ML16008A689
| ML16008A689 | |
| Person / Time | |
|---|---|
| Issue date: | 04/20/2006 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | |
| References | |
| NRC-981 | |
| Download: ML16008A689 (316) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
Advisory Committee on Reactor Safeguards Reliability and Probabilistic Risk Assessment Subcommittee Docket Number: (not applicable)
Location: Rockville, Maryland Date: Thursday, April 20, 2006 Work Order No.: NRC-981 Pages 1-315 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1323 Rhode Island Avenue, N.W.
Washington, D.C. 20005 (202) 234-4433
1 1 UNITED STATES OF AMERICA 2 NUCLEAR REGULATORY COMMISSION 3 + + + + +
4 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS (ACRS) 5 SUBCOMMITTEE ON RELIABILITY AND RISK ASSESSMENT 6 + + + + +
7 THURSDAY, 8 APRIL 20, 2006 9 + + + + +
10 ROCKVILLE, MARYLAND 11 + + + + +
12 The subcommittee met at the Nuclear 13 Regulatory Commission, Two White Flint North, Room T-14 2B1, 11545 Rockville Pike, at 8:30 a.m., George E.
15 Apostolakis, Chairman, presiding.
16 COMMITTEE MEMBERS:
17 GEORGE E. APOSTOLAKIS, Chairman 18 J. SAM ARMIJO, Member 19 MARIO V. BONACA, Member 20 RICHARD S. DENNING, Member 21 THOMAS S. KRESS, Member 22 OTTO L. MAYNARD, Member 23 WILLIAM J. SHACK, Member 24 JOHN D. SIEBER, Member 25 GRAHAM B. WALLIS, Member NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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2 1 ACRS/ACNW STAFF:
2 ERIC THORNSBURY, Designated Federal Official 3 PANELISTS:
4 ALAN BEARD, GE 5 SID BHATT, GE 6 DAVID HINDS, GE 7 THEO THEOFANOUS, GE 8 RICK WACHOWIAK, GE 9 NRC STAFF:
10 MARTHA C. BARILLAS, NRR/DNRL 11 SUD BASU 12 AMY CUBBAGE, NRR 13 JIM GASLEVIC 14 LYNN MROWCA, NRR 15 BOB PALLA, NRR 16 LAUREN QUINONES, NRR/DNRL 17 LARRY ROSSBACH 18 NICK SALTOS, NRR 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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3 1 C O N T E N T S 2 PAGE 3 Introduction, Chairman Apostolakis . . . . . . . 4 4 Introduction to Presentations, Amy Cubbage . . . 5 5 Presentation by GE 6 Overview:
7 David Hinds . . . . . . . . . . . . . . . 8 8 Rick Wachowiak . . . . . . . . . . . . . . 10 9 Internal Events Risk Management and Severe Accident 10 Prevention:
11 Rick Wachowiak . . . . . . . . . . . . . . 47 12 13 14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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4 1 P R O C E E D I N G S 2 (8:33 a.m.)
3 CHAIRMAN APOSTOLAKIS: The meeting will 4 now come to order.
5 This is a meeting of the Advisory 6 Committee on Reactor Safeguards, Subcommittee on 7 Probabilistic Risk Assessment.
8 I am George Apostolakis, Chairman of the 9 Subcommittee. Members in attendance are William Shack, 10 Sam Armijo, Mario Bonaca, Rich Denning, Tom Kress, 11 Otto Maynard, Jack Sieber, and Graham Wallis.
12 The purpose of the meeting is to begin our 13 review of the ESBWR probabilistic risk assessment.
14 The Subcommittee will gather information, analyze the 15 relevant issues and facts, and formulate proposed 16 positions and actions as appropriate for deliberation 17 by the full Committee.
18 Eric Thornsbury is the Designated Federal 19 Official for this meeting.
20 The rules for participation in today's 21 meeting have been announced as part of the notice of 22 this meeting previously published in the Federal 23 Register on April 4, 2006.
24 A transcript of the meeting is being kept 25 and will be made available as stated in the Federal NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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5 1 Register notice.
2 It is requested that speakers first 3 identify themselves and speak with sufficient clarity 4 and volume so that it can be readily heard.
5 We have received not written comments or 6 requests for time to make oral statements from members 7 of the public regarding today's meeting.
8 We will now proceed with the meeting, and 9 I call upon Ms. Amy Cubbage, the NRR's project 10 manager, to introduce the presentations.
11 MS. CUBBAGE: Good morning. I'd just like 12 to give a few opening remarks to set the stage for the 13 presentations you'll be hearing from GE today and 14 tomorrow. There will be a staff presentation tomorrow 15 afternoon as well.
16 The application for certification is 17 submitted in August and then supplemented in 18 September-October. The application was accepted for 19 docketing on December 1st, 2005, and since that time 20 we have received Revision 1 of the design control 21 document in three different pieces as listed here.
22 The one piece that has not been submitted 23 yet is Revision 1 of Chapter 19 of the DCD, which is 24 the PRA.
25 We did provide preliminary requests for NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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6 1 additional information to GE on severe accidents.
2 Those were provided to GE in RAI letter number three, 3 which was sent to them in December. That should be 4 '05, a typo there, and GE is in the process of 5 revising the PRA to address these RAIs and also to 6 incorporate the changes that were made between 7 Revision 0 and Revision 1 of the DCD.
8 So as you can see here some of the 9 chapters of the Revision 1 of the PRA have been 10 submitted and have been provided to the committee.
11 The additional chapters, I believe some of them are 12 coming today and others will be here within a week or 13 two.
14 At that time we'll have a complete 15 Revision 1 of all the PRA documents.
16 Just the overall certification schedule.
17 We're currently issuing RAIs to GE, and that will 18 proceed through October '06, and then we're expecting 19 all of the RAI responses to be received through 20 November '06.
21 We're planning to issue the SER with open 22 items in October '07, and at that point we'll begin 23 the process of closing those open items and issuing 24 supplemental SERs as necessary in assumed 15 months' 25 duration to complete that effort, and then we will NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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7 1 start the rulemaking period, which is assumed to last 2 12 months.
3 CHAIRMAN APOSTOLAKIS: When you say 15 4 months, starting when?
5 MS. CUBBAGE: Starting with the issuance 6 of the SER with open items. So --
7 CHAIRMAN APOSTOLAKIS: October '07, 15 8 months after that?
9 MS. CUBBAGE: Right, and that's just an 10 assumption at this point. Until we know the number 11 and scope of open items, we won't be able to establish 12 a firm schedule for that. If the number and scope of 13 open items is small, we may be able to proceed quicker 14 than that.
15 CHAIRMAN APOSTOLAKIS: So we may go to 16 2009.
17 MS. CUBBAGE: That's right.
18 CHAIRMAN APOSTOLAKIS: And the ACRS is 19 involved there?
20 MS. CUBBAGE: The ACRS would be involved.
21 Right. I would expect a lot of involvement at the SER 22 with open item stage, and then as we're issuing the 23 supplements. Of course, if there's any topics of 24 interest early on, we could provide more meetings like 25 this to provide you with an overview of different NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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8 1 topics.
2 So that's all I had.
3 MEMBER WALLIS: And you said that there 4 are other presenters tomorrow afternoon?
5 MS. CUBBAGE: Yes, tomorrow afternoon.
6 MEMBER WALLIS: We're due to adjourn at 7 12:15. So they may be talking to themselves.
8 MS. CUBBAGE: I say afternoon. Mid-9 morning. Sorry. It's noted on your agenda.
10 And what we are doing, briefly, tomorrow 11 is just going over the RAIs that we've issued, a 12 summary of those, and then Office of Research is going 13 to be presenting information on confirmatory severe 14 accident calculations.
15 MEMBER WALLIS: Just a core catcher?
16 MS. CUBBAGE: Is Office of Research going 17 to? I don't know. That is a question for GE.
18 At this time I'd like to introduce Stephen 19 Hinds to make some remarks for GE.
20 MR. HINDS: Good morning. I'm David Hinds 21 from the GE ESBWR Engineering Manager.
22 I'd just like to hurriedly introduce our 23 team that we have here today. We have Rick Wachowiak 24 over here. He is PRA lead. He will be the main 25 speaker today.
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9 1 And we also have Sid Bhatt over here, who 2 will also be supporting Rick and making some 3 presentations this afternoon.
4 Supported by Alan Beard, basically if you 5 ask some questions that we need to point in his 6 direction supporting the presentation.
7 And then coming in later we'll have 8 Theofanous, who will be supporting us on our severe 9 accident analysis.
10 And we have a day and a half planned here 11 with the focus, overview of our PRA as well as our 12 severe accident analysis, and we'll go I suppose as 13 deep as we can within the day and a half time period, 14 and I'm sure we'll be back here to see you again.
15 We look forward to sharing information 16 with you here today. The PRA with the ESBWR has been 17 done in parallel with the design and we're going to 18 cover some of that process, but it has been a very 19 interesting process using the PRA as a design tool 20 such that we can incorporate risk insights into the 21 design as we go along. It brings upon certain 22 challenges we're actually closing out and completing 23 in the PRA, but it's a very good design tool and 24 useful in our design process, and Rick will cover that 25 in more detail.
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10 1 So I'll turn it over to Rick.
2 MR. WACHOWIAK: Good morning. I guess I'm 3 supposed to sit close to the microphone.
4 CHAIRMAN APOSTOLAKIS: Do you mind 5 standing up?
6 MR. WACHOWIAK: I don't mind standing up.
7 CHAIRMAN APOSTOLAKIS: We want to see your 8 body language.
9 MR. WACHOWIAK: I'll go ahead and start 10 from here.
11 The first part of the presentation is 12 going to be an overview of what it is we're going to 13 do today and tomorrow and talk a little bit about the 14 philosophy of how we used the PRA as a design tool, to 15 be able to say. So the agenda for the meeting or at 16 least the GE presentation, this is all printed in the 17 agenda, but we want to cover an overview of how we use 18 risk management. We're going to talk about severe 19 accident prevention, which is pretty much the Level 1 20 PRA; severe accident mitigation, which discusses the 21 various phenomena of severe accident; containment 22 system performance. Once we get beyond the phenomena 23 of severe accidents, what does the containment do as 24 a system itself?
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11 1 analysis as it relates to a design PRA, a non-site 2 specific design PRA.
3 Tomorrow we'll talk about external events, 4 shutdown, and then conclude with some of our insights 5 and other information about how we'll be proceeding as 6 we go into the future.
7 The purpose of the meeting, one, to 8 outline the strategy for how we use risk management 9 land ESBWR design. We want to be able to demonstrate 10 to you the robust nature of the ESBWR as it relates to 11 severe accidents and the way we prevent and mitigate 12 severe accidents.
13 We're also going to talk more about how we 14 use the PRA as a design tool for designing and also 15 for licensing nuclear power plants.
16 Now, in the DCD phase of this whole 17 design, which is what we're discussing now, we have to 18 build a PRA that will support the design that goes in 19 and is being reviewed for the DCD, and we needed to do 20 certain things. We can't do everything at this point 21 because we don't know everything at this point, and we 22 may never know everything, but we get closer as time 23 goes by.
24 What we want to make sure we can do is 25 that this PRA needs to be able to demonstrate that we NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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12 1 meet the established goals, risk goals. We want to be 2 able to demonstrate that the ESBWR design is actually 3 better than what's currently out there. So not only 4 meeting the goals, but we want to meet and exceed the 5 goals. It's hard to say with goals which way is 6 exceed.
7 Also in this process, we're extending the 8 use of defense in depth into the severe accident 9 scenarios themselves, and we'll talk about that on a 10 later slide. We want to be able to identify systems 11 that are important to risk and provide a basis for the 12 design reliability assurance program.
13 Those two things are some things that are 14 going to be a constant dialogue with the NRC over the 15 DCD process because some of the things that you need 16 in order to identify what goes into these pieces are 17 not necessarily available to go into the analysis at 18 this point.
19 So we have to figure out how we balance 20 what we know at this time in the design versus what we 21 think it's going to be in the future and what controls 22 need to be placed on how we address these things in 23 the future. I think that's going to be a constant 24 dialogue, and it's not settled business yet.
25 Finally, we want to be able to provide a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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13 1 framework for the plant specific PRA. In the end as 2 we go through all of the iterations for the PRA during 3 the design phase, during the licensing, the ultimate 4 output is going to be something that the utilities can 5 use in their operation of the plant. And because it 6 has gone through the licensing phase, it will be 7 something that the NRC is familiar with, unlike with 8 the current plant PRAs where there was kind of, you 9 know, the plant guys knew some things, the NRC knew 10 some things, and nobody quite matched up.
11 But we should all be in sync when we get 12 through this process here.
13 MEMBER DENNING: Before you move on from 14 this slide, when you talk about demonstrating ESBWR 15 meets established risk goals, by that do you mean the 16 quantitative health objectives?
17 MR. WACHOWIAK: Yes, and the CDF and log 18 release frequency goal.
19 MEMBER DENNING: Right. Have you 20 established goals yourself that are more stringent 21 than those goals or different than those goals?
22 MR. WACHOWIAK: In some cases we have, and 23 it is kind of built in down here. Demonstrate that 24 it's better. Let's take the core damage frequency 25 goal. The subsidiary goal is established at ten to NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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14 1 the minus four per year.
2 Well, the EPRI URD took that down another 3 level, ten to the minus five per year. We still don't 4 want to be in that range. We're looking at below ten 5 to the minus six for all the things that we know 6 about. We're trying to do as good as we can to be 7 below ten to the minus seven for the things that we 8 know about at this point, and we think we've 9 established that.
10 But those are not -- below the ten to the 11 minus six, it's more of a squishy goal rather than a 12 hard goal. We want to get there, but that's how we're 13 using the PRA to drive us toward that range.
14 And once again, remember that where we are 15 now with knowing what we know at this current phase of 16 the design, if our target is below ten to the minus 17 seven, as things come up we have room to address them 18 and room to see how we want to proceed with those.
19 CHAIRMAN APOSTOLAKIS: Which is exactly 20 the point I wanted to raise. I mean, you can't 21 demonstrate that you need to establish goals because 22 your PRA is necessarily incomplete, correct? I mean 23 you can afford three orders of magnitude below, 24 chances are you will meet it, but at this point, I 25 mean, we have got knowledge that there are, you know, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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15 1 many holes in the PRA because you don't have a plan.
2 MR. WACHOWIAK: I would agree with that.
3 CHAIRMAN APOSTOLAKIS: I mean, you need a 4 fire assessment. Every other sentence says, you know, 5 "We don't have information. This is generic. This is 6 generic. We don't have information," which is fine.
7 I mean, that's the situation, but we can't really say 8 that we're demonstrating we're meeting the goals. I 9 mean, we're doing what we can with what we have now.
10 Of course, if we violate the goals now, we are in 11 trouble.
12 So do we have the microphone finally? Ah, 13 there you are.
14 (Discussion was held off the record.)
15 MR. WACHOWIAK: All right. One of the 16 things that was associated with this demonstration, 17 one, you really can't demonstrate until you're done 18 and you know everything that you don't know now, and 19 even when you get to that point, there's still the 20 unknown unknowns, and you'll never get all the way 21 down. But we're talking about demonstrating using 22 what we know now.
23 There are also cases that we looked at and 24 we know that we need to know more information to get 25 to there, and so what we've done in our process is NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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16 1 we've specified some design requirements that says, 2 okay, the analysis is going to assume in the fire area 3 it's a fire thing, but it's really in the flood 4 scenario. We're going to specify where some of the 5 fire protection piping needs to be in the control 6 building because we want to assure an assumption that 7 we put into the flooding analysis. So we're providing 8 design requirements out of the PRA to address some of 9 these unknowns at this point.
10 MEMBER WALLIS: Does your PRA include 11 deliberate human actions in some way?
12 MR. WACHOWIAK: Acts of commission?
13 MEMBER WALLIS: Yes. Do you have it so 14 that it's robust in terms of acts of commission?
15 MR. WACHOWIAK: The current design phase, 16 the current DCD PRA does not include acts of 17 commission.
18 MEMBER KRESS: There was some explanation 19 for that, having to do with the fact that no operator 20 actions are required for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or something.
21 MR. WACHOWIAK: No operator actions are 22 required for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, but we have to remember that no 23 operator actions required doesn't mean no operator 24 actions will happen. But the way that our goal is in 25 designing the control systems of this passive plant is NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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17 1 that if the operators start to do something and then 2 they stop, the plant should move itself back into the 3 stable state as opposed to where in some of the acts 4 of commission and existing plants, where operators 5 start getting into things they send down a different 6 path and it gets kind of unknown.
7 What we're trying to do with this design 8 is make it so that if they do something, recognize 9 that they're going the wrong way and go hands off 10 again, it's supposed to stabilize back into the safe, 11 stable state condition. We're not far enough along in 12 the design of the control systems to be able to prove 13 that, but that's the goal that we have in mind.
14 The scope of the DCD PRA for internal 15 events at full power, we've got Level 1, Level 2, and 16 Level 3, and you have to recognize Level 3 is not a 17 real Level 3. It's a Level 3 using imaginary 18 information provided to us in the URD for population 19 and things like that. And we really only look out 20 about ten miles from the site boundary in addition to 21 that. So it's maybe a three minus.
22 Internal events. For shutdown we've done 23 Level 1 and in the process of completing a simplified 24 Level 2, which is going to be in one of these 25 submittals here that will come up shortly.
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18 1 External events. We've done internal 2 fires, flood, and high winds. As you said, on what we 3 believe is a conservative bounding basis, once again, 4 the details to do a detailed analysis of these are not 5 here yet.
6 Seismic margins on the safety systems 7 we've provided, and all of this is associated for the 8 internal events at the Level 1, and we've covered in 9 the internal fire and flood both full power and 10 shutdown analysis. So that's also the initial Rev. 0 11 that you may have seen didn't have the shutdown for 12 fire and flood in it. We've completed that analysis, 13 and we are in the process of writing that up, and 14 we'll talk about it a little tomorrow when we get to 15 the fire and flood, but you don't have those documents 16 yet.
17 Okay. Let's talk a little bit about the 18 extended defense in depth. Historically the classical 19 design and analysis work that was done for previous 20 plants provided defense in depth certainly, but it was 21 using the design basis or single failure type of 22 assumptions.
23 For an accident you have an accident under 24 the parameters and a single failure, and then you make 25 sure that you have defense in depth associated with NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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19 1 providing the fuel barrier, providing the reactor 2 coolant boundary barrier, providing the containment 3 barrier, still under that whole same framework.
4 Here what we've done is we've moved that 5 on into the severe accident arena where we're looking 6 at multiple failures of maybe components within the 7 same systems or components across barriers, and 8 looking at how we can provide defense in depth against 9 things that went beyond what were looked at before.
10 And I kind of say this in that the main 11 objective is to address common cause type failures.
12 I'll get to the sub-bullets here in a second.
13 We also look at defense in depth on the 14 containment side, not only given a degraded core 15 that's still in the vessel, which was historically 16 done for defense in depth, but now we're looking at 17 what kind of protection we have for core in the floor 18 type scenarios, and we'll get to some of those later 19 this afternoon and talk about the areas where we've 20 addressed that.
21 Now, one of the places where we're using 22 the PRA as a design tool is in this area of the 23 extended defense in depth. How is it that we can 24 protect against some of these multiple failure 25 scenarios?
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20 1 Historically when a plant came across some 2 common cause failure issue, the only option it really 3 had was to do an augmented QA, if you will, on those 4 components that you may see common cause failures 5 there.
6 Well, we are in the design process. We 7 have the luxury of doing something else in addition to 8 that and adding diversity to our systems to try to 9 eliminate some of the common cause or eliminate the 10 effects, strong effect, of some of the common cause 11 failures, and that's something that because we're 12 using the tool this early, we can cost effectively 13 provide that.
14 CHAIRMAN APOSTOLAKIS: Are you coming back 15 to this issue later?
16 MR. WACHOWIAK: I didn't have any specific 17 bullets on that. So --
18 CHAIRMAN APOSTOLAKIS: Well, it would be 19 nice to see an example.
20 MEMBER DENNING: Specifically what were 21 you looking for, George?
22 MR. WACHOWIAK: A specific example?
23 CHAIRMAN APOSTOLAKIS: Yeah. I mean, --
24 MR. WACHOWIAK: You know, actually in the 25 next presentation I do talk about how we use a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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21 1 combination of passive and active systems and diverse 2 control systems. So I think I have an example there.
3 So we'll get into that.
4 MEMBER ARMIJO: But was that an output of 5 this process or was that already going in and you had 6 planned to do that? In other words, are you really 7 using the PRA to gain insights that will help you 8 create diversity that pays off?
9 MR. WACHOWIAK: The answer to that is most 10 of the time. Because there are other things that are 11 in the we'll say the different requirements documents 12 that are out there that say, well, you've got to look 13 at diversity.
14 MEMBER ARMIJO: Right, generally speaking.
15 MR. WACHOWIAK: So if we hadn't done a 16 PRA, we probably would have gotten there anyway, but 17 in general, those documents to some degree came out of 18 previous risk analysis. So it's kind of in there.
19 However, where we are doing this is when 20 we say -- when we look at what the PRA is telling us.
21 Here's a common cause failure that we need to address.
22 We go back and we say, "What kind of diversity do we 23 have in the design to address things like that?"
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22 1 which instrument and control systems themselves needed 2 to be diverse from the other instrument and control 3 system.
4 MEMBER KRESS: How did you quantify the 5 effect of that diversity? Did you change the beta 6 value?
7 MR. WACHOWIAK: Basically, that's what we 8 did.
9 MEMBER KRESS: But you had no way to know 10 what to change it to?
11 MR. WACHOWIAK: At this point in the 12 design and procurement, yes, it was looking 13 conceptually.
14 MEMBER KRESS: So you use expert opinion 15 or something?
16 MR. WACHOWIAK: Expert opinion.
17 Conceptually what would the effect of using diverse 18 control systems have on this, and conversely, what was 19 the effect of saying that we don't need that diversity 20 requirement here? What would that do to us in terms 21 of our design PRA?
22 Yes.
23 MEMBER SIEBER: I was going to ask a 24 question about diversity in the INC area. My question 25 really goes to the extent to which you use diversity.
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23 1 For example, in the digital INC scheme, you could have 2 diversity in computer, here's Train A, here's Train B, 3 here's Train C. But they could all use common 4 software, which sort of defeats the principle of 5 diversity because if there's a mistake here and you 6 replicate it over here, a mistake in both places and 7 it will fail both places.
8 To what extent have you fleshed out the 9 degree to which diversity would be required not only 10 in higher order, but also in software and techniques, 11 databases, et cetera?
12 MR. WACHOWIAK: We've looked at basically 13 all of those types of issues. We are specifying the 14 two INC systems need to be diverse. What we mean by 15 diverse there is different hardware platform, 16 different vendor. I think it would be different 17 vendor, different operating system in some case. It's 18 going to be different -- I've already covered 19 hardware.
20 So we did address those things. Now, is 21 it possible that some of the different diverse INC 22 systems could have some overlap? And the answer there 23 is yes.
24 But the question then is: where is that 25 appropriate? Where we are in the design phase on that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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24 1 right now is we've got, if you will, a diversity 2 matrix that the INC guys and the procurement guys are 3 looking at, which is the kind of diversity we want to 4 have in this system, and they're in the process of 5 evaluating different vendors under a multitude of 6 different criteria, including the diversity criteria, 7 to try to assign the correct vendor system hardware 8 for each of those different systems, and that's 9 ongoing at this point.
10 MEMBER SIEBER: When you finally certify 11 ESBWR, will the INC portion be included in that 12 certification, or would that be done at the COL stage?
13 MR. WACHOWIAK: I guess that's --
14 MEMBER SIEBER: Or don't you know?
15 MR. WACHOWIAK: I'm going to have to defer 16 because those are policy decisions, and I don't get to 17 make those.
18 MEMBER SIEBER: Well, make it, you know.
19 (Laughter.)
20 MR. HINDS: Hi. This is David Hinds.
21 As much as possible, the INC system is 22 part of the certification, but we are using the DAC 23 approach, or design acceptance criteria approach, but 24 we're moving as rapidly as possible to close as much 25 of the DAC or design acceptance criteria open issues, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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25 1 and it will be flowing through certification and some 2 of it into COL as well.
3 But the major issues that affect, I guess, 4 the essence of your question and diversity, we intend 5 to close that as soon as possible, but we did take the 6 back-up approach. So some of that is going on as we 7 speak.
8 MEMBER SIEBER: I can see why you would do 9 that, because if you specify today what you would do 10 by tomorrow, it would be obsolete.
11 MR. HINDS: That's the reason for the DAC 12 approach. The design acceptance criteria, for anyone 13 that's not aware of what I'm speaking of, defining the 14 design in the form of a criteria as opposed to just 15 the end result of we selected this piece of equipment 16 because, as you say, the INC system has become 17 obsolete rapidly. So we're defining the criteria, and 18 then as rapidly as we can we're filling in details 19 that can help us to firmly answer questions such as 20 this, the defense in depth, although we have to 21 maintain a certain amount of flexibility due to 22 obsolescence of software and hardware, and that's the 23 balancing act we're working with in the INC system.
24 MEMBER SIEBER: Okay. Thank you.
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26 1 because you may prefer to answer this question, and 2 that is from your perception, what are the regulatory 3 implications of this extension into the control of 4 severe accident processes? Specifically, I'm 5 wondering about things like as far as the core catcher 6 is concerned where there might be a lot of 7 phenomenological uncertainty that could affect our 8 perception of what the probability of failure that is.
9 I mean, it's possible that you could say, 10 well, it doesn't need a high confidence or a low 11 failure probability because we've got a lot of margin 12 in our risk space. Whereas, our perception of safety 13 systems from the conventional view is that they have 14 to have very high likelihood of success.
15 When you get into the domain of core 16 catchers and things like that, from a regulatory 17 viewpoint, what kind of criterion do you think are in 18 front of you? Do you have to really demonstrate with 19 high confidence the core catcher will work or is it 20 really just an element of defense in depth?
21 MR. HINDS: Well, I guess I'll start and 22 let Rick get into more details, but my view on devices 23 such as that is that it is very much an extension of 24 the safety of the plant and taken into another step 25 beyond where the current generation of plants are. So NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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27 1 you certainly can make I'll say a somewhat valid 2 argument that the reliability of those systems because 3 they're much behind the front line as opposed to the 4 typical safety systems which are in the plants today 5 front line systems, that the reliability would be 6 different.
7 Rick, if you want to jump in there as far 8 as probability and any discussions you have related to 9 reliability and probability of the core catcher or the 10 BiMAC.
11 MR. WACHOWIAK: Right. At this point in 12 time what we have said is that the BiMAC itself, the 13 core catcher for those who haven't seen the future 14 presentations here, we believe that it's a non-safety 15 component. At this point it will be treated as a 16 written system, which means that we will have some 17 kind of reliability controls or availability-18 reliability controls on it. That hasn't been defined 19 yet, what needs to be controlled.
20 Now, I think your specific question gets 21 to the uncertainty of the phenomena of how this 22 device, which effectively nobody has seen before --
23 what's the confidence that we have that it's going to 24 work, and how much confidence do we actually need to 25 have to show that it's going to work?
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28 1 And I'm trying to think if we have this 2 anywhere else in the presentation. I know I don't 3 have it in one of mine. Theo may have it there.
4 We want to remember that the BiMAC itself 5 was added to the floor of the containment because 6 chiefly to address an uncertainty. In the previous 7 ALWR design that GE had, ABWR, we showed that at least 8 at that point in time, we showed that if we could get 9 water on top of the core in the lower dry well and it 10 was spread to a large enough degree, that we would be 11 able to prevent continued core concrete interaction 12 and prevent the base MAAP penetration by the melt.
13 There have been uncertainties associated 14 with that. I don't think that that point has been 15 refuted, but it's just not certain whether that's 16 going to happen in all situations.
17 So what we've done is we've added the 18 BiMAC as another layer of protection to address that 19 kind of uncertainty. So does the BiMAC have to be 20 perfect? Well, it doesn't change the fact that the 21 floor and spreading is still there, and we should 22 still in most cases be able to cool pool the corium 23 from the overlying pool, but it's there mainly to 24 address those areas where we're uncertain if that was 25 going to work.
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29 1 So to get back to the point, it's not 2 there as a replacement for what was done in the past.
3 It was there to augment what was done in the past. So 4 for that matter I see it as an augmentation, and we 5 don't have to be 100 percent certain. We should be 6 able to show that within a fairly large band of 7 certainty, this is going to be a good design.
8 Does that answer your question?
9 MEMBER DENNING: Not totally, but I 10 understand.
11 MEMBER WALLIS: I'm not sure it does 12 because you're sort of qualitative, but your PRA says 13 it's going to work with 99 percent effectiveness.
14 That's a pretty high effectiveness for something 15 that's so unusual 16 MR. WACHOWIAK: Okay, and we'll talk about 17 that in the presentation after lunch about how we 18 determine that 99 percent effectiveness. Based on our 19 evaluation and calculations, we think it's better than 20 99 percent, but we've backed off on that mainly for 21 the purpose of -
22 MEMBER WALLIS: How many tests did you do 23 to verify this?
24 MEMBER SIEBER: Only one.
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30 1 said it was 99 percent effective, you also notice that 2 in there we didn't really even address, you know, what 3 if it's not there. How effective would the 4 containment be if it's not there?
5 And in one of the upcoming chapters 6 unfortunately that you don't have yet, we will 7 specifically be answering that question.
8 CHAIRMAN APOSTOLAKIS: Can we go on?
9 MR. WACHOWIAK: I think so.
10 Okay. I think we've talked about this 11 quite a bit,b ut let me emphasize in using the PRA as 12 a design tool, our thoughts are we want to eliminate 13 severe accident vulnerabilities. We want to make sure 14 that these things aren't built into the plant up 15 front. We want to get them out as we see them.
16 So this provides us a systematic way of 17 doing this, not just guessing at what might be a 18 vulnerability. We actually go through and look for 19 the vulnerabilities and address them in a systematic 20 way.
21 MEMBER WALLIS: Now, does it play a more 22 important role than DBAs? I mean, could we do away 23 with DBAs if we used PRAs as a design tool?
24 What's your experience?
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31 1 addressing things in different ways. We would have to 2 do probably more things in the PRA or maybe move some 3 of the same things that we had been doing in the DBA 4 analysis into the PRA if we tried to do that. So at 5 this point we start in the PRA with everything we know 6 from the DBA analysis, and we have that as a given 7 that it's going to work that way.
8 And it starts us at a good point, good 9 starting off point to go and do a robust analysis. If 10 we did away with all of the DBA analysis, we wouldn't 11 be starting on as firm a ground with the PRA, and we 12 would have to add a lot of that back in. So I'm not 13 sure from our point of view, from the design point of 14 view, what kind of relaxation that would give.
15 On the licensing side, that's up in the 16 air. You know, as long as you see the analysis, then 17 maybe you have confidence in what we're doing. So 18 we're not proposing to eliminate the DBA analysis at 19 this point in time.
20 We've talked a little bit about this. As 21 a matter of fact, most of the questions this morning 22 have come up. On the effectiveness of using this to 23 eliminate vulnerabilities, if we don't know everything 24 we need to know to remove vulnerabilities. As anybody 25 who has done PRA knows, the details tend to be where NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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32 1 you find issues that haven't surfaced before because 2 we're not looking at a simple single failure sort of 3 thing. We're looking at multiple failures and 4 interactions among multiple components that could 5 cause multiple failures, and typically those kinds of 6 things aren't in the details.
7 However, we think we've addressed through 8 the way we apply common cause and some of our 9 sensitivity analyses to identify potentials for these 10 failures might be, and we think we have addressed that 11 through adding different diversity requirements and 12 also other design requirements that come through as we 13 proceed.
14 That said, the next bullet makes it very 15 attractive to do this because at this point if we can 16 identify things before we actually have them designed, 17 especially before we have them constructed, it's much 18 easier to correct things that we would determine.
19 In the end, an imperfect tool is better 20 than no tool at all, better than guessing, and we 21 think that as long as we apply this in a prudent 22 manner, we're not going to take things way overboard, 23 but we are going to find a number of vulnerabilities 24 that have been identified without using the tool.
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33 1 perspective of where things are and how we deal with 2 the PRA in a design that is proceeding in parallel.
3 On the conceptual design block down in the 4 end, what we're really trying to say is is the design 5 feasible. We don't really have a lot of actual 6 design. We've got concepts of how systems might work.
7 When we're applying a risk assessment in 8 that manner, we're really doing it qualitatively.
9 What kind of redundancy are we doing to need, do we 10 think we'll need for this system? Should there be 11 diversity applied to some of these things? It's all 12 in a qualitative sense.
13 And we're looking at defense in depth at 14 the conceptual level. Pretty much it's based on what 15 was found in the past. What problems did we have with 16 previous plants, and what don't we want to have 17 problems with now?
18 As we move to the next phase where I 19 believe we are now in the qualitative design base or 20 the DCD phase, the questions that we're trying to 21 answer here are can this design be licensed. Okay.
22 We've specified most of our major 23 components. We now are at the point where we can do 24 a combination of qualitative and quantitative PRA to 25 address specific things, defense in depth between NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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34 1 systems. We can apply common cause factors, but we're 2 still in the qualitative range for some things like in 3 the fire and flood type of analyses, seismic type 4 analysis.
5 We think that we can eliminate sequence 6 type vulnerabilities, things that would be the big 7 hitters, if you will in the final PRA.
8 As we move through the detailed design, 9 this question comes in the later part. Will it be 10 licensed? Do we have enough information for this 11 thing to be licensed?
12 By then we believe that we'll have the 13 components specified. We'll be able to do a 14 quantitative PRA, albeit with gaps. We won't have 15 detailed evaluation of the humans that aren't trained 16 on the systems yet. We won't have plant specific 17 data. We won't have some of the things that are being 18 looked at in the current PRAs.
19 I call this system level vulnerabilities 20 eliminated, but it's really just more of a progression 21 till we can do more with it.
22 By the time we get to construction, we end 23 up with all of our components not actually just being 24 specified, but being described. We can do more 25 detailed PRA, and finally get to the point where we NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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35 1 think we've addressed things.
2 I get to the hypothetical out in the last 3 column here. The plant is in operation. All of the 4 components are described again. They all needed to be 5 described before here, but what I'm just mainly trying 6 to get at with this next slide is that we are still 7 working on the PRA even after the design is done, and 8 so --
9 MEMBER WALLIS: Well, by described, you 10 mean their performance has been quantified.
11 "Describe" is a very vague term. You mean you 12 actually got a measure of how they will perform.
13 MR. WACHOWIAK: Yeah, I kind of put that 14 into this block, but, yeah, the performance is known.
15 MEMBER DENNING: At the construction 16 design level there, where is it to become a site 17 specific PRA, and where's the hand off to the utility 18 in your concept here?
19 MR. WACHOWIAK: In my concept, somewhere 20 in here is where the COL application occurs and now 21 this is being debated, but you know, some say it's 22 here. Some say it's here, but at the COL application, 23 it becomes a site specific PRA. That still has some 24 of these issues associated with it. It's not till you 25 get to this construction level where you're actually NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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36 1 saying, "Okay. This is what's there. We've seen it.
2 We know how it's going to -- you know, we know what 3 the field routing was. We know what the fragilities 4 are."
5 At that point that's kind of somewhere 6 around here. The hand off to the utility we're 7 looking at right here, but we're bringing the utility 8 people in all along through that whole process so that 9 what we give them meets their needs.
10 MEMBER WALLIS: So the PRA that we have 11 seen is where on this picture?
12 MEMBER SIEBER: The second column.
13 MEMBER WALLIS: It's qualitative?
14 MR. WACHOWIAK: Qualitative and 15 quantitative.
16 MEMBER WALLIS: It tends to be very 17 quantitative. It makes some assumptions and some 18 bounding things, but I don't know whether it has much 19 of this qualitative. I'm not quite sure what a 20 qualitative barrier is anyway.
21 MEMBER SIEBER: Since you don't know what 22 the components are.
23 MEMBER WALLIS: Very simplified, but it's 24 still quantitative.
25 MR. WACHOWIAK: Yes. That's why I put NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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37 1 down as a combination there of the two.
2 CHAIRMAN APOSTOLAKIS: Quantitative means 3 what?
4 MR. WACHOWIAK: Qualitative means that 5 there's judgment applied to major areas. So, for 6 example, in the fire area we've said, okay, we don't 7 know where the routing of the cable is. We don't know 8 what the heat loads from a specific cabinet is going 9 to be, things like that, but we do know from past 10 designs that if we confine our cables to where the 11 design drawings say they're supposed to go and we put 12 in typical types of cabinets that have been used in 13 plans before, we'll get this type of performance.
14 And so we qualitatively bound that and 15 used that as an input to the fire risk analysis.
16 CHAIRMAN APOSTOLAKIS: Maybe a better word 17 would be something along the lines of "significant 18 assumptions made" or something. But qualitative is a 19 red flag for a log of people. Okay? And it's not 20 your fault, and it doesn't really mean anything. Your 21 explanation was really something else, that you have 22 to make major assumptions because you don't know.
23 MEMBER WALLIS: Simplify it. Simplify it 24 as much as --
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38 1 significant assumptions I think or something along 2 those lines.
3 MEMBER WALLIS: Qualitative to me means 4 all waffle, and it's good enough or some sort of vague 5 statement.
6 MR. WACHOWIAK: You know, I don't even 7 think we're at the it's good enough in the first 8 column. You know, there's other significant judgments 9 and --
10 CHAIRMAN APOSTOLAKIS: Major --
11 MR. WACHOWIAK: -- thing are made, you 12 know. So I guess maybe it's a way of thinking about 13 it.
14 CHAIRMAN APOSTOLAKIS: Yeah, I wouldn't 15 even call it judgment because judgment is everywhere.
16 It's the assumptions. It's the magnitude of the 17 assumptions that is different. So we need a better 18 word.
19 The statement is no defense in depth 20 issues is not quite right. You probably mean design, 21 a new wall or something, but defense in depth, I mean, 22 it could be a problem, right, that is imposed? And 23 that problem can be posed even when the plant is in 24 operation. And that's in the name of defense in 25 depth.
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39 1 MR. WACHOWIAK: Right, and --
2 CHAIRMAN APOSTOLAKIS: So you mean design 3 defense in depth issues are a result at that point.
4 MR. WACHOWIAK: I'll go with that.
5 CHAIRMAN APOSTOLAKIS: Well, I mean, you 6 don't have to go with that.
7 (Laughter.)
8 MR. WACHOWIAK: I agree with that.
9 Somewhere along in this phase here we do address which 10 programmatic issues we're going to use, but that's not 11 the --
12 MEMBER ARMIJO: The design is frozen. The 13 design is finished.
14 MEMBER SIEBER: In the seismic area, there 15 is a point where somebody does detailed design of 16 hangers and supports.
17 MR. WACHOWIAK: Yes.
18 MEMBER SIEBER: Where is that in that 19 chart? Matched to the right or there?
20 MR. WACHOWIAK: That's in the middle 21 column somewhere, I believe.
22 MEMBER SIEBER: So everything is going to 23 be precalculated and predesigned and no fit in the 24 field kind of --
25 MR. WACHOWIAK: That's the intent, yes.
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40 1 MEMBER SIEBER: Okay. Well, the old 2 plants, all the small and medium bore piping was fit 3 in the field kind of.
4 MR. WACHOWIAK: Right.
5 MEMBER SIEBER: That's why we went and had 6 700 modifications.
7 MR. WACHOWIAK: The engineering schedule 8 that I work from has those activities in those to 9 complete.
10 MEMBER SIEBER: That's where it will be, 11 right.
12 MEMBER ARMIJO: Where do you expect to be 13 for a certified design? When do you think? Is it a 14 detailed design? At what point is this thing ready to 15 be certified?
16 MR. WACHOWIAK: This is one of these 17 things where I'm not sure that anybody has actually 18 settled on that yet, but it's --
19 MEMBER SIEBER: It's going to be between 20 these.
21 MR. WACHOWIAK: It's between these two 22 columns. If you talk to our friends at NEI, they say 23 the beginning of the second column.
24 MEMBER SIEBER: No, tell them no.
25 MR. WACHOWIAK: It's just I think there's NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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41 1 differences of opinion on that, and we're settling in 2 where it is. We certainly know that it's going to be 3 at least in this column here because that's what we're 4 submitting for certified designs.
5 Through the design work, we're getting 6 into this phase now. So it's somewhere in there.
7 MEMBER SIEBER: You will be between the 8 two, between the design basis.
9 MEMBER KRESS: Tell me. Do you see any 10 value in Level 3 PRA in the design certification 11 stage? Now, be truthful.
12 MR. WACHOWIAK: With the order of 13 magnitude of frequencies and releases that we're 14 looking at here, no.
15 MEMBER KRESS: It's just not going to 16 happen, is it?
17 MR. WACHOWIAK: We're showing that we're 18 very far away from any types of specified goals.
19 MEMBER KRESS: That would be my guess, 20 too.
21 MEMBER SIEBER: Ask me.
22 MEMBER KRESS: Well, that would have been 23 my opinion. It's a subject we debate sometimes.
24 MR. WACHOWIAK: We do the analysis, but we 25 would be very surprised if we found that that was NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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42 1 limiting in our design.
