ML24198A132
| ML24198A132 | |
| Person / Time | |
|---|---|
| Issue date: | 06/25/2024 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | |
| References | |
| NRC-2914 | |
| Download: ML24198A132 (1) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
Advisory Committee on Reactor Safeguards Fuels, Materials, and Structures Subcommittee Open Session Docket Number:
(n/a)
Location:
teleconference Date:
Tuesday, June 25,2024 Work Order No.:
NRC-2914 Pages 1-121 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1716 14th Street, N.W.
Washington, D.C. 20009 (202) 234-4433
NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
(202) 234-4433 WASHINGTON, D.C. 20005-3701 www.nealrgross.com 1
1 2
3 DISCLAIMER 4
5 6
UNITED STATES NUCLEAR REGULATORY COMMISSIONS 7
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 8
9 10 The contents of this transcript of the 11 proceeding of the United States Nuclear Regulatory 12 Commission Advisory Committee on Reactor Safeguards, 13 as reported herein, is a record of the discussions 14 recorded at the meeting.
15 16 This transcript has not been reviewed, 17 corrected, and edited, and it may contain 18 inaccuracies.
19 20 21 22 23
1 UNITED STATES OF AMERICA 1
NUCLEAR REGULATORY COMMISSION 2
+ + + + +
3 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 4
(ACRS) 5
+ + + + +
6 FUELS, MATERIALS, AND STRUCTURES SUBCOMMITTEE 7
+ + + + +
8 OPEN SESSION 9
+ + + + +
10 TUESDAY 11 JUNE 25, 2024 12
+ + + + +
13 The Subcommittee met via Video-14 Teleconference, at 10:00 a.m. EDT, Ronald G.
15 Ballinger, Chair, presiding.
16 SUBCOMMITTEE MEMBERS:
17 RONALD G. BALLINGER, Chair 18 VICKI M. BIER, Member 19 VESNA B. DIMITRIJEVIC, Member 20 GREGORY H. HALNON, Member 21 CRAIG HARRINGTON, Member 22 WALTER L. KIRCHNER, Member 23 ROBERT MARTIN, Member 24 DAVID A. PETTI, Member 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
2 THOMAS ROBERTS, Member 1
MATTHEW W. SUNSERI, Member 2
3 ACRS CONSULTANT:
4 DENNIS BLEY 5
7 DESIGNATED FEDERAL OFFICIAL:
10 ALSO PRESENT:
11 MARKUS BURKARDT, EPRI 12 NATHAN GLUNT, EPRI 13 STORM KAUFFMAN, MPR Associates 14 FRED SMITH, EPRI 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
3 P-R-O-C-E-E-D-I-N-G-S 1
10:00 a.m.
2 CHAIR BALLINGER: This meeting will now 3
come to order.
4 This is a meeting of the Advisory 5
Committee on Reactor Safeguards, Fuels, Materials, and 6
Structures Subcommittee.
7 I'm Ron Ballinger, Subcommittee Chair for 8
this meeting. Members in attendance are Tom Roberts, 9
Dave Petti, Bob Martin. Greg Halnon is on the Metro 10 on his way. We have a number of people on the remote, 11 not the least of which, let's see if I can get 12 everybody.
13 I know Craig Harrington is on the line.
14 Most of the people in here will recognize that he's a 15 new member, will recognize that name from EPRI.
16 Who else? Vesna Dimitrijevic, Vicki Bier.
17 Walt is not on; probably will be.
18 MEMBER KIRCHNER: I'm here, Ron.
19 CHAIR BALLINGER: Okay, got it.
20 Who else? Well, I'm sure I've missed 21 somebody. Well, our consultants, Dennis Bley and 22 Stephen Schultz, are also either here online. And, 23 again, I probably missed somebody, but they'll correct 24 me.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
4 This is an information briefing.
1 EPRI, I'll say a little bit later, has 2
submitted three topical -- three reports that are 3
under review currently by the staff. And they all are 4
related to what's called the ultimate licensing 5
strategy. And the reports aren't out. I don't need 6
to name them.
7 The ACRS was established by statute and is 8
governed by the Federal Advisory Committee Act, FACA.
9 The NRC implements FACA in accordance with its 10 regulations found in Title 10 of the Code of Federal 11 Regulations, Part 7.
12 This committee can only speak through its 13 published letter reports. We hold meetings to gather 14 information and preform preparatory work that will 15 support our deliberations at a full committee meeting.
16 The rules for participation at all ACRS 17 meetings were announced in the Federal Register on 18 June the 13th, 2019. The ACRS section of the U.S. NRC 19 public website provides our charter, bylaws, agendas, 20 letter reports, and full committee transcripts of both 21 the full and subcommittee meetings, including slides 22 presented there.
23 The agenda for this meeting was posted 24 there. A portion of this meeting may be closed to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
5 protect EPRI proprietary information pursuant to 5 USC 1
662(c)(b)(C)(4).
2 As stated in the Federal Register notice 3
and in the public meeting notice posted on the 4
website, members of the public who desire to provide 5
or oral input to the subcommittee may do so and should 6
contact the Designated Federal Officer, who happens to 7
be Christopher Brown. A communications channel has 8
been opened to allow members of the public to monitor 9
the open portions of the meeting.
10 The ACRS now invites members of the public 11 to use the Teams link to view slides and other 12 discussion materials during these open sessions. We 13 have not received any requests to make oral statements 14 from the public regarding today's meeting.
15 Written comments may be forwarded to 16 Christopher Brown, today's DFO. There'll be an 17 opportunity for public comments and we have set aside 18 ten minutes in the agenda for comments for members of 19 the public during the meeting.
20 So, why are we have this meeting? There's 21 an ongoing rulemaking to increase -- to allow 22 increased enrichment. One of the directives from the 23 Commission, as part of that rulemaking effort -- he 24 made it, Greg Halnon is now here.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
6 One of the requirements of that rulemaking 1
was that fuel -- FFRD, fuel fragmentation, relocation, 2
and dispersal, be addressed as part of that.
3 There's a Technical Basis Document that 4
was produced that we have reviewed and a significant 5
part of that Technical Basis Document was not present 6
because there were comments related to so called 7
Option 5 which dealt with ALS. That's the acronym 8
that we'll use for that. And these documents are 9
related to that Option 5 and so called ALS.
10 I might add that we have come a very long 11 way. Some of us are old enough to remember that, in 12 the early days, we used regulation and defense-in-13 depth much to our benefit. Appendix K covered an 14 awful lot of things that we didn't know about.
15 You might recall that during the Second 16 World War, the Liberty Ships decided that they'd use 17 welding. And we lost as many welded Liberty Ships due 18 to brittle fracture as we did the torpedoes, almost.
19 And that resulted, ultimately, in what amounts to 20 Section 11 of the ASME boiler and pressure vessel 21 code.
22 So, inspection and repair -- excuse me --
23 inspection and repair in Section 11 has largely been 24 derived because of our industry and efforts related to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
7 safety. Appendix K was the same way.
1 Our materials choices back in those days 2
were made based on the best available information. I 3
might add that Alloy 600 for steam generators, its 4
major use before the nuclear side was in the dairy 5
industry.
6 And so, we chose Alloy 600 and we have --
7 Section 11 has saved us a lot because of those 8
materials choices.
9 So, all during this time for the last 20 10 years, much research has been ongoing related to 11 inspection and repair and materials choices and 12 prediction of materials behavior.
13 The ALS effort which includes inspection 14 and repair, fracture mechanics, all kinds of the 15 technology and data that's been generated all this 16 time, the ALS is almost a product of that long 17 standing effort.
18 So, we're about to embark on what amounts 19 of a revolution, and not an evolution, in the way we 20 do things regarding inspection and repair and 21 materials behavior.
22 I might add, by the way, that Craig 23 Harrington has recused himself for obvious reasons 24 from this. He's online, but he can't participate in 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
8 our deliberations.
1 So, with all of that rumination, who's 2
going to go first? Fred, the floor is yours.
3 MR. SMITH: Thank you. Fred Smith from 4
EPRI.
5 So, I'm going to go over an overview of 6
ALS, highlight a few features, and then, we'll have 7
deep dive or deeper dive into different reports as we 8
go through the day.
9 So, as you mentioned, there are three 10 reports that compose the topical report. The one in 11 the center, which is a leak-before-break credit. It's 12 a compendium of the others. It pulls them all 13 together.
14 It also addresses several topics that are 15 not addressed in either the fracture mechanics or the 16 LOCA analysis. I'll walk through briefly the content 17 of each of these reports.
18 One thing I want to point out is, in the 19 increased enrichment rulemaking, there was a proposal 20 that ALS be modified to convert large-break LOCA from 21 a design basis event to a beyond-design-basis.
22 And we -- the industry took exception to 23 that because we felt that like, while maybe have some 24 merit, would really extend the period for review, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
9 complicate the review, and isn't necessary for -- to 1
deal with FFRD.
2 So, any actions along that line separate 3
and apart from this submittal.
4 CHAIR BALLINGER: I don't know about the 5
other folks here, but I'm having a little trouble 6
hearing you. Can you get a little closer to the mic?
7 MR. SMITH: Okay.
8 So, is that a little better?
9 CHAIR BALLINGER: Thank you.
10 MR. SMITH: Yes, sorry about that.
11 So, in the leak-before-break, there are 12 several key elements. And we'll talk about one is a 13 section on safety benefits. I won't go through all 14 the details on the safety benefits, but they derive 15 from three general areas.
16 The use of high enrichment, high burnup, 17 is a much more efficient utilization of uranium. And 18 so, the entire fuel cycle gets shrunk by the use of 19 high enrichment, high burn-up. And so, that means 20 that the front end has less mining impact, less 21 transportation
- impact, and the fabrication is 22 particularly impacted.
23 You know, the burnup increase is about a 24 20 percent increase. And so, the fuel insert 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
10 fractions would be expected to be reduced by about 20 1
percent. And that means that on the back end, the 2
high level waste discharge going forward would be 3
reduced commensurate.
4 And so, there are a number of benefits 5
associated with that, fewer dry cask loading 6
campaigns, fewer casks on the pad, and then, 7
ultimately, less transportation to a repository once 8
one is developed and approved.
9 Overall, you know, the industry today is 10 undergoing a very healthy growth period. When we 11 started this, that was not necessarily the case and we 12 hope it continues. But the economic benefits of the 13 higher burnup and enrichment are sufficient that could 14 make a difference in plants deciding to terminate 15 their license early.
16 And so, that means that this supports 17 international and national goals for low carbon 18 emissions. While it's not necessarily an NRC 19 directive, it is a national directive, I believe.
20
- Also, the question subjects are 21 complicated and there are relatively few experts in 22 many of these areas. And particularly the dispersion 23 area, there's a lot of research necessary to 24 understand and address that.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
11 The ALS approach eliminates dispersion.
1 So, that eliminates the demand on those resources, 2
both from an industry and for the Commission.
3 So, there's several pages in the report 4
discussing safety benefits. I just wanted to 5
highlight them here today.
6 The discussion on regulatory guidance, 7
particularly about the history of leak-before-break.
8 And while we don't suppose to enter into what the 9
staff might choose to incorporate in new regulations, 10 it obviously has an impact on the overall 11 implementation of this topical.
12 There's a policy about leak-before-break 13 and we would expect that that would be updated. And 14
- then, whatever downstream regulatory or other 15 documents needed to be adjusted, we would be watching 16 carefully with the staff as they finish the rulemaking 17 process.
18 We will talk about defense-in-depth near 19 the end of the day today, different perspectives on 20 that, but we have included defense-in-depth mostly for 21
- all, in
- fact, all but one leak-before-break 22 application that we reviewed did not address defense-23 in-depth, but we chose to do so as part of this.
24 And then, we talk about methodology and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
12 the overall leak-before-break topic. So, the report 1
summarized just results from the LOCA analysis report 2
on the piping rupture results.
3 This is for large, intermediate break, and 4
small break. Also, it evaluates the non-piping 5
ruptures. It does not do a LOCA analysis as such, but 6
it goes back and reviews the design basis for these 7
kinds of non-piping components.
8 And just to confirm that there's no 9
unexpected issues associated with them.
10 And
- then, there's the summary and 11 conclusion section where we discuss the limitations of 12 the analysis.
13 The first implementation of this is 14 modular and it does -- it is applied directly to 15 Westinghouse NSSS configurations with Westinghouse 16 fuel is intended to be extendable with the 17 supplemental analysis so that other NSSS 18 configurations can apply it.
19 There are several that are interested in 20 it. Other vendors can apply it and other fuel designs 21 can it. And we have several people interested. And 22 I think Paul Clifford is here from Framatome and if 23 you would like to say a few words about your company's 24 view?
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
13 MR. CLIFFORD: This is Paul Clifford, 1
Framatome. Yes, even though we don't have a 2
presentation, don't take that as to be a lack of 3
interest or support for the EPRI ALS.
4 Framatome fully supports this robust 5
technical and regulatory solution to fuel dispersal 6
and we will work with our customers on a means to 7
adopt it similar to the pilot program that 8
Westinghouse is going to be presenting today.
9 And we will be closely monitoring the 10 staff's review to really understand the areas of 11 difficultly, the areas of concern with the staff, and 12 any limitations and conditions that the staff may 13 impose on the approval of these three reports.
14 And we will be adapting our methods to not 15 only address those areas, but also, we will be closely 16 monitoring the rulemaking to understand the extent to 17 which risk would be allowed to be credited in the 18 implementation of new LOCA methods, including LOCA 19 methods that will be used to show compliance or to 20 show implementation of the ALS.
21 Thank you very much.
22 MR. SMITH: So, while not every utility 23 will elect to extend their burnup limits, not everyone 24 has the same operational impact of the burnup limits.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
14 Some have margin that they can use to 1
achieve their other goals. We believe ALS can apply 2
to every PWR in the country that elects to do so. And 3
we're not here to talk about a BWR version, but EPRI 4
is working on elements for BWRs as well.
5 So, the fracture mechanics report, as I'm 6
sure you all know, the xPLRs are jointly developed.
7 Probabilistic fracture mechanics analysis developed 8
jointly by the NRC and EPRI.
9 And so, we will talk about the analysis 10 and how it applies to this application. The report 11 will -- I will warn you, the report is fairly 12 comprehensive in that it does have cases that are not 13 directly applicable to ALS.
14 So, it has smaller diameter piping, for 15 example. And those are clearly annotated in the 16 report. We are only applying the xLPR results to main 17 cooling loop piping systems. But the report does and 18 is comprehensive and covers a wide range of piping 19 configurations.
20 There's a discussion on benchmark and 21 validation comparison to 1829 as a figure of merit.
22 And one of the key results for ALS is the time between 23 a leak -- detectible leakage and a LOCA.
24 And so, we credit that as part of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
15 justification that operator response would be well 1
inside that envelope and a LOCA would be included 2
based on that operator response.
3 There's discussion on the degradation 4
models that are in xLPR and why they apply to the 5
application that's being used, and then, conclusions, 6
of course.
7 And then, finally, Westinghouse has done 8
a significant amount of LOCA work to support this.
9 They've looked at all of their NSSS configurations and 10 fuel types that we believe will be -- will most likely 11 implement the soonest.
And so, there's a
12 comprehensive discussion on that analysis.
13 So, limitations and conditions in the end 14 of the report. And then plant-specific requirements 15 for implementing the LOCA analysis.
16 And just -- while it's not part of this 17 submittal there is a reference that has been accepted 18 for review that updates the Westinghouse LOCA 19 methodology is also under review.
20 DR.
SCHULTZ:
- Fred, one question 21 association with application to other facilities.
22 You mentioned BWR and Paul talked about 23 Framatome. What about combustion engineering plants 24 and B&W plants? Is that something that the utilities 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
16 are going to need to address or does EPRI have that in 1
their forward plans -- forward looking plans?
2 MR. SMITH: There's been, particularly, 3
the CE digital plants, what I call the CE digital 4
plants, the large plants, there's a lot of interest 5
there.
6 And we believe that that will occur, 7
whether EPRI sponsors it or the vendors in conjunction 8
with the individual utility sponsor it. The number of 9
utilities -- the number of plants of that nature is 10 fairly limited.
11 DR. SCHULTZ: Would it move into the 12 owners groups, then? The PWR owners group, for 13 example?
14 MR. SMITH: It could. We haven't gone 15 that far to decide how to do it. But there are really 16 only five plants like that in the U.S. and three of 17 those plants are probably not that interested.
18 DR. SCHULTZ: Thank you.
19 CHAIR BALLINGER: Is there international 20 interest in this?
21 MR. SMITH: There's a lot of international 22 discussion about it. But the world is different in 23 different places. Right?
24 So, the fuel costs and the back end costs 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
17 are very different than the United States. And so, 1
annual cycles are -- have been more the norm.
2 One of the main drivers in the U.S. is the 3
PWRs into 24-month cycles. And while our engagement 4
with international members have said they are looking 5
at perhaps increasing their cycling, no one has yet 6
said we're ready to go to 24-month cycles except the 7
UAE.
8 CHAIR BALLINGER: I was going to say, 9
there are a number of CE like plants.
10 MR. SMITH: Yes, that's right, that's 11 right. So --
12 MEMBER PETTI: And how about Korea? Is 13 there any --
14 MR. SMITH: Yes, yes.
15 MEMBER PETTI: That's what I mean, 16 specifically.
17 MR. SMITH: Korea?
18 MEMBER PETTI: Yes.
19 MR. SMITH: We have -- we speak with them, 20 we meet with them twice a year and they are very 21 interested in what we're doing. But they haven't 22 committed to doing anything yet.
23 MEMBER PETTI: So, is if fair to 24 characterize it as, you know, there's a lot of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
18 interest. But from a licensing perspective, the U.S.
1 is leading and people are watching?
2 MR. SMITH: That's right, that's right.
3 PARTICIPANT: Well, I should add that, in 4
2014, ASN in France did redefine LOCA to follow TBS 5
transition break size and everything above that.
6 So, I'm not sure U.S. is leading per se, 7
I think what I see here is certainly the use of leak-8 before-break to strengthen the argument in the U.S. I 9
think is significant.
10 So, certainly looking forward to seeing 11 what you have to say there. It might put some meat on 12 the bone where it probably needs to be.
13 MEMBER PETTI: I just -- I know you guys 14 are going to get into the details. It would be 15 helpful to talk a little bit about what topical listed 16 fractured mechanics is on the record so people don't 17 it's voodoo, you know, sort of stuff.
18 You know, what's the industry coming up 19 with now? You know, give us that perspective.
20 MR. SMITH: Yes, I think we --
21 MEMBER PETTI: I'm sure your next 22 presentation will cover that.
23 MR. SMITH: So, I'll turn this over to 24 Markus or Nathan, okay.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
19 MR. GLUNT: Perfect segue to that one, 1
thank you. So, I'm Nate Glunt. I am from EPRI's 2
Material Reliability Program.
3 I'll be starting off this presentation and 4
then passing it over to Markus here, Markus Burkardt 5
from Dominion Engineering. He worked with us on the 6
XLPR work. And so, we'll be presenting on the xLPR 7
probabilistic fracture mechanics analysis specifically 8
for ALS.
9 As Fred mentioned, our analysis does 10 include other line sizes other than ALS, what ALS is 11 concerned about, but we'll just focus on ALS.
12 So, first of all, the outline, as I said, 13 I'll take everyone through the background. I'll talk 14 a little bit about xLPR and where we've used it. And 15 then turn things over to Markus for the scope. And 16 then he'll go through the summary of xLPR analysis 17 cases and get into those key results that I know you 18 all are really interested in. And then we'll finally 19 finish off with some conclusions.
20 So, we do piping and fracture mechanics, 21 so we have our own whole list of acronyms. And fuels 22 has their own list of acronyms. I'm sure you all with 23 your specialties have your own as well. So, we did 24 include this list of acronyms here at the beginning so 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
20 if anyone needs to refer back to, please feel free.
1 I'm pretty sure you all know what ACRS 2
means. That's the first one on there. But please 3
feel free to refer back. We know it can be quite 4
confusing at times.
5 CHAIR BALLINGER: What makes you so sure?
6 (Laughter.)
7 MR. GLUNT: One more back, Fred. One 8
more?
