ML18136A576
| ML18136A576 | |
| Person / Time | |
|---|---|
| Issue date: | 04/16/2018 |
| From: | Michael Snodderly Advisory Committee on Reactor Safeguards |
| To: | |
| Snodderly M | |
| References | |
| NRC-3655 | |
| Download: ML18136A576 (53) | |
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NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
(202) 234-4433 WASHINGTON, D.C. 20005-3701 www.nealrgross.com 1
1 2
3 DISCLAIMER 4
5 6
UNITED STATES NUCLEAR REGULATORY COMMISSIONS 7
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 8
9 10 The contents of this transcript of the 11 proceeding of the United States Nuclear Regulatory 12 Commission Advisory Committee on Reactor Safeguards, 13 as reported herein, is a record of the discussions 14 recorded at the meeting.
15 16 This transcript has not been reviewed, 17 corrected, and edited, and it may contain 18 inaccuracies.
19 20 21 22 23
1 UNITED STATES OF AMERICA 1
NUCLEAR REGULATORY COMMISSION 2
+ + + + +
3 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 4
(ACRS) 5
+ + + + +
6 NUSCALE SUBCOMMITTEE 7
+ + + + +
8 OPEN SESSION 9
+ + + + +
10 MONDAY 11 APRIL 16, 2018 12
+ + + + +
13 ROCKVILLE, MARYLAND 14
+ + + + +
15 The Subcommittee met at the Nuclear 16 Regulatory Commission, Two White Flint North, Room 17 T2B1, 11545 Rockville Pike, at 1:01 p.m., Ronald G.
18 Ballinger, Chairman, presiding.
19 20 COMMITTEE MEMBERS:
21 RONALD G. BALLINGER, Chairman 22 DENNIS BLEY, Member*
23 MICHAEL CORRADINI, Member 24 JOY REMPE, Member 25 1($/5*5266
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2 GORDON R. SKILLMAN, Member 1
MATTHEW W. SUNSERI, Member 2
3 ACRS CONSULTANT:
4 STEPHEN SCHULTZ 5
6 DESIGNATED FEDERAL OFFICIAL:
9 ALSO PRESENT:
10 PAUL CLIFFORD, NRR 11 SARAH FIELDS, Public Participant*
12 VICTOR HATMAN, Framatome 13 NICHOLAS KLYMYSHYN, PNNL 14 BRETT MATTHEWS, Framatome 15 JONATHAN ROWLEY, NRR 16 17
- Present via telephone 18 19 20 21 22 23 24 25 1($/5*5266
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3 T-A-B-L-E O-F C-O-N-T-E-N-T-S 1
2 Opening Remarks 3
by Ron Ballinger 4
4 5
Fuel Seismic/LOCA Regulatory Regulatory Requirements 6
............. 13 7
8 Public Comments................. 39 9
10 Move to Closed Session
............. 41 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1($/5*5266
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4 P R O C E E D I N G S 1
1:01 p.m.
2 CHAIRMAN BALLINGER: This meeting will now 3
come to order. This is a meeting of the Advisory 4
Committee on Reactor Safeguards, NuScale Subcommittee.
5 I'm Ron Ballinger, aka Roland, chairman for today's 6
subcommittee meeting.
7 Members in attendance today are Dick 8
Skillman, Mike Corradini, Matt Sunseri, Joy Rempe, and 9
our consultant, Steve Schultz. And I think that 10 Dennis Bley is on the phone. And we may --
11 MEMBER BLEY: Yes, he is.
12 CHAIRMAN BALLINGER: Very good. And we 13 may have one other member, Pete Riccardella, if he 14 doesn't get chosen for jury duty.
15 The ACRS was -- the subcommittee will 16 receive an informational briefing to prepare to review 17 the staff's evaluation of NuScale's topical report, 18 TR-0716-50351-P, NuScale applicability of AREVA method 19 for the evaluation of fuel assembly structural 20 response to externally applied forces. Today we have 21 members from the NRC, our staff, and Framatome to 22 brief the subcommittee.
23 The ACRS was established by statute and is 24 governed by the Federal Advisory Committee Act, FACA.
25 1($/5*5266
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5 That means that the Committee can only speak to 1
through its published letter reports. We hold 2
meetings to gather information to support our 3
deliberations.
4 Interested parties who wish to provide 5
comments can contact our office requesting time after 6
the meeting announcement is published in the Federal 7
Register. That said, we set aside ten minutes for 8
comments from members of the public attending our 9
listening in our meetings.
10 Though I should remember that Mike 11 Snodderly is the federally designated official for 12 this meeting. The ACRS section of the US NRC public 13 website provides our charter bylaws, letter reports, 14 and full transcripts of all full and subcommittee 15 meetings, including slides presented there.
16 The rules for participation in today's 17 meeting were announced in the Federal Register on 18 April 13th, 2018. The meeting was announced and is an 19 open and closed meeting. We will close the meeting 20 after the open portion to discuss proprietary 21 material, and presenters can defer questions that 22 should not be answered in the public session at that 23 time --- to that time. No statement or request for 24 making an oral statement to the Subcommittee has been 25 1($/5*5266
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6 received from the public concerning this meeting.
1 Our transcript of the meeting is being 2
kept and will be made available as stated in the 3
Federal Register notice. Therefore, we request that 4
participants in this meeting use the microphones.
5 That means make sure the little green light is on when 6
you speak and off when you're not speaking.
7 Participants should first identify themselves and 8
speak with sufficient clarity and volume so they can 9
be readily heard.
10 We have a bridge line established for the 11 public to listen to the meeting. We also have another 12 bridge line established for Framatome and ACRS people.
13 To avoid disturbance, I request that attendants put 14 their electronic devices like cell phones in the off 15 or noise free mode.
16 We will now proceed with the meeting. I 17 will call on, let's see --
18 MEMBER REMPE: Ron, before we start, do we 19 have hard copies of the slides?
20 MR. SNODDERLY: Yes, sorry.
21 MEMBER REMPE: Okay, ha, ha, ha.
22 CHAIRMAN BALLINGER: I'm just so used to 23 having things electronically, that I just don't ---
24 MEMBER REMPE: Yes. Well, that situation 25 1($/5*5266
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7 with the slides, I'd like copies of all of them today.