2 MEMBER SIEBER: Do you have any estimate 3 as to what the uncertainty is at this point in time in 4 your analysis? I mean, you can get it to three 5 decimals, but if your certainty is four orders of 6 magnitude, you know.
7 MEMBER WALLIS: Well, this is a real 8 mystery slide. I'd love you to explain this one.
9 MR. WACHOWIAK: Just to answer the 10 uncertainty question, we have to look at uncertainty 11 in several different ways, and so uncertainty itself, 12 I'm not sure can be a number. There are things that 13 we can do quantitative, you know, like Monte Carlo 14 type uncertainty and get some information from that.
15 We can do sensitivity analyses and we can get other 16 information from that.
17 But I guess the question is if we say that 18 core damage frequency is three times ten to the minus 19 eight, are we really talking about a three times ten 20 to the minus seven or three times ten to the minus 21 four? Do we know where it falls in that range?
22 This would be a qualitative answer. I 23 think that where we are right now is that we probably 24 have an order of magnitude span on what we know.
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43 1 conservative or some of the numbers that we put into 2 the analysis can compensate for some of that because 3 we know we've been on the high side with some of the 4 things like initiating event frequencies and things 5 like that.
6 Also in features of the plant that we've 7 chosen not to credit in the analysis at this point.
8 So, yeah, there's some uncertainty, but it's not all 9 uncertainty toward the high end.
10 CHAIRMAN APOSTOLAKIS: You say we're going 11 to have a discussion of the core damage frequency 12 later?
13 MR. WACHOWIAK: Yes.
14 CHAIRMAN APOSTOLAKIS: So let's go on to 15 this.
16 MR. WACHOWIAK: So the intent of this 17 slide is to kind of address some perceptions about 18 what it is that the PRA that we have now is good for, 19 and I'm trying to think of it now in the ASME 20 capability category sort of thing.
21 Where we are now is that for some things 22 in the PRA we could do anything, you know, anything up 23 to the full capability Category 3. There are other 24 things where we're not quite there. So it's really a 25 continuum.
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44 1 Probably if you went point by point in 2 ASME, you'd find that we had a significant number of 3 holes because we just don't know enough now.
4 CHAIRMAN APOSTOLAKIS: Can you remind us 5 what capability means?
6 MR. WACHOWIAK: Capability category, well, 7 that's the category where you can use it for, you 8 know, the different type of changes, and that's the 9 mindset that I had here when I was creating this.
10 CHAIRMAN APOSTOLAKIS: The dark blue means 11 they're more capable?
12 MR. WACHOWIAK: Dark blue means --
13 CHAIRMAN APOSTOLAKIS: Higher capability.
14 MR. WACHOWIAK: It's probably more 15 weighted toward --
16 CHAIRMAN APOSTOLAKIS: -- those where you 17 are.
18 MR. WACHOWIAK: Where you are.
19 CHAIRMAN APOSTOLAKIS: The more they color 20 them, that's where you are.
21 MR. WACHOWIAK: Yeah, and we see that as 22 we move forward, we're going to be striving toward the 23 best or toward the state of the art. We're probably 24 not going to get there till well after operation.
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45 1 know everything, but the idea is that in the design 2 phases, this is the right kind of mix for the DCD 3 phase, and to look at things later, we want to be at 4 the higher end.
5 CHAIRMAN APOSTOLAKIS: Is the length of 6 the bars an indication of the uncertainties in the 7 PRA?
8 MR. WACHOWIAK: No. It's an indication of 9 what information is available to apply to the models 10 that are said in the standards that we should be 11 applying. So there are certain things that the 12 standard says you have to do with your event tree 13 analysis. Okay?
14 We've done all of those. I believe we're 15 at the high end with that. There are other things 16 that it says you need to do with operator actions.
17 We're at the low end for that because we have just a 18 bounding stream analysis.
19 MEMBER WALLIS: You're not going to change 20 the structure of that significantly, but you will 21 change the entries. You'll change the numbers.
22 MR. WACHOWIAK: And change the details.
23 MEMBER WALLIS: But I don't think you'll 24 change the structure. The PRA we've seen is probably 25 going to be about the same throughout. It's just that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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46 1 your numbers --
2 MR. WACHOWIAK: We may add some detail, 3 and there's a potential to make some things clear in 4 the future. We may expand the event trees to include 5 more specific decision points, but the structure is 6 the same.
7 MEMBER WALLIS: So it's still capable.
8 It's capable now.
9 CHAIRMAN APOSTOLAKIS: I don't know that 10 this kind of slide helps. May we move on? Let's just 11 go on.
12 MR. WACHOWIAK: Okay.
13 CHAIRMAN APOSTOLAKIS: Let's go to 14 something that we can really -- let's start seeing 15 numbers.
16 MR. WACHOWIAK: We think we've got it.
17 CHAIRMAN APOSTOLAKIS: So where are we 18 now? We are done with the overview?
19 MR. WACHOWIAK: Yes.
20 CHAIRMAN APOSTOLAKIS: Okay. then what's 21 next, the prevention?
22 PARTICIPANT: Internal events.
23 CHAIRMAN APOSTOLAKIS: We were talking 24 about the qualitative. Now we can move on to 25 something quantitative.
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47 1 MR. WACHOWIAK: Okay. The intro is the 2 same.
3 MEMBER WALLIS: Key features, do we have 4 this? Where are we? What is this? Prevention.
5 MR. WACHOWIAK: Internal events risk 6 management.
7 MEMBER WALLIS: We don't have it.
8 MEMBER KRESS: Yes, you do.
9 MEMBER WALLIS: We have mitigation.
10 CHAIRMAN APOSTOLAKIS: I didn't have it.
11 Now I have it. Do you have it?
12 MEMBER WALLIS: I haven't got it, by 13 George.
14 MR. WACHOWIAK: It looks like this.
15 CHAIRMAN APOSTOLAKIS: So we're looking at 16 ESBWR internal events risk management?
17 MR. WACHOWIAK: Yes.
18 CHAIRMAN APOSTOLAKIS: Okay.
19 MR. WACHOWIAK: The features of the plan 20 are set out so that we have passive safety systems, 21 active we call asset protection systems, and support 22 system diversity. What we try to do for most types of 23 systems is we have the passive function backed up by 24 an active function, and then the way that the support 25 systems are set up, they tend to support in a diverse NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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48 1 way.
2 And this is the kind of target arrangement 3 that we look at for each thing at a function by 4 function level. Then we have functions that back up 5 functions. We'll go specifically into some of those.
6 CHAIRMAN APOSTOLAKIS: Let's move on.
7 Let's move on.
8 MR. WACHOWIAK: The systems that we have 9 for the different functions. Passive system, you'll 10 see that everything --
11 MS. CUBBAGE: Is lined up on the handout.
12 MR. WACHOWIAK: -- is lined up on the 13 handout. I think we used a different font on this 14 system.
15 So anyway, we have passive systems lined 16 in all of the columns, sometimes multiple passive 17 systems. We have active systems to back up all of 18 these. Reactivity control, very important system for 19 the plant. We have two essentially passive systems 20 that address reactivity control.
21 We have two additional active systems that 22 will provide backups to different aspects of those.
23 Pressure control, once again, passive.
24 You can see SRV in two columns. There's a passive 25 function on it. It lifts on spring pressure here.
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49 1 It's inactive. You open the valves, and we'll talk 2 about those.
3 Inventory control, which is a little bit 4 different in this plan. We'll talk about that later, 5 and high pressure. I mean, inventory control, low 6 pressure. Inventory control low pressure. Gravity 7 driven cooling system would be the passive system.
8 Back that up with fuel and aux. pool cooling system in 9 LPCI mode, and fire water injection.
10 CHAIRMAN APOSTOLAKIS: Why do you need the 11 active backup systems? What's the whole idea there?
12 Why not the passive only?
13 MEMBER SIEBER: You create an accident to 14 get the --
15 MEMBER KRESS: Asset protection.
16 MEMBER SIEBER: -- stuff to work.
17 MEMBER ARMIJO: Well, you've got to 18 operate the plant.
19 CHAIRMAN APOSTOLAKIS: I can ask you guys 20 over at -- can we get GE's answer?
21 Why do we need active systems? The answer 22 may be simple, but --
23 MR. WACHOWIAK: The answer is simple.
24 It's recovery from the scenarios. The passive systems 25 are extremely reliable, get you very quickly to a very NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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50 1 safe state, but what it takes to recover from that 2 state tends to be expensive.
3 CHAIRMAN APOSTOLAKIS: Why is that so? I 4 mean, what do you need? Give me more detail.
5 MR. WACHOWIAK: For example, when you open 6 the DPVs, you've basically created a steam line break 7 inside the containment, and that affects different 8 components that are inside the containment. That 9 affects the EQ life of the cabling and solenoids and 10 all of the electric components that you have inside 11 the containment. It affects stress on things that 12 you've evaluated to say that we can take so many of 13 these transients.
14 So you may have to reanalyze or replace 15 components that are inside the containment. If you 16 get into a scenario where you actually have to use the 17 passive systems, I think here you're creating a lot of 18 stress on equipment that's inside the dry well when 19 you use some of the passive systems.
20 So we have the active systems there that 21 we can use to provide the same function and get us to 22 a safe, stable state without causing an expensive 23 recovery period.
24 CHAIRMAN APOSTOLAKIS: And then the 25 opposite question is, you know, if that's the case, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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51 1 why don't you just use active systems? And is it such 2 a big deal to have it declared as non-safety related?
3 That's really one of the benefits here. The active 4 systems are --
5 MEMBER SIEBER: Yes, yes, yes.
6 MR. WACHOWIAK: It is less expensive to 7 buy and to maintain when they're not safety related.
8 CHAIRMAN APOSTOLAKIS: And the reliability 9 of these systems expected by most reasonable people to 10 be the same as that of safety related systems, right?
11 MR. WACHOWIAK: It would be similar to the 12 types of things you'd see on oil platforms or in other 13 industrial activities where high reliability is 14 required.
15 So remember these active systems also --
16 most of these, main condenser, feedwater, if those 17 systems aren't reliable, the plant doesn't make any 18 money, and if they're not making any money, then 19 what's the point of building it in the first place.
20 CHAIRMAN APOSTOLAKIS: Maybe it's obvious 21 to people. You have the active systems because, you 22 know, they don't create such a mess if you use them, 23 right?
24 MEMBER SIEBER: Right.
25 CHAIRMAN APOSTOLAKIS: But you still have NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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52 1 the passive systems.
2 MR. WACHOWIAK: Right.
3 CHAIRMAN APOSTOLAKIS: Which are the 4 safety related systems.
5 MR. WACHOWIAK: That's correct.
6 CHAIRMAN APOSTOLAKIS: Overall you have a 7 benefit, right? Compared to a system, a reaction 8 that's only active?
9 MEMBER WALLIS: Well, you need the active 10 so that you can talk about a CDF of ten to the minus 11 eight.
12 CHAIRMAN APOSTOLAKIS: My question is what 13 is the ultimate gain of using a combination of the 14 two. What is it that you are gaining from that? Is 15 it dollars? Is it perceptions?
16 MEMBER SIEBER: Yes, yes.
17 CHAIRMAN APOSTOLAKIS: Is it both?
18 MR. WACHOWIAK: Well, it is dollars 19 because the passive systems are much simpler systems.
20 Okay? So making a system safety related adds some 21 exact cost associated with it. If it's a complicated 22 system, the cost is more than if it's a simple system.
23 If it's a simple system, it doesn't add as much cost.
24 So we like our safety systems to be the 25 passive systems.
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53 1 MEMBER SIEBER: The passive system is what 2 gives you the low PRA numbers. If you didn't have 3 those, you'd be --
4 CHAIRMAN APOSTOLAKIS: That's the whole 5 point. They don't give any number.
6 MEMBER SIEBER: Yeah, they do.
7 CHAIRMAN APOSTOLAKIS: It's the active 8 components that give you the numbers. Do you have any 9 number anywhere that says this is the probability of 10 failure of the passive, truly passive system? No.
11 You've assuming --
12 MEMBER KRESS: That's called a focused 13 PRA, which I think the staff is asking him to do.
14 CHAIRMAN APOSTOLAKIS: No, no.
15 MEMBER SHACK: Let GE answer the question.
16 CHAIRMAN APOSTOLAKIS: They assume that 17 these active systems are not there. There is an 18 explicit statement someplace that says we assume that 19 the passive components do not fail, right?
20 In your passive system if you have a check 21 valve that has to open, then you look at the failure 22 rate of the check valve, but you never look at the 23 failure of the tank or, you know, what are not coming 24 down.
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54 1 direction.
2 CHAIRMAN APOSTOLAKIS: Gravity may reverse 3 itself, yes.
4 MEMBER SIEBER: There you go.
5 MR. WACHOWIAK: We didn't address the 6 gravity reversing itself. What we did look at though 7 is there are components in the systems that we call 8 passive. Now, we have to remember here that passive 9 is now a defined term. Passive -- a pipe is passive.
10 We have pipe breaks in that analysis. We look at pipe 11 breaks. That's a failure of a passive component.
12 MEMBER ARMIJO: As an initiator 13 MR. WACHOWIAK: As an initiator, but there 14 are passive things that we call passive because 15 they're operated only using essentially stored energy.
16 It's not energy that we have to create.
17 So these DPVs that are fired using DC 18 power from a batter, it's a split valve, DC power, 19 that's been declared to be a passive component.
20 We have the failure rates of those types 21 of passive components that need to change state in the 22 PRA. That's where we get the numbers for the passive 23 features.
24 MEMBER ARMIJO: What is an ARI?
25 MR. WACHOWIAK: Alternate rod insertion, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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55 1 and I'll cover that on probably the next slide. I 2 define all of these things.
3 MEMBER ARMIJO: Okay.
4 CHAIRMAN APOSTOLAKIS: So the combination 5 of passive and safety related, non-safety related, 6 overall results in benefits. It's cheaper; they're 7 less expensive to design?
8 MR. WACHOWIAK: Less expensive design.
9 CHAIRMAN APOSTOLAKIS: What else?
10 MR. WACHOWIAK: By definition it's adding 11 diversity. So it gets us to the lower -- somebody 12 said it gets us to the lower CDF. It does because 13 inherently it has to add diversity. If you have an 14 active system and a passive system, they don't operate 15 the same way. They don't have the same types of 16 components.
17 MEMBER SIEBER: Fewer components to fail.
18 MR. WACHOWIAK: In many cases, there are 19 fewer components to fail. Some active systems are 20 fairly simple, but in general --
21 MEMBER ARMIJO: Passive systems are also 22 easier to maintain than active systems.
23 MEMBER SIEBER: You don't have to do 24 anything.
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56 1 anything.
2 MEMBER MAYARD: You will have some active 3 systems that will be safety related, I would think.
4 MEMBER SIEBER: No.
5 MEMBER MAYARD: No?
6 PARTICIPANTS: No.
7 MEMBER MAYARD: Nothing? We'll see when 8 you get to operation.
9 (Laughter.)
10 MR. HINDS: This is David Hinds.
11 Just to add just a couple of points just 12 while we're on the topic, one thing to point out is 13 that the column on the right, the active systems, 14 they're not enough to license the plant by themselves.
15 So there would be additional systems one way or 16 another, the safety systems. Then it becomes a choice 17 of are those safety systems active or are they 18 passive.
19 So we would require those safety systems 20 regardless. So, in essence, the column would not go 21 away. It's just a matter of those systems, do we 22 choose to design them as a passive system or as an 23 active system. They would still be necessary.
24 And then some of the failure modes of the 25 typical active systems that have a large number of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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57 1 pumps and motor operated valves and things of that 2 nature, we went with the thought process of removing 3 as many of those active failure prone components as 4 possible, but the system needed to be there regardless 5 of whether it was active or passive to perform that 6 safety function.
7 So I don't think we're in a case of 8 whether we could remove a large number of systems.
9 It's just a matter of whether we choose to design them 10 as active or passive.
11 MEMBER WALLIS: The passive aren't 12 necessarily more reliable. They may not operate as 13 designed. Your ability to predict how they operate 14 may not be as reliable as it is for an active system.
15 MEMBER SIEBER: That's true.
16 MEMBER WALLIS: So it's not clear to me 17 that passive is necessarily better.
18 MEMBER SIEBER: Well, you're reliant upon 19 all of your thermal hydraulic analytical codes, and 20 given what I know about that, I like --
21 MR. HINDS: We're reliant upon things such 22 as static head of water in a tested integrated system 23 as opposed to a conked (phonetic) head of water we 24 felt would result in a more reliable configuration as 25 well as there are economics involved as well.
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58 1 MEMBER SIEBER: But the differential 2 pressures that derive the flows are small in passive 3 systems compared to, you know, a 5,000 or more starter 4 pump.
5 MR. HINDS: And another note, too. Many 6 of the components in the active category in this slide 7 are typical power producing components that are 8 necessary to generate electricity.
9 MEMBER WALLIS: But there are ways that 10 passive systems can fail. I mean, you can have a pipe 11 that's supposed to be full of water. For historical 12 reasons it may have air in it.
13 MEMBER SIEBER: Or steam.
14 MEMBER WALLIS: And may not function the 15 way it's supposed to function.
16 We should probably move on, but this whole 17 idea that passive is necessarily more reliable I'm not 18 sure is true.
19 MEMBER MAYARD: But those are applied to 20 active components, too.
21 MEMBER WALLIS: That's right.
22 MEMBER MAYARD: If you're not meeting your 23 tech specs with water where it's supposed to be --
24 MEMBER WALLIS: Have examples of that 25 where the pipe that's supposed to be full of water is NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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59 1 full of air. Then your pump can't suck.
2 MR. WACHOWIAK: So this is one of those 3 examples where we really build on the safety analysis, 4 the DBA analysis, because those types of questions, 5 will it work, are answered in the DBA analysis for the 6 most part.
7 Well, let's talk about the functions here.
8 Reactivity control function. We start with RPS, 9 reactor protective system. That's similar to most 10 BWRs. It's a SCRAM function, failsafe I&N. So if it 11 gets a signal it SCRAMs a plant. If it loses power --
12 MEMBER WALLIS: This is a case where you 13 don't rely on gravity, right?
14 (Laughter.)
15 MEMBER WALLIS: You're pushing against 16 gravity.
17 MR. WACHOWIAK: We're pushing the rods 18 against gravity, but remember we are using a head of 19 water to get them going, and then the flow through the 20 core is actually what brings them all the way in. So 21 it's against gravity, but it's still the passive 22 direction when it goes that way.
23 Often a rod insertion, a question that was 24 asked earlier, what does that do? It provides a 25 backup to the RPS I&C function. So if for some reason NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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60 1 that passive I&C function doesn't work --
2 MEMBER WALLIS: Now, do you credit that in 3 your outsource analysis?
4 MR. WACHOWIAK: Yes.
5 MEMBER WALLIS: In your CDF?
6 MR. WACHOWIAK: Yes.
7 MEMBER WALLIS: So it's an active system, 8 but it's credited --
9 MR. WACHOWIAK: In the PRA analysis, in 10 everything except for the seismic margins analysis, 11 we've credited all of these functions that I will be 12 talking about.
13 CHAIRMAN APOSTOLAKIS: Is this a safety 14 related system?
15 MR. WACHOWIAK: RPS is safety related.
16 ARI is not safety related.
17 PARTICIPANT: Well it's active.
18 MEMBER WALLIS: Without BSE.
19 MEMBER BONACA: It's going to be what tier 20 one says.
21 CHAIRMAN APOSTOLAKIS: RPS is not mired?
22 MEMBER BONACA: No, not yet.
23 MR. WACHOWIAK: ARI is not safety related.
24 The fine motion control rod drive is also non-safety 25 related. That's the typical way that we would move NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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61 1 the control rods in this plant. It's different than 2 what's in the BWR 2 through 6 out there now. It's an 3 electrically driven screw arrangement to move the rods 4 in and out of the core for normal power control.
5 MEMBER WALLIS: Excuse me. Now, this 6 inserts different rods.
7 MR. WACHOWIAK: Same rods.
8 MEMBER WALLIS: Oh, the same rods.
9 MR. WACHOWIAK: All rods have this 10 function.
11 MEMBER WALLIS: No extra rods. It's the 12 same rod, different wave, but --
13 MR. WACHOWIAK: Right. So when we get a 14 SCRAM signal, we also tell this fine motion control 15 rod to start spinning its screws there. So if for 16 some reason the stored energy control rod motion 17 doesn't get all the rods, the ones that are back 18 behind it, they take a little bit longer, but they 19 also get driven into the core.
20 And then finally for the standby liquid 21 control system, it's a sodium pentaborate solution 22 just like in the existing plants. However, in our 23 configuration, we have no pumps here. The solution is 24 in a tank that's pressurized with nitrogen, and when 25 you open the squib valve, the high pressure nitrogen NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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62 1 drives the liquid into the core region, and I think 2 maybe many of you have looked at that analysis.
3 MEMBER MAYARD: Is the ARI -- is that a 4 fast insertion?
5 MR. WACHOWIAK: It makes the same thing 6 happen as the SCRAM function, and so it's just barely, 7 barely slower. The SCRAM function individually opens 8 up all of the solenoid valves on each hydraulic 9 control unit to vent each one. The ARI vents the 10 header. So it, in effect, does the same thing, but 11 it's not, in fact --
12 MEMBER SIEBER: It's not as close.
13 MR. WACHOWIAK: It seconds different.
14 MEMBER MAYARD: But you really have three 15 systems putting the rods in the normal SCRAM. the ARI 16 is the backup.
17 MR. WACHOWIAK: An ARI is the backup to 18 the instrument and control portion. The RMCRD is the 19 backup to the actual motion of the control rod. So 20 it's really one backup system.
21 Once again, this configuration is 22 extremely reliable, and when we look at our numbers, 23 ATWS comes out to be less than one percent of total 24 CDF with this configuration.
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63 1 the main steam system. Obviously -- well, not 2 obviously, in this plant it's capable of handling most 3 of the transients, except for the ones where there's 4 an isolation of that system for some other reason.
5 It's capable of handling 100 percent of rated steam, 6 100 percent bypass capability on this plant. We're 7 not limited by what we can put into the condenser.
8 The isolation condenser system now would 9 be the next level of defense here. So this is one of 10 these cases where the non-safety system is what we 11 look at first. That's what we want to have. That's 12 our preferred method of removing decay heat. If for 13 some reason that won't work, that doesn't work or it 14 becomes isolated, we move to the isolation condenser 15 system or ICS, which provides decay heat removal. The 16 key here is if this system goes into operation, we 17 never lift any SRVs. So the challenge in the 18 containment is eliminated essentially. It removes the 19 heat. The isolation condenser pool is outside the 20 containment.
21 And with this system we can sustain our 22 safe shutdown condition for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> with no human 23 actions. With human action we can -- you know, as 24 long as decay heat support it, we can stay there.
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64 1 don't have either one of those, we do have safety 2 relief valves, basically ASME type valves on the 3 pressure vessel provides the backup, discharges into 4 the suppression pool so that we minimize the impact on 5 the containment itself. It really mostly discharges 6 to the suppression pool because there are some that 7 can go into the dry well, but those are sequenced on 8 later.
9 Even in a transient where we did isolate 10 the main steam and isolation condensers don't come on, 11 there's several minutes before we pressurize the 12 reactor enough to actually lift the SRVs.
13 MEMBER SIEBER: They're spring loaded 14 safety valves?
15 MR. WACHOWIAK: Spring loaded.
16 MEMBER SIEBER: Not pilot operated.
17 MR. WACHOWIAK: They are pilot -- they're 18 dual -- no? Alan has --
19 MR. BEARD: This is Alan Beard with GE.
20 They are spring loaded safeties when they 21 are externally actuated relief valves, but only ten of 22 the 18 actually have the external actuation for a 23 relief function.
24 MEMBER SIEBER: Okay.
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65 1 and ten are a combination safety relief valve.
2 MEMBER SIEBER: Okay. How many valves 3 does it take to comply with the code? One hundred 4 percent flow, all 18 or some fraction?
5 MR. BEARD: A limiting situation is 6 actually an ATWS event, and we need all 18 valves for 7 that case. For the ASME over pressurization with 8 SCRAM, it's significantly less than 18.
9 MEMBER SIEBER: Okay. Thanks.
10 MEMBER WALLIS: Now, there's no DPV on 11 this slide?
12 MR. WACHOWIAK: No. This is the pressure 13 control or over pressure protection on the vessel.
14 The DPV is there for allowing the low pressure systems 15 to actuate. This is just keeping the vessel intact 16 following a scram or an ATWS.
17 So the DPVs don't play a role in what I'm 18 calling pressure control. Pressure control is keeping 19 from over stressing the vessel.
20 MEMBER WALLIS: With regard to filing?
21 MR. WACHOWIAK: As a matter of fact, 22 because we have time in this plant from when you would 23 reach that pressure, if it was not an ATWS, I'm not 24 sure of the timing of the ATWS because I really 25 haven't looked at that for actuating DPVs. We would NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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66 1 have -- operators could in that several minute time 2 frame actuate those.
3 We didn't take credit for any operator 4 actions in that short of a time frame.
5 MEMBER WALLIS: Another way to 6 depressurize.
7 MR. WACHOWIAK: It would be another way.
8 The result of this type of configuration 9 in our analysis is that the vessel over pressurization 10 comes out to be a negligible impact. We don't see any 11 sequences or at least anything that significantly 12 affects the core damage to get there, not in the limit 13 of precision that we're looking at.
14 MEMBER WALLIS: There are sequences that 15 you pursue though.
16 MR. WACHOWIAK: Yes.
17 MEMBER WALLIS: Where the vessel pops and 18 it pops the containment.
19 MR. WACHOWIAK: Yes. We have those.
20 MEMBER WALLIS: Just the number associated 21 with that is very small.
22 MR. WACHOWIAK: They just die out through 23 the quantification and don't quite make it to the end.
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67 1 because of an isolation condenser system. We'll get 2 to that in a second.
3 Feedwater system, once again, that's what 4 we want to use if at all possible. It's available 5 most of the time, a highly reliable system. It does 6 require our preferred power system which would either 7 be -- you know, it's what has typically been called a 8 pass off-site power. We have some other capabilities 9 in this plant, but for now we'll just call that the 10 preferred power system there, not diesel generator 11 backed up. It takes the grid type power.
12 Capable of handling any transient and 13 small LOCAs. We can deal with those, and actually up 14 to some fairly significant LOCAs if we can get the 15 system back in line.
16 MEMBER SIEBER: Just keep pumping.
17 MR. WACHOWIAK: Just keep pumping until 18 you run out of water basically.
19 MEMBER ARMIJO: How big a break would that 20 be?
21 MR. WACHOWIAK: Essentially we could 22 handle any break. The problem is the timing. When 23 does the system isolate and when can you get it back 24 in service, and I think in the different LOCA 25 scenarios, I think we my have credited it in the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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68 1 medium LOCA, which is essentially a three inch line 2 break.
3 The next backup is the isolation condenser 4 system. We saw that in the pressure control. If 5 these come into operation, it provides the pressure 6 control, but because it's closed loop cooling, it 7 condenses all of the reactor steam. We don't need any 8 kind of makeup.
9 Once again, that was key for not lifting 10 the SRVs or not losing inventory. So as long as we're 11 not losing inventory, this can keep us in that state 12 for at least 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, potentially forever.
13 Finally, the other backup that we have 14 that actually starts, comes into service at about the 15 same time as the isolation condenser system, is the 16 control rod drive. Here our control rod drive pumps 17 are not your father's control rod drive pumps.
18 They're 500 GPM each. We have two of them, fairly 19 substantial. Provides backup high pressure injection 20 function that could be used independently of these.
21 This is backed by our non-safety diesel 22 generators. So it could be off-site power or on-site 23 power.
24 Handling any transient. When I say here 25 "most LOCAs," the flow rates were designed with the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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69 1 small LOCA in mind, but what we see is if it's a steam 2 LOCA also because of where the water level comes out, 3 this 1,000 GPM that we can put in with these two pumps 4 quickly balances decay heat and we can keep the core 5 covered with these systems even if the plant 6 depressurizes and there's a bigger LOCA.
7 This combination here, once again, these 8 are all systems that are in the analysis. They help 9 maintain the low CDF, and when we see later in the 10 results one of the reasons why this doesn't make it 11 negligible with this configuration is what happens 12 between the 24 and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and what has to happen 13 there.
14 We're finding the PRA to address that, but 15 we haven't quite addressed it yet.
16 And we've got the low pressure function.
17 We didn't credit in the PRA the condensate 18 function. A lot of existing plants look at condensate 19 for providing low pressure injection. When we looked 20 at it, we saw that there were so many commonalities 21 with the feedwater system that we just previously 22 talked about, and the feedwater system was already 23 credited in those analyses. We didn't see a lot of 24 extra benefit to adding the condensate system.
25 So it's there. It's just not on my list.
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70 1 We thought it was fairly dependent and it wouldn't 2 make much difference in the resolves. So then we get 3 to low pressure then. We've got the gravity driven 4 cooling system.
5 Here's our passive operation, the tanks 6 that you saw inside the vessel there in our sketch on 7 the front of each page or each presentation. It's 8 inside the containment. All water that we need is 9 already there inside the containment. It doesn't need 10 to be augmented in any scenario where the containment 11 remains intact.
12 Back up to that would be the fuel 13 auxiliary pool cooling system in LPCI mode. LPCI mode 14 of operation can transfer suppression pool water into 15 the vessel just like existing LPCIs do.
16 Power, once again, on this one is backed 17 by the non-safety diesel generators. We have a third 18 method of getting water into the plant through our 19 diesel driven fire pump. We have provided a hard 20 connection to put that fire water into the vessel if 21 needed.
22 We don't need any AC power to run this.
23 It's independent.
24 So again, this combination along with the 25 high pressure helps maintain the low CDF.
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71 1 Talking about the depressurization 2 function, depressurization valves, we call them the 3 DPVs. Passive operation, once again, that means it's 4 stored energy. It's a squib valve. It has got a 5 charge on it. You applied power from the batteries 6 however it gets there, but power from the batteries 7 that fires these.
8 They open. It discharges directly into 9 the dry well. A fairly large opening when they all go 10 off.
11 It provides complete depressurization, and 12 that's the key for the GDCS operation, is that you get 13 the dry well and the reactor at the same pressure so 14 that the head of water in the GDCS tank can allow the 15 system to drain.
16 We do have --
17 MEMBER SIEBER: How long does it take to 18 get that equalized pressure? It's a matter of 19 seconds, right?
20 MR. WACHOWIAK: Yeah, it's not very long.
21 Do you remember, Alan?
22 MEMBER SIEBER: Ten to 30 seconds?
23 MR. WACHOWIAK: It's in the DCD. I can 24 look it up.
25 MR. BEARD: Yes, this is Alan Beard again.
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72 1 Actually the sequence is the initial 2 depressurization is through the safety relief valves, 3 the relief function.
4 MEMBER SIEBER: Right.
5 MR. BEARD: We blow it down to about 20 6 pounds gauge before we'll open up the DPVs to lessen 7 the transient on the blow-down in the dry well. So 8 overall to get down to that zero differential 9 pressure, it's on the order of 30 seconds.
10 MEMBER SIEBER: That's what I figured.
11 Thanks.
12 MR. BEARD: That's one of these things 13 where in the design basis analysis, we look at the 14 sequence a little bit differently. We looked at the 15 DPVs independent from the SRVs when in actuality the 16 real sequence is the SRVs open first, and then the 17 DPVs open second, and what we tried to do in the PRA 18 is that we don't want to specifically just say you 19 have to have both. We look at what kind of redundancy 20 we actually have here.
21 For GDCS operation, we need the DPVs. For 22 some of the other things, LPCI or fire water, the SRVs 23 by themselves are sufficient to operate those systems.
24 MEMBER MAYARD: And these are considered 25 passive valves, DPVs?
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73 1 MR. WACHOWIAK: The DPVs are considered 2 passive, yes. Squib valves that are powered by our 3 batteries, all stored energy devices.
4 MEMBER ARMIJO: What actuates those 5 things? What causes the battery to send the signal to 6 this squib valve? How do they work?
7 MR. WACHOWIAK: Essentially what happens 8 is we've got our level control system, and I'll just 9 go through the simple case on level control. As in 10 the existing BWRs, there's a Level 1, which will be 11 the ECCS actuation level. That signal then is going 12 through the different systems and sends a signal to 13 open the SRVs first and the DPVs and then the GDCS 14 valves. It goes through that system.
15 The I&C is powered by the batteries, and 16 the power that goes to the valves also comes from the 17 batteries. So it's a digital I&C system that's doing 18 that.
19 MEMBER ARMIJO: Okay. Thanks.
20 MR. WACHOWIAK: Okay. So again, this is 21 a very reliable configuration the way it is. The high 22 pressure sequences amount to less than two percent of 23 our CDF. So we see if we have a low core damage 24 frequency. Everything tends to be in the low pressure 25 range.
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74 1 We talk about the decay heat removal 2 function here. This really only applies to the Level 3 2 analysis, but we'll look at it here in the list of 4 functions.
5 The main condenser is available. That's 6 where we want the heat to go. That's the easiest way 7 to transfer it to the ultimate heat sink. If we get 8 into one of these other scenarios, once again, ICS 9 will do it by itself, and you start thinking that ICS 10 is a pretty important system in this plant. It 11 provides a lot of functionality, a lot of protection 12 in many things.
13 We've got the passive containment cooling 14 system which, if there is steam in the dry well, it 15 will perform its function. It won't perform its 16 function if you don't have steam and the dry well has 17 got to condense the steam.
18 This one, again, doesn't need any support 19 systems at all for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. If you open the DPVs, 20 the passive containment cooling system starts working.
21 We say for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> because at somewhere after 24 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br /> the design requirement in that 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> --
23 MEMBER WALLIS: This is on the noted 24 containment?
25 MR. WACHOWIAK: Yes, it is.
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75 1 MEMBER WALLIS: And so you've got all of 2 these noncondensables that have to go somewhere.
3 MR. WACHOWIAK: That's correct.
4 MEMBER WALLIS: So in order to keep track 5 of them in evaluating your effectiveness in 6 condensation, I guess we're going to get into that.
7 MR. WACHOWIAK: We'll get into that in the 8 presentation this afternoon. I talked specifically 9 about how the noncondensables are dealt with in the 10 PCCS, but in general, if we start out with a LOCA it's 11 fairly simple.
12 Pressure suppression containment works 13 like GE pressure suppression containments have in the 14 past. The steam drives the noncondensables through 15 the vents in the suppression pool and they're trapped 16 in the suppression pool.
17 But the way the PCCS works, it also 18 provides a mechanism for driving the noncondensables 19 in the suppression pool. So in the long run, all of 20 the nitrogen is in the suppression pool, and the PCCS 21 is a self-regulating device then that can operate 22 indefinitely as long as you have water.
23 And at this 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> point or analytically 24 we show later than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, but at that point you 25 need to get more water. We have an automatic means of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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76 1 opening some valves to automatically bring -- seeing 2 gravity driven more water there, but there are other 3 backups to that.
4 MEMBER SIEBER: As far as condensation is 5 concerned, it doesn't make any difference whether it 6 contains it or not.
7 MR. WACHOWIAK: That's correct.
8 MEMBER SIEBER: If there's not 9 noncondensables in there, then it's the same 10 inventory.
11 MR. WACHOWIAK: For a Level 1 analysis, 12 whether it's inert or not doesn't make any difference.
13 MEMBER SIEBER: That's right.
14 MR. WACHOWIAK: Another backup system to 15 all of this. As long as you have enough inventory in 16 the vessel, you've got the reactor water clean-up 17 system. It can operate in a shutdown cooling mode.
18 So just like RHR works now, our reactor water clean-up 19 has that same RHR function. It can be placed into 20 operation back by the non-safety diesels. It does 21 require service water and things like that to operate.
22 MEMBER SIEBER: It is basically a high 23 pressure system.
24 MR. WACHOWIAK: Yeah, it operates at high 25 pressure in reactor water clean-up mode.
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77 1 MEMBER SIEBER: Right.
2 MR. WACHOWIAK: And then you can switch it 3 into a shutdown cooling mode that can go essentially 4 from rated pressure all the way down to cold shutdown.
5 MEMBER ARMIJO: But can that by itself 6 provide all of the decay heat removal you need or just 7 a fraction of it?
8 MR. WACHOWIAK: Yeah, go ahead.
9 MR. BEARD: Yeah, Alan Beard with GE 10 again.
11 It is a full pressure rated system. The 12 heat removal capacity will not match the decay heat 13 curve for about the first hour. We do need some --
14 MEMBER ARMIJO: Something else.
15 MR. BEARD -- the first hour of heat. In 16 about the first hour though we come into the decay 17 heat curve, and the reactor water clean-up system by 18 itself will be able to locate the decay heat.
19 MEMBER ARMIJO: Thank you.
20 MR. WACHOWIAK: The one point I want to 21 bring out here is if we're looking at the challenge to 22 keeping the vessel or the core covered, if we have the 23 injection functions that we've talked about earlier, 24 we don't need the containment heat removal function 25 for more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. We will talk about that a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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78 1 little bit more in the Level 2 analysis.
2 But in the first day if we don't activate 3 any of these things, we still don't get to a point 4 where our active systems are being challenged or where 5 the -- it's not the active system. It's where the 6 level in the vessel is being challenged.
7 Someone asked a little bit before about 8 how some of these diverse control systems were. This 9 is our schematic from Chapter 7 in the DCD.
10 Essentially how we get the actuation of the DCD and 11 the GDCS valid.
12 MEMBER WALLIS: This is all illegible and 13 proprietary. None of the printing came out in this.
14 MEMBER SIEBER: It works for me.
15 MEMBER DENNING: Yeah, it's out of focus, 16 even on the printed page.
17 MEMBER SIEBER: Don't worry about it.
18 MR. WACHOWIAK: It's not fuzzed up 19 intentionally. It's a process where you go from a 20 drawing to a PDF back to a drawing to a printing.
21 MEMBER SIEBER: It works for me.
22 MEMBER DENNING: This is PRA.
23 MR. WACHOWIAK: But you'll find this 24 drawing in the DCD, Chapter 7.
25 MEMBER SIEBER: There you go.
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79 1 MR. WACHOWIAK: It's in there.
2 MEMBER SIEBER: As a PDF.
3 MR. WACHOWIAK: Yeah, meeting all of the 4 pixel requirements that were done.
5 Essentially we've got two -- for each 6 valve, whether it's a DPV or whether it's a GDCS 7 valve. We've got one valve. On that valve there are 8 two drivers or two charges for the squib. So the 9 squib needs to fire to open the valve. We've got two 10 of them on there. Each one gets a signal from a 11 different train to the system.
12 Look at the bottom one here. It's a 13 simple one. This is the safety related I&C system.
14 Its signals come in from all four divisions. It votes 15 on whether or not we've actually received the signal 16 that we expected to see.
17 It sends a signal to -- independently 18 sends a signal to two different load drivers, which 19 allow power to go to that squib and actuate it.
20 We've duplicated that from a different 21 division on here, but we've also provided a parallel 22 signal in from what we call the diverse protection 23 system to perform the same function.
24 Now, what's the diverse protection system?
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80 1 the plant. We call it diverse. So we're pretty much 2 saying that it's diverse in manufacturer, hardware, 3 software, that looks at the different ECCS functions 4 and provides a backup signal, if you will, to those 5 different functions.
6 So if for some reason we have got some 7 failure in the safety system, we have a backup system 8 for that. It can fire one of these. The part that's 9 common here is the DC power comes from the station 10 batteries, and we didn't duplicate the diverse station 11 battery.
12 MEMBER ARMIJO: If sensors failed, would 13 this system operate? The sensors that say, okay, 14 something is wrong; level is wrong. If those sensors 15 failed?
16 MR. WACHOWIAK: We would have to fail --
17 with this configuration here, we would have to fail at 18 least four sensors, two in each system, where two in 19 each system. So two in the safety related system, two 20 in the non-safety system would all have to fail. So 21 if you have any two that work in the safety system and 22 any two that work in the non-safety system, this will 23 actuate. So you would have to fail three. I'm sorry.
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81 1 or any two in the diverse system that work will get 2 this actuation.
3 MEMBER ARMIJO: Okay. Thanks.
4 CHAIRMAN APOSTOLAKIS: Rick, it seems to 5 me this is a natural place to break.
6 MR. WACHOWIAK: Okay.
7 CHAIRMAN APOSTOLAKIS: The next one is an 8 event tree. Question?
9 MEMBER BONACA: Just a question generally 10 to do with the reactor safety systems which most of 11 them, they're not safety related.
