ML23333A065
| ML23333A065 | |
| Person / Time | |
|---|---|
| Issue date: | 11/01/2023 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | |
| References | |
| NRC-2589 | |
| Download: ML23333A065 (1) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
710TH MEETING, ADVISORY COMMITTEE ON REACTOR SAFEGUARDS Docket Number:
N/A Location:
teleconference Date:
11-01-2023 Work Order No.:
NRC-2589 Pages 1-129 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1716 14th Street, N.W.
Washington, D.C. 20009 (202) 234-4433
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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
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UNITED STATES OF AMERICA 2
NUCLEAR REGULATORY COMMISSION 3
+ + + + +
4 710TH MEETING 5
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 6
(ACRS) 7
+ + + + +
8 OPEN SESSION 9
+ + + + +
10 WEDNESDAY 11 NOVEMBER 1, 2023 12
+ + + + +
13 The Advisory Committee met in hybrid 14 format, In-Person and via Video-Teleconference, at 15 8:30 a.m., Joy L. Rempe, Chairman, presiding.
16 17 COMMITTEE MEMBERS:
18 JOY L. REMPE, Chairman 19 WALTER L. KIRCHNER, Vice Chairman 20 DAVID A. PETTI, Member-at-Large 21 RONALD BALLINGER, Member*
22 CHARLES H. BROWN, JR., Member 23 VICKI M. BIER, Member 24 VESNA B. DIMITRIJEVIC, Member 25 GREGORY H. HALNON, Member NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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JOSE MARCH-LEUBA, Member 2
ROBERT P. MARTIN, Member 3
THOMAS E. ROBERTS, Member 4
MATTHEW W. SUNSERI, Member*
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ACRS CONSULTANT:
7 DENNIS BLEY 8
10 DESIGNATED FEDERAL OFFICIAL:
11 HOSSEIN NOURBAKHSH 12 13 ALSO PRESENT:
14 SUSAN COOPER, RES*
15 ALAN KURITZKY, RES 16 17
- present via video-teleconference 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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P R O C E E D I N G S 2
(8:30 a.m.)
3 CHAIR REMPE: So, good morning. This 4
meeting will now come to order. This is the first day 5
of the 710th Meeting of the Advisory Committee on 6
Reactor Safeguards.
7 I'm Joy Rempe, Chairman of the ACRS.
8 Other members in attendance are Ron Ballinger, Vicki 9
Bier, we expect Charles Brown to be joining us soon, 10 Vesna Dimitrijevic, Greg Halnon, Walt Kirchner, Jose 11 March-Leuba, Bob Martin, Dave Petti, Tom Roberts, and 12 Matthew Sunseri. I note we do have a quorum.
13 Today, the Committee is meeting in person 14 and virtually. The ACRS was established by the Atomic 15 Energy Act and is governed by the Federal Advisory 16 Committee Act. The ACRS section of U.S. NRC public 17 website provides information about the history of this 18 committee and documents such as our charter, bylaws, 19 Federal Register Notices for meetings, letter reports, 20 and transcripts of all full and subcommittee meetings, 21 including all slides presented at the meetings.
22 The Committee provides its advice on 23 safety matters to the Commission through its 24 publically available letter reports.
25 The Federal Register Notice announcing NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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this meeting was published on October 13, 2023.
2 This announcement provided a meeting 3
agenda as well as instructions for interested parties 4
to submit written comments or request opportunities to 5
address the Committee.
6 The Designated Federal Officer for today's 7
meeting is Mr. Hossein Nourbakhsh. I guess it's 8
actually Dr. Hossein Nourbakhsh, sorry.
9 A communications channel has been opened 10 to allow members of the public to monitor the open 11 portions of the meeting. The ACRS is inviting members 12 of the public to use the MS Teams link to view slides 13 and other discussion materials during these open 14 sessions.
15 The MS Teams link information was placed 16 in the Federal Register Notice and the agenda on the 17 ACRS public website. Periodically, the meeting will 18 be open to accept comments from participants listening 19 to our meeting. Written comments may be forwarded to 20 Dr. Nourbakhsh, today's Designated Federal Officer.
21 During today's meeting, the Committee will 22 consider the following topic, Level 3 Probabilistic 23 Risk Assessment. We'll also have our planning and 24 procedures session at 1:00 p.m. today.
25 Note that the public -- the NRC public NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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meeting website indicates there will be an ACRS 2
planning and procedures subcommittee meeting today at 3
noon.
4 And that meeting has been cancelled. That 5
is, I mentioned previously, as indicated in the 6
agenda, our full committee planning and procedures 7
meeting will occur at 1:00 p.m.
8 A transcript of the open portions of the 9
meeting is being kept and it's requested the speakers 10 identify themselves and speak with sufficient clarity 11 and volume so they can be readily heard.
12 Additionally, participants should mute themselves when 13 they're not speaking.
14 At this time, I have several items of 15 person interest. First, I'd like to acknowledge the 16 many contributions of former Commissioner Forrest J.
17 Remick, who passed on October 9, 2023. Appointed by 18 President George
- Bush, Dr.
Remick became a
19 Commissioner on December 1, 1989. And he served until 20 his term expired on June 30, 1994.
21 Dr. Remick has the distinction of being 22 the only person to serve the NRC in the multiple roles 23 of an Office Director in the Office of Policy 24 Evaluation, OPE, an Administrative Judge on the Atomic 25 Safety and Licensing Board, Vice Chairman and Chairman NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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of our ACRS, and an NRC Commissioner.
2 His service as the Director of OPE came 3
during the crucial period after the Three Mile Island 4
Unit 2 accident. And he provided important policy and 5
technical advice to the Commission.
6 And a different type of note, I am happy 7
to announce that Ms. Andreas Torres is joining the 8
ACRS as a Senior Program Analyst of the PMDA Branch.
9 Many of you remember Andreas because of 10 the assistance she provided when she was completing a 11 rotational assignment with ACRS this year. In 12 particular, her assistance with our international 13 regulatory advisory committee outreach activity was 14 valuable during this rotation.
15 What you may not know are her excellent 16 credentials, which include over a decade of service 17 with the U.S. NRC and a Master of Science in program 18 management from George Washington University. So, I 19 hope you'll join me in officially welcoming her back 20 to ACRS on a permanent basis.
21 And third, I'm happy to announce that Rob 22 Kirsch is joining ACRS as the Technical Assistant.
23 Rob has over 30 years of experience in the nuclear 24 field, including power and non-power reactors, fuel 25 cycle, radioactive materials, and decommissioning.
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Since 2014, he served as Commissioner Baran's 2
technical assistant for reactors.
3 Prior to that time, he served as 4
Commissioner Magwood's technical assistant for 5
reactors, Chairman Klein's technical assistant for 6
both materials and reactors, and 18 years, he served 7
in NRC's Region III Office.
8 So, I hope you'll join me in officially 9
welcoming Rob to joining us.
10 So, at this time, I'd like to ask other 11 members if they have any opening remarks?
12 Hearing none, I'd like to ask Vesna 13 Dimitrijevic to join -- to lead us in our first topic 14 for today's meeting. Vesna?
15 MEMBER DIMITRIJEVIC: Yes, good morning.
16 Can you hear me well?
17 CHAIR REMPE: We can.
18 MEMBER DIMITRIJEVIC: Okay, all right, 19 good morning. So, I would like to invite Alan, and I 20 think, Susan Cooper, Alan Kuritzky and Susan Cooper to 21 give us the presentation on the Level 3 PRA project 22 for Volumes 3 and 4.
23 Just to continue the discussion which we 24 had at our staff committee meeting and some questions 25 which we have brought up in this meeting on the, you NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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know, the low -- early fatality frequencies on the 2
human actions after the core melts.
3 So, Alan and Susan, or Susan, I don't know 4
who's going to begin. Please take it over.
5 MR. KURITZKY: Thank you very much, Dr.
6 Dimitrijevic. This is Alan Kuritzky from the Office 7
of Research. And I am the project program leader for 8
the Level 3 PRA project.
9 And as Dr. Dimitrijevic had mentioned from 10
-- that we had a meeting -- a subcommittee meeting 11 from October 19th. And this is kind of a somewhat of 12 a continuation of that meeting.
13 I'll try not to retread too much ground, 14 but a little bit of information with the last meeting, 15 I'll recap just to kind of bring everybody up to speed 16 if you weren't there on the 19th.
17 I'd also like to express my appreciation 18 to all the members here for their time. I know you're 19 very busy with lots of new reactors, advanced reactor 20 stuff, and we've got to shoe horn us other projects in 21 where you can. So, I do appreciate the commitment of 22 time and your attention for today's meeting.
23 I also want to acknowledge, that while I'm 24 speaking up here, I'm talking about work in Volumes 3 25 and 4 that was performed by many, many technical NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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experts in the agency as well as are at National Lab 2
and commercial contractors.
3 And while I can't name all of them since 4
there were so many of them, I do suggest people look 5
at the title pages and reports in the acknowledgment 6
sections and see all the wonderful experts that we 7
have either in house or contractors that have 8
contributed to this work.
9 And I appreciate all the effort they've 10 put into this project. So, they're really supported 11 me tremendously.
12 So, I also want to mention that I'll be 13 presenting most of the slides in today's presentation.
14 But as Dr. Dimitrijevic had mentioned, Susan Cooper 15 will be presenting some information on the Level 2 PRA 16 human reliability analysis. So, when we get to those 17 slides, I'll pass it off to her. She is not here in 18 person. She works remotely from Delaware. And so she 19 will tie in at the appropriate time.
20 With that, if we can go on to the next 21 slide, please? Just a quick outline of what we're 22 going to talk about today. And again, like I said, 23 this is on the Volumes 3 and 4 of the Level 3 PRA 24 project that we are kind of focusing on some 25 particular issues that were follow on to the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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subcommittee meeting back on October 19th.
2 I will, again, give a quick background of 3
the work and some very brief summary results, not the 4
detail level we did last time.
5 And then, focus primarily on some insights 6
and the parameter and modeling on certainty and how it 7
was treated in this project as well as the Level 2 8
HRA, the post-core damage HRA that Dr. Cooper will 9
talk about.
10 Next slide, please? Okay, so, just very 11 quickly, this project was kicked off back in 2011 with 12 the staff's requirements memorandum came out in 13 response to SECY-11-0089.
14 That directed the staff to do a complete 15 full scope Level 3 PRA project. And that means that, 16 not just are we looking at the two reactor cores on 17 site, we're also looking at spent fuel in both the 18 spent fuel pools and through dry cask storage.
19 We're also looking at all reactor modes of 20 operations, so not just full power, but also low power 21 and shutdown. And we're looking at all hazards to 22 prevent damage from fires type of events, high winds, 23 et cetera, everything except for intentional sabotage, 24 security related events are out of scope.
25 And we're also, by the way, looking at NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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things, not only individually in terms of each 2
radiological source on site, but also in an integrated 3
fashion.
4 We have a task to look at the impact and 5
the effect of having an accident in one radiological 6
source on site like a reactor or spent fuel pool and 7
the response to a potential accident at one of the 8
other sources.
9 The reference plant for the site, or the 10
-- excuse me, the reference site for the project is a 11 two-unit Westinghouse Pressurized Water Reactor with 12 large dry containments.
13 And many of the insights and things that 14 we derive and information we derive from this project 15 is directly applicable to that reference site, but 16 there are other things that might be more applicable 17 to similar type plants or other PWRs of the fleet as 18 a whole when it comes to maybe possibly some of the 19 consequences of information.
20 Next slide, please? Okay, so, just to 21 quickly to put everybody in context, we're going to 22 produce off of this work and it's going to be released 23 publically, and it's eight volumes which consist of 24 probably around 20 reports, maybe slightly over 20 25 reports.
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The different volumes are shown on this 2
graphic. Summary Volume 1 up in the upper left hand 3
corner, that's the one that's going to capture the 4
high level insights and results, perspectives, 5
comparisons to other studies, et cetera.
6 Once that gets published at the end of the 7
project, that's probably the volume that's going to 8
get the most eyeballs going forward. So, there's a 9
lot of work that will go into that volume.
10 Volume 2, the background volume includes 11 a description of the reference site and plant. It 12 also discusses at a high level the technical approach 13 to the various parts of the study as well as just some 14 general background information on the project.
15 Volume 3 through 8 involve all the 16 technical material.
17 Volume 3 which was released publically for 18 comment back in April of 2022 covers the reactor at 19 power, internal events, and floods. It includes 20 volumes from the Level 1 PRA for both internal events 21 and Level 1 PRA for internal floods.
22 And then it has volumes for the Level 2 23 and 3 where the internal events and floods are 24 combined because internal floods make such a small 25 contribution, it didn't make sense to do a Level 2 and NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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3 reports for them separately.
2 And then, lastly, includes an overview 3
volume. That was something that came about when we 4
first were presenting the preliminary public --
5 preliminary results to senior management back in 2018.
6 Because this study had a cutoff date of August 2012, 7
and it was many years later, and there were 8
significant changes in plant equipment and procedures 9
since that time, it was felt that we should probably 10 do something to reflect what that impact would be.
11 Particularly, we're talking about the 12 limitation of FLEX strategies and mitigation 13 strategies as well as they also implemented or 14 installed the new path to shutdown seal to the reactor 15 coolant pools.
16 Both of those were believed to have 17 significant impact on the risk profile. And so, we 18 thought that we wanted to at least capture what the 19 potential impact would be.
20 It would have been too much work to try 21 and redo the whole study from the beginning, 22 incorporating those elements. But we want to do a 23 section to be studied where we actually saw what the 24 impact was and wanted to focus to some extent on those 25 results as they were more representative of a current NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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plant operation design.
2 So, that is all summarized into the 3
overview report. And then, that Volume 3 set of 4
reports and Volume 2, as I said, were released for 5
public comment in April 2022.
6 We've since addressed their comments. And 7
those reports -- the Volume 3 reports are with 8
publications right now with the administration for 9
final Office of Administration for final publication.
10 Volume 2, we're holding back because it 11 references all the other reports. So, we can't really 12 tie up the references to that until the rest of the 13 reports are done, too. So, it will get actually 14 published when we publish Volume 1 at the end.
15 Volume 4, which is the other volume that's 16 a topic of today's meeting, is the background power 17 for internal fires and external hazards. We have 18 actually quantified the risk of internal fires from 19 seismic events and from high winds.
20 We have done a
qualitative semi-21 quantitative screening analysis for other hazards. And 22 for those similar to Volume 3, the Level 1 reports for 23 fire, seismic, and wind are in separate volumes.
24 We also, in Volume 4, see for the high 25 wind, we combined the other hazard tree analysis so NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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there's a Part 1 and Part 2 to that. And for Level 2 2
and 3, we have one combined volume for each of those 3
PRA levels that cover fire, seismic, and wind.
4 But unlike Volume 3 where the internal 5
flood isn't particularly called out separately, 6
Volumes 4D and 4E, there actually are separate 7
sections everywhere that we talk about the fire, we 8
talk about results for seismic, we talk about results 9
for wind all separately.
10 Next slide, please? And then the other 11 volumes that are listed here to still come out in 12 public comment, Volumes 5 through 8 and including 13 Volume 1, will all come out sometime in 2024, calendar 14 year 2024.
15 Those dates in there are in gray because 16 they demonstrate some level of uncertainty for any 17 project deliverable that's more than a few months out 18 because the availability of key personnel is very 19 uncertain.
20 Next slide, please? This is a table that 21 we showed back at the ACRS subcommittee meeting. It 22 just gives a high level summary of some of the key 23 risk metric results.
24 Again, the more detailed stuff is included 25 in background slides for this presentation since we NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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discussed it at fairly length -- at fair length in the 2
subcommittee meeting.
3 But just as a quick recap, we look at the 4
first rows of the table, you see core damage frequency 5
and large related release frequency which are two of 6
the surrogate risk measures that are used most heavily 7
by the NRC.
8 And we can see that the results, 9
particularly if you're looking at the last comp of the 10 2020 FLEX case, you can see that we're fairly -- that 11 we're below those risk metrics, but not with a huge 12 margin.
13 Whereas, if you look at the last two rows 14 which are the two risk metrics that are associated 15 with the Commission's safety goal policy statement, 16 the two quantitative health objects, that's individual 17 early fatality risk and individual latent cancer 18 fatality risk, you can see there by the green numbers 19 that there's quite substantial margin between the risk 20 that we estimated in the 2020 FLEX case and what the 21 QHO metric is.
22 MEMBER MARCH-LEUBA: Can I interrupt you 23 for just a --
24 MR. KURITZKY: Yes.
25 MEMBER MARCH-LEUBA: I wanted to ask you NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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at the end of my question whether you think that the 2
Level 3 expense of the formula Level 3 PRAs worth it?
3 Okay?
4 Let me tell you where I'm going. Level 3 5
is obviously the best testing that we have of those 6
green numbers, given the assumptions. But it gets 7
very expensive and possibly and long -- is this the 8
wrong microphone again?
9 (Off-microphone comments.)
10 MEMBER MARCH-LEUBA: Okay. So, where was 11 I going? Yes. What do you gain by spending all this 12 money on a Level 3 that you don't have with a Level 2?
13 Is it worth it?
14 If it was your money and you were 15 designing a new reactor and they tell you, now you 16 have to spend three years and $10 million doing your 17 Level 3 and you're stuck in Level 2.
18 MR. KURITZKY: Okay, thank you for that 19 question. I have to say that the actual answer to 20 that question is probably above my pay grade. But my 21 experience with this project, and one of the 22 objectives of the project, by the way, was to get an 23 idea of the cost and effort to do a Level 3 PRA.
24 Because I think when this project was 25 first envisioned, the Commission at the time, the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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Chairman at the time and one of the Commissioners, 2
were probably thinking, you know, is this something we 3
want to have the industry go ahead and do Level 3 PRAs 4
or either the existing fleet or for the new reactors.
5 And I think since the Commission has 6
turned over quite a bit since then, I don't think the 7
push is there anymore.