1 I do get them, but yes.
2 MR. SNODDERLY: And then, Ron, one other 3
thing before we get started, can we confirm that 4
Framatome is on the phone line?
5 CHAIRMAN BALLINGER: Yes.
6 (Off microphone comments.)
7 MR. SNODDERLY: Oh, is there anyone from 8
NuScale on the line?
9 CHAIRMAN BALLINGER: Well, they don't have 10 to be here.
11 MR. SNODDERLY: No, they don't have to.
12 I just --- I was curious. Okay, yes, let's --- Paul?
13 CHAIRMAN BALLINGER: Okay, Paul. I mean, 14 is there anybody in management that would like to make 15 a statement?
16 MR. ROWLEY: Well, I'm not technically 17 management, project manager is my title, but I'll give 18 opening remarks for the NRC. Thank you for having us 19 today. My name is Jonathan Rowley. I'm the project 20 manager for Framatome activities that come into the 21 NRC.
22 Today, myself, Nick Klymyshyn, and Paul 23 Clifford will give you some information on our review 24 of ANP-10337. We know this is important to you to 25 1($/5*5266
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8 assist you with your review of the NuScale. So 1
hopefully the information you find today will be 2
sufficient to help you with that. So with that, I'll 3
turn it over to Paul Clifford for the NRC's 4
presentation.
5 MEMBER REMPE: So I have another question.
6 I'm just full of them, or something, ha, ha. But we 7
won't go there on that. But okay, so the materials we 8
were given for this do not include the staff SE of 9
this ANP document.
10 MR. ROWLEY: They do not, ma'am.
11 MEMBER REMPE: Pardon?
12 MR. ROWLEY: No, they do not.
13 MEMBER REMPE: So the ground rules are a 14 bit strange, because we're supposed to, in the future, 15 review NuScale's topical on the applicability of this 16 fuel for their reactor. We can see the ANP document 17 from Framatome, but we can't see the staff SE and 18 their evaluation of it apparently. Is that the ground 19 rules, and there was some agreement made on that?
20 MEMBER CORRADINI: Well, if I might try, 21 so we asked for an information briefing to try to 22 understand the background of the Framatome/AREVA 23 analysis which is being referred to in terms of 24 applicability for the NuScale design. We have no 25 1($/5*5266
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9 intention nor, I think, it was agreement with the 1
staff that we wanted to write a letter or even 2
entertain a review of the staff's SE, strictly we 3
wanted to get background information for the 4
applicability topical. So the short answer is yes.
5 MEMBER REMPE: Okay. I don't know. I 6
guess I don't remember this being agreed to by all of 7
ACRS. But if we did, and I've forgotten, I guess I 8
misunderstood the ground rules. Because if I look at 9
what I see in the Framatome document, there're some 10 things that I have questions about, like simulated 11 irradiation.
12 And I just am kind of curious. Are we 13 allowed to ask questions about their review? Because 14 apparently the staff has approved this ANP document.
15 So are we supposed to say, okay, it's approved. So we 16 only can do the delta on how this approved fuel 17 applies to NuScale, even though we may not fully 18 understand what's meant by some of the things in the 19 ANP document.
20 MR. ROWLEY: Well, the SE has not been 21 approved yet. We're in the direct SE stage. So that 22 is soon to be issued to Framatome for their review and 23 comment. But our position is not finalized just yet.
24 So we are leaning toward approval, but it's not 25 1($/5*5266
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10 approved yet.
1 MEMBER REMPE: So we are allowed to ask 2
questions about what's in the ANP document. Because 3
I just want to make sure. Because I'm going to be 4
asking questions that you probably have in your SE.
5 But I didn't --- I want everyone to understand why I'm 6
going to be asking those questions and if they are 7
allowed before I get into this meeting.
8 MEMBER CORRADINI: You can ask anything 9
you want.
10 MEMBER REMPE: Yes.
11 CHAIRMAN BALLINGER: As always.
12 MEMBER REMPE: Well, just wanted to 13 understand and make sure you understand that I 14 couldn't see everything to prepare for this meeting.
15 (Off the record comments) 16 CHAIRMAN BALLINGER: Make sure you little 17 light is on.
18 MR. CLIFFORD: It is somewhat of an 19 awkward situation, because you're right. Usually we 20 finish our topical report, we submit it to the ACRS, 21 you have time to review the staff's safety evaluation, 22 then you ask questions on how we did our review.
23 But this is a little different. I think 24 you're free to ask any questions you want to Framatome 25 1($/5*5266
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11 to understand their methodology better so that you 1
understand how it will be applied to NuScale. And 2
I'll do my best to answer any questions on our review.
3 But it's still open, so it is a little awkward.
4 CHAIRMAN BALLINGER: It's an informational 5
meeting.
6 MEMBER REMPE: Well, are we going to see 7
your SE before we ever get to the final approval of 8
this topical for NuScale? That was the other 9
question. Because I would like to see it. And I was 10 a little puzzled when I was told, no, no, you can't 11 see that. So I'd like to make sure that doesn't 12 happen.
13 MR. SNODDERLY: Some other background, so 14 this topical, along with a number of other topicals, 15 was presented to the ACRS and the subcommittee 16 chairman for review. And we said that we didn't think 17 it warranted review. So it did not come to P&P, but 18 it was --
19 MEMBER REMPE: But it was a decision by a 20 subcommittee ---
21 MR. SNODDERLY: There was a decision that, 22 you know, for operating plants with other workload, 23 who knows why. But that is one reason why, you know, 24 we did have an opportunity. We said we didn't want to 25 1($/5*5266
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12 review it. But we did want to review the applicable 1
2 MEMBER REMPE: I thought usually those 3
things came to full ACRS for P&P. But anyhow, I 4
guess, whatever.
5 MR. SNODDERLY: That's my understanding.
6 So we're here, we have a status. I mean, we can --
7 MEMBER CORRADINI: But let's just clarify 8
what Mike said so there's no confusion. The topical 9
report on the structural thing came up through P&P, 10 and we passed. And in our normal P&P procedures, we 11 passed. We can look back, but it wasn't even this 12 year. It was a couple of years ago.
13 MEMBER REMPE: Well, I'm a little --- I 14 guess I didn't fully understand that we'd be put in 15 this situation at this meeting. So that's why I just 16 wanted to bring it up on the record. Thank you.