12 MR. WACHOWIAK: That's correct.
13 MEMBER BONACA: Okay. How do you envision 14 that that will affect testing? And how do you account 15 for, for example, if you have less test requirements 16 since you impose on the systems because now you have 17 the reliance on the passive systems as a major 18 blackout.
19 You know, I can see advantages there for 20 the operator. How do you account for those? And do 21 you foresee it will be different with panel 22 availability of the system because they're not being 23 tested as frequently?
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82 1 nothing while we're waiting for an accident or 2 transient to happen. All of those active systems, 3 except the SRVs, really have some function to play in 4 the operation of the plant.
5 FAPCS is sued for water transfer and pool 6 cooling and pool clean-up, things like that. So all 7 of these active systems that we have need to be 8 operating, most of them continuously, some of them 9 very periodically in order to do your role operation 10 of the plant.
11 So the list of things that are in standby 12 for the active to perform these active portions of the 13 function is a very small list.
14 MEMBER BONACA: Very small list. Okay.
15 Thank you.
16 CHAIRMAN APOSTOLAKIS: Okay. We'll break 17 until 10:27.
18 (Whereupon, the foregoing matter went off 19 the record at 10:13 a.m. and went back on 20 the record at 10:31 a.m.)
21 CHAIRMAN APOSTOLAKIS: So we are back in 22 session please.
23 MR. WACHOWIAK: Okay. Now that we're back 24 and I'm on, I wanted to go through a couple of the 25 event trees here. With the time frame we have, we NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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83 1 couldn't necessarily go through all of them. I want 2 to just talk about a couple of representative event 3 trees.
4 The first one, I think, is the general 5 transient. This is the way we'd like the things to 6 go, well, at least the top part.
7 You have some sort of transient with 8 successful RPS. Bypass valve opens to the main steam 9 line. We have feedwater available. We're okay.
10 That's not so much different than what you see in any 11 BWR.
12 So as we go through the different systems 13 here, if for some reason we don't have the bypass or 14 we don't have the feedwater system, what we end up 15 with is in --
16 MEMBER WALLIS: When I was reading this, 17 there's all of the acronyms and things, some of which 18 didn't seem to even be defined anywhere. This diagram 19 is full of these PRFLs and things. You have to figure 20 out what it means.
21 I have great difficulty even in the list 22 of acronyms finding some of these.
23 MR. WACHOWIAK: I'm sorry. In the 24 presentation itself or you are looking in --
25 MEMBER WALLIS: In the document, in the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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84 1 document.
2 MEMBER SIEBER: Proprietary.
3 MR. WACHOWIAK: Yeah, that's a --
4 MEMBER WALLIS: Maybe they're hidden in 5 the text somewhere or something, but anyway it's just 6 a comment on this.
7 MR. WACHOWIAK: Yeah, the headings for 8 these things should be in Chapter 3 of the PRA, and I 9 thought we had those.
10 MEMBER WALLIS: Maybe they're in there 11 somewhere, but they're not gathered together so that 12 you can find --
13 CHAIRMAN APOSTOLAKIS: Also in the printed 14 version and the electronic version in some of these 15 event trees you just can't read your headings, 16 especially for the loss of power, which contains a 17 sequence that is a dominant sequence, number 44. It's 18 really impossible to read the headings, and I notice 19 you don't have a tree here.
20 MR. WACHOWIAK: Not on this presentation, 21 and I do have it on my computer. We can talk about 22 that one, too, if you wanted to. We'll figure out how 23 to do that in the document. We're somewhat bound up 24 by our software and the ability to get the nice 25 pictures out of the software and into a document. We NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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85 1 can make it into a stand alone drawing for you and 2 send it as a stand alone printed drawing, but to send 3 it electronically, it's in the format of the software, 4 and I'm not sure that that's --
5 CHAIRMAN APOSTOLAKIS: Do you have a 6 bigger figure, you know? You know, print it and send 7 it to Eric.
8 MR. WACHOWIAK: We can send hard copies of 9 the event tree, and we can send all of those. We 10 could seen, you know, big, 11 by 17 hard copies.
11 MEMBER SIEBER: That would be useful.
12 MR. WACHOWIAK: Once again, it loses a 13 little bit when you convert it into the PDF, but we'll 14 see what we can do. If it's possible to get that 11 15 by 17 scanned into a PDF that's got a high resolution, 16 we can do that.
17 But when we go from the software and print 18 to the PDF, it loses it.
19 CHAIRMAN APOSTOLAKIS: You have to go to 20 the microphone and identify yourself, please, with 21 sufficient clarity and volume.
22 MR. BHATT: My name is Sid Bhatt, and I'm 23 from GE.
24 Regarding this form place, you have been 25 using only the 11 by eight -- 11 by 17, and it's NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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86 1 easier to read. I agree with you, and we can provide 2 you for what Rick has been saying in Section 3.
3 Basically that's where all of those trees are defined, 4 and we can give you that set so that you can see T-44 5 and other things too. But that is probably the best 6 way to give it to you, would be a hard copy if it's 7 okay.
8 CHAIRMAN APOSTOLAKIS: Yes, sure. We'll 9 take that.
10 MR. WACHOWIAK: Okay, and we'll do that.
11 The question about all the different 12 headings here being defined somewhere. I know we 13 discussed them in Chapter 3, in the original and in 14 Rev. 1, Rev. 0 and Rev. 1, but you're right that there 15 isn't a "here's a list where all of them are."
16 CHAIRMAN APOSTOLAKIS: Part of the problem 17 is that the actual headings of these three, for 18 example, where it says "I," you're not going to find 19 an I because you will find IC in the list of acronyms.
20 You see you have an I there on the fourth 21 column? It's really IC. So if you go through the 22 list of acronyms looking for I, you're not going to 23 find it. You're going to find the IC.
24 And for some reason you're using U1CF when 25 it's high pressure injection, right? These are the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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87 1 computer --
2 MR. WACHOWIAK: It's one version of high 3 pressure injection.
4 CHAIRMAN APOSTOLAKIS: So these I doubt 5 you will find in the list of acronyms because they are 6 just computer acronyms used in the calculations.
7 MR. WACHOWIAK: Basic event --
8 CHAIRMAN APOSTOLAKIS: The actual systems 9 are below.
10 MR. WACHOWIAK: Right.
11 CHAIRMAN APOSTOLAKIS: Well, you know, the 12 completely scrutable PRA will be produced when there 13 is a really complete PRA, which means never.
14 It's okay. I mean, we don't want you to 15 be shocked.
16 MR. WACHOWIAK: I'm just trying to 17 remember where I was.
18 (Laughter.)
19 CHAIRMAN APOSTOLAKIS: These things 20 happen, but it was interesting that especially that 21 transient for the loss of feedwater and loss of 22 preferred power, which were really of interest, there 23 is no way you can read the headings. It's not a 24 matter of finding any of the acronyms. You just can't 25 read them at all.
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88 1 MR. WACHOWIAK: You can't read it when it 2 got into the file. We'll get that fixed. It may take 3 a separate document to do that. Getting it into the 4 one concise document is difficult.
5 CHAIRMAN APOSTOLAKIS: Well, today you are 6 giving us an overview of the whole thing.
7 MR. WACHOWIAK: Yes.
8 CHAIRMAN APOSTOLAKIS: And then I hope at 9 the end of the meeting or maybe at the end of the day 10 and at the end of tomorrow we can identify some topics 11 on which we would like a more detailed presentation 12 some time in the future.
13 MEMBER WALLIS: Well, apparently the Spell 14 Checker doesn't work on the PRA either because there's 15 typos all over the place.
16 MR. WACHOWIAK: In these?
17 MEMBER WALLIS: "Inyection" and 18 "suppresion" and "equilisium." I mean three typos in 19 one chart.
20 CHAIRMAN APOSTOLAKIS: I can assure you 21 PRA has nothing to do with it.
22 MEMBER SIEBER: Hey, the PRA folks are 23 doing the best they can.
24 CHAIRMAN APOSTOLAKIS: Why don't you go?
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89 1 we don't have the regular power conversion system, 2 which would be the main steam along with feedwater.
3 We move and we check the isolation condenser. Three 4 of four goes into operation; we're okay.
5 I think I heard a question somewhere in 6 the audience about passive things that need some kind 7 of a signal to actuate. The isolation condenser 8 itself is one of those systems where if we lose power 9 or lose the signal, the I&C signal goes into operation 10 on its own. So it would be activated, and so long as 11 we keep water in the upper pools, it will take us out 12 as long as we need.
13 We don't have the isolation condensers.
14 We asked do we over pressurize the vessel, and here 15 you notice that we've used one of the 18 SRVs. The 16 likely case in the loss of ICs is that we would have 17 some IC capability. We just wouldn't have enough to 18 prevent the actuation of the SRVs.
19 After we get into more detail, we can see 20 what value should be put there and what we actually 21 need to prevent failure of the vessel versus just in 22 the ASME's range, the stress on the vessel.
23 CHAIRMAN APOSTOLAKIS: So these, the 24 second here out of the success criteria --
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90 1 criteria.
2 CHAIRMAN APOSTOLAKIS: So these were 3 presumably derived by doing the appropriate thermal 4 hydraulic calculations.
5 MR. WACHOWIAK: Yes.
6 CHAIRMAN APOSTOLAKIS: And somebody is 7 checking those, the status of it, I suppose.
8 MR. WACHOWIAK: We're checking those, yes.
9 The next one we get to if we do 10 successfully keep the --
11 MEMBER WALLIS: Well, what's the 12 probability of 17 of these things failing?
13 CHAIRMAN APOSTOLAKIS: Very low.
14 MR. WACHOWIAK: Very low, and it's the 15 same probability as 16 failing and 15 failing and 14 16 failing. So once again, we didn't really get into 17 revision of that number so much since you don't have 18 the ability to resolve it down to the difference 19 between 11 failing and 18 failing. It's the same 20 thing.
21 MEMBER SHACK: What calculations do you 22 use for the PRA, what thermal hydraulic code?
23 MR. WACHOWIAK: We can talk about that a 24 little bit later, but it's a combination of things.
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91 1 looking at things like for that one feedwater pump can 2 provide injection since one feedwater pump is capable 3 of 45, 50 percent of rated flow, certainly it can take 4 decay heat. We have a hand calculation for that.
5 For other things where we have our design 6 basis analysis, and this particular case here, three 7 or four isolation condensers, we've used Track G in 8 the design basis calculation to show that that's 9 success, and we've just adopted that here in the PRA.
10 Other things that are a little more 11 complicated that involve multiple failures. We 12 couldn't just lift directly from the safety analysis, 13 and we've done calculations with MAAP 4 on those, and 14 we're in the process of discussing with the staff how 15 to resolve any sort of uncertainties or other issues 16 associated with using that code.
17 MEMBER WALLIS: Well, these are very 18 simplistic. On the idea that isolation can then -- it 19 either works or it doesn't, it's just not quite like 20 a pump. I mean, it could get blanketed with no 21 condensables and work to some extent. There's a whole 22 lot of these things which can partially work.
23 And the FEPRA says it's there or it isn't 24 there, which is very unrealistic for some of these 25 systems.
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92 1 MR. WACHOWIAK: Yeah, we didn't really 2 address partial failures of the systems, but if you do 3 go into the default tree for the isolation condenser, 4 the purge valves for the noncondensables are in there 5 to the extent that we would need those.
6 So we didn't really look at saying, well, 7 we have two and a third equivalent heat exchangers.
8 We've just said does it function the way it's supposed 9 to, just like you would in the active PRA.
10 MEMBER WALLIS: And the other thing is if 11 you put the uncertainties in the thermal hydraulics 12 into this, then you could be moving from one branch to 13 another because of, you know, being on the tail end of 14 some probabilistic distribution of the heat transfer 15 coefficient or something, and that's not in here 16 either.
17 MR. WACHOWIAK: That's not in here in that 18 exact what. What we've done, and we're still 19 addressing this, is that when we set the success 20 criteria or the threshold for saying success versus 21 failure, when we use MAAP what we did was we didn't 22 look at actual heat-up of the clad and the onset or 23 the failure of the clad. What we really looked more 24 at was did we uncover the core.
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93 1 it's success or not should address things like those 2 types of thermal hydraulic uncertainties. The 3 question that we're dealing with now is is our method 4 for calculating when we get to the top of the core --
5 is that an adequate way of doing it?
6 I think that at least at the preliminary 7 stage we have I can't call it agreement yet, but we 8 have a conceptual agreement that those thermal 9 hydraulic margins could be handled by setting the 10 threshold at the top of fuel rather than doing the 11 detailed calculations.
12 So, again, I would think that this is 13 something that's appropriate at this DCD phase to use 14 that type of a conservative analysis to address 15 success criteria and maybe do something more detailed 16 as we move forward. But I think there's other 17 uncertainties that would be bigger than that 18 particular one when we justify the margin.
19 We're working on that.
20 CHAIRMAN APOSTOLAKIS: The way I 21 understand it, today's presentation will not get into 22 methods for doing things, to quantifying. You're just 23 presenting results and --
24 MR. WACHOWIAK: Okay.
25 CHAIRMAN APOSTOLAKIS: -- how it was done.
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94 1 MEMBER WALLIS: Can't we ask that? Can't 2 we ask if we wish how did you get something?
3 MR. WACHOWIAK: You can ask.
4 CHAIRMAN APOSTOLAKIS: You can ask.
5 MEMBER WALLIS: But they're not going to 6 reply?
7 CHAIRMAN APOSTOLAKIS: What I think we 8 should do as we go on, we should identify -- let's not 9 wait until the end of the day -- that we would like to 10 revisit in more detail at a future time, and here you 11 have -- I mean, when you have 18 lines, then the issue 12 of common cause failures, I guess, becomes important, 13 and at some point in the future we'd like to discuss 14 this with you, how you did it.
15 You say in the document you used the 16 alpha factor method, and I looked at the table there 17 and some of the numbers appear to be low to me, but 18 there may be a good reason for that. So this is one 19 items we have to do in the future.
20 MR. WACHOWIAK: Okay.
21 CHAIRMAN APOSTOLAKIS: Get more into the 22 methods for doing things because you have extremely 23 done that in so many places that it drives them out of 24 style. Also the failure of data, that you use the 25 uncertainty analysis that you did.
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95 1 I guess this meeting is not really methods 2 oriented. It's more this is what we did; this is the 3 results, and in the future we will have done this with 4 some of the methods.
5 MR. WACHOWIAK: Okay.
6 CHAIRMAN APOSTOLAKIS: Is that agreeable?
7 Great. Thank you.
8 MR. WACHOWIAK: And we'll be happy to 9 revisit those.
10 CHAIRMAN APOSTOLAKIS: Great.
11 MR. WACHOWIAK: Or we can arrange it.
12 Gather my thoughts again. I'll move into 13 the high pressure injection sort of range that is 14 again here, one of two CRD or one of two -- these are 15 feedwater trains, I guess, rather than -- it would be 16 one of those typos that you are talking about. It 17 could be one of four feedwater pumps.
18 The reason we ask that again here is 19 because this could have failed because of the steam 20 bath and not just the feedwater. We pick up that 21 dependence again by looking at feedwater or control 22 rod drive here.
23 Once again, the single control rod, if we 24 get through this path, the single control rod drive 25 pump is sufficient to keep the core covered. Balances NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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96 1 decay head before we get to the top of fuel.
2 If we need to go into the low pressure, we 3 look at a combination of SRVs and the active system to 4 provide that or, conversely, the DPVs and our passive 5 systems to provide the injection. The combination of 6 things in the passive systems is addressing a little 7 more than the short-term cooling, is set up to allow 8 us to address a long-term cooling there. We do think 9 that there may be some conservatism in the way that we 10 have addressed this, at least looking at the 11 equalizing lines.
12 Finally, when addressing the low pressure 13 injection systems, if the DPVs have actuated, have 14 actually actuated, we put this in here again because 15 the training and dependence for the operators is 16 different between these two. So we asked for that, 17 again, in that scenario, to pick up that dependence.
18 In the end, the way we've drawn these 19 trees, they look fairly simple. The underlying fault 20 trees that go into these are a little more complex 21 that way. It's a tradeoff of how people like to do 22 these analyses. Some like to see more detail in 23 default trees. Some like to see more detail in the 24 event trees. For illustrative purposes, I think it's 25 easier to show in the event trees, but again, it's a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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97 1 choice for how we address these things.
2 I just mention a couple of other things.
3 The question came up about what happens if we stress 4 the vessel, if we take that as a transfer into one of 5 our other trees and we analyze that as an initiator 6 going into the other tree. Similarly, we do the same 7 thing with ATWS, where we have a separate event tree 8 that discusses the sequence of events that would 9 happen in an ATWS.
10 MEMBER WALLIS: Now, when you use this for 11 design --
12 MR. WACHOWIAK: Okay.
13 MEMBER WALLIS: -- do you say that you 14 want something like the same probability in each one 15 of these branches or do you say we want a low 16 probability at the beginning so that we don't get into 17 some of these sequences later on? How do you decide 18 you're going to have a certain number of DPVs, for 19 example?
20 Presumably it's based upon some kind of 21 balancing of the various contributions to the PRA. So 22 how do you do that in the design? How do you use 23 something like this for design?
24 MR. WACHOWIAK: The way that we did that 25 was remember the columns from earlier this morning?
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98 1 MEMBER WALLIS: But what about quantity.
2 You're going to say we want a certain probability at 3 this price, don't you? Therefore, we're going to have 4 a certain number DPVs. Is that the sort of thing you 5 do?
6 MR. WACHOWIAK: Yes.
7 CHAIRMAN APOSTOLAKIS: In other words, if 8 we want higher reliability on the left --
9 MR. WACHOWIAK: Right, more reliability on 10 the left.
11 MR. WACHOWIAK: What we really want to do 12 is we want to minimize these high pressure scenarios.
13 MEMBER WALLIS: But you can do that by 14 different parts of the --
15 MR. WACHOWIAK: You can do it with 16 different parts.
17 MR. WACHOWIAK: Right, right.
18 MR. WACHOWIAK: In the first phase where 19 we looked conceptually at what we're going to do when 20 we had discussions, based on experience from previous 21 plants, the question on SRVs and it wouldn't be 22 experience with DPVs, but experience with things like 23 SRVs, the question was: what type of redundancy would 24 we like to see in this system?
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99 1 I've seen before, I think if we had at least an 2 additional three, that should give us a low enough 3 probability here that would drive the numbers toward 4 the direction we want to have in the low pressure core 5 damage so that the bulk of the core damage frequency 6 would be in the lower pressure scenario.
7 So that was what I call a qualitative 8 judgment on that. So we do that, put that into the 9 conceptual design. Then we take the conceptual design 10 and put it into actual fault trees and use it that 11 way. So we confirm --
12 MEMBER WALLIS: But how did you balance 13 things? I mean, you can change around tremendously 14 the importance of different steps in this process, and 15 they're in default tree. So 21 SRVs or ten instead of 16 18 or I mean, you can change the importance of certain 17 of these branches by design, right?
18 MR. WACHOWIAK: That's right.
19 MEMBER WALLIS: How do you decide what to 20 do?
21 MR. WACHOWIAK: I think the key here is 22 that you can't only use this to optimize that because 23 there --
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100 1 have an answer that's --
2 MR. WACHOWIAK: We didn't do it that way 3 is what I'm saying.
4 MEMBER WALLIS: You don't have an explicit 5 --
6 MR. WACHOWIAK: We didn't say --
7 MEMBER WALLIS: -- logical --
8 MR. WACHOWIAK: -- you have to have a 9 number that's this good here.
10 CHAIRMAN APOSTOLAKIS: And from the PRA 11 perspective, whether you have a ten or 16 or 14 lines 12 is irrelevant. I mean, PRA cannot distinguish among 13 these. I mean, you bring in the common cause failures 14 after three or four or five at the most redundant 15 lines. Then the number is the same. So you have to 16 use some other argument why you want to go to 17.
17 MR. WACHOWIAK: That's right.
18 CHAIRMAN APOSTOLAKIS: And that's what I 19 think you said, you know, that this is not the only 20 way to do this. I mean, actually the issue of common 21 cause failures and their use in design is a real one 22 because the methods have been used, you know, for 23 existing plants as an assessment tool, and so on, and 24 the numbers that you're getting are not very sensitive 25 to certain things a designer can do, like having extra NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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101 1 lines or increasing the separation. I mean, it's all 2 a matter of judgment.
3 MEMBER BONACA: I say it's look at what --
4 you know, is that you really more than -- I mean, the 5 PRA helped you, but you really used a lot of the BWR 6 experience.
7 CHAIRMAN APOSTOLAKIS: Exactly.
8 MEMBER BONACA: And the PWR as a basis.
9 I mean, that's where you start from, and I think 10 that's an advantage. You have that advantage. You 11 should use it.
12 MR. WACHOWIAK: We want to get as close as 13 possible to what the design is going to look like 14 before we even have to go into one of these detailed 15 models.
16 MEMBER WALLIS: But there's no concept of 17 what sort of the optimum design strategy would be or 18 anything like that? It's just what you happen to 19 have? You draw a figure and you take what you've got 20 and you say, "Well, that looks okay."
21 MR. WACHOWIAK: Well, no. One of the 22 things that we looked at actually got on this 23 particular figure, but it would have been on the 24 reactor water clean-up line break outside the 25 containment, and we went through. We had our NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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102 1 conceptual design of how we wanted that to look. We 2 modeled what was there, and when we looked we saw, you 3 know, this break outside the containment fraction, the 4 core damage frequency is higher than we wanted it to 5 be. We want it to be negligible. We don't want a 6 break outside the containment leading to core damage 7 in a bypass. What can we do so that this is no longer 8 a non-negligible sequence?
9 So we went back to the designers and said, 10 "What can you do to increase the reliability of the 11 isolation of that system?"
12 And we added an extra automatic isolation 13 valve or isolation itself. It's not really just one 14 valve. We added an extra automatic isolation from a 15 diverse system into that line which now when we put 16 that back into the model, lo and behold, the 17 containment bypass sequences are now negligible.
18 So that's really the process we went. We 19 didn't try to say we have a target value for each of 20 these branches. We do know that in general we want 21 the bypass sequences to be negligible. We want the 22 high pressure sequences to be low, and we want the 23 overall core damage frequency to be low in terms of 24 what people are used to seeing.
25 CHAIRMAN APOSTOLAKIS: I can see the PRA NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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103 1 being careful because you move down to lower levels, 2 the system and component. Then the value of the PRA 3 begins to diminish because the models are not so 4 sensitive by that.
5 MR. WACHOWIAK: We can find other things.
6 We found places where we identified manual valves that 7 are used for maintenance that would need to be 8 instrumented and alarmed because if they are left in 9 a misposition condition after maintenance, it tended 10 to drive up the reliability of some of these or under 11 liability of some of these systems.
12 So we go back to the design and say, you 13 know, we understand you're going to have component 14 checklists for these things, but let's add something 15 else on top of that. We want to make sure that these 16 aren't left in a state where they may not be able to 17 perform their function.
18 So we use it that way rather than trying 19 to set a target reliability for each step along the 20 way. Once again, optimizing the entire plant that 21 might get us into a -- if we tried to hit targets for 22 every individual piece rather than looking at the end, 23 we would get into a problem that might be hyper over 24 constrained rather than one that's just over 25 constrained now.
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104 1 MEMBER ARMIJO: Rich, but what is the 2 requirement for 18 SRVs? You've done this analysis --
4 MEMBER ARMIJO: ATWS. Okay. For that how 5 many do you need?
6 MR. WACHOWIAK: Eighteen.
7 MEMBER ARMIJO: Eighteen.
8 MR. WACHOWIAK: To meet the ASME code for 9 ATWS analysis, you need to have 18. So that drives 10 that, and the PRA didn't say you need more than 18.
11 MEMBER WALLIS: So 18 barely meets the 12 ASME?
13 MR. WACHOWIAK: Well, it meets it. I 14 wouldn't say "barely meets it." It meets it.
15 MEMBER WALLIS: But you said you had to 16 have 18 to meet the -- does that mean if you had 17 17 you wouldn't meet it?
18 MEMBER SHACK: You wouldn't meet the code.
19 MR. WACHOWIAK: You couldn't meet the 20 code.
21 MEMBER WALLIS: You wouldn't meet the 22 code. Okay.
23 MR. WACHOWIAK: In the PRA we ran a 100 24 percent ATWS case, and looked at things like when 25 feedwater ramping down and reactivity control as the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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105 1 level came down, and determined that we would not get 2 the vessel to a place where it would fail, and I don't 3 remember what the specific number that we used was for 4 that, with nine SRVs open.
5 So we looked at the expected scenario for 6 an ATWS and looked at how many SRVs did we have to 7 have open before we would actually get to the point 8 where we were failing the vessel, not just exceeding 9 code, but failing the vessel.
10 CHAIRMAN APOSTOLAKIS: Coming back to the 11 issue of having more reliable systems on the left, 12 aren't these the systems that really are involved in 13 the design basis accidents so that the conservative 14 analyses there indirectly lead you to very reliable 15 systems?
16 MR. WACHOWIAK: Certainly the design basis 17 analysis uses the reactor protection system.
18 CHAIRMAN APOSTOLAKIS: Right.
19 MR. WACHOWIAK: The design basis analysis 20 uses the isolation --
21 CHAIRMAN APOSTOLAKIS: Right.
22 MR. WACHOWIAK: It uses these SRVs. It 23 uses the DPV and GDCS systems. The FAPCS is probably 24 not included in the design basis, and the fire water 25 injection is not included in the design basis.
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106 1 As CRD is an injection system for some of 2 the sequences, it isn't analyzed or it isn't used in 3 the design basis, but once again, we set the criteria 4 based on an ALWR URD requirement that we do have an 5 active system to mitigate small LOCAs.
6 CHAIRMAN APOSTOLAKIS: Okay.
7 MR. WACHOWIAK: Okay. To go to just 8 another example here, the feedwater line break. The 9 feedwater line break is what we call large steam LOCA.
10 Steam LOCAs depressurize the vessel on their own. So 11 once again -- and it's in the dry well. Just showing 12 we don't need to ask things about the DPDs in these 13 scenarios. We can go directly to the low pressure 14 systems.
15 MEMBER WALLIS: This is a large LOCA and 16 a feed --
17 MR. WACHOWIAK: Feedwater line break.
18 MEMBER WALLIS: Now, Table 5.2, it says, 19 "The probability of large steam LOCA . . . train A is 20 5E to the minus one." It doesn't make any sense to 21 me. The probability of the LOCA is .5? This is Table 22 5.2, 5-2.
23 MR. WACHOWIAK: Your notes?
24 MEMBER WALLIS: My notes on page 5.5-D.
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107 1 have built a plant at all. I don't understand what 2 that number means. Is that the initiation of this 3 whole --
4 MR. WACHOWIAK: That would not be the 5 initiation that we --
6 MEMBER WALLIS: It doesn't make sense.
7 MR. WACHOWIAK: I'm not sure of the origin 8 of that value or the context that it's used off the 9 top of my head.
10 MEMBER WALLIS: Well, maybe someone can 11 answer that later in the day.
12 MR. WACHOWIAK: Yes.
13 CHAIRMAN APOSTOLAKIS: The large LOCA, 14 Graham?
15 MEMBER WALLIS: It says, "Probability of 16 LSLOCA" -- large steam LOCA I guess that means -- "in 17 FWTA," FW train A, point -- well, you can look into 18 those, but there's some numbers in that table that are 19 really strange, strangely high. It's Table 5-2, and 20 in my version it's page 5.5-D.
21 MR. WACHOWIAK: The specific acronym 22 you're saying is -- can you read that off?
23 MEMBER WALLIS: It says, "Probably of 24 LSLOCA."
25 MR. WACHOWIAK: LSLOCA.
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108 1 MEMBER WALLIS: That means large steam 2 LOCA, right? Does it mean that? In feedwater train 3 A.
4 MR. WACHOWIAK: We'll find that out, see 5 what happened there.
6 MEMBER WALLIS: Now, maybe if train B is 7 okay, but train A is in trouble.
8 CHAIRMAN APOSTOLAKIS: Now, I think the 9 subcommittee would very much like to see a detailed 10 discussion here of the dominant sequences.
11 MR. WACHOWIAK: Okay.
12 CHAIRMAN APOSTOLAKIS: Okay? Like this 13 sequencing the loss of prepared power and two or three 14 others. So maybe at the next meeting we can do that.
15 MR. WACHOWIAK: Okay.
16 CHAIRMAN APOSTOLAKIS: Walk us through it.
17 Tell us what the data used were, where they came from, 18 common cause failures, the whole works. That would be 19 a useful thing to see. Okay? So that's another item 20 for the future.
21 So initiating events.
22 MR. WACHOWIAK: We'll talk about what we 23 used for initiating events. We covered the spectrum 24 of transients, grouping them as appropriate, various 25 loss of coolant accidents. Basically the reason we NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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109 1 split those up is that where the different 2 penetrations come into the vessel makes a difference 3 somewhat in how the response is and what the actual 4 outcome is going into the Level 2.
5 MEMBER WALLIS: What does loss of the 6 condenser entail? The condenser is three. You don't 7 have any water flowing through the coolant side or 8 something?
9 MR. WACHOWIAK: It could be several 10 things. You could lose the water on the cooling side.
11 You could lose the vacuum so that you get a hole and-12 -
13 MEMBER SIEBER: Air bound.
14 MR. WACHOWIAK: -- air bound.
15 MEMBER WALLIS: It's more likely that you 16 partially lost it, isn't it? For some reason the 17 vacuum doesn't work very well or something. Again, 18 all of these things are extreme cases. Certainly it 19 isn't there, which seems to be very unlikely.
20 MR. WACHOWIAK: Then in those cases what 21 we have to look at is what I think is on the next 22 slide, is going back to how we got those numbers, and 23 if you go into the NUREG, it gives a list of where the 24 various numbers came from, and things like partial 25 losses of condenser were either included or excluded NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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110 1 in all those different values, and we summed up the 2 ones where the failure mode is still retained in the 3 ESBWR even though we may have augmented the design so 4 that some of these failure modes for transients --
5 MEMBER WALLIS: That's also bothered me.
6 You go back to this NUREG, which is based on past 7 history. You're going to build a much better plant.
8 MR. WACHOWIAK: That's right.
9 MEMBER WALLIS: The condenser won't look 10 quite like all of the old condensers, and yet you're 11 going to use the same number for its failure because 12 that's all you've got? Is that it?
13 MR. WACHOWIAK: Well, there's two things.
14 There's one, we do have it. That's always a plus.
15 It's always good to go with something that you do 16 have.
17 But our objective here on the PRA is to 18 identify things that are associated with the 19 mitigating features of the plant. We're not 20 necessarily trying to reduce the CDF just by saying, 21 well, we're going to eliminate or reduce the 22 initiating event frequencies because remember, once 23 again, initiating events especially on the transient 24 side aren't necessarily hardware issues. It's 25 hardware and people issues, and what we thought would NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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111 1 be a good representation for this phase of the design 2 is to use the values that were based on operating 3 experience at plants, propagate them through the 4 analysis, show that the configuration of the plant can 5 withstand those, and if in the end we do find out that 6 we have a reduced initiator frequency for something 7 because we can prove that the design is better than 8 what's out there, then in a later stage we may use 9 that, or maybe we save that until we get to the 10 operational PRA after we actually have some real data 11 with operating these new systems.
12 So we made the decision to use the 13 existing database for initiating events, and the only 14 place where we really took things out is if something 15 in the existing database, that feature or that failure 16 mode that was there just isn't there anymore in the 17 ESBWR. We took some of those out. So there are some 18 tweaks on the values, but they were fairly consistent.
19 The other thing that we did with this is 20 in the LOCA frequencies. Now, you saw we had a whole 21 bunch of different LOCAs there on the previous page, 22 and you can't go into any of these documents and find 23 where is the GDCS line break or where is a -- you 24 know, they're based on existing plant type numbers.
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112 1 was we looked at how it was done, how it was 2 apportioned for the existing plants, used the same 3 values, but just reapportioned those values associated 4 with the piping sizes and classes that we have in this 5 plant.
6 So it's essentially the same LOCA values 7 that were used that were found in the other documents, 8 just reapportioned.
9 MEMBER WALLIS: So when do you use the 10 valves which you're going to stick open? You use 11 exactly the same valves in 2020 when you build this 12 reactor as were operating experience in 1987 to 1995?
13 Nothing has improved in 25 years?
14 MR. WACHOWIAK: We expect improvement in 15 25 years, but the key that we wanted to say is that 16 the reason -- we don't want to eliminate consideration 17 of I'll call it vulnerabilities, but consideration for 18 certain sequences just because we're speculating that 19 20 years from now we're going to have better SRVs.
20 CHAIRMAN APOSTOLAKIS: The question is:
21 is it worth the effort to argue with he NRC staff --
22 MEMBER WALLIS: That's it.
23 CHAIRMAN APOSTOLAKIS: -- why you use a 24 lower probability distribution when, in fact, it 25 doesn't seem to affect much?
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113 1 MEMBER WALLIS: The whole process, the 2 whole regulatory process seems to inhibit improvement.
3 CHAIRMAN APOSTOLAKIS: To some exhibit.
4 MEMBER WALLIS: Because you know some 5 number that's 40 years out of date, and you know it 6 and it has been approved, we'll stick with it and we 7 won't try to do any better.
8 PARTICIPANT: Or increased margin.
9 MEMBER DENNING: But during the operation, 10 they'll --
11 MEMBER WALLIS: You will see that.
12 CHAIRMAN APOSTOLAKIS: On the other 13 extreme you have people who, you know, and you see 14 that mostly in the aerospace business. We change the 15 design and, boy, they hit the failure rate by a factor 16 of ten or 20, and then of course, nobody believes it.
17 So I think what these guys are doing is much better, 18 staying with the numbers even though you know that the 19 distribution will make it have shifted.
20 MR. WACHOWIAK: In our optimization of the 21 design, if we find out that one of these assumptions 22 for something that we know is going to be better is 23 impacting other parts of the design, like, you know, 24 because we did this now we have to have -- I don't 25 know -- MSIDs that weigh a million pounds. I don't NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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114 1 know. Something that affects the rest of the time.
2 Then we can take a hard look at those and see if 3 there's something that we can do.
4 But for the cut-through that we're doing 5 at this phase, we thought it prudent to look at 6 existing operating experience, initiating events that 7 come from all sorts of different things, not just from 8 looking at a particular design or some component or 9 some system.
10 And I think I've covered everything on 11 here.
12 CHAIRMAN APOSTOLAKIS: Yeah, you've 13 covered it.
14 MR. WACHOWIAK: Basic event data. Now, 15 this is another one of these places where we had to do 16 something. We needed to use generic data 17 CHAIRMAN APOSTOLAKIS: How old is the URD?
18 I mean, that's a long time ago, isn't it?
19 MR. WACHOWIAK: Yes.
20 CHAIRMAN APOSTOLAKIS: How old is it?
21 MR. WACHOWIAK: How old is it?
22 CHAIRMAN APOSTOLAKIS: '80s, late '80s?
23 MR. WACHOWIAK: '80s sounds correct.
24 CHAIRMAN APOSTOLAKIS: They assure me 25 there have been PRAs for BWRs all over the place. I NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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115 1 mean, why didn't you use those, or did you check and 2 the numbers were more or less the same?
3 Because the later PRAs probably include 4 plant specific information. They are more realistic 5 numbers. I don't think it's a major issue, but I'm 6 just curious. I mean, just because it's a document 7 blessed by somebody, we have to stick to it?
8 MEMBER WALLIS: Yes.
9 MR. WACHOWIAK: It's more coming from our 10 customers' request that we use the URD as a --
11 CHAIRMAN APOSTOLAKIS: I see.
12 MR. WACHOWIAK: -- guide for our design, 13 and the data that's in there is included in that 14 table.
15 Now, we did look through there and 16 compared it to things that we used in the Lungmen 17 plant which we're building now in Taiwan. We've got 18 a PRA for that. We have some experience from other 19 things factored in, but we've looked at some of these 20 failure rates with respect to the group's experience 21 from looking at operating plants.
22 We're not seeing, you know, orders of 23 magnitude difference in these values. So I think at 24 this phase of the design, I think the good enough 25 principle applies here.
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116 1 Now, if there's something that is very 2 important and we address some of these in the 3 sensitivities; we looked at these new squib valves.
4 Is the reliability in the URD for squib valves, is 5 that appropriate for what we're using here? And we 6 tried to see if there was some kind of sensitivity to 7 that. There is some sensitivity, not necessarily 8 enough to change our minds on things, but generally 9 that's where we get them from, and we think that it's 10 a conservative way to go.
11 It can be refined in the future, but you 12 know, with some of the new equipment, we're not really 13 going to know until we operate and start testing some 14 of these things.
15 CHAIRMAN APOSTOLAKIS: Speaking of the 16 squib valves, I didn't want to raise it, but you did.
17 On Table 4.6-5, list of system common cause failures, 18 this is the gravity driven system. There is a 19 probability of the common cause failure of all squib 20 valves equal to three times ten to the minus five.
21 And the probability -- oh, no, I'm sorry.
22 For two valves, for two squib valves is ten to the 23 minus five, 3.6, ten to the minus five. The 24 probability of one valve failing is three, ten to the 25 minus three. So if you're going to take the ratio, I NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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117 1 come up with a beta factor of .012.
2 Now, the beta factor usually is around ten 3 percent, and you are going here with one percent, and 4 I wonder how that came about.
5 MR. WACHOWIAK: Well --
6 CHAIRMAN APOSTOLAKIS: One percent is 7 pretty low.
8 MR. WACHOWIAK: Ten percent seems fairly 9 high.
10 CHAIRMAN APOSTOLAKIS: But that's the 11 number that --
12 PARTICIPANTS: No, no.
13 CHAIRMAN APOSTOLAKIS: First of all, 14 that's one of the problems with PRA. I mean, we are 15 dealing with all of this as if they were nothing, you 16 know. I don't like that percent. Make it one percent 17 or make it one in 1,000.
18 Well, it could be .06, right? It doesn't 19 go down by an order, but let me -- no. I mean there's 20 very strong evidence that the beta factors above .1, 21 extremely strong, in fact, based on data. In some 22 cases it's close to .2, okay, and I have a figure if 23 you'd like. I'll send it to you, where there is all 24 sorts of information, and the average is about .1.
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118 1 valves or for --
2 CHAIRMAN APOSTOLAKIS: No, no, for all 3 kinds of components.
4 MEMBER WALLIS: Everything.
5 CHAIRMAN APOSTOLAKIS: Interestingly 6 enough, for space systems it's also .1, and people now 7 are scratching their head. What's magical about .1?
8 But anyway, but the bigger factor here of 9 .012, it seems to me, has to be justified on the basis 10 of something, and again, you don't have to answer now, 11 but next time, these are the kinds of questions you're 12 going to get.
13 MR. WACHOWIAK: Okay.
14 CHAIRMAN APOSTOLAKIS: It's awfully low.
15 It's awfully low, in my view. I mean, there is no 16 basis for it. Okay?
17 Now, for four valves, I understand that.
18 In fact, another thing is for four valves, only four 19 squib valves fail to open. It's three, ten to the 20 minus five. For two valves, its 3.6, ten to the minus 21 five. I mean, that's incredible accuracy.
22 MEMBER WALLIS: Well, there are some more 23 accurate figures in some other tables.
24 CHAIRMAN APOSTOLAKIS: And then the CCF 25 for all seven squib valves in the GDCS lines, failure NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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119 1 to open is 1.5, ten to the minus five. That indicates 2 sensitivity of the model to the number of valves that 3 I don't believe is there.
4 So all of this is on the transcript now.
5 Next time we discuss this, right?
6 MR. WACHOWIAK: Okay. We can discuss how 7 we got those different common causes.
8 CHAIRMAN APOSTOLAKIS: Yeah. You say you 9 used the alpha factor method, but one of the key 10 elements in the methodology that the NRC and EPRI have 11 developed is that you go back and look at actual 12 common cause failures and you screen out the ones that 13 don't apply to you, and I don't know whether you did 14 that, but if you did that, then you probably screened 15 out more than you should have.
16 MEMBER WALLIS: Well, I think in order to 17 achieve credibility, you have to look at some of 18 these things in the detail that George is looking at 19 it, and you folks have to justify what you did.
20 CHAIRMAN APOSTOLAKIS: Yeah, because you 21 know, the last line there says "low CDF to design 22 rather than data values." Well, I just showed you a 23 data value that may be a driver, in fact, because in 24 order of magnitude it's an order of magnitude. You 25 know, an order here, an order there. Pretty soon NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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120 1 you're talking about pretty low values.
2 I'm not saying I'm right. I'm saying we 3 need an answer to what I just said.
4 MR. WACHOWIAK: We will discuss that.
5 CHAIRMAN APOSTOLAKIS: Very good.
6 MR. WACHOWIAK: I did want to bring up one 7 other point here, is that we do have components that 8 in this plant we don't expect to be tested except on 9 a refueling interval basis, and if we use demand data 10 from some of these generic sources from that, some 11 data are actually based on quarterly type test 12 intervals. So we adjusted those, basically converted 13 the quarterly test interval data into an hourly rate 14 and we applied a longer test interval.