8 So, I would say -- and so, we're going to 9
have a section in the summary report that addresses 10 what we found out about that. It's going to be 11 somewhat limited in its utility because, one thing we 12 have discovered, we'll probably do it from the 13 beginning if we really thought about, is that doing a 14 Level 3 PRA is very case specific.
15 It's very much dependent on what's the 16 quality and completeness of the Level 1 and/or Level 17 2 studies that the site has. Okay, that's very 18 important.
19 What scope is involved? Are we looking 20 just at internal events and internal floods? Are we 21 looking at other hazards? Okay, that becomes very 22 important contributor to the scope.
23 Again, in our case, we're looking other 24 hazards, I mean, other radiological sources besides 25 just the reactors. That's another complication.
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Even for just a reactor, besides what 2
level of PRA has already been completed and the 3
quality of that PRA are the people that did that PRA, 4
are they still available?
5 The people that did the Level 1 and 2 PRAs 6
are available to support the Level 3 PRA, that is a 7
much more efficient approach than for bringing in new 8
people that, you know, those people have long since 9
disappeared or they were contractors that are now not 10 available. And now, you're kind of starting from the 11 beginning.
12 So, there is a tremendous amount of 13 variability based on several factors. In our case, in 14 particular, another major objective of the project was 15 to increase the level of PRA capabilities with the 16 staff. We are a risk-informed organization and we 17 want to become more risk-informed as we go forward.
18 And so, it's necessary that we have a 19 sufficient stable of experienced PRA analysts here to 20 be able to handle all the potential applications that 21 are risk-informed, et cetera, and the projects that 22 might be risk -- involve a quantification of risk.
23 So, we have made a focus of bringing up a 24 lot of junior and mid-level people and bringing them 25 up into more experienced ranks with the PRA, all NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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levels of the PRA. Because of that, we -- I think 2
we've succeeded very well in that and that we really 3
a lot of people and they have greatly increased their 4
PRA capabilities.
5 But because of that, the level of effort, 6
compared to just bringing in a high powered consulting 7
firm who can sit there and crunch out your Level 3 8
PRAs, that'd be totally different.
9 So, again --
10 MEMBER MARCH-LEUBA: I'm not questioning 11 why you're getting out of CDF, I mean, obviously, a 12 training -- I guess the training is worth it?
13 The question I'm posing myself, I'm a bank 14 and you're designing a new reactor. And you come with 15 your Level 2 PRA results with have a magenta ones in 16 the table, saying that satisfies the requirements.
17 Now, give me $10 million so I can do the green ones.
18 Try to convince me why it's worth it.
19 MR. KURITZKY: So, again, what I was 20 getting at, I wasn't trying to sell the advantage of 21 the project, but the point is that, the estimate, what 22 the cost is, we don't have -- our estimates of what 23 the cost would be would not be the same as the one 24 that the bank is going to find.
25 So, the reality is, whether it's worth it NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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or not, you know, depends on how much it costs, which 2
I'll try to give you an idea, we're not going to know 3
exactly how much it would cost someone else to do it.
4 But the benefits -- we've seen quite a few benefits 5
from doing the full Level 3.
6 We've learned a lot of interesting things.
7 There's some good insights in there. We've also 8
identified quite a few uncertainties that need to be 9
addressed, again, underlying the need to be risk-10 informed, not risk-based, of course. But whether it's 11 worth it or not, that trade off, you know, that's a 12 good question.
13 The comments that we've received from NEI 14 on both Volumes 3 and Volume 4 have been focused along 15 those lines. Saying, hey, we don't see the value in 16 going forward and doing the full, for the operating 17 fleet, you know, the existing -- the new reactors, 18 advanced reactors, that's a different policy decision.
19 But they believed it wasn't worth it.
20 I don't know, I think there was a lot of 21 value in doing one to kind of see what those insights 22 are. Are you going to get incrementally enough value 23 from doing other ones to make it worth the cost? I 24 can't give you a definitive answer on that. Again, it 25 depends on how much it costs.
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So, I believe there are benefits from it, 2
whether they justify the cost, I would not would do.
3 I certainly would not state, yes, definitely. That I 4
will not say.
5 But can say, that it's not even.
6 MEMBER MARCH-LEUBA: Right, the bank is 7
the one that decides the cost benefit?
8 MR. KURITZKY: Right.
9 MEMBER MARCH-LEUBA: And the regulator 10 comes in, well, I don't care what your cost is, you 11 have to do it.
12 MR. KURITZKY: Adequate protection.
13 MEMBER MARCH-LEUBA: I just wanted to put 14 the concept here on the record. Because whenever we 15 have people sitting in the back of the room which are 16 the Applicants, they all say, woo, this is too 17 expensive. And more than expensive is the time delay.
18 Because I am designing a new reactor, I don't have 19 time to do this.
20 MEMBER BIER: I have a couple of comments 21 and questions related to Jose's point.
22 First of all, I agree that $10 million 23 sounds like an awful lot. And I don't believe that's 24 what it would cost a licensee to do that's on their 25 own design.
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I mean, it's a long time since I've know 2
the cost of PRA first hand, but years ago, it was $2 3
million for the entire thing, including Level 3. So, 4
things may have changed a lot since then.
5 But the other question that I had for you, 6
Alan, is sort of for the NRC's purposes in doing this, 7
not whether industry should do it, but regarding the 8
NRC's projects, it seems like there is sort of 9
multiple objectives or multiple benefits of the 10 project.
11 One is, maybe plant insights, as you said, 12 although some of those may be very plant specific or 13 location specific.
14 Some of it is methodology like codifying 15 is this an acceptable methodology for industry to use 16 in doing this? Some of it is just internal like, you 17 need more people inside NRC who know how to do Level 18 3 and how to interpret it, et cetera.
19 What do you see as the biggest advantages 20 of having gone through this whole effort?
21 MR. KURITZKY: Okay, thank you, Dr. Bier.
22 So, I would say, again, it's kind of preliminary for 23 calling out, but from my personal opinion so far, I 24 think the biggest benefit has been the fact that the 25 NRC now has staff and even contractors that are much NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
24 1
more familiar and experienced with dealing with PRAs.
2 So, whatever issue should come up, whether 3
it be for a existing reactor or a new or advanced 4
reactor, we're in a much better position to deal with 5
those issues from a risk-informed perspective.
6 So that one, to me, is probably one of the 7
biggest benefits. I think we also discovered some new 8
insights that differ a little bit from NUREG-1150, 9
which was the last major NRC sponsored Level 3 PRA 10 project, which most of the work was in the late '80s 11 for that and was published in 1990.
12 But there is, I think, we have discovered 13 there's been a number of advances, a number of things.
14 But honestly, post-9/11, the vulnerability studies, 15 when we were doing those, there was some things that 16 we discovered because, by that time, we had more 17 advanced modeling, advanced tools for modeling through 18 acts of aggression which impacted the timing of core 19 damage, and which then -- which leads to the timing --
20 or not enough time available to take protective 21 action.
22 So, that, I think helped refocus our 23 attention on what are the biggest risk drivers? So, I 24 think that there were definitely things that we 25 learned from the study that will benefit the agency in NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
25 1
all kinds of ways in the risk-informed arena.
2 You know, as Dr. March-Leuba said, would 3
the bank bankroll another one? That, I don't know.
4 You know, again, the cost would be a lot less, as you 5
said, the cost would be way less than what we said.
6 But would it even -- still, would it be too expensive 7
to warrant the incremental benefit you'd get from 8
doing one? I can't weigh in on that.
9 But I do think that we did learn a number 10 of very interesting things. As you can see, even the 11 difference between what the risk term, in fact, have 12 been used in the NRC risk-informed program, CDF and 13 LERF, you know, core damage frequency and large early 14 release frequency as compared to what are the margins 15 with some of these risk metrics we took with those 16 associated with the quantitative health objectives is 17 a different story.
18 And what you -- how you want to use that, 19 what you want to make of that, that's other people and 20 other pay grades, but I mean, there is some very 21 interesting information that we've 22 MEMBER PETTI: Will that be captured? I 23 have this question about comparisons to 1150.
24 Are you planning to do that in the first 25 volume?
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MR. KURITZKY: We -- yes, in the Volume 1, 2
we're hoping to have a section where we look at NUREG-3 1150 and make some comparisons. I think some of the 4
-- we've already been, to some extent, looking into 5
that.
6 Dr. Keith Compton who is our lead for the 7
Level 3 PRA consequence analysis, Level 3 PRA 8
incremental will have the whole Level 3 piece has been 9
looking some of the information on NUREG-1150.
10 It's a little bit difficult, I think, my 11 initial understanding from Keith is that sometimes 12 it's a little difficult to make the comparisons, to 13 dig out exactly how things were done in NUREG-1150.
14 But we already are looking into those to 15 some extent and seeing where, you know, why are we 16 getting certain results different than they did? And 17 that is going to be a focus for the summary volume.
18 MEMBER PETTI: Good, okay.
19 MEMBER HALNON: Alan, I'd like to get one 20 question out of the way in my mind, maybe it's an easy 21 answer, maybe it's not.
22 I'm not a mathematician, I'm an operator.
23 So, I'm looking at this graph, I'm an operator, when 24 can zero be zero? I mean, I see a 10 to the minus 13, 25 that's getting into a world that operators don't deal NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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with.
2 When is zero zero?
3 MR. KURITZKY: So, I understand, you're 4
uncomfortable with the number 10 to the minus 12.
5 MEMBER HALNON: Anything greater than all 6
the zeros on the other side of the --
7 MR. KURITZKY: So, yes, good comment. So, 8
the idea here, in fact, the summary table for this 9
that's in the actual overview part doesn't even have 10 those numbers as dashes or zeros. I think it says, as 11 zero --
12 MEMBER HALNON: Okay, so when do the 13 numbers turn into dashes?
14 MR. KURITZKY: So, these -- and then 15 there's a footnote that says if somebody wants to know 16 the number, somebody in the real world may not care 17 whether 10 to the minus 8, 10 to the minus 12, 10 to 18 the minus 13, it's something they're not going to deal 19 with.
20 But it's important from a
risk 21 quantification because it's the nature of what the 22 metric is you're looking at.
23 And in this particular thing, it's 24 population weighted. So, therefore, you have a very 25 low number defined by the population.
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There's a number of reasons why that 2
number's so low and I'm going to get into that when we 3
go into our future slides. But --
4 MEMBER HALNON: If you want me to indulge 5
in extremely low numbers, I know nothing would -- that 6
aren't meaningful, that's fine.
7 What I just wanted to know is, is that 10 8
to the minus 13th and the next one 10 to the minus 8, 9
is that a significant difference?
10 In mathematics space, you're going to say 11 yes. In reality, is it?
12 MR. KURITZKY: Yes, I believe it is.
13 MEMBER HALNON: Okay. So, I'm going to 14 listen throughout this to hear that reality. I don't, 15 you know, if all I hear is mathematician stuff, then 16 I'm going to call foul on it because we need to keep 17 this in reality space.
18 MR. KURITZKY: Okay, very good.
19 MEMBER BIER: Well, another way of asking 20 that question is not just is, you know, is 10 to the 21 minus 13 actually zero?
22 But also just, is that number meaningful, 23 you know, do we know that it's 10 to the minus 13 as 24 opposed to 10 to the minus of 9 or 10 to minus 17?
25 (Off-microphone comments.)
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MEMBER BIER: You know, yes or a 2
significant figures there.
3 MEMBER MARCH-LEUBA: This is what the 4
question is a follow up, something I've been dying to 5
put on the record. The age of the earth is considered 6
to be 5 billion years.
7 In your numbers, it's 10 to the minus 10.
8 Over 10 to the minus 10 per year, we have meteorites 9
that hit the earth so hard that ejected the moon, that 10 the bottom of the Indian Ocean is now in the top of 11 the Himalayans.
12 So, 10 to the minus 10 is zero. Okay?
13 Because in this calculation, you didn't have 14 earthquakes that put the bottom of the Indian Ocean in 15 the Himalayans.
16 So, and we did have a -- I was -- I 17 wouldn't call it a retreat, but an international 18 meeting of ACRS like members.
19 And I appreciated much one of the Japanese 20 members, which I don't remember his name, says, we 21 need to start concentrating on these terminal events 22 because that's what really is going to be on these new 23 reactors. And according to your calculations, these 24 are for all reactors 10 to the minus 13.
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that's the age of the earth, I mean, anything lower 2
than that, obviously, your calculation is incorrect.
3 So, roughly, at 10 to the minus 7, in my 4
mind, is 10 to the minus 7, is where you need to start 5
considering external events and your calculation is 6
incomplete. And certainly, I was going to say 7
incorrect, but certainly incomplete.
8 CHAIR REMPE: So, to try and get us back 9
to Volumes 3 and 4, which is the topic of the meeting 10 and we do a letter, and the topic of the letter, I'd 11 like to talk a little bit more about benefits, not 12 only to the NRC, but also to industry who has helped 13 participate in this.
14 And I was wondering, your qualitative 15 screenings approaches and methods, that's something 16 that could be cited as a benefit even in these volumes 17 before you get to the summary that you've made some 18 progress in thinking about approaches that people 19 could adapt? Is that a true statement?
20 MR. KURITZKY: Yes, I think so. We did a 21 fairly extensive screening of the other hazards.
22 Anders Gilbertson who is now with NRR, but 23 was a researcher on this, and performed a very 24 detailed evaluation of hazards and did some very good 25 screenings, both qualitatively and some NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
31 1
quantitatively, depending on the particular hazard 2
using the criteria from the PRA -- the ANS, ASME Level 3
4 So, there's a lot of good insight there as 5
to why we do or don't consider certain events and 6
someone else can take a look at that, another 7
stakeholder can take a look at that and say, hey, all 8
right, well, this is the approach they used.
9 Is that -- well, if I follow that 10 approach, is that something that will get me a similar 11 result or not? You know, it depends on the specifics 12 of the site.
13 CHAIR REMPE: Okay.
14 MR. KURITZKY: But and again, I do want to 15 caution that because we do it one way doesn't 16 necessarily mean that it's an NRC approved approach.
17 Someone mentioned that before about 18 whether we had approaches that demonstrates other 19 approaches that other people use.
20 In most cases, they probably can. But 21 again, the NRC has actual reg guides and other 22 guidance that tells licensees what are approved 23 approaches.
And we are not undermining or 24 countermanding any of that.
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32 1
done or the approaches we've used and they believe 2
that they want to adjust the guidance, if, for some 3
reason, we did something different than what the 4
current guidance says, then that will be a separate 5
effort.
6 So, we are not -- no one should take what 7
we've done today, this is the NRC approved way to do 8
that. This is what we felt was the best way to do it 9
within our time and resources and level of information 10 we had available.
11 But it doesn't -- isn't, you know, a tacit 12 approval that this is an appropriate approach. So, in 13 most cases, it probably is, should be an appropriate 14 approach.
15 But in any case, yes, going back to your 16 comment, Dr. Rempe, yes, I think the screening 17 analysis we take is very useful for them to have 18 documented. And again, that's Volume 4C.
19 MEMBER DIMITRIJEVIC: Alan?
20 MR. KURITZKY: Yes, Dr. Dimitrijevic?
21 MEMBER DIMITRIJEVIC: So, here, first, I 22 just want to -- the level of -- come back to the 23 screening. I just want to say something from the 24 previous discussion and Jose's questions.
25 How I see this question is not is the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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Level 3 worth it and whoever, you know, that 2
investments, I want to stay totally out of the 3
investment part.
4 But my question for the industry would be, 5
is the Level 3 ready to be used? Because this is why 6
I think it's a little above your pay grade and pay 7
grade of every PRA analyst, can we, with a straight 8
face, present those numbers and say that we believe 9
we're done?
10 You know, even with -- because that's 11 definitely zero. So, if we present a number which 12 says that given the a lot of Volume 6, in the original 13 early fatality risk is in the, you know, you need a 14 thousand times years than the age of the universe, can 15 we say this with straight face? And I would not be 16 able to do that.
17 So, my thing is, is not how much it costs, 18 are the technical abilities of Level 3 ready to be 19 used? So, that's what -- how I would ask that 20 question.
21 The second thing is, that when it comes to 22 the screening of hazards, I know the study you said 23 that you actually did believe there was a couple 24 hazards, I think maybe three, that you didn't really 25 think there was enough knowledge.
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Are we able to screen those hazards that 2
you sort of left for the future? But they not 3
considered screened out?
4 Those hazards are, I think there was like 5
heavy load drop and intense precipitation and the 6
space events. So, does that mean sort of we screen 7
all the hazards except the three which require future 8
work?
9 MR. KURITZKY: So, let me see if I got 10 your question correct, Dr. Dimitrijevic.
11 Are you saying, did we screen everything 12 except those three? Was that the --
13 MEMBER DIMITRIJEVIC: Yes, is that how 14 your position, is everything screened except those 15 three which require further work?
16 MR. KURITZKY: Yes, my understanding is, 17 based on the criteria in the standard, except for the 18 several that we have quantified, everything else, the 19 plant has screened out except for the ones that we 20 mentioned.
21 Locally, intense precipitation is one 22 that, because of the particular, let's see, what is 23 it, topographical conditions of a referenced plant, 24 flooding from versus the ultimate cooling source would 25 be a threat to the plant.
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But potentially very high rainfall, you 2
know, locally heavy precipitation might be. But 3
because at the time, there was active research into 4
upgrading that methodology and the data, so we did not 5
pursue it.
6 So, I don't know what the impact on the 7
referenced plant would be. Space weather is clearly 8
something out of our realm of capability to analyze at 9
this junction in time, though it's certainly something 10 that I can envision being a concern.
11 I mean, I can envision it being a concern 12 for a lot more than just a nuclear power plant.
13 I don't remember what the third one was, 14 but I think, beyond those, we -- I think we've handled 15 or addressed everything that was in the standard.