17 CHAIRMAN BALLINGER: Sure.
18 MR. SCHULTZ: Paul, what's the approximate 19 time of your completion and interaction with 20 Framatome?
21 MR. CLIFFORD: Well, the technical staff, 22 we've completed our draft SE. And then it goes to 23 DPR. Do they still call it DPR?
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13 MR. CLIFFORD: Ha, ha, ha. And then they 1
complete the safety evaluation.
2 MR. ROWLEY: So, Mr. Schultz, let me 3
answer your question. We will have it finished by 4
next month.
5 MR. SCHULTZ: That's fine. Thank you.
6 MR. CLIFFORD: Okay. So I'm here today.
7 I've just got ten brief slides just to kind of give 8
you some background of what the regulatory 9
requirements are. And that'll help start the 10 conversation with how AREVA's addressed each of the 11 regulatory requirements in their topical report.
12 So it's broken into --- first, I'll 13 identify the applicable regulations, and then 14 separately I'll talk about the requirements for the 15 operating basis earthquake, the OBE, the safe shutdown 16 earthquake, SSE. And then we'll be getting into some 17 combined events.
18 So GDC-2, and it's listed at the bottom 19 here in its entirety on the slide, is all about 20 defense in-depth. And what I mean by that is that 21 safety related system structures and components, 22 including fuel, must be designed to withstand the 23 effects of earthquakes without loss of capability to 24 perform their intended safety functions.
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14 Now, this includes combined effects of 1
both the natural phenomena, in this case the 2
earthquake, in combination with whatever accident-3 induced loads there are, for each of the components to 4
perform their intended function under those particular 5
accident conditions.
6 10 CFR 50, Appendix S implements GDC-2 7
specifically for earthquakes. It establishes the 8
definitions of OBE and SSE and identifies what SSCs 9
are required to perform their functions.
10 Specifically, SSEs are necessary to assure, one, the 11 integrity of the reactor coolant pressure boundary, 12 two, the capability to shut down the reactor and 13 maintain it in safe shutdown conditions, and three, 14 the capability to prevent or mitigate the consequences 15 of accidents that would result in potential offsite 16 exposures. That's directly from the regulation.
17 Now, how do those regulations then 18 translate to specific types of accidents? We'll start 19 with the OBE. An OBE is not a postulated accident.
20 It's expected to occur during the lifetime of the 21 reactor. Plants are not required to shut down 22 following a seismic event up to OBE ground motion and 23 may restart without NRC involvement and without 24 inspection. And that includes even if they're tripped 25 1($/5*5266
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15 on other signals, such as a loss of offsite power.
1 All system structures and components 2
important to continued safe operation, that would be 3
safety related and non-safety related, must remain 4
functional and within their applicable stress rate and 5
deformation limits.
6 So basically, this is -- an OBE is treated 7
just like any design-basis analysis that you need to 8
do. You have to design each of your components to 9
withstand some of the reactor trips, be capable of 10 dealing with everyday stresses of normal operation.
11 OBE gets lumped into that.
12 Now we get into safe shutdown earthquake.
13 This is a postulated accident. It's not expected to 14 occur during the life of the plant. And the reactors 15 must shut down following any seismic event beyond OBE 16 ground motion.
17 When we're talking about fuel assembly 18 components, we deal with the three key safety 19 functions. And that is that the fuel rod cladding 20 maintains a fission product barrier, the spacer grids 21 maintain geometry, and the guide tubes maintain a 22 pathway for control rod movement.
23 So when we're talking specifically about 24 what are the design requirements for the fuel 25 1($/5*5266
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16 components themselves, we deal with their safety 1
functions. And they must be capable of maintaining 2
those safety functions.
3 But what has been kind of the source of 4
confusion are these other concepts that I'm getting 5
into now. There are three concepts on this slide that 6
are all very important.
7 First of all the first bullet, in getting 8
back to GDC-2, back in the defense in depth 9
requirements, that the system structures and 10 components important to safety must be capable of 11 performing their intended function when exposed to the 12 combined loads of SSE ground motion in combination 13 with the functional and accident loads during the 14 accident for which the SSE is designed to mitigate.
15 This is kind of a source of confusion, 16 because you can imagine, well, you could logically 17 argue that if you have seismically qualified RCS 18 piping, then why would you need to postulate loads 19 associated with an earthquake in combination with 20 loads associated with a LOCA if, in fact, the systems 21 were designed to withstand the earthquake. In other 22 words, the earthquake doesn't initiate the LOCA.
23 This goes back to defense and depth. So 24 it's not causal effects, it's not that the earthquake 25 1($/5*5266
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17 is causing the LOCA, or the earthquake is causing a 1
loss of offsite power. The earthquake is causing any 2
other potential accident. It's just defense in depth.
3 Your safety related components must be designed to 4
withstand these combined effects, even though they're 5
not causal.
6 MEMBER CORRADINI: I hear what you're 7
saying. I want to make sure though that I appreciate 8
the difference. Because from the standpoint of 9
analysis, it doesn't matter whether it was causal or 10 not. You're saying that you have an additive of ---
11 MR. CLIFFORD: Yes.
12 MEMBER CORRADINI: Okay. So it doesn't 13 matter how I got a loss of coolant, it doesn't matter 14 how I had a small break LOCA, it doesn't matter how I 15 had whatever failure it is. I first had the seismic 16 event, and I have this initiator --- something's 17 initiated and I have to show that they can survive 18 both together.
19 MR. CLIFFORD: Right. You basically take 20 your accelerations that you calculate separately for 21 your seismic, and then your accelerations and loads 22 that you calculate separately for your LOCA, and you 23 combine them.
24 MR. SCHULTZ: Paul, when you say that this 25 1($/5*5266
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18 is caused some confusion, do you mean that you just 1
want to make it clear today that this is what the 2
intent of the language is?
3 MR. CLIFFORD: Yes.
4 MR. SCHULTZ: Or do you mean that the 5
licensees or vendors have been confused?
6 MR. CLIFFORD: I think the staff and the 7
industry has been confused. And maybe I can get to it 8
now. I think in the past you designed components.
9 The easiest one to talk about is your grid cage. Grid 10 cages in the past were very rigid structures, 11 parallel, perpendicular strips of metal that were very 12 rigid.
