ML20206M308
| ML20206M308 | |
| Person / Time | |
|---|---|
| Issue date: | 05/05/1999 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | |
| References | |
| ACRS-T-3076, NUDOCS 9905140238 | |
| Download: ML20206M308 (119) | |
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O FFICIAL TRANSCRIPT OF PROCEEDINGS NUCLEAR REGULATORY COMMISSION ADVISORY COMMITTEE ON REACTOR SAFEGUARDS
Title:
MEETING: RELIABILITY AND PROBABILISTIC RISK ASSESSMENT AND MATERIALS AND METALLURGY TRO4 (ACRs; RETURN ORIGINAL ~^..
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LOCATION:
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DATE:
Wednesday, May 5,1999 PAGES: 1 - 99
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t' DISCLAIMER UNITED STATES NUCLEAR REGULATORY COMMISSION'S ADVISORY COMMITTEE ON REACTOR SAFEGUARDS MAY 5, 1999 The contents of this transcript of the proceeding of the United States Nuclear Regulatory Commission Advisory
>O i,/
Committee on Reactor Safeguards, taken on May 5, 1999, as s
reported herein, is a record of the discussions recorded at 1
the meeting held on the above date.
)
This transcript had not been reviewed, corrected I
and edited and it may contain inaccuracies.
l i
J
1 1
UNITED STATES OF AMERICA i
()
2 NUCLEAR REGULATORY COMMISSION 3
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 4
5 MEETING:
RELIABILITY AND.?ROBABILISTIC RISK 6
ASSESSMENT AND MATERIALS AND METALLURGY 7
8 U.S. NRC 9
Room T-2B3 10 11545 Rockville Pike 11 Rockville, Maryland 12 Wednesday, May 5, 1999 13 The subcommittee met, pursuant to notice, at 8:30 14 a.m.
15 MEMBERS PRESENT:
16 WILLIAM L.
SHACK, Chairman, ACRS 17 JOHN BARTON, Member, ACRS 18 MARIO BONACA, Member, ACRS 19 MARIO FONTANA, Member, ACRS 20 THOMAS S.
KRESS, Member, ACRS 21 DON W. MILLER, Member, ACRS j
22 DANA A.
POWERS, Member, ACRS 23 ROBERT L.
SEALE, Member, ACRS 24 ROBERT E. UHRIG, Member, ACRS 25 GRAHAM B.
WALLIS, Member, ACRS O
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PROCEEDINGS i
2
[8:30 a.m.]
3 DR. SHACK:
The meeting will now come to order.
4 This is a meeting of the ACRS Subcommittees on Reliability 5
and Probabilistic Risk Assessment and on Materials and i
6 Metallurgy.
l l
7 I am Dr. William Shack, Chairman of the 8
Subcommittee on Materials and Metallurgy.
Dr. Apostolakis 9
is the Chairman of the Subcommittee on Reliability and 10 Probabilistic Risk Assessment.
11 ACRS members in attendance are John Barton, Mario 12 Bonaca, Mario Fontana, Tom Kress, Donald Miller, Dana
'13 Powers, Robert Seale, Robert Uhrig, Graham Wallis.
14 The focus of this meeting is to review those
)
15 topical reports prepared by the Electric Power Research 16 Institute for risk-informed in-service inspection.
17 The subcommittees will gather information, analyze 18 relevant issues of facts, and formulate proposed positions 19 and actions as appropriate for deliberation by the full 20 committee.
21 Michael T. Markley is the cognizant ACRS staff 22 engineer for this meeting.
23 The rules for participation in today's meeting 24 have been announced as part of the notice of this meeting
'l 25 previously published in the Federal Register on April 14, j
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3 1
1999.
2 A transcript of the meeting is being kept and will 3
be made available as stated in the Federal Register notice.
4 It is requested that speakers first identify themselves and 5
speak with sufficient clarity and volume so that they can 6
readily be heard.
7 We have received no written comments or requests 8
for time to make oral statements from members of the public.
9 This, again, is the second presentation on risk-inforraed 10 in-service inspection that we've seen.
We've previously 11 reviewed, a few months ago, a proposal from the ASME on one 12 approach to risk-informed inspection.
This is another 13 alternate.
14 We will now proceed with the meeting and I will
()
15 call upon Dr. Jeff Mitman of EPRI to begin.
16 MR. MITMAN:
Good morning.
My name is Jeff Mitman 4
17 and I'm the EPRI project manager for risk-informed ISI.
I 18 would like to turn it over initially to Ham Fish of the New 19 York Power Authority and let him begin the introductory 20 remarks.
21 MR. FISH:
Good morning.
I'd like to introduce 22 the members of our team.
23 DR. SHACK:
Please use the microphone.