9 MR. SMITH: Backwards?
10 MR. GLUNT: Yes. So, this is actually our 11 sixth time meeting in this building or the other 12 building, I guess, to discuss xLPR and how it could be 13 used for ALS.
14 So, we have the ML numbers, if anyone's 15 interested in those other presentations. A notable 16 one is just over a year ago. This was also presented, 17 of course, to ACRS before. So, keeping track of those 18 and just making sure everyone's aware of that.
19 So, now, we'll get more into the 20 background and scope. And Fred stole my thunder a 21 little bit before.
22 You know, xLPR is what we consider a state 23 of the art probabilistic fracture mechanics code. But 24 we do consider it state of the art, because we have 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
21 benchmarked it with probabilistic fracture mechanics 1
codes from all over the world.
2 What's unique is that it was jointly 3
developed by EPRI, specifically, MRP, but it involved 4
dozens and dozens of folks and NRC Research. And so, 5
it's the industry working together with the regulators 6
to solve a problem.
7 The code itself is specific for nuclear 8
power plant piping. And it's -- the most important 9
aspect of it, it gives you the ability to 10 quantitatively analyze risks in piping.
11 When we speak about risk in piping, we're 12 generally speaking about leakage, possibly rupture.
13 But with the code, you can look at the probability of 14 initiation of cracks in the first place and their 15 growth. And so, risk is whatever you define it to be.
16 There's thousands of outputs from the code.
17 Now, the code has been used in a few 18 select areas already. Most notably, the NRC and EPRI 19 worked together on analyzing the impact of primary 20 water stress corrosion cracking on leak-before-break 21 analyses.
22 This forms the basis for a lot of what 23 we're going to discuss here today as well. And so, 24 that is -- I consider it a separate project, of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
22 course, from ALS. It's totally separate. But we use 1
a significant amount of what we've learned there in 2
those analyses in our ALS work.
3 So, what xLPR is, it's not voodoo. So, 4
it's fairly simple from a high level. Once you get 5
into the inner workings of the code, it's very 6
complex, of course. But what we have with xLPR is 7
essentially a
probabilistic structure or a
8 probabilistic wrapper.
9 So, all of the -- there's thousands of 10 inputs that can go into the code. And the vast 11 majority of them, you can define as distributions.
12 So, you have a distribution of material 13 properties, crack behavior, loads. So, you can -- the 14 user chooses which inputs you want to define as a 15 distribution. The code then samples and works through 16 time-stepping before sending everything to a
17 deterministic fracture model.
18 The deterministic fracture model is 19 actually a set of different deterministic models that 20 make up crack growth. So, you have crack initiation.
21 Then you go into growth, transitioning that crack 22 through wall, through-wall growth, and, finally, 23 failure or rupture of the piping.
24 There's also deterministic modules on 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
23 leakage rates, in-service inspection, crack opening 1
displacements.
2 So, the heart of xLPR is these series of 3
deterministic models. We just have a probabilistic 4
wrapper around it. But for a case, the user goes in 5
and defines their input set. You can choose whether 6
your inputs are constant or distributions.
7 The code samples the distributions for one 8
single case, sends it to the deterministic models and 9
you get an output. And the code starts again, sample 10 again, run through the deterministic model, and you 11 get an output.
12 By the end, you do this tens of thousands 13 or hundreds of thousands of times and you have your 14 statistical analysis at the end. You have your 15 probabilistic fracture mechanics analysis. And so, 16 you're just running many times through deterministic 17 models by sampling what you put into them.
18 CHAIR BALLINGER: This may come later, but 19 all of all the distributions, which one is the 20 broadest? So, which model has the most uncertainty?
21 MR. BURKARDT: Maybe leak rate. I was 22 going to say crack growth rate. Crack growth rate 23 equations have a distribution that varies out towards 24 the magnitude and crack growth rate. And likewise, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
24 crack initiation will still have --
1 CHAIR BALLINGER: I thought were going to 2
say initiation.
3 MR. BURKARDT: Well, both have, you know, 4
multiple orders of magnitude of variation within the 5
input distributions. And so, you can get situations 6
where you have cracks initiating very early and 7
growing very quickly.
8 And also, ones where cracks, you know, 9
initiate very late and grow very slowly, too. But 10 that also accurately represents the level of 11 variability that's in these materials as well.
12 And then there's substantial, you know, 13 variability that's, you know, partially due to 14 microstructure or other processing of the materials 15 that influences the cracks, you know, susceptibility 16 to PWSCC crack initiation or to crack growth.
17 And rather than trying to model those 18 microstructural details, those are then, you know, 19 basically captured by having a distribution on inputs 20 associated with the crack growth or crack initiation 21 models.
22 MR. GLUNT: Yes, and we have several 23 different initiation models as well.
24 MEMBER KIRCHNER: Ron, this is Walt. A 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
25 corollary kind of question would be, do you find -- or 1
maybe you're going to come to this -- do any of these, 2
starting with the probabilistic inputs, does any one 3
of those that you show here in this diagram dominate?
4 MR. GLUNT: It depends on the type of 5
analysis. We find that welding residual stresses for 6
have a significant impact, of course, with primary 7
water stress corrosion cracking.
8 I mean, that generally dominates. And so, 9
we look at -- the xLPR group has done a significant 10 amount on the investigation into welding residual 11 stresses for these weld types.
12 MEMBER KIRCHNER: So, if I may follow up, 13 then, is that an issue that --
14 CHAIR BALLINGER: Excuse me, Vicki.
15 MEMBER BIER: Go ahead with the follow-up 16 and then I'll ask mine.
17 MEMBER KIRCHNER: My follow-up would be, 18 do you find this mostly at vessel to piping welds?
19 MR. GLUNT: So, the welding residual 20 stress analyses that we have cover a number of 21 different welds. So, the reactor vessel, nozzle to 22 piping welds are significant.
23 But also, you know, we have done analyses 24 for other lines with pressurizer, of course, that's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
26 below the limitations that we're looking at here. But 1
even the steam generator has similar metal welds, 2
we've investigated as well.
3 So, it's very particular to the design of 4
the weld. And so, there's a lot of sensitivity 5
analyses that have been done throughout the xLPR work 6
on the welding residual stress analysis.
7 CHAIR BALLINGER: So, I'm to assume that 8
the weld residual stress issue has been dealt with for 9
years and years and years. And there are various --
10 all your acronyms have MSIP and all that kind of 11 stuff. Does xLPR account for the fact that a weld may 12 have been dispositioned in some way?
13 MR. GLUNT: You're one slide ahead. So, 14 on the next slide, I'll discuss that.
15 CHAIR BALLINGER: Okay.
16 Oh, Vicki?
17 MEMBER BIER: So, before we get to the 18 next slide, I'll ask my question which is, you have 19 the fracture mechanics model being totally 20 deterministic, which I understand.
21 And in generally known certainty analysis, 22 there can be a wide range of how much uncertainty 23 there is in the model itself.
24 You know, some analyses may be the, you 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
27 know, it really is just a matter of physics and all of 1
the uncertainty is coming from the input parameters, 2
other fields like climate change, for example, there 3
can be different communities of scholars with 4
different models and the model on uncertainty itself 5
can be a big factor in the output.
6 So, I guess two questions. One is, where 7
in that spectrum do you place your model, you know, 8
are there a lot of modeling assumptions that are not 9
reflected in your parameter uncertainty?
10 And second of all, just was there any 11 attempt made to quantify or estimate the extent of 12 model uncertainty?
13 MR. BURKARDT: So, I'll get to the 14 treatment of uncertainty within xLPR for the different 15 models and also the overall assessment in just a 16 couple of slides.
17 But just kind of really quick preview of 18 that, the models are intended to be, you know, best 19 estimate type models with best estimate type inputs 20 consistent with the probabilistic approach.
21 And, you know, by having xLPR developed by 22 both, you know, NRC and industry on a collaborative 23 basis, you know, we made sure to include, you know, 24 all the subject matter experts in the various areas 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
28 associated with each of the individuals models that 1
were included within xLPR.
2 And also, had, you know, development and 3
review from both sides just to ensure that, you know, 4
everyone agreed that, yes, those are, in fact, the 5
best estimate models to be included.
6 MEMBER BIER: Okay, thanks.
7 MEMBER HALNON: So, I wanted to follow up 8
along the same themes, and so, I listened to you talk 9
and Nathan are describing the user experience with the 10 code and having this freedom to describe the 11 uncertainties, the probability distributions functions 12 of various parameters, it seems to me that this would 13 be data driven, correct?
14 So, is the database or those sort of 15 things that rich that we have the latitude to allow 16 users to do anything they want with that information?
17 I mean, how easy is it to generate the 18 kind of data that would otherwise supply a code like 19 xLPR?
20 You know, I think of safety, a capital S 21 in doing these kind of analysis, you know, you have to 22 have pretty strict criteria on what, you know, the 23 sources of information feeds the codes.
24 Is it really that much information out 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
29 there to deviate from, you know, some established set 1
based on R&D that's been done already? And isn't it 2
very expensive to go out and make the data that would 3
otherwise feed a code like this?
4 MR. GLUNT: So, Markus is ready to jump 5
all over this one, but I'll start with, you know, 6
through -- yes, the code does allow you to select what 7
you want. And the code is powerful and it is built 8
for these special circumstances where you want to look 9
at a very specific welding residual stress or a 10 material properties one, you can do that.
11 However, the code also does come with 12 standard properties already built in, database is 13 full, thousands of pages of inputs already prepared by 14 the industry and NRC together to select what we do 15 consider the best estimates.
16 So, while the code can, and you can use it 17 as you see fit, it can do all these different 18 properties or whatnot. We do also provide what we 19 consider the best estimates of the majority of the 20 inputs.
21 MEMBER HALNON: Best estimates with, you 22 know, best estimates like probability distribution 23 functions or two best estimates -- we use the word 24 best estimate when you are referring to a
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
30 probabilistic input, it's a little confusing.
1 MR.
GLUNT:
That's best estimate 2
distribution.
3 MEMBER HALNON: Thank you.
4 CHAIR BALLINGER: Member Harrington, 5
within the limitations of your conflict of interest?
6 MEMBER HARRINGTON: Absolutely. I'm in an 7
awkward place here. I would just like for Nate and 8
Markus to speak to the uncertainty report in regard to 9
Vicki's question.
10 MR. GLUNT: Yes, that's coming up in the 11 presentation.
12 MEMBER HARRINGTON: Thank you.
13 MR. GLUNT: Continuing moving on, as I 14 said, some of these questions will be asked in the 15 slides and what's coming up next.
16 So, more about what the xLPR code actually 17 has. So, as we said, it's for nuclear power plant 18 piping, specifically, it is for piping butt welds.
19 And it can analyze either dissimilar metal or similar 20 metal welds with crack orientation being either axial, 21 circumferential, or it can actually do both at the 22 same time.
23 And it can also analyze multiple cracks 24 around the circumference for a circumferential, for 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
31 instance.
1 So, it's not limited to just a single 2
crack, it's whatever the user puts in or the models 3
initiate. The cracks that we do analyze are shown to 4
the right in the middle, I'm not sure how to explain 5
that, but we do have the ability to analyze a surface 6
crack.
7 So, after either initiation or the user 8
inputs a crack themselves, we have a surface crack 9
which then grows until it reaches 95 percent through-10 wall, becomes a transitioning through-wall crack that 11 defined more like a trapezoidal shape.
12 And then, finally, we grow directly into 13 an idealized through-wall crack into continue to grow 14 around the circumference.
15 So, we really start from crack initiation 16 until it goes through-wall all the way around to 17 failure.
18 And when we talk about initiation, we can 19 have the crack initiate either by stress corrosion 20 cracking, fatigue, or both, or we can actually have 21 the user input whatever situation they want with 22 cracks, multiple fracture on the surface, a single, 23 that's up the user as well.
24 Crack growth is the same. You can look at 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
32 stress corrosion cracking, fatigue, or both combined.
1 And then we do have the ability to look at mitigation.
2 So, we have built into the code, inlay, onlay, 3
overlay.
4 We can include mechanical stress 5
improvement process, so MSIP, through changing 6
evolving residual stresses at whatever point in time 7
you choose. And then chemical mitigation.
8 Now, a lot of the results that we're going 9
to speak about today do not necessarily include 10 mitigation because once you mitigate, we found that 11 it's extremely effective.
12 If you change the welding residual 13 stresses, the crack growth is going to stop. And 14 that's the point of it and that's -- we're very happy 15 to see that in the analysis. But it is part of it, so 16 there were cases run with different mitigation 17 strategies included as well.
18 And then the last two points I think are 19 extremely important and they're going to lead into 20 what Markus is going to discuss later.
21 We have the ability to include in-service 22 inspection and we also have the ability to include 23 leakage detection and how that impacts the results.
24 And I won't get into that too much now 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
33 because you will directly see that in some of the 1
results that Markus will show later.
2 MEMBER HALNON: And as you read through 3
all these different capabilities, and it struck me 4
that it's almost the V.C. Summer crack exactly. Did 5
you lay over that operating experience with this?
6 MR. GLUNT: Yes, the V.C. Summer, the 7
stresses were directly used in early benchmarking.
8 MEMBER HALNON: And it showed good 9
results?
10 MR. GLUNT: It did. I actually worked at 11 V.C. Summer before coming to EPRI. And so, when I 12 started on xLPR, that's the first case I ran.
13 MEMBER HALNON: And we may have run across 14 each other because I was the guy that fixed it.
15 MR. GLUNT: Oh, there you go. Yes, we 16 have, outside of ALS as part of the xLPR program 17
- overall, it was benchmarked against unknown 18 circumstances.
19 CHAIR BALLINGER: By implication of what 20 Greg's and your comment, the -- you can deal with a 21 complex residual stress pattern as you go through the 22 wall?
23 MR. GLUNT: Yes, you can. Yes, the 24 welding residual stress pattern is defined as 24, 26 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
34 points through the wall. And so, you can get very 1
complex and there's the ability of the code to 2
actually sample that as well if you choose to do so.
3 So, it can look at very complex stresses.
4 So, we've talked a lot about the inputs and what it 5
looks like going into xLPR. This slide does a very 6
brief discussion of what the results look like coming 7
out of xLPR.
8 Now, again, this is overly simplified 9
because you can pull out intermediate results 10 throughout, but the easiest results to pull out, of 11 course, are the probabilities of first crack, first 12 leak, and rupture which is shown over here to the 13 right just as an example.
14 You can also pull out individual crack 15 results. So, when we talk about type, it's whether 16 it's surface, transitioning, or idealized through-17 wall, the position around the circumference, leak 18 rates associated with it, and then, of course, the 19 growth, so the stress intensity factors that go with 20 it.
21 The number of cracks is tracked along with 22 the probability of non-repair and the stability 23 ratios. That's all easy to get out of the code.
24 And then, finally, we'll talk a lot about 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
35 leakage here today. So, you can pull leak rates from 1
individual flaws or the total from all flaws.
2 And to your point earlier, you asked about 3
mitigation, this is just an example for demonstration 4
purposes, but that figure there to the right does show 5
mitigation after 49 years. And you can see what the 6
impact of mitigation and ISI have on the analysis as 7
well.
8 CHAIR BALLINGER: I'm a gearhead in this, 9
so you'll have to bear with me. Does it handle 10 multiple initiation, multiple crack initiations which 11 then coalesce?
12 MR. BURKARDT: It does, yes.
13 CHAIR BALLINGER: Because that's typically 14 what we see.
15 MR. GLUNT: Coalescence is a lot of -- it 16 is a big part of xLPR. But for some of the analyses, 17 we just started with very long flaws to already get 18 past the coalescence point, so very long flaws 19 representative of multiple flaws coalescing as well.
20 MEMBER HALNON: And that's axial and 21 circumferential?
22 MR. GLUNT: They don't combine together, 23 they individually, you can.
24 MR. BURKARDT: So, we can model multiple 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
36 crack initiation of axial flaws, multiple crack 1
initiation of circumferential flaws.
2 We allow multiple circumferential flaws to 3
coalesce into larger circumferential flaws. But given 4
that multiple axial flaws are out of plane of each 5
other, we don't allow for those to coalesce with each 6
other.
7 And we also don't treat coalescence of 8
axial and circumferential flaws into some off axis 9
sort of scenario, either.
10 CHAIR BALLINGER: I'm thinking of what's 11 been happening in France with their multiple 12 initiation, residual stress, thermally induced stuff.
13 MR. GLUNT: Yes, yes, we do have the 14 ability to coalesce flaws and we have looked at that 15 as well.
16 MEMBER ROBERTS: I'm just trying to go 17 back to the -- just trying to understand how to 18 interpret the red and the blue and the, you know, like 19 in 20 years, the red and the blue are on top of each 20 other. And then the blue takes off before the red 21 does.
22 So, I would assume the blue take off 23 before the red is the leak-before-break. How do you 24 interpret when the red and the blue lines are on top 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
37 of each other?
1 MR. GLUNT: For those cases, so, this 2
output is -- I'm sorry, it's a little jagged, it's for 3
demonstration purposes.
4 You don't have a significant number of 5
leaking cracks in this case. And so, each time you 6
see a jump, it's essentially another leaking crack or 7
another crack leaking or going to rupture.
8 And so, these are cases when they've sort 9
of caught up to each other.
10 MR. BURKARDT: You do also still see that 11 the blue line corresponding to leakage is to the left 12 of the red line corresponding to rupture. So, that 13 shows, you know, leak prior to rupture.
14 But, yes, as Nate pointed out, if the 15 probabilities are equal, that means that all of the 16 cracks that have leaked have then, at that point, also 17 ruptured as well. And so, that's what he meant with 18 the one catching up to the other.
19 MEMBER ROBERTS: So, is there any meaning 20 to the very left hand part of that curve, the 20 to 25 21 years or so where they just start on top of each 22 other?
23 MR. BURKARDT: So, what I'm saying is, at 24 that point, the blue line starts prior to the red line 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
38 starting.
1 So, the meaning there is that the first 2
crack that leaks, leaks for a couple of years from, 3
you know, say, 20, 24 to 27 years and then, it 4
ruptures at 27 years.
5 Then, you get the second crack that leaks 6
at 30 years, the second crack ruptures at 32 years.
7 MEMBER ROBERTS: Okay, thanks. So, 8
somewhere to the left of this curve, they would have 9
diverged? Is that when the red would have been 10 approximately zero at some point before the blue comes 11 on scale?
12 MR. BURKARDT: That's correct, yes, 13 they're all, you know, zero prior to that 1 minus 4 14 number.
15 MEMBER ROBERTS: Okay, thanks.
16 MR. GLUNT: Now, I'll turn everything over 17 to Markus to walk you through some of the quality 18 assurance that we discussed. And then through more 19 details of the xLPR analysis.
20 MR. BURKARDT: Thank you, Nate. So, yes, 21 so, xLPR, we developed under a very rigorous quality 22 assurance program. And that quality assurance program 23 was designed to use selected elements of ASME NQA 24 2008 as well as NQA-2008-1a-2009 Addenda, both of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
39 which are endorsed for meeting NRC's 10 CFR 50, 1
Appendix B quality assurance requirements.
2 xLPR program has very extensive technical 3
documentation with over 100 reports issued supporting 4
documentation of the individual modules as well as the 5
framework.
6 There's also very extensive verification 7
and validation that we performed for the xLPR code 8
with over 4,000 verification tests performed.
9 And for each individual module as well as 10 the overall software being validated against operating 11 experience, finite element analysis simulations and 12 also other probabilistic fracture mechanics codes.
13 And so, the details of the quality 14 assurance now is applied as part of the xLPR 15 development process is documented in what we call like 16 the top level report which is NUREG-2247.
17 As part of the development process also, 18 we had an external review board that, you know, 19 reviewed and provided input on, you know, the overall 20 development approach.
21 Since then, xLPR is actually currently 22 going through a global PFM benchmark that's being sort 23 of jointly organized by the OECD, NEA, and CSNI.
24 And so far, this benchmark has found that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
40 xLPR represents a state of practice in terms of PFM 1
modeling capabilities.
2 This is an international benchmark with 14 3
different PFM codes all around the world that are 4
being used to model various different deterministic 5
and also probabilistic problems as part of the overall 6
benchmark.