16 CHAIR REMPE: I think it was heavy load 17 drop is what --
18 MR. KURITZKY: Oh heavy load drop, yes, 19 yes, thank you.
20 CHAIR REMPE: And I mean, that's happened.
21 MR. KURITZKY: Yes, heavy load --
22 CHAIR REMPE: -- and you couldn't analyze 23 that?
24 MR. KURITZKY: Yes, I don't remember what 25 the specific reason -- I don't recall what the -- what NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
36 1
it says in the report about heavy load drop --
2 MEMBER DIMITRIJEVIC: So, my point is, we 3
cannot say they're all screened. Three of them are 4
certainly, you know, hanging in there. We need more 5
knowledge about them. That's what my point is.
6 MR. KURITZKY: Yes, yes, definitely. Yes, 7
I agree wholeheartedly, yes.
8 CHAIR REMPE: Could you add some of your 9
thoughts about Vesna's question about could you -- is 10 it ready for prime time? Level 3, is it ready to be 11 presented with a straight face, is I believe what she 12 said?
13 MR. KURITZKY: So, again, this is my 14 personal opinion, because -- and I'm not authorized by 15 NRC to make statements broad based like that.
16 But again, my personal opinion, we're 17 dealing with something that has a lot of uncertainty.
18 If you have Level 1 -- we've been 19 regulating CDF and LERF for a lot of years. Right?
20 And there's a lot of uncertainty in the calculation or 21 estimation of CDF. Okay?
22 But yet, and so, as I mentioned before, we 23 don't have a risk -- we don't risk-based regulation, 24 we do risk-informed because we acknowledge there's 25 uncertainty and we have to balance that uncertainty or NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
37 1
compensate for it with other things like defense in 2
depth and safety
- margin, right, deterministic 3
approaches.
4 But we can use it to help inform our 5
decisions which is really what it's range is.
6 Now, as you go from Level 1 to Level 2, 7
you go from any A to B, you're adding more. And the 8
more you add, the more uncertainty you have. Right?
9 And particularly because, as we're going 10 from Level 1 to Level 2 to Level 3, we're actually 11 getting into, at least in my opinion, more uncertain 12 areas.
13 So, you're seeing an expansion of that 14 uncertainty.
15 The numbers are naturally getting all 16 right, because you're adding more things to go wrong.
17 So, even though the tone of uncertainty is getting 18 broader, the numbers are getting lower. So, maybe 19 you're still and can demonstrate below an acceptable 20 level.
21 But again, that's a case by case 22 situation.
23 As we're going to talk about in the later 24 slides, the parameter of uncertainty, which I only --
25 I don't give a lot of credence to it, personally, but NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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you have -- we have failure type distributions and 2
even at Level 1, 2, and 3.
3 In Level 3, we only do parameters for a 4
very small piece, but still, they're failing type.
5 But what I believe is the bigger 6
uncertainty that really throws the question, is this 7
ready for prime time? Is the modeling ready?
8 Because there's many things that we either 9
don't include in the models, that we don't have 10 sufficient information to do a good job of modeling on 11 the simplifications, or we have to make, you know, key 12 assumptions.
13 And some of those, if we do sensitivity 14 analyses on them, we see, you know, just engineering 15 judgment or sensitivity -- quantified sensitivity 16 analysis, you see how these things can make a big 17 difference.
18 And that doesn't mean whether or not 19 something goes from 16 minus 13 to 10 to 20 minus 12 20 because of ground runs. It's 16 minus 13, maybe 260 21 minus 7.
22 There's going to be one example that I'm 23 going to get to later on in this presentation that has 24 some very substantial impact on that. And those are 25 early fatality risk value.
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So, the more uncertainty you have, 2
obviously, the less useful the results. Right? Or 3
you have to use them with more care. You have to use 4
them with more care.
5 I still think that it can be useful, but 6
you have to take it into context. I mean, you can't 7
make a decision based solely on it. You have to use 8
that as another piece of information to help make an 9
argument that's going to involve multiple pieces of 10 information.
11 MEMBER BIER: So, that brings up another 12 good point about the modeling uncertainty.
13 I mean, currently, when we do uncertainty 14 analysis, we do only a parametric uncertainty. And 15 then, we might say, okay, there's a factor of three 16 uncertainty around that 6 minus 13 or whatever.
17 But it may be, in fact, much greater once 18 we have model uncertainty in there and we don't really 19 have very good ways of quantifying that.
20 So, in cases where the modeling 21 uncertainty really swamps the parameter uncertainty, 22 I think, you know, again, doesn't mean it might not be 23 worth doing, but it seems like we need, you know, a 24 new level of caveat on that kind of situation rather 25 than just, yes, this is accurate to, you know, a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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factor of three or a factor of ten.
2 MR. KURITZKY: And Dr. Bier, thank you for 3
that comment because that's really something I had 4
mentioned before. I'm not a huge of parameters for 5
that very reason.
6 MEMBER BIER: Yes.
7 MR. KURITZKY: Because I think the 8
modeling uncertainties greatly outweigh the 9
parameters.
10 But I do want to take exception, we do 11 have ways of treating model uncertainty --
12 MEMBER BIER: Okay.
13 MR. KURITZKY: -- through sensitivity 14 analysis.
15 It's not complete and, as I was going to 16 mention, I'll mention it now, when we do our 17 sensitivity analysis, we're doing them in a, not a 18 great term, but it's called stove pipe situation.
19 We're looking at them individually.
20 MEMBER BIER: Yes.
21 MR. KURITZKY: So, we're not looking at, 22 you know, here's a different model for this aspect of 23 the PRA as much as we think that might be with 24 sensitivity analysis, here's some other ones.
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and that one that way, and this one this way. We 2
don't -- we can't take, you know, if ones -- the 3
combinations are endless.
4 So, even one at a time, we only have a 5
certain number we can look at.
6 But yes, I believe all those modelings are 7
what's really the big thing that you have to consider.
8 MEMBER REMPE: Okay, colleagues, we have 9
-- there's -- Walt has a question and we'll let him go 10 first.
11 And Dennis and Susan both have their hands 12 up.
13 And I didn't see how long they've been up, 14 but then, we need to move on because we've spent a 15 long time on the first six slides.
16 Go ahead, Walt.
17 VICE CHAIR KIRCHNER: Okay, quickly, Alan, 18 while it's up, could you, later in your presentation, 19 comment on the FLEX versus the 2012 results and 20 whatever insights you would extract from those deltas 21 there?
22 And I'm looking at the, you know, the last 23 two columns and the delta between 2012 and FLEX.
24 MR. KURITZKY: Certainly.
25 So --
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VICE CHAIR KIRCHNER: Any insights that 2
you gained from that.
3 You can come back to it, if it's part of 4
your talk.
5 MR. KURITZKY: Okay.
6 So, thank you, Dr. Kirchner.
7 That actually is part of that discussion 8
that we're not going to have -- we were not going to 9
have because that was something that we discussed at 10 the subcommittee meeting and I was -- got guidance to 11 focus on other things.
12 But going back to that slide, real 13 quickly, because I can do that for you just real 14 quickly as you look at the numbers.
15 So, if you look at the core damage 16 frequency and the large release frequency and 17 individual latent cancer fatality risk, all those go 18 down around 40 percent from the 2012 case to the FLEX 19 case because they're all based on the same thing, and 20 that's they're driven by station blackout related 21 sequences.
22 Remember, FLEX as it's implemented, is to 23 focus on extended loss of AC power sequences.
24 And so, that's the kind of stuff that it's 25 really good at.
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The referenced plant, its risk profile, 2
its CDF profile is a highly -- it's a large 3
contribution from station blackout sequences.
4 So, FLEX has a fairly significant drop.
5 If you have a plant that its risk profile 6
is core damage profile, it's not heavily contributed 7
to by station blackout sequences, you will not see 8
nearly the impact in FLEX that you have here.
9 So, and the reason the other two large 10 early release frequency, individual early fatality 11 risk don't see as much of an impact is because there 12 were a lot of climbs, but other sequences like 13 interfaces and LOCAs or things that FLEX would not be 14 that effective at.
15 VICE CHAIR KIRCHNER: Yes, I just wanted 16 that on the record.
17 Thank you.
18 MR. KURITZKY: Okay.
19 CHAIR REMPE: Dennis?
20 MR. BLEY: Yes, thank you.
21 We had a lot of discussion about the low 22 numbers, 10 to the minus 13 kind of things.
23 But I think it's important to get some 24 language right here.
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in the plant, the event core damage, the event early 2
-- large early release, and large release.
3 The next two are labeled risk. And Alan, 4
I don't have the report open in front of me, so I'm 5
not sure exactly what these are.
6 They could be the frequency of one or more 7
deaths.
8 They could be the mean value of one or 9
more deaths.
10 But they're not frequencies like the first 11 three.
12 And we had a nice discussion in the 13 subcommittee about why numbers get very small when you 14 go from the event, say, large early release frequency, 15 that can lead to possibly early fatalities.
16 That then is getting distributed. We're 17 not talking about events after this, we're talking 18 about cases where are there people in the path? Are 19 there people in the path close enough to be exposed?
20 What are the weather scenarios? How's the 21 wind blowing?
22 So, it's distributing the results of the 23 release calculation to places where there are people 24 or are not people over a time period during which 25 things change from it being possible to have early NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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fatalities to not being possible during that time 2
frame.
3 So, we just throw these exponential 4
numbers up without -- we've been doing it so long, we 5
forget to tell people what they are.
6 And I don't have the book out in front of 7
me. So, on the two -- last two, I'm not exactly sure 8
what these numbers are.
9 And if you can tell me real fast, Alan, 10 that'd be nice. If you can't, we ought to go back and 11 take a look because people present them in different 12 ways and they can be anything from expected values to 13 frequencies of particular accumulations of events.
14 That's all.
15 MR. KURITZKY: Okay, thank you.
16 I'll try -- okay, just thank you, Dr.
17 Bley.
18 Yes, I think the next slide actually goes 19 directly to that item.
20 CHAIR REMPE: Okay.
21 Then, let's let Susan have her turn.
22 Susan?
23 MS. COOPER: Thanks, Joy.
24 Yes, I just wanted to throw out a little 25 bit more on the topic that we've been discussing and NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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that Dennis just contributed to significantly.
2 I just wanted to take a real quick look at 3
the summary volume for NUREG-1150.
4 And the example results in that -- in the 5
introductory section showed something on the order of 6
1E to the minus 6 for results for early fatality risk 7
and latent cancer risk.
8 So, if nothing else, when we're doing our 9
comparisons with that earlier NRC study, we can see 10 that there is a difference in our results, probably a 11 combination of not only differences in how well we can 12 calculate things, the models and tools we have, but 13 perhaps also operational differences.
14 But in any case, that is, you know, the 15 numbers have some meaning, I think, in that case also.
16 CHAIR REMPE: Okay.
17 I think we're ready to go to slide 7, Mr.
18 Kuritzky.
19 MR. KURITZKY: Hey, here we go, made it.
20 Time for a break? No, I'm sorry.
21 So, just a few insights. I wanted to 22 discuss, since we did most of the results discussions 23 back in the subcommittee, I wanted to focus this more 24 on the preliminary insights.
25 Just some, again, this is something that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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will have to be done when we delve into Volume 1 later 2
and look across the whole study and including the 3
study -- the parts of the study that deal with other 4
things like low power shutdown, spent fuel pool, et 5
cetera, things that haven't already been run to ground 6
in previous studies throughout the technical 7
community.
8 So, one of the things I do want to mention 9
from the work so far on the reactor at power PRAs is 10 this topic we've just been discussing.
11 So, what we see from that previous slide 12 and what we've talked about in October 19th is that, 13 for this plant, in this location, there's a 14 substantial margin to the two quantitative health 15 objectives associated with the condition or safety 16 goal.
17 That's the individual early fatality risk, 18 the individual latent cancer fatality risk.
19 However, those margins are much less when 20 you look at the certainty in these metrics of CDF and 21 LOCA.
22 Now, why is the early fatality risk so 23 low, and as Susan had mentioned, that's something that 24 wasn't nearly as low in NUREG-1150. That's something 25 I think that Keith is looking into.
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And I don't want to bring Keith on to 2
sidetrack us right now, but that's something we are 3
going to try and address in the final summary NUREG.
4 But the reason we're getting numbers that 5
are so low is exactly as Dennis was -- sorry, Dr. Bley 6
was just mentioning.
7 And that is that the type of events that 8
we give with these large fast releases that are going 9
to lead to potential for early fatalities are very 10 low, at least in the study, probably in many studies.
11 And that's because they're really things 12 like interfacing system LOCAs or they're other 13 contained bypass like steam generator tube ruptures 14 that are going to get the radiological release out in 15 a hurry and not be mitigated.
16 And so, that is something or those are 17 things that have very low frequencies.
18 So, right off the bat, you're starting 19 with a very low frequency number.
20 Then, and that's what Dr. Bley was 21 mentioning. Frequencies of events will also be low.
22 But
- then, when we get to the 23 quantification of individual early fatality risk, 24 there's not a number of other factors that we're going 25 to have to consider.
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And for instance, they're listed here in 2
some of the bullets right here, they're the main 3
reasons.
4 One is, you have to have weather 5
conditions that are conducive to having a large 6
exposure event.
7 And that means, relatively stable, low 8
wind speed conditions. So, radiological cloud 9
meanders over people.
10 Second, or second or third, third bullet, 11 you have a very sparse enclosed population at the 12 reference site.
13 And this is, of course, going to differ 14 for other sites.
15 But nonetheless, that release has to be 16 targeted at where the people are.
17 So, if you have -- I think we have 360 18 receptors, okay, so, you know, you have to -- there's 19 only, I think, I can't remember, but in any case, the 20 wind has to be blowing at that sector, and I think 21 only or two have people in it. So, it would have to 22 blowing in that direction.
23 Right there, you're knocking another 24 quarter magnitude or two on top of the frequency 25 results.
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On top of that, the people are going to be 2
evacuated. There is almost all these situations, 3
there is sufficient time to have effective evacuation.
4 So, really, what you have to do is have 5
some people that are not evacuating or get caught in 6
the -- there's very low likelihood of the delayed or 7
slow evacuation that will lead to a high likelihood of 8
that.
9 So, when you multiply the probability of 10 not having successful evacuation or take only the 11 fraction of the cohorts that are not successfully 12 evacuating, they're knocking down another order of 13 magnitude.
14 So, what happens is, that individual early 15 fatality risk number that we see, that 10 to minus 13 16 number, is an amalgam. It's, you know, the 17 multiplication of multiple factors that keep knocking 18 it down.
19 You have a very low frequency and you have 20 a lot of conditional probabilities for various 21 occurrences or just really physical conditions that 22 now start to knock it down by orders of magnitude.
23 In the final summary NUREG, we're hoping 24 to give some kind of a little, you know, it's hard to 25 draw exact numbers for every different case, every NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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different scenario, but to give some ballpark idea.
2 Because this one, the 10 to the minus 2, 3
the 10 to the minus, et cetera, to show how we go from 4
the 10 to the minus, let's say, 6 down to a 10 to the 5
minus 12 or 10 to the minus 13 number.
6 But that's the reason why we come up with 7
such a low number. And it's really what Dr. Bley was 8
saying.
9 You have a low frequency event, but then, 10 you have all these other factors that drive that 11 number further down.
12 MEMBER ROBERTS: Okay, so, that's the 13 individuals early fatality risk.
14 Now, the latent cancer fatality risk on 15 the -- just to clarify a little bit more, you said 16 that first number is the LERF, right? The very low 17 frequency of bypass events?
18 So, that's --
19 MR. KURITZKY: Yes.
20 MEMBER ROBERTS: So, that's just kind of 21 a starting point?
22 MR. KURITZKY: Yes, essentially, like --
23 MEMBER ROBERTS: So, there's still another 24 six plus orders of magnitude for those next three 25 bullets?
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MR. KURITZKY: Yes.
2 MEMBER ROBERTS: You're saying you're 3
going to put together a chart in the final report. I 4
was just trying to get some perspective, are one or 5
more of those more dominant than the others?
6 Because it's kind of hard to see six or 7
seven orders of magnitude between those three bullets.
8 MR. KURITZKY: Again, we're going to try 9
and do that.
10 And I was just mentioning, it's not that 11 easy because they're not just like solid, you know, 12 single numbers that we can just say, this was 10 to 13 the minus -- in all cases, this is 10 to the minus 2.
14 It's going to vary case by case.
15 But we want to get like a typical value 16 like the likelihood of adverse meteorological 17 conditions are generally like around this order of 18 magnitude.
19 And the very sparse, close population has 20 this order of magnitude impact.
21 And the likelihood of delayed evacuation 22 at this order of magnitude and that.
23 To get kind of an idea.
24 But yes, that's the idea, that they will 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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MEMBER DIMITRIJEVIC: Alan? Alan?
2 MR. KURITZKY: Yes?
3 MEMBER DIMITRIJEVIC: Let me just ask you, 4
I mean, you know, the definition of the -- we also 5
struggle with the PRA or definition of large release 6
and large early release.
7 Does a large early release implies large 8
release before, is my question, is initiated?
9 MR. KURITZKY: Yes, it does imply large 10 release before a successful evacuation.
11 Let's say, there was the potential -- in 12 our definition for this site, so there is the 13 expectation of a potential for early fatalities.
14 And that's why that number -- that first 15 bullet has a low number because, just having -- the 16 types of sequences that will have a low likelihood of 17 occurring, there's a very low frequency of things that 18 could potentially not have an evacuation.
19 But even those, it's the potential, it's 20 the expectations or potential for early fatalities.
21 So, you still might be able to evacuate, 22 but you still may get enough exposure that you have 23 early fatalities.
24 So, again, LERF is a surrogate risk metric 25 that has served us well for a long time and will NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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probably continue to serve us well, I'm sure, for the 2
future.
3 But it's not the same thing as what you go 4
to in individual early fatality risk.
5 So, like I said, we're going to try and 6
see if we can make some kind of mathematical 7
connection to show how you get from one to the other.
8 But it's really not -- we're not comparing exactly the 9
same thing.