24 MR. FISH:
Beginning at your left, we've got Carl 25 Fleming, from ERIN Engineering.
Next in, Vesna f)
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Dimitrijevic, from Duke Engineering Services, a major
()
2 contributor to this work on the project; Jeff Mitman, whom I
3 you've met, our EPRI project manager; myself, from the New 4
York Power Authority, where I manage the research and 5
development program for the nuclear effort.
6 Next, Peter Riccardella, from Structural 7
Integrity; and, Glen Smith, the New York Power Authority 8
Project Manager at the Fitzpatrick plant.
Sitting in the 1
9 back, Pat O'Regan, working with us on this project, with 10 EPRI.
11 Our objectives today are to facilitate your review 12 and concurrence of the EPRI risk-informed in-service 13 inspection methodology, in support of a safety evaluation 14 report expected in September of this year.
()
15 The agenda, the organization of our presentation 16 today will be the status of the topical report, the status 17 of the various pilot plants which are participating in this, i
18 an overview of the technical methodology for the 19 risk-informed inspections, and, finally, our summary and 20 conclusions of what we have drawn from where we are to date 21 and what we look forward to.
22 At this point, I'd like to turn it over to our 23 EPRI technical manager, Jeff Mitman.
24 MR. MITMAN:
Thank you, Ham.
What we're going to 25 talk about first is the status of the topical, just a couple
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slides on
- or one slide on the topical, one slide on the
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pilot projects, and the vast majority of the discussion will
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3 be about the technical details of the methodology, 4
The original topical was submitted to the NRC for 5
review in June of 1996.
We reviewed extensive RAIs on that, 6
due to the preliminary nature of that, and from there we've 7
been working on RAI responses, which went into the topical 8
or went into the NRC staff back in November of last year.
9 We've also spent a lot of time revising the 10 topical.
That came to the staff on April 15, copies of 11 which were also supplied to the ACRS.
12 The topical revision has included extensive 13 enhancements of the procedure and basis description, quite a 14 bit of lessons learned information from the pilot programs, O
( f 15 resolutions of questions and comments from the NRC, and 16 we've also incorporated quite a bit of related EPRI research 17 information.
18 The expectations are for a draft SER in June of 19 this year, with a final SER in September of this year.
20 A quick discussion of the related ASME code cases.
21 There are two that are applicable to the EPRI methodology.
22 There is a third that the WOG Westinghouse ASME research 23 uses.
The one that's used there is N-577, but we won't be 24 talking about that today.
25 N-560 was approved or code case N-560 was approved
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in 1996.
It applies to BJ welds in the Class I system only.
2 It excludes socket welds and it allows for inspection, ten 3
percent of the inspection sampling of the Class I BJ welds.
4 A revision to that code case was started this year 5
and it's about halfway through the approval process and our 6
expectations are for approval of that this year.
7 N-578 is an alternate code case that also uses the 8
EPRI methodology.
It was approved in 1997.
It applies to 9
Class I, II, III piping and may include non-code piping.
10 Inspection criteria there are 25 percent of the 11 high risk welds, ten percent of the medium risk welds, and 12 zero percent of the low risk welds.
13 Likewise, a revision was started on that this 14 year.
It's about halfway through the approval process and,
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15 again, we're expecting approval this year.
16 The differences are a comparison of the two code i
17 cases, the risk assessment process is the same.
The 18 consequence analysis is the same.
The degradation analysis 19 is the same.
The distinction is in the element selection 20 process.
21 As noted on the slide, for the N-560, we do ten 22 percent of the BJ welds.
For N-578, we do 25 percent of the i
23 high, ten percent of the medium, and zero percent of the 24 low.
Both methodologies yield comparable risk results.
25 DR. WALLIS:
Is it ever good to do zero percent of I
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anything?
4
()
2 MR. MITMAN:
The way we pick welds, and we'll get 3
into that a little bit later, you'll see why we feel it's 4
okay to pick zero percent of the low risk welds.
5 DR. WALLIS:
In case you were wrong, you might 6
want to have at least some sample from what you called low 7
risk.
8 MR. MITMAN:
As I said, let's go on with the 9
degradation and consequence analysis and you'll see where 10 that comes from.
11 I want to talk about the pilot plants at this 12 point.
There has been quite a bit of work that's been done 13 already and the work continues.
As I said, there are two 14 code cases, two different scopes, if you will, that we've
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15 applied the methodology to.
Vermont Yankee was the first 16 plant to use the methodology and we received the first 17 industry SER on that back in November of last year.
That's 18 an N-560 case and it was done on Class I piping only.
19 ANO-2 is Combustion Engineering PWR.
We did a i
20 full plant evaluation of that under code case N-578.