15 CHAIRMAN APOSTOLAKIS: Yeah, the results 16 of the problem there, unfortunately I cannot find it 17 now, but you used some formulas to do some things that 18 are not clear to me what they mean, and we definitely 19 need some explanation in the future.
20 MR. WACHOWIAK: Okay.
21 CHAIRMAN APOSTOLAKIS: How you did that.
22 You said, you know, using well known formulas this is 23 where we got, and I hope I'll find it and let you know 24 where it is.
25 MR. WACHOWIAK: Okay. That would be in --
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121 1 CHAIRMAN APOSTOLAKIS: Failure rates, you 2 know, how they were --
3 MR. WACHOWIAK: In Rev. 1 we included what 4 the formulas were.
5 CHAIRMAN APOSTOLAKIS: Oh, I don't know 6 which rev. I looked at. Oh, okay. I found it. I 7 found it. It's in Section 5.2 of the PRA. Okay?
8 Component reliability database, 5.2.
9 So if you guys come back later and address 10 these issues, for test periods greater than a year, 11 this is what we do. For others we do something else.
12 For components whose test period is from six months to 13 one year it is suggested that the upper bound on 14 demand failure probability be used as a computation of 15 mean, the median, and then the new mean is that value 16 times the error factor.
17 That's not true. So not that it makes a 18 hell of a difference, but we don't want to -- in 19 addition to the typos to have also --
20 MEMBER WALLIS: I think you need to look 21 at it, and the same thing in thermal hydraulics.
22 The devil is often in the details.
23 CHAIRMAN APOSTOLAKIS: Yes.
24 MEMBER WALLIS: And you find something 25 which is unjustifiable in the details sometimes.
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122 1 CHAIRMAN APOSTOLAKIS: In the details, of 2 course, what they do is they create an image, a 3 section.
4 MEMBER WALLIS: Absolutely. You don't 5 need many false details to discredit the whole thing.
6 CHAIRMAN APOSTOLAKIS: Yeah. So please 7 look at that in Chapter 5, 5.2, and then we know we'll 8 talk about it. Okay? Good.
9 Human actions.
10 MR. WACHOWIAK: Human actions. This will 11 probably be another one that you're going to want to 12 have --
13 CHAIRMAN APOSTOLAKIS: I suspect it will 14 be, yes.
15 MR. WACHOWIAK: But at this stage of the 16 game of the design, we did a very simplified version 17 of human actions. We looked at two different things, 18 pre-accident actions. Basically it was looking for 19 places where we expected maintenance to potentially 20 leave systems in an unknown unavailable state.
21 Then we looked at what controls were 22 placed on some of these things to see if there was 23 something that we could do with quantification. For 24 things where we just relied on check lists or just 25 standard things that the plants do, we kept the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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123 1 standard value. If there were additional controls 2 like alarms or indications or things, we would do 3 different things.
4 We took the most credit when it was, you 5 know -- and alarmed in the control room stayed on 6 these valves.
7 MEMBER WALLIS: I'm just looking at my 8 notes. I wrote on one page here where you were 9 looking at some -- "operator errors are judged to be 10 a non-significant contribution." I think you're 11 talking here about operation of depressurization 12 valves or something.
13 But it's just an assertion. There's no 14 explanation of why, and I just wonder how many of 15 these sorts of statements are allowed in the PRA. You 16 simply say we judge something to be nonsignificant 17 without any justification, particularly operator 18 actions. How do you really know what they're going to 19 do unless you've got some basis, how they perform on 20 a simulator or something?
21 So I just picked it out and we should ask 22 why whenever we see statements like that.
23 MR. WACHOWIAK: Was that related to the 24 error of commission or was that related to --
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124 1 have to look at page 2.3-4 to see the context, but 2 this is the kind of thing I pulled out.
3 MR. WACHOWIAK: Two, point, three, dash, 4 four, assuming initiating events.
5 MEMBER WALLIS: Right. It's an initiating 6 event, isn't it?
7 MR. WACHOWIAK: Right.
8 MEMBER WALLIS: Yes, okay.
9 MR. WACHOWIAK: So in that context --
10 MEMBER WALLIS: I think it was opening a 11 valve when they shouldn't do it or something 12 MR. WACHOWIAK: Yeah, it was causing an 13 initiating event.
14 MEMBER WALLIS: Causing an initiating 15 event.
16 MR. WACHOWIAK: By doing something that 17 they --
18 MEMBER WALLIS: And you just said that so 19 you assume they won't do it.
20 CHAIRMAN APOSTOLAKIS: Yeah, you are 21 right. We will need to have a special session on 22 these things, especially tables --
23 MEMBER WALLIS: Well, how long are you 24 going to take though? If you go into the details, 25 it's going to take a long time.
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125 1 CHAIRMAN APOSTOLAKIS: Well, it could be 2 a two day meeting. Table 6-1 and 6-2, actually 6-2 is 3 fascinating. You have --
4 MEMBER WALLIS: Where are we here?
5 CHAIRMAN APOSTOLAKIS: It's probably --
6 the numbers you have there probably come from the EPRI 7 ACR model, right? One called the reliability model.
8 MR. WACHOWIAK: Yes, that sounds right.
9 CHAIRMAN APOSTOLAKIS: And if they do, you 10 are probably the only organization at work that's 11 using it, and you have are remarkable table here. You 12 are giving us probabilities of failure as a function 13 of time, available time, 30 minutes, 60 minutes --
14 MEMBER WALLIS: Aren't they all one year 15 minus one, one year minus two, one year minus three?
16 CHAIRMAN APOSTOLAKIS: Yeah, and also you 17 are classifying them according to the behavior type, 18 skill, rule and knowledge. So this is really a 19 remarkable achievement here.
20 MEMBER WALLIS: I say it must be very 21 rough estimates in my notes.
22 CHAIRMAN APOSTOLAKIS: But the thing is 23 that this is of great interest to some of us on this 24 committee because we're trying in another context to 25 convince the NRC staff that we do need time dependent NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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126 1 -- I mean the distribution for the probability of 2 failure given the time.
3 But this is definitely something -- you 4 say you are relying on EPRI NUREG CR-1278 and NUREG 5 CR --
6 MEMBER WALLIS: Is that Table 6-1 there, 7 too?
8 CHAIRMAN APOSTOLAKIS: Yes, there is a 6-9 1, but that is pre-initiated.
10 MEMBER WALLIS: A detection interval of 11 8,640 --
12 CHAIRMAN APOSTOLAKIS: That's one year.
13 MEMBER WALLIS: That's a pretty long time.
14 CHAIRMAN APOSTOLAKIS: No, they don't mean 15 detection. You mean inspection, I think, human 16 inspections.
17 MR. WACHOWIAK: That's inspection.
18 MEMBER WALLIS: It says detection.
19 CHAIRMAN APOSTOLAKIS: It says detection.
20 MR. WACHOWIAK: Detection, it's from when 21 you operate it this time until when you go back and 22 operate it again.
23 MEMBER WALLIS: Oh, it doesn't mean it 24 takes a year to figure out what's going on.
25 CHAIRMAN APOSTOLAKIS: It's the interval NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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127 1 between tests.
2 MEMBER WALLIS: I thought it meant that it 3 would take him a year to figure it out. Me, too.
4 MR. WACHOWIAK: It is from when we make a 5 mistake until we believe there's opportunity to 6 discover it.
7 CHAIRMAN APOSTOLAKIS: It's the degree of 8 detection, right?
9 MR. WACHOWIAK: Yes.
10 CHAIRMAN APOSTOLAKIS: Between tests.
11 Detection is the wrong word.
12 MR. WACHOWIAK: I believe detection is 13 correct because it might be between tests or it might 14 be between operation. Like let's say it's an FAPCS 15 valve and they go to do a full water transfer and they 16 say they got water on the wrong place. Oh, we detect 17 it when we're doing this other operation.
18 So it's when you can detect it. Sometimes 19 it's test interval. Sometimes it's operation 20 intervals.
21 CHAIRMAN APOSTOLAKIS: the problem with 22 detection is that it's also used in other contexts.
23 Anyway, these are the tables we needed, 6-24 1, 6-2.
25 MEMBER WALLIS: Almost every table can be NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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128 1 questioned.
2 CHAIRMAN APOSTOLAKIS: The whole Chapter 3 6.
4 MR. WACHOWIAK: The tables in Chapter 6, 5 and one of the things that we'll talk about that and 6 now it looks like where we'll be for quite some time 7 until all of the human factors analysis and all of 8 those things are wrapped up, we're probably going to 9 be retaining this type of structure for the next year, 10 year and a half or so before it gets significantly 11 changed in the PRA.
12 So if you would have asked me this six 13 months ago, I would have said we're probably going to 14 go to something different in the future, but now I 15 think that's a good topic because I think that the 16 way the schedule is working out, we'll be using this 17 for some time.
18 CHAIRMAN APOSTOLAKIS: Well, yeah, but 19 also at the same time you want to do something that's 20 reasonably defensible, right?
21 You know, I hear mixed comments regarding 22 this AHCR model, even from the original developers.
23 MR. WACHOWIAK: Okay.
24 CHAIRMAN APOSTOLAKIS: I think it would 25 behoove you to go and talk to one or two of those NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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129 1 guys. Give them a call. I mean, what's going on with 2 these models?
3 You know, they run simulator experiments, 4 you know. Then we hear that they were overly 5 enthusiastic in using the results of the experiments 6 to produce these numbers. I don't know what to 7 believe myself, and we had a subcommittee meeting on 8 human reliability about a year ago, last December, 9 well, last December, and some folks from the utilities 10 and EPRI presented their calculator, the APRI 11 calculator, which allows you to use -- it's really a 12 problem that allows you to use one of four models.
13 One of the four models is the AHCR, and 14 the guy from the utility told us nobody is using it.
15 Do you remember that. Do you remember that?
16 PARTICIPANT: Yes.
17 CHAIRMAN APOSTOLAKIS: So now if nobody is 18 using it and you're the only ones, I'd like to 19 understand why. I think I know why. Because it's the 20 only model that gives you information like what you 21 have in 6-2, time and probability of failure.
22 MR. WACHOWIAK: And it's somewhat 23 independent of the variables that we don't know at 24 this point in time.
25 CHAIRMAN APOSTOLAKIS: Anyway, I think NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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130 1 it's something to look into.
2 MR. WACHOWIAK: Okay. In the end, one 3 thing that we didn't include in the PRA is the repair 4 and recovery in the base model. We did look at 5 recovery of off-site power based on the NUREG curves, 6 so the loss of off-site power from 1992 through -- or 7 '82 through 2006 I think are the latest one.
8 I want to back up. One --
9 MEMBER BONACA: One comment regarding the 10 previous slide.
11 MR. WACHOWIAK: Yeah.
12 MEMBER BONACA: I think to me interesting 13 is also how do you -- you know, you had 14 configurations, and you identified that because for a 15 certain system you have a lot of involvement that is 16 maintained and taken out and in. Okay. You could 17 really improve the safety of the plant by modifying 18 maybe that system there.
19 Have you had any -- how do you --
20 MR. WACHOWIAK: Modifying the which 21 system?
22 MEMBER BONACA: I mean the plant.
23 MR. WACHOWIAK: Oh, okay.
24 MEMBER BONACA: Well, take the CRDF 25 system. I mean, you have so many valves there, you NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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131 1 know, butanized to a valve being persistent or, you 2 know, each line and then tested and so on and so 3 forth. Is there any better way to do it?
4 I mean, I'm trying to understand how do 5 you use the PRA to give an input to design. Here 6 you're talking about modeling this human actions, but 7 it seems to me that you have the opportunity to modify 8 the necessary human action at this stage of design, 9 and that's what I would like to understand at some 10 point, not necessarily today, but at some point I'd 11 like to understand how you came to this ESBWR.
12 How did the PRA contribute to it?
13 CHAIRMAN APOSTOLAKIS: I think, Mario, 14 part of it was in the original utility requirement 15 where they decided that for the first what, 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, 16 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />? The design should not require any operator 17 intervention.
18 MEMBER BONACA: Yeah. No, I understand.
19 CHAIRMAN APOSTOLAKIS: So they just 20 followed up, right?
21 MR. WACHOWIAK: The design matches that.
22 In our model here, we look at some of these active 23 systems that can be actuated using operator actions.
24 We do look at a sensitivity that says what happens if 25 we do analyze it the way the ERD said no operator NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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132 1 actions for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and take a look at the effect of 2 the overall results on that and the revision to that 3 analysis is in the process of being updated before 4 that's done.
5 So we do look at it in that sense, but I 6 think the place where we're more going to use this is 7 as we develop our instrument and control systems for 8 the plant and the layout for the simulator and after 9 the simulator, for the control room and for the remote 10 shutdown panel, and where different actions need to 11 take place.
12 Where we find in the PRA some of these 13 actions to be important actions, we might say, you 14 know, maybe you want to put that somehow in the 15 automated system or maybe you want to insure that 16 that's in the control room and not out in the field.
17 That would be the way that we would use 18 that, but at this point in the overall scheme, all 19 we've gotten to is identifying the higher level 20 operator actions to the people that are doing the 21 human factors analysis. So when they go through their 22 process, we'll be factoring this sort of thing into 23 it.
24 So that's the process for doing it. We've 25 identified what's important and then modeling of that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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133 1 goes into the way that the human interface is put 2 together from the plant, and then we'll be able to 3 come back later and see if we did any good or if it 4 didn't make much difference, but I think we can do 5 that. We're just on the front end of it right now.
6 CHAIRMAN APOSTOLAKIS: So in one of your 7 sensitivity analyses you assumed that all the human 8 actions --x 9 MR. WACHOWIAK: Prevailed. All the post.
10 CHAIRMAN APOSTOLAKIS: Post initiated.
11 MR. WACHOWIAK: Post initiated actions are 12 failed, except for the recovery of off-site power.
13 That's one where the typical thinking for that was the 14 grid associated loss of off-site power, and it would 15 be different people addressing that, but there are 16 contributions from the things that are on site. So we 17 may want to relook at how we did that if there's any 18 dependence there on the no post accident operator --
19 MEMBER MAYARD: Even though off-site power 20 may be restored, the operator still would have some 21 action, closing some breakers to get power into the 22 plant.
23 MR. WACHOWIAK: Yes, that's one of those 24 areas where we made the statement, "Yes, we did that."
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134 1 factors really imply operator actions when we did it.
2 And we recognize that. I think that's 3 getting into Rev. 1 of that part of the analysis. So 4 it's another thing to verify.
5 Oh, I know why I went back. I left 6 something off the slide. Part of the process that we 7 did look at is on the back end. You know, you put all 8 of these things in your fault tree models, and you 9 could end up with cut sets that have a whole bunch of 10 different operator actions in them. We did do an 11 evaluation of the cut sets to make sure that we didn't 12 have any highly dependent operator actions there.
13 There were a couple of things that either 14 they weren't dependent or they didn't exist or we did 15 a judgment call. Really are the two operator actions 16 together -- is the value that was used sufficiently 17 high that it really would be expected to cover the 18 combined action? That would be the case where we 19 would have some of those, where there are .2 for 20 operator actions, .2 times .2 for the double actions, 21 probably like a range where we'd expect anyway. So 22 that process went through on the back end to look at 23 those.
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135 1 bounding type things for things that we just knew the 2 answer to ahead of time. Design basis assumptions for 3 things that matched up well with the Track G analysis, 4 and then we used MAAP results for the other things.
5 We're in the process now of resolving 6 where we should be between that and track. When we 7 did look at the success criteria, the way we arranged 8 this was we didn't just say this system, what does it 9 have to do. We looked at it in the context of the 10 sequences where the systems were used, took a look at 11 all the sequences, looked at the different attributes 12 of those sequences and determined if there were any 13 specific limiting sequences to use for that success 14 criteria, and we used it all.
15 So in some cases the success criteria 16 might be conservative, but we tried to apply the same 17 success criteria to the same functions throughout the 18 PRA just to make it simpler for analysis purposes.
19 We're working on a topical for this that 20 we've been discussing with Nick and others.
21 CHAIRMAN APOSTOLAKIS: You say all 22 sequences reviewed. Was the PRA reviewed by anybody?
23 MR. WACHOWIAK: What I meant there was 24 when we were determining the success criteria, we 25 didn't just look at a system in isolation. We looked NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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136 1 at the system as to how it was used in the sequences 2 where it was used in the PRA. So we looked at all of 3 those. All of the sequences of a particular system 4 was credited for success.
5 Then what we did was we went through that 6 list and said, okay, what are the attributes of these 7 different sequences, and is there any one particular 8 sequence or one or more -- actually on some there were 9 two sequences -- that really would make that a more 10 limiting success criteria on that particular function?
11 And the ones that were the limiting, that 12 had the limiting attributes were the ones that we used 13 to determine the success criteria for the system.
14 CHAIRMAN APOSTOLAKIS: Yeah, I understand 15 that, but this is a broader threshold now.
16 MR. WACHOWIAK: Okay.
17 CHAIRMAN APOSTOLAKIS: Did you have a 18 group reviewing the PRA itself?
19 MR. WACHOWIAK: Outside of this project, 20 no. So we got various contractors and subcontractors 21 looking at different things, but they were all under 22 the task that I am.
23 CHAIRMAN APOSTOLAKIS: Because you 24 mentioned the ASME standard, and as you know, there is 25 a PRA review requirement there. Of course, I mean, in NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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137 1 this design certification business, what is the role 2 of the PRA? Because in the ASME standard you are 3 supposed to use it for some real action. So the PRA 4 is very important.
5 But here my feeling is that this is really 6 a supporting kind of analysis. It's not essential, 7 isn't it? Maybe the staff can answer that.
8 I mean, does the PRA have to be PRA 9 reviewed?
10 MS. CUBBAGE: I mean, it is a requirement 11 in Part 52 that they do submit the PRA, and it is 12 primarily used to insure that the insights have been 13 incorporated in any design requirements that were out 14 of the PRA are factored into the design.
15 But I guess to some extent you're right.
16 It is more of a supportive tool, and it also helps us 17 guide our review to the more risk significant areas.
18 CHAIRMAN APOSTOLAKIS: The moment you say 19 "insights," it sends a message. Don't do it. Any 20 time you use the word "insights," not you personally.
21 I think that the word "insights" should be banned from 22 the English language.
23 "Insights" means made by the state of the 24 art or state of the practice job, but they gained 25 insights, and 52, of course, says that, but there is NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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138 1 not a drive for the PRA to be peer reviewed.
2 If we do a minor change in an existing 3 LWR, we demand all sorts of PRA reviews, but from this 4 thing, no.
5 MEMBER BONACA: -- at some point between 6 conceptual design and completion of the plan. The PRA 7 will be in a situation where, in fact, the peer review 8 is worthwhile. I think at this stage I'm not sure 9 that I would consider it worthwhile.
10 CHAIRMAN APOSTOLAKIS: Worthwhile and 11 required are two different things. If the owner of 12 the ESBWR decides not to do anything on a risk 13 informed basis, his PRA does not have to be peer 14 reviewed. Only when the owner says, "I'm going to 15 invoke 1174."
16 MEMBER BONACA: I'm only talking about --
17 you know, I would expect that this PRA would be much 18 more substantial when we can close up --
19 CHAIRMAN APOSTOLAKIS: Sure.
20 MEMBER BONACA: So at that point I would 21 expect that there would be a higher expectation.
22 CHAIRMAN APOSTOLAKIS: No, but as Nick 23 said already, that time is running out. I mean, if 24 you have a peer review group that comes back and says, 25 "We don't like the HRA," you would say, "I'm not NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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139 1 going to change," unless they say, "Well, then we 2 resign."
3 Because, you know, there are certain 4 things that are cast in stone, as you are advised.
5 Anyway, there is no requirement. You haven't done it, 6 that's fine. Let's move on.
7 MR. WACHOWIAK: We do remember though that 8 the part of the process that we're talking about here 9 and that we talked about this morning is we intend to 10 deliver a PRA to the plant that will be operated, and 11 they will use that PRA. So somewhere before we get to 12 that stage, they've got to have that or else they 13 don't have the complete package.
14 So the question is when, not if.
15 MEMBER ARMIJO: In your internal 16 procedures, I'm sure you have internal design reviews 17 by independent parties, but whether that has to go 18 outside of General Electric to some other peer review 19 I don't know, but certainly before you would issue a 20 document like that to the utilities, you would have an 21 independent design review of the work done to satisfy 22 your management that you've got a quality product.
23 MEMBER SIEBER: QA program.
24 MEMBER ARMIJO: Yeah, more, I guess, from 25 QA.
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140 1 CHAIRMAN APOSTOLAKIS: Okay. Let's go on.
2 That's the bottom line. Why are you 3 reporting 310 to the minus eight when Chapter 11 you 4 say that the mean value is eight, ten to the minus --
5 what is this 310 to the minus eight? It's the median?
6 It must be the median.
7 MR. WACHOWIAK: This is the value that you 8 get when you use the point estimates for all of the 9 values. Now, what's in Chapter 11 using the 10 simulation code --
11 CHAIRMAN APOSTOLAKIS: Yeah, you've got 12 the on site.
13 MR. WACHOWIAK: -- the mean looks like it 14 comes out to be a different value.
15 CHAIRMAN APOSTOLAKIS: It is eight, ten to 16 the minus eight, and I believe that's the number you 17 should be reporting. I mean all of the regulatory 18 documents refer to mean times. I mean it's not a big 19 deal. It's just problematic.
20 MEMBER WALLIS: What's the worst it can 21 be?
22 CHAIRMAN APOSTOLAKIS: The 95th percentile 23 is around two, ten to the minus seven.
24 MEMBER WALLIS: There's one up at E minus 25 five.
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141 1 CHAIRMAN APOSTOLAKIS: No, no, no, no.
2 The 95th percentile.
3 MEMBER WALLIS: Yeah, I know.
4 CHAIRMAN APOSTOLAKIS: Which is 5 remarkable, remarkably narrow, right? Think about it.
6 This is the media, 310 to the minus eight, and the 7 upper bound is maybe four times that, a narrow factor 8 of four for a design that has never been built, right?
9 MEMBER WALLIS: Why is frequency on log 10 scale? This is not log or is it frequency?
11 CHAIRMAN APOSTOLAKIS: This is log.
12 MEMBER WALLIS: Frequency. I had a little 13 trouble.
14 CHAIRMAN APOSTOLAKIS: No, this is the 15 frequency. This is 1.10, ten to the minus --
16 MEMBER WALLIS: No, it depends on the 17 scale.
18 CHAIRMAN APOSTOLAKIS: No, but this is 19 from the computer probability.
20 MEMBER WALLIS: Yeah, but is it 21 probability per unit of logarithmic increment or --
22 MEMBER DENNING: It looks like it is.
23 See, these are equal logarithmic --
24 CHAIRMAN APOSTOLAKIS: This is the table.
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142 1 the upper bound to the core damage frequency is 1.8, 2 ten to the minus seven.
3 MEMBER WALLIS: What is the mean?
4 CHAIRMAN APOSTOLAKIS: The mean is eight, 5 ten to the minus eight. I think you should report the 6 mean.
7 MEMBER WALLIS: Well, I have a problem.
8 Is it plotted on a log scale? Now, I concluded from 9 their numbers up here that they must be probably for 10 unit of frequency, not per unit of log frequency.
11 It's actually different.
12 CHAIRMAN APOSTOLAKIS: Forget about the 13 figure. The figure is just for communications. The 14 table is actually from the computer.
15 MEMBER WALLIS: So it's the table.
16 CHAIRMAN APOSTOLAKIS: The table, yes.
17 MR. WACHOWIAK: Both are from the computer 18 program.
19 CHAIRMAN APOSTOLAKIS: The table is the 20 real frequencies.
21 MR. WACHOWIAK: Yes.
22 CHAIRMAN APOSTOLAKIS: Okay.
23 MR. WACHOWIAK: One of the difficulties --
24 CHAIRMAN APOSTOLAKIS: I mean does it 25 bother you to report eight, ten to the minus eight?
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143 1 You seem to be --
2 MEMBER SIEBER: He's happy.
3 CHAIRMAN APOSTOLAKIS: For heaven's sake, 4 that's low. It's way low actually.
5 MEMBER SIEBER: We're falling into the 6 sun.
7 MR. WACHOWIAK: To try to compare things 8 on an equal basis then, using that value in the mean 9 from that particular computer program would be 10 problematic for us because of all the different places 11 where we're trying to compare. For the different 12 scenarios, the fire, the floor and everything else, 13 this number is what's comparable across the different 14 ones.
15 So I understand. I understand what you're 16 saying there, and we will investigate how to present 17 this. It generates difficulties in talking about 18 things like raw values and things. If you take that 19 mean from there when the computer program is 20 calculating all of these other values using this 21 number.
22 CHAIRMAN APOSTOLAKIS: But it should be 23 using the mean, but that's easy to do.
24 Anyway, do you know that the age of the 25 earth's crust is 310 to the ninth years?
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144 1 MR. WACHOWIAK: Yes.
2 CHAIRMAN APOSTOLAKIS: So what you're 3 saying here is that if we had a reactor built when 4 the earth's crust will start to forming and we had to 5 run it then, then you are just an order of magnitude 6 worse than that. It's an incredible number, isn't it?
7 Ten to the minus eight.
8 MR. WACHOWIAK: What we're trying to say 9 here is that for just about anything that we could 10 think of, we've found a way plus a diverse way of 11 dealing with it, and in most cases more than that. So 12 what we're trying to say here, and I think we've used 13 this in other presentations before is that we think 14 we've addressed everything that we know.
15 MEMBER WALLIS: This is where actually 16 permission to comment, I mean, just to talk about 17 disgruntled employees rather than any other kind of 18 event, but people doing things to deliberately cause 19 an event really begins to be very important when you 20 have numbers like this for the things that you 21 analyze.
22 MEMBER MAYARD: Yeah, but one of the 23 things that we tend to not take into account from the 24 human performance standpoint are the positive 25 attributes, like they did not take any repair NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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145 1 activities into account.
2 CHAIRMAN APOSTOLAKIS: Oh, I know that.
3 MEMBER MAYARD: And if you don't watch any 4 of your emergency planning scenarios and stuff, what 5 the human can do from a maintenance, design, 6 modification, a lot of things that they can do that we 7 never take positive credit for in a PRA. So --
8 MEMBER WALLIS: The probability of an 9 operator going absolutely nuts is probably bigger than 10 ten to the minus eight.
11 CHAIRMAN APOSTOLAKIS: I think most of 12 them dominate this culture.
13 MR. WACHOWIAK: It's tentative.
14 MR. WACHOWIAK: Well, I think what we're 15 trying to accomplish here is to address the things 16 that we know about and the things that we can know 17 about using this methodology. Is that the actual core 18 damage frequency? Well, we don't know because there's 19 things we don't know about, and maybe there's other 20 tools that are better for doing that.
21 But for using this method, we think we've 22 addressed just about everything associated with the 23 design of this plant to make the chance of a core 24 damage event so remote that we aren't, that it's a 25 vulnerability that's been addressed. We don't see NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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146 1 that anymore.
2 So I agree that there might be something 3 out there that isn't included that could address core 4 damage frequency, and it's probably things that can't 5 be addressed using these methodologies.
6 CHAIRMAN APOSTOLAKIS: Let me ask you 7 something else. I mean, we're going now to a 8 different place. It is tempting to me to go back to 9 the beginning of the use of PRA now that you ask.
10 It's up to you. Look at the numbers we were producing 11 at the time, although the reactor safety numbers were 12 not that bad, and then see what happens in the 13 intervening years, how many times we were surprised 14 and knew things happened and so on, and this agency 15 had to promulgate extra rules.
16 Doesn't history apply here? Can I count 17 the number of times I was surprised in the past and 18 say, well, gee, maybe in the future I'll be surprised.
19 Therefore, is there anything different here?
20 MR. WACHOWIAK: I wouldn't discount being 21 surprised in the future.
22 CHAIRMAN APOSTOLAKIS: But is it a 23 different situation? I think in some sense it is 24 because --
25 MR. WACHOWIAK: But I think it is a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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147 1 different situation.
2 CHAIRMAN APOSTOLAKIS: -- you have just 3 said that we are eliminating a lot of the stuff we 4 learn from experience in the NWR.
5 MR. WACHOWIAK: That's right.
6 CHAIRMAN APOSTOLAKIS: So we didn't have 7 that benefit at that time, but you know, I remember 8 the first PRA topical meeting in Newport Beach, 9 California, where everybody was reporting for -- you 10 know, we did a fault tree analysis for this system, 11 and the magic number was ten to the minus six, which 12 became ten to the minus four as people came to their 13 senses.
14 So I don't know. I don't think you or I 15 or anybody has an answer to that, but this is 16 something, I mean, when you go to such low numbers and 17 you have new designs that have never been billed. You 18 really have to worry about these things. That's where 19 structure of this defense in depth comes to the 20 rescue.
21 MEMBER WALLIS: Well, they don't need a 22 containment if they've got ten to the minus eight.
23 CHAIRMAN APOSTOLAKIS: We are way over 24 time here.
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148 1 going to finish up?
2 CHAIRMAN APOSTOLAKIS: We're supposed to 3 finish at 11:30. He is so slow.
4 (Laughter.)
5 MR. WACHOWIAK: Just a few more pages.
6 MEMBER WALLIS: This is a very funny 7 figure to me.
8 CHAIRMAN APOSTOLAKIS: Which one is funny?
9 This one?
10 MR. WACHOWIAK: This figure here.
11 MEMBER WALLIS: I would conclude that you 12 way over designed your LOCA response and you way under 13 designed your loss of power. I mean, if that's the 14 dominant thing, maybe you should have another diesel 15 or something. Maybe you can relax your LOCA defense.
16 MR. WACHOWIAK: The actual thing is the 17 loss of feedwater, is what's --
18 MEMBER WALLIS: You can do something about 19 that, bring on more pumps or something.
20 MR. WACHOWIAK: The loss of power causes 21 a loss of feedwater.
22 CHAIRMAN APOSTOLAKIS: I mean these event 23 trees are awfully similar, aren't they?
24 MEMBER MAYARD: We don't want to penalize 25 them though for wearing down the --
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149 1 (Laughter.)
2 MEMBER WALLIS: It's a very funny design.
3 Only susceptible to one major accident.
4 MEMBER KRESS: That's all right.
5 MEMBER WALLIS: You can relax your LOCA 6 now. You don't need anything like as much water and 7 all of that stuff because it's --
8 CHAIRMAN APOSTOLAKIS: No, no, no.
9 MEMBER WALLIS: That was ten to the minus 10 eight.
11 CHAIRMAN APOSTOLAKIS: If you relax it, 12 the contributions will change.
13 MEMBER WALLIS: Once the economists look 14 at it, they'll say, "Wait. How are we paying for this 15 medium LOCA .8"?
16 MEMBER KRESS: We had a concept once that 17 tried to allocate the risk contributions to various 18 sequences. It just never went anywhere. It was a 19 bad --
20 MEMBER WALLIS: No, but there is a --
21 there must be an economic penalty to way over 22 designing for LOCA.
23 CHAIRMAN APOSTOLAKIS: Well, that's not 24 our business.
25 MEMBER SIEBER: Not with passive systems.
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150 1 MEMBER WALLIS: That's why I was surprised 2 though.
3 CHAIRMAN APOSTOLAKIS: Okay. What do you 4 want to tell us?
5 MR. WACHOWIAK: I want to say that we 6 understand why this is, and we are looking at that 7 from other reasons because as you said, over designing 8 for a LOCA versus these, the thing that causes this is 9 really more of an operational issue, and we're looking 10 at optimizing it because of operations and economics.
11 So before we're done, you'll probably see 12 a difference went up there, but not because the PRA is 13 driving that.
14 We did accomplish what we wanted to do 15 here. Bypass we wanted to be negligible. ATWS we 16 wanted to be negligible. High pressure sequences we 17 wanted to be negligible, and the containment can deal 18 with these.
19 We think that the design is robust. We 20 have put in, as inputs, things that helped us look at 21 what the design was capable of doing. We think we 22 came to that. The probability of a severe accident, 23 say, it's remote, and we think that -- well, we know 24 that the use of the PRA as a design tool helped insure 25 that because as we went through this process, there NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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151 1 are thousands and thousands of things that need to be 2 optimized, and we continue to come back and say, 3 "Okay. What is that going to do in the PRA so that we 4 insure that it stays the way that we like it to be?"
5 Combination of the passive safety and 6 active non-safety systems and the diversity that we 7 built into this thing because really what gets us to 8 the remote chance of a severe accident based on the 9 techniques and the things that we know about this 10 design.
11 MEMBER DENNING: But you didn't put up the 12 one that shows now take away the actual systems and 13 what happens.
14 CHAIRMAN APOSTOLAKIS: Yeah, the 15 sensitivity analysis.
16 MEMBER DENNING: The sensitivity analysis.
17 CHAIRMAN APOSTOLAKIS: These are very 18 convincing arguments, and you didn't say anything 19 about them.
20 MR. WACHOWIAK: Yeah.
21 CHAIRMAN APOSTOLAKIS: We'll get that next 22 time. Okay?
23 MR. WACHOWIAK: We could do that next time 24 or we can try to find a slot tomorrow for it.
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152 1 just have a short discussion of it because it is so 2 interesting.
3 CHAIRMAN APOSTOLAKIS: Seeing all of the 4 active systems.
5 MR. WACHOWIAK: And we can talk about 6 that, but realize when I talk about those, those are 7 all based on our Rev. 0, and we're in the process of 8 revising that to Rev. 1. So the numbers may be a 9 little bit different when you finally get the whole --
10 CHAIRMAN APOSTOLAKIS: We have to discuss 11 also this timing business because, you know, if we 12 have a meeting in December and we go into the details 13 and we don't like something and you say it's took late 14 now and we can't change it, I mean, we have a problem.
15 So have that in mind.
16 MEMBER WALLIS: They have a problem.
17 CHAIRMAN APOSTOLAKIS: They have a 18 problem, right. They have. That may be fine, but you 19 know, this is not just a formality.
20 MR. WACHOWIAK: And I would agree that if 21 we had the meeting in December and that was the 22 conclusion --
23 CHAIRMAN APOSTOLAKIS: So you guys will 24 contribute to the discussion whenever, the next 25 meeting. Okay?
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153 1 MR. WACHOWIAK: Okay.
2 CHAIRMAN APOSTOLAKIS: Okay. Thank you 3 very much. This was very informative.
4 We'll reconvene at one o'clock.
5 (Whereupon, at 11:57 a.m., the meeting was 6 recessed for lunch, to reconvene at 1:00 p.m.)
7 CHAIRMAN APOSTOLAKIS: On the record.
8 Okay. We're on the record.
9 MR. THEOFANOUS: I'll be covering Chapter 10 21 of this 33201 and I hope to, by this coverage, to 11 create an opportunity for you to ask questions.
12 Obviously, I cannot cover all the details, but I will 13 try to skim over the whole subject.
14 The work was done by myself and Professor 15 Dinh who used to work with me until about a year ago 16 and now he is chair of Nuclear Safety at the Stockholm 17 Institute of Technology in Sweden. And what do we 18 mean by severe accident treatment is that we are 19 considering containment integrity threats due to 20 severe accident phenomena. So the part of phenomena 21 we're going to cover this afternoon. I'm not going to 22 cover it myself, but it will be covered in the 23 following discussion, containment integrity due to 24 decay heat removal failures and those failures might 25 occur in the long term. So this is more like a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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154 1 systems question and that's why we're leaving it to be 2 handled separately in a separate positive PRA.
3 Our approach is an interactive assessment 4 management approach. This is because this is a new 5 reactor basically we're working on. The reactor was 6 just finished in design, we're finishing up some of 7 the design. So we had an opportunity to affect the 8 design to the interest of forwarding the final touches 9 to the reliability of the safety process of this 10 ESBWR.
11 So we worked on it for about a year and 12 during that time as you will see, we developed a 13 number of new procedures and hardware that we think 14 improve even better this severe accident rate of this 15 reactor. Because of the nature of the passivity of 16 the reactor, because of the very extremely low core 17 damage frequency, we felt that the right way of doing 18 this severe accident treatment was by placing great 19 emphasis on bonding high confidence evaluation. It 20 wouldn't do us any good to say we had a reactor that 21 has 10 to the minus umpteen core damage frequency but 22 now we have high probabilities where we will know very 23 well how the debris may attack the concrete on the 24 floor of this reactor should it ever happen to occur.
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155 1 evaluations that we're ascribing for and emphasis on 2 bonding evaluations, we came up with a number of new 3 procedures and hardware that would aim for eliminating 4 some of those analyses for which we could not 5 accomplish that goal. So our conclusion now is that 6 containment failure is physically unreasonable for all 7 severe accident scenarios except the postulated large 8 steel explosions in very deeply flooded low drywell.
9 It's not that we're saying that these 10 kinds of scenarios, hypothetically large explosions, 11 we're not saying that they will fail. What we're 12 saying is we can not demonstrate with high confidence 13 and high reliability the assessment that this will be 14 so.
15 MEMBER WALLIS: Are you saying that --
16 MR. THEOFANOUS: It's important to point 17 out that it's less than one percent of the core damage 18 frequency falls in that category.
19 MEMBER WALLIS: You're saying all 20 scenarios, but there is a scenario where the reactor 21 vessel is over pressurized and it pops and that 22 popping of the vessel leads to popping of the 23 containment. You're not talking about that kind of --
24 MR. THEOFANOUS: No, no. All scenarios 25 that are --
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156 1 MEMBER WALLIS: You're talking about core 2 melt scenarios.
3 MR. THEOFANOUS: Core melt scenarios, 4 right. And this scenario that you are suggesting is 5 such an extreme scenario that it's not even showing 6 anywhere in this core damage frequency.
7 MEMBER WALLIS: It's in the PRA though.
8 MR. THEOFANOUS: Yes, it's in the PRA.
9 Right. But it's what you call a residual risk. I'll 10 discuss residual risk in a moment.
11 So the people thought the issues in our 12 assessment that we had to basically consider and then 13 take action on are summarized here. There are just a 14 handful. This is a simplified reactor and we thought 15 it really requires a simplified approach rather than 16 a very complex approach.
17 So the first question was do we want to go 18 with universal retention. I don't think I need to 19 explain to you universal retention, but it's a very 20 popular scheme now since we developed it a long time 21 ago. It does sound that, and actually I have written 22 papers on that, it does help that not only the ESBWR 23 but all BWRs are ideally suitable for this concept, 24 ideally suitable because they have welded steel and 25 they don't suffer from this focusing effect that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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157 1 created a monetary issue or problem for pressurized 2 water reactors.
3 Why you decided not to pursue that here, 4 that's because as you know all the boiling water 5 reactors, the lower head is perforated by penetration 6 so that if you really want to make sure that you're 7 going to hold everything inside, you have to support 8 this penetration from falling off. So we suggested 9 that as a possibility because I was very concerned 10 about making sure that this reactor, in fact, I was 11 very concerned about all reactors, we cannot assure 12 the coolability if something should happen.
13 So I was concerned at least for these new 14 generation reactors that we can assure coolability if 15 ever this was to occur. So I said why don't we put a 16 plate somewhere on the support guide tubes and weld it 17 on there on the outside on the housing so that one 18 supports from the other and in fact, such a plate 19 would not only be good for holding everything up in 20 case a melt came to the lower head, but actually it 21 would be quite beneficial in cutting off the driving 22 force behind velocity steam that would come out in the 23 case of high pressure which also takes care of the so-24 called containment heating problem. But that deal was 25 not agreeable to the designers and I was corrected and NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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158 1 I forgot to change it here, not really the designers, 2 but the design managers. So they felt that it would 3 be causing a lot of problems with the maintenance, the 4 operation.
5 Then as we were discussing those things, 6 then we came up with another idea that we thought at 7 the end actually may be awfully better. So sometimes 8 there's a silver lining. Sometimes it's better to 9 find some difficulty or some resistance because then 10 you come up with something better. So we came up with 11 the ex-vessel core coolability idea that I believe is 12 more robust than even the in-vessel and so we're now 13 with the ex-vessel coolability.
14 The reason that this came to that 15 isbecause natural ex-vessel coolability cannot be 16 assured. I don't think I need to explain that to you.
17 You know this very well. It hasn't been possible to 18 demonstrate that if you have a melt that is allowed to 19 fall on the floor and you have water before or after, 20 I don't care when you have it, you cannot demonstrate 21 that this thing is coolable.
22 In Sweden, the Swedish reactors, as you 23 know, they have also very large pools under the 24 reactors. In fact, they put those pools there, many 25 meters, I think it's maybe about ten meters deep.