13 When you applied a load to them, they 14 would just --- they wouldn't experience a significant 15 plastic deformation. They'd be rigid, and then they 16 would rack. And when they racked, that's when you 17 determined that's your critical load, your buckling 18 load, we call it. Because the strut had buckled. And 19 so you would have to make sure that you designed your 20 system so that you wouldn't buckle.
21 With modern designs and with the 22 introduction of more limiting assumptions in your 23 seismic analysis, that being you've got these design 24 certifications, so you have these new reactors coming 25 1($/5*5266
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19 in. They want to build one reactor anywhere. So they 1
look at the worst envelope. They take the worst soil 2
conditions, the worst seismic accelerations, and they 3
want to say, well, I can build one assembly cage that 4
will survive the worst of the worst. That way I can 5
market it anywhere in the world. I'm not restricted 6
to where I place this reactor.
7 And as a result, you're seeing more pipe 8
loads. And you also have new grid cage designs that 9
will experience more --- have more flexibility, more 10 ductility as a component. So they'll absorb more of 11 that energy. They'll start to deform before they 12 buckle. So you have to take that into account.
13 MEMBER BALLINGER: So what you're saying, 14 again, is that since the calculation doesn't care 15 whether you call it a safe shutdown earthquake or a 16 LOCA, if you add the loads together it's like having 17 loads above and beyond a safe shutdown earthquake.
18 MR. CLIFFORD: Yes.
19 MEMBER BALLINGER: So it's, in effect, the 20 same as increasing the safe shutdown earthquake.
21 MEMBER REMPE: So that philosophy, if 22 you're trying to combine loads, the thing about, like, 23 when you irradiate something, and you cook and look, 24 shouldn't you have a load that's under affluence in 25 1($/5*5266
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20 addition to an acceleration? I mean, how far do you 1
go with combined loads? If you take it out of the 2
reactor, you're no longer exposing it to the 3
radiation. Do you see what I'm kind of saying? How 4
far do you want to go with combined loads?
5 MR. CLIFFORD: Okay. I mean, I think we 6
can get into more details of how they run the tests 7
and how they determine what the critical loads are at 8
their defined failure points and then how they verify 9
those loads with their finite element methods, models.
10 Maybe when we get into that, that'll make more sense.
11 MEMBER REMPE: Yes. I just am kind of 12 wondering though. I mean, that's a combined load too.
13 MR. CLIFFORD: Yes. Right. Okay, so the 14 second, I think, key concept is the second bullet 15 here.
16 I think the capability to perform their 17 function, whether it's a safety related valve that 18 needs to close, or it's a safety related pump that 19 needs to start up and inject borated water, or maybe 20 it's a safety related trip function which has to 21 initiate a reactor trip, or your guide tubes have to 22 stay in a configuration where you can free fall your 23 control rods, the ability for those to perform their 24 intended function is often judged against the 25 1($/5*5266
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21 performance of the fuel during those accident 1
conditions, and functionality being both capability 2
and timing of the actions.
3 And this is a critical issue, because a 4
reactor trip is a good example. You have a reactor 5
trip. The purpose of that trip is to ensure that you 6
don't fail the cladding so that you don't have offsite 7
consequences.
8 Well, what does functionality mean, that 9
you still can drop those rods? I mean, if the rods 10 drop, right now you have an analysis that shows if I 11 get a trip at 0.6 seconds, and I get a trip signal at 12 one second, and I decay the magnets holding up my 13 control rods, that takes 0.6 seconds. And then they 14 fall in in 2.3 seconds. The combined time of that, 15 that 3.1 seconds or whatever, I won't fail rods.
16 But if I delay, because there is, say, 17 deflection in my guide tubes that causes more friction 18 for my free falling control rods, and that delays the 19 bottoming out of those control rods to, say, instead 20 of 2.3 seconds now it's 3.5 seconds, or 4.5 seconds, 21 that safety related function no longer performed its 22 intended function. The intended function was to 23 prevent exposures. But because it was delayed, it 24 didn't perform its intended function. Do you 25 1($/5*5266
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22 understand?
1 So it's timing. It's not just performance 2
function. It's performance function in the time for 3
which the analysis was done.
4 MEMBER CORRADINI: So I think I hear you, 5
but let me just make sure. But the initiator is 6
superposed regardless of timing, and yet you're 7
worried about timing about the response?
8 MR. CLIFFORD: Yes.
9 MEMBER CORRADINI:
So that's more 10 conservative than I guess I would have expected. So 11 if I understand your logic with the first bullet, I've 12 got some sort of seismic event, and I have some sort 13 of other initiator. They could happen in some sort of 14 time sequence, but the way the analysis is, those two 15 accelerations and loads are superposed on each other.
16 And then the fuel assembly's got to show survival and 17 the three functions, as you noted on the previous 18 slide.
19 MR. CLIFFORD: Right.
20 MR. SCHULTZ: So what you're saying, Paul, 21 is don't just assume you're done when you demonstrate 22 that the rods go in.
23 MR. CLIFFORD: Right.
24 MR. SCHULTZ: You have to demonstrate that 25 1($/5*5266
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23 they go in with sufficient timing to prevent the 1
damage that might occur in the transient.
2 MR. CLIFFORD: Correct. Because you, I 3
mean, let me get to the next bullet, and I think it 4
kind of wraps it all up.
5 I think the next bullet --- in the next 6
few slides we're going to start talking about how we 7
combined events, you know, why we combined or how we 8
combined them. So it's important that we introduce 9
this concept that the event combination with the 10 largest combined loads may not necessarily be the most 11 limiting event combination.
12 It goes back to GDC-2 and Appendix S. You 13 have to show that each system that's important to 14 safety performs its intended function.
You've 15 demonstrated somewhere in your licensing basis that 16 each system performs its intended function. And the 17 requirement is under the loads.
18 So if you have to close a main seam 19 isolation valve, you've designed the main seam 20 isolation valve to close under the loads associated 21 with a steam line break. It has to perform that 22 function under those loads in combination with any 23 loads associated with a safe shutdown requirement.
24 That's the design-basis for that component. It has to 25 1($/5*5266
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24 perform that function due to defense in depth.
1 MEMBER CORRADINI: But it might be a 2
different initiator for a different component, that's 3
your point, is what I thought that means.