21 Likewise, Entergy received an SER approving that in December 22 of last year.
23 ANO-1 is an N-560 application.
It was submitted 24 last year and we're currently finalizing responses to RAIs 25 that the staff sent us in the last month or so.
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1 Fitzpatrick is other full plant application, GE J
()
2 boiliug water reactor.
We did 14 systems there and we're in 3
final preparation of the submittal for that.
4 The following plants are all Class I only 5
applications and they're in various stages of completion.
6 Braidwood is about 80 percent complete, South Texas 70-75 l
7 percent complete, River Bend and Waterford haven't started 8
yet, but we expect to do those later this year.
l 9
At'this point, I'd like to start to talk about the 10 methodology itself.
We'll go through the -- initially, I 11 just want to go through the process itself at a very high 12 level and then we'll take a closer look at each of the 13 steps.
14 The first step is to determine the scope.
Do you
)
15 want to do BJ welds only?
Do you want to do full plant 16 evaluation?
How many systems do you want to include?
Where 17 do you want to draw the system boundaries and stop?
That's 18 determination of the scope.
19 Then there are two independent analyses that need 20 to be performed, the consequence analysis and the damage 21 mechanism analysis.
They can be done in either order, they 22 can be done in parallel.
The output of both of those is --
23 neither of those output is input to the other one.
So they 24 can be done in parallel.
And probably 50 or 60 percent of 25 the total work is involved in the two analyses, the
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consequence analysis and the damage mechanism analysis.
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Once that's completed, we do a second check
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3 looking at plant history, what we call a service review of 4
the plant.
From there, we do segment risk categorization, 5
where we take the output from the consequence analysis and 6
the damage mechanism analysis, put those together and 7
categorize our welds into high, medium and low risk regions.
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8 From there, we decide which specific welds we want 9
to -- welds or elements we want to inspect and we also 10 determine the inspection methods, what kind of NDE we want 11 to perform.
12 Afterwards, we go after the -- we do a risk impact 13 assessment and then we finalize the program.
There is a 14 feedback -- there are two feedback loops, one coming out of O)
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15 the risk assessment, whereby if we decide that the risk 16 impacts are unacceptable, we can go back and add welds, 17 re-allocate elements, do what's necessary to ensure that we 18 have acceptable risk impacts.
19 Also, there is a feedback loop at the end of the 20 project, where we do long-term performance monitoring, 21 whereby we watch what's going on in the plant, what's going 22 on in the industry, and, if necessary and as appropriate, we 23 modify -- go back and modify the various analyses to make 24 sure that we're looking in the right places and we're 25 looking for the right things.
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The heart to the process is the risk matrix and I
()
2 will show that in the next slide.
But before I bring up the 3
matrix itself, I'd like to talk a little bit about the two 4'
-- some of the concepts behind the risk matrix.
5 On one axis, we have the consequence evaluation, 6
where we're looking at core damage in large early release 7
and the input to that is both probabilistic insights and 8
deterministic insights.
There are four impact groups that 9
we're considering; initiating events, degradation of systems 10 and/or trains, degradation of the containment, or 11 combinations of the three above.
The output for that is a 12 consequence ranking of high, medium, low or none.
13 On the other side, we have the degradation 14 analysis, where we're looking at pipe rupture potential and
()
15 here we're looking at degradation mechanisms, which damage 16 mechanisms apply or are potentially applicable to each 17 piping segment.
1 18 We do extensive service experience evaluations 19 there and the output for that is a rupture potential ranking 20 of high, medium and low.
21 That goes into the risk evaluation matrix and here 22 we have the matrix, we have the consequences across the X 23 axis, degradation across the Y.
We end up with three 24 consequence rankings, high, medium, low and none, and, 25 again, the degradation analysis of high, medium and low.
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Then we divide into three risk regions high, medium and
()
2 none, again.
3 DR. KRESS:
Your conditional probabilities, I 4
assume, are weighted by the initiating events or added up 5
for all initiating events.
6 MS. DIMITRIJEVIC:
The conditional pipe failure.
7 So given the -- if we have a pipe failure, what would be the 8
conditional core damage.
9 DR. KRESS:
You do a conditional for each pipe 10 segment, for example.
11 MS. DIMITRIJEVIC:
Right.
12 DR. SHACK:
But then he has a frequency of 13 challenge that determines whether it's high or medium.
14 DR. KRESS:
So the frequency does enter into it.
()
15 MR. MITMAN:
Frequency does enter into that 16 classification.
17 MS. DIMITRIJEVIC:
Frequency of challenge for the 18 system, yes.
But actually frequency enters through the pipe 19 failure frequency.
20 DR. APOSTOLAKIS:
It's similar to the component, 21 is it not?