7 There have been several conference 8
publications on this word and the final benchmark 9
report is expected to be published later this year.
10 All right, so on the -- go back, please, 11 there we go. So, the right one, yes, thank you. To 12 the uncertainty slide, please. Thank you.
13 All right, so the topic that everyone 14 wants to hear about, uncertainty. So, first, I just 15 wanted to talk about, you know, what we mean by 16 uncertainty.
17 And in this case, we're talking about the 18 knowledge of the knows and also the unknowns that 19 affect model predictions. And so, Nate mentioned that 20 we're using a probabilistic approach in the overall 21 assessment. And so, what we mean by this is we're 22 using best estimate models to describe a very complex 23 system. Each of these models are linked together and 24 integrated.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
41 So, what we then do is, we quantify the 1
uncertainties in the inputs, reduce them as best as we 2
can to get best estimate uncertainties that accurately 3
reflect the range of variation of that given input.
4 And then, account for the uncertainties by 5
propagating them forward through each model using the 6
Monte Carlo method.
7 So, with random sampling and then, working 8
through a deterministic model, and then, aggregating 9
the overall results and
- then, characterizing 10 statistics on those overall results for each of the 11 individual samples that are then propagated through 12 that model.
13 Now, the xLPR program has an uncertainty 14 report which summarizes and consolidates information 15 on the sources of and also the treatment of 16 uncertainties within every single one of xLPRs 17 modules, crack initiation, crack growth, crack 18 coalescence, solutions, leak
- rate, in-service 19 inspection and so on.
20 And
- then, also within the overall 21 framework as well. And so, this table here just kind 22 of summarizes, you know, where certain details on that 23 treatment is included both in the uncertainty report 24 and also beyond that uncertainty report.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
42 But regarding descriptions of specific 1
uncertainties in the model reports, we speak to, you 2
know, uncertainties associated with the basic model 3
form that was selected.
4 The inputs that are, you know, the best 5
estimate inputs that are recommended as well as the 6
range of validity for those individual inputs.
7 We also assess individual assumptions that 8
were made as part of the model development.
9 And then, also, you know, summarized the 10 verification and validation efforts of those models.
11 And we discuss any sort of uncertainty that's included 12 or any sort of after uncertainty bias that the model 13 and the either conservative or non-conservative 14 direction.
15 And also, acknowledge that conservative 16 and non-conservative may change depending on what sort 17 of input you're -- or output you're considering.
18 We also speak to the limits of 19 applicability for the models and if any sort of 20 interpellation methods are applied and any acts 21 thereof.
22 Within the model validation reports, we 23 then also speak to any sort of model bias or 24 uncertainty relative to, you know, laboratory data, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
43 field data, data from, you know, alternate models or 1
from finite element analysis.
2 And then, in the scenario report, we then 3
also speak to uncertainty associated with sampling the 4
divergence of the results.
5 MEMBER HALNON: I just wanted to explore 6
the uncertainty and the leak rate aspect. Because 7
you're not just dealing with physics, you're dealing 8
with operator performance, quality of procedures, 9
historical ability of the plant, lots of different 10 things.
11 What is the baseline assumptions for leak 12 rate that gives you a reasonable uncertainty? Because 13 that could be huge. Well, you just -- well, let's 14 look at -- you just assume that it complies with the 15 Reg Guide 1.45 or --
16 MR. BURKARDT: No, that --
17 MEMBER HALNON: -- is that actually go 18 further?
19 MR. BURKARDT: So, for the leak rate, what 20 we do is, we -- based on crack size, we calculate a 21 crack opening displacement.
22 And then, you know, we basically calculate 23 a leak rate through a crack of that size with the 24 crack opening displacement at a given temperature and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
44 pressure.
1 MEMBER HALNON: Well, I get that that, you 2
know, you can over this or whatever you want to do, 3
but what about the detaching piece of it?
4 I mean, isn't that part of this is that 5
you're assuming that very little leak rates are going 6
to be detected, therefore, you have time?
7 MR. BURKARDT: So, in the xLPR analysis 8
what we basically report out in our report and on our 9
P480 is we assume a
one gallon per minute 10 detectability threshold for leaks. And then we also 11 quantify time from one-gallon per minute to a large-12 break LOCA.
13 MEMBER HALNON: Okay, so you didn't have 14 any uncertainty by being very conservative in how much 15 or how little --
16 MR. BURKARDT: Exactly.
17 MEMBER HALNON: -- that can be detected?
18 MR. BURKARDT: And so, then, Storm, in his 19 presentation will speak to the fact that, you know, 20 although that might be a number that plants commit to 21 in tech spec space, that in actuality, plants can 22 detect much, much smaller leak rates.
23 MEMBER HALNON: Right, and that's where 24 the variability comes from, that one PPMs well proven, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
45 so I get that, thanks.
1 MR. BURKARDT: And then, additionally, 2
xLPR also applies uncertainty to the calculated leak 3
rate as well, given that there's uncertainty in the 4
crack morphology that could impact the calculated leak 5
rates and applies that to leak rates below ten gallons 6
per minute.
7 DR. SCHULTZ: Markus, an administrative 8
question, the -- you described a very complex 9
development program for this computer code and this 10 development.
11 And many, many reports and a good QA 12 program from the outset that sounds very good to have 13 done. On the user side, how many users are involved 14 with the application of the code? What's the training 15 program associated with the use of the code? How is 16 that controlled?
17 MR. GLUNT: So, the code itself is 18 distributed by EPRI through an MOU with the NRC. And 19 it is publicly available to anyone. The code comes 20 with training documentation, significant documentation 21 on the theory behind it, practical exercises and 22 whatnot.
23 There's no dedicated training class to do 24 the code. We have gone internationally as well as 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
46 domestically to train folks who are interested in 1
doing a similar analysis to this.
2 But to be quite honest, the user base is 3
really generally EPRI, our contractors, NRC, their 4
contractors, and a few others throughout the world 5
that are trying things out.
6 So, it's publicly available. It's out 7
there for anyone. But we do provide -- it's a very 8
complex code. We provide as much as we possibly can 9
to train them and then, we're also always available 10 for questions and there's a specific xLPR@nrc emails 11 and xLPR@EPRI emails where we do get a lot of feedback 12 from folks and questions and work with them.
13 MR. BURKARDT: We have a user manual 14 that's like 150, 200 pages long and then, beyond that, 15 we have basically training material that's provided 16 that is sort of the equivalent of like six days of --
17 six full days of training lectures.
18 Both on detailed training regarding the 19 individual models that are included within the code as 20 well as how to interface with the inputs, interface 21 with the framework, how to run the code, and then, how 22 to, you know, extract and manipulate results.
23 DR. SCHULTZ: Is there a need for version 24 control of the code? In other words, are there 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
47 several versions out there as its been developed? We 1
hear results about applications, is it something we 2
need to pay attention to?
3 MR. GLUNT: Yes, within the MRP-480, so 4
there are several versions out there that are --
5 several versions during development when some of these 6
analyses were done.
7 And then, we've released two versions 8
since then and we're about to release another version 9
as well.
10 With MRP-480, we have an entire session 11 dedicated to the analysis of what are the differences 12 in the versions and do the versions potentially change 13 anything about the analysis?
14 So, we only have the latest available 15 through EPRI's distribution. So, we take down the old 16 ones and encourage people to get the latest and 17 greatest.
18 So, yes, there are slight differences in 19 the versions. But a lot of them are fixing well known 20 bugs or enhancing the user experience by adding new 21 capabilities to the code that makes it simpler or 22 faster to run.
23 MR. BURKARDT: And so, the general 24 recommendation is to, you know, apply the lasted 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
48 release version of xLPR code to --
1 DR. SCHULTZ: So, there's not a user's 2
group that you know how the users are?
3 MR. GLUNT: Yes, every user has to -- or 4
the NRC actually has requirements.
5 We have to have everybody sign an end user 6
license agreement, provide their country of origin, 7
all that stuff to it because there are limitations on 8
who can receive the code. So, we do track all that.
9 DR. SCHULTZ: Very good, thank you.
10 MR. BURKARDT: So on the topic of 11 uncertainty quantification propagation, there's just 12 a couple more items. In the inputs group report which 13 is thousands of pages long, we document the 14 recommended distributions on various inputs and 15 parameters for I think 33 different sample cases, 16 basically three different components and 11 scenarios 17 that you might want to analyze for those components.
18 And in the different module subgroup reports, again 19 defining recommended distributions for input model 20 parameters, and in the scenario analysis report 21 discussing sampling strategies that are applied. So 22 just very comprehensive discussion of all, you know, 23 aspects of uncertainty for all of the details that go 24 into every single input and model within the code.
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49 MEMBER PETTI: Just a question about your 1
validation test matrix, you know, there are people who 2
make their living on this sort of stuff and making 3
sure that all the modules are actively interrogated 4
through the validation test matrix, so that you make 5
sure you've got a validation case for stress corrosion 6
cracking, thermal fatigue, all the pieces of the code 7
get accurately exercised by a validation case. Is 8
that, I mean is your validation data broad and deep 9
enough to be able to make a statement like that?
10 MR. BURKHARDT: Yeah, so each individual 11 model has its own validation report where basically 12 with any available data that module is then validated, 13 and in the absence of data, looking at alternative 14 models, looking at results from finite element 15 analysis, and if none of those were available, then in 16 a couple of cases we did have to do some validation 17 using expert judgement, but in general trying to lean 18 as heavily as possible on validation with you know, 19 either field or test data or alternative models.
20 CHAIR BALLINGER: Dennis?
21 DR. BLEY: Yeah, this is Dennis Bley.
22 Just a historical question, lots and lots of years ago 23 when NRC was doing its work on fracture mechanics they 24 had Oak Ridge developing a probabilistic fracture 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
50 mechanics code which was kind of interesting as we 1
went week to week in working with them how things 2
jumped around. Is this an extension of that work or 3
is this done completely separate from that?
4 MR. BURKARDT: Are you referring to the 5
FAVOR code, Dennis?
6 DR. BLEY: Huh, you're testing my memory 7
now. I think that's right.
8 MR. BURKHARDT: This is yeah, unrelated to 9
the FAVOR code, they're both probabilistic fracture 10 mechanic codes but with pretty different applications.
11 I think Oak Ridge was involved in some of the xLPR 12 development process, particularly in the leak rate 13 calculation aspect, they developed the LEAPOR module, 14 and so that was their involvement there, but I think 15 yeah, different from the FAVOR code.
16 DR. BLEY: Okay, thanks.
17 CHAIR BALLINGER: Is FAVOR pressure vessel 18 related?
19 MR. BURKARDT: Yeah, FAVOR is pressure 20 vessel related.
21 DR. BLEY: Yeah, that's right.
22 MR. BURKARDT: You know, similar metal 23 levels in piping. So now we've talked about xLPR and 24 Fred introduced the ALS overall, so how do the two fit 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
51 together? So NUREG-1829 is a NUREG report that 1
estimates loss-of-coolant accident frequencies, and in 2
this case, the LOCA frequencies were estimated through 3
an expert elicitation process. That report was 4
developed a number of years ago now as part of an 5
evaluation of the technical adequacy of redefining the 6
design basis break size, which is the largest pipe 7
break to which 10 CFR Part 50.46 applies to a smaller 8
size.
9 And so as part of the ALS research work 10 for FFRD, we applied xLPR to validate the NUREG-1829 11 LOCA frequency estimates for use in this high-burnup 12 fuel licensing effort, and then also to evaluate the 13 potential for leakage as a precursor to a LOCA rupture 14 to be detected in a sufficient amount of time to allow 15 for a reactor shutdown and to reduce decay heat levels 16 before that LOCA rupture would potentially occur. And 17 so as Fred noted, this work is published in MRP-480 18 which was published earlier this year, the document 19 tells the gory details of this work.
20 So NUREG-1829 gives LOCA frequency 21 estimates based on expert elicitation approach, and 22 those are provided, the results that we'll be 23 comparing against, are the ones in Table 1 of that 24 report. And so in addition to that, 1829 considered 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
52 LOCA-sensitive piping systems that are associated, and 1
their associated degradation mechanisms. Now the xLPR 2
scope for the ALS is focused on piping welds greater 3
than NPS 14, and so really what this means is that 4
we're focused on the main loop piping components with 5
these xLPR analyses, and so I'll be focusing on 6
discussion specific to those here today. And so kind 7
of in these tables, and then in later portions of the 8
presentation kind of use like a blue box to indicate 9
those. Now, although the focus of today's discussion 10 is on the main loop piping welds, MRP-480 does 11 document further analyses for a range of other piping 12 systems that are covered in NUREG-1829 as well.
13 So the xLPR analysis cases that we 14 considered here, they were developed to apply primary 15 water stress erosion cracking and/or fatigue, as the 16 material degradation mechanisms that were explicitly 17 modeled. NUREG-1829 does consider additional material 18 degradation mechanisms not included in xLPR, and in 19 MRP-480 we reviewed those and dispositioned any such 20 other degradation mechanisms and really identified 21 that the PWSCC mechanism, which we assessed here was 22 kind of the primary mechanism of concern and therefore 23 the mechanism of focus in our assessment.
24 We either modeled flaws that were present 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
53 at the start of the simulation, basically instantiated 1
at time zero modeled as flaws of engineering scale 2
with initial size of a couple millimeters, such that 3
fracture mechanic principles apply, or we also 4
considered cases where we used the initiation models 5
for both PWSCC and fatigue to calculate the time to 6
flaw initiation and to allow also the potential for 7
multiple flaw initiation. We then performed an 8
extensive set of sensitivity studies to determine the 9
impact of changes to certain key analysis inputs with 10 these sensitivity studies modeling different input 11 selections for various parameters such as the 12 geometry, loading, welding residual stress profiles, 13 initial flaw sizes, or also seismic effects.
14 In this work as Nate kind of alluded to, 15 we considered the results of recent NRCE technical 16 letter reports documenting analyses that were 17 developed to look at the leak-before-break issue in 18 dissimilar metal piping butt welds in PWR plants. And 19 so there were two technical letter reports that came 20 out of this work. In that joint work, NRCE research 21 and EPRI worked together to develop the overall case 22 matrix, but then these reports reflect NRCE and their 23 contractors own input selection and also then their 24 own conclusions that they drew from those analyses 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
54 that were performed.
1 And so these two reports, you know, we 2
consider as part of the work, the kind of term, the 3
first one, the piping system analysis report, which 4
documented xLPR analysis for reactor vessel outlet 5
nozzles and reactor vessel inlet nozzles in a 6
Westinghouse four-loop PWR, and this report really 7
included a very extensive set of sensitivity studies, 8
as this was one of the earlier uses of the code, in 9
probing a lot of different aspects of the code and its 10 models. And the xLPR generalization study report, the 11 second report, and took the learnings from the piping 12 system analysis and extended that to other piping 13 systems that contained alloy 2182 dissimilar metal 14 butt welds that are received prior leak-before-break 15 approvals from the NRC staff on a deterministic basis.
16 And so this report then included a slightly reduced 17 set of sensitivity studies for analyzed component, as 18 was informed by the results of the piping system 19 analysis, so here we really focused on the key 20 sensitivity studies that we noted were more driving of 21 the results as found in the piping system analysis.
22 So Nate touched on the results that you 23 can get from xLPR, so there's a couple of particular 24 interest for the ALS that I'll be reporting on here 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
55 today. One is the time between one gallon per minute 1
detectable leakage and rupture of a large-break LOCA, 2
in this case large-break LOCA we're characterizing as 3
5,000 gallons per minute. Another is the probability 4
of rupture conditional on crack initiation. Now I 5
mentioned some of the cases we model using the initial 6
flaw model rather than explicitly modeling crack 7
initiation, and so there you already have flaws in 8
every single realization at time zero.
9 In order to consider those results also 10 for the comparison to NUREG-1829, we take those 11 probabilities of rupture, given an initial flaw, and 12 then scale those by the probability of initiation at 13 80 years to approximate the probability of rupture 14 conditional on initiation. And we document some 15 benchmarking in MRP-480 assessing the impacts of this 16 sort of approximation, and so we found that the two 17 approaches were within a factor of about 2.5 of each 18 other. And then the final output that we discuss as 19 well is the 80 year rupture LOCA frequency, in which 20 case we calculate this from the probability of rupture 21 80 years by then dividing that by 80 years as well.
22 So we have a question from Walt?
23 MR. KIRCHNER: Yes, thank you. Thanks, 24 Ron. In your sensitivity studies, did you look at 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
56 stress levels that you might see in a safe shutdown 1
earthquake load on these critical areas that you 2
identified of key interest? Like the example of both 3
the outlet and inlet nozzle welds and such, did you 4
look at the stresses that you might see for the safe 5
shutdown earthquake kind of loads that might -- lead 6
to a larger break LOCA in the piping systems?
7 MR. BURKARDT: Yeah, I believe for the 8
reactor vessel outlet nozzle we had some sensitivity 9
studies that looked at both loading and frequency 10 associated with safe shutdown earthquakes, and changes 11 to those inputs.
12 CHAIR BALLINGER: I've got a question, 13 it's been gnawing at me when I saw 82, 182, it made me 14 realize it. All of these welds that are less than, 15 what, four inches, have been required to be 16 dispositioned in some way, right? Am I correct? In 17 other words stress improvement, some kind of thing has 18 had to be done for these welds, not the least of which 19 is to get the welds out and use 52 and 152.
20 MR. GLUNT: Right, or inspect them more 21 frequently.
22 CHAIR BALLINGER: Or inspect them more --
23 so how many welds does what we're talking about, how 24 many of the welds are there that this actually applies 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
57 to?
1 MR. GLUNT: This is only the reactor 2
vessel, the reactor vessel nozzles, steam generator 3
nozzles, this is all --
4 CHAIR BALLINGER: Those have all been 5
dispositioned.
6 MR. BURKARDT: So we have a figure 7
actually in MRP-280, it's Figure 4-2, and so there we 8
look at the number of dissimilar metal welds and their 9
current status based on their cold leg temperature, 10 hot leg temperature or pressurizer temperature. And 11 so for all of the operating plants, all pressurizer 12 temperature welds have been mitigated either using 13 overlayer MSIP. The hot leg, large majority of them 14 have been mitigated as well --
15 MR. GLUNT: But not all --
16 MR. BURKARDT: But not all, and then at 17 the cold leg, actually, there's a decent number that 18 have been unmitigated, but given that PWSCC is a 19 thermally activated process, it progresses the 20 disease, so to say, progresses more slowly at that 21 colder temperature.
22 MR. GLUNT: So as significant amount of 23 the hot leg, of course, as he just said are mitigated, 24 those that are not mitigated are still inspected per 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
58 Code Case N-770 more frequently than other components, 1
and so if they're not mitigated they're managed.
2 CHAIR BALLINGER: Are any of these results 3
likely to affect the ten-year ISI? The code 4
requirement?
5 MR. GLUNT: For the mitigated? Because 6
the unmitigated hot leg is only five years.
7 CHAIR BALLINGER: Five years, okay.
8 MR. GLUNT: Yes, yes.
9 MR. BURKARDT: Yeah, and for many of these 10 cases we actually modeled the xLPR analysis, body of 11 xLPR analysis case is considered models inspections 12 every ten years, even though inspections per N-770 are 13 more frequent, such as the five years for the hot leg, 14 as Nate noted.
15 MR. GLUNT: So yeah, any relaxation should 16 not have an impact on these results.
17 DR. SCHULTZ: But we're not talking here 18 about industry programs that may be related to 19 extending the inspection frequency? Assuming that in 20 this case the industry would be committing to 21 retaining inspection frequency, is that correct?
22 MR. GLUNT: Or analyzing any impact of 23 relaxing in inspection frequency. As Markus says, 24 it's the unmitigated hot legs from N-770 is inspection 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
59 every five years, we modeled every ten years, based on 1
my probabilistic fracture mechanics, or based on my 2
deterministic fracture mechanics experience, it'd be 3
tough to ever get to ten years, so I don't think we 4
would be challenged by that in reality, because --
5 DR. SCHULTZ: You modeled it for 10 years 6
as a conservatism?
7 MR. GLUNT: That's correct. So we --
8 DR. SCHULTZ: How much impact does that 9
make? Or you'll show that?