4 MR. CLIFFORD: Well, one way to look at it 5
is this. You have your design, this is where I was, 6
you have your functional requirements for each 7
component. And you demonstrate that that component 8
performs its function under its loads. GDC-2 says, 9
well, in addition to that, superimpose loads 10 associated with a safe shutdown requirement.
11 MEMBER CORRADINI: Okay. Even though the 12 design-basis for each one of those components could be 13 different?
14 MR. CLIFFORD: It's absolutely different.
15 Each one of them's different. And I think, in the 16 past, the second bullet is a good example here, the 17 last bullet, I mean. What we're saying here is in the 18 past we've always looked at earthquake and then 19 earthquake plus LOCA. That's where we focused our 20 attention.
21 And that's because you have ground motion 22 associated with earthquake, and you have basically a 23 pipe width or, you know, you have the response of your 24 vessel. The vessel movement is the result of a large 25 1($/5*5266
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25 steam, I mean, a large water break. So that breaks, 1
the vessel shifts, you can easily see how both of 2
those events separately impose accelerations on your 3
fuel assemblies. And so they're evaluated.
4 So I think, in the past, people were 5
looking at this and saying, well, what's the limiting 6
event for me? It's going to be, well, which one gives 7
me the highest combination of accelerations? It's 8
going to be LOCA, SSE. And so you evaluate that.
9 But when you combine those events, what is 10 the design-basis you're trying to demonstrate? It's 11 ECCS, because it's a LOCA. So you look at ECCS, you 12 show that ECCS performs its function. But ECCS is not 13 a very limiting event when it comes to design and fuel 14 performance and the fact that there's no expectation 15 of cladding integrity during a LOCA.
16 And the real logical consequences are 17 based on extremely bounding assumptions with 18 significant core damage that's unrelated to ECCS 19 performance. So that event, while giving you the 20 maximum accelerations, is not very limiting with 21 respect to the functionality of all the other safety 22 systems that have to be demonstrated with SSE.
23 MEMBER BALLINGER: So again, so what 24 you're saying is pick the main seam isolation valve, 25 1($/5*5266
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26 for example.
1 MR. CLIFFORD: Yes.
2 MEMBER BALLINGER: It's got a certain 3
design-basis. But you're saying it really doesn't 4
have a design-basis, because the actual design-basis 5
or requirement for operation has to do with multiple 6
loads that are added on top of one another. So in 7
effect, there's an envelope for every SSE important to 8
safety.
9 MR. CLIFFORD: Well, every load associated 10 with SSE will get combined with each of the components 11 in their evaluation. And there's a plant. They have 12 to evaluate a steam line break. They evaluate a steam 13 line break, they have a limited number of fuel rods 14 that can fail. And that's tied directly into the 15 offsite dose consequences.
16 They do that analysis, that mean steam 17 isolation valve has to shut in 2.1 seconds. If it 18 doesn't shut at 2.1 seconds, now there's a return to 19 criticality, and you fail 20 percent of the core, and 20 you don't meet your offsite doses. So the 21 demonstration that the plant is designed for a steam 22 line break, including the response of everyone of the 23 systems, not just the main seam isolation valves, is 24 completed in Chapter 15 of your FSAR.
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27 You look at Chapter 15, you can walk 1
through it, and you can show that each one of those 2
components performed its intended function, and you 3
limited offsite consequences to whatever your 4
licensing basis is. And maybe your licensing basis is 5
no fuel failure. So you've done that. But each one 6
of the component design analyses would verify that 7
each component's capable of performing its function.
8 MEMBER BALLINGER: So if you pull the 9
string on this you're, in effect, saying that every 10 plant is different. So if I put a plant in Idaho 11 versus a plant in California, the main steam isolation 12 valve will not be --- can't be designed until we know 13 what the SSE is or any other loads that are applied to 14 that.
15 MR. CLIFFORD: Right. With very 16 different seismic envelopes, you're going to have 17 different ---
18 MEMBER CORRADINI: But there's nothing new 19 to this regulation.
20 MR. CLIFFORD: There's nothing new to 21 this. There's nothing new, but it was confusing in 22 the past because of the change that I mentioned 23 earlier. In the past, people would look at it and 24 say, okay, if it's changed now, it's become more 25 1($/5*5266
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28 important, or it's become a bigger source of 1
confusion. It's because you no longer can use a 2
bounding analysis like you used to use.
3 You used to say, okay, with my rigid 4
structure, my rigid grid cage structure, I have a 5
maximum load before it racks. So it's the same. I 6
just have to make sure that I don't deform my grid, 7
deformation being the buckling, okay.
8 Now, if you allow plastic deformation, 9
this is the key, if you allow plastic deformation so 10 you start closing the rod pitch, you start changing 11 the thermal-hydraulic channels, if you start changing, 12 you allow this to happen. Now it becomes very 13 sensitive to what other accident you're trying to 14 verify.
15 LOCA is not sensitive to this. You can 16 take the entire assembly, and you can squeeze it 17 together. But it's not going to make that big of a 18 difference on your P-clad temperature. But it is 19 going to change your DNBR. And if you have a loss if 20 flow event, you can't survive much of a deformation 21 before you start failing rods which means that all the 22 system structures and components that were designed to 23 prevent you from failing those rods no longer perform 24 their intended function.
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29 MEMBER CORRADINI: So I guess I want you 1
to repeat that. Because I --- so what it comes down 2
to is a way in which the structural design has changed 3
is the reason that we have to be more careful, is what 4
I hear you saying.
5 MR. CLIFFORD: Yes. It's being driven by 6
two things. The first thing is you have cage designs 7
now that will deform before they buckle.
8 MEMBER CORRADINI: Versus being robust all 9
the way through the SSE?
10 MR. CLIFFORD: Robust before they buckled.
11 MEMBER CORRADINI: Correct. I'm sorry, 12 you said it. I didn't say it correctly.
13 MR. CLIFFORD: Yes.
14 MEMBER CORRADINI: And there was a second 15 point?
16 MR. CLIFFORD: The second one was, I 17 think, what we're seeing in NRO space is there just --
18
- they're taking the worst, of the worst, of the 19 worst, so they getting higher acceleration. So 20 they're getting more loads.