22 MS. DIMITRIJEVIC:
Yes.
If there is no need for 23 surrogate component, because we are looking at actual pipe.
24 DR. APOSTOLAKIS:
Jeff, what was the logic behind 25 this matrix?
I mean, this is a decision matrix here.
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You've given the categorization of the consequences of a
/%( )
2 pipe break and the degradation category, you decide that 3
something is low, medium.
What was the logic of that?
For 4
example, how did you decide that if the degradation category 5
is high and the consequences are low, then it becomes a 6
medium.
7 MR. MITMAN:
The logic behind the matrix concept
]
8 itself was driven by a desire to back away from having to do 9
detailed probabilistic calculations or detailed calculations 10 of the damage mechanisms.
We wanted to come up with a 11 process that was easier to apply, yet was accurate and gave 12 valid results.
13 So that led us to the concept of a matrix where we 14 can bend things easily.
)
15 DR. APOSTOLAKIS:
Well, we can talk about easy 16 easy is, but this -- the purpose of this risk evaluation, 17 this matrix is to lead you to a decision how to treat a pipe 18 segment, is that correct?
19 MR. MITMAN:
Right.
20 DR. APOSTOLAKIS:
So given now that you have done 21 the consequence evaluation and all that, whether that's easy j
l 22 or not is a separate issue, the logic of this 23 decision-making process, what was it?
I mean, why is medium 24 degradation category and low consequence category leads to a 25 low category six segment?
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MR. MITMAN:
Vesna?
(
2 MS. DIMITRIJEVIC:
What we tried to decide in this 3
category, we said, okay, well, let's assume the old pipe in 4
the plant breaks and CCBP.
If they're going to go in danger 5
of ten-to-the-minus-six, which is the danger where you're 6
actuully making the decision, if we're expecting that we can 7
be above the ten-to-the-minus-six, because those CCBPs have 8
the ranges between ten-to-the-minus-four and above, then we 9
said this is a high.
10 If we say we're expecting the piping in the plant 11 breaks, it's still be under ten-to-the-minus-six, and then 12 for this region between, we say, okay, between 13 ten-to-the-minus-six, eight, and ten-to-the-minus six, if we 14 don't really -- we're going to put the medium because we
(
's 15 were not sure really which way because of all the answers in 16 this.
17 So we did this in order to cover our certainty 18 ranges.
19 DR. APOSTOLAKIS:
But that was the uncertainty on 20 the consequences?
21 MS. DIMITRIJEVIC:
Both, because when we estimate 22 the pipe failure ranges, also, based on the presence of the 1
23 degradation mechanism.
So this is built to cover I
24 uncertainties.
If we expect, based on our knowledge, that 1
potential for the total CDF to be above 25
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ten-to-the-minus-six, we put it in high.
()
2 DR. APOSTOLAKIS:
And then what does it mean?
If 3
a segment is medium, what do you do to it?
4 MS. DIMITRIJEVIC:
You're going to see this 5
through the -- it's coming.
We will have a different 6
selection for this.
Carl, would you like to add something?
7 Did I miss something?
8 MR. FLEMING:
Carl Fleming, from ERIN.
I think 9
that part of George's questions could be answered that the 10 logic is really risk equals frequency times consequence.
11 And if this were done in a fully quantitative way, we'd 12 simply take the frequency of the pipe rupture, multiply it 13 by the conditional probability of core damage, and then get 14 the risk.
)
15 In the EPRI risk matrix approach, uncertainties 16 are addressed by looking at this in a very course, discreet 17 way..
Instead of numerically quantifying the conditional 18 core damage probability in each case and numerically 19 quantifying the frequency of pipe rupture, they're put into 20 broad categories.
21 So the logic of high, medium and low stems from 22 the concept of risk equals frequency times consequence.
23 DR. APOSTOLAKIS:
I understand that.
But my 24 question is this; presumably, there is a certain frequency 25 of inspections and so on that corresponds to medium, high of O
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these entries.
?
2 MS. DIMITRIJEVIC:
Of risk.
L 3
DR. APOSTOLAKIS:
Of risk.
Now, you don't have a 4
quantitative estimate of the impact --
j i
5 MS. DIMITRIJEVIC:
Of inspection.
6 DR. APOSTOLAKIS:
-- of the inspection on these 7
two categories.
8 MR. FLEMING:
No.
9 DR. APOSTOLAKIS:
So this is purely judgment now.
10 You are hoping that --
11 MS. DIMITRIJEVIC:
We're estimating total risk 12 from those locations.
13 DR. APOSTOLAKIS:
Yes, but --
14 MS. DIMITRIJEVIC:
So let's say that not one of
)
15 those locations is ever inspected, this is the total risk.