10 MR. BURKARDT: It's not shown here 11 explicitly, but it's a substantial impact given that 12 at hot leg temperatures, crack growth rates can be 13 fairly quick, and you can have flaws just below the 14 detectability limit grow through all in you know, 15 under ten years, but the five year interval is 16 designed to help manage that and detect those flaws 17 prior to --
18 DR. SCHULTZ: So you do it not as a 19 conservatism, but a demonstration as to what the 20 difference would mean?
21 MR. BURKARDT: Yeah and I believe there's 22 also a sensitivity study in the piping system analysis 23 work that looks at the impact of changing the 24 inspection frequency as well from five to ten years, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
60 so that's explicitly modeled in --
1 CHAIR BALLINGER: But N-770 resets the 2
clock on some of the distributions to zero, right?
3 Doesn't change the initiation time, but it just, if 4
your inspection is designed to detect flaws or detect 5
defects every five years, then the five years, that's 6
time zero on the initial flaw, but not the initiation 7
time, so how does that work?
8 MR. BURKARDT: So inspection within xLPR 9
is handled sort of as a post-processing and inspection 10 is also, rather than being handled on just a 11 deterministic yes, no type of inspection, you're 12 calculating a probability of detection as a function 13 of the depth of the flaw, and then that corresponds to 14 probability of non-repair and basically model the 15 evolution of the flaw within xLPR assuming not 16 inspections, no leak rate detection, and then after 17 the fact you basically assess the impact that you 18 would have from either an in-service inspection or 19 leak rate detection on those results.
20 CHAIR BALLINGER: I'm just trying to 21 understand the effect on ALS of inspections, and it's 22 significant, I think.
23 MR. BURKARDT: Yes, it is, and we'll show 24 the impact of inspections versus no inspections.
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61 CHAIR BALLINGER: I see the reports, but 1
I'm just thinking of the overall concept of ALS as it 2
applies to the whole process of increased enrichment.
3 MR. BURKARDT: So diving into the 4
comparison to NUREG-1829, I just first wanted to 5
provide a little bit of context on the NUREG-1829 LOCA 6
frequencies that I'll be showing on the next slide.
7 As noted, those were based on expert elicitation and 8
from those Table 1 results which show a median fifth 9
and 95th percentile included from Table 1, and so 10 those are total PWR LOCA frequencies after 11 overconfidence adjustment using an error-factor scheme 12 and our 40 year fleet average values. These 13 considered the typical in-service inspection and leak 14 rate detection resolution as required by tech spec 15 limits as part of that expert elicitation process.
16 Those results are also presented on a per-plant basis 17 for each of the distinct LOCA categories, and consider 18 both piping and non-piping passive system 19 contributions.
20 So then here we're showing the xLPR LOCA 21 frequency results for 80 years, and those are shown 22 with the various different points on each of these 23 charts, and I'll kind of speak through what each of 24 them mean. On the left are the results where we 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
62 credit leak rate detection but do not credit in-1 service inspection, and when leak rate detection alone 2
is credited, the majority of the results are actually 3
zero, but you know, we wanted to still consider those 4
results overall in this comparison to NUREG-1829. So 5
what we did is we developed a 95% upper bound based on 6
a one-sided confidence interval using a binomial 7
distribution. And this then considered the number of 8
realizations that were run for a specific xLPR 9
analysis case as well as the probability of initiation 10 for cases that were modeling the initial flaw model 11 rather than modeling probability of initiation 12 explicitly. And so those are shown in the green open 13 circles with the downward pointing arrows, with the 14 downward pointing arrow implying that if more 15 realizations were
- run, that you
- know, those 16 probabilities would be even lower.
17 Now there are three cases which did have 18 explicit ruptures with leak rate detection, and so 19 those are shown explicitly with the yellow circles.
20 But those three cases are all due to modeling that, 21 you know, we looked into it and see that modeling not 22 representative of plant conditions and operations, and 23 it's common, and in a similar manner in the technical 24 letter reports which initially performed those 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
63 analyses, those cases are situations like where the 1
overlay application caused a rupture, or the initial 2
flaw was deeper than the inlay depth, resulting in 3
atypical flaw geometries that xLPR really isn't 4
capable of handling. All of those cases were also 5
sensitivity cases, and then as relevant to ALS, you 6
know we investigated those further, including the 7
implications thereof.
8 Now the figure on the right, we then --
9 that shows what the results would look like if you 10 additionally credit in-service inspection and as we 11 noted those are corresponding to the 10-year in-12 service inspections which are actually less frequent 13 than as required for these types of components. And 14 so then when you consider both in-service inspection 15 and leak rate detection, the LOCA frequency results 16 that are estimated by xLPR are in a similar order of 17 magnitude as the median NUREG-1829 LOCA frequency 18 estimate. So further validates the LOCA frequency 19 estimates from 1829 for application in the ALS work.
20 So then another key output is the time 21 between detectable leakage and large-break LOCA. And 22 so just to kind of help unpack what this output is and 23 what it means and how we're considering it, I'd first 24 like to kind of give an example of what this means for 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
64 single xLPR realizations, so one, we'd just have one 1
set of inputs that's then propagated through the xLPR 2
model before we have the many, many realizations for 3
a given case, and then the many different cases for 4
different welds that we look at. And so this is 5
really fundamentally a deterministic problem, where 6
we're evaluating the evolution of a flaw growth from 7
a part through-wall flaw to a transitioning through-8 wall flaw, and then an idealized through-wall flaw.
9 And so then in the chart, on the top right 10 here, you see the leak rate as a function of time, and 11 we're calculating this leak rate based on flaw size 12 and parameters as discussed earlier. And so you see 13 that the leak rate starts, and in this case it 14 actually starts leaking at a leak rate just below on 15 gallon per minute, then we reach a one gallon per 16 minute threshold, in like 24 and a half years, 17 continues leaking, transitions from a transitioning 18 through-wall flaw, trapezoidal flaw, to an idealized 19 through-wall flaw, and then continuous leaking as it 20 grows, and then eventually a large-break LOCA and 21 rupture then occurs in 31 and a half years.
22 And so when we're talking about the time 23 from detectable leakage to large-break LOCA, those are 24 the two time points that we're considering, and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
65 calculating the difference in times between those for 1
a given realization. And so that's something that can 2
only be calculated for realizations that result in a 3
large-break LOCA or a rupture. In this case since 4
we're looking at time between detectable leakage and 5
large-break LOCA, it's for all realizations that have 6
a large-break LOCA.
7 MR. GLUNT: And, obviously, for these 8
cases you cannot have leak rate detection or ISI on 9
for the component. You have to wipe those away for 10 the sake of just getting results, because if you have 11 leak rate detection on, you're obviously not getting 12 anything, so.
13 MR. BURKARDT: So this is more to, you 14 know, we assess the potential for LOCAs with leak rate 15 detection in-service inspection in the comparison to 16 NUREG-1829, but then to better characterize what the 17 time from detectable leakage to LOCA would be, 18 assuming no inspections and assuming no leak rate 19 detection, you just start up your plant and run it for 20 80 years and look away the entire time, you know, 21 that's really what we're trying to characterize here.
22 MEMBER HALNON: Well, I get this, I mean, 23 you're just telling everybody don't worry about it, 24 it's going to take over five years to have a real bad 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
66 problem. I mean 100 gallons a minute is a bad 1
problem, but clearly within the capability of the 2
plant to deal with. And I realize this is not a pipe, 3
but it was so -- fracture mechanics done for the 4
Davis-Besse head event that caused additional 5
problems, some of the mechanics that it could go as 6
fast as 12 weeks before it ruptured.
7 Am I to take away from that, as an 8
uninformed and very ignorant fracture mechanics guy 9
that there's a lot of variability in the assumption, 10 such that this is only one result that could occur, 11 that there could be some that are quite more 12 catastrophic and quicker?
13 MR. BURKARDT: Yes, so this is just an 14 illustrative example realization, I just picked one 15 where you can kind of see the nice progression, and 16 then we'll speak more to the specific results for the 17 full population of xLPR analyses up next.
18 MEMBER HALNON: So we'll get more detail 19 this afternoon?
20 MR. BURKARDT: We'll get into more detail 21 in the next 30 minutes.
22 MEMBER HALNON: Oh, okay.
23 CHAIR BALLINGER: I think we -- this is 24 impossible, right? We do have leak detection, we do 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
67 have inspections, and so for an uninformed member of 1
the public to read this bothers me, because this is 2
impossible, but you wonder sometimes --
3 MR. BURKARDT: So the basis for us really 4
doing this --
5 CHAIR BALLINGER: I know why you're doing 6
this, I'm just saying, this is your PhD against my 7
PhD.
8 MR. GLUNT: But we're really trying to 9
look into it whether, you know, we're not turning a 10 blind eye to it for five years. The goal of this in 11 the first place was to see if we had sufficient time 12 to shut down the reactor and remove enough decay heat 13 so that we would not experience an FFRD.
14
- Now, what they need for that is 15 significantly less than this, so all we can do is 16 produce the statistics to show if it were worst case 17 scenario, what would that actually look like? Even 18 though we know that shutting down the reactor itself 19 will remove the stresses that would likely cause the 20 rupture, so we're removing the impetus behind any 21 rupture in the first place, but it just feeds into the 22 defense and depth of ALS itself.
23 MR. BURKARDT: So Storm will speak to 24 detectability of leak rates in plants and time that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
68 operators need to shut down the plant, and then this 1
is kind of input to that discussion, as it feeds into 2
ALS.
3 MR. SMITH: In your summary, don't you 4
characterize the probability of when you credit leak 5
rate detection and --
6 MR. BURKARDT: Yes.
7 MR.
SMITH:
- Yeah, and that 8
characterization is what?
9 MEMBER KIRCHNER: To Ron's point on this 10 view graph, what would be a typical tech spec for leak 11 detection and hence shutdown of the plant and 12 inspection of where the source of the leak is? How 13 many gallons per minute?
14 MR. GLUNT: For pressure boundary leakage 15 there is no allowable, the allowable is zero. You 16 find it, you shut it down and fix it. Traditional 17 leak-before-break uses generally one gallon per 18 minute, because that is the tech spec limit for 19 unidentified leakage, so it's conservative. So yes --
20 MEMBER KIRCHNER: Would it be useful to 21 put that -- some dotted line on this diagram to 22 indicate that this would be an unacceptable operating 23 condition?
24 MR. BURKARDT: Yes, it would be useful to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
69 include in this FAVOR.
1 MEMBER ROBERTS: Can you speak to the 2
second to last bullet, the ore seismic effects? So 3
the other three I think you turned off, or it would 4
help the story, but doing seismic effects would worsen 5
it?
6 MR. BURKARDT: So it would, now seismic 7
effects are more considered in the rupture 8
calculations for xLPR, when it's a safe-shutdown 9
earthquake and it doesn't feed directly into the leak 10 rate calculation. What the generalization study does 11 consider is when it calculates probability of rupture 12 and also time between detectable leakage and rupture, 13 it considers the seismic loads on a non-probabilistic 14 basis and every one month time step, in basically more 15 and more conservatively assessing when the rupture 16 would occur, assuming that whatever the seismic loads 17 are would occur every time step rather than just at 18 whatever the input earthquake's frequency is.
19 MEMBER ROBERTS: So on this curve, the 20 vertical part would move to the left, presumably?
21 MR. BURKARDT: As I mentioned, it's not 22 tied to the leak rate calculation, but if anything, 23 like if for the rupture time, it would maybe, you 24 know, the time on the right would shift to the left 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
70 just slightly, where this curve ends. Yeah, but we 1
didn't see a big impact in the cases where we did look 2
at that.
3 CHAIR BALLINGER: But if you had a safe-4 shutdown earthquake or even a design-basis earthquake, 5
the plant would be shut down, that's a onetime event 6
and they would re-inspect everything.
7 MR. BURKARDT: Yes.
8 CHAIR BALLINGER: So the clock gets reset 9
to zero again.
10 MR. BURKARDT: Yes.
11 MR. GLUNT: We find that we reset the 12 clock a lot on this, to be quite honest, and so that's 13 the problem.
14 CHAIR BALLINGER: Somebody ought to say 15 that.
16 MR. GLUNT: Yes, we are having to look at 17 cases that are highly, highly, incredibly improbable, 18 for the sake of having any results at all, because if 19 we came in here and honestly said well it already has 20 deterministic leak-before-break, so we know it's not 21 going to, that's not enough. We're trying to add the 22 meat on the bone as we said earlier.
23 MEMBER ROBERTS: Did you use NUREG-1903 in 24 your benchmarking?
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
71 MR. BURKARDT: I'm not sure that I'm 1
familiar with NUREG-1903.
2 MEMBER ROBERTS: That was the adjunct 3
study -- for the 1829 was still valid for seismic 4
- loads, called Seismic Considerations for the 5
Transition Break Size. His conclusion was that the 6
seismic spectrum wouldn't really effect the results 7
from 1829, but it also talks about a lot uncertainties 8
in that, I was wondering if you'd look to that and 9
concluded that that conclusion was still valid based 10 on what you'd done. Your response to Walt's question 11 I think basically said yes, but I was just wondering 12 if you'd looked at that study.
13 MR. BURKARDT: Yeah, I don't know if I 14 looked at 1903 too closely, Storm, did you in your 15 investment?
16 MR. KAUFFMAN: I would need to take that 17 as a look-up. I looked at a lot of references. 1903 18 sounds familiar, I don't remember what I got out of 19 it.
20 MEMBER ROBERTS: Okay, thank you.
21 MR. BURKARDT: So that was kind of the 22 picture for one individual realization. Now within a 23 single xLPR analysis case, remember we ran multiple 24 cases for given welds and then cases for multiple 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
72 different welds. Basically within one case you run, 1
you know, at least 10,000 or up to several hundred 2
thousand realizations, you may then have multiple 3
realizations that then have a large-break LOCA. And 4
so then what we did is we characterized the 5
distribution of times from detectable leakage, one 6
gallon per minute detectable leakage to a large-break 7
LOCA for that individual case. And so this figure 8
just kind of illustrates what that looks like for one 9
such case.
10 As Nate pointed out, for these points to 11 even exist, we need to not credit in-service 12 inspection or leak rate detection which is 13 unrealistic, right, but again, we're just trying to 14 conservatively assess what this time would look like 15 if for some reason your in-service inspection or leak 16 rate detection were ineffective. And so then yeah, we 17 considered the distribution of results for each of 18 these analyses as part of the overall assessment of 19 the time between detectable leakage and large-break 20 LOCA for each analyzed component. We then used these 21 distributions for each individual case as a sort of 22 screening exercise, basically looking at the most 23 limiting cases for further review, so we really 24 understand what's happening in those more limiting 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
73 cases.
1 I mentioned we performed some further 2
investigation, both of the three point that have non 3
zero occurrence of rupture with leak detection is 4
those three yellow points on the comparison to NUREG-5 1829 figure, as well as for the cases that have 6
minimum times, so of all of the realization that had 7
large-break LOCA, the very most limiting ones of 8
those, if the time between detectable leakage and 9
rupture was less than three months we looked into 10 those in more detail also to better understand them.
11 All of these cases that we looked into further were 12 sensitivity studies, and they were defined to inform 13 the understanding of the base case results by 14 investigating inputs that were known to have influence 15 in the overall xLPR results, but they were also less 16 constrained by maintaining fidelity to realistic plant 17 conditions as well.
18 And so then in these re-investigations, 19 you know, kind of depending on the case, in some cases 20 we re-ran those with refined time-stepping to better 21 understand what's happening, and in other cases 22 considered updated input model parameters, including 23 as recommended in the NRC technical letter reports 24 that reported out on those cases. So really we wanted 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
74 to further investigate the inputs, the intermediate 1
variables and the outputs to better understand the 2
overall applicability of that scenario as being 3
modeled. We then, once that was complete, we then 4
reviewed the details of the lapsed time results for 5
all xLPR analysis cases as applicable to each of the 6
main loop piping components that we modeled.
7 And so this then considers the full 8
population of cases that results in realizations 9
resulting in large-break LOCA, and kind of summarizing 10 the conclusions for each of these in the table below, 11 and I'll just run through these very quickly. For the 12 reactor vessel outlet nozzle, there were like 27,000 13 realizations that resulted in large-break LOCA, and as 14 we evaluated those further and did some statistics to 15 characterize that distribution. The reactor vessel 16 inlet nozzle, which is at cold leg temperature showed 17 no occurrence of cracking, leakage, large-break LOCA 18 or rupture. The reactor coolant pump nozzle, which is 19 also at cold leg temperature, for the xLPR analysis 20 cases that modeled flaw initiation showed no 21 occurrence of leakage whatsoever and therefore no 22 significant probability of large-break LOCA. But then 23 the cases that did model initial flaws in every single 24 realization starting at time zero did have some large-25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
75 break LOCAs, but the minimum time from detectable 1
leakage to large-break LOCA was 25 months. For the 2
steam generator inlet nozzle, so in this case, all 3
steam generator inlet nozzles in the U.S. PWR fleet 4
have been mitigated and xLPR results showed no leaks 5
or ruptures in those mitigated components. For the 6
steam generator outlet nozzle, there were two 7
realizations where the time from detectable leakage to 8
large-break LOCA was zero months, but then when we 9
considered in-service inspections, these two scenarios 10 are very unlikely, and I'll explain why we conclude 11 this in the next couple slides.
12 And again, all of these cases consider 13 unmitigated components, and as we discussed earlier, 14 right, at the hot leg temperature a majority of the 15 components are mitigated at this point as well. So 16 again, just further conservatisms baked into the 17 overall assessment of how the results are being used, 18 although attempting to use best estimate inputs for 19 the individual analyses consistent with the 20 probabilistic approach. So for the reactor vessel, we 21 have a question from Walt, so we'll go ahead and take 22 that before I start the next slide.
23 MEMBER KIRCHNER: Yes, I was struck on 24 your previous slide where you were indicating no 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
76 predictions of breaks for the cold leg loops. Is it 1
that temperature sensitive between the cold leg and 2
the hot leg that on the hot leg nozzle you actually 3
had realizations of large break LOCA and you had none 4
for the cold leg nozzles?
5 MR. BURKARDT: Yes, substantially so.
6 MEMBER KIRCHNER: And it's just a function 7
of temperature?
8 MR. BURKARDT: Yes.
9 CHAIR BALLINGER: The rule of thumb for 10 stress corrosion cracking and baking a cake is that 11 for every 15 degrees C it's a factor of two.
12 MEMBER KIRCHNER: Okay, so it's that 13 sensitive, so there's a threshold. So do you see any 14 cliff-edge effects then, with that kind of phenomenon?
15 MR. BURKARDT: No cliff-edge effect, it's 16 just a continuous function of temperature, and just as 17 the temperature goes up, crack initiation rates, 18 frequencies, and crack growth rates increase 19 accordingly to the activation energies that define 20 that distribution, or define that by way of the 21 Arrhenius effect.
22 MEMBER KIRCHNER:
And to Ron's 23 introductory remarks when this session started, so you 24 don't see any potential brittle facture kind of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
77 events?
1 MR. BURKARDT: No, we do not.
2 MEMBER KIRCHNER: Thank you.
3 MR. BURKARDT: Thank you. So for the 4
reactor vessel outlet nozzle, as I mentioned there 5
were some 27,000 realizations that had large-break 6
LOCAs, and so we're showing all 27,000 of those in the 7
upper right figure. What we wanted to do was define 8
a 95/95 one-sided tolerance interval and so we define 9
that such that there's a 95% probability that the 10 constructed limit is less than 95% of the population 11 of interest for the surveillance intervals selected.
12 So for this distribution of times, the 95/95 one-sided 13 tolerance interval lower bound is 19 months, and so we 14 calculated this considering the distribution-free 15 assurance-to-quality criterion that's described in 16 Chapter 24 of NUREG-1475 for F-1.
17 Now in the bottom right figure I show the 18 lower tail of this distribution that depicts the 19 subset of data that would fall outside of this 95/95 20 one-sided tolerance interval lower bound. And so you 21 can see there are a couple points with slightly 22 shorter times than the 19 month time, but again, I 23 want to remind folks that all of these results do not 24 credit leak rate detection or in-service inspection, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
78 and if leak rate detection or in-service inspection 1
are credited, no large-break LOCAs are modeled to 2
occur.