21 MEMBER CORRADINI: Because they wanted to 22 be applicable across ---
23 MR. CLIFFORD: If I go back to my days of 24 combustion engineering, you would design a 16 by 16 25 1($/5*5266
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30 assembly for Palo Verde. And you would design a 1
different 16 by 16 assembly for SONGS. The one at 2
SONGS would have thicker grid straps.
3 MEMBER CORRADINI: Because it was ---
4 MR. CLIFFORD: Because it was in a higher 5
seismic envelope. So you would design the fuel for 6
the seismic envelope. So you would have site specific 7
fuel designs. But now, we're not really doing it, 8
we're moving away from that.
9 MEMBER CORRADINI: Okay.
10 MEMBER REMPE: I meant to follow-up on 11 Ron's question. You could still have a bounding 12 seismic envelope. So you don't, like, have a 13 different design requirement for a plant in Idaho 14 versus a plant in Wisconsin, right, as long as you 15 found a seismic characteristic?
16 MR. CLIFFORD: Right. It depends on how 17 much work you want to do analytically versus how much 18 hardware you want to change.
19 MEMBER REMPE: Yes.
20 MEMBER BALLINGER: But that's fine for the 21 fuel, because the fuel comes out. And you can change 22 out the fuel. But that was then, this is now. What 23 about this main steam isolation valve for an existing 24 plant?
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31 MR. CLIFFORD: Oh, it's been designed.
1 MEMBER BALLINGER: It's been designed in 2
accordance with what you're saying, okay.
3 MR. CLIFFORD: Absolutely. None of this 4
is new. None of this is new. It's just become more 5
important, because now we're seeing deformation, and 6
I'll get to the deformation, whereas in the past we 7
didn't have deformation, allowable deformation of the 8
grid cage.
9 So here we get to the combined. You can 10 divide it into two. There's SSE+transients and then 11 SSE+LOCA.
And you can divide them because 12 SSE+transients, the accelerations on the fuel is not 13 significantly different than SSE alone. Because a 14 loss of flow doesn't cause the core barrel to move 15 which would then add more acceleration to your 16 existing SSE. But a LOCA would.
17 So I think that's historically why you've 18 seen SSE+LOCA and then SSE. Now, what we're seeing 19 is, to show the functionality of all of your safety 20 related components, there has to be an SSE+transient 21 requirement. And there has to be a demonstration.
22 MEMBER CORRADINI: But then just to make 23 sure I'm clear, and the reason you've added that 24 additional review space is because of the way the 25 1($/5*5266
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32 structural design of these newer fuel assemblies are 1
coming out, such that you could get what I'll call 2
non-linear effects that have to be considered.
3 MR. CLIFFORD: Correct. It's certainly 4
non-linear effects that would affect how you do the 5
- analysis, but then just having an allowable 6
deformation. In the past, you didn't have the 7
allowance for deformation. It was dumped to form your 8
grid cage.
9 MEMBER CORRADINI: End of story.
10 MR. CLIFFORD: End of story. Now there's 11
-- I sense somewhat of a relaxation to allow 12 deformation. But if you want to allow deformation, 13 you just have to account for it.
14 So when we talk about SSEs+transients, as 15 I mentioned earlier, you've got many different systems 16 that respond to many different types of accidents, 17 your reactor protection system, your ESFAS, is 18 engineered safety features actuation signal, respond, 19 and both have the response and the timing of the 20 response.
21 And the second half of the sentence is 22 right from Appendix S, "To assure the integrity of the 23 reactor coolant boundary, capability to shut down the 24 reactor and maintain safe shutdown condition, and the 25 1($/5*5266
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33 capability to prevent or mitigate the consequences of 1
accidents." So applicants must demonstrate that their 2
RPS and ESFAS are capable of performing the intended 3
safety features when exposed to combined loads, as 4
we've been talking about.
5 And when you get into allowable grid 6
deformation, this is where it gets a little sticky, in 7
a sense. This plot here shows DNBR degradation during 8
a loss of flow. There's a change in DNBR, there's a 9
function of time. DNBR is decreasing with reactor 10 coolant flow, as your pumps coast down. And then it's 11 turned around as your rods start falling.
12 So it's very -- it's time-dependent. So 13 it takes the actuations of you have to get a trip 14 function that initiates a trip, you've got to drop 15 your rods. And you've got to do this in a certain 16 sequence, in a certain timing. And it's very 17 dependent on that timing.
18 If there's an allowance for grid 19 deformation, then that grid deformation may alter the 20 local thermal-hydraulic condition such as delay of 21 DNBR degradation changes. Or if you delay your scram 22 insertion time, then you can just see from this 23 figure, you know, where's it going to bottom up and 24 turn around. If you delay this another second, you've 25 1($/5*5266
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34 decreased DNBR that much more.
1 So the demonstration of your SSCs, not 2
SSEs, SSCs, must take into account any allowance for 3
grid deformation and the impacts of that grid 4
deformation on local thermal-hydraulic conditions and 5
scram insertion time.
6 MEMBER CORRADINI: But your second bullet, 7
as you describe it with the example, is more 8
appropriate for the transient AOOs than it is for the 9
LOCA.
10 MR. CLIFFORD: Correct.
11 MEMBER CORRADINI: As I understand it.
12 MR. CLIFFORD: Right.
13 MEMBER CORRADINI: Okay, okay. Right, 14 right.
15 MR. CLIFFORD: LOCA also needs to account 16 for any grid deformations, and those grid deformations 17 may be larger for a LOCA, because you have the 18 combined accelerations which could cause further 19 deflection or deformation of your grid cage. Because 20 that's high loads, because you combine two different 21 loads. But they still have to account for it. But at 22 the same time, it may be less sensitive to changes in 23 geometry.
24 Let me go back to this one more time. So 25 1($/5*5266
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35 do you all understand you have Chapter 15 of your 1
EFSAR? We've analyzed all of the accidents that 2
you're required to analyze, and you've performed the 3
demonstration analysis where you've demonstrated that 4
using all of these systems that are surveilled in your 5
tech specs, that have set points that are dictated in 6
the licensing basis of the plant, if everything 7
performs as designed, you will meet the requirements 8
of your license.
9 And every event has a
different 10 requirement. And GDC-2 and Appendix S says that all 11 those systems that have to respond to each one of 12 those accidents have to be designed to survive your 13 SSE loads in combination with whatever loads are 14 associated with the accident they're trying to 15 mitigate.