16 DR. APOSTOLAKIS:
That's right.
So now the 17 question is, if the degradation category is medium and the 18 consequence category is medium, then you say medium.
19 MS. DIMITRIJEVIC:
Right.
20 DR. APOSTOLAKIS:
But you don't know now what the 21 impact of what you're doing on risk is.
You just guess that 22 this would be a reasonable thing to do.
23 MS. DIMITRIJEVIC:
At this monent, the only thing 24 which we are trying to do is to divide locations -- I mean, 25 valves and the piping, based on the risk significance.
We
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are not looking at inspections yet at all.
(
).
2 DR. APOSTOLAKIS:
Yes, but in order to decide that
.3 something is medium, high or low, you have to have some idea l
4 of what the impact is.
5 MS. DIMITRIJEVIC:
Yes.
We have some idea of what 6
probability of failure is and what is the consequence.
7 DR. APOSTOLAKIS:
Without inspection.
l 8
MS, DIMITRIJEVIC:
Without.
i 9
DR. APOSTOLAKIS.
And you don't have any idea what 1
1 10 happens to these probabilities with inspection.
11 MS. DIMITRIJEVIC:
No.
12 DR. APOSTOLAKIS:
No.
13 MS. DIMITRIJEVIC:
Neither do we and neither does 14 anybody.
I mean, this is a very difficult thing to
()
15 estimate.
So basically, in this moment, we are not really 16 trying.
When.we try to calculate back to risk, we will try 17 to do that.
18 DR. APOSTOLAKIS:
So there is a judgment here that 19 by doing high or medium, you know this is good enough.
20 That's really what it comes down to.
21 DR. SEALE:
Are you going to show us a little 22 later that all three mediums are comparable in risk and that 23 all of the mediums are discernibly greater risk than low?
24 MR. MITMAN.
Yes.
25 DR. SEALE:
And conversely, mediums and high.
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MR. MITMAN:
Right.
We'll go into that a little
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2 bit later.
3 DR. SEALE:
Okay.
4 MR. MITMAN:
You wanted to add something?
5 MR. RICCARDELLA:
Let me just make a comment.
6 There was a judgment, as you said, George, made in the 7
beginning, when we set up these categories, and that 8
judgment was based on looking at what we currently do under i
9 ASME code requirements and coming up with something which we 10 think is at least equivalent or better.
11 There was a judgment at that end.
But as you will 12 see as we get on with the presentation, we have now 13 implemented this in a number of pilot studies and when we 14 complete those pilot studies, we've done delta risk I
()
15 calculations and quantified the difference between what we 16 were doing before and what we're doing after.
I 17 DR. APOSTOLAKIS:
Including the impact of 18 inspections.
19 MR. MITMAN:
Yes.
20 MS. DIMITRIJEVIC:
Yes.
21 MR. RICCARDELLA:
Yes.
22 DR. APOSTOLAKIS:
And it's in this report?
23 MS. DIMITRIJEVIC:
It's Section 3.7.
24 MR. DINSMORE:
This is Stephen Dinsmore, from the 25 staff.
I'd like to add something.
When EPRI first came in, 1
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they just had this matrix and ever since then, we've been
()
2 pushing them to at least estimate the delta risk.
So at the 3
end, they've come up with this methodology to estimate the 4
delta risk.
So they use this process to select and to guide 5
their inspection selections and then they use this delta 6
risk calculation to make sure that things are okay.
7 DR. SHACK:
Just a sort of related question.
You 8
have sort of a conditional or damage probability associated 9
with these things, that you don't really calculate.
You 10 calculate from the guidelines that you've given based sort 11 of on the number of backup trains and you associate a 12 numerical value of the conditional core damage probability 13 with those.
14 How robust is that?
I mean, how many PRAs did you
)
15 look at before you decided you could really bend them this 16 way and have a conditional core damage probability that was 17 in the range that you were assigning to each of those 18 categories?
19 MS. DIMITRIJEVIC:
It's plant-specific, so we look 20 in the specific plant PRA when we do this.
Every plant, 21 different events will fit into different categories.
It's 22 not really so diverse.
You will see also the pipes which 23 result in the LOCA lead to the high consequences and things 24 like that.
25 But this matrix is generally applicable to the
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methodology, but you apply it on specific plants, you look
()
2 at specific events and specific conditional core damage 3
probabilities.
4 DR. SHACK:
Okay.
Maybe I misunderstood it.
I j
5 thought when you looked at the plant specific, you were 1
1 6
really deciding, with this particular event, you had 2.5 l
7 backup trains.
8 MS. DIMITRIJEVIC:
Yes.
I 9
DR. SHACK:
And that was the plant-specific thing, 10 but you really didn't calculate the conditional core damage l
11 probability.