3 And for the steam generator outlet nozzle, 4
so there's just one case that modeled an unmitigated 5
steam generator outlet model which is the 6
Generalization Study Case 4.1.4, and so this case had 7
54 realizations out of 100,000 that resulted in a 8
large-break LOCA, and of those there are two 9
realizations where we did see leak rate going from 10 less than one gallon per minute to greater than 5,000 11 gallons per minute in a single time step, time step 12 being one month, and so that corresponds to time from 13 one gallon per minute detectable leakage to large-14 break LOCA of zero months.
15 Both of these cases occurred due to 16 multiple large flaws coalescing, which then resulted 17 in very, very long flaws, that once they grew through-18 wall had extremely high leak rates right from the get-19 go. In this case, we think about in-service 20 inspection, because those are being applied also for 21 these types of components, and the scenarios are 22 highly unlikely once the in-service inspection is 23 credited. You then basically have a probability of 24 non-detection on the order of 1E minus five or less, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
79 given that the flaws are present with depths exceeding 1
10% through-wall for multiple inspection intervals.
2 And so on the two figures on the right I 3
show that crack depth is a function of time for these 4
two realizations, and for each of these, like for the 5
first one you see flaws exceeding 10% through-wall at 6
about 21, 22 years, and the flaw doesn't even go 7
through-wall until after 60 years, even after 8
coalescing. And for the second one, flaws again kind 9
of get past 10% through-wall, maybe at 24 years or so, 10 and then you know finally grow through-wall at like 11 72, 24 years. So there's many opportunities to 12 perform in-service inspections, and these are modeled 13 every 10 years for this case, and those in-service 14 inspections, right, we use a probability of detection 15 curve that's a function of depth as calibrated to data 16 from the EPRI Performance Demonstration initiative 17 program where inspectors are basically using mock-ups 18 to characterize detection rates for different flaws.
19 And so when we consider these two 20 realizations among the overall population of 100,000 21 realizations for this case and the 80 year simulation 22 time, when you credit in-service inspection, the 23 annual occurrence of this scenario is then on the 24 order of 1E minus 12 per year. And then furthermore, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
80 this is only applicable to one U.S. PWR, which has an 1
unmitigated steam generator outlet nozzle.
2 So then moving on to the conclusions, so 3
we looked at NUREG-1829 LOCA frequency estimates, and 4
so when we credit in-service inspection, leak rate 5
detection, the occurrence of rupture results were on 6
a similar order of magnitude as the LOCA frequency 7
estimates from 1829. The only non-zero results that 8
we even saw were for cases that included modeling 9
that's not representative of plant conditions and 10 operations, and for cases with zero ruptures with leak 11 rate detection we then used a 95% upper bound based on 12 a one-sided confidence interval to allow for 13 comparison to the NUREG-1829 LOCA frequency estimates.
14 CHAIR BALLINGER: And these are for 15 unmitigated welds, right?
16 MR. BURKARDT: That's correct.
17 CHAIR BALLINGER: So if you have 18 mitigation -- gone.
19 MR. BURKARDT: It's even lower, yeah. For 20 components relevant to the ALS, large-break LOCA did 21 occur when not crediting in-service inspection or leak 22 rate detection for the reactor vessel outlet nozzles, 23 and considering those cases we developed a
24 distribution of times that's characterized by 95/95 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
81 one-sided tolerance interval lower-bound of 19 months, 1
but then when you do credit in-service inspection, 2
leak rate detection, large-break LOCA does not occur 3
for the reactor vessel outlet nozzle. For the 4
unmitigated steam generator outlet nozzles, which is 5
applicable to only one U.S. PWR, it's highly unlikely 6
when crediting in-service inspection, and large-break 7
LOCA does not occur for the reactor vessel inlet 8
nozzle, reactor coolant pump nozzle, and mitigated 9
steam generator inlet nozzles.
10 And so these results overall demonstrate 11 that there's sufficient time between detectable 12 leakage and large-break LOCA to shut down the reactor 13 and prevent the large-break LOCA from occurring, 14 following detection of the leakage, and they also 15 further demonstrate the significant benefits of in-16 service inspection and leak rate detection in 17 precluding large-break LOCAs. So MRP-480, which I 18 mentioned, contains all of the gory details, it also 19 includes applicability criteria for each of these 20 conclusions to the ALS.
21 CHAIR BALLINGER: Where do we sit? I'm 22 trying to --
23 MR. SMITH: About 10 minutes before we're 24 done.
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82 CHAIR BALLINGER: Oh, is that what you're 1
-- I was looking for the -- I'm trying to figure out 2
where we are with respect to the agenda.
3 MR. SMITH: We're in section two.
4 MR. GLUNT: Four more slides.
5 CHAIR BALLINGER: Okay, all right. Okay, 6
good.
7 MR. GLUNT: Okay, so I'm going to 8
transition the next few slides in a bit of a different 9
direction. You've heard about everything with xLPR 10 and how we're looking at the time from detectable 11 leakage to rupture, but I do want to go back, and 12 since the ALS mentioned so much about leak-before-13
- break, what does traditional leak-before-break 14 actually look like? And so these slides will take you 15 through at a very high level of traditional 16 deterministic leak-before-break and where the 17 conservatisms lie.
18 So great oversimplification, leak-before-19 break can essentially be set up into four individual 20 steps. You start by postulating a through-wall crack, 21 I'm going to mess up and say flaw at some point, but 22 in this case, flaw and crack and synonymous, so I 23 apologize ahead of time, but you start by postulating 24 a through-wall crack and then you grow that crack 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
83 until it reaches your leakage detection threshold 1
limit, and that is your leakage crack size. You 2
further look at the size that crack would need to be 3
to reach failure, and that is your critical crack size 4
calculation, and then finally this fourth step is you 5
go back and compare them. You compare your critical 6
crack size, so the crack size that causes failure, 7
compare that to your leakage crack size, the crack 8
size that would occur that produces your leakage 9
threshold. Now each of these have their own 10 conservatisms embedded within them, and the next three 11 slides will go through that.
12 So I'll start with the first and the last 13 steps, because the conservatisms are kind of similar.
14 As you can see, we totally ignore the role of crack 15 initiation when it comes to traditional leak-before-16 break, we go directly to a through-wall flaw, so 17 there's no crack initiation and there's no crack 18 growth accounted for, which kind of throws ISI out the 19 window if you're going straight to a through-wall 20 crack. Beyond that, it only looks at idealized 21 through wall cracks, and so in xLPR we have crack 22 initiation, surface growth, into a transitioning 23 through-wall crack, but again, traditional LBB you 24 start with idealized through-wall crack, so you're 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
84 missing the entire life cycle of that crack up until 1
that point.
2 Similarly, on the last step when you're 3
doing a crack size comparison, you're ignoring the 4
role of crack growth between the leakage crack size 5
and the critical crack size calculation. Time is not 6
accounted for in any way in this analysis, instead 7
you're doing a margin calculation, so you just want to 8
make sure your critical crack size is twice the size 9
of your leakage crack size. And so whether it takes 10 100 years to grow from one to the other, it doesn't 11 matter, it's simply a margin. There's also an 12 additional margin for the stresses that you are 13 applying on your leakage crack size, so if you apply 14 1.4 times the stresses and make sure it still doesn't 15 fail as well. So those are the conservatisms on the 16 first and last point.
17 Next slide is the conservatisms in the 18 second part, which is the leakage crack size 19 calculation. We've already talked about it quite a 20 bit on here, but the leakage crack size calculation is 21 basically what produces leakage representing your 22 leakage detection threshold. With traditional LBB, 23 with a factor of 10 applied to it, so for the majority 24 of leak-before-break applications you start with a one 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
85 gallon per minute leakage threshold, because this 1
corresponds with the tech spec limit for unidentified 2
leakage. You then apply a factor of 10 to it, so 3
you're actually looking at what crack would cause 10 4
gpm leakage, which is quite conservative, but that 5
does account for uncertainty on the leak rate. And 6
then finally, the next slide is our critical crack 7
size calculation.
8 The conservatism that lies within here is 9
inherent to a
general deterministic fracture 10 mechanics. So when you're doing limit load or elastic 11 plastic fracture mechanics there's safety factors 12 included, which is no different in this case. The 13 technical basis for LBB also includes the suggestion 14 of including conservative inputs, which is followed 15 throughout this process of course, so your inputs that 16 you're selecting are conservative in the first place, 17 especially when you think about design basis versus 18 operating basis calculations. Finally, you are 19 ignoring the pipe-end restraint effects. So this is 20 something we've been doing a bit more work in lately.
21 22 In a vacuum, if you have two pipes 23 connected by a butt weld and you have loading on it, 24 it will eventually experience double-ended guillotine 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
86 break. But in reality, we do not have two pipes out 1
in space, we have large restraints on either end of 2
the piping, vessels, steam generators, pumps, branch 3
lines in between, everything like that, and we've 4
found that in reality as the flaws or cracks grow, the 5
moments actually reduce, and that the moments reduce 6
make it even more unlikely that you'll have a double-7 ended guillotine break. Now none of that is included 8
within a traditional leak-before-break evaluation, 9
because it is a simplified analysis trying to 10 demonstrate an extremely low probability of rupture.
11 So there are four steps in it, and each step has 12 inherent conservatism built in, where we can go look 13 at xLPR and use it to quantify some of those 14 conservatisms and fill in some of the blanks that 15 aren't available in traditional LBB. And that was my 16 quick overview of traditional LBB.
17 MR. SMITH: So some of the takeaway with 18 this is that all the pipes credited in ALS have been 19 evaluated through this traditional, deterministic LBB 20 process, and part of the conclusions of that process 21 is that the probability of rupture is exceedingly 22 small, and so the LBB process reinforces what we 23 already have heard about 1829 and xLPR, so it's kind 24 of an additional, independent evaluation of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
87 integrity of the large bore piping system.
1 CHAIR BALLINGER: And you have confirmed 2
the wisdom of the people that wrote Section 11. Okay, 3
this is where we're supposed to break. We should ask 4
the members if there are any questions right now, any 5
questions from the members or members that are online, 6
consultants, Dennis, any questions before we recess 7
for lunch? Hearing none, thank you very much, we will 8
recess until 1:00, according to our schedule. Thank 9
you very much.
10 (Whereupon, the above-entitled matter 11 went off the record at 11:54 a.m. and resumed at 1:00 12 p.m.)
13 CHAIR BALLINGER: Okay. We're back in 14 session now. I'll remind folks that you'll have an 15 opportunity for closed session after this. So I'm not 16 sure who's up next. So Storm?
17 MR. KAUFFMAN: Thank you. I'm Storm 18 Kauffman with MPR Associates supporting EPRI in 19 assessing burnup extension an FFRD. I'm going to pull 20 some of the material that you've already heard this 21 morning together into hopefully a big picture that you 22 can understand why we have a number of individual 23 parts to what we're doing. Next slide. Thank you.
24 This is an outline of the presentation 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
88 slides I'll be using. Fundamentally, the purpose of 1
the report in this meeting is to cover how the 2
industry proposes to address fuel fragmentation, 3
relocation, and dispersal in a somewhat nontraditional 4
manner. The presentation I'm giving will provide an 5
overview of the alternative licensing strategy, then 6
talk about some precedence associated with parts of 7
the ALS, address leak detection and response, non-8 piping assessment because what you've heard about with 9
xLPR is limited to piping failures. And finally, 10 provides a summary.
11 My section will be followed by closed 12 session to talk about fuel -- by Fred talking about 13 defense-in-depth and then the fuel thermal analysis.
14 Next slide. Why do we need an alternative licensing 15 strategy? Traditionally for handling the situation we 16 find ourselves with FFRD would be to gather a lot of 17 data, develop computer models, and obtain everybody's 18 agreement that the computer models were a conservative 19 representation of what's going on.
20 We did an evaluation in 2020 and concluded 21 that that was not a near term process to bring to 22 conclusion, that we needed to work on some 23 alternative. The 2020 report, if you look in the 24 ADAMS database actually lays out several alternatives.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
89 And it's been overtaken by events. So be careful that 1
you get current 2024 report if you're referencing what 2
we're doing, not the 2021.
3 CHAIR BALLINGER: Do we have that?
4 MR. KAUFFMAN: The 2024 one? Both? Yes, 5
the 2021 was submitted but not reviewed by the NRC.
6 It was submitted to --
7 CHAIR BALLINGER: I'm looking for Chris.
8 Yeah, we'll check.
9 MR. KAUFFMAN: Okay.
10 CHAIR BALLINGER: Okay.
11 MR. KAUFFMAN: It's just I know that 12 sometimes when you do a search in ADAMS, you may not 13 get the hit you expect. Anyway, the purpose of the 14 ALS process is to provide a technical justification to 15 be able to exclude FFRD so we do not have to justify 16 a model that conservatively predicts the consequences.
17 To do that, we needed to piece together several 18 different analyses.
19 We initially looked at a single approach 20 and decided and it would be best to use a combination 21 of leak-before-break and low probability of occurrence 22 for large break and protruding analysis for smaller 23 breaks. And that's what I'll be explaining how they 24 all fit together. The advantage -- next slide, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
90 please. The advantages of Alternative Licensing 1
Strategy is it lets us consider risk insights by 2
providing possible generic approach for the industry.
3 It minimizes licensee and NRC effort.
4 In other words, every licensee doesn't 5
have to develop their own justification for extending 6
burnup. And NRC doesn't have to review all those 7
individual justifications. In addition, the ALS is 8
largely consistent with the NRC Alternative 5 or the 9
increased enrichment rulemaking.
10 When I say largely consistent, the NRC 11 regulatory basis actually went beyond what we're 12 proposing. And that's discussed in EPRI's response or 13 NEI's response to the increased enrichment basis 14 document. Finally, the advantage ALS also lets NRC --
15 (Simultaneous speaking.)
16 MEMBER ROBERTS: Hey, Storm. Fred 17 mentioned briefly earlier this morning about the main 18 motivation was schedule. Did not go all the way to 19 Alternative 5. I was wondering if you can comment on 20 that. It seems like there's more issues with 21 Alternative 5 like other parts of the safety basis 22 that are tied to the large-break LOCA, the containment 23 design such as leak rate assumptions, the containment 24 testing, ECCS sizing, availability requirements, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
91 redundancy, all those things are tied to the existing 1
large-break LOCA.
2 And it just seems like going farther is 3
more than just a scheduler. But there's an awful lot 4
of the existing fundamental safety basis that need to 5
be reconsidered. And maybe that's a burden of 6
schedule because it will take a long time to 7
reconsider those individually. But I wondered if you 8
had any perspective on just the implication of going 9
all the way to Alternative 5.
10 MR. KAUFFMAN: You drew the correct 11 conclusion in that try to extend all the way to 12 Alternative 5 involves many collateral issues and 13 would not be readily done in a short time frame. If 14 you look at the history of assessing large breaks and 15 dealing with
- them, it's only been limited 16 applications. And I'll talk about some of those as 17 examples, but only limited applications of modifying 18 the design basis -- assumptions that have been 19 accepted. And part of the reason why you can do that 20 is there's very low likelihood of occurrence. And 21 there's a high assurance that we will have margin and 22 defense-in-depth which Fred will talk about. Okay.
23 MEMBER ROBERTS: Yeah, thanks, Storm. And 24 all of that would require more evaluation, whether 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
92 there's some actual loss of defense-in-depth or safety 1
margin that will go along with all the things that I 2
mentioned. Again, that may be another way of saying 3
schedule. It'd be a long time to go through that.
4 But it may also end up potentially affecting actual 5
margins that are maintained now for a large-break LOCA 6
that actually provide margin in other ways that -- I 7
just wanted to say that and to see if that was part of 8
your thought process.
9 MR. KAUFFMAN: Well, right now, there's 10 not an explicit requirement to analyze for FFRD. So 11 we're trying to establish the appropriate approach.
12 And I wasn't trying to shortchange you on the answer.
13 I get to a few points on subsequent slides that will 14 help.
15 CHAIR BALLINGER: You say there's no 16 specific requirement to analyze FFRD. It's in the 17 rule. It's in the draft rule.
18 MR. KAUFFMAN: Yes, we're headed there.
19 CHAIR BALLINGER: Okay.
20 MR. KAUFFMAN: But right now, it's still 21 a draft rule. Next slide. So what's the basis for 22 ALS? Well, we had a discussion on leak-before-break 23 and why that makes it very likely that you'll have a 24 large break LOCA. We actually start in ALS with the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
93 fact that a large-break LOCA inducing FFRD is not a 1
credible event.
2 Why is that? Well, first of all, the 3
rupture -- large rupture of the main loop piping is 4
highly unlikely. It's extremely unlikely. The main 5
loop piping is already approved for leak-before-break.
6 NUREG-1829 which has been discussed some 7
this morning shows that the frequency of those large 8
breaks in the loop piping on a plant basis with 9
allowance for expert overconfidence factor is less 10 than one in a million per year. Then xLPR as we've 11 heard about this morning supports the order of 12 magnitude that is given in 1829 and extends the 13 validity of the extremely low likelihood of occurrence 14 to plant life of 80 years. If you look back at 1829, 15 most of the analysis was done at 25 and 40 years as 16 there were a couple of components that were looked at 17 for 60 years.
18 But we wanted to assure that our approach 19 worked to 80. And then there's a question about time 20 for operator action. We didn't have an established 21 method for calculating or estimating how long you have 22 for the operator to respond.
23 The xLPR analysis as described this 24 morning shows if a leak -- a detectible leak were to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
94 precede rupture, you're still 19 months away from that 1
rupture when the leak first becomes detectable. So 2
you have a long time for the operators to respond.
3 And I'll get to that in more detail in a minute.
4 The ability for the operator to respond 5
depends on the angle to detect a leakage. And we 6
evaluated the methods for detectable leakage or 7
detecting leakage. I'll talk about those in more 8
detail.
9 Finally, the main loop piping is crucial 10 before break. And some clients do not have smaller 11 piping approved. We needed to come up with an 12 alternative approach to justify the acceptability of 13 breaks for smaller lines. That's what Jeff will talk 14 about in his session. Next, please. Next again.
15 Okay. So there's different components 16 that we have to look at as the source of possible 17 primary leaks or ruptures. And I'm careful -- try and 18 be careful not say loss of coolant because loss of 19 coolant is actually defined in the regulations as a 20 piping break. But for completeness in defense-in-21 depth purposes, we'll look to other component failures 22 to assure there is not an unexpected risk of somewhere 23 other than piping.
24 When looking at the non-piping -- can I 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
95 get some water? Thank you. All right. When looking 1
at the non-piping, there are a number of existing 2
evaluations that have been done for license renewal, 3
life extension, and other reasons. We divided up the 4
territory into several different categories.
5 There are locations that are screened for 6
extremely low probability. In other words, the break 7
is not expected to occur, reactor pressure vessel.
8 There are bolted connections which fail in a somewhat 9
different way. It has to be looked at in accordance 10 with how bolts fail, their component bodies, and 11 active component failures.
12 Active component failures are pretty easy 13 to rule out. There isn't any active component that 14 can cause the loss in the quantities that can cause 15 FFRD. Next slide. There are a number of regulations 16 that deal with preventing large-break LOCAs.
17 And Professor Ballinger, this goes back to 18 something you've mentioned a couple of times which is 19 the importance of the ASME code requirements, namely 20 having ductile materials and instructional analysis in 21 accordance with the code. And there's also procedural 22 requirements that are imposed in the plant or in the 23 plant design that help minimize the chance that you'll 24 have a pressure transient that might lead to damage to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
96 the reactor coolant pressure boundary. So those all 1
go together as part of the picture that supports ALS.
2 Also, you may be aware there's always 3
consideration of changing existing procedures or 4
making design changes. When a licensee references 5
ALS, any design changes will subsequently have to be 6
addressed as part of the overall licensing basis which 7
would then include ALS presumably if the NRC accepts 8
it. Next slide, please. Leak-before-break has not 9
always existed.
10 Leak-before-break originated as a response 11 to the unresolved Safety Issue 2 in the 1980s which 12 had to do with asymmetric pressure blowdown loads and 13 had the possibility of basically distorting the plant 14 geometry.