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159 1 Professor Becker suggested that they put those pools 2 there so that the melt as it comes out, fragments and 3 it's supposed to be coolable. Well, that creates 4 great news with steam explosions first of all and 5 we've done calculations of that and you find that 6 indeed the pedestals in that case will not hold it if 7 you had a steam explosion and even the coolability 8 problem is not right because you have such deep pools 9 that actually will not remain coolable and we have a 10 problem this way.
11 So we have come up within this what you 12 call the Boundary-Internal Melt Arrest and 13 Coolability. I think I should use this for pointing, 14 Boundary-Internal Melt Arrest and Coolability device, 15 this BiMAC which accomplishes this purpose very well 16 as you will see in a moment. It will accomplish the 17 purpose of first of all allowing you to not have water 18 there at the time that the melt comes out. That's 19 where the measurable core is going to occur and if 20 there is a concern about steam explosion, that will be 21 the time with your concern about steam explosion.
22 The reason that it allows you to start off 23 without having the lower drywell flooded is because 24 the moment that water is added to BiMAC and this can 25 be done essentially instantaneously after the melting, NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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160 1 BiMAC is effective to operate as an impenetrable 2 device. That is a boundary of which the melt cannot 3 penetrate.
4 The concept is very similar to universal 5 retention in the sense that we have still a boundary.
6 We have water coolable below. Because of this as long 7 as the thing is actually a nuclear boiling and we've 8 demonstrated that's the case, the temperature on the 9 other side of the still is so low that actually the 10 fuses melt. And the size and the wall thickness of 11 those pipes are such that so that they have 12 significant integrity so that even a small steam 13 explosion will be no problem to them.
14 Having established this robust coolability 15 posture for this reactor ex-vessel, we won't need to 16 be concerned about ex-vessel phenomena because of the 17 nature of this device basically will catch anything 18 and everything that comes down. There is no scenario 19 dependence. It's going to come 20 percent first, 30 20 percent later, but you know it's not going to be 100 21 percent coming in all at once. But even if it did, 22 that's fine. It's going to be all contained inside.
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161 1 it's part of the accident and we end up with deep 2 water pools especially subcool water pools in the 3 lower drywell. And then other one is what if we have 4 a high pressure scenario in which the vessel failed at 5 high pressure and gave rise to what is known as the 6 direct containment helium.
7 So for this problem, we ended up with 8 BiMAC. For this problem, we ended up with some 9 procedure changes and some hardware changes that 10 minimize the scenarios that gives us all the water in 11 the lower drywell and for this one, we basically did 12 nothing except do a fundamentals based analysis that 13 shows that no matter what happens the ESBWR drywell in 14 containment will not be overstressed by the direct 15 containment heating.
16 So my opinion, the serious issue as far as 17 the safety of this reactor as far as your evaluations 18 is this one here. Does it work as we say it's going 19 to work? The other ones, this is one percent of the 20 whole CDF and that's another one of the whole CDF.
21 Actually, it turns out quite interesting 22 from a very fundamental and from a technical point of 23 view. So I don't know to what extent you want me to 24 go over those, but I have them here and I will start 25 going. But please if you feel that you want to go NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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162 1 more, spend more time here, I'll be very happy to.
2 So the way that I have arranged this 3 presentation is in the same order as in the report 4 which I hope all of you have had with you since last 5 August, actually since last November and I hope you 6 had a chance to look at it. But here, I'm going to go 7 in reverse order. I'm going to first go here and then 8 here and then there.
9 All right. Just to summarize then, the 10 severe accident threats and failure modes, direct 11 containment heating, because in here, it's a failure 12 of a reactor drywell. I remind you that the ABWR 13 assumed that in this scenario would fail the drywall 14 and that was one of the reasons that actually the NRC 15 staff in their evaluation report, they assigned the 16 maximum possible for conditional containment failure 17 probability. It was because of that support failure 18 and they did a very hypothetical analysis actually.
19 I still don't know how they ended up with failure 20 because it's not possible to make those reactors fail 21 with suppression pool because of this. You will see 22 in a moment why. So that's one issue.
23 The other issue is a much smaller one and 24 that is if you don't fail catastrophically in the 25 drywell, can you fail the liner because the liner is NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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163 1 containment boundary and if you did, then you would 2 have trouble. The liner, of course, will fail because 3 of thermal effects if it fails while the drywell will 4 fail because of pressure overstress.
5 Then ex-vessel explosions, the concern 6 here is the pedestal of course along with the liner 7 failure because of the energetics of the explosion.
8 But here in addition, we have a new twist because of 9 the BiMAC and we need to know if the pipes, those 10 pipes that they put there will survive an explosion.
11 And finally on the basemat melt 12 penetration, that is the, I guess, the current state-13 of-the-art. I don't know if you want to call it 14 state-of-the-art, but the current approach is that if 15 what if we can show that we're not going to penetrate 16 the basemat melt in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> maybe you're okay.
17 That's the 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> rule and then maybe if we can show 18 that actually for this reactor you can show that it 19 will survive maybe up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, maybe even more 20 than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. That's all right.
21 But with the BiMAC, we eliminate all that 22 because there would be no attack at all and for a BWR, 23 this one, with a small containment, that's very good 24 because you don't have to worry about any condensables 25 coming in.
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164 1 Therefore, we have translated the problem 2 from sort of hypothetical analysis, basically 3 sharpening the pencil, about how long does it take the 4 melt to go through the process and does it go faster 5 this way or this way and so on, all this stuff. Here 6 we're putting a boundary that cannot be penetrated and 7 therefore our concern is to show that what does it 8 take to fail this boundary. So our problem is to 9 something else, more of an engineering, more tangible 10 and I'll show you in a moment BiMAC can be tested the 11 full scale. So it's a much more, much better domain 12 in which to operate on technical grounds.
13 By the way, I know you have heard, that we 14 have large quantities of melt on the floor. People 15 are going to say, I'm not going to say because I don't 16 care to, but people will say, "We don't know.
17 Actually it's maybe going faster this way than that 18 way." So a big issue these days about that again from 19 what I heard. So this is good and this is simple and 20 very easy to apply and I believe one day I hope many 21 reactors will use this, not only the ESBWR, very 22 similar things, pipes and downward.
23 So for the BiMAC again we need to worry 24 about burnouts, something I call burnout. The burnout 25 can occur if the thermal loading locally or in one or NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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165 1 more of those tubes is about the critical heat flash 2 of the water boiling on the inside. That's one way of 3 failing.
4 Another way of failing is that you have so 5 much power going into those tubes that actually the 6 two-phase flow actually gets water depleted. So 7 actually you get the sense of the water coming in and 8 the steam coming out around so in that case there's no 9 water to create boiling.
10 Of course, we need to worry also about 11 stability because we want to make sure the flow is 12 reasonably stable going through.
13 And finally, we need to worry about melt 14 impingement, melt coming out heating whatever is on 15 top of the pipes making sure that they will not be 16 eroding. This we call it sacrificial layer we put on 17 the top essentially to protect the pipes.
18 A couple more, an illustration here, a 19 depiction of the three failure modes and please 20 forgive me for too many acronyms, but DCH as everybody 21 knows, EVE is ex-vessel explosion again is well known, 22 and BMP basemat melt penetration. By that we're 23 referring to the melt eating up the concrete. So 24 those are our three issues and was read and 25 interpreted here. What it shows is that's too NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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166 1 complicated, but mainly I want to show you this is 2 scenario three is one percent of the CDF which is 10 3 to the minus 8 roughly. That is the high pressure 4 scenario. Ninety percent of low pressure scenarios so 5 all the high pressure scenarios there which is shown 6 over here. We need to worry about DCH.
7 For all the low pressure scenarios over 8 here, scenario one, we need to worry about DCDs. So 9 therefore, the question arises in those scenarios, how 10 many of them, what fraction of them, are very deep 11 water pool and what it shows here less than one 12 percent and that would be a deep water pool. The rest 13 of them are either no water at all or very low water.
14 So in this way, this is what I meant.
15 Those are relatively unimportant because that's one 16 percent and that's one percent. However all of them, 17 any accident, anything that's going to lead to large 18 melting of the core has to be dealt with in a 19 coolability point of view. So that's why all 20 pervasive features in the accidents is this part here 21 which surrounds everything. So that's why I put a lot 22 of emphasis on that.
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167 1 with red so that I remember also not to forget 2 something. First of all, upper drywell/lower drywell, 3 that's our nomenclature. As far as DCH, the volumes 4 are important of the lower drywell. That's where the 5 mixing is occurring. It's going to lead to 6 pressurization of the drywell. Very fundamental to 7 BWRs and relative to high pressure scenarios and 8 containment heating is these vents which allow these 9 volumes to vent through the water into the wetwell.
10 So that when you pressurize, you're 11 initially releasing. Remember now. We're talking 12 about here many hundreds of minutes of speed of the 13 steam and how is it coming out of here. Actually, 14 it's quite phenomenal what can occur and we've done, 15 you see a tremendously interesting gas flow particles 16 occurring over there. So in almost no time at all, 17 this pressurizes and the space here is totally out of 18 scale. That's why I emphasized to tell you this is 19 not to scale. Over here, there is a restriction 20 because of the supporting vessel. So over here, there 21 is like a 70 percent reduction in the flow heading.
22 So first, we pressurize that. Then you 23 have to pressurize that and that behaves as a closed 24 volume as long as the vents are not clear just like 25 the LOCA. So if you're interested in the integrity of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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168 1 this thing, you have to be sure you calculate 2 correctly vent clearing.
3 All right. But then once the vents open 4 up, then the issue is whether the vent capacity of 5 those vents can compensate for the supply energy in 6 the upper drywell. We'll show you what that is.
7 All right. So as far as DCH, those are 8 the key components and there's still another one that 9 I want to point out here and that is again another 10 present core well in that there is some skirts over 11 here that they are calling refueling skirts and 12 basically they are closing off that space. This is a 13 metallic head of the drywell. That can become a 14 limited component in pressure. We're showing that the 15 force is isolated so whatever happens over here, that 16 upper head doesn't know it because of that. It has 17 holes basically that are communicated from here to 18 here.
19 The other important thing that's crucial 20 for an integrity point of view is that the head is 21 immersed in a whirlpool that is a pool and the heat 22 flies from the upper head because there is 23 installation here into the drywell head actually is 24 very low. It's so low that you won't even cause water 25 to boil. So if you want to do a structural analysis NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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169 1 of this thing, you should be doing it with a cold CAD 2 of the upper drywell. That's very important for 3 assessing the fragility of the drywell.
4 CHAIRMAN APOSTOLAKIS: What is the name of 5 that pool above the spherical thing?
6 MR. THEOFANOUS: This pool over here?
7 CHAIRMAN APOSTOLAKIS: Yes.
8 MR. THEOFANOUS: Well, this pool is --
9 CHAIRMAN APOSTOLAKIS: It's a separate 10 pool. It's not --
11 MR. THEOFANOUS: It's separate. It's 12 actually separates the PCCS from the pools.
13 CHAIRMAN APOSTOLAKIS: Yes, PCCS.
14 MR. THEOFANOUS: It's separate from that 15 and it is there, I guess, I don't know why that is 16 there. It's just a reactor for the fueling pump.
17 They want to have some space there for refueling.
18 About steam explosion, you're talking 19 about this page over here and that is something like 20 maybe seven or eight meters deep and it has about ten 21 meters in the round which is a really big space and 22 your concern is that there are doors and those are the 23 hatches over here and here through which people are 24 coming for the refueling purposes. The pedestal is 25 made out of two and a half meters reinforced concrete NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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170 1 and that is not just to take care of spillage. This 2 is just because of structural consideration because 3 the reactor is very big and very heavy. That's what 4 defines the very robust walls. To my knowledge, those 5 are the most robust walls that are in pressure-6 suppression containments.
7 The thing on the DCH that I forgot to 8 mention and I do want to point out is these little 9 horizontal lines that go like that and those are 10 called lips and I found out. I was suggesting to 11 people that we want to put lips there because we will 12 most likely, this DCH most likely is going to fail the 13 liner here just by splashing about. If it hits, it 14 would very likely fail. So I didn't want to hear a 15 communication from the back liner space from here up 16 to these parts of the container boundary.
17 But then I found out and we checks that 18 this is part of a normal practice. Every so often, 19 they make lips from the liner that are going to the 20 concrete sort of like compartmentalizing the liner.
21 So you could very well, if you failed the liner over 22 here, but that doesn't communicate with the back liner 23 space over here. So in addition to having those 24 anchors into the concrete that hold the liner, you 25 also have those lips.
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171 1 Going back to then steam explosion as you 2 will see, I don't believe there's any problem with two 3 and a half meter reinforced concrete for steam 4 explosions for the pedestal, although if you do a real 5 humongous steam explosion like the ones that we can 6 actually compute, we find out that we are getting 7 there even to the upgraded. We also did structural 8 vibrations and we found out that although normally 9 people thought the pedestal would take about 100 or 10 150 kilo-Pascal seconds, it turns out we're showing 11 even 600 kilo-Pascal seconds almost four or five times 12 that with these walls you will begin to just reach a 13 seepage. Also it's very robust from an explosion 14 point of view.
15 But it is initially the hatches which are 16 likely to fail if they are overloaded and of course, 17 there is the issue of the BiMAC that we want to make 18 sure that we don't run above 600 kilo-Pascal seconds.
19 CHAIRMAN APOSTOLAKIS: I don't quite see 20 where the BiMAC is.
21 MR. THEOFANOUS: You'll see that in a 22 moment. I'm coming to that. That's the third item.
23 I just finished with the explosion. So the third item 24 is the basemat melt penetration which we said we want 25 to protect with the BiMAC and I'll come to the next NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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172 1 one to show you the design, but the BiMAC fits right 2 in here covering the whole space and the last point to 3 make here is that with BiMAC working plus the PCCS we 4 have no possibility of long term failure of this. And 5 that's very comforting.
6 So here is the BiMAC, and the concept 7 basically is make a jacket with pipes and those pipes 8 are lined up with some intonation. It is largely a 9 two dimensional point. We have chosen this to be ten 10 degrees and that ten degrees comes from the idea that 11 a ten degree is the critical heat flux because 12 remember now these pipes are going to heated from 13 above sort of like that.
14 All right. Now as you increase from there 15 as you go to a different level, of course, you make it 16 possible for the evaporation to go at higher 17 velocities and that creates more agitation and most 18 important, we see a wetting of the wall as the vapor 19 sluices by and when that happens, you get an increase 20 of the heat flux and that increases pretty steeply for 21 about up to about 15 degrees or so. Then it sort of 22 levels out a little bit and therefore you go to a very 23 high orientation when it goes very high. So our 24 interest here is to try to cut that. So that's why 25 it's not five, ten degrees. Then those pipes then NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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173 1 come, here you have a vertical segment. In this way, 2 then we can protect the floor. We can protect the 3 walls. We protect even the sumps.
4 The other consideration here is to making 5 sure that there is enough capacity inside of this 6 dish, if you like, that will catch not only one core 7 but more than one core. We can catch four cores.
8 MEMBER WALLIS: This is made of concrete, 9 this brownish stuff or is this --
10 MR. THEOFANOUS: This is the normal 11 concrete. This is something that's in there.
12 MEMBER WALLIS: What's this?
13 MR. THEOFANOUS: This other stuff here, 14 that is additional concrete. We call it sacrificial 15 material. The one on the top especially will be made 16 out of refractory material like zirconia that would 17 resist impingement of the melt. From the point of 18 view of, let's say, having a melt on the top of it, I 19 don't care whether there is any concrete or not. I 20 don't care what concrete is there, but we were 21 concerned about possible melt coming out in some 22 velocity and coming and hitting it and penetrating 23 those pipes. Of course, if you penetrate the pipes at 24 that point, you're --
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174 1 pipes. I presume it's not a cone one there.
2 MR. THEOFANOUS: It's a cone that is a two 3 dimensional cone. It's like what you see here is a 4 cut through this way.
5 MEMBER WALLIS: Okay, but in the other 6 direction --
7 MR. THEOFANOUS: The other one is 8 straight.
9 MEMBER WALLIS: Okay.
10 MR. THEOFANOUS: Okay. So I'll come to a 11 --
12 MEMBER WALLIS: It's almost like a valve.
13 MR. THEOFANOUS: Yes, like that. Now it's 14 very interesting to point out something that's a 15 little harder to conceive, but I think I can explain 16 it that if you make this cut that is shown over here 17 is through a diameter of the drywall that is normal to 18 our view. Now if you begin to cut now with additional 19 slices going away or forward from there, then you'll 20 find that this dimension is going to get smaller, 21 smaller and smaller.
22 MEMBER MAYNARD: The angle would stay the 23 same.
24 MR. THEOFANOUS: The angle will stay the 25 same. So that's basically going to get smaller. So NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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175 1 near the end, you're going to end up with channels 2 that are very short in this direction, in the incline 3 direction and long in the vertical direction. All 4 right. That's important and I'll come back to that.
5 Now it's important from the point of view of thermal 6 loading. I'll explain something that's quite 7 interesting from a thermal loading point of view.
8 That's that. That's one called boundary 9 internal. We are bounding inside. I personally 10 believe that, I believe for a long time, that you can 11 have a lot of core on a floor like this like an inner 12 reactor on the concrete with lots of water in the tub 13 and I think eventually it will become cooler.
14 MEMBER WALLIS: Now this comes out and 15 floods from the top as well.
16 MR. THEOFANOUS: I'll explain that in a 17 moment, but let me finish my thought here which is 18 eventually it will be cooled, but we can't demonstrate 19 that. That's the problem. So it's very possible that 20 this BiMAC never comes into play even if you --
21 MEMBER WALLIS: When does it switch on?
22 Do you wait --
23 MR. THEOFANOUS: I'll come to that.
24 MEMBER WALLIS: Do you wait until you --
25 MR. THEOFANOUS: You're very impatient.
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176 1 You're very impatient. Just wait a minute.
2 MEMBER WALLIS: Well, you've spoken all 3 the time. I can speak --
4 MR. THEOFANOUS: You can ask a question if 5 you like, but don't talk to me for the future of 6 what's coming up.
7 CHAIRMAN APOSTOLAKIS: Can you point to 8 the certainly BiMAC itself? The BiMAC consists of 9 what?
10 MR. THEOFANOUS: The BiMAC consists of 11 this dish and then you're right that there is an 12 integral piece of that which is the lines that are 13 coming from GDCS, the lines which are coming in and 14 I'll come to that in a moment. I want to give you 15 sort of a global view, not too much of the technical 16 details because I think more detail plots later I'll 17 show you.
18 I'd also like to answer this very 19 question. What I said before, BiMAC works right away 20 and the reason is that it is connected to the GDCS.
21 So the moment you turn on the valve, that valve 22 supplies this central part that goes that way. So 23 it's filled up right away and the flow is running out 24 of all of those pipes which means that it's 25 essentially it's immediately effective for cooling.
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177 1 However at some point the GDCS is going to 2 run out of water and especially --
3 MEMBER WALLIS: I'm not quite sure of 4 that. We have an event. We haven't gone through the 5 vessel yet. Do you switch this thing on before?
6 MR. THEOFANOUS: No, no. We said --
7 MEMBER WALLIS: When do you switch it on?
8 MR. THEOFANOUS: I'll get to it.
9 MEMBER WALLIS: No, I'm with you. I want 10 to know what's happening.
11 MR. THEOFANOUS: I said before but you 12 weren't thinking. You were a little bit paying 13 attention to something else.
14 MEMBER WALLIS: Okay.
15 MR. THEOFANOUS: I said earlier we are 16 switching it on after the initial core of the melt.
17 We don't want to have water there when the first core 18 occurs because it will give us steam explosions.
19 MEMBER WALLIS: The first core. That's 20 right.
21 MR. THEOFANOUS: Okay. So we're switching 22 it on after the first core and then after that 23 happens, then we have plenty of water there and it 24 continues.
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178 1 actually have melt on the floor? How do you know?
2 MR. THEOFANOUS: By temperatures. Again 3 we'll come to those issues in a moment. I think now 4 let's first just get -- make sure that we understand 5 that and then we'll find some of those.
6 MEMBER WALLIS: What is on the lid? What 7 is the lid?
8 MR. THEOFANOUS: Yes. If you let me 9 explain, I was trying to get there.
10 CHAIRMAN APOSTOLAKIS: Okay. Let him 11 talk.
12 MR. THEOFANOUS: So we want this to be 13 very basic in the concrete. I got into this stuff 14 because I was telling you that this may never even 15 come into play even if you have a problem. Okay.
16 It's better than here. So what we have here, we have 17 a grate with support poles which are not illustrated 18 here which are basically holding a plate also.
19 Actually you don't know there's anything there. It's 20 just a steel plate that is thin.
21 It's like two millimeters thick on the 22 steel plate and the reason why it's thin is because I 23 want it. That's not an important part of the 24 consideration but I wanted it. It is a high pressure 25 melt injection, I have a melt jet coming out at high NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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179 1 velocity. I want this to melt right away rather than 2 splattering. I want to melt locally right away and 3 then the melt is going to flow right in here and I say 4 I think most of it is going to be captured, because 5 there is a high velocity steam. By the time, you have 6 it reach here, this high velocity steam has expanded 7 to about 20 times the area.
8 Therefore, that stagnation pressure holds 9 the plate down and therefore, this plate is quite 10 resilient as long as you have enough support for it 11 and it will just stay there and the melt will catch.
12 Some melts will come out. That is discussed in the 13 report. I don't want to take time for this now. So 14 small amounts will come out, but it's good to have it 15 there.
16 So now, I'm also showing that the 17 operation of this initially will be with water coming 18 in from here and then going out from the vertical 19 pipes, all the vertical pipes. Okay. Now later on 20 when the water finishes coming in here, then we have 21 other downcomers which are, now this time the pool is 22 already filled up and our water is coming in from 23 those channels that are not heated or from the 24 downcomers.
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180 1 and how again we say it's very important for this and 2 to inquire in this report the very high level ability 3 for switching on the water coming in, high level 4 ability also for not switching it wrongly on. All 5 right. It was not our job to design completely the 6 sensing elements, however, just talking with designers 7 we have some ideas we can use, for example, 8 thermocouples that are embedded in here so the moment 9 that something came in, you know it's high 10 temperature.
11 You can use also spring actuated nitrogen 12 bottles which hold some pressure so that when the 13 temperature goes high, some detector melts and then 14 opens up and opens up the valve. I like basically to 15 make this spositively activated based on very high 16 temperatures in here.
17 MEMBER WALLIS: And the brown stuff there 18 is?
19 MR. THEOFANOUS: The sacrificial material 20 like I said before. The important part is at the top.
21 The top should be something that is very resistant 22 like a refractory material, zirconia, something like 23 that and it would be like 20 centimeters. You don't 24 need very much there.
25 All right. So now it is from the point of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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181 1 view of evaluating. I'm now going to the three topics 2 and again please use your prerogative as a committee.
3 You can tell me that there's too much detail here.
4 Let's go to BiMAC. But my idea is to at least touch 5 on these issues to then finally come to BiMAC.
6 So the direct containment heating, I'm 7 going to cover a number of items. One item is 8 containers depressurization. Is it possible you have 9 sitting there a vessel sitting there all buttoned up 10 with very high temperatures for such a long time. We 11 asked that question first. Then the parameter range 12 covered, also whole range parameters and results.
13 Then the thermal loads. And that finishes the 14 catastrophic part.
15 Then over here is thermal loads to liner.
16 And then we want to compare to fragility. The 17 fragility we have nothing with do with the fragility.
18 This was taken from one other chapter of 33201 and 19 summary of bounding approaches, we'll conclude, just 20 like finish here.
21 First, this potential for this container 22 depressurization, I should remind that you for PWRs 23 the DCH depressurizes.
24 So I asked the question initially after 25 can this happen and there are three possibilities.
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182 1 There is the possibility of the isolation condenser, 2 the pipe that goes into the isolation condenser.
3 There is the, here it explains in detail, main steam 4 line and then SRV that hangs off from there and so we 5 have three places.
6 But actually the one that is important is 7 this because here is closed first and it operates 8 continuously and therefore you get especially into 9 high temperature or element in the element. You get 10 hydrogen produced and now you have also good thermal 11 conductivity material that is found out here.
12 The other thing to point out is this is 13 high pressure source steam and hydrogen can carry all 14 the heat. That's why you saw exactly that it's not 15 convection in the steam environment. Normally, you 16 wouldn't have expected it. It was in fact it's high 17 pressure steam and high density, so it can carry all 18 the heat around.
19 So the question is will that fail and we 20 took the typical materials for the construction 21 materials and what is showing here is showing that 22 this is the count of the material strength and this is 23 the temperature and here is the main steam line, here 24 is the isolation condenser and here is the SRV. What 25 that means is that the main steam line should be NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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183 1 between 1,000 and 100 degrees to fail, the isolation 2 projection in this range and the SRV in this range.
3 The SRV is made much more substantial because it has 4 to take loads and that's why it has more strength.
5 That's why it can take higher temperature.
6 So the question now basically is can you 7 actually achieve this kind of temperature in the MSL 8 which as I showed you the MSL is heated by the flow 9 going to the SLV. Just happens the MSL was a pipe, a 10 thinner one, so that's why it's here. The typical 11 core transient, it doesn't really depend on what core 12 you use. You will find that you get a lot of 13 oxidation and get a lot of snowballing effect and you 14 get temperatures of 3,000 degrees for two and a half 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />. So all you have there is like a quicken path 16 with 3,000 degrees over here. Gas is naturally 17 conducting.
18 And you ask the question will you ever 19 reach 1,000 degrees? I think you will. But I didn't 20 want to just arrive just to that and say okay, we 21 don't have DCH problem. It was kind of fun to work 22 through the dynamics of the DCH as well. So that's 23 what we've done. That's what I want to show you how 24 that works.
25 First point because I've seen analysis of NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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184 1 people not so BWRs. Several of my old NRC friends 2 wanted to see a real good BWR, DCH analysis. So I 3 think this is going to do that. But I've seen people 4 that have done interpretations of experiments as well 5 as PWR calculations trying to get the fallout and then 6 they average out over the whole cross-section area of 7 the space which is fine.
8 Actually you see that we've done CRD 9 simulations and I think I'll get into a problem here 10 if somebody knows how to do that. You find out that 11 you get a supersonic jet out here. It's something 12 like 600 meters per second, this fantastic speed you 13 get and this jet comes and hits the bottom floor and 14 is diverted and becomes a wall jet around the floor 15 and then it's diverted again and becomes a vertical 16 jet with hundreds of meters per second out here. If 17 you average it out, it just like a fizzle, well not 18 quite a fizzle but it is much lower of course because 19 this is a big area.
20 So I believe that this as well as any 21 other reactor that I have done for PWR before this 22 process here is tremendously intense. In fact, I was 23 so curious about this that I even did a few 24 experiments in my lab with a scale to that. We did 25 some experiments and it's an amazing force. So NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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185 1 there's very little doubt in my mind that we really 2 have a high pressure melt ejection unit right here.
3 And what the other fundamental physics 4 here is that you have a liquid mass. Liquid masses 5 are microscopic in inertia. So therefore it is not so 6 easy to accelerate those masses and get them out 7 before they fragment and mix with steam. So the 8 reason we have this very fine fermentation is because 9 of the melting velocity and the instabilities which 10 created basically an atomizing mechanism that is very 11 fine.
12 MEMBER WALLIS: Why does this high 13 velocity, very hot jet, why does it get diverted, not 14 simply drill a hole?
15 MR. THEOFANOUS: Why does it do what?
16 MEMBER WALLIS: The high velocity jets can 17 drill holes as well as get splashed. They can drill 18 holes in things. Why doesn't it drill a hole right 19 through the base?
20 MR. THEOFANOUS: Because like we're 21 saying, we're protecting that with the refractory 22 material.
23 MEMBER WALLIS: Oh. Well --
24 MR. THEOFANOUS: Before you can actually, 25 there's five meters of concrete on the floor and it's NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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186 1 on top --
2 MEMBER WALLIS: Five meters, that stuff is 3 five meters thick, that brown stuff.
4 MR. THEOFANOUS: No, but it's all 5 connected together. It is sitting on the top of the 6 --
7 MEMBER WALLIS: I would think it would 8 destroy some of your tubes.
9 MR. THEOFANOUS: Well, you might think so, 10 but --
11 MEMBER WALLIS: Well, I'm just asking.
12 Does it destroy?
13 (Several speaking at once.)
14 MR. THEOFANOUS: No, I'll just tell you 15 now. It doesn't destroy the tube.
16 MEMBER WALLIS: You just told us it had 17 tremendous force and all this stuff. So I would think 18 you --
19 MR. THEOFANOUS: Yes, we know exactly what 20 the force is. We know. We've --
21 MEMBER WALLIS: So you have analyzed the 22 survival of the tubes.
23 MR. THEOFANOUS: Sure. In the report. In 24 the report, you will find the stagnation pressures for 25 the --
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187 1 MEMBER WALLIS: You will find all that 2 stuff. Okay.
3 MR. THEOFANOUS: So now the problem we 4 want to solve here is therefore steam coming out at 5 high velocities, mixing up very intensely reducing 6 very fine automatization of the melt and especially it 7 is zirconia that's there and oxidating it and 8 releasing the oxidation energy from the point of view 9 of most gas coming out. It doesn't make much 10 difference because you have one more hydrogen or more 11 steam, the same thing so it's all there. We have 12 another containment here. So it doesn't really matter 13 whether it's hydrogen or steam.
14 However, there is extra energy that is in 15 this initial oxidation and that heats up the gases and 16 that's important. Before the gases go through this 17 operational pool, the temperature is very important 18 because that really generates the peak of the pressure 19 and there you need to account correctly for all that.
20 So we have them not coming out. Then 21 steam after that. Automatization, oxidation fine 22 scale. The stuff is blown out into the space over 23 here and there it separates some of the bigger pieces.
24 They fall off. The velocities are very low by the way 25 out here, very low. But this volume is pressurizing NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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188 1 now quickly and will continue to pressurize like as if 2 it was a closed volume until the vent's clear. That 3 is a process that can take like a second. So it's 4 very intricate and you want to calculate that 5 correctly.
6 Now I want to contrast that a little bit 7 with what we did for issue resolution for pressurized 8 water reactors. This was our probabilistic framework 9 that we used and you'll see here that there is a lot 10 of detail like there is amassed how much O 2 you have 11 or how much zirconia and how much was steel and then 12 how you get pressurization as a result of these 13 compositions and then something we call the coherence 14 (PH) ratio which has to do with how much of the steam 15 is in to see how much of the melt here in this process 16 and all this was happening in the closed because there 17 was a lot of static containment. It was in a closed 18 volume. It couldn't go anywhere. So in fact, in this 19 case, the dynamics were not so important. It was 20 what's important was the maximum pressure and that's 21 why also Marty Pilch who worked with me together to do 22 this serious problem. He used what's called a two 23 cell equilibrium model which basically does the same 24 thing that my model did except that one was just like 25 an equilibrium thermal dynamics. So take that and put NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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189 1 it equal and put it equal.
2 So here for this reactor, it's not enough 3 to get the final pressure because you have an optimum 4 volume pretty sure we can -- So we want to get the 5 dynamics so the full -- is needed. So we use the 6 same. We call it convection limited containment 7 heating (CLCH). We use that same model but now in a 8 full transient model. The model assumes basically 9 that the steam and the melt come to what -- the 10 perimeter at some rate in which the melt is being 11 carried out as fine particles to go out. So that 12 defines the rates of contact, the rate of containment 13 and the steam going down. Okay?
14 Then basically that's what we did and the 15 reason I put this up here because I want to show you 16 that the evaluation for PWRs, thanks to the presence 17 of this suppression pool and the venting from that 18 volume from the drywell to the wetwell actually is 19 totally insensitive to essentially all that stuff. So 20 you can assume the whole mass and even more, almost 21 anything you can do, you can not overpressurize this 22 area.
23 So what you've done here, that's new, is 24 you've extended the model to make it transient and 25 then we coupled to event clearing model and then each NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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190 1 one of those models were verified in the transient --
2 And here is to illustrate for you the 3 facilities which were used, the data we used, came 4 from. This is IET series. It's called integral 5 effect tests that were run in counterpart, two series 6 (PH) SND at 1/10th scale. That's the South Sea 7 facility at 1/10th scale and then at 1/20th scale, at 8 I think it's called core exit facility -- used real 9 materials and they used -- Pretty significant sized 10 experiments. That's what we used every time for very 11 fine my model and Marty Pilch's model and we could get 12 done the job for the PWRs.
13 I'm using the same data here but now also 14 paying a lot of attention to the transient itself and 15 I'll show you in a moment the results.
16 MEMBER WALLIS: I have no idea what you're 17 modeling here.
18 MR. THEOFANOUS: I'm sorry.
19 MEMBER WALLIS: I have no idea what you're 20 modeling. What is this supposed to be modeling?
21 MR. THEOFANOUS: What the experiment is 22 modeling?
23 MEMBER WALLIS: Yes.
24 MR. THEOFANOUS: It is modeling the 25 process I described to you.
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191 1 MEMBER WALLIS: It's modeling the entire 2 containment with the venting and everything.
3 MR. THEOFANOUS: No. I said this is for 4 PWRs. Okay. This is for PWRs, pressurized water 5 reactors.
6 MEMBER WALLIS: So what is it modeling 7 then?
8 MR. THEOFANOUS: So it's modeling their 9 containment heating processes in what is dry container 10 which means there is a reactor, there is a reactor 11 cavity, there is a --
12 MEMBER WALLIS: You're squirting something 13 into this containment and --
14 MR. THEOFANOUS: They are squirting 15 something into the cavity of a PWR and then you have 16 a containment which is this one here which is like 17 what is dry containment to find how much pressure you 18 get. In this case for PWR, you're also going to know 19 how much hydrogen you get and you're going to know 20 whether that hydrogen is going to combust or not. So 21 it was a real challenge here to find also the hydrogen 22 produced and the combustible hydrogen because that 23 evolved into the final pressure here.
24 Now in our case, we are interested in the 25 -- And CLCH model was found to work as well actually NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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192 1 in telling the hydrogen and final pressure and 2 everything. Here we are interested in reactor 3 containments. So some of those tests were done with 4 nitrogen only in the large volume here. So we used 5 those obviously because those are the ones that are 6 relevant for the present comparison. That's that.
7 The other one -- So that's for the DCH phenomenon 8 itself.
9 Over here, we have the vent clearing, what 10 I was telling you before, and those are the PSTF 11 experiments. Those were actually done when I was a 12 little child. A long time ago. I remember those 13 tests. Actually I've been inside those facilities at 14 the time I was a consultant and we were looking over 15 those tests. I was sitting on the other side of the 16 test and those are full scale actually. Those are 17 full scale and that full scale is the same full scale 18 as we have in the ESBWR. Actually it's exactly the 19 same.
20 MEMBER DENNING: But that's the easy part 21 of the problem. Right? That's just acceleration of 22 the slug and it's just verified how long it takes to 23 accelerate.
24 MR. THEOFANOUS: Yes. But you'd better do 25 it though because -- So I'll show you in a moment.
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193 1 It's a very interesting dynamic because of that. So 2 what happens here you get a supply of vapor going into 3 some of the models of drywell. That pressurizes and 4 that pushes through the down carbon and through the 5 vents and pushes it right out and pressurizes this and 6 this. So that's the dynamics we're interested in 7 doing.
8 So I want to show the verification of the 9 reports and they're coming together to do the full 10 DCH. Here is an example of the IET DCH test model 11 experiments. This is typical comparison with the vent 12 clearing. The vent clearing, you like to know you 13 catch the peak and also the time of the clearing. In 14 the report, you'll find more details about both of 15 those things. It's interesting to point out that in 16 this test here and this is for the significant one 17 notice that we are much even in the long term and the 18 reason is that there was such a big facility here the 19 velocities were negligible. If you look at the Argun 20 test, you find that the experimental data, they show 21 the decline even in times like this and the reason is 22 you have heat losses which of course you don't care 23 about.
24 All right. So now the dynamics, there are 25 three regimes that I've identified for quantifying the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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194 1 log. So we just go on and run some calculations and 2 show further pressure and velocity. We wouldn't 3 understand what's going on and what drives it. So 4 what drives it here is that Regime I you hold 5 hypothetical because it is a very humongous area of 6 failure of the lower head. There is something around 7 one meter in diameter all at once forming. If that 8 was to occur, you'd have pressurization that is so 9 strong because of DCH that actually the pressure in 10 the lower drywell which is this exceeds the pressure 11 in the upper drywell very significantly just because 12 of that restriction I was telling you about.
13 All right. So we form a structure first 14 and then it reaches a maximum, but then of course as 15 it goes to high enough pressures, it is able to vent 16 faster. So you have a decrease. Then it cuts --with 17 it. So from that point on, the pressure is essentially 18 made the same and then at that point, it finishes the 19 blowdown. At this point again, this cools and the 20 wetwell gradually arises as the contents of the 21 drywell atmosphere vents into the water.
22 MEMBER DENNING: Those are results of your 23 analytic tool?
24 MR. THEOFANOUS: Yes.
25 MEMBER DENNING: And in this case you have NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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195 1 basically two separated volumes.
2 MR. THEOFANOUS: Yes.
3 MEMBER DENNING: Whereas in the PWR, you 4 had only one line.
5 MR. THEOFANOUS: One and it wasn't even 6 passing. The PWR, it was like we only looked at the 7 final result.
8 All right. So that's hypothetical.
9 That's Regime I. That's a very extreme regime, but 10 even that one doesn't fail. By the way, you'll see in 11 a moment that the containment is beginning to be 12 challenged around this pressure. So around 11 to 12 13 bar.
14 MEMBER DENNING: Is that what the 15 fragility is?
16 MR. THEOFANOUS: Yes, that's the fragility 17 for the drywell. I'll show you in a moment. Then the 18 Regime I is if you took an extreme of the case we have 19 used for a creep rupture in pressurized water reactor 20 the one we had during DCH and for that only, we used 21 0.55 meters in diameter. So we have given a 22 probability distribution of the possible sizes. Where 23 11 narrow I was reminding myself the other day is a 24 narrow distribution but the very upper outside end of 25 that was 0.55.
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196 1 This calculation here was around 0.5. I 2 wanted to be exactly literally correct when I said we 3 took the upper limits. I just had the calculation 4 around yesterday of 0.55 and of course, that's a very 5 slight difference from that.
6 So in effect, what the source here is that 7 this initial difference in pressure between the lower 8 and upper drywell is limited to a very short time.
9 Instead of a peak here, you get an inflection point.
10 They join together. Again there is a peak and there 11 is some panning order, finally catches up here with 12 the wetwell. Eventually from there, it goes out like 13 that.
14 I want to tell you that it takes something 15 like about 30 seconds, 40 seconds, to do the full 16 blowdown, but the main part is during the time that 17 you put in the melt out and I'll show you how one is 18 to do that and the shorter you make that melted 19 premium time the more big piles you make over here 20 because it happened before the event is cleared. The 21 longer you make the melted premium time the more 22 you're spreading out the energy into the steam. So 23 now from one point of view, that helps you oxidize 24 more. It helps you more contact, more energy comes 25 out, but on the other hand, the cooling spreads it out NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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197 1 brings in this suppression pool after the clearing.
2 So from one hand, that helps on one hand. On the 3 other, no matter what you do you can't get into -- So 4 that is Regime II. That's the upper end of the 5 category range for PWRs and those would be PWRs. The 6 reason we did that by the way is because some PWRs 7 have no penetration to the lower head. That means it 8 will suffer from creep rupture and then we have to 9 know how big the area is. In this reactor as well as 10 in some other PWRs where there are penetrations you 11 essentially never expect to have a creep rupture 12 scenario.
13 And then finally Regime III is the most 14 likely scene for a boiling water reactor and that is 15 if one or more of the penetrations fail and it doesn't 16 really matter whether it's one or two or three or four 17 because if you fail more penetrations then the melt 18 comes out sooner. It doesn't not bleed so much so 19 that the final area is not so different from having 20 one and you let it -- and in the process of melt 21 coming through the hole is un plated, un plated, un 22 plated, and eventually comes out to something like in 23 this case about 30 centimeters. That is a huge hole.
24 So therefore the relevant area for getting 25 steam out is 30 centimeters diameter hole. In that NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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198 1 case, Regime III as you see the dynamics are much more 2 benign and this is the steam that is falling out the 3 melt. That is again a creep rupture-like scenario like 4 the one I showed you.
5 So here is the coverage. We've done 50, 6 100, 300 cones. Three hundred cones is basically more 7 than what you have there even if you accounted for 8 everything. The diameters, these are typical of creep 9 rupture. These are smaller. I'm sorry. Penetration 10 failure. These are smaller than those because a 11 smaller amount of mass therefore less oblation. Then 12 0.5 is for the creep rupture I was telling you.
13 The temperature inside the vessel was 14 taken to was taken to be 100, 150, 100. Actually, the 15 higher the temperature is the less density of the 16 steam inside and therefore the less potential for 17 oxidizing. So actually you make it more severe by 18 using a lower temperature and that's why you use lower 19 temperature.