12 MS. DIMITRIJEVIC:
But that translates --
13 DR. SHACK:
Yes.
That translates, but not from 14 that plant's PSA.
Isn't that sort of arbitrarily assigned?
15 MS. DIMITRIJEVIC:
How many backup trains is 16 plant-specific.
What you can count as a train is 17 plant-specific.
If some plant keeps a train with a l
18 probability of failure that's ten-to-the-minus-two, that 19 counts as a train.
If that is ten-to-the-minus-one --
20 DR. SHACK:
It doesn't count.
21 MS. DIMITRIJEVIC:
-- it doesn't count as 22 half-train.
So what do you count as a train is 23 plant-specific.
So basically, it's a completely equivalent 24 if as you were running the PRA.
Basically, this table was 25 validated with a lot of PRA runs and always gives the same
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category, because it's basically principles of PRA are
()
2 concentrated in this table, because this is what PRA 3
sequences are, how many times you call for something, how 4
many backup trains you have, and what are their values.
5 DR. SHACK:
Okay.
And you say lots of PRA runs, 6
and I guess my question is, is that lots of PRA runs on two 7
plants or how many plants did we look at?
8 MS. DIMITRIJEVIC:
We looked at four plants and it 9
depended on the plant as to what was the number, between 10 five and 20 PRA runs per plant.
We didn't have any i
11 disagreements, l
12 DR. APOSTOLAKIS:
Yes, I went through 3.7.
You 13 say that while there can be a bounding analysis or if it 14 doesn't work, then you do a more realistic quantitative
)
15 analysis, but then you go on and say that this can be done, 16 but then there is a whole paragraph why it cannot be done, 17 because it's very difficult, and I agree.
18 Then in the examples that you have in here 19 somewhere from the actual plants, I didn't see the impact, 20 the quantitative estimate of the impact of the in-service 21 inspection.
22 So is that really something that you have done or 23 something that could be done in principal, but it's not 24 really done?
25 MR. MITMAN:
On VY ANO-2, ANO-1, we've done O
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realistic analysis on some of the systems, as required,
()
2 where we couldn't show qualitatively that risk was 3
improving.
i 4
On ANO-2, we've also done some Markovian analysis 5
that further, in more detail, looked at several systems in 6
the ANO-2 plant.
So those analyses have been done.
7 DR. SHACK:
And when you say you did that, you 8
actually computed the conditional core damage probability 9
for that plant from the PSA, not from the binding value of j
10 the CCDP that you have.
11 MR. MITMAN:
Vesna, correct me if I'm wrong, but 3
12 if I remember correctly, we actually looked at each of the 13 pipe segments on VY and ANO-2, calculated the conditional 14 core damage probability, and then used those to validate the 15 delta CDF calculations.
16 MS. DIL"ITRIJEVIC:
But we do also use a bounding 17 if you're in the medium range, because we can have a lot of 18 else with the different CCDPs in that train and we used the 19 upper value.
In every range, we will use the upper value in 20 bounding, because then it's considered.
So we don't go to 21 every specific valve that refers to CCDP.
We will take the 22 highest value for this range.
j 23 DR. APOSTOLAKIS:
So did you see a significant 24 input?
25 MS. DIMITRIJEVIC:
Of?
l O
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DR. APOSTOLAKIS:
Of the inspection?
2 MR. MITMAN:
No.
3 MS. DIMITRIJEVIC:
We didn't see it.
We just saw 4
ten-to-the-minus-six and ten-to-the-minus-nine.
5 DR. APOSTOLAKIS:
So inspection did not help in 6
any way.
7 MR. MITMAN:
Nc.
8 DR. APOSTOLAKIS:
So why are we doing all this?
{
9 MR. RICCARDELLA:
It started out as negligible.
10 DR. APOSTOLAKIS:
Why are we doing all this?
11 MS. DIMITRIJEVIC:
We asked ourselves from the 12 beginning this question a lot of times and basically the 13 answer that I got most often is that so we take a look and 14 we don't miss something.
But risk-wise, there is no 15 justification for doing it.
16 DR. KRESS:
It's defense-in-depth.
17 DR. APOSTOLAKIS:
So in-service inspection can be 18 dropped.
19 DR. KRESS:
It's defense-in-depth.
There is large 20 uncertainty in this area.
21 DR. APOSTOLAKIS:
That's very good.
22 MR. MITMAN:
They have a value impact analysis.
23 DR. APOSTOLAKIS:
In the report, in several 24 places, you say that the service experience to date provides 25 a strong indication that the frequency of pipe ruptures is ANN RILEY & ASSOCIATES, LTD.
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only very weakly correlated to the inspection processes.