16 So if you allow something to occur that 17 changes the geometry, the base geometry of your fuel, 18 or changes how the control rods insert, that has to be 19 fed into your Chapter 15 analysis. Otherwise, you 20 don't have a demonstration analysis for your entire 21 plant's design. So whereas 20 years ago or so when we 22 said no deformation, then a loss of flow or a loss of 23 flow with SSE, there was no difference, because there 24 was no deformation.
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36 MEMBER CORRADINI: So I'm sure the 1
applicant who you're reviewing is going to tell us, 2
but from your perspective, what's the benefit in 3
having a flexible grid structure?
4 MR. CLIFFORD: I would leave that to ---
5 MEMBER CORRADINI: Because what you're 6
telling --- what I'm hearing you telling me in a very 7
precise but limited way is that I've changed my design 8
philosophy. My design philosophy must account for 9
non-linear effects, I won't say non-linear, will 10 account for effects that have a potential change in 11 geometry which brings in a whole class of transients 12 that would never have to be considered.
13 MR. CLIFFORD: Correct.
14 MEMBER CORRADINI: Simply because I could 15 rest assured that the geometry remained the same after 16 the seismic event. That's what I hear you saying.
17 MR. CLIFFORD: Correct. And designs are 18 changing. And you could say they're probably being 19 driven to improve your thermal-hydraulic performance.
20 You get mixing veins, you get differences to provide 21 enhancements, and heat transfer, and that type of 22 thing.
23 MEMBER CORRADINI: Okay, thank you.
24 MR.
CLIFFORD:
- Okay, so that was 25 1($/5*5266
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37 SSE+transients. Now we're kind of getting to 1
SSE+LOCA. We all are familiar with this. ECCS is a 2
safety related system to mitigate the consequences of 3
a LOCA. You have to meet 5046 analytical limits to 4
ensure coolable core geometry in accordance with GDC-5 35.
6 Applicants must demonstrate that the ECCS 7
is capable of performing its intended safety function 8
when exposed to the combined loads. And that means 9
you have to maintain a coolable geometry, show that 10 fuel rod fragmentation does not occur, you meet the 11 specific analytical requirements of PCT and maximum 12 LOCA oxidation to show that maintained ductility so 13 you don't shatter your fuel upon quench. You maintain 14 material insertion if required, and you remove long 15 term decay heat. And if there is an allowance for 16 grid permanent deformation, that must be accounted for 17 in your ECCS performance demonstration.
18 So those are the regulatory requirements.
19 Any further questions?
20 MEMBER CORRADINI: If I might, just ask it 21 differently. The anticipation is, with this new 22 design, with this modified design philosophy, that 23 there is potentially not a difference in challenge 24 here as much as there'd be a challenge on the 25 1($/5*5266
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38 transient side. That's the impression I'm left with 1
in your discussion.
2 MR. CLIFFORD: You mean from a LOCA 3
perspective?
4
`
MEMBER CORRADINI: Right.
5 MR. CLIFFORD: It's no different. It's no 6
different.
7 MEMBER CORRADINI: Right.
8 MR. CLIFFORD: If you can go to the EFSAR 9
for several plants today, and you'll see a LOCA 10 analysis, and then you'll see a special SSE+LOCA 11 analysis where they've decreased the rod to rod 12 spacing and they've redone their LOCA assessment to 13 show that they're stable at 2,217 percent. But you're 14 not going to see the same in any other event.
15 MEMBER CORRADINI: Okay. That helped, 16 thank you.
17 MR.
CLIFFORD:
Another thing that's 18 important to mention is that it's not just the changes 19 in how NRO, how they use bounding analyses, bounding 20 inputs to their seismic, or the change in grid strap.
21 But there's also, you know, we identified that these 22 irradiation effects have a first order effect on the 23 fuel assembly's response --
24 So when they take that into account, you 25 1($/5*5266
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39 know, this new information, they realize that some of 1
their --- maybe their previous assumptions weren't ---
2 I wouldn't say accurate, but just didn't account for 3
the new phenomena. Are we good?
4 (No audible response) 5 MR. CLIFFORD: Okay. Next on the agenda 6
is Framatome.
7 MEMBER BALLINGER: Well, we have a few 8
things we have to do first. Since this is the only 9
open session version, we now need to ask if there are, 10 well, there are no members of the public here. So we 11 need to ask if there is anybody on the public phone 12 line that would like to make a comment. So the line's 13 open, right.
14 MR. SNODDERLY: Yes. Is Sarah Fields 15 there?
16 MS. FIELDS: Yes, I am.
17 MR. SNODDERLY: Okay. Just want to make 18 sure you're there.
19 MS. FIELDS: Yes. It's a challenge to 20 understand everything and wrap my head around it. So 21 this is just --- I wonder how this is going to affect 22 this NuScale design certification application. In the 23 beginning, you mentioned the topical report, but that 24 wasn't --- I didn't quite catch which topical report 25 1($/5*5266
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40 that was.
1 MEMBER CORRADINI: Ms. Fields, you can 2
submit --- we can't answer the questions as we're in 3
the middle of the meeting. But if there's questions 4
you need clarification on, you can send an email to 5
Mike Snodderly, and he will answer your questions.
6 MR. SNODDERLY: Yes, so Sarah ---
7 MS. FIELDS: All right. Okay, I'm just 8
supposed to make a comment.
9 MR. SNODDERLY: Yes, that's ---
10 MS. FIELDS: Yes.
Well, thank you. And 11 I will just send a few questions to Mr. Snodderly.
12 MEMBER CORRADINI: Right, and ---
13 MR. SNODDERLY: I'll take an action item, 14 Ms. Fields, to send you the publicly available NuScale 15 report. It won't have the proprietary information.
16 It'll be blacked out. But I think that's what you 17 were asking. And then that report refers to this 18 report, okay.
19 MS. FIELDS: And I do wonder how this --
20
- this is just a comment --- how the public will be 21 able to review this information and a lot of other 22 information that is not made publicly available in 23 this design certification process and after, you know, 24 as you go on with the rest of your meeting today, 25 1($/5*5266
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41 which is not going to be available to the public.
1 Oh, another comment is I hope you will get 2
the transcript for this meeting and the transcript for 3
the previous meeting up on the ACRS website page as 4
soon as possible. Thank you.