10 So, unfortunately, I don't have a better 11 answer for you. But LERF is not exactly the same --
12 in the same alignment when you just go -- when you 13 calculate individual early fatality risk.
14 LERF isn't like, here's the first step and 15 now, you can add these other steps. Okay?
16 It's going to be, these types of events 17 are listed in that first bullet, and then, these other 18 types of things.
19 Whether those are specific to LERF, many 20 of them will be LERF, but LERF may include other 21 things that are not part of that.
22 I don't know if the reverse is true, 23 probably -- I don't know. We do have things that we 24 can sort of do LERF that might not have --
25 Yes, we do have things that we consider to NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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be LERF that were not -- that we ultimately show were 2
not contributors to individual early fatality risk.
3 Because the frequency was so low or the 4
magnitude of the release just wasn't high enough to 5
have a reasonable expectation of early fatalities.
6 So, again, they're not the same exact 7
thing. So, it's a little difficult to just make that 8
into a mathematical expression.
9 But at least we can have some idea of what 10 these other factors are so that, in just people's 11 minds, we can say, hey, whether it's exactly LERF or 12 not, the frequency of such events is either 10 to the 13 minus 6 range, how we get into the 10 to the minus 13?
14 Well, here's some of the factors of getting us to a 15 much lower number.
16 That's really what we're trying to get to.
17 Okay, so, moving on to the second bullet, 18 so latent cancer fatality risk, and as we've talked on 19 the previous slide, it also had a fairly decent margin 20 to the QHL, but not nearly as much as large early 21 release rates.
22 But the reason it does have a significant 23 margin is, again, for some of the very same factors 24 that we saw -- that I just discussed for early 25 fatality risk.
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Because those same factors are why you 2
have very low doses in the early phase.
3 And effective protective measures also 4
mean that we have fairly low doses at the latent or 5
the early -- excuse me, in the late phase.
6 So, combined together, there's a fairly 7
low likelihood of having latent cancer fatalities 8
also, just not nearly as low as the early fatality 9
risk.
10 Next slide, please?
11 Okay, so, just to dig -- we talked a 12 little bit about this, but to dig a little deeper, 13 peel another layer of the onion off on the early 14 fatality risk.
15 First of all, let me just mention that, in 16 our Level 3 PRA, again, I mean the consequence 17 analysis, risk analysis reports, part of the Level 3 18 individual piece, we report risk -- a number of risk 19 factors. I think there's over a dozen risk factors 20 that we reported results for.
21 And they're basically broken into two 22 different categories, those that are related to early 23 health effects and those that are not related to early 24 health effects.
25 And the reason we break them into those NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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two types or it's because contributors are pretty 2
similar for those two categories. Like almost 3
everything is in each of those categories is 4
relatively similar.
5 For the early health effects, the primary 6
drivers, I think we kind of mentioned this a few 7
minutes ago, are interfacing system LOCAs if they 8
bypass containment and we have a very large release.
9 And that's primarily the main 10 contributor primarily to internal events because 11 that's where we have the model.
12 There's a little -- there's a modest 13 contribution to seismic because the largest seismic or 14 our model seismic is a very large seismic event that 15 has -- it doesn't bring the ocean on top of Kathmandu 16 or whatever it was, but it does lead to a very 17 destructive earthquake.
18 And Because there was wide scale damage at 19 the plant, we assigned that to the release category 20 that has the highest source term magnitude, which is 21 the interfacing system LOCA.
22 So, that's why you get some contribution 23 of seismic from the interfacing system LOCAs.
24 The other two that really contribute to 25 early health effects are steam generator tube NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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ruptures, both before core damage and after core 2
damage.
3 The pre-core damage ones, pressure induced 4
steam generator tube ruptures primarily come following 5
an ATWS event, anticipated transient without SCRAM 6
where there is at least one secondary side valve open, 7
either the operators have intentionally opened or it's 8
stuck open, but that's your relief -- release path.
9 And those particularly are -- contribute 10 to internal fires and seismic events. Those are the 11 ones that have a higher ATWS contribution. So, they 12 have a bigger contribution from these pressure induced 13 steam generator tube ruptures.
14 The other big contributor to the early 15 health effects is post-core damage, thermally induced 16 steam generator tube ruptures. And that's after core 17 damage when you have high gases in the steam generator 18 tube, then you end up having a steam generator tube 19 rupture there and then, again, you have potentially 20 bypassed release.
21 And those affect actually of the hazards 22 having a contribution from those, though particularly 23 high wind and internal fires are a particularly large 24 contribution for releasing thermal inducted steam 25 generator tube ruptures.
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Next slide, please?
2 Oh, a question?
3 MEMBER BIER: If I can just make a brief 4
comment, kind of echoing some of what Jose has been 5
talking about?
6 If I was asked before this presentation, 7
what do I think the biggest contribution to early 8
fatality risk is? I would have said interfacing 9
systems LOCA.
10 And so, is there a lot of nuance that we 11 gain from the analysis about some of these other 12 contributors or, you know, could we have had this 13 conclusion without doing the Level 3?
14 MR. KURITZKY: So, that's a good question, 15 the -- a fair question.
16 And yes, would also assume ISLOCA. I 17 mean, even though we must -- I'm a Level 1 PRA guy, so 18 my level is Level 1 PRA.
19 I thought Level 2 and Level 3 was just 20 hoodoo voodoo stuff, I don't know.
21 Even success rate, I always thought --
22 this is one of the eye openers -- I always thought the 23 success criteria you get in a Level 1 PRA or the 24 thermal hydraulics guys were on the MELCOR or whatever 25 at, and here's, you know, two out of three pumps, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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whatever, here's this affect.
2 That was -- there was -- that's what the 3
answer is. Now, we'll go play our numbers game on the 4
rest of it, but that's the answer.
5 Well, I started -- I had to review that 6
section of the report when I was, years ago starting 7
this project. And I'm like, whoa, whoa, you know, we 8
just took a few cases here, a few cases there.
9 You know, at this end of the LOCA section, 10 you know, that may not hold a totally different thing 11 at that end.
12 And you know, so, there was uncertainty, 13 right, throughout all of it. It was a big eye opener 14 is sort of the rest of it.
15 But nonetheless, ISLOCA was something we 16 all, of course, knew by definition, it's the 17 interfacing LOCA that goes -- it's potentially a thing 18 that goes up containment -- it bypasses containment.
19 So, we know that's important.
20 But we learned certain things, first is, 21 ISLOCA is, as I was mention later, is something that 22 the frequency of ISLOCA, we had taken some data that 23 Idaho National Lab had in their operational database 24 to come up with quantification -- the drivers of 25 ISLOCAs are primarily large leakage through closed, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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shut valves and/or motor operated valves in the RHR 2
system, primarily.
3 And we portray some very minor amounts of 4
data to come up with frequencies of what's the 5
likelihood of that happening? And the numbers were 6
not -- didn't seem realistic.
7 So, we actually decided to go with an 8
expert solicitation to come up with a better idea of 9
the frequency of those things happening as well as the 10 distributions to use for the analysis.
11 And so, we learned quite a bit about the 12 mechanisms of ISLOCAs. So, we always learn other 13 things about -- we also learn, yes, we knew ISLOCAs 14 that, in Level 1 space, we don't know the temperature 15 of new steam rupture options of those in the core 16 damage if steam ruptures are a major contributor. We 17 don't look at that on Level 1 space.
18 But there are other things that do show up 19 to be important.
20 ISLOCAs, specifically for internal events, 21 Because that's where we found we didn't have any cases 22 in high winds or fires where we thought ISLOCAs were 23 going to occur.
24 So, there are other things that contribute 25 to risk.
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So, when we look now at non-external 2
events, but all hazards, there were different things 3
that now show up to be important contributors.
4 So, yes, we can surmise many of these 5
things, A, priority, this either confirms it or gives 6
us more information.
7 In some cases, it might countermand an 8
understanding we had before that's less likely to 9
occur, especially after we've had this for many years.
10 But yes, so there's incremental increase 11 in information and knowledge. Whether the banker 12 wants to pay for this or feels it's worth paying for 13 it, that is an open question.
14 MEMBER BIER: But there is an increase?
15 MR. KURITZKY: Right.
16 Okay, I think we've finished this.
17 Next slide, please?
18 And Dr. Rempe, I'll let you let me know 19 when we're running out of time.
20 CHAIR REMPE: Okay.
21 MR. KURITZKY: What's that?
22 Okay, okay, so, for those risk factors 23 other than the early health factors, which are things 24 like latent health effects, affected population, land 25 contamination, et cetera, so those, again, all them, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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generally have the same set of drivers also.
2 The two biggest things that drive them are 3
late containment failures due to over pressure that 4
occur tens of hours after vessel breech and the 5
releases are not scrubbed by either an overlying pool 6
of water or by containment sprays.
7 So, you get a fairly large release.
8 Also, there are events that occur several 9
hours after vessel breech and due to combustion 10 events, whether through deflagration or detonations, 11 and that caused the rupture of the containment.
12 And again, those also are unscrubbed. No 13 overlying pool of water, no containment spray.
14 So, those two really drive the other than 15 early health effects measures.
16 We have another one more specifically for 17 seismic events is contained isolation failure.
18 And that's Because, some of this --
19 particularly the larger sized events, they can 20 structurally damage the containment isolation system.
21 So, you can get, particularly there, you can get a 22 release that is not mitigated.
23 And the last one, again, the thermally 24 induced, that's the post-core damage steam generator 25 two ruptures.
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This one contributes to across the board 2
for all these hazards but, primarily, from land 3
contamination.
4 Actually, for the other risk measures, 5
it's just a few percent contributor, but it's over 10 6
percent for land contaminations.
7 Okay, next slide, please?
8 And just a few more insights before we 9
move on to Level 2 HRA.
10 So, this is something we just discussed 11 quite a bit at the subcommittee meeting.
12 One of the things that we did for this 13 study is, we wanted to have a good understanding of 14 severe accident progression in the longer term as well 15 as impact on radiological release.
16 So, we carried out the severe accident 17 progression analysis until a stable condition was 18 reached with a seven-day backstop.
19 And oftentimes, that seven-day backstop is 20 what ended the analysis.
21 So, in doing so, we identified one of the 22 major contributors to these non-early health effects 23 risk metrics was the -- what I just talked about, 24 which was containment over pressure, tens of hours 25 after vessel breech, which eventually grows to release NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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large enough that it becomes a major contributor, what 2
we call large, and then, becomes a major contributor 3
to increased risk fatality as well as the other risk 4
metrics.
5 And because of that analysis, we know two 6
things that are very important to take away from that.
7 That if you can do something to prevent 8
that over pressure, then two or three days after the 9
event initiation, you can prevent that large release.
10 So, if you could do something like 11 containment venting or restore containment heat 12 removal, you can prevent that release -- that large 13 release from every occurring.
14 On the flip side, if someone were to 15 perform a Level 2 PRA and submit its results, and they 16 only modeled severe accident progression for 48 or 72 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> after the event, essentially, then there's a 18 good chance they're going to really under rate the 19 expected risk.
20 The other one that has a
large 21 contribution to these latent -- these non-early health 22 effects is the one I mentioned in the last slide, too, 23 which is the several hours after vessel breech, you 24 get a -- either a deflagration or a detonation in the 25 combustive gas.
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And that one is, particularly the way we 2
treat combustion in our study, we can treat combustion 3
as a casket process, probabilistic process.
4 Many other Level 2 PRAs treat combustion 5
deterministically. In other words, they set a level 6
that, once the concentration of a combustible gas in 7
containment gets to this level, you are definitely 8
going to ignite it.
9 You have you deflagration, whatever, that 10 knocks the level down. And then, you can start 11 building up again.
12 Well, if you do that, you never really get 13 the high levels of concentration that can lead to such 14 an energetic deflagration or detonation, you can 15 really challenge containment.
16 If we treat it statistically, there's a 17 probability that you might not detonate at those lower 18 levels. That even if that probably is not that high, 19 it's still there and so, there's the potential that 20 you will build up to a much higher level of 21 concentration of combustible gas so that if it does 22 ignite, you can have a very energetic event that's 23 much more likely to fail containment.
24 So, that's,
- again, a
modeling of 25 uncertainty issue or, you know, the choice that people NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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make compared to studies that have also modeled 2
combustible gases but with surpass the process are 3
results are fairly similar in terms of the results.
4 Okay, next slide, please?
5 Okay, I get my dry throat to get a break.
6 Dr. Cooper will now carry us through the 7
post-core damage human reliability analysis.
8 Take it away, Susan.
9 MR. BLEY: Alan, before you go, this is 10 Dennis again.
11 I just wanted to say something in support 12 of your statistic approach.
13 And you probably are aware of this, but we 14 were out talking with the NST people some years ago 15 and they tried to recreate fires both, I think, both 16 Class A and Class B fires by setting things up in 17 their hoods exactly the same, starting the fire in 18 exactly the same way.
19 And every time they did it, they got a 20 very different progression of the fire.
21 So, I think you're on the right approach.
22 MR. KURITZKY: Thank you, Dr. Bley.
23 Yes, I think that's a good analysis, thank 24 you.
25 MS. COOPER: All right, good morning, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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everyone. This is Susan Cooper from the Office of 2
Research. And I'm going to talk a little bit about 3
the Level 2 HRA analysis that was performed to support 4
the Level 3 project.
5 The actual development of this approach 6
and the application for quantification occurred back 7
in 2015, 2016. At that time, I was not aware of 8
anyone else that had developed an HRA approach to 9
address Level 2.
10 Also, at that time, severe accident 11 management guidelines, SAMGs, were relatively new on 12 the scene so far as a tool in the toolbox for 13 utilities to address accidents that progressed to 14 Level 2.
15 So, this posed a new problem for HRA. And 16 the SAMGs were definitely the focus of that, but there 17 were some things that went along with that that were 18 important for us to try to consider and get a handle 19 on how to model.
20 The SAMGs themselves were different than 21 EOPs. They are a guidance, not step by step oriented 22 procedures. And there are options not necessarily 23 just one thing to do. And they're also are 24 hierarchies, depending on the plant conditions.
25 Also, less training and experience and NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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also, the decision maker changes, the power shifted 2
from the control room to the technical support center.
3 And the emergency director there in the 4
technical support center was the final decision maker 5
supported by what are called SAMG evaluators.
6 So, there's a different team associated 7
with implementing these procedures.
8 So, the approach that we developed is 9
principally based on, you know, our understanding of 10 the SAMGs and other procedures at the reference site.
11 But then, most importantly, based on 12 information collected during a plant site visit, 13 especially one done in summer of 2013 where I 14 interviewed a number of operators and resident 15 inspectors,
- trainers, managers who had the 16 responsibility of being emergency director and the 17 TSC.
18 And they also, that the reference site had 19 the previous year conducted a mini-E drill that went 20 into using SAMGs.
21 And there were specific things that were 22 done in the TSC in using emergency damage mitigation 23 guidelines, EDMGs, even though there's no explicit 24 procedural link between those procedures and the 25 SAMGs.
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Also, based on a recommendation from 2
Dennis, I looked very closely at Gary Kline's 3
naturalistic decision making approach, specifically, 4
two models that he has.
5 One for team decision making and another 6
called recognition prime decision making.
7 So, both of those were important for us to 8
try to understand what was really a team in the 9
context of post-core damage and what is an expert and 10 what is the process for decision making?
11 Next slide, please?
12 CHAIR REMPE: Susan, this is Joy.
13 MS. COOPER: Yes?
14 CHAIR REMPE: And maybe Dennis may have to 15 help me remember, but after Fukishima, we had 16 presentations from the BW owners' group as well as the 17 PWR owners' group, as I recall.
18 And about the SAMGs and how they were 19 being changed to address Fukishima.
20 And your comment about the decision maker 21 going to the TSC is not consistent, and maybe, again, 22 I did -- my takeaway from those discussions were that, 23 it depended on the plant.
24 But the -- my takeaway was, generally 25 speaking, that the TSC folks just recommend to the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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operators they are the ones who are still the final 2
decision makers because they may know, well, that 3
particular --
4 Because their basing their decisions on 5
what instrumentation is still working and trying to 6
say, okay, two out of three say this. And one may say 7
something different.
8 But the operators may still know, well, 9
one of these often doesn't behave as expected.
10 And your comment about the TSC being the 11 key decision -- or the power goes into the TSC, is 12 that just something that this reference plant or is --
13 This one kind of puzzles me that, you 14 know, when you make that statement --
15 MS. COOPER: So, yes.
16 MR. BLEY: So, okay --
17 MS. COOPER: Dennis, you want to go ahead 18 or I mean, I can go ahead.
19 MR. BLEY: Yes, I was just going to try to 20 clarify what happened back then.
21 Early on in our discussions with various 22 people associated with the industry, it was always 23 said, the licensed operators in the plant were the 24 decision makers throughout this.
25 But as the SAMG work went on and the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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industry as a whole worked on this together, that kind 2
of shifted in a --
3 You'll even find, my memory is, in the 4
procedures where it tells you to consider these, that 5
operational control does shift to the TSC.
6 Now, maybe not all plants have implemented 7
it the same way. The people who are hands on and 8
actually do things still have a voice and are the only 9
ones who are allowed to operate the plant.
10 And maybe some of our folks that came out 11 of industry can say more about this.
12 We also had an NEI arranged session, and 13 this was on the boiling water reactors, not the -- we 14 never got around to having it with the pressurized 15 water reactors --
16 But they brought in people from one of the 17 plants and big charts of the SAMGs and how they were 18 going to use them and the other related procedures, 19 and walked through a number of possible events and how 20 decisions would be made and how things would progress.
21 And I think the Committee still has that 22 information somewhere in our archives. I could 23 probably help with that if people need help.
24 Anyway, that's a quick summary.
25 MS. COOPER: Yes.
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MR. BLEY: And Susan, what you found might 2
be different.
3 MS. COOPER: Well, no, I think that's 4
probably consistent.
5 Although, remember now, we were dealing 6
with procedures from 2012.