The NRC worked through that and 15 subsequently concluded that the process of leak-16 before-break could be used to justify excluding the 17 asymmetric break. Then in the subsequent years, the 18 NRC and the industry went back and forth on several 19 other extensions of leak-before-break. Next slide, 20 please. Oh, sorry. Back up, yeah. That's it.
21 I've talked about the fact that we've 22 looked at component failures in addition to piping 23 failures. There was actually a comment in a SECY in 24 1988 that noted that other breaches in the fluid 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
97 system boundaries such as failed manways or value 1
bonnets must be examined to determine whether they 2
control EQ profiles. So that was about EQ as if FFRD 3
didn't exist as a problem then.
4 But we considered that was an indication 5
that we needed to address bonnet failures in addition 6
to piping failures. Next. In addition, what I've 7
already discussed, there'd been a couple of cases 8
where leak-before-break has been more broadly applied.
9 In this particular reference, the comment was made 10 that all Westinghouse PWR primary coolant piping has 11 been qualified before leak before break and that the 12 success criteria applied for baffle bolting can be 13 applied to this new fuel design to enable the 14 exclusion of several phenomena which are shown over in 15 the green box on the right, namely, no fuel 16 fragmentation caused by blowdown, hydraulic loads, and 17 10 CFR 50.46 limits must be met.
18 That failure mechanism is different than 19 FFRD. But it does involve fragmentation and the 20 acceptance eventually by NRC of leak-before-break as 21 a way to exclude that phenomena. Next slide. I just 22 went over a couple of examples.
23 There are a number of places where leak-24 before-break has been used to justify excluding large 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
98 piping breaks for certain purposes. First row is the 1
USI A-2 I mentioned. Then there's more traditional 2
ones of pipe whip and control rod. Sorry.
3 And finally, there's baffle bolting and 4
the NGF fuel structural analysis. Note there is one 5
place where NRC has not accepted applying leak-before-6 break, namely, GSI-191. In that case, the NRC 7
identified a number of criteria that they were 8
concerned about and decided that leak-before-break was 9
not a suitable solution.
10 MEMBER HALNON: I expected to seal 11 package, the RCP seal package. Is that on this?
12 Because that's a component of failure.
13 MR. KAUFFMAN: The RCP seal package won't 14 result in a rupture or loss rate that's equivalent to 15 larger than a 14-inch pipe break.
16 MEMBER HALNON: A small break? All right.
17 MR. KAUFFMAN: It's taken care of by the 18 poor cooling analysis as opposed to being excluded by 19 leak-before-break or other evaluations.
20 DR. BLEY: Storm, it's Dennis Bley.
21 MR. KAUFFMAN: Yes.
22 DR. BLEY: Can you go back to that slide?
23 Yeah, I don't remember this coming up actually during 24 GSI-191, did it? Did they made a decision or did it 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
99 just not come up?
1 MR. KAUFFMAN: Well, there were several 2
letters from both NRC and the licensees that were 3
exchanged that I think extended over a period of two 4
to three years. I'd have to go double check. But I 5
guess the best way to answer it is there is stuff in 6
the files. I don't know to what extent it was brought 7
to the ACRS' attention in discussions with GSI-191.
8 DR. BLEY: Okay. So some people objected 9
to part of GSI-191 because the low probability of a 10 large break was what was going on?
11 MR. KAUFFMAN: No, I think what you said, 12 I got turned around. Namely, GSI-191 resolution was 13 not allowed to credit leak-before-break to resolve it.
14 So GSI-191 was not dependent on leak-before-break.
15 DR. BLEY: Okay. That's interesting. I 16 just don't remember that discussion coming up at all, 17 but okay.
18 MR. KAUFFMAN: Next slide. Leak 19 detection, leak detection has always been required.
20 The most applicable guidance document is Reg Guide 21 1.45. And there are technical specifications that 22 limit continued operation with a leak from the primary 23 system.
24 We'll talk about some of that this morning 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
100 mainly. Unidentified leakage, you don't know where 1
it's going. It's limited to one gallon per minute.
2 If it exceeds that, then the plant has to be shut down 3
in accordance with this tech spec.
4 As you can see, this is from the standard 5
BWR -- PWR. I was going to say BWRs are different.
6 But PWR standard tech specs for Westinghouse show that 7
in general you got a limit of one gallon per minute.
8 And then you have to be in Mode 3 within 9
36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> and Mode 5, although there are a few plants 10 that go to Mode 4 instead within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. I need new 11 glasses. The leak detection that you depend on for 12 those technical specifications includes a number of 13 diverse instruments.
14 There are requirements in Reg Guide 145 15 for how to meet diversity requirements. But they 16 include everything from containment sump level to 17 radiation level in the containment, airborne 18 radiation,
- humidity, containment pressure and 19 temperature. Some plants have acoustic emission to 20 basically hear a leak.
21 In the limit where you've got months as 22 xLPR predicts to detect a leak, eventually the guy in 23 the warehouse calls up and says, you've used up all my 24 boric acid. What's going on at the plant? Because 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
101 there are lots of peripheral effects that a large 1
amount of time will bring or make obvious.
2 The important thing about what was 3
discussed this morning on the many months for operator 4
detection is this is not something that if you were 5
doing a PRA would be subject to a human-error factor 6
because of urgency, because of environment. This is 7
something that the operators on multiple shifts in 8
multiple indications have the ability to detect. So 9
it's incredible that operators will not detect a 1 gpm 10 leak which is what we've assumed for xLPR in the 11 period of time before it would rupture.
12 I'd note that experience has shown that 13 you can actually detect leaks down to about 0.05 or 14 about 1/20th of tech spec limit. And in general, 15 plants shut down considerably before 1 gpm is reached 16 because they don't want to be in a situation where 17 they're in violation of the tech spec because they 18 didn't act fast enough. Next slide.
19 In addition, there are a number of 20 different ways that indications of leakage are 21 supposed to be interpreted. And this is discussed in 22 the WCAP that's referenced here, the idea being to 23 have different metrics to evaluate leakage indications 24 against. So if you've got some confusion indications, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
102 this detailed guidance helps the operators wade 1
through and determine whether or not there's 2
possibility of leakage that may be infused or 3
otherwise massed by other things going on.
4 MEMBER HALNON: Storm, to be clear, 5
there's no annunciator alarm that says you have 6
greater than something leakage in the RCS. This is 7
usually at least a four-hour if not a full shift 8
procedure of taking the readings and watching tank 9
levels and humidities and everything else. So I just 10 want to make sure that this is not misunderstood that 11 there's a leak annunciator. There may be some that 12 are somewhat similar if you will like charging tank 13 levels or something to that effect.
14 MR. KAUFFMAN: Or I believe there's some 15 sump.
16 MEMBER HALNON: Probably computer monitors 17 maybe. But --
18 MR. KAUFFMAN: Yes. And --
19 MEMBER HALNON: -- again, it's an 20 algorithm, a calculation of many different things.
21 MR. KAUFFMAN: Different clients have 22 different methods. Historically, it was a manual 23 process once every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. A lot of plants have 24 automated it. But I agree. I do not intend to imply 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
103 that there's an alarm that says you've got 1
2 MEMBER HALNON: And in fact, containment 3
radiation has become more and more moot since we've 4
got such clean fuel.
5 MR. KAUFFMAN: Right.
6 MEMBER HALNON: You're really just 7
throwing water into the atmosphere. So cooler 8
discharge, sump levels, those are all solid. Some of 9
these things are a little bit more ambiguous.
10 MR. KAUFFMAN: And that's part of the 11 reason why we wanted to make sure we had adequate time 12 as shown by the xLPR analysis to evaluate. Thank you.
13 Next.
14 MEMBER BIER: Hi. If I can go back. This 15 is Vicki Bier. I have a question on, I think, the 16 previous slide. I was having trouble finding my mic 17 on my phone.
18 You mentioned that there are numerous 19 other things that would go wrong if there was a 20 significant leak like the guy in the warehouse saying, 21 hey, I'm running out of boric acid. What's going on?
22 I agree that at a plant with good safety culture, that 23 would absolutely happen.
24 But we already say with Davis-Besse that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
104 the people responsible for changing filters were 1
saying, hey, why are we going through so many filters 2
and they're all full of rust? It seemed unusual. But 3
it never got raised to a level of, hey, where's all 4
this rust coming from and what should we do about it?
5 So I don't know. I don't think you 6
necessarily need to comment on that. But I just 7
wanted to raise that point if you want to address it.
8 MR. KAUFFMAN: I was very conscious of 9
Davis-Besse. It's kind of the poster plant for 10 primary leakage attentiveness. And there are a number 11 of things that were done following Davis-Besse that 12 help address those concerns.
13 But that's why it's so important to show 14 that there's a long time available for other personnel 15 to note the problem, even if there's a culture.
16 Nineteen months is enough time for INPO to come in.
17 And there's quarterly reporting, not the sort of 18 things that you can take credit for in the safety 19 analysis.
20 But in the real world, there's a lot of 21 eyes on primary leakage as a performance indicator.
22 And if they've got continual loss of water at one 23 gallon per minute, that's equivalent to one of those 24 not biggest but medium sized gasoline trucks that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
105 deliver fuel to gas stations, equivalent in about a 1
week. You're putting that much water in containment, 2
somebody is going to notice.
3 MEMBER BIER: Okay. Thank you. I 4
appreciate the answer.
5 CHAIR BALLINGER: There's always --
6 MEMBER BIER: Go ahead.
7 CHAIR BALLINGER: -- a claim that for 8
Davis-Besse at no time did they exceed the 9
unidentified leakage rate during the thing. But 10 that's kind of a misnomer because the identified 11 leakage at the time was very high. And so nowadays, 12 that kind of identified leakage would never be defined 13 as identified leakage. And there's a bare metal 14 walkdown --
15 MR. KAUFFMAN: Yes.
16 CHAIR BALLINGER: -- that has to be done.
17 And that happened after South Texas.
18 MR. KAUFFMAN: And if you go back to the 19 WCAP criteria, I think it's -- no, sorry, that. So 20 those criteria are also designed to give you different 21 perspectives so you don't ignore the fact that the 22 leak rate is creeping up very slowly or you recognize 23 that the baseline leak rate is different from your 24 last shutdown.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
106 MEMBER HALNON: There's some corroborating 1
data. I feel like what happened at V.C. Summer, it 2
was about a third of a gallon a minute for the cycle.
3 And we had hundreds of pounds of boric acid in 4
containment. And the initial lockdown after the 5
outage, it made it painfully clear that there was an 6
RCS leak somewhere.
7 Eventually, we found it in this place. So 8
it happened in one cycle, but it stayed very small to 9
the point where it didn't really ring any bells on the 10 leakage or radiation monitoring. But it was slow 11 enough that you were able to see visually very simply 12 it was a problem.
13 MR. KAUFFMAN: And the process where you 14 make sure that the leak rate is not increasing gives 15 you the ability to separate what the cause is from 16 just the indication. So the criteria here requires 17 the operating staff to address increased leakage. The 18 only example I found in operating experience where 19 this didn't work reasonably well or very well was one 20 place where they actually had two leaks.
21 And one was, I think, a seal. And they 22 fixed that and said, aha, we're good. And within a 23 few days thereafter, they found they still had a leak.
24 So that shows that there's an ability if you've got 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
107 some reasonable period of time for operators to 1
recognize more than one leak or follow up more.
2 MEMBER HALNON: And the other piece of all 3
this that we're not talking too much about is that if 4
it's unidentified, you don't have very much margin.
5 But if it's determined that you identify it as part of 6
the pressure boundary leak, you're shutting down 7
immediately. So all these are pressure boundary 8
leaks. It sounds like you can identify it and go up 9
to 10 gallons per minute. You've got to go shut the 10 plant down immediately to comply with tech specs.
11 MR. KAUFFMAN: I agree with you, but we're 12 looking at it from the standpoint of knowing we've got 13 a pressure boundary leak and we want to do something 14 about it. But the operators have an indication maybe 15 leakage. And --
16 MEMBER HALNON: And it's a great incentive 17 to try to identify it. When you're talking about a 18 half a gallon or 0.05 gallons per minute, you can 19 probably go find a drip somewhere and say, okay, 20 that's a packing leak. I'll identify it and put it in 21 a 10 gallon per minute. There's a lot of different 22 things that go on relative to leakage. I think the 23 point you're trying to make is it's slow enough so 24 that any one of those probably will be found out in a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
108 cycle during the next refueling outage, not before.
1 MR. KAUFFMAN: Correct. The idea is there 2
are multiple indications available to multiple 3
personnel over many months. And if this were in a 4
PRA, you could probably justify the group human error 5
rate of 10 to the -6 of this.
6 MEMBER HALNON: The surveillance, like you 7
said, is done every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. That's a tech spec also 8
because you have to go look. It's not somebody 9
notices an increase in leakage. You have to look.
10 It's tech spec surveillance. So you have to benchmark 11 against your previous readings.
12 MR. KAUFFMAN: Thank you. Next slide.
13 Non-piping, so there are components in the loops that 14 are big. And if they broke in two or broke into a 15 significant rupture, the leak rate could exceed what 16 was shown. Core cooling can be assured.
17 However, the assessment in NUREG-1829 18 included in the statistics that Markus showed this 19 morning the component failure rate too. So where he 20 was comparing the piping results from xLPR, he was 21 comparing that to NUREG-1829 where the number is 22 piping failures, active failures, component failures.
23 In general, 1829 predicts the component failures or 24 about equivalent probability piping failures.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
109 Component failures are not, however, 1
normally considered in most design analysis. They're 2
excluded. And if we can go back to the slide with the 3
picture. Keep going. Thank you.
4 So the colors here show the different 5
regions of the plant. And the ones that are in the 6
right purple or magenta are places where the rupture 7
is excluded based on design margins and other 8
criteria. So there are quite a few components that 9
are taken off the table at the start.
10 We looked at the other components that had 11 the potential to cause large loss of coolants and 12 referenced a number of studies and also considered 13 leak analysis or leak prevention associated with 14 license renewal and life extension and concluded that 15 those processes provide high assurance that the 16 components will not rupture. Even if a leak developed 17 in a component, it's highly unlikely that we get an 18 opening large enough to be equivalent to a double-19 ended guillotine break. Next slide. We're all the 20 way back to where we were.
21 Okay. So we have assessed non-piping 22 ruptures, although again 10 CFR 50.46 defines LOCAs as 23 being caused by a piping failure. And I think this is 24
-- I just said all of these. Licensee then reports a 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
110 number of the references we looked at had detailed 1
assessments of prior operating experience.
2 But most of them were of a visage like 3
2010, 2005, 2000, or earlier. So using NRC's licensee 4
event report database, we looked at whether or not 5
there were any events that had occurred since those 6
other references were written and didn't find any 7
indications that there were vulnerabilities that 8
weren't being addressed. In general, leaks are 9
detected somewhere in between 0.05 gpm and about 0.5 10 gpm, so with a margin to what ALS xLPR analysis 11 considered. Next.
12 So in summary, the alternate licensing 13 strategy is an assemblage of different justifications 14 for different portions of the plant or different 15 conditions to justify treating FFRD as not credible.
16 It's not credible because large LOCA will not occur.
17 And those portions that I've talked about include 18 NUREG-1829, extremely low likelihood of occurrence, 19 xLPR analysis, leak-before-break, justifies that will 20 not have a main loop piping rupture, assessment of 21 non-piping components or cooling analysis for small 22 breaks, operating experience which shown anything that 23 will be of concern that we missed.
24 And we will need obviously to have 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
111 criteria for implementation at individual plants.
1 That's discussed in an appendix in the EPRI report.
2 But we think that for a non-traditional solution, this 3
provides a fairly comprehensive justification to 4
exclude FFRD from the design basis based on it not 5
being credible. Any other questions?
6 CHAIR BALLINGER: Why are you using the 7
word, non-traditional? What you're describing is the 8
use of results, analysis, and history which is 9
anything but non-traditional.
10 MR. KAUFFMAN: Correct. I was using non-11 traditional as a shortcut for saying we're not going 12 to develop a model and show that FFRD has acceptable 13 consequences. Instead, we're going to justify that 14 FFRD will not occur.
15 DR. SCHULTZ: It's the dispersion that 16 won't occur.
17 CHAIR BALLINGER: Yeah, that's what I was 18 about to get at.
19 DR. SCHULTZ: No fragmentation will occur 20 to some level in performance. But it's the dispersion 21 22 MR. KAUFFMAN: Yes.
23 DR. SCHULTZ: -- portion of it. I just 24 wanted to make a comment when we bring up Davis-Besse 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
112 that I don't want to leave the impression that's 1
anything in the industry's experience that wasn't 2
addressed. And that comprehensive and extensive 3
safety culture program was instituted not just by 4
utility industry and the manufacturing industry and 5
the NRC. It was pervasive through the industry. And 6
it has made a difference in industry performance over 7
the last many years.
8 MR. KAUFFMAN: If there are no other 9
questions, then Fred Smith will talk a little bit more 10 about defense-in-depth.
11 MR. SMITH: So we've said it several 12 times. I'll reiterate it again that LOCA induced FFRD 13 is extremely low likelihood. You have three 14 independent indications supporting that.
15 1829, the xLPR analysis, and the LBB 16 piping qualification process all align to say this is 17 an extremely low likelihood. The layers of defense as 18 you began the meeting begin with the design. And so 19 piping system design has specific requirements for 20 material selection, geometry, stress, and any number 21 of factors that are providing, promoting the 22 performance that we're seeing.
23 The fabrication is another layer where 24 welding procedures qualify welding training programs, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
113 QA, material qualifications, welding inspection, et 1
cetera. So that's another layer of defense. The 2
abnormal and normal operating procedures prevent 3
severe stresses in piping systems from occurring.
4 The ISI program and leak rate detection 5
program all are layers of defense to preclude large-6 break LOCA -- to keep large-break LOCA at a low 7
frequency of occurrence. And then the ECCS is a 8
mitigating action that is credited for the small and 9
intermediate-break that we're doing but not for the 10 large-break LOCA and describe why that is acceptable.
11 So if we look at these and consider two scenarios, one 12 where if we had a short time between detectable leak 13 and LOCA, we have a different story.
14 So if the xLPR analysis was the time to 15 detectable to LOCA was a week, we would probably have 16 a very different story to tell. But at 19 months or 17 even a tenth of that, it's very different. So those 18 first three layers are in place all the time per a 19 scenario.
20 If we had a small period of time, then the 21 operator response liability on there, responding might 22 be less. And that might be a contributor to risk.
23 But with very long period for detection, it's not 24 credible, I don't think, in anywhere close to 19 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
114 months that this could be not detected and the plant 1
would not shut down.
2 And so that's a big increase in our 3
knowledge of performance of the plants. We didn't 4
have ECCS actuations of small, very short periods of 5
time. You would probably have to rely upon ECCS 6
systems.
7 But with such a long time and rely upon 8
the operator shutting the plant down, the plant is 9
shut down. And anywhere close to -- within weeks or 10 perhaps even months, the stored energy is all but 11 gone. Decay heat is gone. The motive force for 12 forcing a flaw to failure is gone. And even if you 13 did have a failure, which there's no mechanism for 14 that to occur, then there's not enough energy in the 15 fuel to cause clad rupture and fuel dispersal. So --
16 MEMBER HALNON: If we can go back to your 17 leak detection, I actually think you might -- I can 18 make an argument that you've got the operator response 19 swapped. If you have a short time between leakage and 20 LOCA, it means it's probably increasing. Or it gets 21 a lot of operator attention. Believe me. It gets a 22 tremendous amount you do a leak rate probably almost 23 continuously, snapping a line every four hours.
24 MR. SMITH: That would be a change in the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
115 system you mean.
1 MEMBER HALNON: Yeah.
2 MR. SMITH: Yeah.
3 MEMBER HALNON: I would say that you got 4
much more reliable operator response if it's a shiny 5
object on the wall in the control room --
6 MR. SMITH: Yeah.
7 MEMBER HALNON: -- as opposed to a 8
complacency of that's only increased to 0.05.
9 MR. SMITH: Yeah, I didn't mean to intend 10 that. The scenario I was trying to address is you do 11 have highly qualified, highly proceduralized 12 activities by the control room. And they do an 13 incredible job. If they were to miss once, then the 14 consequence of that for a short period of time would 15 be higher potentially, higher risk, than if you have 16 200 shots on goal.