5 MEMBER BALLINGER: Thank you. Are there 6
any other members of the public that would like to 7
make a comment?
8 (No audible response) 9 MEMBER BALLINGER: Hearing none, we need 10 to close the line. And we need to go into closed 11 session. And so that means that folks need to verify 12 that there's nobody here that they don't want to be 13 here.
14 (Whereupon, the above-entitled matter went 15 off the record at 1:46 p.m.)
16 17 18 19 20 21 22 23 24 25 1($/5*5266
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1 Regulatory Requirements Associated with Fuel Assembly Performance Under Seismic and LOCA Conditions ACRS NuScale Subcommittee March 21, 2018 Paul M. Clifford Division of Safety Systems Nuclear Reactor Regulation
2 Agenda
- 1. Applicable Regulations
- 4. Combined SSE+Transient
- 5. Combined SSE+LOCA
3 Applicable Regulations
- 10 CFR 50 Appendix A, General Design Criteria for Nuclear Power Plants (GDC), Criterion 2, Design bases for protection against natural phenomena 3/4SSCs important to safety, including reactor fuel, shall be designed to withstand the effects of earthquakes without loss of capability to perform their safety functions 3/4combinations of the effects of normal and accident conditions with the effects of the natural phenomena Structures, systems, and components important to safety shall be designed to withstand the effects of natural phenomena such as earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches without loss of capability to perform their safety functions. The design bases for these structures, systems, and components shall reflect: (1) Appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have been accumulated, (2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena and (3) the importance of the safety functions to be performed.
4 Applicable Regulations (cont)
- 10 CFR 50 Appendix S, Earthquake Engineering Criteria for Nuclear Power Plants 3/4Establishes definitions for the Operating Basis Earthquake (OBE),
Safe Shutdown Earthquake (SSE), and safety requirements for relevant SSCs 3/4Implements GDC-2 Operating basis earthquake ground motion (OBE) is the vibratory ground motion for which those features of the nuclear power plant necessary for continued operation without undue risk to the health and safety of the public will remain functional.
Safe-shutdown earthquake ground motion (SSE) is the vibratory ground motion for which certain structures, systems, and components must be designed to remain functional.
Structures, systems, and components required to withstand the effects of the safe-shutdown earthquake ground motion or surface deformation are those necessary to assure:
(1) The integrity of the reactor coolant pressure boundary; (2) The capability to shut down the reactor and maintain it in a safe-shutdown condition; or (3) The capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposures comparable to the guideline exposures of 50.34(a)(1).
5 OBE Requirements
- OBE is not a postulated accident and is expected to occur during the lifetime of the reactor. Plants are not required to shut down following a seismic event up to the OBE ground motion, and may restart (without NRC involvement) if tripped on other signals during the event (e.g., loss of switchyard or offsite power).
- SSCs necessary for continued safe operation must remain functional and within applicable stress, strain, and deformation limits.
3/4All fuel assembly components maintain operational functionality (I) When subjected to the effects of the Operating Basis Earthquake Ground Motion in combination with normal operating loads, all structures, systems, and components of the nuclear power plant necessary for continued operation without undue risk to the health and safety of the public must remain functional and within applicable stress, strain, and deformation limits.
6 SSE Requirements
- SSE is a postulated accident and is not expected to occur during the lifetime of the reactor. Plants are required to shut down following a seismic event beyond OBE ground motion.
- With respect to fuel performance, applicant must demonstrate that fuel assembly components are capable of performing their intended safety functions under SSE conditions:
3/4Fuel rod cladding maintains fission product barrier 3/4Spacer grids maintain geometry of fuel bundle array 3/4Guide tubes maintain pathway for control rod movement (ii) The nuclear power plant must be designed so that, if the Safe Shutdown Earthquake Ground Motion occurs, certain structures, systems, and components will remain functional and within applicable stress, strain, and deformation limits. In addition to seismic loads, applicable concurrent normal operating, functional, and accident-induced loads must be taken into account in the design of these safety-related structures, systems, and components.
7 SSE Requirements (cont.)
- SSCs important to safety must be capable of performing their intended function when exposed to the combined loads of SSE ground motion in combination with functional and accident loads (during the accident for which the SSC is designed to mitigate).
- Capability to perform their intended function often judged against the fuel rods performance under a wide range of accident conditions 3/4 Functionality being both capability and timing of action
- Maximum combined loads associated with SSE+LOCA; however, acceptance criteria used for judging functionality of SSCs may be less restrictive under LOCA conditions relative to other transients.
3/4 For example, during a postulated LOCA there is no expectation of fuel rod cladding integrity and offsite dose calculations are based on bounding assumption of significant core damage
8 SSE+Transient Requirements
- For AOOs and non-LOCA transients, RPS and ESFAS actions and the timing of these actions are essential to assure the integrity of the reactor coolant boundary, the capability to shut down the reactor and maintain it in a safe-shutdown condition, and the capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposures.
- Applicant must demonstrate that RPS and ESFAS are capable of performing their intended safety functions when exposed to the combined loads of SSE ground motion in combination with functional and accident loads during the accident for which the SSC is designed to mitigate.
9 Allowable Grid Deformation Spacer grid deformation potentially creates an unanalyzed condition relative to the UFSAR analysis-of-record (performance demonstration) 3/4 May alter local thermal-hydraulic conditions 3/4 May delay scram insertion The demonstrated performance of SSCs designed to prevent or mitigate the consequences of accidents, including the timing of such actions, would need to account for impacts associated with changes in local TH conditions and scram insertion.
Loss of Forced Flow - MDNBR vs Time
10 SSE+LOCA Requirements
- Emergency Core Cooling System (ECCS) is a safety-related system credited to mitigate the consequences of a postulated LOCA.
3/4 50.46 analytical limits ensure a coolable core geometry in accordance with GDC-35
- Applicants must demonstrate that ECCS is capable of performing its intended safety function when exposed to the combined loads of SSE ground motion in combination with functional and accident loads during a LOCA.
3/4Maintain a coolable geometry 3/4 Fuel rod fragmentation does not occur 3/4 ECCS performance must satisfy 50.46 requirements 3/4Control rod insertability maintained, if required 3/4Long-term decay heat removal Allowable spacer grid permanent deformation (resulting from combined SSE+LOCA loads) must be accounted for in ECCS performance demonstration.