So
()
2 that's a general statement then.
Even if you use this more 3
sophisticated approach, that 's still true.
4 MR. MITMAN:
That's true.
5 MS. DIMITRIJEVIC:
Very true.
6 MR. ALI:
This is Syed Ali from the ctaff.
I just f
7 wanted to clarify one thing.
When you say that the 8
experience is that the in-service inspection has real flaws, 9
that's bat cally related to the Section 11, ASME Section 11 10 inspections.
11 Based on the actual experience that the plants had 12 and the regulations actually followed, there are several 13 augmented inspection programs, for example, for IGSCC and 14 FAC, which have indeed found flaws.
()
15 DR. APOSTOLAKIS:
Well, originally, I thought 16 myself that this statement referred to experience, so ASME 17 Code Section 11 didn't help us.
But now they're saying that 18 even with this, they don't expect to see an impact, which is 19 a very interesting conclusion.
20 MR. MITMAN-The methodology is there to help you 21 decide where to do the ASME Section 11 inspections.
Now, we l
22 continue and we work with the augmented programs and there 23 is a lot of value in particularly the FAC programs and the 24 IGSCC programs.
But the ASME Section 11 required 25 inspections, I think it's safe to say, we feel has very
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little impact on the safety of the plant.
()
2 DR. APOSTOLAKIS:
But you are also saying that 3
this thing does not have a significant impact, not just -- I 4
want to make that clear, in my mind.
Not just the current 5
Section 11.
But even if you do this methodology, which is 6
more sophisticated, includes additional failure modes, it's 7
hard to see an impact.
8 MR. MITMAN:
That's correct.
Pat, you wanted to 9
add something?
10 MR. O'REGAN:
Pat O'Regan, from EPRI.
I just want 11 to emphasize what Jeff said.
This methodology takes credit 12 for and integrates the augmented inspection programs.
As 13 Syed mentioned, IGSCC and FAC do actually have a substantial 14 safety impact and we are taking credit for that.
15 So the delta you're seeing is actually on the 16 Section 11 portion, not crediting the augmented programs.
17 MR. MITMAN:
And Carl?
18 MR. FLEMING:
George, with regard to the insights 19 from service experience that back up this conclusion about 20 the benefit of inspection, the underlying reason for that 21 statement or that conclusion is that when we look at service 22 experience, we find that we find piping, some small number 23 of pipe f ailures and ruptures due to two general classes of 24 failure mechanisms.
25 The degradation mechanisms, some of which are I
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actually amenable to inspection, and also we have loading
()
2 conditions, like water hammer, vibration fatigue, 3
over-pressurization, frozen pipes, things like that.
And if 4
you look at the whole piping service experience, only a 5
fraction of those failure mechanisms provide you enough 6
warning time that a ten-year interval inspection process is 7
going to give you an opportunity to prevent the failure.
8 So that's one of the reasons for that conclusion.
9 A second reason --
10 DR. APOSTOLAKIS:
Ten years is too long, you're 11 saying?
12 MR. O'REGAN:
No.
Some mechanisms don't give you 13 warning times such that if you did an inspection today, you 14 could prevent a failure tomorrow.
Then another basis for 15 this insight is that a large fraction of the Class I pipe 16 and Class II and III pipe out there isn't being subject to 17 inspection.
The inspection programs that we do have from 18 Section 11 are only looking at a small fraction, a small 19 sample of the existing welds.
20 So when we go out and look ac the service 21 experience, you find the vast majority of the pipe that 22 produces the service experience has never been inspected for 23 ASME Section 11 purposes, because the percentages are 25 24 percent for Class I, 7.5 percent for Class II, and so forth.
25 So these are some of the underlying reasons to l
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support that conclusion.
(( )
2 DR. APOSTOLAKIS:
So just to close this.
In your 3
opinion, is this a good idea or not?
4 MS. DIMITRIJEVIC:
Is it a good idea to do these?
5 DR. APOSTOLAKIS:
To inspect.
Not the EPRI 6
approach.
I know this is a good idea.
7 MS. DIMITRIJEVIC:
They don't inspect at all in 8
the Section 11.
9 DR. APOSTOLAKIS:
What?
10 MS. DIMITRIJEVIC:
Is your question, is it would 11 they be able to inspect at all?
12 DR. APOSTOLAKIS:
Yes.
13 MS. DIMITRIJEVIC:
Well, we have a different 14 opinion.
My opinion is no, but basically the people who --
()
15 because I am a PRA person.
The people who are actually 16 engineers and who work on inspection, they think it's a good 17 idea to take a look at what is going on.
18 DR. APOSTOLAKIS:
Now, even for a PRA person, 19 though, maybe your conclusion is based on the fact that you 20 looked at core damage frequency and large early release 21 frequency.
