event progression. For AOO events where the system energy
increases over either a short or extended period of time, a loss of EDAS can result in more severe consequences in terms of fuel and containment figures of merit than a loss of EDAS at the time of the initiating event. In these cases, staff determined that the EDAS system is relied on in the safety analysis to mitigate the consequences of the progression of those AOOs by maintaining the ECCS valves closed, thus enabling the ability to achieve safe shutdown of the module (i.e., the safety analysis assumes EDAS functions to maintain the ECCS valves in the closed position and an intact RCPB to allow the DHRS to remove decay heat). Examples of events where EDAS is assumed to remain functional during the entire design-basis period and perform these mitigating functions, includes, but is not limited to, decrease in feedwater temperature (FSAR Section 15.1.1), increase in feedwater flow (FSAR Section 15.1.2), increase in steam flow (FSAR Section 15.1.3), steam pipe failures (FSAR Section 15.1.5), and uncontrolled rod withdrawal at power (FSAR Section 15.4.2). Therefore, the staff concludes that the EDAS is needed to meet the Chapter 15 safety analysis acceptance criteria prescribed in Table 15.0-2 for ensuring the SAFDLs are met by assuring MCHFR is maintained above the CHF analysis limit. The staff notes that failure to meet the SAFDLs, as required by 10 CFR 50, Appenidx A, is not necessarily indicative of a failure to maintain the fuel fission product barrier nor considered a safety-related function. design-specific considerations.
EDAS is classified in the FSAR as a non-safety-related system. Based on the assumed functionality of the system in the safety analysis transients characterized above, the staff assessed whether EDAS meets the definition of safety-related in 10 CFR 50.2. An SSC that is relied on to remain functional during and following a design basis event to assure the capability to maintain a safe shutdown condition is defined as a safety-related SSC. SECY-94-084 defines a safe shutdown condition to be a condition where the reactor is shutdown, decay heat is being removed, and containment of radioactive material is provided. While the SAFDLs are not explicitly referenced in the 10 CFR 50.2 definition of safety-related SSCs, nor are a direct indication of fuel clad damage, they are typically used as the measure to demonstrate safe shutdown through sufficient decay heat removal and containment of radioactive materials during and following AOOs. Demonstration of the safe shutdown criterion ensures that fuel clad damage is unlikely to occur as a result of an AOO and the safety-related SSCs are sufficient to protect this fission product barrier. Accordingly, the staff reviewed and audited engineering documentation to confirm that the fuel fission product barrier would remain intact in the case of EDAS failure during an AOO. The applicant stated that a loss of EDAS is not expected to occur during the life of a module and the staff did not validate this assertion. Nonetheless, NuScale performed MCHFR and peak clad temperature (PCT) analysis of a spectrum of state-points for an ECCS blowdown, which is representative of a loss of EDAS, at a combination of powers, pressures, and temperatures (ML23304A367). This analysis demonstrates that a failure of EDAS at high power, pressure and temperature results (( )). The report concludes that the clad temperature excursion lasts for less than 10 seconds before returning to temperatures less than the initial value; and after this excursion, the transient behaves similarly to the longer-term transient; decreased core power and continuous liquid coverage ensure margin to CHF is maintained over the long-term; and no loss of coolable geometry is anticipated due to low PCT compared to the 2200°F limit. While the staff did not review or approve the post-CHF models utilized in the calculations performed by NuScale, and while other fuel failure mechanisms besides CHF were not explicitly evaluated, these results still provide useful insights into the applicability of EDAS to the safety-related criterion (i.e., whether EDAS is needed to ensure the fuel fission product barrier remains intact). In addition, the staff audited (ML24211A089) NuScale sensitivity calculations of peak containment pressure resulting from various non-LOCA events with subsequent loss of EDAS. The limiting results from these studies indicate a peak containment pressure of (( )) which is below containment design pressure.
Therefore, based on the above, the staff finds that EDAS does not meet the definition of safety-
related because it is not needed for ensuring a safe shutdown condition of the reactor.
Specifically, the staff finds that there is reasonable assurance that the reactor will shutdown, decay heat will be removed, and fuel and containment integrity will be maintained without reliance on EDAS.
As noted above, EDAS is relied on in the safety analysis for ensuring the SAFDLs are met by demonstrating MCHFR is maintained above the CHF analysis limit. Based on its role to protect the SAFDLS, as required by multiple GDCs including GDCs 10 and 34 which are evaluated within this Section of the SER, the staff considers EDAS to be a non-safety-related SSC that performs an important to safety function. SSCs that are relied on to satisfy the GDCs are subject to the quality assurance requirements of GDC 1, Quality standards and records.
GDC 1 specifies that programmatic quality standards for SSCs important to safety provide adequate assurance that these SSCs will satisfactorily perform their safety functions specified in the GDCs. Accordingly, EDAS conforms to consensus standards and augmented quality attributes to ensure the quality of the system is commensurate with the importance of its safety functions. Based on the design, augmented standards, and controls assigned to the EDAS, as documented in the FSAR, the staff finds that there is reasonable assurance the system will function as designed. See Chapter 8 and Chapter 16 of this SER for the staffs detailed review of the EDAS design, augmented quality attributes, and controls. The staff review of the EDAS modeling in the probabilistic risk assessment is in Section 19.1 of this SER.