7 But the bottom line is that the 8
Westinghouse SAMGs have a very specific indefinite 9
transition from the control room to the TSCs so far as 10 decision making shift and when the TSC takes over.
11 And that's when the thermal couples reach, 12 I want to say, 1,800, I can't remember, but, you know, 13 basically, the definition of core damage.
14 And obviously, the concern then is, who 15 are those decision makers?
16 Now, I can't speak for industry as a 17 whole, but what I found, at the reference site was, it 18 didn't leave operations Because the three, no, four 19 decision maker managers who would have been -- had the 20 role of potential emergency director and the TSC were 21 all either current or former SROs licensed at that 22 plant.
23 On top of that, the -- so, the SAMG 24 evaluator who is the one in the Westinghouse SAMG 25 structure, actually comes up with the operational NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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approach is, in fact, the operations representative in 2
the TSC, a slot already assigned, and he is in charge 3
with support from engineering.
4 For the mini-e-drill that was conducted in 5
2012, it happened to be an SRO, but it will always be 6
someone that was a licensed operator.
7 I even talked to that SRO while he was on 8
shift in the Unit 1 control room.
9 So, for this referenced plant, that was 10 their model was that, you know, operations operators 11 were still going to be very much in control.
12 Now, recognize with SAMGs and even, you 13 know, linking them to EDMGs, we're mostly talking 14 about actions and equipment outside the control room 15 and, you know, portable equipment and so forth.
16 So, anyway, the bottom line is that, while 17 it shifted for this plant, it didn't really get out of 18 control of the typical operating operators' group or 19 the operational group.
20 So, that was an important insight that I 21 got from that plant site visit. And very much changed 22 my view of what the team was for implementing SAMGs.
23 It was certainly still a larger team, but 24 it was still within the group of people that 25 ordinarily are in charge of operations.
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CHAIR REMPE: Okay, thank you.
2 MS. COOPER: Steve's got his hand up.
3 MR. SCHULTZ: Susan, this is Steve 4
Schultz.
5 MS. COOPER: Yes?
6 MR. SCHULTZ: So, a quick question here.
7 MS. COOPER: Yes?
8 MR. SCHULTZ: You've talked about what was 9
done in the overall work that you performed in 2012.
10 With the work that came in with the FLEX 11 strategies and the equipment availability and so 12 forth, did you update the overall evaluation of human 13 reliability in this respect once that was implemented, 14 that would have been fully implemented a couple years 15 after the time frame that you're talking about here?
16 MS. COOPER: The short answer is, no.
17 And Alan can probably speak better to how 18 HRA was addressed for the FLEX sensitivity cases.
19 Remember, this is the FLEX work is not a 20 fully performed PRA and HRA effort.
21 So, the answer is no.
22 I will say that, you know, as also the 23 current lead for the integrated site risk task that we 24 will at least qualitatively take some of that into 25 consideration when we consider a site wide event that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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involves the two reactors, spent fuel pools, and dry 2
cask storage all at once.
3 But so far as the Level 2 HRA work that 4
was performed, no, we did not update the Level 2 to 5
take into account FLEX.
6 MR. SCHULTZ: That -- I'll listen to Alan 7
on that one, too.
8 But the overall approach sounds good to 9
take that into account as you look at the impact of 10 that --
11 MS. COOPER: Yes.
12 MR. SCHULTZ: -- in your review.
13 Thank you.
14 MS. COOPER: Mm-hmm.
15 All right --
16 MR. KURITZKY: Susan, sorry, Susan, just 17 Because Dr. Shultz just had -- he mentioned my name, 18 so I have to pipe in because I love the sound of my 19 voice.
20 So, Dr. Schultz, as Susan said, we did not 21 update the Level 2 HRA once the newer SAMGs came in, 22 I think was the beginning of your question.
23 And so, with -- and with the FLEX, as 24 Susan mentioned also, we did a very course evaluation.
25 So, we don't -- we didn't do a detailed HRA.
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And again, I want to re-emphasize that 2
that doesn't mean other people incorporated FLEX into 3
some risk-informed licensing amendment shouldn't be 4
doing a detailed HRA. They very well might need to do 5
that.
6 But for purposes of our study, we didn't 7
do it.
8 So, the fact that the -- that is was new 9
SAMGs really wouldn't impact our FLEX analysis.
10 The one place where we were considering 11 using the new SAMGs was for low power and shutdown, I 12 believe, because I think shutdown was not part of the 13 original SAMGs.
14 But then, it did become part of the 15 updated ones, but I don't think, I'm looking at Jeff 16 Wood, I don't think we ended up doing anything with it 17
-- with the updated SAMGs, even for low power 18 shutdown.
19 Well, nod your head, I can say it, 20 otherwise, you have to come to the mic.
21 That's correct. Jeff says that's correct.
22 MR. SCHULTZ: That's great, I appreciate 23 that.
24 It sounds, from Susan's description and 25 from what you've provided, it sounds like you will NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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have enough information available as to how the 2
analysis was performed and could be updated so that an 3
overall evaluation would be very helpful.
4 Thank you.
5 MS. COOPER: Yes.
6 MR. BLEY: This is Dennis.
7 MR. KURITZKY: Susan --
8 Go ahead, Dennis.
9 MR. BLEY: Okay.
10 Just a quick thing, I think it would be 11 very, well, helpful, but also honest to at least have 12 some statement of what the impact of not having 13 brought it into current conditions might be on the 14 results so that people don't over interpret the 15 existing results.
16 That's all.
17 MR. KURITZKY: Okay, thank you, Dr. Bley, 18 I took a note.
19 MEMBER ROBERTS: This is Tom Roberts.
20 Susan, I wonder if you could address the 21 implication or evaluation you did of habitability in 22 the various places since you're assuming actions 23 you're taking in the control room, TSC, whatever 24 locations the portable equipment in this model is 25 being used?
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MS. COOPER: Okay, so the -- that sort of 2
plays into the slide that is up right now. The first 3
part of the Level 2 HRA was what was referred to in 4
the method as a screening process.
5 And in fact, a Level 2 PRA lead did most 6
of this work to identify the plant conditions and so 7
forth that would allow us to understand which of the 8
various SAMGs were the highest priority and how the 9
Westinghouse SAMGs worked. That's the only one that 10 they're going to be working on.
11 And then, along with that, you know, some 12 detailed tables that gave us timing of various things 13 that were going on, including SAMG entry, plant 14 conditions, and the environmental conditions and 15 various locations throughout the plant, equipment 16 availability, survivability, and stuff like that.
17 So, that was the hand off to the HRA 18 analyst from the Level 2 PRA lead with some very 19 detailed information on what was going on in time.
20 Now, with respect -- so, that fed into the 21 formal HRA including what's listed on the slide as a 22 feasibility assessment.
23 One of the -- which is the definition of 24 which is borrowed from fire PRA, HRA guidelines, 25 NUREG-1921, specific feasibility criteria, including NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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habitability or environmental concerns for the action 2
location and the travel path. So, that was definitely 3
considered explicitly in the HRA.
4 Did that answer your question?
5 MEMBER ROBERTS: Partially. Were there 6
cases where habitability concerns precluded a step in 7
the SAMG that you would have otherwise accredited?
8 Or were there some that were close and it 9
degraded the probability of the action being taken 10 correctly?
11 MS. COOPER: So by the time the actual 12 method was applied, I was no longer the HRA lead, and 13 I don't recall any right now. I did look briefly 14 through the quantification report, and I didn't spot 15 anything.
16 What I will tell you is kind of a 17 lingering question for one of the actions that we 18 walked down at the plant site. That was use of a 19 portable pump to feed the containment spray system 20 from the yard outside of the aux building. And we 21 were unable to find any information on what the 22 environment would have been there in the yard, so 23 there was a question as to whether or not that would 24 have been a radiation problem.
25 So we did have some discussion about that.
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I think it's in the report, that it might take some 2
more time to get a radiation survey before they would 3
go and start the action, but we did not -- we were not 4
able to track that information down to know exactly 5
what the situation would be.
6 But I will say, one thing that we -- that 7
was done in this HRA approach for Level 2 is we said 8
we're not going to take any timing constraints from 9
the PRA as some sort of surrogate success criteria, or 10 whatever. The HRA analysts themselves developed the 11 times by which they thought the operators could 12 complete the actions, and in general it was intended 13 to be quite generous.
14 We did see some differences between how 15 easy it was to walk through deployment of that 16 portable pump in the walkdown versus the talk-through 17 in the conference room. So we expected that they 18 would have some difficulties that they would 19 eventually overcome, but I would need more time.
20 So I don't recall if there were any that 21 were precluded, but we did have some gaps in our 22 knowledge as to whether or not some things might have 23 to be performed somewhat differently.
24 MR. KURITZKY: Susan, if I could just --
25 and, again, I can't say definitively, but the whole NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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idea, as Susan was mentioning earlier, that we had a 2
screening process for determining which actions could 3
be taken. So as part of that screening process, if 4
there were actions that we felt the conditions were 5
that action had to be taken, or in transit to that 6
location would have been problematic, then they would 7
be screened out of consideration for the level.
8 MEMBER ROBERTS: And part of the 9
motivation for my question is there is a separate 10 issue. There is the proposal to double the allowable 11 deterministic control room dose, and I'm just 12 wondering what the risk significance of that might be.
13 The paper that proposed that says there isn't any 14 because risk analyses don't model operator doses in 15 the risk analysis, and it sounds like that may not be 16 an accurate statement based on the work that Susan is 17 describing.
18 And I was wondering if you had an overall 19 perspective on whether there is a potential risk 20 significance to doubling the deterministic allowed 21 control room dose or whether that would just, you 22 know, be a round off here.
23 M
R K
U R
I T
Z K
Y 24 So, and, Susan, I'll let you speak in a second 25 if you want to.
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But, Mr. Roberts, my response to that is 2
we didn't -- and it's going to be one -- actually one 3
of the examples they give for model uncertainty, if we 4
have time to get there later.
5 But the -- we did not do a very detailed 6
analysis of those environmental conditions for a 7
number of reasons, which I'll explain later. But, so 8
the level of resolution of our analysis might not be 9
to the extent that we could analyze something like 10 that with this -- with this particular model.
11 What you mentioned is something that 12 theoretically would go into that, either the initial 13 screening -- that's probably where it's most likely to 14 happen, because if you have -- if you have the onsite 15 radiological conditions, and you have a mapping of it, 16 and say, okay, well, this level is too high now for 17 them to take action, and those get screened out, you 18 can see what the impact of not having -- being able to 19 take those actions would be. But right now the 20 resolution of our model I don't think is such that we 21 would be able to evaluate the impact of that.
22 Susan, do you have anything else on that?
23 MS. COOPER: No. Although I will say that 24 I don't think any of the actions that were addressed 25 in the Level 2 HRA were taken in the control room.
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Anyway, so just to conclude on this slide, 2
the Level 2 HRA that was performed was a formal HRA 3
application, including, you know, discussion of how 4
the human failure events were defined, formal 5
feasibility assessment, qualitative analysis, and then 6
quantification. There were separate decision trees 7
used for quantification for diagnosis and execution.
8 In both cases, there was an emphasis on 9
whether there was existing guidance for performing the 10 actions. In other words, if -- so in the SAMG space, 11 if a particular SAMG said, "Look for ways to get water 12 into the containment spray system." And as I was told 13 by the SRO who was in the mini-E drill, he said, "Oh, 14 well, those EDMGs are like little procedures that are 15 already written up, so I thought we would go use one 16 of those."
17 So if that's the case, then there is some 18
-- you know, there is already something to work with, 19 so the hierarchy for the -- for the diagnosis tree was 20 whether that little -- that little set of procedure 21 steps were -- and EOPs, we had higher confidence that 22 they had been tested out and would work. EDMGs and 23 the like were another level where there was some 24 confidence that they had been -- had been tested or 25 exercised.
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And then of course if you had to make up 2
something from scratch, that was the lowest level of 3
confidence on whether they were going to be able to 4
come up with a workable strategy. And the execution 5
trees were similar, again, more looking at how much 6
experience -- typically, the field operator would be 7
doing this, and how much experience he or she had with 8
actually implementing the procedure.
9 There is a paper from PSA 2015 that 10 describes generally the approach, and also has an 11 example of the diagnosis tree. I guess I don't --
12 Alan will have to speak to the actual Level 2 PRA 13 report to say how much of the HRA is in that report 14 that would be documenting the method and its 15 application. I'm not as familiar with that.
16 So that's the short summary, I guess you 17 could say, of the Level 2 HRA.
18 MEMBER DIMITRIJEVIC: Susan?
19 MS. COOPER: Yes.
20 MEMBER DIMITRIJEVIC: So I still see 21 sensitivity that's in the reports, and that -- do you 22 have any collection of the results of sensitivity 23 events, if those actions were not considered?
24 MS. COOPER: No. I'm afraid I was not 25 involved in that work. That would have been Don NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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Helton and Stacey Hendrickson, neither of which are 2
available today. Maybe Alan would be able to remember 3
something. I do not know anything about that. I was 4
not involved.
5 MEMBER DIMITRIJEVIC: All right. So all 6
of those actions, the goal is to prevent the 7
containment failure, right? Given the amount either, 8
you know, through the prevent containment bypass or 9
containment failure, right?
10 MS. COOPER: Yes. Yes.
11 MEMBER DIMITRIJEVIC: And that --
12 MS. COOPER: Well, some of them are also 13 for you know, scrubbing fission products also.
14 MEMBER DIMITRIJEVIC: Right. Yeah, to 15 reduce releases, right.
16 MS. COOPER: Right.
17 MEMBER DIMITRIJEVIC: Okay. So, however, 18 in this slide which we discussed so much in the 19 beginning, because of those green numbers, there is 20 something else which is very interesting, and that's 21 that this containment is not performing greatly. You 22 know, the condition of containment failure probability 23 is very close to one, right?
24 MS. COOPER: Mm-hmm.
25 MEMBER DIMITRIJEVIC: I mean, it's NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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presented in some other results, not of this 2
particularly, but we can see, you know, the difference 3
between the larger things -- you know, the large 4
releases and condition -- core damage frequency.
5 So I was wondering, are those actions 6
mostly considered for preventing early releases or 7
early containment failures? I was very interested 8
actually in sensitivity analysis, and I saw some 9
partial ones, so I was sort of like wondering what was 10 importance of those actions.
11 MR. KURITZKY: Okay. Just -- sorry.
12 MS. COOPER: Go ahead, Alan.
13 MR. KURITZKY: Okay. So just -- I don't 14 have the numbers off the top of my head, but in Volume 15 3C, which is the Level 2 PRA for internal medicine 16 floods, I was going to mention actually on the last 17 slide, there is an appendix -- I think Appendix C --
18 which is entirely devoted to uncertainty analysis.
19 And in there they have the results of many 20 of the sensitivity -- or all of the sensitivity 21 analysis we performed for Level 2. There is one where 22 we I think raised all of the Level 2 HEPs by order of 23 magnitude. And then we lowered them by an order of 24 magnitude, so it gives you what the impact of that 25 was.
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And then, also, we did another sensitivity 2
analysis where we considered additional actions that 3
and I guess this is something I was going to talk 4
about maybe on a different slide. But, again, because 5
we used the seven-day -- we carried this interaction 6
analysis out to seven days, but for the level -- HRA 7
for the Level 2 space, we only considered one action 8
in general, one action before vessel breach and one 9
action at or shortly after vessel breach.
10 So then you have that whole other up to 11 seven days, or however many days where you're -- where 12 the action is progressing, but we're not considering 13 any other attempt by the operators to do anything to 14 prevent containment failure or mitigate the release.
15 And so we went and looked at several other 16 actions that could be taken in that timeframe to see 17 what the impact would be, and it was fairly 18 substantial, if you credited those additional actions.
19 The main one was controlling containment 20 pressure to avoid that overpressure failure, either by 21 venting or by restoring heat removal -- containment 22 heat removal, because, again, that long-term late 23 overpressure containment failure was the big driver of 24 this, and primarily because of station blackout 25 contributions.
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And so if you could take actions in that 2
seven-day period to prevent that overpressure failure, 3
you could definitely have a big impact on large 4
release frequency and all the latent -- the latent 5
cancer fatality risk metric and the other long-term 6
non-early health effects metrics.
7 So there is discussion on raising or 8
lowering the HEPs in that Appendix C to Volume 3C, and 9
there is also discussion on the -- in the Level 2 10 portion of I think Volume -- the overview report for 11 internal events and floods, Volume 3, so long as we 12 have just three. I think they discuss also the impact 13 of considering other actions in that seven-day period.
14 MEMBER DIMITRIJEVIC: Yeah. I think all 15 of that is right, so the sensitivity said. And it 16 didn't really sound to me anything alarming where I 17 saw them, but now when I look at that slide which you 18 presented earlier today, what I see is that you have 19
-- that slide gave us the core damage frequency of the 20
-- you know, the -- let's say for the -- without FLEX, 21 1.5E minus 4, and it gives us the large release 22 frequency of 1.1E minus 4.
23 So that means that containment 24 conditional containment of failure probability is very 25 close to one. So I was just wondering how much those NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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human recoveries actually help us there, so that's why 2
I asked the questions.
3 MR. KURITZKY: And just to follow off 4
that, the reason that the conditional containment 5
failure probability is so close to one, or I think in 6
the.7 range or.6 range, is because those, again, are 7
station black -- non-recoverable station blackout 8
sequences.
9 And so if nothing is done to ameliorate 10 that, to prevent containment overpressurization, then 11 eventually you're just going to just build up over 12 time. You're just going to build up pressure in the 13 containment. And even though it's a large dry 14 containment, it's very robust. If we just keep 15 building up the pressure from MC -- you know, from 16 molten core concrete interaction, you're going to 17 eventually just get an overpressure failure in most 18 cases. So --
19 MEMBER HALNON: I just want to say, 20 listening to all of this, I was trained as an SRO back 21 in the '80s and '90s, and we wrote the SAMGs in the 22
'90s, somewhere around there. And we knew all this 23 beforehand. We knew that you had to maintain 24 containment. We knew that during severe accidents you 25 had to take actions to maintain those barriers and to NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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-- so what new insight did we gain that we didn't 2
already know?