20 The tm needs some explanation. That is 21 the --
22 MEMBER WALLIS: What is the temperature of 23 the core area?
24 MR. THEOFANOUS: The core is around 2500 25 degrees, maybe higher.
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199 1 MR. THEOFANOUS: The t m is what you call 2 the mixing time or melted varying time and that is we 3 have this formulation for calculating that in the 4 pressurized water reactor case and use the same one 5 because basically there is steam and -- like things 6 going out but we played what we call metrics and as I 7 told you that's a matter of use. But typically for 8 these kinds of situations we have about seven to ten 9 seconds of time for this to come out.
10 If you make this melt time, of course, 11 given an area if blowdown of the steam is fixed by the 12 area and the pressure so now if you said that I'm 13 going to take this t m to be very short, what that 14 means is that you're going to allow a lot of the steam 15 in the area up high during which the melt is coming 16 out basically to be not useable because it -- and 17 there's nothing more to oxidize. So by making that 18 too short, you're making higher the defaults, you try 19 to make higher the defaults, however you are -- That's 20 why we call it convection conductivity. It's really 21 limited by that process. But we've done 3.6, ten 22 seconds, so a whole range of different choices here.
23 And here are the results. By the way an 24 important parameter that we call the DCH scale 25 expresses that coherence between the melt coming out NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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200 1 and the steam coming out. Those are two 2 characteristic times for that process. This ratio, 3 it's very important because when that ratio is less 4 than one, as I said before, the process is still 5 limited and it's less than what it is the elastic 6 pressure again. So for example in a dry container 7 even, if that's very small you get much more pressure 8 than compared to if it is but one. So actually in a 9 dry container, if you plotted the pressure increase 10 versus this coherent ratio you find out another steep 11 increase up to one and up to one should have straight 12 up.
13 So what you see here is what we have and 14 our cases are anywhere from as low as 0.104 to as high 15 as 1.3. So we have covered the whole spectrum of 16 likely contacts between the steam and the -- I should 17 point out the pressures however. The first peak is 18 very modest in relation to the fragility. The second 19 peak is also very modest. As you're going to this, 20 these are creep rupture scenarios you get about six 21 bar. Then the temperatures, I'll show you in a moment 22 how the temperature does. It looks like it goes up 23 and then it goes down and eventually settles in about 24 a minute settle to some value and that value is around 25 one thousand degrees.
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201 1 MEMBER DENNING: You're not showing that 2 first kind that you first showed us because that's not 3 considered credible.
4 MR. THEOFANOUS: I wanted to do that 5 because I wanted to provide a backdrop against which 6 you can see where the conservative case is and then 7 the more likely case is. So we also did run outside 8 of the report outside of Chapter 21 additional 9 sensitivities about condensation and dust cooling, 10 oxidation efficiency composition and drywell 11 atmosphere and so on and basically same results. So 12 here then putting it together, here is the upper bound 13 is six bars I was showing you before, upper bound of 14 the loading that you could have and it really doesn't 15 decept the fragility. I don't want to get into any 16 games about saying so much of that is like this and so 17 much of that this. Just I used here the complimentary 18 cumulative distribution. So everything is below that.
19 Then for the fragility which is as I said 20 we got from another chapter of the VDOT report is 21 initially here. You see that for the 50 percent 22 values about 16 bars. This value here around 11 or 12
-5 23 is running two percent only. Over here is 10 . So 24 it's really just there's no intersection whatsoever.
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202 1 to belabor that anymore. This is a conservative area 2 as it is as in the PWR case the creep rupture is on 3 the upper limit of the size and upper bound of 4 available materials participating and no new section 5 at all.
6 The temperatures now, coming to 7 temperatures, here is a typical behavior we see. We 8 see a very high pressure pulse -- temperature pulse in 9 the lower drywell. Of course, it makes sense because 10 not only have you got 2,000 degrees in the melt but 11 now you get the oxidation area and you have a 12 tremendous energy machine for using there. So you can 13 reach another 1,000 degrees when you cover it.
14 Now why does it go so steeply down is 15 because after the melt gets out of there then 16 basically it washes out with the cool steam and 17 hydrogen that come out from the vessel expanding and 18 cooling down. So that's the issue I intend to show 19 now. But keep in mind this temperature on the 1,000 20 degrees because that's really a benchmark against 21 which to say now if I have this for a few minutes on 22 the upper drywell what will happen with the liner and 23 the liner started sagging. Obviously if the liner had 24 no anchors, you would see the liner sort of falling 25 off by its own weight because it's really that one NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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203 1 that's stripping off.
2 However, in the case of which we are 3 covered so well by those anchors, the way that has to 4 be self supported for each, let's say, cell, that is 5 so small that it just doesn't do anything. In fact 6 creep helps us because it helps relieve the stresses 7 so there is no cracking.
8 MEMBER ARMIJO: Why doesn't it buckle and 9 pull away?
10 MR. THEOFANOUS: No, it will do some 11 buckling. In fact, in the report, I didn't know if I 12 had time here, but in the report you'll find pictures 13 in which you see the full buckle. It makes like a 14 wavy structure and that's why I'm saying it helps you 15 because it can creep without peering, without creating 16 cracks because of the high temperature. And then 17 again to mention the lips again on the -- We make no 18 claim by the way for wire integrity in the lower 19 drywell not in light of these temperatures I wouldn't 20 and not in light of the fact that there's all kinds of 21 melts flashing all over the place.
22 Ex-Vessel Explosions and BiMAC pipe 23 crushing and the pedestal failure, what we're saying 24 here is that we are saying that if we had a deep pool 25 and if we had pools of melt that are tens per second NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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204 1 which can't be excluded, you know, people usually will 2 use and I've seen people use tens of kilograms per 3 second and rarely you see hundreds of kilograms per 4 second, but this is very heavy material. If you have 5 a core there, who is going to tell you you're not 6 going to get a few hundreds at least.
7 So we used the 700 kilograms per second in 8 our calculations and we found that in doing the 9 impulses on the form that it can be significant. With 10 these kinds of pools, we find that because the 11 pedestal is quite far away and because especially 12 shower pools can vent (PH) the energy we find that the 13 impulses are rather low.
14 The impulses by the way are the figure 15 here because these are millisecond scale pressure 16 pulses which show the detail of the pulse, the detail 17 of the pressure transient, is not important but rather 18 the integral on the code. So using impulses to measure 19 explosive release energy and then we use the impulse 20 to measure fragility.
21 MEMBER WALLIS: Now in the PRAs it says 22 that the probability of an EVE is zero for depths less 23 than 0.7 meters. Then it becomes one when you get up 24 to 1.5.
25 MR. THEOFANOUS: Where are you now?
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205 1 MEMBER WALLIS: I'm reading Section 8.3-4.
2 The notes from the PRA that we're reviewing here.
3 MR. THEOFANOUS: From the PRA.
4 MEMBER WALLIS: It says that the 5 probability of an EVE is insignificant for water 6 levels less than -- Is this something you did or 7 something they did?
8 MR. THEOFANOUS: The rupture scenario --
9 MEMBER WALLIS: It says that when water up 10 to here you have no EVE and when you have water up to 11 here, it's a probability of one.
12 MR. THEOFANOUS: He did that.
13 MEMBER WALLIS: I'm just wondering. Can 14 you really predict with that precision that nothing 15 will happen when it's up to here and it's inevitable 16 when it's up to here? Can you really predict with 17 that precision?
18 MR. WACHOWIAK: This is Rick Wachowiak 19 from General Electric. That's a calculational tool if 20 you will. What we're saying is when it's --
21 MEMBER WALLIS: It's not a modeling of the 22 physics.
23 MR. WACHOWIAK: When it's below, what Theo 24 is going to show you in a minute is when it's below 25 the lower threshold there is no way that we're going NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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206 1 to have a steam explosion that's going to affect any 2 of the structures or any of the equipment. When we 3 get to the deeper subcooled pools what he's saying is 4 that we can't rule out that there may be some damage.
5 So when we did the calculation --
6 MEMBER WALLIS: You took it as one.
7 MR. WACHOWIAK: -- we said when it's high 8 we assume that. We'll just take the worst case.
9 MR. THEOFANOUS: No, he's not asking that.
10 MEMBER WALLIS: So he has to --
11 MR. THEOFANOUS: He's asking how do you 12 know that what fraction of scenarios are for shallow 13 pools, what fractions are for --
14 MEMBER WALLIS: I'm also asking how well 15 can you really say that it's zero for a certain height 16 and then it suddenly becomes one.
17 MR. WACHOWIAK: And what I think he's 18 going to show you is that even with the one meter or 19 two meter that it really shouldn't be one. It should 20 be --
21 MEMBER WALLIS: It's very unlikely. He's 22 going to show it.
23 MR. WACHOWIAK: -- some small fraction.
24 MEMBER WALLIS: So we have to listen to 25 them all.
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207 1 MR. WACHOWIAK: Yes.
2 MR. THEOFANOUS: Unfortunately.
3 MEMBER WALLIS: Okay. That's all right.
4 You'll get to it.
5 MR. WACHOWIAK: It's just a calculational 6 tool that we use.
7 MR. THEOFANOUS: I thought you were asking 8 about the fraction of scenarios that --
9 MEMBER WALLIS: No, I was asking about the 10 probability of an EVE depending on pool depth.
11 MR. THEOFANOUS: Oh. Then let's go on.
12 MEMBER WALLIS: You're going to get to 13 that? Okay.
14 MR. THEOFANOUS: I'll get to that. All 15 right. So what you said is that there was a --
16 prohibiting information of such pool but design 17 changes -- they really are. So --
18 MEMBER WALLIS: So you mustn't switch it 19 on too soon.
20 MR. THEOFANOUS: Yes. As usual.
21 MEMBER WALLIS: All right.
22 MR. THEOFANOUS: I don't have it here, but 23 I put that --
24 MEMBER WALLIS: So more water isn't 25 necessarily better. It could be worse.
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208 1 MR. THEOFANOUS: Of course. That's why I 2 don't want to have water there.
3 MEMBER WALLIS: Not yet. Not until you 4 need it.
5 MR. THEOFANOUS: And I don't need the 6 water there when the -- in the reactor vessel. Now 7 what we mean by prohibiting, you have to prohibit 8 that, just make it less likely for having water there, 9 that means that there was a GDCS overflow for example 10 if we had let it when revising the original design it 11 would basically almost virtually guarantee you're 12 going to lots of water down there.
13 There was another one that would allow 14 overflow the suppression pool which again would almost 15 guarantee that you're going to get into some flooding 16 situation. That was taken care of. So that's what we 17 mean by containment layouts and systems and then in 18 addition to that as I explained already in the case of 19 BiMAC we want to make sure that we require the 20 reliability of, I don't know, the reliability of 10-3 21 for failing to supply the water when needed and the 22 same reliability of 10-3 for supplying the water too 23 early. So that's a systems question. So we are going 24 to get down to a shouting match about how we're going 25 to assure this 10-3 but that's a systems question NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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209 1 which we believe is more properly a problem for the 2 COS stage in the license.
3 According to bounding estimates and 4 impulses the conclusion is here. Fragility is the 5 additional margin even for subpooling. So here the 6 real picture, that's the basemat. There is a BiMAC, 7 basically a concrete structure with pipes and with 8 some cover of -- on the top of it and there on the 9 floor, there is the grating and these are the two and 10 a half meters thick pedestal wall. These are the 11 hatches I mentioned before. So if you want to know 12 why for example we keep that value for about two 13 meters it will be lineated again what we foresee the 14 deep pool or fire pool it's because if it was more 15 than about two meters above this floor it would be 16 exposing the hatch door to the explosion. So the 17 issue here is one in which we have differing levels 18 of water up here and that comes out at about ten (PH) 19 ton per second.
20 What kind of pulses here can I get here 21 and at the BiMAR? That's the question. Then will the 22 structure survive this pulse? So already I mentioned 23 the release rate and we did calculations for the one, 24 two and five meter deep pools. We considered such a 25 rate in subpool water and what we're finding is at the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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210 1 floor it's about 100 kilo Pascal seconds pulse up here 2 if some cooled pool. If we have saturated water pool, 3 we do nothing. And then, for the side walls because of 4 the distance and because of the venting you get about 5 40 to 50 kilowatts Pascal seconds, but also in the 6 fragility mode.
7 Now this is new. This is -- that these 8 actually DYNA3D I think it's called -- is the 9 commercial version which is operating for commercial 10 purposes. This is something that's used for national 11 security issues and of course is exercised a lot with 12 high explosives. Now high explosives may give you 13 assorted pulses, however, most of these is for 14 cracking purposes. However, for our purposes here, 15 one or two millisecond pressure pulses are also pretty 16 steep. So we believe that's very appropriate in terms 17 of the natural frequency structures. So that would be 18 if there's a real disaster these days.
19 And I referenced in the Chapter 21, I 20 referenced a rather extensive document when this part 21 was published from Livermore and we tried a lot of 22 compiled data of this --
23 MEMBER WALLIS: There was just a one shoot 24 bang or does it bang and then bang again? When you're 25 pouring the stuff into the pool, you have an explosion NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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211 1 and everything comes together again. You're still 2 putting stuff in. Does it explode again? Several 3 times?
4 MR. THEOFANOUS: Yes. Sure. That is one 5 of the issues that arises if you have very deep pools.
6 MEMBER WALLIS: Right.
7 MR. THEOFANOUS: That's why I don't want 8 to say much about very deep pools. That's why I tried 9 to stay away from deep pools because if I have a one 10 meter pool and I have an explosion in there and the 11 water goes all over the place, you're not going to 12 have a pool anymore.
13 MEMBER WALLIS: Well, it falls back down 14 again.
15 MR. THEOFANOUS: Yeah, but how long will 16 it take for the water pressure for the --
17 So the calculations actually were very 18 detailed with millions of notes and a very detailed 19 representation of the -- By the way, those are 20 symmetry planes and that means in a symmetry plane the 21 thing is not allowed to move normally, but it's free 22 to move this way and a very detailed presentation of 23 all the rebar, the concrete, the -- bar, the -- bar, 24 the mercury bar, everything is there in these 25 calculations.
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212 1 And here is actually a very interesting 2 movies to show how the -- Of course, that's highly 3 exaggerated. This is the 600 kilos Pascal second 4 welding (PH) that we put into this loading as well and 5 what happens in this case is you begin to have -- This 6 is illustrated here by the yielding of the rebar and 7 by the crashing of the concrete which is shown by this 8 red area. So basically in the area where the concrete 9 is, you crack it and the rebar yields and you have 10 failing. It takes that kind of energy to be put in to 11 create failure.
12 This is represented schematically here.
13 We've done calculations with the obstacles here, here 14 and here and there was no failure. Over here is what 15 you just saw, some failure. So I just draw just 16 schematically. That's why this dotted line, some kind 17 of a cumulative salable probability that starts 18 arising between here and here.
19 As I mentioned before, what was wrong 20 before about failures of those structures was actually 21 a paper that I did many years ago. At that time, we 22 considered one and a half meters concrete with rebar 23 and that was failing right around here, at around 100, 24 150 kilos Pascal seconds. Because of this paper, I 25 think most people, you go out there and you ask people NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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213 1 that know about this problem how much does it take to 2 fail the model within 150 kilo Pascal seconds. So 3 actually we were very pleasantly, we were anticipating 4 some increase but that is a very significant decrease 5 in fragility because of the size and the concrete.
6 Nothing special on the concrete by the 7 way. This is just a normal 5,000 psi concrete. You 8 can get that. If you have 10,000 psi concrete, it's 9 going to be even better.
10 MEMBER DENNING: On the DYNA3D when you 11 run that analysis, do you actually put in, you don't 12 put in just the kilo Pascal seconds. You put in a 13 certain --
14 MR. THEOFANOUS: The pulse, yes.
15 MEMBER DENNING: The pulse, right.
16 MR. THEOFANOUS: Any report you'll see all 17 kinds of pulses. For example, it will be like twice 18 the maximum pressure, half of the width of the pulse.
19 You'll see a pulse here in the report. So what you 20 are showing here then is that for the pedestal in the 21 report you will find a number of compilations that 22 will show you get in the report only about 100 kilo 23 Pascal seconds. So it's a huge margin. I believe 24 when we have pools like that, one, two meter pools you 25 cannot fail the pedestal by a --
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214 1 Because of what Graham was saying before, 2 I don't want to say to defend an eight meter pool and 3 what happens with that. So therefore we decided we 4 don't want to have pools like that and we managed to 5 do this by not flooding into --
6 MEMBER WALLIS: Theo, you have this pool 7 and you have an explosion in it. Is the explosion in 8 the middle of the pool or is it near the wall?
9 Doesn't it make a difference where it is?
10 MR. THEOFANOUS: Of course.
11 MEMBER WALLIS: Because it attenuates 12 there.
13 MR. THEOFANOUS: Yes. Of course it makes 14 some difference.
15 MEMBER WALLIS: So you can blow a hole in 16 one side of it or near that side.
17 MR. THEOFANOUS: No, actually what we have 18 done here to account for that kind of thing here 19 similarly we have proceeded, if you look at the report 20 again, you'll find that the radial, actually symmetric 21 operation basically with the diameter of ten meters to 22 a diameter of only about four meters. So that means 23 we put the explosion close enough to the wall as if it 24 was coming from the edge of the reactor vessel and 25 what you would see again is sort of very conservative NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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215 1 but it gives you an idea that what we've done is a 2 conservative picture.
3 MEMBER WALLIS: But the stuff that is 4 coming out, you said it's in a jet, a high velocity 5 jet.
6 MR. THEOFANOUS: It's in a jet.
7 MEMBER WALLIS: So it could go way off to 8 one side and it could actually go very, very close to 9 the pedestal wall, couldn't it, before --
10 MEMBER SIEBER: No.
11 MR. THEOFANOUS: No, it couldn't do that.
12 There is no reason to do that because that stuff is 13 heavy and it's not --
14 MR. THEOFANOUS: But it's driven by its 15 own gravity. It's not at high pressure.
16 MEMBER WALLIS: So it's not high pressure 17 anymore.
18 MR. THEOFANOUS: No.
19 MEMBER WALLIS: That's a low one.
20 MEMBER DENNING: That's a different 21 scenario.
22 MR. THEOFANOUS: It's a different scenario 23 now.
24 (Several speaking at once.)
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216 1 and falling out.
2 MR. THEOFANOUS: Yes.
3 MEMBER DENNING: This is low pressure 4 scenario.
5 MR. THEOFANOUS: It's a different 6 accident.
7 MEMBER WALLIS: This is low pressure 8 scenario. Okay.
9 MR. THEOFANOUS: It's a different 10 accident. We started high pressure scenarios for 11 those that we do DCH. Low pressure scenarios the 12 issue is not DCH but these explosives.
13 MEMBER WALLIS: And there's nothing in 14 between that could be both?
15 MR. THEOFANOUS: There is nothing in 16 between unfortunately.
17 MEMBER WALLIS: Okay.
18 MEMBER SHACK: It's estimated to 90 19 percent.
20 MR. WACHOWIAK: This is Rick Wachowiak 21 again. There's not any way really to get water in the 22 lower drywell in the high pressure scenario. So 23 that's the main reason why we don't have to consider 24 the combined effect. There's just no high pressure 25 scenarios we can find where --
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217 1 MEMBER WALLIS: You can't drain the pool.
2 MR. THEOFANOUS: What?
3 MEMBER WALLIS: You can't drain the pool.
4 Is that it?
5 MR. THEOFANOUS: No. All right. Next.
6 CHAIRMAN APOSTOLAKIS: Wait, wait.
7 Comrade Theofanous. Is this a good time to take a 8 break?
9 MR. THEOFANOUS: Excellent time because we 10 are changing subjects.
11 MEMBER WALLIS: He presents the stats.
12 CHAIRMAN APOSTOLAKIS: One other question.
13 There's a lot of slides in your handout. Are these 14 part of the severe accident mitigation or do they 15 include the containment systems performance?
16 MR. WACHOWIAK: They do not.
17 MEMBER DENNING: They do not.
18 CHAIRMAN APOSTOLAKIS: Well, there was an 19 hour2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br /> and a half.
20 MEMBER DENNING: Are you sure you want to 21 take a break at this time?
22 MR. THEOFANOUS: Yes. There is enough for 23 two and a half hours according to the agenda.
24 CHAIRMAN APOSTOLAKIS: You had 12:30 p.m.
25 to 3:00 p.m. Yes, you're right.
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218 1 MR. THEOFANOUS: That's two and a half 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. Right?
3 CHAIRMAN APOSTOLAKIS: Two and a half 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. So let's take a break.
5 MR. THEOFANOUS: We are midway now.
6 CHAIRMAN APOSTOLAKIS: We'll be back at 7 2:45 p.m. Off the record.
8 (Whereupon, the foregoing matter went off 9 the record at 2:33 p.m. and went back on the record at 10 2:51 p.m.)
11 CHAIRMAN APOSTOLAKIS: Back on the record.
12 MR. THEOFANOUS: So we are in to steam 13 explosions. We're now going to look at the BiMAC 14 itself. From a structural point of view, the BiMAC is 15 supported by concrete which itself is similarly top of 16 basemat. The pipes are schedule 80 pipes. That means 17 one centimeter. We would have pretty significant 18 figures basically for structural purposes. They are 19 10 centimeters in diameter and embedded into this 20 sacrificial layer which is like 27 meters.
21 Now the question initially is if you have 22 an explosion here what does it take to crash those 23 pipes. Obviously, if we are sitting and those pipes 24 are right below the explosion and there is enough 25 impulse to crash them, then at least in that location NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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219 1 you're not going to be able to shoot the water that 2 you need in order to prevent melt completing.
3 I do want to make a general remark and put 4 this into perspective. We have like 100 square meters 5 floor area. You have an explosion that is sitting 6 someplace with impulses right under it, the localized 7 impulse. So that's going to be like being hit by a 8 truck. Actually, I don't think it's going to mean 9 very much for the whole function of the device, but I 10 still nevertheless would like to know what an 11 explosion will do to those pipes.
12 Again, analyze them with DYNA3D and see 13 that they support to each other. We found planes of 14 symmetry so that we could analyze this for extreme 15 detail, representing both the pipe, the wall thickness 16 and the concrete above and below it. The results 17 tells us how the quality of the metal yields and 18 whether the concrete cracks. This was for 220 kilo 19 Pascal per second welding and you see a significant 20 crack in the concrete.
21 I do want to say that this cracking of the 22 material which is especially important for high 23 pressure material itself, I mean the material is 24 important for basically resisting any oblation in the 25 pipes after you pour in the crack a little bit it NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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220 1 carries over.
2 MEMBER WALLIS: So the pipe's intact, but 3 the concrete is cracked. Is that what you're saying?
4 MR. THEOFANOUS: I didn't say anything 5 yet.
6 MEMBER WALLIS: Well, I know.
7 MR. THEOFANOUS: I haven't said anything 8 yet. I'm trying to put into perspective.
9 MEMBER WALLIS: I'm just trying to 10 interpret your last figure, the last figure you showed 11 us.
12 MR. THEOFANOUS: Oh, the last figure, that 13 last figure was to show --
14 MEMBER WALLIS: You said that concrete was 15 cracked. Now what about the pipe? Is the pipe okay?
16 MR. THEOFANOUS: For this kind of a 17 loading the pipe is some narrow -- oh, I understand 18 your question. I beg your pardon. In some location 19 where the pipe is incorporated with the other pipe, 20 that is in those similar things, they begin to yield.
21 You take that --
22 MEMBER WALLIS: But it's intact. It's 23 intact.
24 MR. THEOFANOUS: It's intact, yes. But we 25 take that to be the beginning of failure of the pipes.
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221 1 Once it starts yielding significantly even in a narrow 2 area, then that's the beginning of the crashing.
3 So if we put these results in a 4 probability plot again, for 99 percent of the 5 scenarios we have essentially no explosions. So that 6 is covering for most of it. This is for what we call 7 the low level.
8 For the one to two meter levels, our 9 results show that you can have a hundred. You can 10 have even more, maybe up to about 150 kilo Pascal per 11 second. So that shows schematically here that there 12 is some distribution that we don't know what it is but 13 that is what is shown on the dotted line. And also 14 it's shown here that somewhere around 200 kilo Pascal 15 seconds or maybe about that you begin to get 16 significant yielding of the pipe.
17 So that's why then the CFP starts rising 18 over here and the whole intent of this is to show that 19 for the scenarios that we played we have integrity.
20 But there is just no comparison, not even anywhere 21 near. The purpose of that is show that even if by 22 chance you had some small depth like one or two 23 meters, you could begin to interfere with the 24 integrity of the pipes.
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222 1 model would be used to get this dots?
2 MR. THEOFANOUS: We used PM alpha which we 3 used before and to me that is the state of the art.
4 The way it works is you get the melt into the water 5 and the PM alpha which is the mixing core.
6 MEMBER KRESS: Premixing.
7 MR. THEOFANOUS: The Premixing core, the 8 PM alpha, it basically tell you what are the possible 9 ranges of special space and time distribution so if 10 melt fractions and steam void fraction. Then we take 11 that --
12 MEMBER KRESS: That takes care of --
13 MR. THEOFANOUS: Oh, if you like, we have 14 it in the back of the report. We have the whole 15 evaluation basis of those cores.
16 MEMBER KRESS: Just one question. What 17 sort of triggering do you have there? Does it trigger 18 --
19 MR. THEOFANOUS: We use significant 20 triggering. Significant triggering means that once 21 you get the premixture we can put a trigger in.
22 MEMBER KRESS: The trigger time occurs 23 after you get this premixing volume?
24 MR. THEOFANOUS: Yes. Right. Any time 25 you have premixing. In other words, anytime --
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223 1 MEMBER KRESS: You can trigger any time.
2 MR. THEOFANOUS: Right. So the equation 3 you take is -- since you don't know. Triggering is a 4 kind of a spontaneous event that you don't know how to 5 predict it.
6 MEMBER KRESS: Yeah.
7 MR. THEOFANOUS: So you are saying that 8 for all the evolutions with the premixture we are 9 looking for cases where and you know how to drive the 10 quality of the premixture from the point of 11 explosivity. So we're finding the worse premixtures.
12 The way you create a trigger is by taking one cell 13 and mixing the fuel that's there with the water very 14 rapidly. That creates a pulse.
15 MEMBER KRESS: And that expands.
16 MR. THEOFANOUS: And that expands and then 17 this calculation is done with M which is an explosion 18 point which also we have fully documented and viewed 19 it and all that and I have in an appendix to the 20 Chapter 21 you will find all the verification basis 21 for the PM alpha but because this was done extensively 22 before I didn't want to bore you with that stuff. So 23 I didn't include it here.
24 MEMBER KRESS: Some of the members have 25 had the privilege of hearing that before.
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224 1 MR. THEOFANOUS: Yes.
2 MEMBER KRESS: Another question I have is 3 you're pouring at a certain rate.
4 MR. THEOFANOUS: High rate, yeah.
5 MEMBER KRESS: The very high rate. Can 6 you delay your trigger until you get it all in?
7 MR. THEOFANOUS: Yes, we can, but at that 8 point what happens is --
9 MEMBER KRESS: You have too much melt for 10 the water.
11 MR. THEOFANOUS: Yes, exactly. We are 12 getting into the physics now of the explosion. What 13 happens here is if we have too much melt and we don't 14 have enough water then the melt --
15 MEMBER KRESS: So somewhere in there 16 there's --
17 MR. THEOFANOUS: That's what I was saying 18 before.
19 MEMBER KRESS: Okay. Now I understand 20 what you're referring to. Thank you.
21 MR. THEOFANOUS: All right. So I think 22 now we are switching to the last topic which is the 23 basemat melt penetration and this is to illustrate the 24 scope of the work and what's all the different loading 25 mechanisms that we have and the different criteria NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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225 1 that we have to consider and then we have to challenge 2 if it has integrity or no integrity.
3 What you see here is there is a thermal 4 loading on the jet impingement. All right. So this 5 is we have local peaking right here because of the 6 oblation depth and you'll find an extensive discussion 7 of that in the report. So I'm not going to go through 8 that here. It's just to show you that you just can 9 kind of impact that layer. And that's why we went 10 into a refractory material so that we can be pretty 11 sure that we're going to pack it.
12 The second item has to do with thermally 13 loading from imagine now we have this -- which is full 14 of melt and it is a natural circulation and now that's 15 going to produce a thermal loading to the bottom and 16 to the sides and now we want to show that this thermal 17 loading would be possible to be accommodated by 18 loading on the other side that so that it will over 19 here. If this is categorized by decay heat flux, this 20 is a local criteria and this job here is done by 21 taking into account any possibility of the local 22 peaking of the heat flux.
23 MEMBER WALLIS: So are you doing a thermal 24 shock analysis of this stuff?
25 MR. THEOFANOUS: Thermal shock?
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226 1 MEMBER WALLIS: Yes, the sudden thermal 2 loading.
3 MR. THEOFANOUS: It's not the sudden 4 thermal loading. Yes, we can discuss it if you want.
5 MEMBER WALLIS: The sudden thermal --
6 7 MR. THEOFANOUS: But it's not a sudden 8 thermal loading. First of all, even if it was, it 9 would have no impact in this kind of situation. So 10 two answers. Do you want me to elaborate?
11 MEMBER WALLIS: So you have or have not 12 done a thermal shock analysis.
13 MR. THEOFANOUS: Huh?
14 MEMBER WALLIS: I'm just trying to find 15 out if you did a thermal shock analysis.
16 MR. THEOFANOUS: No, I didn't do a thermal 17 analysis. I think it's irrelevant to this problem of 18 thermal shock analysis. So if you disagree with me, 19 we can discuss it.
20 The point I'm trying to make is that this 21 evaluation involves local peaking. So it's not 22 sufficient to say I have this on the floor or I have 23 anomalous heat flux. My heat flux is less than this 24 average. That's not good. You have to make sure that 25 watery you always are below. The water is always NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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227 1 below the heat flux. So that is a more sticky 2 evaluation because you're looking for all the peaking 3 of the flux and not so conventionally know that there 4 can be all kinds of distributions. So we need to get 5 to those distributions.
6 The second topic however has to do with 7 the possibility in the pipe of basically depleting of 8 water as it's boiling out. So that's what defines the 9 size of the pipe. That defines in fact this 10 consideration and this consideration you find the 11 size. You can see very easy, in fact, these are very 12 small pipes which in some ways would be desirable from 13 a structure integrity point of view because they are 14 kind of small and have very, very thick walls.
15 Basically it would be indestructible. But if I did 16 that then I would be susceptible to both this and 17 this. So that's why the ball park stands in the 18 middle because we say we want to optimize that because 19 we were doing testing on that for the COL and we want 20 to optimize the test.
21 But this one here, that has to do with 22 depletion of the water. It doesn't care if the 23 profile is like this or like that. It really cares 24 about the total thermal power it's putting on the 25 pipe. Of course with that sensitivity, it also NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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228 1 demonstrates it doesn't go back the shape.
2 So two things you're looking for there in 3 this. You're looking actually not two, but three 4 things. We're looking for critical heat fluxes down 5 from the horizontal pipe and on the vertical segment 6 No. 1. No. 2 we're looking for the average like a 7 bounding average heat flux I can have again on the 8 horizontal and on the vertical and this is for this 9 problem and then I'm also looking for the local 10 peaking that they have and this is for that. Then in 11 addition, of course we have the explosions which we 12 just talked about. So those are the topics I want to 13 cover now.
14 Again, the same picture as before, but now 15 a little bit more detail, I think I'm going to give 16 you more detail about how this thing looks. So now if 17 I look at it from the top, this is what I was telling 18 you before. As you take slices this way, this pipe 19 gets shorter and they get longer. Okay? And we have 20 a main distributor here that the distributor is sized 21 and the downcomers are sized. The downcomers are 22 distinct because they are sized in a way that they 23 will provide no significant frictional resistance 24 compared to the frictional resistance of the two-phase 25 flow over here. So there is no starvation of the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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229 1 flow.
2 MEMBER ARMIJO: I guess I don't understand 3 that drawing. Are they all pipes or is this --
4 MEMBER SIEBER: Yes.
5 MEMBER ARMIJO: So there's pipe that --
6 MEMBER SIEBER: It just goes everywhere.
7 MR. THEOFANOUS: Yes.
8 (Several speaking at once.)
9 MR. THEOFANOUS: Maybe too --
10 MEMBER ARMIJO: -- How did that work?
11 MR. THEOFANOUS: And also presenting the 12 sumps which are by the way not always very well 13 protected in the plants, in previous plants. We want 14 to protect the sumps too and the sumps are important 15 to have there for operational purposes. But you don't 16 want to have bypass of the BiMAC by getting the melt 17 from here to here and then going out into -- this 18 would be a tremendous for the point of view into 19 basemat because you lose a lot of the concrete. So in 20 the two near the edge there, we then worked with the 21 people in the design and made them to be hiding the 22 wall as much as possible. Hiding the wall means 23 increase this dimension, decrease this dimension so 24 they can be covered just like the wall of the pedestal 25 by the pipes.
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230 1 MEMBER WALLIS: Can we go back again? The 2 sequence of events, when do you turn on the water for 3 this and when does the hot melt come out and impinge 4 on this?
5 MR. THEOFANOUS: Well, we wait until melt 6 comes out.
7 MEMBER WALLIS: So it's not water when the 8 melt first comes out?
9 MR. THEOFANOUS: There is no water from 10 when the first melts come out. The moment the first 11 melt comes out the water is initiated.
12 MEMBER WALLIS: The moment --
13 MR. THEOFANOUS: We don't want water 14 there. We have these pipes, the downcome is from the 15 GDCS.
16 MEMBER WALLIS: So the initial thing is 17 just to heat up of the refractory by the melt. Is 18 that what's going on?
19 MR. THEOFANOUS: Yes. We are making these 20 pipes to be large enough so that when they open they 21 will flood this pretty quickly. So you don't want to 22 really have the water starting earlier than before.
23 MEMBER SIEBER: A quick question. Maybe 24 you could, if you melted the entire core and some 25 surrounding structures --
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231 1 MR. THEOFANOUS: Yes.
2 MEMBER SIEBER: What level of melt would 3 you get in that sump?
4 MR. THEOFANOUS: The next slide.
5 MEMBER SIEBER: Well, I'm looking at the 6 slides.
7 MR. THEOFANOUS: Maybe the next to that.
8 MEMBER WALLIS: The next after the table.
9 MR. THEOFANOUS: It would be better to 10 show you in numbers rather than give you --
11 MEMBER SIEBER: Well --
12 MR. THEOFANOUS: Just for example either 13 you can wait or you don't hardly wait. So we're going 14 to come to the next one. What is this here is BiMAC 15 as a fraction of melt pool height resulting in average 16 heat flux. That's the question you just asked.
17 Correct?
18 MEMBER SIEBER: Yes.
19 MR. THEOFANOUS: Okay. So here now we 20 have a table that says here is the height of the melt 21 and this is in meters 0.2, 0.4, 0.6, 0.8, all in 22 meters. That's the volume now of the melt. We are 23 converting that volume with the typical density of two 24 tons and then you can see therefore that a typical 25 whole pool with floating melt in it would be about 300 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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232 1 tons. So what you see here is that you have such an 2 amount of melt in the BiMAC, it would be somewhere 3 between 0.8 and one meter of height the melt would be 4 in there.
5 MEMBER SIEBER: And where does that place 6 it on the side wall? Does it get to the side wall or 7 go back to --
8 MR. THEOFANOUS: That would be all the 9 space that would be inside of that --
10 MEMBER SIEBER: Up to where the point is?
11 MEMBER WALLIS: Where is a meter on that 12 map?
13 MR. THEOFANOUS: All the way, it would be 14 essentially I think up to about here.
15 MEMBER SIEBER: Okay.
16 MR. THEOFANOUS: Now an important point to 17 make here is that remember we're in a low pressure 18 scenario. That means the melt that comes out first 19 would be the melt that is molten at the time and 20 suddenly you would not wait until 100 percent of the 21 melt melts before it fails. It will come out some 22 time before. It will be a fraction of this 300 points 23 that it comes out. So that one is going to come out 24 as one lump in a way.
25 MEMBER SIEBER: Right.
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233 1 MR. THEOFANOUS: Any material that comes 2 after out is going to be coming out at the rate in 3 which is melting which is going to be dribbling down.
4 MEMBER SIEBER: Yes, a dribble. But it 5 could start that way too.
6 MR. THEOFANOUS: It could also.
7 MEMBER SIEBER: Also you'll lose the 8 control drive of mechanism penetration and you'll 9 dribble out and then all of a sudden the bottom will 10 come out and you'll dump a load and then from then on 11 it's dribbling out.
12 MR. THEOFANOUS: Exactly. So then as far 13 as heat fluxes the important thing to remember is that 14 not all material comes together as a melt. So that 15 comes out and you have this and you fill up to some 16 time. Now additional material that is dribbling is 17 going to see a water pool, a cold water pool, and it's 18 going to solidify and it's going to solidify there and 19 it's going to make debris then which however is a 20 fraction of this 300 tons which will not participate 21 in the energy balance of the melt that is loading the 22 BiMAC to the bottom because the BiMAC can be loaded 23 downwards only by the melt, not by the debris that is 24 cooled.
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234 1 may not cooled the debris bed.
2 MR. THEOFANOUS: If it is not cool that's 3 all right. But you know my own -- the significant 4 fraction of it is going to be somewhere and it's going 5 to be coolable because there's no reason for it to 6 remelt because it is all cool from the bottom anyway.
7 So it's not really into a dry quicker but it's a wet 8 quicker if you like.
9 MEMBER SIEBER: The part that comes out as 10 a lump --
11 MR. THEOFANOUS: No. We said it can be a 12 pool.
13 MEMBER SIEBER: A pool. It's going to be 14 still molten while this other stuff is solidified.
15 MR. THEOFANOUS: That's right.
16 MEMBER SIEBER: And it's going to be very 17 difficult to remove heat from this molten pool in my 18 view compared to what it would be. The stuff that 19 dribbles and drips down, that's pretty easy.
20 MR. THEOFANOUS: Well, exactly. That's 21 why you're putting BiMAC there because if it was easy 22 to remove the heat, then we wouldn't need to put the 23 BiMAC.
24 MEMBER SIEBER: Even with BiMAC --
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235 1 tell me in a minute how you're going to fail the 2 BiMAC. That's where we're going through in the 3 analysis.
4 MEMBER SIEBER: Right.
5 MR. THEOFANOUS: You could always 6 legislate of course that it will fail, but I think the 7 idea here is to --
8 MEMBER WALLIS: After a while what happens 9 this GDCS pool keeps pouring water into this thing?
10 MR. THEOFANOUS: That's what's going to 11 happen, the emptying is going to stop and then you 12 have natural convection.
13 MEMBER WALLIS: But then you have no 14 cooling underneath.
15 MR. THEOFANOUS: No cooling where?
16 MEMBER WALLIS: No flow in the pipes 17 anymore.
18 MR. THEOFANOUS: Natural convection 19 because in the pipes --
20 MEMBER SIEBER: They don't crush the 21 pipes.
22 MR. THEOFANOUS: -- are in the water pool.
23 So the water would be coming through the pipes.
24 MEMBER WALLIS: Oh, so it keeps on running 25 itself.
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236 1 MR. THEOFANOUS: Of course. If it didn't 2 cool down, it wouldn't do any good.
3 MEMBER WALLIS: Well, I was just wondering 4 about that.
5 MR. THEOFANOUS: Of course. Okay. So we 6 have then the torus here and then taking the --
7 MEMBER WALLIS: Doesn't entrain stop when 8 it goes and recycles around? Is it pure water that 9 goes around? Is there junk in the water?
10 MEMBER SIEBER: There will be sooner or 11 later.
12 MR. THEOFANOUS: This is natural 13 convection. It's not forced pumping.
14 MEMBER WALLIS: No.
15 MR. THEOFANOUS: -- sump there is suction.
16 MEMBER WALLIS: The water is on the pool 17 sitting onto of the molten core.
18 MR. THEOFANOUS: Yes.
19 MEMBER WALLIS: And there's nothing going 20 on that is putting stuff into the water. It always 21 seems to be so placid just sitting there being cooled.
22 MR. THEOFANOUS: Yeah. Then we have --
23 these areas --
24 MEMBER WALLIS: And you call it cert city.
25 A cert city is not very placid, is it?
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237 1 MR. THEOFANOUS: Who?
2 MEMBER WALLIS: This Icelandic lava pool 3 that goes into sea. Isn't that cert city? You called 4 one of your --
5 MR. THEOFANOUS: That's very placid.
6 MR. WACHOWIAK: That was an experiment.
7 MR. THEOFANOUS: Let's look at the steam 8 explosion for a while. That is all but placid. So we 9 take the areas and from the material that's there and 10 from the decay power and the decay power can either be 11 tacked to the material at the time we essentially have 12 all the core, but in respect to the total and then it 13 doesn't change anymore. So you see here the decay 14 power increases because the material increases and in 15 here it reached already all the core, all the fuel.