17 MEMBER HALNON: The operator response has 18 a much higher impact in a short time --
19 (Simultaneous speaking.)
20 MR. SMITH: Yeah, that was what I was 21 trying to communicate.
22 MEMBER HALNON: Okay. I can buy that.
23 MR.
KAUFFMAN:
There are fewer 24 opportunities for operator recovery if the time period 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
116 is shorter. So if somebody makes a mistake, then your 1
assurance that that mistake will be corrected is 2
reduced.
3 MEMBER HALNON: Okay. So the reliability 4
of the operator has a much higher impact in the short 5
period of time versus the long term because of the 6
single mistake made.
7 MR. SMITH: So in the short time scenario 8
9 MEMBER HALNON: Yeah, I got it.
10 MR. SMITH: -- you might expect ECCS 11 system actuation. ECCS system is not perfect. It's 12 highly reliable. But there are equipment variations 13 and equipment issues that are in the analysis side 14 that are accounted for. In reality, they may or may 15 not occur. And so --
16 MEMBER HALNON: I get it now. I think I 17 know what you're trying to say.
18 CHAIR BALLINGER: My experience as an 19 actual operator is that when -- not in this world but 20 in another world was that when something bad is 21 happening quickly, it really gets your attention in a 22 hurry.
23 MR. SMITH: Yes.
24 CHAIR BALLINGER: So you don't miss it.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
117 MR. SMITH: Right. That's right. You 1
don't --
2 CHAIR BALLINGER: You don't miss it.
3 MR. SMITH: Yeah.
4 CHAIR BALLINGER: And if you do miss it, 5
there's somebody crawling over your back.
6 MR. SMITH: Yeah, I agree. I agree with 7
that. So from a risk perspective, having the long 8
time between detectable leakage and a LOCA makes you 9
less dependent upon the ECCS. And not having to rely 10 upon it as we're doing does not increase the risk of 11 an unfortunate consequence.
12 So if you have multiple shots on goal, 13 high, high assurance that you're going to shut the 14 plant down. And there will not be any fuel dispersal 15 consequences. And so in the very short period 16 scenario here, like I said, if xLPR told me the time 17 was two weeks, I'm not at all sure that we would be 18 able to make the arguments that we are making. But 19 even if it's a factor of 10 less than the results we 20 have now, there's high confidence that operators will 21 shut the plant down and mitigate any dispersal 22 consequences. So --
23 MEMBER ROBERTS: Could I clarify the last 24 row on the previous table? Could you back to the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
118 table? The last row, second column says, some 1
dispersal may occur impacting containment.
2 This ties back to what Storm was saying.
3 That's based on the RIL, I assume, and the research 4
has been done to date which is not conclusive in terms 5
of its results. I mean, the RIL would imply that's 6
the case.
7 If you had RIL, impact is that you put 8
more activity in containment. But people can make up 9
other stuff too. It's a whole lot more significant.
10 So is that basically a judgment that's likely the 11 case? Is that the way to read that?
12 MR. SMITH: Well, the NRC part on 13 dispersal consequences said this is a potential 14 consequence. And so we don't know how much because 15 there's a lot of research that has not been done to 16 quantify the mobility of dispersed material among 17 other things. But certainly dispersed material would 18 find its way in the containment, and it would require 19 some evaluation.
20 MR. KAUFFMAN: I think the reason we 21 focused on containment was it's the third barrier to 22 fission product release. We've already damaged the 23 fuel clad and the RCS. So it was a little bit 24 different perspective than you're thinking. That's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
119 your last barrier. You don't want FFRD and dispersal 1
to fail it.
2 MEMBER ROBERTS: Okay, thanks. I 3
understand. That does presuppose some of the things 4
that are uncertain. And the research information 5
letter won't have them. But ultimately, containment 6
is the last barrier that would be the last line of 7
defense for things like criticality if that were 8
possible or loss of cold -- and that kind of thing.
9 Okay, thanks.
10 MR. SMITH: So kind of summary that from 11 a potential risk for the ALS approach, the biggest 12 potential consequence would be the first operator does 13 not detect the leak rate exceeding the tech spec. Now 14 that's very unlikely considering the importance of how 15 it's proceduralized or how they train or have a skill 16 to do this at least every three days but really more 17 often than that. So the likelihood of that operator 18 missing this is very small.
19 But if they did, then there are -- the 20 next guy on the next shift is going to come up and 21 detect it. The symptoms will become increasingly 22 obvious as the flow slowly increases or the volume and 23 temperature accumulates. It will be easier to detect.
24 So we believe it's not credible that given 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
120 the time frames that we are talking about that we 1
won't be detected. So we believe that shutting the 2
plant down is a credible barrier and a very reliable 3
barrier. So the other potential risk is the reliance 4
upon xLPR.
5 And so while it's a very important element 6
of this, we have well qualified code just like we have 7
in the LOCA area.
And we understand the 8
uncertainties. We understand how it performs, and we 9
have large amounts of margin to address any potential 10 gaps of that understanding.
11 So we don't believe that's a critical 12 element of defense-in-depth. So that was the last of 13 my slides. If you have any other questions.
14 CHAIR BALLINGER: Questions from members 15 or consultants?
16 Hearing none, this constitutes the end of 17 the open session. So by -- yeah, that's what I was 18 about to do. You're way ahead of me. So we need to 19 go out for public comment. Are there any members of 20 the public that would like to make a comment? If 21 there are, would you state your name and then provide 22 your comment?
23 Hearing none, this is the end of the open 24 session. I'm assuming we're going to have a closed 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
121 session. There's another set of slides.
1 And so what we need to do is to take a, I 2
don't know, ten-minute break while we get set up and 3
verify that we have people in the room that should be 4
here to hear this. So let's take a ten-minute break 5
so we get sorted out. And who's going to be the 6
gatekeeper for the online?
7 You'll do that? So Chris Brown will be 8
the gatekeeper. And we'll have to rely on the EPRI 9
folks if there's somebody that we don't see. So let's 10 recess until -- well, let's call it 2:15.
11 (Whereupon, the above-entitled matter went 12 off the record at 2:03 p.m.)
13 14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
© 2024 Electric Power Research Institute, Inc. All rights reserved.
w w w. e p r i. c o m Fred Smith Sr. Technical Executive ACRS Meeting of the Fuels Materials, & Structures Subcommittee June 25, 2024 Introduction to EPRIs Alternative Licensing Strategy to Address LOCA induced FFRD
© 2023 Electric Power Research Institute, Inc. All rights reserved.
2 ALS Submittal Introduction*
- Does not include removal of LB-LOCA from design bases
© 2023 Electric Power Research Institute, Inc. All rights reserved.
3 Key Features - Leak-Before-Break Introduction
- Safety Benefits Reduced Fuel Cycle Impacts including High Level Waste and other Radiological Impacts Support Nuclear Plant Low Carbon Emissions Reduced industry and NRC demand on scarce specialized resources Regulatory Guidance
- Current Guidance and potential changes to Regulations
- Defense-in-Depth Methodology Leak-Before-Break
© 2023 Electric Power Research Institute, Inc. All rights reserved.
4 Key Features Piping Ruptures Non-Piping Ruptures Summary and Conclusions
- Initial Application - Westinghouse NSSS Systems using Westinghouse fuel Extensions to other PWRs with appropriate small break and intermediate break LOCA analysis Other NSSS systems Other fuel designs Other vendors analysis methods
- Appendix A Requirements to Apply ALS to Specific Plants
© 2023 Electric Power Research Institute, Inc. All rights reserved.
5 Key Features - xLPR Introduction xLPR Probabilistic Fracture Mechanics
- Evaluated Case Matrix - Full case matrix includes non-primary loop coolant piping which is not applicable to ALS scope
- Benchmarking and validation Comparison to NUREG-1829 Time between detectable leakage and LOCA Evaluation of applicable degradation mechanisms Conclusion
© 2023 Electric Power Research Institute, Inc. All rights reserved.
6 Key Features - LOCA Overview of Cladding Rupture Analysis Methodology Bounding Model development Cladding Rupture Results 2-Loop 3-Loop 4-Loop Summary and Implementation Evaluation of Limitations and Conditions Plant-Specific Implementation Requirements Relies on previously submitted Methodology Report:
WCAP-18850-P, Adaptation of the FULL SPECTRUM LOCA (FSLOCA)
Evaluation Methodology to Perform Analysis of Cladding Rupture for High Burnup Fuel, February 2024.
© 2024 Electric Power Research Institute, Inc. All rights reserved.
7
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w w w. e p r i. c o m TOGETHERSHAPING THE FUTURE OF ENERGY
© 2024 Electric Power Research Institute, Inc. All rights reserved.
w w w. e p r i. c o m Craig Harrington and Nate Glunt EPRI Materials Reliability Program (MRP)
Markus Burkardt and Gideon Schmidt Dominion Engineering, Inc. (DEI)
ACRS Meeting of the Fuels Materials, & Structures Subcommittee June 25, 2024 xLPR Probabilistic Fracture Mechanics Analysis for the ALS Overview and Key Analysis Results
© 2024 Electric Power Research Institute, Inc. All rights reserved.
9 Outline
Background
Scope Summary of xLPR Analysis Cases Key Results
- LOCA frequency compared to NUREG-1829
- Time between detectable leakage and LOCA Conclusions
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10 List of Acronyms Nominal pipe size NPS Advisory Committee on Reactor Safeguards ACRS US Nuclear Regulatory Commission Technical Letter Report NRC TLR Alternative licensing strategy ALS Probabilistic Fracture Mechanics PFM Combustion Engineering CE Pressurized water reactor PWR Cold leg CL Primary water stress corrosion cracking PWSCC Dissimilar metal weld DMW Pressurizer PZR Diametre nominal DN Reactor coolant pump RCP Fuel fragmentation, relocation and dispersal FFRD Reactor coolant system RCS Hot leg HL Reactor vessel inlet nozzle RVIN In-service inspection ISI Reactor vessel outlet nozzle RVON Leak-before-break LBB Stress corrosion cracking SCC Large-break loss-of-coolant accident LBLOCA Steam generator inlet nozzle SGIN Leak rate detection LRD Steam generator outlet nozzle SGON Loss-of-coolant accident LOCA Weld residual stress WRS Mechanical Stress Improvement Process MSIP Extremely Low Probability of Rupture xLPR Materials Degradation Matrix MDM
© 2024 Electric Power Research Institute, Inc. All rights reserved.
11 Previous NRC Interactions NRC ADAMS Accession Number Event Date ML22166A345 NRC Public Meeting to Discuss Use of the Extremely Low Probability of Rupture Code for LOCA Frequency Estimates 06/14/2022 ML23019A148 NRC Public Meeting to Discuss Use of the Extremely Low Probability of Rupture Code for LOCA Frequency Estimates 01/19/2023 ML23164A190 ACRS Fuels, Materials, and Structure Subcommittee Meeting 05/18/2023 ML23312A003 Pre-Submittal Meeting to Discuss the Use of the ALS to Address LOCA Induced FFRD 11/08/2023 ML24156A244 Introduction to Alternative Licensing Strategy; LOCA-Induced Fuel Fragmentation, Relocation and Dispersal 06/06/2024
© 2024 Electric Power Research Institute, Inc. All rights reserved.
12 Background and Scope
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13 Background
xLPR is a state-of-the-art probabilistic fracture mechanics code jointly developed by the NRCs Office of Nuclear Regulatory Research and the Electric Power Research Institute (EPRI)
Provides new quantitative capabilities to analyze the risks (e.g., leakage or rupture) associated with nuclear power plant piping systems subject to active degradation mechanisms
© 2024 Electric Power Research Institute, Inc. All rights reserved.
14 xLPR Overview
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15 xLPR Model Attributes Geometry Piping butt-weld Materials Dissimilar metal weld Similar metal weld Crack orientations Circumferential and/or Axial Multiple cracks Crack initiation SCC, Fatigue, Both Crack growth SCC, Fatigue, Both Mitigation Inlay, Onlay, Overlay, Mechanical Stress Improvement Process (MSIP)
Chemical Inservice inspection (ultrasonic testing)
Leakage detection 15 Surface Crack Transitioning Through-Wall Crack Idealized Through-Wall Crack
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16 Direct Results from xLPR Probabilities
- First Crack
- First Leak
- Rupture Individual Crack Results
- Type
- Position
- Leak rate
- Growth
- Stress Intensity Factors Number of cracks Probability of non-repair Stability ratio Leakage rate
- Individual flaw
- Total for all flaws
© 2024 Electric Power Research Institute, Inc. All rights reserved.
17 xLPR Quality Assurance Built under rigorous quality assurance program
- Selected elements of ASME NQA-1-2008 and NQA-1a-2009 Addenda, which are endorsed for meeting NRCs 10 CFR Part 50, Appendix B, quality assurance requirements
- Extensive technical documentation Verification and validation
- 4,000+ verification tests
- Validation of each physical model and of complete software against operating experience, finite element analysis simulations, and other probabilistic fracture mechanics codes Externally reviewed Quality Assurance in xLPR development process documented in NUREG-2247 Participated in OECD/NEA/CSNI global PFM benchmark
- Finds xLPR represents the state-of-the-practice in terms of PFM modeling capabilities
- Several conference publications; final benchmark report to be published in 2024
© 2024 Electric Power Research Institute, Inc. All rights reserved.
18 xLPR Treatment of Uncertainty Uncertainty: Knowledge of the knowns and unknowns that affect model predictions Probabilistic approach:
Use of best-estimate models to describe complex system Models linked and integrated Uncertainties quantified, reduced (best estimate), and accounted for by forward propagation through each model using the Monte Carlo method xLPR Uncertainty Report [ML19337C165] summarizes and consolidates information on sources and treatment of uncertainties within the xLPR modules and Framework Specifics Where What Basic model form, inputs, range of validity Module reports Uncertainty descriptions Assumptions and summary of verification/validation efforts Uncertainty/bias factors Limits of applicability, interpolation methods Model bias and uncertainty relative to lab or field data Validation reports Sampling and convergence uncertainty Scenario report Distributions on inputs and parameters Inputs report Uncertainty quantification and propagation Distributions on model parameters Module reports Sampling strategies Scenario report
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19 Study Scope within the Fuels Alternative Licensing Strategy NUREG-1829, Vol. 1 estimates Loss-of-Coolant Accident (LOCA) frequencies
- Evaluated the technical adequacy of redefining the design-basis break size (largest pipe break to which 10 CFR 50.46 applies) to a smaller size
- Estimated LOCA frequencies through an expert elicitation process As part of research into an alternative fuel licensing strategy (ALS) for fuel fragmentation, relocation, and dispersal (FFRD), xLPR was applied to:
- Validate NUREG-1829 LOCA frequency estimates for use in high burnup fuel licensing
- Evaluate probability that leakage as a precursor to a LOCA /
rupture will be detected in sufficient time to allow for reactor shutdown and reduce decay heat levels before a LOCA / reactor coolant system (RCS) piping rupture occurs MRP-480 (EPRI 3002023895, freely available) has been published, documenting the details of this work
© 2024 Electric Power Research Institute, Inc. All rights reserved.
20 Line Size Considerations NUREG-1829 gives estimates of LOCA frequencies based on expert elicitation (Table 1)
The expert elicitation considered LOCA-sensitive piping systems and associated degradation mechanisms (Table 3.5)
The goal of the current study is to analyze piping welds > NPS 14 (> DN 350) in support of alternative licensing strategy (ALS) for FFRD
© 2024 Electric Power Research Institute, Inc. All rights reserved.
21 Summary of xLPR Analysis Cases
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22 Summary of xLPR Analysis Cases xLPR analysis cases were developed applying Primary Water Stress Corrosion Cracking (PWSCC) and/or fatigue as the material degradation mechanisms Either modeled flaws as present at the start of the simulation or used initiation models to calculate the time to flaw initiation
- All flaws at initiation were modeled as flaws of engineering scale Sensitivity studies were performed to determine the impact of changes to analysis inputs
- Sensitivity studies modeled alternate inputs for parameters such as geometry, loading, weld residual stress profiles, initial flaw sizes, or seismic effects
© 2024 Electric Power Research Institute, Inc. All rights reserved.
23 Summary of xLPR Analysis Cases The results of recent NRC analyses are used where possible and supplemented with additional xLPR analysis cases as needed TLR-RES/DE/REB-2021-09 (ML21217A088)
Referred to herein as xLPR piping system analysis Documented xLPR analysis of representative reactor vessel outlet and inlet nozzle welds in a Westinghouse four-loop PWR Includes extensive set of sensitivity studies TLR-RES/DE/REB-2021-14 R1 (ML22088A006)
Referred to herein as xLPR generalization study Documented xLPR analysis of other piping systems containing Alloy 82/182 dissimilar metal piping butt welds which had received prior LBB approvals from the NRC staff Includes reduced set of sensitivity studies per analyzed component, as informed by xLPR piping system analysis Shorthand numbering #.#.## is used to refer to specific xLPR analysis cases Results of Interest for ALS Time between 1 gpm detectable leakage and rupture or LBLOCA (lapse time)
P(RupturelInitiation) P(RupturelInitial Flaw) x P(Initiation)
Average 80-year rupture (LOCA) frequency = P(Rupture) / 80 yrs
© 2024 Electric Power Research Institute, Inc. All rights reserved.
24 LOCA Frequency Compared to NUREG-1829
© 2024 Electric Power Research Institute, Inc. All rights reserved.
25 LOCA Frequency Results from NUREG-1829 Table 1 NUREG-1829 LOCA frequencies used for comparison are:
- Based on expert elicitation
- From Table 1 Median, 5th percentile, and 95th percentile Total PWR LOCA frequencies after overconfidence adjustment using error-factor scheme 40 yr fleet average values Consider typical ISI with LRD resolution as required by tech spec limits
- Results are presented on a per plant basis, for each distinct LOCA category
- Considers piping and non-piping passive system contributions
© 2024 Electric Power Research Institute, Inc. All rights reserved.
26 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0 1
10 100 LOCA frequency (yr-1)
Effective break size (in)
NUREG-1829 95th percentile NUREG-1829 Median NUREG-1829 5th percentile xLPR results with ISI & LRD 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0 1
10 100 LOCA frequency (yr-1)
Effective break size (in)
NUREG-1829 95th percentile NUREG-1829 Median NUREG-1829 5th percentile xLPR results w/ LRD xLPR results w/ LRD (95% upper bound) 95% UB based on one-sided confidence interval (binomial distribution), considering # of realizations and probability of initiation xLPR LOCA Frequency Compared to NUREG-1829 Table 1 When considering ISI and LRD, LOCA frequencies estimated from xLPR are on a similar order of magnitude as median NUREG-1829 LOCA frequency estimates Focus of ALS Crediting LRD, Without Crediting ISI Crediting LRD and ISI
© 2024 Electric Power Research Institute, Inc. All rights reserved.
27 Time Between Detectable Leakage and Large-Break LOCA
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28 Time from Detectable Leakage to LBLOCA For a Single xLPR Analysis Case Realization Results shown depict example leak rate time history for one realization modeled in xLPR
- Component modeled: Unmitigated Alloy 82/182 reactor vessel outlet nozzle dissimilar metal weld
- Key modeling options selected:
Initial flaw model (i.e., initiation at time = 0)
PWSCC growth only One circumferential crack No inservice inspection, leak rate detection, mitigation, or seismic effects LBLOCA = 5,000 gpm leak rate Part Through-Wall Transitioning Through-Wall Idealized Through-Wall Flaw grows through-wall and begins leaking LBLOCA and Rupture occurs 0.1 1
10 100 1000 10000 20 25 30 35 Leak Rate (gpm)
Time (EFPY)
Leak Rate for Example Realization Part Through-Wall Flaw Transitioning Through-Wall Flaw Idealized Through-Wall Flaw
© 2024 Electric Power Research Institute, Inc. All rights reserved.