3 MR. KURITZKY: Again, that's something 4
that we will probably more -- get in a more structured 5
fashion when we do the summary NUREG.
6 MEMBER HALNON: Okay.
7 MR. KURITZKY: But for right now, there's 8
just -- there's anecdotal things that come up. And, 9
again, you know, many of these things that Dr. Bier 10 mentioned, for instance, ISLOCA, something that we 11 knew going in --
12 MEMBER HALNON: Yeah. We knew that.
13 MR. KURITZKY: Okay. So we get further 14 confirmation. We get maybe further details. We might 15 learn something that's different. In terms of risk, 16 there may be things that engineering-wise or 17 operational-wise we know that we would try and do 18 these actions.
19 But what's the likelihood of success?
20 What are the impediments? What's the -- you know, 21 given that there are certain less-than-ideal 22 conditions, what's the impact on the likelihood of 23 seeing these things? And what, if anything, can we do 24 if those things don't succeed? Are there other 25 options?
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So those are all thought out from a 2
deterministic point of view already in the plants.
3 Obviously, you know, we're just doing a study trying 4
to evaluate the risk. What happens is the actual risk 5
is all a function of how the plants are designed to 6
operate.
7 MEMBER HALNON: Okay.
8 MR. KURITZKY: So we're looking at getting 9
additional information that can help us going forward, 10 either confirm what we are already doing or what the 11 plants are already doing, or looking for other 12 alternatives or understanding what's the quantitative 13 impact received in risk space.
14 MEMBER HALNON: So, okay, I'll wait until 15 Volume 1 gets written. I know it's been 12 years 16 since we started this. Another decade to get to the 17 next -- what is the next -- that's -- I apologize.
18 That's not right. When do you think Volume 1 will be 19 at least drafted?
20 MR. KURITZKY: Okay. So you don't have to 21 apologize. I would love anybody to shout from the 22 rooftops about that, because I have been fighting for 23 about 10 years, 12 years, to have people dedicated to 24 work my project instead of being pulled off to other 25 projects. So, believe me, I feel your pain.
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The intention is to get it done, as you 2
saw before, in 2024, to get them all done. Whether we 3
can meet that schedule, again, depends whether the 4
people that are the key producers of this work are 5
allowed to work on this project or they do other 6
things.
7 Unfortunately, because these people have 8
become very good, or they were extremely well thought 9
of as agency experts, they are put on almost every 10 issue that comes in.
11 MEMBER HALNON: And I recall you said 12 earlier that Volume 1 would be the most focused.
13 MR. KURITZKY: Yeah.
14 MEMBER HALNON: So I'll --
15 MR. KURITZKY: That will be.
16 MEMBER HALNON: -- I'll save my non 17 deterministic -- my deterministic mindset to that. It 18 will --
19 MS. COOPER: Yeah. And if I could just 20 add, from the HRA perspective, without having done 21 this work, there would be a big, fat 1.0 certain 22 failure for every human action in the Level 2, if we 23 had not done this work.
24 Now, granted, some of the HEPs for human 25 error probabilities for some of these actions are NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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pretty, you know, high compared to what you might find 2
in the Level 1 PRA, but they are not all -- they are 3
not all, you know,.1 or something like that. There 4
are real numbers in there.
5 And as Alan pointed out in the -- from his 6
summary of what's in the appendices for sensitivities 7
for Level 2, the HRA does have an impact on the 8
results. So it would be a big difference, you know, 9
as demonstrated with the sensitivities if the HRA 10 values were different.
11 So being able to credit what may seem 12 obvious to an operator, but, you know, the PRA/HRA 13 analyst needs to have a very strong paper trail, if 14 you will, to credit these kinds of actions. And so 15 this is a significant -- significant breakthrough I 16 think.
17 MEMBER HALNON: Okay. Thank you.
18 MS. COOPER: All right. I think it's back 19 over to you, Alan.
20 MR. KURITZKY: Okay. Thank you. Thank 21 you very much, Susan.
22 Okay. So next slide, please, Jonathan.
23 So I think we're running very short on 24 time here, so I have a number of examples of model 25 uncertainty that we don't necessarily have to get to.
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But I do just want to go over the approach of our 2
parameter and modeling uncertainty.
3 So very
- quickly, for parametric 4
uncertainty, we handle that just like every other PRA 5
generally does. We assign distributions to all of the 6
basic events in the model, and we propagated those 7
through and did Monte Carlo sampling to come up with 8
the distributions.
9 One thing -- and in doing so, we also 10 included distributions for the -- for the main FLEX 11 events, so we assigned distributions to those, non-12 constrained, non-informative distributions for those, 13 because we didn't have the data. But we also 14 considered the state of knowledge correlation for 15 those when you're sampling for similar components. So 16 all that was rolled up into the parametric uncertainty 17 analysis.
18 One thing that we did differently than 19 many typical Level 2 PRAs is we directly linked our 20 Level 1 event trees to our Level 2 containment event 21 trees. So we were able to pass through, cut set 22 information on certain industry distributions all the 23 way through to the release category frequencies, so 24 they got good distributions on the release category 25 frequencies.
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Going on to the Level 3 part, the 2
consequence
- analysis, the only input in the 3
consequence analysis that we actually sampled was the 4
meteorological data, the weather. Everything else, 5
the other inputs from -- go in the NACS (phonetic) 6 were only treated as sources of model -- we identified 7
model uncertainty for those.
8 So, but nonetheless, we did carry through 9
the quantification of the uncertainty analysis through 10 the Level 3, so that we were able to come up with 11 complementary cumulative distribution functions, which 12 are reported for all the risk metrics in the Level 3 13 reports.
14 We also came up with tables where we 15 identify specific selected values of the different 16 metrics and provide the mean, the 5th, the 95th 17 percentile exceedance frequencies at those levels, 18 like for instance for latent containment -- for latent 19 cancer fatalities. You know, one fatality, 10, 100, 20 1,000 fatalities, always we provide the exceedance 21 frequencies at 5th percentile, 95th percentile, mean.
22 One thing we did run into some difficulty 23 with was we have some fairly high failure probability 24 events. I mean, I'm talking failure probabilities of 25
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careful because if you have any type of a broader 2
distribution on those, you're going to keep sampling 3
above 1.0, which is obviously not something we can do.
4 Our code, SAPHIRE, will discard any 5
samples that are above 1.0. But if you have these 6
very high failure probabilities, you will get a lot of 7
discarded samples which can affect the results. So we 8
had to -- we limited the -- we used a threshold 9
limitation on the -- on the error factor to make sure 10 that you didn't have too many discarded samples.
11 The actual output -- while we consider the 12 output distribution, the ratio of the 95th percentile 13 to the 5th percentile is fairly tight for all the 14 hazards, and when we calculate that -- and, again, I 15 go back to my saying that I -- I don't put a lot of 16 faith in parametric uncertainty. I'm more interested 17 in modeling uncertainty. But, nonetheless, we -- the 18 standard tells you to do it. We do it. Everybody 19 does it. The ratio of the 95th to the 5th for the 20 different hazards, as you see on the slide, range from 21 four to 14. Four was for internal fires.
22 For internal events, it was about eight, 23 the ratio from 95th to 5th. Looking at the results 24 from NUREG-1150 for the three PWRs that were analyzed, 25 their internal event range for the 95th to 5th, I NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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think were like eight, 14, and 20, so this is in line 2
with that, on the lower end, but definitely in line 3
with what was obtained for the NUREG-1150 plants.
4 Much greater ranges for the PWRs in that 5
study, I think partly because they had much lower 6
frequencies of core damage. But in any case, for the 7
PWRs, it was somewhat in the same range. So there is 8
parametric uncertainty in how we treated it.
9 Do you want to flip to the next slide, 10
- Jonathan, so we can quickly so modeling 11 uncertainty, to me, that's the big elephant in the 12 room, or whatever it is. That's the thing that 13 really, you know, is what we have to keep mind of.
14 And I want to stress that though the modeling 15 uncertainties are voluminous, there is many of them 16 and they can be very impactful, that doesn't mean you 17 can't use the results. It means you have to use the 18 results in a smart fashion, and you use them in an 19 appropriate context.
20 Okay. And so, but given that, we address 21 modeling uncertainty like every other PRA does. We 22 identify the key assumptions in those areas that are 23 most uncertain. We use engineering judgment to help 24 us determine whether we think these are going to be 25 important.
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And then we take the ones that we think 2
are most important or particularly deal with some very 3
-- an issue that is of much interest in the -- to the 4
NRC or the technical community, and we perform 5
sensitivity studies for those. And, again, those are 6
one-off sensitivity studies. We don't mix and match 7
different things to change at the same time generally.
8 We went and performed sensitivity studies 9
for quite a number of them. Those that we identified 10 as -- or that we thought would be important but we 11 couldn't do sensitivity studies, either because of 12 lack of resources or lack of information, we identify 13 as candidates for future research.
14 The following slides will provide examples 15 of each type, ones that we did sensitivity studies for 16 and ones we just put in the future research bin.
17 But one thing actually that's not on those 18 slides that I just want to mention as a very big 19 source of modeling uncertainty is anytime that you bin 20 something, for example, for seismic events, we have 21 eight seismic bins. Obviously, earthquake -- based on 22 seismic acceleration level.
23 You obviously can have unlimited set of 24 earthquakes, from barely feeling it to when whatever 25 goes on the top of, you know, Himalayas.
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So we put them into eight bins, and you 2
have a lower and upper peak ground acceleration for 3
each bin. And so we select a single representative 4
PGA to be used for the fragility analysis for that 5
bin. So when we calculate the likelihood of 6
components failing because of the seismic 7
acceleration, we're not doing it for a whole 8
distribution within that failure. We're doing it for 9
a selected value.
10 The same thing for going to -- with these 11 category frequencies. We carry all of the information 12 through to the release categories, but in coming up 13 with the source terms to represent each release 14 category, we have to pick a specific MELCOR run that's 15 going to have a set of source terms that we're going 16 to use for the consequence analysis.
17 And that one set is being used for all the 18 severe accident sequences that are in that release 19 category bin. So those, by definition, whenever 20 you're bidding things, you're going to have a lot of 21 uncertainty there.
22 As I mentioned earlier, one of the other 23 things, too, we looked at was the interfacing system 24 LOCA frequencies, and we did an expert elicitation for 25 that.
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Just to go to the idea of where all this 2
information is --
3 MR. BLEY: Alan?
4 MR. KURITZKY: -- I've been -- yes.
5 MR. BLEY: Yeah. Quick question. The way 6
you stated that kind of bothered me. It sounds like 7
we'd pick the bins and then we just took whatever 8
happened rather than picking the bins to put together 9
scenarios that were similar in the ways that matter 10 for this category. Can you clarify which approach you 11 took?
12 MR. KURITZKY: Thank you, Dr. Bley, for 13 keeping me honest. I was shortcutting, yes. So 14 whenever we do bin things, and this is for the release 15 categories example, we are picking severe accidents 16 that we believe all will behave similarly in terms of 17 long-term severe accident progression and radiological 18 release.
19 But given that, we have a finite number of 20 bins. We have to keep it small enough to make the 21 Level 3 analysis manageable. And so, by that nature, 22 we are including sequences in the bins that do not --
23 are not all mirror copies of each other. So there are 24 going to be instances where sequences are similar in 25 very many aspects, but there may be some aspects where NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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they diverge.
2 If they diverge enough and at frequencies 3
great enough, then we may have to create another bin.
4 But, again, we have 16 release categories already.
5 Probably do not want to do too many more than that or 6
you're going to get with an impracticable situation.
7 But, yes, we do bin them based on 8
similarity of characteristics, how we expect release 9
category space to impact source term, timing, and --
10 MR. BLEY: Which limits the uncertainty 11 quite a bit.
12 MR. KURITZKY: Yes. Exactly. So I didn't 13 mean to overstate the impact on uncertainty from the 14 binning. But it just -- the binning, by definition, 15 even with those constraints does -- is a definite 16 source of uncertainty.
17 And it's demonstrated -- if you look in 18 the Level 2 report, for instance, when 3C -- when it 19 discusses source term selection, we go through a 20 number of different MELCOR runs for each release 21 category. And we have to pick sometimes between 22 several different ones, decide which one we think does 23 the best job of matching the breadth of sequences in 24 that bin.
25 So you can get a flavor for some of the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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variation when you look into that section of the 2
report.
3 Okay. So, Dr. Rempe, this -- what time --
4 I have to wrap up by 10:25 or something? Is that the 5
6 CHAIR REMPE: We still need to have public 7
comments, and we were hoping that this part --
8 presentation would be done by 10:30. I'm --
9 MR. KURITZKY: Okay.
10 CHAIR REMPE: -- not going to hold you to 11 it. We do have letter writing after this.
12 MR. KURITZKY: Okay.
13 CHAIR REMPE: But please try and wrap up.
14 MR. KURITZKY: All right. Yeah. So 15 that's essentially the case. I just want to mention 16 on this slide one last thing.
17 CHAIR REMPE: And I do realize it's the 18 members' fault --
19 (Laughter.)
20 MR. KURITZKY: Thank you. Group exercise.
21 So, anyway, I kind of alluded to this 22 before I think. So all the modeling uncertainty 23 information, because there were so -- so many areas of 24 modeling uncertainty, oftentimes we'll have a single 25 section in the report that covers the uncertainty or NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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the modeling uncertainty, an example being buying a 3C 2
to Level 2 PRA for internal medicine floods.
3 There is an Appendix C that actually 4
covers it all very nicely. And as I mentioned, 5
there's a section in -- a summary section in Appendix 6
C which does a nice job of summarizing the modeling 7
uncertainty in that appendix.
8 Other cases like the Volume -- the Level 9
3 reports, there's several categories of max inputs, 10 and there are so many uncertainties associated with 11 each it made more sense to discuss those uncertainties 12 within each section where we discuss those different 13 max input -- categories of max input parameters.
14 So, for instance, Volume 3D, Section 3, 15 you'll see them broken out separately by section. So, 16 again, depending on the report, the volume of 17 information, the number of uncertainties, they may be 18 in one section or one appendix, or they may be 19 distributed in different sections in the report.
20 Next slide, please?
21 For the last two slides, one gives 22 examples of things that we addressed for sensitivity 23 analysis, the other ones we did not. This reaction 24 progression time, we have already talked about the 25 seven-day thing. I don't need to -- I don't think I NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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have to elaborate any more on that.
2 Another one actually we ended up hitting 3
-- talking when we're discussing some other question, 4
we looked at the potential for other actions in that 5
seven-day period that weren't in the base case model.
6 And we saw that -- that there was definite additional 7
benefit for preventing a large release if you 8
considered some of these actions in the later 9
timeframes.
10 And, again, that was -- that essentially 11 was controlling overpressure. That was containment 12 venting or getting containment heat removal restored 13 to prevent that overpressure failure. And if you 14 coupled that with precluding combustion, then you 15 really had an even bigger.
16 The biggest one I want to mention here is 17 the low-dose cancer risk estimation, because use of a 18
-- of a low-dose truncation value in the qualification 19 of latent cancer fatality risk, has a definite impact.
20 If you limit -- only include doses that if you -- or 21 if you exclude in that quantification, you exclude 22 doses that are comparable to what you would just get 23 from natural sources.
24 And if you do that, you have a much 25 greater latent cancer fatality risk because the bulk NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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of that risk is coming when people move -- long after 2
the accident people come back and spend the rest of 3
their lives with very low doses in the background, 4
additional doses in the background.
5 And so, statistically, you will build up 6
a number of latent cancer fatalities. But if you --
7 if you don't include the ones that are in the same 8
ballpark as natural background radiation, then you 9
greatly reduce those.
10 MEMBER PETTI: Alan, what was the cutoff 11 level?
12 MR. KURITZKY: In our -- we used something 13 from a 2010 health physics study paper, and so our 14 cutoff I believe was in order to be considered you had 15 to have at least five rem in one year, and at least 10 16 rem cumulative. You had to get a least five -- five 17 rem in one year after the accident, same year after 18 the accident, and 10 -- and at least 10 rem.
19 MEMBER PETTI: So these are much higher 20 than actual background seen in elevated cities around 21 the 22 MR. KURITZKY: Yeah. I mean, the -- I 23 can't speak to that. I think they are somewhat tied 24 to like the EPA PAGs.
25 MEMBER PETTI: Yeah. Yeah.
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MR. KURITZKY: But you know a lot more 2
about it than I do, so --
3 MEMBER BALLINGER: This is Ron. When you 4
say five rem in a year, for radiation workers, 5N 5
minus 18, that's the number -- that's the number I 6
keep in my head from a long time ago as not being --
7 not resulting in a statistically increased cancer 8
risk. So you're probably right.
9 MR. KURITZKY: Again, in my specialty, but 10 that -- yeah, that's --
11 MEMBER PETTI: No, not that Alan says it.
12 I remember reading it. You know, it was tied to EPA 13 PAGs.
14 MEMBER BALLINGER: Once in a lifetime is 15 25.
16 MEMBER PETTI: Which makes sense. Good.
17 Thank you.
18 MR. KURITZKY: Last one on this. I just 19 want to -- I only want to mention it because it has a 20 big impact on early fatality risk, goes back to the 21 numbers we were talking about before.
22 So remember early fatality risk was 10 to 23 the minus 13, very low number. So one thing that we 24 saw that had a very big impact was that early fatality 25 risk for seismic events, we already considered NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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degraded evacuation for seismic and high-wind events.
2 We have a degraded evacuation model and -- but we 3
wanted to also look at what happens if the evacuation 4
times were even greater or the shielding was less 5
effective than even when we considered our base case 6
degraded evacuation model.