16 So there is no more than whatever decay here is and 17 this decay heat is taking some conservative value 18 appropriate to the timing of these things, typically 19 a few hours and now you have removed about 35 or 36 of 20 the most megawatts. We take that then and we say how 21 was it removed. It was removed downwards, upwards, 22 and sideways.
23 What are the fluxes for doing that or the 24 other? The fluxes are as you see here for the upward 25 they go 45 to 100 to 205 to 271. So those are the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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238 1 upward fluxes. The downward fluxes 15, 43, 74, 100 2 and up, about almost 100. Side flux in this case did 3 not even have any side. It was only on the conical 4 part. After that, 300, 320, 350. So those are 5 average fluxes.
6 Please keep those in mind because now what 7 I want to do is take these other fluxes and then we'll 8 going to apply to them a peaking factor so we can also 9 find what the local fluxes will be. Now we've done 10 this job with the concrete fluid dynamics basically 11 calculating natural convection and this is actually a 12 very accurate simulation. Those are based on what's 13 called Lusardi simulation. That means they account 14 for all the random movements --
15 MEMBER WALLIS: Excuse me. This is in the 16 core again?
17 MR. THEOFANOUS: That's the core. That's 18 the melt. The situation is holding and the important 19 things are that in this high value we get tubal mixing 20 in the main part of the pool. We have stable 21 stratification at the very bottom and you have 22 descending cool layers along the walls because the 23 walls are cool. You have the BiMAC there, remember?
24 So this is cool. So it does that.
25 The important thing to remember is that in NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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239 1 all those problems we have a constant temperature 2 bundle condition because all these things are 3 surrounded by crusts because it is cooled here, here 4 and everywhere. So just crusts. So it's an actual 5 thermal bundle condition. That's why they put another 6 calculation. That's what you find. This is the 7 velocity distribution. It's again tubal over here and 8 it is a nice sliding layer over here.
9 Now to point out since I have the picture 10 up there, when I have the near-edge channels with the 11 vertical pipes over here, I'm going to have, remember 12 those channels are also shorter in the incline and 13 along that way and what this does is it creates a 14 whole layer on the vertical side that floats along and 15 impinges right in that corner where the incline 16 begins. That can locally load and you want to know 17 about that. They can locally load higher heat flux 18 because of that impingement in natural convection.
19 That's all natural convection and then it surrounds it 20 just like that. So that's what it's stating over 21 here. That can be quite significant. It can be three 22 times the other heat flux locally and you get that 23 only near the edge channels. You don't get that in 24 the other channels.
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240 1 of all the results and basically we're having a number 2 of scenarios which are defined in terms of what you 3 want of the BiMAC, near the edge, near the center, 4 different -- we find a number of things.
5 MEMBER WALLIS: What's in the --
6 MR. THEOFANOUS: I'm sorry.
7 MEMBER WALLIS: The corium contains the 8 control rods and everything like that?
9 MR. THEOFANOUS: Yes, everything.
10 MEMBER WALLIS: And it all stays in there.
11 There is none of it which is evaporates or anything 12 like that. It all stays in there?
13 MR. THEOFANOUS: Only volatile --
14 MEMBER WALLIS: Homogeneously distributed.
15 MR. THEOFANOUS: Only volatile fission 16 products will vaporize from this side of the vessel.
17 MEMBER WALLIS: Right. They are slowly --
18 MR. THEOFANOUS: So what we find here is 19 that the up to down, what's important, those are the 20 fluxes, up, down and on the sides and of course, 21 there's no vertical for the near-edge samples because 22 you see there is no vertical segment. The core, it's 23 applicable because there's a vertical segment.
24 Those are average fluxes and then we take 25 here the ratio of q up to q down and you find that in NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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241 1 the -- oh, the important thing is ABC and MNO those 2 are 2D simulations. Two D is much cheaper to do 3 because basically you're assuming that there is no 4 movement in the direction normal to the slides that 5 you are calculating. In a way what that does is it 6 restricts the turbulence. It restricts natural 7 convection, it can only rotate this way, but it cannot 8 go over that way and that has a restricting effect on 9 turbulence.
10 So as a result of that, the q up to q down 11 is about two in a 3D simulation which is one of those 12 cases C and M basically repeating Case C but in 3D and 13 repeating M in 3D, this ratio is more than three, 3.4, 14 3.5. And in Chapter 21, there is one calculation of 15 each. This is taken from Chapter 21. Since that 16 time, essentially we had nothing else to do. So we 17 had a lot of time to calculate in between. So we've 18 done lots of those 3D calculations since that time 19 which are very laborious and very computer intensive 20 because now you end up with millions of notes 21 especially on fine grid.
22 MEMBER DENNING: And those are DNS.
23 MR. THEOFANOUS: Those are DNS, yeah.
24 Large simulations so you solve in all directions. But 25 any way, we confirmed these values of about 3.4, 3.5 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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242 1 and we're going to probably make an addendum for that 2 but we're going to publish these results in the 3 literature. So in that publication, we're going to 4 add these results.
5 MEMBER DENNING: Going back to the NES.
6 MR. THEOFANOUS: NES.
7 MEMBER DENNING: So this is NES.
8 MR. THEOFANOUS: Yes.
9 MEMBER WALLIS: Is the Agency going to 10 accept a design which is only verified by CFD?
11 MR. THEOFANOUS: I think that is for you 12 to decide.
13 MEMBER WALLIS: Not me. I was just 14 wondering about the Agency.
15 MR. THEOFANOUS: Well, first we have to 16 explain to them what CFD is to the Agency and then 17 they have to decide if they are going to accept it or 18 not.
19 That's why I give you a few more results 20 here so you can get a handle on what we mean by CFD.
21 What's possible to do at CFD?
22 MEMBER WALLIS: So how confident? What's 23 the probability that you're right?
24 MR. THEOFANOUS: I'm going to explain to 25 you.
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243 1 MEMBER WALLIS: The CFD. How do you 2 assess that?
3 MR. THEOFANOUS: I'm going to explain what 4 CFD is.
5 MEMBER WALLIS: I understand what CFD is.
6 MR. THEOFANOUS: Let me explain to you 7 what CFD is and then I'll tell you how confident I am.
8 MEMBER WALLIS: CFD isn't very good for 9 natural convection, is it? The turbulence model.
10 It's just any simulation.
11 MR. THEOFANOUS: This is --
12 (Several speaking at once.)
13 MR. THEOFANOUS: In fact, we are not going 14 in this area. If you want to talk more, we can talk 15 more. You tried to do with a certain model for 16 example. A CFD will total the results. If you do 17 Lusardi simulation, you get wonderful results. Some 18 of that is in the report.
19 MEMBER WALLIS: Wonderful, full of wonder?
20 MR. THEOFANOUS: No, full of wonderful 21 results. Now I knew you were going to be a little 22 skeptical about it so I picked that one.
23 MEMBER WALLIS: Okay.
24 MR. THEOFANOUS: You might like that. So 25 one question one might ask, exactly, how good CFD is.
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244 1 So we are for example of course prepared because of 2 our experiment that we did, the appropriate experiment 3 that we did for the industrial retention for 4 Westinghouse, those are half scale experiments, so 5 half scale natural convection experiments.
6 We have interpreted that with the CFD. We 7 adjusted the parameters. We have interpreted smaller 8 experiments with other people before us, new 9 experiments, but this one is a big experiment and it's 10 part of the typical hydro-dynamics.
11 Somebody might ask and we did ask 12 ourselves a more fundamental question. How can we 13 actually predict the stability? When you start 14 something going off, you are going to develop a 15 pattern of rolls of fluid that rises and falls and 16 some very interesting things happen there and we 17 happened to observe them quite coincidentally because 18 we had an experiment that we used for this, for this 19 one.
20 But we have an experiment that we'll call 21 it the "better experiment" in which we were interested 22 all done up and was interested to know what makes 23 burnout in nuclear boil. We can go into that if you'd 24 like but it's essentially one about burnout. It's a 25 previous -- but we'll come to that by the way in a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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245 1 moment because we care about burnout with BiMAC.
2 So it's interesting to know what makes 3 burnout and people will tell this all is a super idea 4 and there is interference with the water coming down 5 and the steam going up and it's none of that, nothing 6 of the sort actually. It has nothing to do with the 7 burnout. So we had that experiment which we were 8 doing for NASA.
9 MEMBER WALLIS: It may have been improved 10 by the NRC.
11 MR. THEOFANOUS: Yes. They're still 12 around. So we have here this better experiment which 13 was developed for NASA and what this is a 100 micron 14 thickness glass which has on the top of it about 100 15 nanometers of titanium very good deposited. So it's 16 very, very smooth and it is very almost optimistically 17 smooth. But there are thin, but eventually these are 18 thin. It serves as an instantaneous temperature 19 locally over that whole surface if you can observe it 20 with a infrared high speed camera and that's what we 21 have here. So you have 100 nanometer and this is two 22 by four centimeters, 20 by 40 millimeters.
23 And we can now see fluxes that are three 24 times equal to it in here even with an anoscopically 25 smooth surface. That's another story. But then when NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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246 1 you started off and observe you get some interesting 2 patterns forming. Ah, maybe let's see if maybe we can 3 predict those patterns.
4 So this experiment was underway. We have 5 laying on the top of this nano-film. Then we have 6 here a glass mirror, a gold mirror, which are to see 7 that whole area with a high speed infrared camera 8 which heightens in high speed. So we run into 9 thousands of frames per second and the resolution is 10 really at some microns. So it's really a very 11 accurate measurement and each pixel will tell us the 12 temperature instantaneously there.
13 So then this is the moon is very beautiful 14 but again, I didn't tell the space to do it again. So 15 it shows you here the experiment, the development of 16 this runny -- this cellular structure, how it's 17 starts. This is tremendable time and this is what the 18 CFD will give us color coded. So to me, that's really 19 remarkable to catch that. With the velocity and the 20 stability and the development of the cellular 21 structure, you can do very well.
22 Now I'm going into more mundane things 23 then. The central samples were decided from the table 24 that a bounding downward flash on the horizontal is 25 100 kilowatt per square meter. By the way, I point NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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247 1 out that in these slides this is wrong because the 2 computer played a weird game on me when I was pasting 3 it and this line by mistake was pasted up here. So 4 just put an arrow that shows it on the --
5 So for the central samples we have 100 and 6 we have applying to local peaking which by the way I 7 didn't point out the amounts of local peaking in the 8 previous. Here is the peaking over here. This is the 9 old 1.25 because you apply to the 100 and get the 125.
10 Here is the peaking on the incline and here is the 11 peaking on the vertical. So applying those peaking 12 factors there give us near-edge samples 100 and 300, 13 that's the factor of three, and the radial channels 14 it's is 320, 450 and that's --
15 MEMBER WALLIS: What's the BTUs per hour 16 per square foot?
17 MR. THEOFANOUS: What?
18 MEMBER WALLIS: What is that in BTUs per 19 hour2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br /> per square foot?
20 MR. THEOFANOUS: Okay. Let me see. If 21 you could tell me how much is square foot --
22 MEMBER WALLIS: Is it 300,000 or something 23 like that?
24 MR. THEOFANOUS: Okay. So if it's 300,000 25 then this would be one-third of that. So it would NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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248 1 100,000. I'm just rescaling because everybody knows 2 that --
3 MEMBER WALLIS: And I know it's completely 4 wrong.
5 MR. THEOFANOUS: All of those could be 6 wrong. It's very convenient because it's thousands.
7 So now we are running into another interesting topic 8 and that is how much thermal loading will those pipes 9 take. At this time I address that question was for 10 universal intention and people were asking me. Some 11 very skeptical people were saying the bottom of that 12 lower head and very, very bottom is so flushed that in 13 theory you should take zero critical heat flux. But 14 of course, you don't because even however so slight 15 the inclination that we have actually creates lenses 16 and those lenses of water they escape and periodically 17 this happens and as the boiling occurs there, you have 18 a micro-layer forming on the surface and as long as 19 the lenses escape and the flattening of the water 20 happens, we think the time interval is that is less 21 than what it takes to dry that micro-layer, you're 22 fine.
23 And we demonstrated that this is so by 24 experiment which this was later incarnation of that 25 experiment and the very first experiment. Don't have NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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249 1 the picture because it's not a nice clear picture. It 2 was a computer data based, but what it is is basically 3 a slight incline just like models the very bottom of 4 a reactor vessel but in a channel geometry. That's 5 where it's actually relevant to the BiMAC and we have 6 pipes and we filled it up to some point and we let it 7 go in natural convection and we heated it from the top 8 and what you find is those lenses form and escape, and 9 then we've got critical heat fluxes in the very, very 10 bottom of the pool of over 300 kilowatts per square 11 meter.
12 We went to this channel here because for 13 the standard it was interesting to see if we could get 14 more not for the bottom. Nobody cares for the 15 bottom. It's for the sides because for PWRs you get 16 this focusing effect and we put a channel so that 17 natural convection hopefully would create a smooth 18 current and we decreased the critical heat flux here 19 and indeed it increases it. So here we have the 20 channel geometry of whirlpool configuration of four 21 and this was done for Westinghouse.
22 Here I showed you the real facilities and 23 it's pretty large. So it was full scale flash of the 24 lower head and it goes into a riser and in the back 25 here, there is a downcomer and there is a condensation NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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250 1 time. So you get boiling here with the heat boiling 2 from the top. The width by the way of this, the width 3 of this box which creates the heat is 15 centimeters.
4 So the heat is going downwards, boils. The two-phase 5 flow goes to the riser and we see all kinds of 6 interesting instability phenomenon that occurs like 7 geysering and stuff like that's important for other 8 things for boiling water reactors.
9 And then up here, the steam condenses in 10 the coil and then we have the downcomer. So it goes 11 like that. So in a full, when we say running in full 12 natural simulation mode, we're running it so that the 13 water is enough to create a continuous flow. But we 14 have also been running in a pool of boiling water 15 which the water is so low here that it doesn't close 16 the loop. So that's what it is.
17 And here we have, this is a 300 power 18 diesel generator with 400 kilowatts power coming in 19 and this is controlling the power surge so that we 20 could have any power surge we want and so all this 21 good stuff. And here, this guy is a big guy. So it 22 gives you the idea of the size of this.
23 All right. So Configuration 1 was the one 24 that was natural convection. It was only the very 25 bottom part with a very slight inclination that I was NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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251 1 describing before. And this is the critical heat flux 2 expressed as a function of the angle is like that.
3 The characteristic dimensions of that channel was very 4 similar to BiMAC with about 14 or 15 centimeters by 10 5 centimeters, something like that about 10 centimeters.
6 Then the Configuration 4 also in the pool 7 volume. That means putting the power over the whole 8 thing in Configuration 4. You see 90 degrees you get 9 about a megawatt which magically, Graham, that's your 10 magic number even though it's vertical and then all 11 those points are what we did for Configuration 4. So 12 for us, that will give you an idea.
13 For the incline part of our BiMAC, we are 14 about here. So we would expect about 400 kilowatts 15 per square meter for the vertical part. For the 16 vertical pipe we would expect about a megawatt as 17 limits. So that is represented over here. Critical 18 heat flux. This is for the incline section. This is 19 for the vertical section. So this plot is made of two 20 parts. One part is the incline and the other part is 21 the vertical and over here is the heat flux and the 22 black is near central channels. So near central 23 channels with high goes to a maximum but a very small 24 maximum and not strong. That was more near the edge 25 of the channels and then it falls off. Then for the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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252 1 near edge channels, the blue, that it goes to that 2 local peaking that I was describing before. That's 3 because of the descending layer.
4 MEMBER WALLIS: Now heat flux is defined 5 based on the flattened area or the --
6 MR. THEOFANOUS: Based on the flat area.
7 MEMBER WALLIS: Or the two -- the flat.
8 MR. THEOFANOUS: The flat area, yes. An 9 equivalent flat area and then over here, what you see 10 is the thermal loading on the vertical wall.
11 MEMBER WALLIS: So an equivalent flat 12 area, don't you mean the actual flat area? You don't 13 know --
14 MR. THEOFANOUS: Well, the calculation, in 15 the calculation you don't make the boundary like that 16 in a calculation of getting from a wall.
17 MEMBER WALLIS: You use the superficial 18 area.
19 MR. THEOFANOUS: Yes. And to put that in 20 terms of the margins are defined in this way and we 21 find margins of course but this is a departure from 22 one in this ratio. So you find the minimun and even 23 that is about 60 percent margin and also near the top 24 of that. Actually, when we run these experiments, we 25 find that this for the BiMAC you find out that this NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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253 1 flux here near the end of the incline is going to be 2 much higher I believe because also you have natural 3 convection there. Remember this one also based on 4 full boiling and also I think the other part on the 5 vertical side. So that's what that is.
6 And so at this point, this is the vertical 7 transposition of thermal loading to alpha G. Critical 8 heat flux is alpha G. Thermal loading is what comes 9 out from the peaking of natural convection. Where the 10 trouble is that you have 60 percent margin to failure.
11 This needs to be remembered to put in context and 12 that's really tough of being extremely conservative 13 on the thermal loading and reasonably conservative for 14 the critical heat flux. So in a way, again there's no 15 intersection between load and fragility and we see the 16 failure of this thing is physically unreasonable.
17 So for someone then again going back to 18 the question that Jack was asking for the survival of 19 that, that's how we decide those things. We find the 20 loading. You find what is day-to-day failure, compare 21 the two and say okay, you'll fail with that. This is 22 pending of course information because I'll be the 23 first one to say that for -- and that is quite 24 different from the CRD question that Graham asked 25 before.
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254 1 When you actually want to make use of 2 something of that is of an empirical nature which is 3 the critical heat flux is empirical, what you make 4 sure is, let me finish, you want to make sure that 5 your experiment is really representative of the real 6 condition.
7 MEMBER WALLIS: Now, Theo --
8 MR. THEOFANOUS: So therefore I would say 9 that BiMAC as far as critical heat flux is concerned 10 needs to be confirmed with real experiments and we can 11 go into that. Yes.
12 MEMBER WALLIS: This is my stuff. But you 13 have this corium and sitting on this layer which I 14 thought you said was sacrificial.
15 MR. THEOFANOUS: Yes.
16 MEMBER WALLIS: When it's gone, don't the 17 pipes seal the corium?
18 MR. THEOFANOUS: Of course.
19 MEMBER WALLIS: Corium interacts with 20 steel.
21 MR. THEOFANOUS: Yes. Before --
22 MEMBER WALLIS: Does corium eat the pipe?
23 MR. THEOFANOUS: No.
24 MEMBER WALLIS: Why not?
25 MR. THEOFANOUS: For the same reason, it NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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255 1 doesn't hit the pipe --
2 MEMBER WALLIS: There are all kinds of 3 Utechics and stuff.
4 MR. THEOFANOUS: The same reason that it 5 doesn't do that for the --
6 MEMBER WALLIS: So it's cold.
7 MR. THEOFANOUS: No, for the same reason 8 it doesn't do it for --
9 MEMBER WALLIS: Does it crust the --
10 MR. THEOFANOUS: Because it crusted it.
11 Right.
12 MEMBER WALLIS: Okay.
13 MR. THEOFANOUS: Because now corium cannot 14 exist at temperatures of --
15 MEMBER WALLIS: So the crust protects the 16 pipes, although the sacrificial layer is gone.
17 MR. THEOFANOUS: Yes. Basically what 18 happens is that it's a self-adjusting situation. If 19 the thermal conduction resistance is more than what 20 the thermal loading is, there is going to be a little 21 bit more until now it's just as much as the thermal 22 loading to the cooling. But it will never eat more 23 than that.
24 I show just for engineering purposes, I 25 emphasize that because in CFD when you know what NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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256 1 you're doing, you actually are making predictions 2 based on basic physics and we talked about that. For 3 that one if you check your calculation and make sure 4 that all the physics are presented, then you're fine.
5 You don't need ULPU experimentation. Even then we 6 have a lot of comparisons as I mentioned before, but 7 this one is totally empirically based. I claim that 8 we cannot really predict critical heat flux yet 9 correctly even on a horizontal pool boiling facing 10 upwards. So I certainly don't want to tell that you 11 can predict it facing downwards or inclined.
12 So that's why I went through very special 13 pains here actually to show you that on the basis of 14 principles this BiMAC is a good concept and that is 15 principal evaluations. It just so turns out that we 16 were lucky in that we had channel data for ULPU that 17 are quite applicable to both dimensions as well as 18 orientation of interest here. So that gave us a very 19 good idea of what we can expect when we do full scale 20 experiments to BiMAC which in fact you can do full 21 scale. We can actually make full scale without any 22 big deal and we plan to do this.
23 All right. That is all for the critical 24 heat flux. But we're not finished yet because we said 25 we also want to make sure that there is enough water NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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257 1 depletion so that near the end of the channels I end 2 up with a 70 percent void fraction and 70 percent void 3 fraction, I don't know where the liquid is. Most 4 likely liquid is on the bottom but not at the top and 5 I want to make sure they have liquid everywhere to 6 keep the wetting the walls because that's underlined, 7 this rewetting of the walls, to actually very 8 interesting because nuclear boiling in fact is a 9 misnomer here and as it is, even in nuclear boiling in 10 misnomer even on the flood plate faces upwards.
11 The reason it is a misnomer is by the time 12 you go to near critical heat flux levels actually the 13 whole surface is covered by vapor film and all the 14 cooling is happening with the micro-layer that is 15 hidden underneath that film. So the only difference 16 between a plate facing upwards and the plate facing 17 downwards is in the renewal process of that film maybe 18 thinning and thickening again. What you don't want to 19 do is you don't want to have that film go to zero even 20 for a short time because that's going to be burnout, 21 although for vessel retention for vessels as well as 22 for BiMAC when you have significant wall thickness 23 there is enough thermal inertia and the fluxes are low 24 enough so that even if you dried out temporarily 25 you're not going to go to very high temperatures and NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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258 1 before the temperatures get to the first point you're 2 going to still be able to rewet and recover the film.
3 Okay. So that's -- and we're going to go 4 to that and we're perplexed about that because what do 5 you use it for getting the natural convection and 6 incline in the pipe like that. There is no literature 7 for measure. So I remember that many years ago when 8 I was doing the retention and we were doing the ULPU 9 the French decided to sort of a similar experiment, 10 but they wanted to go more fundamental and they did 11 the SULTAN facility more fundament than us.
12 We tried to mock up the reactor because I 13 believe that the right way of doing critical heat flux 14 at least at this time is by mocking up the real 15 situation. The French thought they could build a 16 straight channel that is facing downwards, so 15 17 centimeters just like whirlpool, four meters long, 18 facing downwards. They put it on the platform so they 19 could orient it from vertical to near horizontal and 20 they thought they supplied forced flow through that 21 and they figured that -- they measured pressure drop 22 and they measures critical heat flux. So the idea was 23 that take fundamental data presumably which then can 24 be used in some codes whatever to predict critical 25 heat flux and of course this never happened.
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259 1 So at the end of this experiment as far as 2 contributing to data for the critical heat fluxes, 3 they contributed zero because at the end then they 4 started using my data from whirlpool. However it did 5 contribute us now because I remember that they 6 measured pressure drop and I said now I can see if I 7 can calculate correctly pressure drops on incline 8 channels of the size of kilometers and there is no 9 other data anywhere to find on that, so sort of 10 sitting there getting resolved.
11 So we have this nice set of data, very 12 appropriate distances like four meters. We were 13 interested in about four meters or five meters. The 14 dimensions there 10 degree inclination was included in 15 the data. The characteristic length was 15 16 centimeters. They also got 15 centimeters. The 17 channel length four meters. The pressures were all 18 the way from one atmosphere to I think five or ten 19 atmospheres. I forget now. Power levels accounted to 20 kilowatt per square meter. They get detail pressure 21 drop data and again here from the top.
22 So we took this and we made a boiling 23 model which was basically an equilibrium model in 24 equilibrium boiling using LOCA Martinelli for the 25 pressure drop modified by as far as the void fraction NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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260 1 modified by something that is a function of the 2 inclination and this came out from an obscure paper 3 that nobody knows about. It was published in Thermal 4 Engineering or something in Russia back in the `70s or 5 `60s which they actually did exactly that thing. They 6 took LOCA Martinelli and they found how they want to 7 correct LOCA Martinelli for orientations other than 8 horizontal and by using that, we got actually very 9 nice interpretation of the shorter experiments. So by 10 having this kind of basis, I can say that we are 11 calculating correctly pressure drops through the 12 channels under all kinds of fluxes that will fall even 13 well beyond fluxes I'm interested in.
14 Having said that, now all I need to do 15 simply check and find what is the gravity imbalance I 16 get in those channels match it against my pressure 17 drop and then I get my natural convection. Simple as 18 that. So now having that, I get this. Here is the 19 heat for different heat flux levels. They must 20 formulate natural convection of course increases as 21 you increase the flux, reaches a maximum and the 22 gradually decreases and that's because of two phase 23 friction up here.
24 So remember the point of interest for us 25 is from here to here, somewhere inside here and the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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261 1 flow in this situation is very stable. The flow is 2 such that it's actually self exhausting because any 3 increase of void fraction the net change in gravity 4 here is more than the change of friction in the range 5 of interest and that is the definition of having a 6 stable flow.
7 The next question, the more interesting 8 question, is what is the void fraction. As I said, I 9 didn't want to see here at this kind of flux, I didn't 10 want to see 70 percent void fraction there and 11 fortunately I don't. I see, like in the upper limit, 12 I see 40 percent void fracture. So in the most I'm 13 going to be in some kind of a slight -- because I knew 14 anyway which means bubbles are forming, they are going 15 fast and then very high frequencies of wetting and 16 rewetting in the sense of the micro-layer. So that's 17 the story for this.
18 So BiMAC then, so besides the point I made 19 already which says that the BiMAC needs to be verified 20 by experiments and what I visualize here is full scale 21 experiments. That means the full dimension, full 22 pipe, full length, vertical downcomer with real power, 23 power shape, whatever I want to do that so I can 24 define the local critical heat flux, No. 1. No. 2, 25 also I want to run experiments which are going to be NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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262 1 subscale, maybe half scale or quarter scale, in which 2 I have many pipes, many pipes, which are maybe loaded 3 differently. So I want to see the actions between the 4 channels between the pipes and whether that can have 5 any -- I cannot conceive of any detrimental effect of 6 that, but it's good to really have that and it's not 7 a big deal to get that.
8 So in addition to those conditions, we say 9 that BiMAC needs to be at least RTNSS and that implies 10 a qualification of function in its design state and 11 this is shown now in terms of principle in 12 development. So this is really the experiments we're 13 talking about in the COL and then in addition the 14 identification of continuing ability to function as 15 design throughout the operating life and that means 16 this will require simply testing of this orientation 17 of control which goes back to the probability of 18 actuating this, measuring and actuating.
19 MEMBER WALLIS: So it just sits there 20 after an accident for the next ten years or something 21 so percolating away?
22 MR. THEOFANOUS: I'm sorry?
23 MEMBER WALLIS: After the accident, it 24 just sits there and it percolates away for the next --
25 forever.
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263 1 MR. THEOFANOUS: Well, no because you --
2 MEMBER WALLIS: Until you get a solid lump 3 and it closes up.
4 MR. THEOFANOUS: Yes, because decay heat 5 slowly goes away. Yes.
6 MEMBER WALLIS: But there is quite a long 7 time this thing has to sit there and function.
8 MR. THEOFANOUS: Well, you don't have much 9 choice, do you? You have it inside the vessel, inside 10 the lower head.
11 MEMBER WALLIS: It has to be somewhere.
12 MR. THEOFANOUS: Inside the lower head.
13 It's going to be sitting there the same length of 14 time. But it is better to have it sitting somewhere 15 percolating rather than going through the concrete I 16 think.
17 MEMBER KRESS: And it's eventually 18 solidified in the radiation.
19 MR. THEOFANOUS: Yes. Sure. Like I say, 20 I expect that in reality there is so much water there 21 I believe that BiMAC actually will not really be 22 needed. But you want to make sure that you say that's 23 a boundary that just cannot be penetrated. That's the 24 intent of the BiMAC. It can be demonstrated to be 25 true.
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264 1 MEMBER KRESS: When you did your CFD 2 calculations, the heat flux, did you assume a uniform 3 mixture of the core and the metal and --
4 MR. THEOFANOUS: Yeah.
5 MEMBER DENNING: Now is that a good 6 assumption? Can there be separation of --
7 MR. THEOFANOUS: You can get separation, 8 but really not very much at all to anything. If 9 anything, the separation was actually pursued by some 10 people. I believe not rightly so after our work for 11 the Agency standard but for the purpose of finding you 12 get more heat going upwards than downwards. So for 13 upward heat flux we get separation they go more 14 upwards.
15 MEMBER WALLIS: So you're --
16 MR. THEOFANOUS: I worry about downwards.
17 MEMBER WALLIS: So your water after awhile 18 gets saturated with cesium iodide and stuff like that.
19 MR. THEOFANOUS: There's a lot of water 20 there.
21 MEMBER WALLIS: Presumably it does.
22 MR. THEOFANOUS: There's a huge amount of 23 water.
24 MEMBER DENNING: When you said saturated, 25 did you mean literally saturated?
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265 1 MEMBER WALLIS: I mean just --
2 MEMBER DENNING: Or means gets a lot it 3 in.
4 MEMBER WALLIS: Gets a lot of it in. I 5 don't know what saturated means. Eventually, 6 presumably dissolving fission products get in the 7 water and it keeps go round and round.
8 MEMBER DENNING: Sure.
9 MEMBER WALLIS: So then you get chemistry 10 going on and stuff. There's a lot of term analysis to 11 be done of what it is that you have there that's 12 cooling this debris. It's not pure water.
13 MR. THEOFANOUS: There's a huge amount of 14 water. Huge amount.
15 MEMBER WALLIS: That's a qualitative 16 statement.
17 MR. THEOFANOUS: I can tell you exactly 18 how much it is.
19 MEMBER WALLIS: No, but I know. I'm 20 saying that there has to be some analysis of what's in 21 the water after a period of time.
22 MR. THEOFANOUS: That would be a good 23 question to ask --
24 MEMBER WALLIS: Huge or not.
25 MR. THEOFANOUS: Then we can --
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266 1 MEMBER WALLIS: The fouling of your tubes, 2 your tubes foul after awhile.
3 MR. THEOFANOUS: That's an --
4 MEMBER WALLIS: Foul after awhile.
5 MEMBER DENNING: Well, is there debris of 6 some sort in character?
7 MEMBER WALLIS: Through the precipitation 8 or something.
9 MEMBER DENNING: Precipitating out of 10 boiling boundary.
11 MEMBER WALLIS: Right.
12 MR. THEOFANOUS: Actually the fouling 13 improves critical heat flux interesting enough as you 14 know.
15 (Several speaking at once.)
16 MR. THEOFANOUS: Right. In fact real 17 cores that's going to be fouled and they might have a 18 higher margin so you can up the power. All right. So 19 pulling it all together now and that leads us to the 20 end, we have three conclusions or three concluding 21 slides. Conclusion 1 is for the low pressure 22 scenarios and here is a containment phenomena event 23 three, a CPET and what is shown is the major decision 24 points one has to make in order to decide at the end 25 this position of those scenarios. So we have here NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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267 1 that's okay.
2 We have low pressure core melt and water 3 level. We ask the first question. What's the water 4 level in the pedestal because that makes an impact on 5 steam explosion potential failure. So we have three 6 levels defined, already explained the rationale for 7 them and it turns out that this is by far the much 8 more likely. This is like one percent of the cases.
9 This is much less than even one percent because that 10 situation simply we have no other one or we have lots 11 of water. What you have in between is not very 12 likely.
13 Then we follow this branch and already we 14 said that if we take this branch here, the pedestal 15 damage cannot be excluded. And the question then that 16 we next ask is is the pedestal intact? Okay. We say 17 no. Then the next is are we supplying the BiMAC with 18 water? Are the flooding the lower drywell? And of 19 course, in this case, it's already flooded. So it's 20 yes and then debris successfully cooled and again we 21 need to ask that question that related to BiMAC 22 function and as we demonstrated here on the basis of 23 principles, the BiMAC function would be good and it 24 will be coolable but you put a start to indicate that 25 failure or rather the nonfailure BiMAC function needs NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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268 1 to be confirmed experimentally.
2 So here then we have however a containment 3 failure already because we basically destroyed the 4 pedestal. If we are able to destroy the pedestal we 5 destroyed the BiMAC for sure and therefore that means 6 in all those cases you assume containment failure.
7 MEMBER WALLIS: The pedestal supports 8 something, doesn't it?
9 MR. THEOFANOUS: Yes, of course, that's 10 why it's called a pedestal.
11 MEMBER WALLIS: I know. So what happens 12 when it fails?
13 MR. THEOFANOUS: Well, I don't think very 14 much actually except failing the containment because 15 this thing as you very well find out is to get a 16 failure of the pedestal by steam explosion. If you 17 fail, you fail locally. You will not jeopardize the 18 structural integrity of the pedestal function.
19 However we cannot count on containment at that point.
20 That's why this is known as assumed containment 21 failure. That's one percent of the accidents.
22 For all the other cases, we have no damage 23 here. Don't even ask the question. No damage and 24 then here yes, again with very high probability based 25 on requirements we have for these two control and NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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269 1 actuation systems. And then here again, pending 2 verification, the BiMAC function correct. So we have 3 for here physically unreasonable in all these cases.
4 For those two cases, we're saying that we are 5 transferring to CSETs, containment system event trees, 6 because now even though everything is fine here, we 7 need to know what happens after five days. Is the 8 PCCS pool replaced with water? What does it take to 9 not have containment heat anymore at that point? So 10 all these systems affect in the next presentation. So 11 that's what that means. This takes us to that.
12 And this one is the high pressure CPET.
13 The first question of course is is the reactor cooling 14 bundle intact and already I showed you that natural 15 convection is very likely for this reactor as with all 16 reactors because with the high pressure vessel 17 convection of the steam. However we didn't want to 18 come to that on that basis. So we used that in what 19 we're calling our jargon. In Rome we call it splinter 20 scenario. That means since you don't, we can't 21 guarantee that that's what is going to happen, we're 22 going to assume that either that or that happens. So 23 that means we take that as if it was to be the case 24 which means it doesn't fail and that's why this is 25 written in the way that's the ES branch.
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270 1 And then the DCH containment failure no 2 damage we demonstrated. It won't fail. This is 3 physically unreasonable and we demonstrated this 4 branch with the physically unreasonable. Then we have 5 the flooding and the function. So again if it's all 6 yes, yes, yes, it goes to CSET.
7 So the conclusion three is a summary of 8 containment threats and mitigative mechanisms on the 9 systems, all the systems in place. So here is like a 10 capturing of them together for the three threats that 11 we addressed and this is the failure marker. Already 12 we covered that.
13 And here is pretty more crisply what is it 14 that we are putting in place to deal with that. So for 15 example for the DCH we have pressure suppression 16 vents. That's the principal mechanism and we have 17 reinforced confidence support. That allows us to use 18 the high fragility and the events allows to have a 19 limit on how much can be pressurized.
20 Then on the liner thermal failure is the 21 liner anchoring system. On the lower drywell is also 22 the separation by the lips as I mentioned before. On 23 the explosions the pedestal liner failure here again 24 is the dimensions of the wall and the enforcement what 25 holds it together. The BiMAC failure is the pipe the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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271 1 size of the thickness. So it is structurally very 2 robust and backed up by a lot of concrete.
3 Then on the BMP, BiMAC activation 4 functions essentially actuation is through rotation 5 but it would be specifically designed to very high 6 standards of reliability and the diverse and I would 7 like to see passive valve action so to make sure all 8 those scenarios we can flood the lower drywell.
9 Local burnout, natural circulation and the 10 inclination of the pipes, that's what it takes. Next 11 the case for BiMAC, water depletion again, that's 12 natural circulation and inclination and low boil 13 fractions and actually lower heat fluxes also. As we 14 have seen in the local melt-through is the refractory.
15 And I think I have a bunch of back-up slides in case 16 you want to ask me more questions about CFD.
17 CHAIRMAN APOSTOLAKIS: Any questions from 18 the members.
19 MEMBER SHACK: If you don't credit the 20 BiMAC, is the melt spreading and heat flux you get for 21 this comparable to the ABWR?
22 MR. THEOFANOUS: Yes. In fact, more.
23 MEMBER SHACK: More.
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272 1 could have taken the approach to say EPRI criteria and 2 just like ABWR and then just argue that we can take a 3 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or more to eat through the concrete. That 4 was again sort of the traditional approach, but it's 5 not good. I think maybe we should make sure these 6 reactors are having something that we are sure that 7 this will not penetrate.
8 MEMBER WALLIS: Well, it's a very 9 impressive story. I'm just wondering what you have to 10 do to convince the very skeptical agency, the very 11 conservative regulatory body, that they can accept 12 this with a lot of confidence.
13 MR. THEOFANOUS: I think that what we need 14 to do is that we need to for sure make BiMAC 15 experiment which as I said before we can do it full 16 scale. That's why it's convenient.
17 MEMBER WALLIS: But you're going to 18 simulate that corium heating electrically. We're not 19 going to have real corium --
20 MR. THEOFANOUS: Of course.
21 MEMBER WALLIS: So there are always going 22 to be questions about --
23 MR. THEOFANOUS: I'm sorry. I'm sorry, 24 Graham. A kilowatt is a kilowatt and a meter is a 25 meter. Now if you want to be conservative so you can NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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273 1 begin to realize the units of thermal power then I 2 throw my hands up.
3 MEMBER WALLIS: I'm not saying what I 4 want. I'm just asking questions. That's all.
5 MR. THEOFANOUS: I wish it was about 6 safety rules in that category.
7 CHAIRMAN APOSTOLAKIS: Any other 8 questions? Okay. Thank you very much. Let's take a 9 few minutes because we have another hour and a half, 10 guys. Ten minutes. Off the record.
11 (Whereupon, the foregoing matter went off 12 the record at 4:01 p.m. and went back on the record at 13 4:15 p.m.)
14 CHAIRMAN APOSTOLAKIS: On the record.
15 Okay. Next subject is Containment Systems.
16 MR. WACHOWIAK: Containment systems. So 17 this is the continuation on now from the CPET into the 18 CSET. It think there is quickly two things, at least 19 one thing I want to answer from before. I think the 20 question came up peripherally and I'm not sure it was 21 answered, how did we decide which things went, which 22 sequences went, into the high, medium and low water 23 level categories. Basically, what we did was we 24 looked at the scenarios that got us to core damage.
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274 1 fact, but especially the low pressure scenarios that 2 got the core damage.
3 If it was something that was putting steam 4 into the containment and we were condensing steam on 5 the walls and it was condensate from off the walls 6 just getting down into the lower drywell, then we 7 showed that we're only going to get a few centimeters 8 of water down in the buyback. So we called all of 9 those low. If there was a break in like a drain line 10 or a large break in the reactor called liquid type 11 breaks, if it was a large break down low, not a steam 12 break, but a liquid break, enough liquid from those 13 breaks put a lot of water down in there and it got 14 above that value.
15 Now we did look at some other things where 16 some of the breaks were kind of in between and it 17 depended on whether or not you had any injection 18 systems working or not like if it was just a break and 19 the water came out, it would be in the medium 20 category. But if a CRD pump was running, it would 21 have moved it up to the high category, so maybe not 22 quite enough to cover the core, but enough to add a 23 little bit of water. And so it was kind of in between 24 and there were some of those things in the medium 25 category.
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275 1 In the end when we went back and we looked 2 at all the different scenarios that we had to try to 3 see where things fell, like in our Section 7, 4 everything in the top set of cut sets that we 5 described, nothing fell into the medium category. It 6 was either high or low.
7 In this last round when we did the 8 quantification for the containment system event tree 9 we took another look at that with all the sequences 10 that were above the truncation value and there might 11 be one or two sequences that are at the 10-13 level 12 that could fall into there. So what we did was for 13 the purpose of the analysis, we just took some from 14 the low water level and we just put it into the medium 15 level. So the low level came out to be like 0.991 and 16 we made it 0.99 and we put .001 in the medium category 17 just to cover those scenarios that might be just 18 beyond our truncation limit. So that's how we 19 assigned all of those by looking at what specific 20 scenarios got us to the severe accident.
21 Just to be clear on it, the high pressure 22 sequences, we didn't see anything in the high pressure 23 sequences that would have fallen into a medium or high 24 water level category. Those were all low and in the 25 ATWS sequences once again, those all looked like they NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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276 1 were low water level. There were a couple right at 2 the truncation limit that may fall into some of the 3 other categories.
4 MEMBER DENNING: I think that in some 5 scenarios you carefully limit the amount of water 6 addition to prevent overflow into the cavity. Is that 7 true? Isn't that true?