29 Distributions of Time from Detectable Leakage to LBLOCA For a Single xLPR Analysis Case Results for one xLPR analysis case produce a distribution of lapse times Each data point corresponds to one realization which resulted in LBLOCA (without crediting ISI or LRD)
- Note that the lapse time result distributions are truncated at 12 years in NRC TLRs The distribution of results for each xLPR analysis was considered as part of the overall assessment of lapse times for each analyzed component These results do not credit ISI or LRD 0.0 0.2 0.4 0.6 0.8 1.0 0
24 48 72 96 120 144 Probability Time Lapse <= T Time from Detectable Leakage to LOCA (mo)
NRC Case 1.1.6 Data
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30 Investigation of Limiting Cases Considering the distributions of times from detectable leakage to LBLOCA/rupture for each xLPR analysis case, limiting cases were identified for further review Performed further investigation for limiting cases with realizations exhibiting:
- Minimum time between detectable leakage and rupture < 3 months, or
- Nonzero occurrence of rupture with LRD All limiting cases were sensitivity studies, which were:
- Defined to inform understanding of the base case results by investigating inputs known to have influence on xLPR results
- Less constrained by maintaining fidelity to realistic plant conditions Some of these limiting cases were then re-run with:
- Refined time-stepping
- Updated input model parameters
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31 Summary of Time from Detectable Leakage to LBLOCA Summary of Time from Detectable Leakage to LOCA Component Data for all realizations resulting in LBLOCA (~27,000 realizations) were evaluated further. [See following slides]
Reactor Vessel Outlet Nozzle (RVON)
This component is at cold leg temperature. xLPR results showed no occurrence of crack, leak, LBLOCA, or rupture.
Reactor Vessel Inlet Nozzle (RVIN)
This component is at cold leg temperature. xLPR results in cases modeling flaw initiation showed no occurrence of leakage (and therefore no significant probability of LBLOCA). Cases modeling initial flaws did have ruptures, but the minimum time from detectable leakage to LBLOCA was 25 months.
Reactor Coolant Pump Nozzle (RCP)
All SGINs in the US PWR fleet have been mitigated, and xLPR results showed no leaks or ruptures in mitigated components. (Includes results from re-runs of two cases with a more realistic initial flaw size, based on suggestions in the xLPR Generalization Study)
Steam Generator Inlet Nozzle (SGIN)
There are two realizations where the time from detectable leakage to LBLOCA is zero months. When ISI is credited, these scenarios are highly unlikely. [See following slides]
Steam Generator Outlet Nozzle (SGON)
Considers full population of cases with realizations resulting in LBLOCA Summary below reflects results including re-runs of cases (as noted on prior slide)
© 2024 Electric Power Research Institute, Inc. All rights reserved.
32 Time from Detectable Leakage to LBLOCA: RVON The distribution of time from detectable leakage to LBLOCA for all ~27,000 realizations is shown in the upper right figure A 95/95 one-sided tolerance interval is defined such that there is a 95% probability that the constructed limit is less than 95% of the population of interest for the surveillance interval selected For this distribution of times, the 95/95 one-sided tolerance interval lower bound is 19 months
- Calculated considering the distribution-free assurance-to-quality (A/Q) criterion described in Chapter 24 of NUREG-1475R1 The lower tail of the distribution is shown in the lower right figure, depicting the data that would fall outside of the 95/95 one-sided tolerance interval lower bound Results shown do not credit LRD or ISI
- No LBLOCAs are modeled to occur if LRD and ISI are credited 0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0 24 48 72 96 120 144 Cumulative Distribution Time from 1 gpm leakage to LBLOCA (mo)
NRC 1.1.21.048 NRC 1.1.20.037 NRC 1.1.19.047 NRC 1.1.19.046 NRC 1.1.15.043 NRC 1.1.14.018 NRC 1.1.9.017 NRC 1.1.7.036 NRC 1.1.6.010 NRC 1.1.5.009 NRC 1.1.4.008 NRC 1.1.2.006 NRC 1.1.1.004 NRC 1.1.0.001 95/95 Tolerance Interval 0
0.01 0.02 0.03 0.04 0.05 0.06 0
3 6
9 12 15 18 Cumulative Distribution Time from 1 gpm leakage to LBLOCA (mo)
NRC 1.1.21.048 NRC 1.1.20.037 NRC 1.1.19.047 NRC 1.1.19.046 NRC 1.1.15.043 NRC 1.1.14.018 NRC 1.1.9.017 NRC 1.1.7.036 NRC 1.1.6.010 NRC 1.1.5.009 NRC 1.1.4.008 NRC 1.1.2.006 NRC 1.1.1.004 NRC 1.1.0.001 95/95 Tolerance Interval
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33 Time from Detectable Leakage to LBLOCA: SGON There is one case modeling an unmitigated SGON, xLPR Generalization Study Case 4.1.4 This case had 54 realizations out of 100,000 that resulted in LBLOCA Of these, there are two realizations where the leak rate goes from
<1 gpm to >5000 gpm in a single time step Time from 1 gpm detectable leakage to LBLOCA is 0 months In both realizations, this is caused by multiple large flaws coalescing Leads to extremely high leak rates once the flaw grows through-wall These scenarios are highly unlikely when ISI is credited The probability of non-detection is on the order of 1E-5 or less Flaws are present with depths exceeding 10% through-wall for multiple inspection intervals When considering these two realizations among the population of 100,000 realizations and simulation time of 80 years, the annual occurrence of this scenario is on the order of 1E-12 yr-1 Only one US PWR has an unmitigated SGON 0
0.2 0.4 0.6 0.8 1
0 20 40 60 80 Crack Depth (normalized by thickness)
Time (yr)
Crack 1 Crack 2 Crack 3 xLPR Generalization Study Case 4.1.4 Run #8 Realization #2563 0
0.2 0.4 0.6 0.8 1
0 20 40 60 80 Crack Depth (normalized by thickness)
Time (yr)
Crack 1 Crack 2 xLPR Generalization Study Case 4.1.4 Run #8 Realization #7781
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34 Conclusions
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35 Conclusions When crediting ISI and LRD, occurrence of rupture results are on a similar order of magnitude as NUREG-1829 LOCA frequency estimates
- The only nonzero results were for cases including modeling not representative of plant conditions and operations
- For cases with zero ruptures w/ LRD, a 95% upper bound based on a one-sided confidence interval is considered for comparison For components relevant to the ALS, LBLOCA:
- Occurs when not crediting ISI or LRD for RVONs Distribution of times between detectable leakage and LBLOCA is characterized by a 95/95 one-sided tolerance interval lower bound of 19 months Does not occur when crediting ISI and LRD
- Is highly unlikely for unmitigated SGONs when crediting ISI
- Does not occur for the RVIN, RCP, and mitigated SGINs These results demonstrate that there is sufficient time between detectable leakage and LBLOCA to shutdown the reactor and prevent LBLOCA The results further demonstrate the significant benefits of ISI and LRD MRP-480 includes applicability criteria for these conclusions
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w w w. e p r i. c o m Nate Glunt EPRI Materials Reliability Program (MRP)
ACRS Meeting of the Fuels Materials, & Structures Subcommittee June 25, 2024 Traditional Deterministic LBB Process
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37 Crack Size Comparison 02 03 04 Leakage Crack Size Calculation Traditional Deterministic LBB Process Critical Crack Size Calculation Postulated Through-Wall Crack 01
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38 Crack Size Comparison 02 03 04 Leakage Crack Size Calculation Traditional Deterministic LBB Process Conservatism:
Ignores role of through-wall crack growth or progression Does not account for time Margin of 2 on the crack length or 1.4 on the stresses Critical Crack Size Calculation Postulated Through-Wall Crack Conservatism:
Ignores the role of crack initiation Ignores surface crack growth Only utilizes idealized through-wall cracks (ignores transitioning through-wall cracks) 01
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39 Crack Size Comparison 02 03 04 Leakage Crack Size Calculation Traditional Deterministic LBB Process Critical Crack Size Calculation Postulated Through-Wall Crack 01 Conservatism:
Safety factor of 10 on leak rate to account for uncertainty Uses plant leakage detection system threshold (typically 1 gpm) when plants can detect changes in leak rate trends at far lower levels
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40 Crack Size Comparison 02 03 04 Leakage Crack Size Calculation Traditional Deterministic LBB Process Critical Crack Size Calculation Postulated Through-Wall Crack 01 Conservatism:
Includes safety factors in limit load and elastic-plastic fracture mechanics analysis Conservatism in input selection Design basis versus operating basis calculations Ignores pipe-end restraint effects (which can reduce applied moments)
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41
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w w w. e p r i. c o m TOGETHERSHAPING THE FUTURE OF ENERGY
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w w w. e p r i. c o m Storm Kaufman, MPR ACRS Meeting of the Fuels Materials, & Structures Subcommittee June 25, 2024 Loss-of-Coolant-Accident-Induced FFRD with Leak-Before-Break Credit
Outline of Presentation EPRI 3002028673 [ML24121A207]: Loss-of-Coolant-Accident-Induced Fuel Fragmentation, Relocation and Dispersal with Leak-Before-Break Credit -
Alternative Licensing Strategy Presentation outline:
Overview: the Alternative Licensing Strategy (ALS)
- Purpose
- Advantages
- Basis
- Coverage of the reactor coolant system (RCS)
- Regulations and guidance ALS Precedents Leak detection and response Non-piping assessment Summary 43
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44 Overview:
Alternative Licensing Strategy (ALS)
Alternative Licensing Strategy Purpose
Purpose:
Provide technical justification to exclude consideration of fuel fragmentation, relocation, and dispersal (FFRD) from the core cooling evaluation for a loss of coolant accident (LOCA) in a pressurized water reactor (PWR) to allow increasing the fuel burnup limit.
45 Problem Statement FFRD involves multiple phenomena potentially induced in high burnup (HBU) fuel by large-break (LB) LOCAs.
The usual approach of validating methodology against empirical data does not support desired schedule.
Proposed Approach Based on precedents and on existing regulations and guidance define a methodology that shows that:
1)
Burst of clad of high burnup fuel is not credible for LB-LOCAs 2)
Smaller LOCAs do not cause clad burst
Advantages of the ALS as Basis for Burnup Extension Considers risk insights Minimizes licensee and NRC effort
- Standard, generally applicable approach
- Consistent with NRC Alternative 5 of regulatory basis document
[ML23032A504] for increased enrichment rulemaking, but more limited Allows NRC to establish criteria now by avoiding need for
- Additional experimental data
- Qualification of analytical models of consequences (i.e., fuel dispersal) 46
Basis for the ALS LB-LOCA-induced FFRD not credible
- Rupture of piping of RCS main loop extremely unlikely Main loop piping already approved for LBB NUREG-1829 frequency less than 10-6/year threshold for screening Supported by xLPR probabilistic fracture mechanics evaluation of piping
- Extremely unlikely to 80-year plant life
- Ample time (months) to detect precursor leakage and respond Reactor coolant leakage is a focus area
- Multiple means of detection by plant operating staff and others
- Per Tech Specs (TS): shut down, cool down, and depressurization removes driving force needed to cause either LB-LOCA or fuel dispersal Smaller LOCAs, though more likely, shown to not cause clad burst
- Fuel vendor LOCA analysis methodology and results in separate documents 47
Piping:
- Small/intermediate breaks: no HBU fuel clad burst based on vendor-specific LOCA analysis
- Large piping (RCS main loop):
Extremely low probability of failure (NUREG-1829), as confirmed by xLPR evaluation Ample time for operator recognition and response Non-piping - existing evaluations (e.g.,
license renewal/life extension) reviewed
- ALS consistent with existing design basis Screened Bolted Component bodies Active component failures
- No need for changes or further analyses ALS Methodology Coverage of RCS 48
Regulations & Guidance: Large-break (LB) LOCAs Reactor coolant pressure boundary (RCPB) integrity is priority
- Ductile materials
- Structural analysis per ASME Code Section III
- Procedural constraints to avoid adverse conditions
- Inservice inspection (ISI) to detect unexpected degradation in advance
- Plant performance indicator Piping LB-LOCA
- Set of conservative assumptions: single active failure, worst initial conditions, etc.
- Defined in 10 CFR 50.46 49
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50 ALS Methodology Precedents
LBB - Refined Guidance 53 FR 11311, April 6, 1988 Until recently, severe failure for piping has been defined as the instantaneous double-ended guillotine leak regardless of the standards applied to piping. Under leak-before break technology, it has become possible to exclude the double-ended guillotine break from the dynamic structural design basis because it is unrealistic and overly conservative in certain situations. Piping which meets NRCs acceptance criteria now need only postulate stipulated leakage cracks as severe failure.
SECY-88-325, 4/13/1989, 54 FR 18149, Published 5/2/89 Policy Statement on Additional Applications of Leak-Before-Break Technology Additionally, other breaches in the fluid system boundary, such as failed manways or valve bonnets, must be examined to determine whether they control EQ profiles.
ALS Is consistent with modified LBB applicability established in 1988-89 Containment, ECCS, and EQ functional and performance requirements are unchanged Non-piping LOCAs (e.g., bolted closures, pump casings) are assessed 51
LBB Applied to Exclude LOCA Effects WCAP-16498-NP, March 2008 17x17 Next Generation Fuel (17x17 NGF) Reference Core Report Currently, all Westinghouse designed US PWR primary coolant main loop piping has been excluded from consideration for dynamic effects associated with postulated pipe rupture. all current fuel qualification analyses are performed on the basis of postulated rupture of branch lines connected to the primary coolant loop.
The primary success criteria for the baffle bolting program are the same as those documented in SRP Section 4.2 discussed above: i.e., no fuel fragmentation, 10 CFR 50.46 criteria continue to be met, and control rod insertability is maintained. These analyses were also based on LBB exclusion of the main coolant loop piping.
only the branch line breaks not covered by LBB are considered in the licensing basis.
ALS Is consistent in use of LBB for NGF fuel in excluding effects of LB-LOCA from the design basis No fuel fragmentation caused by blowdown hydraulic loads for all fuel vs. no fuel dispersal for HBU rods 10 CFR 50.46 limits must be met after exclusion applied 52
LBB - Summary of Extended Applicability ALS Considers past precedents for application of LBB Exclusion of fuel dispersal from HBU fuel does not affect the requirement for ECCS to mitigate the full spectrum of break sizes and locations. It does eliminate the need to posit fuel fragment dispersal of the highest burnup rods during LOCAs.
The EPRI ALS explicitly considers other possible failures such as valve bonnets, flanges, manways that could be large enough to possibly cause FFRD.
53
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54 Leak Detection and Response
Leakage Technical Specifications
- TS 3.4.13 Limiting Condition for Operation (LCO)
No more than 1 gpm unidentified RCS leakage Operators would act before reaching 1 gpm If not addressed, continued leakage will lead to annunciated alarm and implementing abnormal or emergency procedures 55
Leak Detection Regulatory Guide 1.45, Guidance on Monitoring and Responding to Reactor Coolant System Leakage*
- Unidentified leak rate > 0.05 gpm detection/quantification
- Response time (excluding transport time) of no more than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> for leak rate of 1 gpm
- Leakage Monitoring Parameters Inventory balance Containment sump level or flow Airborne particulate activity Air cooler condensate flow Airborne gaseous activity Containment pressure, temperature, humidity Acoustic emission Video surveillance Pump seal leakage Makeup flow rate Walkdowns Air cooler condensate flow Airborne activity Containment P, T, RH Video surveillance Containment sump level
& flow Acoustic emission Inventory balance Pump seal leakage REACTOR COOLANT SYSTEM Walkdowns 56
- Most PWRs were licensed to and still apply Revision 0
RCS Unidentified Leakage Action Levels WCAP-16465-NP, Standard RCS Leakage Action Levels and Response Guidelines for PWRs, 9/06
- Specifies three action level tiers based on RCS leak rate; lower tier triggers set to focus attention on detection of very small leaks Tier 1:
- One 7-day rolling average daily unidentified rate > 0.1 gpm
- Nine consecutive daily unidentified rate > baseline mean Tier 2:
- Two consecutive daily unidentified rate > 0.15 gpm
- Two of 3 daily unidentified rates > mean +2 day total unidentified leakage > 5,000 gal. (0.116 gpm average over 30 days)
Tier 3:
- One daily unidentified rate > 0.3 gpm or > mean +2
- Long term (operating cycle) total unidentified leakage > 50,000 gal.
- Summarizes operating experience Detected as small as 0.01 gpm while operating Only two RCS piping welds have had leaks If annunciated alarm occurs, plant abnormal/emergency procedures apply 57
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58 Non-piping Assessment
Assessment of Non-Piping Failures 10 CFR 50.46 requires core cooling analysis of range of LOCAs caused by piping failure The ALS also considers potential for non-piping failure to cause FFRD
- Considered as part of life extension/license renewal
- ALS consistent with existing design basis
- No need for changes or further analyses identified 59
Operating Experience - Assess for Relevance Licensee Event Reports
- No events identified that showed gaps in the ALS framework
- Addressed by industry actions 60
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61 Summary
Summary: Alternative Licensing Strategy Addresses LB-LOCA with potential to cause FFRD:
- Extremely low likelihood of occurrence based on NUREG-1829 Below 10-6 per year, considering piping and component failures Consistent with threshold for screening licensing basis events LBB for PWR RCS main loop piping already authorized
- xLPR confirms extremely low likelihood
- xLPR shows long time for operator detection/response before rupture Non-piping components
- Design features preclude failures potentially leading to clad burst Core cooling analyses for LOCAs smaller than RCS main loop
- No clad burst for HBU rods Operating experience
- ALS considers risk insights Criteria for implementation at individual plants ALS Is consistent with NRC precedents & guidance No existing regulations nor guidance specifically for FFRD PWR RCS main loop piping already approved for LBB Exclude events with extremely low probability of failure such as reactor vessel asymmetric loading LBB accepted to exclude fuel fragmentation caused by blowdown hydraulic forces for broken baffle bolts IE rulemaking basis FFRD alternative 62
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63
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w w w. e p r i. c o m Fred Smith Sr. Technical Executive, EPRI ACRS Meeting of the Fuels Materials, & Structures Subcommittee June 25, 2024 Defense-in-Depth
LB-LOCA induced FFRD
- LB-LOCA induced FFRD has an extremely low likelihood of occurrence as supported by
- NUREG-1829 expert elicitation
- Confirmed by xLPR analysis probabilistic fracture mechanics analysis
- LBB piping qualification process with deterministic fracture mechanics, supports a conclusion that the probability of piping rupture is extremely low
- Layers of Defense that support prevention of LB-LOCA
- NSSS piping system design (e.g. material selection, geometry)
- NSSS normal and abnormal operating procedures that limit piping loads
- In-service Inspection
- Leak Rate Detection
- ECCS system actuation mitigates LB-LOCA with conservative equipment performance assumptions
LB-LOCA Induced FFRD Defense Layers Performance Comparison Extended time between detectable leak rate and LOCA (ALS Approach)
Short Time between detectable leak rate and LOCA Barrier Same Same NSSS Piping) System Design Same Same NSSS Piping System Fabrication Same Same Inservice Inspection Highly reliable operator response, indications of leakage increase with time and LRD equipment response accuracy increases Less reliable operator response and LRD equipment response Leak Rate Detection Plant is shutdown and cooled off before LB-LOCA occurs, removing motive force driving LB-LOCA. ECCS not relied upon, so equipment variations have no impact Performance impacted by some equipment performance variations ECCS actuation No cladding rupture so no dispersal.
Some dispersal may occur, impacting containment Fuel Dispersal Consequence
Defense-in-Depth for LB-LOCA induced FFRD in ALS
- Potential risk of ALS approach:
- While it is highly unlikely, if an Operator failed to identify a detectable leak during initial surveillance Plants monitors to threshold well below T/S limit Various operator tools employed to highlight change in plan conditions Surveillance must be repeated in 3 days or less With operator shift changes other personnel will eventually perform this surveillance Given the long time between detectable leakage and LB-LOCA the risk of repletely failing to detect the leak is negligible
- Unit shutdown and cooled off, no motive force to cause pipe rupture
- Even if LOCA could occur, limited/no impact on cladding integrity
- Over reliance on xLPR results
- Current results predict time between detectable leakage and LB-LOCA at 19 months
- Results include appropriate treatment of uncertainties
- ALS approach remains valid even if xLPR is off by factor of 10 (i.e. 1.9 months)
- Critical performance risks for LB-LOCA induced FFRD adequately addressed
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