7 And we saw that in fact it was a very 8
substantial impact on early fatality risk when we 9
considered longer evacuation delays and more degraded 10 shielding. Doesn't have much of an impact on latent 11 cancer, because I just said that that happens much 12 later, but the early fatality risk was multiple orders 13 of magnitude higher if you -- if you had that, you 14 know, for instance a 48-hour delayed evacuation and 15 much-degraded shielding.
16 Next slide, please?
17 There's a question whether my voice will 18 give out or the time will give out first.
19 So here is just a few examples of things 20 that we -- that were canceled for research we did not 21 pursue. One of them got brought up before I think by 22 Mr. Roberts about the environment -- the conditions 23 under which we would take action.
24 So that's something that we treated fairly 25 simply in the study, because of limited information, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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because of the level of detail of our accident 2
management analysis, and obviously resources in the 3
projects. So we didn't delve into it in too great of 4
detail, but enough that we got some reasonable results 5
for use here. But that's something that could 6
definitely benefit from much more detailed analysis.
7 The containment failure paths, one of the 8
major assumptions that we made for that overpressure 9
failure, the one that seems to drive many of the 10 results, is that when that containment failed, it 11 would fail into the tendon gallery.
12 So we did structural analysis that showed 13 there were a couple of different areas that were very 14 likely to have -- be the weak points. One was the 15 tendon gallery, but there is also it could fail into 16 the auxiliary building. The tendon gallery gave worse 17 results, because that ends up then going out to the 18 environment. In the auxiliary building, you get a 19 little bit more shielding and a little bit more 20 reduction in source term, or definitely more reduction 21 in source term.
22 So, have you picked for those to go into 23 the aux building, or if we picked -- they'd have to do 24 the one we have to -- you would see a definite impact 25 on the results. That's an assumption that makes a big NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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difference. We can identify that, but that's 2
something that we didn't further analyze.
3 Also, just the shape and size and the 4
geometry of various failures, containment isolation 5
failure, so it -- where distribution comes from 6
seismic event that can structurally damage the 7
containment isolation system. How are those leakage 8
paths or containment penetrations physically damaged?
9 So that can impact how much gets out, what kind of 10 source term you have.
11 And the last few are just things from the 12 Level 3 model. They're not even the -- Keith will 13 yell at me for picking those, not better ones, but 14 they were examples of just things in the Level 3, the 15 max analysis, where we have uncertainty, which we just 16 identify but we haven't done anything in this failure 17 to quantify.
18 And with that, the last slide just goes to 19 the issue that came up in the subcommittee meeting 20 about where we could find all of this information. I 21 kind of talked about this already. Depending on the 22 nature and the amount of the information, you'll find 23 it either in a dedicated section or appendix in the 24 report or it will be spread in different sections.
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attempt to try and package some of that together in an 2
organized fashion, but it's only going to be -- it's 3
not going to be something that's going to make anybody 4
smile broadly, because it's going to be limited in 5
what we can do, just because there is so much 6
information.
7 And there's no real way to rank like this 8
particular model uncertainty for Level 1 PRA for 9
seismic events versus this Level 2 PRA for internal 10 events, this issue. There is no, you know, rubric 11 which -- to kind of really compare them very well. So 12 it's going to be a lot of judgment call pulling a few 13 key things together. But that is our intention for 14 the summary NUREG.
15 And that's the only thing I had, so --
16 MEMBER PETTI: Alan, just for the record, 17 I looked up radiation dose in Denver is about one rem 18 per year for people living in Denver, compared to the 19 average American. And the average radiation dose for 20 a pilot or an airline employee that flies all the time 21 is three rem per year. So just some numbers for that.
22 So the cutoffs that you guys were using 23 were, you know, previous --
24 MEMBER BROWN: Did they give cancer 25 fatality rates for those numbers?
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MEMBER PETTI: The only thing I saw was 2
that there is no increase in cancer risk for people 3
living in Denver versus other areas. I can't find 4
anything about whether there's increased cancer risk 5
for airline pilots. But I would need to look more.
6 MEMBER MARCH-LEUBA: Going back to the 7
model uncertainty -- and this is not a question, just 8
something I want to place on the record, I didn't see 9
any emphasis on what they call completeness in model.
10 We forgot to model the large tsunami or 11 for this year my heart is we never include 12 cybersecurity in the model. And, in my opinion, it's 13 the largest risk to reactors in 2023, and it will be 14 even greater in '24 and '25.
15 So that's really impossible to quantify, 16 but that is the largest source of uncertainty. What 17 did I forget?
18 MR. KURITZKY: Thank you. Good comment.
19 MEMBER MARCH-LEUBA: Because I'd like to 20 place on the record, the numbers -- the risk numbers 21 you are calculating are non-conservative, lower bound 22 estimates of the risk. The risk can only be higher 23 than the number you calculate, because you forgot 24 something, which will increase it. So I keep saying 25 that, and my PRA friends keep getting upset, but this NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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is the truth.
2 MEMBER DIMITRIJEVIC: Well, we don't need 3
to get upset because, I mean, you are totally right.
4 We -- I am a little upset that you don't look at dose 5
uncertainties, you know, in the thermal hydraulics.
6 In Level 2, they are also incredibly high.
7 There is also so much limits, you know, 8
- that, Alan, what we can do and report in 9
uncertainties. And it would be really, you know, the 10 great benefits from this project if those are 11 identified. You said something in the -- in the --
12 you know, when we were discussing the small numbers, 13 what you said that, you know, the only uncertainty 14 which we can calculate is parametric uncertainty, and 15 you are not big fan of that and neither am I.
16 However, when it comes to the modeling 17 uncertainties, the phenomenological uncertainties, the 18 deterministic status uncertainties, we don't really 19 have a good way to report that. And we definitely 20 don't have a good way to report incompleteness 21 uncertainties because we really -- don't really know 22 what we are missing until we realize we are missing 23 it.
24 So, and all of the sensitivity analysis 25 and modeling uncertainties which identify something NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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important, there is no way we can plot them. So, for 2
example, even when we can start with a simpler -- like 3
a state of knowledge that if you -- you concede that 4
as soon as your point estimates are close to your mean 5
value in -- that implies that almost all parameters 6
are treated as independent, which is not true.
7 And the problem with that is that, you 8
know, often those same components are in common cause 9
groups, and then that's -- that they don't allow you 10 to treat that or state knowledge appropriately. So 11 even in these simple parametrical study we have issues 12 on reporting, and you definitely -- you know, you 13 didn't show us any -- you told us the ranges, but you 14 didn't show us any numbers. Like, for example, do we 15 see the bigger uncertainty ranges in reporting the 16 Level 2 result?
17 MR. KURITZKY: Yeah. The Level -- excuse 18 me, in Volume 3C and Volume 4D, and we have -- we have 19 tables of all of the uncertainty issues we should 20 follow with these categories. As I said, there's 16 21 of them. So there's -- I mean, it's a lot of 22 information. So, yeah, no, I did not provide any --
23 again, my understanding was we were -- I was supposed 24 to limit what numbers I showed at the presentation.
25 All those numbers are in those reports.
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MEMBER DIMITRIJEVIC: You would expect, as 2
you said in the regular discussion in the beginning of 3
this, that you see much higher ranges, for example, in 4
the Level 2, right? And you definitely will expect to 5
see much huger ranges in Level 3, and we don't see 6
those.
7 My question is: so, obviously, you know, 8
this is something which is -- I am not expecting this 9
study to solve, but at least to point to the needs for 10 the much further research in this area. How can we 11 report those modeling uncertainties, incompleteness 12 uncertainties? How can we involve them in actually 13 reporting these, meaningfully reporting the results?
14 So whatever you have, there is a lot of 15 very valuable information, and I saw that you did 16 something in the Level 2 with combining these 17 deterministic and the -- and also in the groupings and 18 everything. I know -- and I look at these happenings 19 very carefully. It's very difficult to look at data 20 and say, "Oh yeah. This is the issue."
21 So, I mean, I certainly hope that a lot of 22 the good things will come out of the -- of your 23 experience in analyzing and reporting uncertainties.
24 MR. KURITZKY: Okay. Thank you.
25 MEMBER DIMITRIJEVIC: I mean, just showing NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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the graphs and numbers, you know, it's not really make 2
everybody saying, ah ha, oh yeah, that's what that 3
means. You know? Everybody is going to look at a 4
number and say, all right, I mean, another factor of 5
the vote, it's no big deal. That's not true. That 6
other factor is totally not true, so -- okay.
7 MR. KURITZKY: Thank you.
8 MEMBER PETTI: Yes. I wanted to get some 9
things clear in my mind. I wrote some things before 10 subcommittee, and I want to make sure they're clear in 11 my mind as we go into letter writing.
12 I always have this belief that external 13 hazards tended to dominate the risk over internal 14 events, just because good engineers can engineer away 15 a lot of issues. Is that still a fair statement? I 16 mean, I understand there's bypass sequences that are 17 there, but is that --
18 MR. KURITZKY: The results for this --
19 again, for this event, we show that internal events in 20 the base case are one of the major triggers, but it's 21 on par with internal fires. Seismic and high wind 22 were lesser at this plant.
23 When you consider FLEX, internal event 24 goes down further because it's primarily station 25 blackouts in the FLEX knocks that (audio NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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interference). We also give more credit for FLEX 2
under sunny day conditions of an internal event in the 3
conditions of the plant -- or the first time they 4
experience after an earthquake or --
5 MEMBER PETTI: But other PRAs show 6
something different, right? That external are more 7
risk-significant than internal?
8 MR. KURITZKY: I don't want to speak to 9
it, because I don't remember the exact numbers. In 10 the -- in a moment, we're going to dig into some other 11 12 MEMBER PETTI: That's -- these are some of 13 the things that I think, yeah, it would be really --
14 MR. KURITZKY: Right.
15 MEMBER PETTI: Second, just on the whole 16 FLEX strategies, you only did Phase 1 and 2 in FLEX, 17 right? You didn't do Phase 3, which may really change 18 the risk profile or -- I just worry about people 19 looking at it and -- because I did it before. FLEX 20 didn't seem to help a lot, but Phase 3 FLEX is not 21 there. And so to have a -- to make sure you don't 22 misinterpret, that that's a very important piece of 23 the overall FLEX strategy. So --
24 MEMBER BALLINGER: Yeah. We visited 25 Phoenix I guess, the Arizona -- the Arizona thing, and NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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I was asking the folks out there, you know, that Phase 2
1 -- 1, 2, and 3, and they told us that more than 3
likely they would be supplying stuff right away.
4 So Phase 1, Phase 2, Phase 3 would -- is 5
just -- you know, it would be compressed. So that 6
would have an enormous effect, I think.
7 So depending on how fast they brought 8
other equipment onsite, it could have an effect -- it 9
would not have an enormous effect because -- a couple 10 of reasons. One is we are only taking analysis out 11 for a certain number of days. The core damage --
12 remember, FLEX is primarily interested in preventing 13 core damage, not mitigating the release. Core damage 14 is occurring much more quickly. It's occurring in the 15 first X number of hours after the initiating event.
16 So you can get more FLEX equipment in 17 there, but core damage has already happened. So where 18 that extra FLEX equipment really comes into play is to 19 extend the life of FLEX. In other words, if you're 20 using FLEX equipment to keep the core cool, and you 21 start to run out of power, this or that, you get more 22 diesel generators, you get more pumps, more fuel, 23 whatever. You get more resources, so you can keep 24 going.
25 We have always stopped the analysis. We NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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either had core damage by then, in which case it's not 2
helping, or we don't have core damage, but we're not 3
we're not considering that long timeframe for core 4
damage. So we've already said you're okay, so it 5
would not really have any impact. It personally would 6
have no impact on the actual analysis.
7 But it's needed if you are relying on FLEX 8
for the long term, but it will not impact, I don't 9
think, the estimation of core damage frequency or the 10 ensuing, you know, risk metrics.
11 MEMBER PETTI: And then my third comment 12 is more for the other members. You know, as the 13 advanced reactor guy, I think about and look at all of 14 the events, and you think of how many of them are 15 driven by station blackout and heat removal, right?
16 And heat removal will be passive in most of the 17 advanced systems, and they will not require electric 18 power to execute their safety function.
19 So it's really going to be interesting 20 when we see, you know, a more complete PRA of one of 21 the advanced systems, because I think it's just going 22 to look so different than what we see here. I think 23 it's going to be an interesting comparison once we get 24 there.
25 MEMBER BALLINGER: Thanks.
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MEMBER DIMITRIJEVIC: Alan, Dave just 2
reminded me of something, which I -- I mentioned in 3
our subcommittee meeting, and I want to bring it over 4
here. You know, your FLEX -- FLEX case includes also 5
something which -- and this is why when I was giving 6
you example of the containment performance I was using 7
the circa 2012 case -- includes not just the FLEX 8
strategies but also improval [sic] in the seals, which 9
is extremely important for four-loop Westinghouse, 10 because risk in the four-loop Westinghouse plans 11 before, you know, the improvements to the seals that 12 was dominated by seal LOCA and loss of component 13 cooling water, you know, that you lose cooling to the 14 seals.
15 So it's not -- you said that this risk 16 level is dominated by loop, but that is after the 17 seals are improved. Before the seals are improved, I 18 am almost sure that the seal LOCA was one of the main 19 contributors. Is that a true statement?
20 MR. KURITZKY: Yes. Seal LOCAs are 21 definitely one of the major contributors. But, 22 remember, seal LOCA is also an outcome oftentimes from 23 the station blackout, too. But those improved seals, 24 we did a sensitivity study on that, in the Level 1, 25 specifically just for the seals, and it reduced CDF by NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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around 14 percent. So it's not going to --
2 MEMBER DIMITRIJEVIC: So, therefore, that 3
FLEX things also -- you know, involves this other 4
case, this case. Also, the last time in the 5
subcommittee meetings, you said that this prolonged 6
operation of turbine-driven auxiliary feedwater, which 7
I was not considering FLEX case, you said that may --
8 it may be considered FLEX case.
9 So is this prolonged operation of 10 turbine-driven auxiliary feedwater, does that have 11 something to do with FLEX or this is independent?
12 MR. KURITZKY: Totally independent. It's 13 just something that we did not credit in the initial 14 model. And so when we went to do -- we gave some part 15
-- we gave some credit for it in the Level 2, in terms 16 of extending the time for it -- for reaction 17 progression, but in the Level 1, we thought it was too 18 unreliable, and so we did not credit it.
19 But we felt in the FLEX -- when we did the 20 FLEX modeling to get things more realistic, since 21 already the FLEX was going to have a fairly high 22 failure probability, on par with the continued 23 turbine-driven aux feed -- if we're going to credit 24 one, we'll credit them both, but, again, they both 25 have a fairly high failure probability.
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But because you just need one or the 2
other, the combination gets you down to a relatively 3
low number, like in internal events we have a.3 4
failure probability of reach. So essentially you have 5
to fail both. You have a 91 percent chance of success 6
of either one or the other, so it has a fairly 7
significant impact on the station blackout sequences.
8 Less so for some of the internal -- some of the 9
external hazards where we give less credit from FLEX, 10 but, you know --
11 MEMBER DIMITRIJEVIC: So factor P, which 12 you use to measure, you know, sensitivity, and we talk 13 about broad distribution, it's combination of the FLEX 14 strategy and the -- crediting this action on auxiliary 15 feedwater, right?
16 MR. KURITZKY: Yes.
17 MEMBER DIMITRIJEVIC: Turbine driven.
18 MR. KURITZKY: Yeah.
19 MEMBER DIMITRIJEVIC: So, actually, there 20 is -- I just want to say that the FLEX sensitivity 21 case is not -- it may be less than 50 percent FLEX.
22 It's mostly -- it's both seals and this auxiliary 23 feedwater. By the way, is this auxiliary feedwater 24 human actions? That's a part of your regular HRA, 25 right?
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MR. KURITZKY: Yeah. For the extended 2
turbine-driven aux feed, that's all -- that's really 3
all human accident, and it's -- and it's a very dicey 4
human accident because they are manually controlling 5
those -- that turbine-driven pump without the benefit 6
of essentially controlling -- you know, without AC and 7
DC power, so they're kind of flying blind. So that's 8
why we didn't credit initially, and we give it a very 9
high failure probability when we do this analysis.
10 But you're right. If we do not consider 11 that, the impact of FLEX is much lower. Instead of 12 having a.09 failure probability, it's a.3. But, 13 again, remember, we used that.09 failure probability, 14 and then we showed how it compared to whether we -- if 15 we used higher or lower values of P, and it didn't 16 make that much difference on the -- on the core damage 17 profile.
18 But if we only did consider FLEX and 19 didn't consider the turbine-driven aux feed, extended 20 turbine-driven aux feed also, then that would be a 21 different case. And maybe we would have had to do a 22 little more rigorous analysis of the FLEX failure 23 probability because it might have had, you know, more 24
-- you know, the value we pick would have to be more 25 influential.
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MEMBER DIMITRIJEVIC: So FLEX here is just 2
basically the cavity of offsite power. Is that what 3
the FLEX is here?
4 MR. KURITZKY: Well, it's not -- it's 5
functionally similar, but it's not actually -- it's 6
not recovering actual offsite power. You're -- what 7
the FLEX is doing is bringing in what -- Phase 1 you 8
actually have the strategy. You're stripping down 9
your batteries to give it -- to extend your battery 10 lifetime maybe two or four hours.
11 MEMBER DIMITRIJEVIC: Right.
12 MR. KURITZKY: To 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. But then 13 you're bringing in a portable diesel generator and a 14 pump, so that you can run things, even though you 15 don't have offsite power.
16 MEMBER DIMITRIJEVIC: Yeah. I mean, the 17 recovering power. That's what I --
18 MR. KURITZKY: Recovering, yes, recovering 19 power.
20 MEMBER DIMITRIJEVIC: So did you consider 21 dependency of that on the time an ELAP (phonetic) is 22 declared? I mean, do you have a different timeframe 23 when was -- to declare ELAP in one hour I think and/or 24 four hours or something? And then I was wondering, is 25 there dependency on the human actions? Is that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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dependent of the timeline of declaring ELAP? That was 2
one of my questions.