8 MR. WACHOWIAK: What we did -- Let me 9 answer it this way. We altered the design so that the 10 design itself will limit the amount of water flow into 11 the cavity. When you get the steam environment in the 12 drywell, the steam as we'll see in a minute there goes 13 into the PCCS, condenses and then goes into the GDCS 14 pool. What we've done is we've designed the GDCS pool 15 so that if it overflows, the overflow water goes into 16 the suppression pool. It doesn't go into the drywell.
17 Things that condense on the wall though 18 will still run down the wall and go down into the 19 water drywall. We've also added to our emergency 20 procedure guidelines instructions that say don't spray 21 the containment unless you are either absolutely 22 positively sure that you're not going to lose core 23 cooling or you know that the core is on the floor. So 24 those are our emergency procedure guidelines because 25 that would be the other way is operator doing NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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277 1 something that would --
2 Okay. And I can't think of the other 3 question right now that I heard on the periphery that 4 we may not have answered, but we'll see when we get 5 through these.
6 I'm going to talk now about the 7 containment systems. We looked at for the last couple 8 of hours, we looked at the basemat melt penetration, 9 EVE, DCH and the robust design that we have for those 10 scenarios. What we haven't necessarily looked at here 11 are the containment bypass and containment 12 overpressurization and the systems that are involved 13 in addressing these particular things.
14 So let's start out with the simple one, 15 the containment bypass. How can you get a containment 16 bypass? You have big penetration that's open to the 17 containment at the time that you have the severe 18 accident. So we went through our list of penetrations 19 that are in the design. They are all listed in the 20 Chapter 6 of the DCD and we did an evaluation. They 21 are all either normally closed during operation, 22 connected to a close system inside the containment, 23 connected to a close system outside the containment or 24 have already been addressed in our break outside the 25 containment evaluation in the Level 1 analysis.
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278 1 Our conclusion is then that we really 2 don't have a credible bypass scenario here. There are 3 a couple caveats on that. No. 1 is there's a bunch of 4 little penetrations that haven't made it in the 5 detailed design phase that we talked about in the 6 third column here this morning. We don't really know 7 what those would be. We're pretty sure how they would 8 come out, but we just don't know yet.
9 Then also some of these that are connected 10 to some of these other systems may be periodically 11 operated during the operation of the plant a very 12 small fraction of the time. But there is a chance 13 that they'd be there. So we retained in our 14 containment system event tree structure the 15 possibility of having the containment bypass from one 16 of the penetrations being open. And the way we 17 addressed that was we looked at what is the likelihood 18 that we're going to have a severe accident where the 19 control systems for these isolation valves would not 20 be available and that's how we kind of assigned the 21 value there.
22 Containment isolation valves tend to be 23 failsafe. They fail closed when they lose power.
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279 1 factor there.
2 MEMBER SIEBER: Did you make any 3 assumptions about vents and drains?
4 MR. WACHOWIAK: Vents and drains are in 5 the detailed design phase that we don't have that 6 information and support.
7 MEMBER SIEBER: I mean they are usually 8 pretty small. On the other hand, it's an opportunity 9 to have a bypass.
10 MR. WACHOWIAK: Pretty small. Now we know 11 what we did in the ABWR analysis for the total of 12 containment bypass, but we really needed to know the 13 detailed information on those small penetrations to 14 figure the aggregate of all those. That will be done 15 again just like that in a later phase. But once 16 again, we did retain this here trying to make sure 17 that we capture the phenomena.
18 Now overpressure protection, our function 19 for overpressure protection is provided by the passive 20 containment cooling system and it can also be provided 21 by the fuel and aux pool cooling system and then 22 finally, if there's a, if we get into a really bad 23 situation now, we could go and do a controlled manual 24 event of the containment through the suppression pool 25 to the elevated release point.
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280 1 Just like at Level 1 like we talked 2 before, we have a passive function backed up by an 3 active function backed up by a redundant active 4 function. So the robust nature of how we deal with 5 the containment overpressurization. Let's talk about 6 some of the individual pieces of this.
7 The PCCS operation during a severe 8 accident. In the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, there is nothing 9 that has to happen. It's completely passive. As a 10 matter of fact, we have some analysis that shows it's 11 significantly longer than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. It gets out 12 toward a two-day period, but the design spec now has 13 to be for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. There's enough water there. So 14 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in, nothing has to happen.
15 Steam in the drywells condensed return to 16 the drywell. It's a closed system. Now in the 17 scenarios where we're looking at this in the severe 18 accident scenario, remember from the containment 19 phenomena of entries, we've already passed through the 20 question did the deluge line to the BiMAC work. Did 21 those lines open? So even though the PCCS goes back 22 to the, sorry, the GDCS pools, those lines are open 23 from the GDCS pools to get it back down to the BiMAC 24 again. So it is a closed system here.
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281 1 that has already been addressed in our quantification 2 of looking at the lower branches where the deluge 3 lines have failed. For the CSET, we always have those 4 lines open.
5 The aerosols that are generated and get up 6 through the water, that's an interesting question 7 about what's ultimately retained in that pool of water 8 there, but what we've seen is that they're carried up 9 with the steam, condense in the PCCS and the aerosols 10 are actually not deposited inside the PCCS heat 11 exchangers themselves. It's carried with the 12 condensate back down into the mixture of water that's 13 back in the containment.
14 The only real issue that we have here is 15 how much non-condensable gets up into and held up into 16 the PCCS. If we do have non-condensables there, it 17 reduces the effectiveness of the system. There is a 18 vent line that's provided and in a couple minutes 19 here, I'm not sure exactly where the slide is, but 20 we'll explain exactly how that works. It does have 21 this. It requires our vacuum breakers, suppression 22 pool to drywell vacuum breakers, to remain seeded in 23 order to make the thing work.
24 So the situation here is on the drywell 25 side the steam gets into the heat exchanger. The pool NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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282 1 outside boils. The condensate comes down through 2 these lines here and comes back to the GDCS.
3 MEMBER WALLIS: There must be some kind of 4 way of separating the condensate from the non-5 condensables which has not been very clear in this 6 picture.
7 MR. WACHOWIAK: Yes, it's difficult to see 8 in this picture. I agree with you, but these are 9 really a pipe within a pipe kind of arrangement to 10 minimize penetrations. I think that's how it was 11 described to me. The condensate comes from the bottom 12 of these.
13 MEMBER WALLIS: So the non-condensable 14 line goes up inside the other pipe. There's a 15 different --
16 MR. WACHOWIAK: And the non-condensable 17 vent line goes up inside so that it's at the top of 18 these end bell tanks so that the condensate -- And 19 because this system condenses faster or at the same 20 rate or faster than it's being supplied, I'm sorry.
21 It condenses at the same rate it is being supplied and 22 the drain goes out faster than it's being supplied.
23 In order for this to work, the drains have to be open 24 just like you're taking a shower. All the water goes 25 down into the drain there. It's coming out of the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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283 1 showerhead and going down in the bottom. A similar 2 sort of thing, it's condensing in here and falling out 3 through the bottom and so this tank here is mostly 4 empty. The top of the tank has non-condensables and 5 steam mixture there.
6 This is piped directly into the 7 suppression pool and it shows a sparger here, but it 8 could be an open pipe. It really doesn't matter.
9 All that really matters is that the submergence of 10 this pipe is less than the submergence of these 11 events. Then you always have a differential pressure 12 between the drywell or the inside of these valves is 13 the same as the drywell and then the drywell pressure 14 is higher than -- I'm sorry. The differential 15 pressure between the end of this pipe and in here, 16 that column of water, is going to be the difference 17 between --
18 MEMBER WALLIS: Where is the level in the 19 vent pipe reaching and where is the level in the --
20 MR. WACHOWIAK: The level is in the vent 21 pipe is always going to be the same as the level --
22 MEMBER WALLIS: The same as inside.
23 MR. WACHOWIAK: Yes. A small difference.
24 MEMBER DENNING: No wait a second.
25 MEMBER WALLIS: No, it's not.
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284 1 MEMBER DENNING: No, but when you have 2 pressure in the drywell, then it's going to drive it 3 down to the submergence and that's where you get your 4 head to drive.
5 MR. WACHOWIAK: Oh, that was your 6 question.
7 MEMBER DENNING: Yes.
8 MEMBER WALLIS: Yes. It's down there.
9 MR. WACHOWIAK: Water in the vent will be, 10 in the vertical vents, will be here.
11 MEMBER WALLIS: But it will be driven down 12 eventually to the vent, won't they?
13 MR. WACHOWIAK: No, because the flow tap 14 is through the PCCS into here. So it equalizes out 15 around here.
16 Now it does fluctuate some going in and 17 out. What the TRACG analysis kind of shows is that 18 this will tend to burp if you will as it builds up 19 some non-condensables. The heat transfer is a little 20 bit less effective. The pressure goes up. It drives 21 the water column down and pushed the non-condensables 22 out and they kind of equalize out there. So this is 23 one of these what again is one of these self-limiting 24 processes such that the only heat that it can remove 25 is how much steam is going into it.
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285 1 So in the end, we end up with a constant 2 pressure that stays at that constant pressure 3 essentially forever. The only way that the pressure 4 in the containment goes down is due to heat transfer 5 through the side walls and outside that way. But no 6 excess heat is transferred out from the PCCS.
7 MEMBER WALLIS: Well, conceivably, the 8 pressure could get to be less in the drywell than it 9 is in the wetwell.
10 MR. WACHOWIAK: If that happens for some 11 reason --
12 MEMBER WALLIS: Can you open the vent 13 valve?
14 MR. WACHOWIAK: There's a vacuum breaker 15 here. Now this is from two separate drawings, but 16 it's meant to show that here's the suppression pool 17 here. Air space of the suppression pool, we have this 18 device here that's a vacuum breaker and there is three 19 of them.
20 MEMBER WALLIS: You send some non-21 condensables back out again.
22 MR. WACHOWIAK: You can send some non-23 condensables back out again and the whole process 24 recycles or it doesn't. It's one of these things that 25 you just can't tell for sure whether they're going to NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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286 1 open and reclose or not. The way that this is 2 designed is it's really like a garbage can lid.
3 MEMBER WALLIS: But it has to close to 4 make the sparger work, doesn't it?
5 MR. WACHOWIAK: It has to be reclosed to 6 make the sparger work. The way that it's designed 7 though is that there's really no way, it's not like 8 the vacuum breakers on MARK 1 that are kind of like a 9 hanging check valve. It's a positive direct action 10 seating by gravity of this. It's a total vertical and 11 it's arranged such that the failure mode is very 12 unlikely for reseeding that vacuum breaker. However, 13 this seeding surface is instrumented and if for some 14 reason it's detected that it hasn't seeded right, 15 there's a butterfly valve that is inside this thing 16 here that can switch positions and isolate that vacuum 17 breaker so that if it's leaking enough it's isolated 18 on its own. If the containment pressure starts to go 19 up again an indication of something gone wrong 20 possibly with these, we would have procedures that 21 would tell the operators to cycle through and try to 22 close those to see if that's the problem. So we do 23 have a way of isolating the failed backing breaker.
24 MEMBER SIEBER: You built the prototype to 25 test this, right?
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287 1 MR. WACHOWIAK: I believe so. We did.
2 MEMBER SIEBER: I've seen pictures of it.
3 MEMBER WALLIS: Stay in the suppression 4 pool. Above the suppression pool.
5 MEMBER ARMIJO: Are there a number of 6 those?
7 MEMBER DENNING: It actually cools down.
8 MR. WACHOWIAK: Three vacuum breakers, six 9 PCCS heat exchangers.
10 MEMBER WALLIS: So all that gas is to go 11 in there.
12 MR. WACHOWIAK: So that is an integral 13 part of the containment system. We consider these a 14 passive type component. Gravity is holding them in 15 place. It's a positive indication that it's the way 16 that it's supposed to be. I kind of went through this 17 and it can be isolated.
18 Let's look at the PCCS itself. There's 19 really no way of failing this thing in the first 24 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />. It's open. It provides the heat transfer.
21 The physical arrangement is what makes it work. So 22 outside of the vacuum breakers there's really not much 23 in the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> that can happen here.
24 However after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, somewhere before 25 72, we need to have more water added in. There is --
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288 1 MEMBER WALLIS: Now wait a minute. There 2 is no way for it to fail? Presumably there is some 3 debris which can be carried around with the steam and 4 get into this thing and block up the non-condensable 5 lines for instance.
6 MEMBER SIEBER: Twenty-four hours.
7 MEMBER WALLIS: Lock up the condensate 8 drain with some debris which flies around and can get 9 up there.
10 MR. WACHOWIAK: I think debris was 11 addressed in the testing of the PCCS.
12 MEMBER WALLIS: Only fine debris would 13 probably block up that condensate line, wouldn't it?
14 MEMBER SIEBER: That line is a pretty big 15 line, right?
16 MR. WACHOWIAK: Yeah.
17 CHAIRMAN APOSTOLAKIS: A big pipe.
18 MEMBER WALLIS: But you said it's 19 unreasonable to consider. Am I doing something 20 unreasonable?
21 MEMBER SIEBER: Again.
22 MEMBER WALLIS: Taboo?
23 MR. WACHOWIAK: I guess maybe I choose my 24 words improperly there. Maybe not unreasonable to 25 consider but --
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289 1 MEMBER WALLIS: If there were flying 2 debris you could in fact conceivably block something 3 that is essential to the operation of the PCCS.
4 MEMBER SIEBER: It could.
5 MR. WACHOWIAK: Like I said, the aerosols 6 were looked at in the test program for the PCCS and 7 that wasn't determined to be a failure.
8 MEMBER WALLIS: It would have to be 9 particulates of some sort.
10 MEMBER MAYNARD: I think you created a 11 challenge with that statement there.
12 MEMBER SIEBER: They were called HU, 13 highly unlikely.
14 MEMBER DENNING: What about molten --
15 MEMBER WALLIS: Are they all reasonable?
16 MEMBER SIEBER: Yes, right.
17 MEMBER DENNING: What about molten 18 material during the high pressure? No, that's later.
19 MEMBER WALLIS: Well, it's latent debris.
20 Someone just left something around the containment.
21 MR. WACHOWIAK: We have looked at debris 22 like that, insulation and things like that, and I 23 believe in the design there is a guard there to keep 24 flying material in the LOCA situation like insulation 25 and other things that would be expected during a NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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290 1 blowdown that could affect that. So that's been 2 addressed. It's the particulate fission products that 3 I believe we'll find the answer to that in the test 4 report for the PCCS.
5 We do have an automatic way considered.
6 It's considered in our analysis. We do have an 7 automatic makeup. The pool reactor for that refueling 8 cavity in the laydown area that's for the steam dryer 9 and separator for refueling purposes, that's all 10 filled with water. Somewhere after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> before 72 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br />, those valves will open up pretty much based on 12 level in the PCCS ICS pools providing enough water for 13 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> worth of operation. Beyond that, we still 14 have a connection to the firewater system that could 15 add water there. FAPCS can add water. We could even 16 make a connection to a hose station outside the 17 reactor building and have a fire truck put more water 18 in there.
19 MEMBER SHACK: So considered in this case 20 means possible.
21 MR. WACHOWIAK: Its automatic makeup.
22 When I said considered here, I really mean what did we 23 put in the fault trees when we did this analysis. So 24 we put this in. We really didn't put that in.
25 MEMBER WALLIS: You didn't put what in?
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291 1 MEMBER DENNING: PCCS.
2 MR. WACHOWIAK: Spontaneous failure of the 3 PCCS.
4 CHAIRMAN APOSTOLAKIS: Is there manual 5 action in the venting?
6 MR. WACHOWIAK: It's in there.
7 CHAIRMAN APOSTOLAKIS: And you said that 8 it was because -- when you do sensitivity analysis?
9 MR. WACHOWIAK: In Revision 0 of the PRA 10 we did not do that. In Revision 1 that we're 11 finishing up part of that chapter as we speak now, 12 that's one of the considerations that we're doing in 13 there. We recognized that we missed that in --
14 CHAIRMAN APOSTOLAKIS: So which one do we 15 have, Rick?
16 MR. WACHOWIAK: You have Rev 0. We did 17 not give you Rev 1 of Chapter 11.
18 CHAIRMAN APOSTOLAKIS: Okay.
19 MEMBER DENNING: How do we test the system 20 and how frequently is it tested and how do you test it 21 to make sure that it would operate, you know, that 22 there isn't something that's happened during normal 23 operation that it's led to corrosion?
24 MR. WACHOWIAK: During the outages, these 25 are part of the inspection program.
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292 1 MEMBER DENNING: They are inspected, but 2 there's no testing possible. Is that true? Or how do 3 you -- You can't test them for function.
4 MR. WACHOWIAK: No. At least not the 5 installed ones.
6 MEMBER SIEBER: Sort of an inactive 7 passive system.
8 MEMBER DENNING: This requires heat 9 condensed to make it really work.
10 MR. WACHOWIAK: That's correct.
11 MEMBER WALLIS: Well presumably if there's 12 any moisture in the drywell in normal operations and 13 it would very slowly set this thing off.
14 MR. WACHOWIAK: Well, not really because 15 there's an active drywell cooling system that provides 16 much more steam condensation effect than this would be 17 subject to. So you wouldn't see it there either.
18 So when we go through the analysis, we 19 find that the PCCS failure including the vacuum 20 breaker portion of that is unlikely in 99 percent of 21 the core damage sequences.
22 MEMBER WALLIS: What does unlikely mean?
23 Is that 10-5 or something?
24 MR. WACHOWIAK: In 99 percent.
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293 1 mean anything to me.
2 CHAIRMAN APOSTOLAKIS: No, in 99 percent 3 it's extremely unlikely.
4 MR. WACHOWIAK: I've done the reverse on 5 this one. It's not going to fail in 99 percent of the 6 cases.
7 MEMBER WALLIS: So essentially it's zero.
8 You mean it's essentially zero.
9 MR. WACHOWIAK: There's a 0.1 failure rate 10 or 99 percent reliability.
11 CHAIRMAN APOSTOLAKIS: No, no. It's not 12 the same thing. In 99 percent of the sequences it's 13 extremely unlikely. That's what that means.
14 MEMBER DENNING: That's what that means, 15 but is that what he means?
16 CHAIRMAN APOSTOLAKIS: Is that what you 17 mean? One percent is not extremely unlikely. That's 18 not -- You cannot mean that.
19 MR. WACHOWIAK: Let me get to my next 20 slide if it is what I think it is. It's this picture 21 here and I'll explain what I meant by that because 22 the statement was accurate and I think we're all 23 probably saying the same thing. So let's make sure we 24 get to there. The way we quantified this containment 25 system of entry, remember we're coming in after NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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294 1 asking the deluge line and all the rest of those 2 things. For each of the different accident subclasses 3 that we would have that would affect things like vapor 4 suppression function, this includes FAPCS also in case 5 there is an issue there.
6 Things that would affect these, what the 7 conditional failure probabilities of these headings 8 would be, we made different accident subclasses and we 9 take all the cut sets upon the sequences and add to 10 those different accident subclasses and append these 11 functions and calculate what the subclass specific 12 split fraction would be for each of these functions.
13 So in 99 percent of our core damage sequences, these 14 numbers are like 10-6, 10-4, 10-8.
15 CHAIRMAN APOSTOLAKIS: That's interesting.
16 MEMBER WALLIS: That's what you're saying.
17 MR. WACHOWIAK: Yes, in one percent of the 18 sequences this note here is about 0.7. 0.6, 0.7.
19 MR. WACHOWIAK: So that's extremely likely 20 then.
21 MR. WACHOWIAK: And that's why I said in 22 99 percent of the sequences it's extremely unlikely.
23 In one percent of the sequences, we're probably going 24 to get to a containment event. So what we would say 25 there is that the reliability to overpressure NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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295 1 protection is about 99 percent.
2 CHAIRMAN APOSTOLAKIS: And tomorrow you 3 will talk to us about the seismic effects.
4 MR. WACHOWIAK: Very briefly, yes.
5 CHAIRMAN APOSTOLAKIS: But these numbers 6 don't change when you consider earthquake.
7 MR. WACHOWIAK: What we did for seismic 8 was a seismic margins analysis and we only considered 9 the safety related systems. So what we were attempting 10 to prove with that is that all of our safety related 11 functions would remain operable up to I think it was 12 two times SSE or 2.4 times SSE, something to that. So 13 we really didn't get into what the degraded 14 reliability of these systems would be in a seismic 15 event. So if that was your question, we didn't do 16 that in the analysis. I wasn't really going to talk 17 a lot about seismic. It's fairly -- It's a simple 18 margin.
19 MEMBER DENNING: In this one percent, what 20 is it that makes them vulnerable? Is there some 21 obvious aspect of that one percent of them that means 22 that you're --
23 MR. WACHOWIAK: They're in high pressure 24 sequences. The reason you would end up having a high 25 pressure sequence is basically because all of your DC NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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296 1 power has failed and amongst other things too, but 2 mainly they all involve no DC power. If you don't 3 have DC power, we're relying on the operator action to 4 provide that extra water to the PCCS. That's why we 5 end up with a very high conditional failure 6 probability there.
7 MEMBER DENNING: We have 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to do 8 it.
9 MR. WACHOWIAK: Once again, we tried to do 10 a screening analysis and we're trying not to overly 11 rely on operator actions, but that tends to be what it 12 is and even the operator action that we have, we're 13 not at the point yet in the design that we're sure 14 that you can do that operator action in all cases with 15 no DC power available because you have to get up into 16 -- To locally operate that valve, you have to be 17 somewhere that may not be a very nice place due to 18 radiation to be to manually operate those valves if 19 you're in that kind of a cinder accident. So we 20 really aren't taking much credit for the manual action 21 when you don't have all your DC power systems.
22 Just to go through it, we solved all these 23 for the different subclasses, some things off on the 24 end, and that's where we come up with our input for 25 the release rates or for the source terms. But in NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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297 1 general, jumping ahead of myself here, for the 2 containment failure probability due to 3 overpressurization, it really comes down to that one 4 percent.
5 Now one of the things that we want to talk 6 about is what happens in the case where you lose the 7 ability for the PCCS to operate. What happens if you 8 lose containment heat removal? Just to get an idea of 9 when the containment is going to be vented or when the 10 containment is going to fail, we hypothetically said 11 let's not have any containment heat removal from time 12 zero. We don't have any scenarios that get us there 13 with any significant probability, but let's just look 14 at what happens if we start there.
15 We're seeing that it's more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> 16 before you get to the point where the operators are 17 going to consider that they would need to vent. Now 18 let's move that into our scenario that we had was a 19 one percent that was on the long term failure of the 20 containment heat removal. That failure is not going 21 to create release here and we think it's more like out 22 here. So you still have another 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after that.
23 So we're talking about a 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> before you really 24 have to vent and that's time that you have to figure 25 out how to get more water up there and do something NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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298 1 else. So it's really a long term scenario in the 2 containment overpressurization. It's not something 3 where we're going to get a failure right away.
4 Now what we did for calculating source 5 terms, we took a much more conservative approach than 6 that and looked at things earlier. The code for 7 calculating the Level 3 doesn't really deal with those 8 long type of scenarios, so we added some of the 9 hypothetical on that side.
10 So here are the results we come up with.
11 Bypass we believe is negligible. Overpressurization 12 within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> is negligible. Overpressure later 13 than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> can occur. Some high pressure sequences 14 once again about one percent. There is mitigation 15 there. It would be a filtered release, but as we 16 agreed up front on this project that we're just going 17 to call those releases.
18 MEMBER DENNING: I'm sorry. Did you say 19 that we're just going to call those releases? You're 20 telling me that you would not take credit for removal 21 of iodine and things like that?
22 MR. WACHOWIAK: When we used it to 23 calculate the source term for the level three.
24 MEMBER DENNING: Yes.
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299 1 through the suppression pool. So we took the reduced 2 source term, but what we're saying what's the 3 reliability of the containment. We added that in to 4 the one where it says we're going to have a release.
5 Not a big one, but --
6 Okay. Any questions on this?
7 CHAIRMAN APOSTOLAKIS: Thank you.
8 MR. WACHOWIAK: Next we're going to have 9 Sid Bhatt talk about the offsite consequences.
10 CHAIRMAN APOSTOLAKIS: You have to do this 11 for design certification?
12 MR. BHATT: We did because I thought we 13 wanted to get an idea of the thought process all the 14 way and see what happens to the final situation and 15 how to --
16 CHAIRMAN APOSTOLAKIS: Do they have to 17 submit a Level 3 PRA?
18 MEMBER DENNING: This isn't the Level 3 19 PRA. It's a consequence analysis.
20 CHAIRMAN APOSTOLAKIS: What is Level 3 21 then?
22 MEMBER DENNING: Well, site specific and 23 things like that.
24 CHAIRMAN APOSTOLAKIS: No, but I'm 25 curious. I don't think it's required.
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300 1 MEMBER WALLIS: Are you going to prevent 2 him from presenting?
3 MEMBER DENNING: But it looks good.
4 MS. CUBBAGE: I'd have to get back to you 5 on that.
6 MEMBER DENNING: But the results are 7 fantastic. That's the point they're going to make. So 8 why not make them?
9 COMM. MEMBER BRADY: You actually are 10 driven from the goal.
11 MS. CUBBAGE: Someone had just mentioned 12 that the severe litigation design alternative review, 13 this factors into that.
14 MR. BHATT: Traditionally, whenever we had 15 once upon a design like ABWR, we used to carry this 16 all the way to the end to see level one, level two and 17 then probably get resuming certain code as you can see 18 and resuming some numbers for the containment 19 phenomenalogy event tree like CPET, what of that, 20 serial accident phenomenon that you want to analyze 21 and then also look into the systems, containment 22 system and suppose they fail, how they all converge 23 and they provide essentially some kind of a key 24 information from the fault tree on the right hand 25 side, some lump end states like bypass, like how to go NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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301 1 through those kind of categories.
2 As you do the fanning process, it's 3 important to kind of figure it out and say where are 4 we are going to go from the offsite consequences for 5 a review for a generic path that we do not have yet a 6 site specific. So this is an attempt. So we created 7 -- I will go through three parts, goals, what kind of 8 process which we have been going through, it's nothing 9 new, what are the results and how does it compare to 10 the goals we tried to look for.
11 So we created three kind of goals which 12 traditionally we have been using. One is the 13 individual risk and again we are looking near the 14 vicinity of the power plant and we used the reference 15 which is given from the National Safety Council 16 essentially defining some kind of a goal --
17 MEMBER KRESS: Is it basically the QHOs?
18 MR. BHATT: Yes. So the second part of 19 this, it is also similar to that.
20 MEMBER KRESS: Who are you going to go to 21 societal leaks? It doesn't fit my -- of society.
22 MR. BHATT: Yes. Understood That's the 23 reason why I cannot put it in any other designation.
24 The to-debt context is comparable.
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302 1 risk.
2 MR. BHATT: And this is an individual 3 risk.
4 CHAIRMAN APOSTOLAKIS: It's called 5 societal risk.
6 (Several speaking at once.)
7 MEMBER KRESS: That's the reason why I 8 quit calling it that.
9 MEMBER WALLIS: When it comes to something 10 like less than one in a million for the societal 11 risks, less than that, isn't it?
12 MR. BHATT: Yes.
13 MEMBER SIEBER: Tom wants it to be --
14 MEMBER WALLIS: Less than 10-6.
15 MEMBER SIEBER: - less than 10-6.
16 (Several speaking at once.)
17 MR. BHATT: And the third one is to create 18 certain sources as you meet certain failures have 19 occurred that's caused the core melt to come out. Now 20 you do have sufficient productivity (PH) scenarios and 21 then if it's released out from the plant in different 22 situations, one way certain things are still there but 23 under technical specification, it allows you to have 24 some kind of a controlled release.
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303 1 show up in the regulations?
2 MR. WACHOWIAK: It shows up in the URD.
3 MEMBER KRESS: Oh, that's a URD provision.
4 We don't have it in the regulations.
5 CHAIRMAN APOSTOLAKIS: What is it that we 6 don't have now?
7 MEMBER KRESS: That third goal.
8 MEMBER SHACK: We just calculated in the 9 Environmental Impact Statement though.
10 MEMBER SIEBER: Yes.
11 MR. WACHOWIAK: Rick Wachowiak from GE.
12 I believe the customers use it in their site --
13 CHAIRMAN APOSTOLAKIS: Yes, but it's not 14 part of the QHO.
15 MR. BHATT: So the whole process is trying 16 to get an idea about what's the variation risk. When 17 you look into it from the point of view of the boxes 18 are intended to kind of get a focus on what the 19 synthesis is all about to kind of get an assessment 20 and kind of gives you a sanity check. The inaccuracy 21 or accuracy of the probabilistic risk assessment 22 numbers will depend upon the upfront like CDF, CSCD, 23 things like that. So they are filtered in.
24 Also you would have to look into what kind 25 of fuel was loaded into the core and for example what NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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304 1 kind of a cycle you are using. If you expose the fuel 2 for a longer time, you have bigger fission inventory, 3 things like that. So that one is calculated by the 4 core entry point of view for ESPWR but at this point 5 in the presentation, you say they are going to running 6 for a 24 month cycle.
7 In terms of the upper lefthand part, we 8 already talked to you about the Level 1 PRA. We are 9 calculating CDF, looking into the cut sets and 10 creating bins, defining what is the containment event 11 3 and the Level 2 type of probabilistic risk number.
12 So all that part provides a certain kind of release 13 frequency for those kind of release categories.
14 Now if you know the release categories, 15 then you say how are we going to calculate the detail 16 fission product release to create a source term and 17 then synthesize source term and release frequencies 18 and using a computer code which has traditionally been 19 used to calculate the consequences.
20 MEMBER KRESS: Is that the EPRI version?
21 MR. BHATT: Yes. So what happens is that 22 curricularly was modified to actually look into the 23 ESPWR essay (PH) features and was benchmarked as the 24 track to have comparisons for the design base 25 accidents so that you can say when the accident NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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305 1 starts, at least the initial point also is okay.
2 There is a separate report which we have provided. I 3 think EPRI provided to NRC. Right? And you have 4 that.
5 So essentially it can also be done by some 6 other code track, mel code, etc. the release 7 fractions. So if you propagate this synthesis process 8 there essentially you do have a source term associated 9 with these different release categories. In this 10 analysis we have 11 of them and for each end state of 11 the CETS for example or the release categories, the 12 radionuclides were lumped into 12 different groups and 13 then we looked into the consequences at the end of the 14 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and at the end of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
15 MEMBER WALLIS: Well, the worst 16 consequences seem to be when the BiMAC system fails.
17 MR. BHATT: Yes.
18 MEMBER WALLIS: And it makes a tremendous 19 difference.
20 MR. BHATT: Yes. Which one is that?
21 MEMBER WALLIS: It makes a tremendous 22 difference whether or not the deluge system in the 23 BiMAC works.
24 MR. BHATT: Which slide are you looking 25 at?
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306 1 MEMBER WALLIS: I'm just reading from my 2 notes from reading the PRA document. I'm not looking 3 at your slides at all. You're talking about release 4 fractions and I said I noticed when I read the PRA 5 document that they depended very much on whether or 6 not the deluge system in the BiMAC worked or not.
7 MR. THEOFANOUS: May I say something?
8 MR. BHATT: Yes, go ahead.
9 MR. THEOFANOUS: Of course it works.
10 MEMBER WALLIS: Yes, of course.
11 MR. THEOFANOUS: That's why you put BiMAC 12 in.
13 MEMBER WALLIS: I know, but I notice how 14 important it is. It's extraordinarily important.
15 MR. WACHOWIAK: This is Rick Wachowiak 16 again. Just remember how we did this calculation.
17 We said if the BiMAC fails, then we will have that 18 release. We did not try to say if the BiMAC fails 19 what's the chance that we're going to have core 20 retention on the floor without the BiMAC. That 21 question wasn't asked and it wasn't answered. So you 22 --
23 MEMBER WALLIS: Bring to the surface.
24 MR. WACHOWIAK: You can't necessarily 25 infer that if BiMAC fails then the release is much NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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307 1 higher.
2 MEMBER WALLIS: Right. I've just looked 3 at the sequence and it says if BiMAC fails or BiMAC 4 doesn't fail. The difference is so when does it 5 matter to any release.
6 MEMBER DENNING: Does the BiMAC failure 7 imply from this assumption that you don't get to 8 scrubbing the suppression pool?
9 MR. WACHOWIAK: I'm not sure how that came 10 out in Revision 0. In Revision 1, it makes it clear 11 which ones with the releases from with the deluge 12 lines are successful so we scrub versus the deluge 13 lines fail. So it's unscrubbed. So there is the 14 distinction that's made. Once again, they are 15 containment failures and the probabilities of those 16 are low enough that they're really not driving this 17 answer. But once again, there is a difference there.
18 MR. BHATT: So Division 1 has the complete 19 story what we have gone through and also of the Level 20 2 which we used this for the OP and bypass scenarios.
21 It also has the CPETS and the CSETS synthesis done and 22 it goes through the end states which are considered 23 here. There are 11 categories and I will go over those 24 quickly here too.
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308 1 come back to the point about the release frequencies.
2 The processes where we again did use for the ALWR URD 3 times. In some cases, we are talking about generic 4 one-part law so we had to use certain databases. So 5 population we used for the Sandia report which was -
6 MEMBER KRESS: The Sandia side, they 7 looked at a lot of sides. Did you chose one of those 8 or what?
9 MR. BHATT: One other thing is the 10 population density which was on a more convoluted 11 side. So here we kind of make things compounded from 12 the point of view of what might go bad and things like 13 that. It may not be realistic. We also for example 14 I assumed there was no evacuation which again is 15 pushing the limit. Then we did say that all this 16 release are going to be happening at the ground level, 17 not at the top level. One of the reasons why is 18 because we are near the vicinity of the harbor. Now in 19 case of a plume was released also as if it had no heat 20 content. This is kind of my field.
21 MEMBER WALLIS: You believe there is 22 caloric theory.
23 MR. BHATT: No, this was --
24 MEMBER DENNING: Based on what your 25 concern was.
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309 1 MR. BHATT: What it says is that, yes, we 2 could push out a number. So basically when a generic 3 calculation like that, we did zero, zero, a million, 4 things like that, just to kind of get an idea.
5 Essentially what it does is that the plume is released 6 at the higher level and with the higher heat content 7 it can propogate further and then you are trying to 8 analyze some goals which are near the vicinity of the 9 font then in that situation so this again is pushing 10 the limit.
11 Then essentially the whole dose at a half 12 of mile is a probably direct sentence (PH). The top 13 line one 10-6 is a kind of a goal.
14 MEMBER KRESS: That's for the atmosphere.
15 MR. BHATT: That is a goal which we have 16 and the plots, there are two plots on this one, the 72 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. Essentially they are theoretical 18 scale. The calculation numbers kind of has significant 19 margin.
20 MEMBER KRESS: Before you leave, the .25 21 sieverts, is that the 50 percent lethal dose?
22 MR. BHATT: No.
23 MEMBER DENNING: Oh, no. That's 25 rem 24 and this gets barely up to the point of health 25 effects.
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310 1 MEMBER SIEBER: It's the first level of 2 detectability. So back on cell change.
3 MEMBER DENNING: Nobody's going to --
4 (Several speaking at once.)
5 MR. BHATT: This again are the 6 requirements I am saying there.
7 MEMBER DENNING: Before you get off of 8 that, I think the place that goes into the coordinate 9 there, that's the core damage frequency of the 10 component. Recognize that because what we're basically 11 looking at are things that are down to 1/30th of the 12 core damage frequency. That's kind of where we're 13 going here.
14 MR. BHATT: Yes.
15 (Several speaking at once.)
16 MEMBER KRESS: This is the SC curves that 17 we're talking about.
18 MEMBER WALLIS: This is cumulative 19 probability consequence.
20 MEMBER KRESS: Yes.
21 MR. BHATT: In terms of how, if you look 22 at the bottom list, probably to what decimal numbers, 23 but you throw out a basis and say this is what it is 24 and then you try to compare them. Then the comparison 25 says that this is the goal which we set for the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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311 1 example for the variation dose which is 10-6 and the 24 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> period case, the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> case. We do meet the 3 goal but politically we say you can say yes. In terms 4 of decimal number, I think it's kind of not that 5 significant because we really do not know with that 6 decimal number.
7 MEMBER SIEBER: Does that include iodine?
8 MR. BHATT: Yes. The 12 groups.
9 MEMBER SIEBER: Right.
10 MEMBER WALLIS: These are individuals 11 risks. So even if there are a million people affected 12 you would still in some cases --
13 MR. BHATT: So for the site specific --
14 MEMBER WALLIS: It's a cycle. You have a 15 million people. Multiplied by a million, you still 16 need more. So it's pretty close to a million people.
17 MEMBER SIEBER: It's an accumulated dose 18 as opposed to a health impact.
19 CHAIRMAN APOSTOLAKIS: The number of 20 people is a pattern because it's expressed in terms of 21 the individual.
22 MEMBER WALLIS: Yes, that is individual.
23 (Several speaking at once.)
24 MEMBER WALLIS: Even if it is that you 25 modify by a hundred thousand, you would still be NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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312 1 within the goal.
2 MEMBER DENNING: The nice thing is you 3 don't kill anybody.
4 MEMBER SIEBER: You never get the levels 5 at that distance that are sufficient to cause cellular 6 change. Now it's below the so-called emergency dose 7 that radiation workers are allowed to get.
8 MEMBER WALLIS: So you can put this in the 9 middle of a city?
10 MEMBER SIEBER: Not my city.
11 MR. BHATT: It's not impossible.
12 (Several speaking at once.)
13 MR. BHATT: Now when you see the site 14 specific application in the PRA where you would see a 15 certain case like there could be in Washington, D.C.
16 or New York City and there is a plant and what kind of 17 the detail whatever, at that time probably this thing 18 should be revisited. For example, one of our customers 19 is already doing that. In those situations, we would 20 probably get the more realistic.
21 CHAIRMAN APOSTOLAKIS: So how is it? Did 22 you do any uncertainty analysis here? What are we 23 talking about?
24 MR. BHATT: Uncertainty analysis --
25 CHAIRMAN APOSTOLAKIS: You did it for the NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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313 1 core damage.
2 MEMBER SIEBER: It's just a number.
3 MR. BHATT: This is just a number. For 4 the core damage frequency, the numbers would be from 5 one PRA and --
6 MEMBER WALLIS: So what's the number --
7 CHAIRMAN APOSTOLAKIS: There are no 8 uncertainties after that.
9 MEMBER DENNING: Max.
10 MR. BHATT: We have propagated the 11 uncertainty. You are right. We have --
-11 12 CHAIRMAN APOSTOLAKIS: So this 3.7 10 ,
13 how high could it be?
14 MR. WACHOWIAK: This is Rick Wachowiak 15 with GE. Let me try to answer that in the best way we 16 can because No. 1 we did not try to propagate any 17 uncertainty. So the Level 1 input is point estimate.
18 But if you remember how we did the Level 2, we looked 19 at bounding parameters to get us to the different 20 release bins. We think we're on the upper edge for 21 calculating the frequency, translating the Level 1 22 frequency into the release bin frequencies.
23 Then when we took the representative 24 source term, we really looked at what would be the 25 upper limit source. I don't want to say bounding NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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314 1 because if we have two cases, one was 10-10 and one was 2 10-13, we tended to look at the 10 -13 case. But we 3 intended to use more bounding values to get the actual 4 source terms. We put them in here and then max'ed 5 those as Monte Carlo stuff for all the rest of the 6 things.
7 So did we specifically do an uncertainty 8 analysis? The answer is no. What uncertainty 9 analysis would be applicable to this? It tends to be 10 more on the Level 1 feeding into the Level 2 that 11 would get us there and then we'll use bounding beyond 12 that. So it's an interesting question. I'm not sure 13 that if we think about the Level 1 uncertainty of 14 knowing one order of magnitude at higher infrequencies 15 and propagating that to here that it would really 16 change much of the answer.
17 MEMBER MAYNARD: Well, you probably had 18 most of the uncertainties there covered by the 19 conservatism that you get built into the parameter 20 analysis like the assumption that you allow your 21 container to contain things that you don't have.
22 MR. WACHOWIAK: That would be -- in fact, 23 you could probably make --
24 MEMBER MAYNARD: Or significantly delayed.
25 MR. WACHOWIAK: So it's a mixture.
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315 1 MR. BHATT: So essentially this whole 2 story with tremendously surprising results bartered 3 across the -- missed frequencies where coming low and 4 then as you add this to reach down the slow sterns 5 helps. But that's partly the purpose of setting some 6 goals for the Level 1 PRA and Level 2 PRA and trying 7 to come out. So essentially this shows tha PRA tests 8 help.
9 (Several speaking at once.)
10 CHAIRMAN APOSTOLAKIS: Is this it?
11 MR. BHATT: I think so.
12 CHAIRMAN APOSTOLAKIS: Any other 13 questions? Okay. This concludes the day's 14 presentations. I would like to thank the speakers. It 15 was very informative. So we'll see some of you 16 tomorrow morning. Thank you. Off the record.
17 (Whereupon, at 5:10 p.m., the above-18 entitled matter was concluded.)
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