3 My other question was concern about this 4
important action on the -- keeping auxiliary feedwater 5
operable for the long time with no -- is this the 6
local action? How does he control those valves 7
bringing steam to the turbine? I mean, how is this 8
action possible without AC and DC power? That's what 9
my actually concern was, but that's an important part 10 of this FLEX activity, but even it's not FLEX.
11 MR. KURITZKY: Okay. So, first, I 12 remember now the first part of your question -- I'm 13 getting too old. I'm sorry. What was the first part 14 again?
15 MEMBER DIMITRIJEVIC: First part was the 16 dependency of the operator action on the time of 17 declaring ELAP and --
18 MR. KURITZKY: Okay.
19 MEMBER DIMITRIJEVIC: -- my second 20 question is on this controlling the turbine-driven 21 pump.
22 MR. KURITZKY: Now I forgot the first one 23 again. No, I'm just kidding.
24 (Laughter.)
25 MR. KURITZKY: So, yeah, in terms of the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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dependencies -- our level of analysis didn't go into 2
a lot of detail. So we're not actually doing any type 3
of HRA where those dependencies would show up. We've 4
picked a value of.3. That covers human actions and 5
equipment failure and severity. Coarse number, at 6
least as picked by engineering judgment, and we've 7
demonstrated that it didn't make that much difference, 8
and so we could live with it. But that's -- but that 9
-- so it doesn't go to that level of detail.
10 The second item -- what was the second 11 one?
12 MEMBER DIMITRIJEVIC: Second one is, how 13 does the -- how does he control this turbine-driven 14 pump from being in operation for long time? For such 15 a long mission time with noise in DC? I mean, just 16 like I am totally mind-boggling. I would not credit 17 that, so if you can just tell me how -- because you 18 didn't include the equipment there. How does he 19 control the steam supply to the turbine? That's what 20 my question is.
21 MR. KURITZKY: So he is mainly controlling 22 the governor valve to control how much steam goes in.
23 And that's the reason why we didn't give it credit 24 initially and give it very -- you know, very modest 25 credit now in the sensitivity analysis, because he is NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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manually controlling -- or they are manually 2
controlling the steam flow in, and they can underfill 3
or overfill the steam generator.
4 They can flood the input -- the steam 5
inlet line to trip off the turbine, so there's -- it's 6
very dicey stuff, and they're doing it manually. And 7
probably a very limited local indication of anything 8
at that point, because (audio interference) power.
9 But you did bring up this -- the 10 long-term, you know, I don't know, because that they 11 can theoretically do without power, so it's dicey.
12 When it comes to having to refill, like, for instance, 13 under normal conditions, we did add events in our 14 event trees to consider long-term cooling, because in 15 the case of RCPC LOCAs are small LOCAs.
16 You would actually keep going on for many 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br />, not just 24, and so we included actions in the 18 event tree to get charging back or to bring more water 19 for the aux feedwater. But under the conditions of 20 station -- of that complete blackout, not just station 21 blackout, but all loss of AC and DC, I don't know how 22 easy it would be to get -- to make up or -- once you 23 used up whatever was in those tanks.
24 But the assumption being over those 25 several days you will come up with something to open NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14TH ST., N.W., STE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
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the necessary valve, in other words, manually 2
overriding the valves or lining up some alternative 3
source. But, again, the analysis doesn't go into that 4
level of detail.
5 MEMBER DIMITRIJEVIC: Okay. All right.
6 Those were my inquiries about it. Okay.
7 CHAIR REMPE: Okay. So, at this time, 8
thank you very much for your presentation and your 9
responses to our questions and comments.
10 I think we need to open the line, which in 11 today's world means just unmute yourself if you're a 12 member of the public who wishes to make a statement at 13 this time or a comment. Some folks may have to hit 14 star six if you're on the phone. And I'm not seeing 15 any hands up or anyone trying to make comments.
16 So, at this time, I'd like us to take a 15 17 minute break approximately. So why don't we come back 18 at 10 after the hour, and we'll -- I believe you have 19 a draft letter to read in, right, Vesna?
20 And before we take the break, though, I'd 21 like to tell the court reporter that I'm going to be 22 asking him to take off for the rest of the day, but to 23 come back at 8:30. Okay?
24 (Whereupon, the above-entitled matter went 25 off the record at 10:53 a.m.)
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Level 3 PRA Project Briefing for Volumes 3 and 4 Advisory Committee on Reactor Safeguards November 1, 2023 Alan Kuritzky Division of Risk Analysis Office of Nuclear Regulatory Research (301-415-1552, Alan.Kuritzky@nrc.gov)
Susan Cooper Division of Risk Analysis Office of Nuclear Regulatory Research (301-415-0915, Susan.Cooper@nrc.gov)
Outline
Background
L3PRA project public reports Summary of results Reactor at-power PRA preliminary insights Post-core-damage HRA Uncertainty analysis Report road maps 2
In a staff requirements memorandum (SRM-SECY 0089) dated 9/21/2011 the Commission directed the staff to conduct a full-scope, comprehensive site Level-3 PRA Reference site
Two Westinghouse 4-loop PWRs with large, dry containments Radiological sources
Reactor cores
Spent fuel pools
Dry cask storage Project scope
All reactor modes of operation
All internal and external hazards (excluding malevolent acts)
Level 1, 2, and 3 PRA (full consequence analysis)
Integrated site risk
3 Background
4 Level 3 PRA Project Public Reports Summary (Vol. 1)
Back-ground (Vol. 2)
Reactor, At-Power, Internal Events and Internal Floods (Volume 3)
Overview-IE/IF (3)
L1-IE (3a)
L1-IF (3b)
L2-IE/IF (3c)
L3-IE/IF (3d)
Reactor, At-Power, Internal Fires and External Events (Volume 4)
Overview-F/S/W (4)
L1-FIRE (4a)
L1-SEIS (4b)
L1-HW/OH (4c)
L2-F/S/W (4d)
L3-F/S/W (4e)
Reactor, LPSD, Internal Events (Volume 5)
Overview-LPSD (5)
L1-IE (5a)
L2-IE (5b)
L3-IE (5c)
Spent Fuel Pool (Volume 6)
Dry Cask Storage (Volume 7)
Integrated Site Risk (Volume 8)
Overview-SFP (6)
L1/L2 (6a)
L3 (6b)
L1-L3 (7)
L1-L3 (8)
Preliminary Schedule for Releasing Draft L3PRA Reports for Public Comment Reactor, at-power, internal events and internal floods (Vol. 2 and Vols. 3x, 3a-3d) (4/22/2022) - comments resolved and currently with ADM for final publication Reactor, at-power, internal fires, seismic events, and high winds (Vols. 4x, 4a-4e) (8/18/2023) - comments received and currently being reviewed Reactor, low-power and shutdown, internal events (Vols. 5x, 5a-5c)
(Q2-2024)
Spent fuel pool, all hazards (Vols. 6x, 6a-b) (Q3-2024)
Dry cask storage, all hazards (Vol. 7) (Q1-2024)
Integrated site risk (Vol. 8) (Q4-2024)
Summary report (Vol. 1) (Q4-2024) 5
6 Summary of Results (All Hazards Combined)
Risk Metric (per reactor-year)
QHO or Subsidiary Risk Metric Circa-2012 Case 2020-FLEX Case Core damage frequency 1E-04 1.5E-04 9.3E-05 Large early release frequency 1E-05 1.9E-06 1.3E-06 Large release frequency N/A 1.1E-04 6.7E-05 Individual early fatality risk 5E-7 7.5E-13 6.6E-13 Individual latent cancer fatality risk 2E-6 6.5E-08 4.0E-08
Reactor At-Power PRA Preliminary Insights (1 of 4)
Combination of reference plant design and site location has substantial margin to the QHOs when considering all hazards combined, though the margins are noticeably less for the surrogate risk metrics of CDF and LERF
Extremely low likelihood of early fatality risk because of the following factors:
very low frequency of bypass events (ISLOCA or SGTR cases) that would generate relatively large and fast releases
relatively low frequency of adverse meteorological conditions (primarily stable, low wind speed conditions)
very sparse close-in population, which limits likelihood of wind blowing in direction of a populated sector very close to the site
low likelihood of delayed and/or slow evacuation of populations toward which winds are blowing
Low likelihood of latent cancer fatality risk because same factors above also lead to low exposure in early phase and effective protective measures limit late phase doses to no more than long-term habitability criteria 7
Reactor At-Power PRA Preliminary Insights (2 of 4)
Offsite public risk metrics related to early health effects primarily result from:
ISLOCAs ATWS leading to an unscrubbed PI-SGTR, with one or more secondary-side relief valves open Post-core-damage TI-SGTRs 8
Reactor At-Power PRA Preliminary Insights (3 of 4)
Offsite public risk metrics other than those related to early health effects primarily result from:
Unscrubbed, late containment failures due to long-term quasi-static overpressure Unscrubbed, containment failures hours after vessel breach due to global deflagration or detonation Unmitigated containment isolation failure (primarily for seismic events)
Post-core-damage TI-SGTRs (primarily for land contamination risk) 9
Reactor At-Power PRA Preliminary Insights (4 of 4)
Selection of 7-day severe accident progression analysis time significantly impacts evaluation of offsite public risk metrics other than those related to early health effects
Radiological release category involving unscrubbed, late containment failures due to long-term quasi-static overpressure (RC-LCF) is a major contributor to latent cancer fatality risk
Frequency of RC-LCF is significantly reduced for shorter analysis times
Action taken to prevent containment overpressure failure in ~2 days after accident initiation can prevent a large release
Level 2 PRAs that only model severe accident progression for 48-72 hours after accident initiation may significantly underestimate plant risk
Radiological release category involving unscrubbed, containment failures hours after vessel breach due to global deflagration or detonation is also a major contributor to latent cancer fatality risk
Combustion is treated as a stochastic (vs. deterministic) process 10
Post-Core-Damage Human Reliability Analysis (1 of 2)
Post-core-damage (Level 2 PRA) human reliability analysis (HRA) differs from traditional Level 1 PRA/HRA because:
the actions are based on general guidance in SAMGs, rather than very step-oriented procedures like the EOPs
there is less training and experience for the operator decisions and actions modeled in Level 2 HRA/PRA than for Level 1 HRA/PRA
there is not necessarily one specific action to take; rather, the staff has to choose from a variety of potential actions
Features of approach in Level 3 PRA project:
Based on reference plant procedures, training, interviews, and walkdowns, as well a mini-E drill conducted by the reference plant in 2012 (i.e., very plant-specific)
Uses Gary Kleins naturalistic decision-making approach and concept of team 11
Post-Core-Damage Human Reliability Analysis (2 of 2)
Features of approach in Level 3 PRA project (cont.):
Detailed screening process performed by the Level 2 PRA lead that assessed expected plant conditions for each defined scenario to determine:
Which SAMG was the highest priority
Timing of SAMG entry, various plant conditions (e.g., vessel breach),
environmental concerns (e.g., habitability), equipment availability and survivability, etc.
Formal HRA including:
Human failure event definition
Feasibility assessment
Qualitative analysis
Quantification
Separate quantification decision trees for diagnosis and execution that assess information availability, quality of procedure support, etc.
12
Parametric Uncertainty
For the Level 3 PRA project, parameter uncertainties were propagated through the linked Level 1 and Level 2 PRA models using a Monte Carlo approach.
For Level 3 PRA, only meteorological data was sampled.
State-of-knowledge-correlation between event probabilities was accounted for in the quantification.
An error factor threshold was applied throughout the L3PRA project for basic events with very high failure probabilities to avoid excessive discarding of samples.
The threshold values are intended to preserve the mean value and anchor the 95th percentile to a probability of approximately 0.95.
The range of the output distribution (95th/5th) for all hazard categories is relatively tight, ranging between approximately 4 and 14.
Complementary cumulative distribution function (CCDF) curves that illustrate the uncertainty in the frequencies of each risk metric are provided in the Level 3 PRA reports.
13
Modeling Uncertainty (1 of 3)
To address modeling uncertainty in the Level 3 PRA project, key assumptions were identified for each PRA model.
The impact of these key assumptions on the results was assessed through engineering judgment.
To the extent practical, sensitivity analyses were performed for those assumptions believed to be most important to the results.
The key assumptions that were not subjected to sensitivity analysis were identified as candidates for future research.
One area of uncertainty (ISLOCA frequencies) was addressed through expert elicitation.
For some reports, modeling uncertainty is addressed in a dedicated report section or appendix (e.g., Volume 3c, Appendix C); in other cases, it is addressed in multiple subsections (e.g.,
Volume 3d, Section 3).
14
Modeling Uncertainty (2 of 3)
Examples of modeling uncertainties addressed by sensitivity analysis:
Severe accident analysis progression time - Reducing analysis time from 7 days to 2 days does not impact LERF or early fatality risk, but significantly reduces LRF and latent cancer fatality risk
Credit for post-core-damage operator actions during an SBO and after vessel breach - Does not impact LERF, but significantly reduces LRF (greatest reduction in LRF occurs from recoveries related to controlling containment pressure, with additional benefit seen if this is combined with controlling combustion)
Low dose cancer risk estimation - Use of a low dose truncation model (as opposed to the LNT model) significantly reduces latent cancer fatality risk
Seismic impacts on evacuation modeling - Early fatality risk from seismic scenarios is highly sensitive to the assumptions regarding evacuation delays and shielding factors; only limited impact on latent cancer fatality risk 15
Modeling Uncertainty (3 of 3)
Examples of modeling uncertainties recommended as candidates for future research:
Further investigate treatment of equipment survivability and instrument degradation in severe accident environments
Better characterize containment failure path (e.g., nature of failure, location, and size)
Better characterize possible seismic containment failure modes, particularly regarding the size of the leak path involved in seismic isolation failure
Examine influence of decontamination plan (levels and unit costs) on dose and cost results
Examine effect of updated methodologies for developing shielding factors when current research is completed
Investigate effect of MACCS modeling of intermediate-and recovery-phase relocation and habitability decision-making 16
Reactor At-Power PRA Road Maps
The Level 3 PRA project will ultimately consist of approximately 20 reports.
Each report contains detailed discussions of important technical issues, assumptions, modeling uncertainties, sensitivity analyses, and candidates for future work.
Due to the sheer volume of information, these discussions are often provided in multiple report sections.
The final summary NUREG report will attempt to gather and organize some of this information.
17
18 Back-Up Viewgraphs
19 2020-FLEX Case Results Level 1 PRA (1 of 4)
CDF by Hazard Category Hazard Category Circa-2012 CDF
(/rcy) 2020-FLEX CDF
(/rcy)
CDF Reduction Internal events and floods 6.47E-05 2.67E-05 59%
Internal fires 6.14E-05 5.34E-05 13%
Seismic events 1.08E-05 8.49E-06 21%
High winds 1.38E-05 4.85E-06 65%
Total 1.51E-04 9.34E-05 38%
20 Level 2 PRA Results (All Hazards Combined)
Level 2 PRA Surrogate Risk Metric Time at which airborne radiological releases are terminated 7 days after event initiation SAMG entry +
60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> SAMG entry +
36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> LERF 1.9E-06/rcy 1.9E-06/rcy 1.9E-06/rcy LRF 1.1E-04/rcy 3.5E-05/rcy 3.5E-05/rcy CCFP 0.680 0.620 0.235 Level 2 PRA Surrogate Risk Metric Time at which airborne radiological releases are terminated 7 days after event initiation SAMG entry +
60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> SAMG entry +
36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> LERF 1.3E-06/rcy 1.3E-06/rcy 1.3E-06/rcy LRF 6.7E-05/rcy 2.6E-05/rcy 2.6E-05/rcy CCFP 0.764 0.679 0.309 Circa-2012 Case 2020-FLEX Case
21 Level 3 PRA Results (1 of 3)
IEIF: internal events and floods F:
internal fires S:
seismic events W:
high winds ALL: all hazards combined
22 Level 3 PRA Results (2 of 3)
IEIF: internal events and floods F:
internal fires S:
seismic events W:
high winds ALL: all hazards combined
23 Level 3 PRA Results (3 of 3)
Accident truncation - airborne radiological release termination time reduced from 7 days after accident initiation to 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> after SAMG entry
Dose truncation - changed from linear no-threshold (LNT) to model based on Health Physics Society position paper, Radiation Risk in Perspective: Position Statement of the Health Physics Society (PS010-2), 2010
Additional Reactor At-Power PRA Preliminary Insights (1 of 2)
Significant risk contributors to offsite public risk metrics related to early health effects:
Failures of RHR system components leading to ISLOCA (primarily for internal events)
Random or hazard-induced failures and operator errors leading to SBO that progresses to core damage and TI-SGTR given high-dry-low conditions 24
Significant risk contributors to offsite public risk metrics other than those related to early health effects:
Events related to combustion (detonations or deflagrations) within containment Failure of manual extension of TDAFW during SBO Random or hazard-induced failures and operator errors leading to SBO Other operator errors from both the Level 1 and Level 2 PRA models 25 Additional Reactor At-Power PRA Preliminary Insights (2 of 2)
Acronyms and Definitions (1 of 2) 26 ATWS anticipated transient without scram CCDF complementary cumulative distribution function CCFP conditional containment failure probability CDF core damage frequency EDMG extensive damage mitigation guideline EOP emergency operating procedure HRA human reliability analysis ISLOCA interfacing systems loss-of-coolant accident L3PRA Level 3 PRA (project)
LERF large early release frequency LNT linear no-threshold LPSD low power and shutdown LRF large release frequency MACCS MELCOR Accident Consequence Code System PI-SGTR pressure-induced steam generator tube rupture PRA probabilistic risk assessment QHO quantitative health objective RHR residual heat removal RCY reactor-critical-year
Acronyms and Definitions (2 of 2) 27 SAMG severe accident management guideline SBO station blackout SFP spent fuel pool SGTR steam generator tube rupture TDAFW turbine-driven auxiliary feedwater TI-SGTR temperature-induced steam generator tube rupture