I mean, if one has other objectives, like I 22 don't want to see any pipe breaks, that's my objective, then 23 perhaps it would be a different conclusion, because we see 24 that by the way the new oversight program, that the 25 objectives now are spread all over the cornerstones.
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Would that change your conclusion?
()
2 MS. DIMITRIJEVIC:
No.
3 DR. APOSTOLAKIS:
Still it would not.
4 MS. DIMITRIJEVIC:
No, because what Carl just 5
mentioned we don't claim the risk from pipe breaks is equal 6
to zero or small.
What we are claiming what inspection 7
does, that is negligible.
And where you're going to see the 8
breaks, like vibration and everything, inspection doesn't do
{
9 a thing.
10 MR. MITMAN.
Pat, did you want to add something 11 here?
12 MR. O'REGAN:
Yes, just a point of clarification.
13 Pat O'Regan, from EPRI.
When we're talking inspections 14 here, at least the discussion, it was just focusing on 15 volumetric examinations.
We are still doing and still 16 recommending doing leak testing and what service experience 17 has showed us is that's where we find most of our leaks, not 18 from the volumetric exams, but the leak testing.
19 And even on a low risk location, that's still 20 recommended to be done.
21 DR. APOSTOLAKIS:
So if we were completely 22 rational, we would keep doing those inspections, but we 23 would drop this other stuff.
24 MR. MITMAN:
I think rational, you'd probably want 25 to go back and, at the very beginning of your design
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process, beef up your leak detection capability.
()
2 DR. APOSTOLAKIS:
Okay.
3 DR. SHACK:
I guess I'm not convinced that that 4
would be true if you include the augmented inspections; that 5
is, flow assisted corrosion and stress --
6 MS. DIMITRIJEVIC:
No, we don't change anything.
7 DR. SHACK:
You're from a PWR, where maybe, in 8
your primary system, that probably is true.
That's a rather 9
broad conclusion.
10 MR. MITMAN.
You're absolutely right.
You want to 11 continue to do the augmented programs.
It's very clear with 12 the FAC program --
13 DR. SHACK:
The augmented programs are, in many 14 ways, much like this; that is, you're looking where you know
()
15 you have a problem.
16 MR. MITMAN Exactly.
17 DR. SHACK:
That's why it's augmented.
18 MR. MITMAN.
And that's why this methodology 19 blends very nicely with the currently existing augmenting 20 programs, because of the similarities in the approach, where 21 you're looking where you expect to find problems.
22 DR. SHACK:
Without come random selection.
23 MR. MITMAN.
Right.
24 MR. RICCARDELLA:
Jeff, let me make a point on 25 that.
Historically, what happened, and I think I said this
()
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like two years ago in this same group, is we had these ASME
()
2 Section 11 requirements to do 25 percent of Class I, ten 3
percent of Class II, which we came up with those 20 years 4
ago when we had very little operating experience.
5 So as we went through the years and did that, 6
those things didn't find much, but we did find problems and 7
where we found problems, we implemented augmented programs.
8 But what happened was the 25 percent type stuff 9
never went away.
So we were inspecting more, but we're 10 doing the augmented, plus we're doing this additional 25 11 percent.
12 The attempt here is to integrate those into a 13 single rational program that looks at the areas where we 14 expect problems and doesn't look at the areas where we don't
()
15 expect problems.
16 MR. SULLlVAN:
This is Ted Sullivan.
I wonder if 17 I could add a couple of points.
One of the reasons why I 18 think traditionally in-service inspection has not found 19 problems is because the inspection methods were not 20 qualified until after a problem revealed itself.
21 The Appendix 8 approaches, which we plan to adopt 22 in the next revision of 50.55 (a), should go a long way in 23 resolving that.
24 Another brief comment having to do with if we were 25 completely rational.
I think being completely rational, I Ol ANN RILEY & ASSOCIATES, LTD.
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think we want to keep in mind defense-in-depth and that's
()
2 part of the reason why the staff really wouldn't agree with 3
a position that we should just look at this purely from a 4
risk perspective and maybe only focus on the areas of 5
augmented inspection.
6 One final point.
I'm not sure that this came out 7
explicitly in the preFentations, I guess, last week to the 8
ACRS on license renewal, but to some extent, license renewal 9
is taking credit for Section 11 in the sense that there is a 10 potential for degradation mechanisms to occur over the long 11 haul and the inspection methods are supposed to be geared to 12 using appropriately qualified techniques to be able to j
13 detect those degradation-mechanisms should they arise.
14 That's another reason why I don't think we should take a O(_,/
15 view too strongly that we should just look at this from a 1
16 risk perspective and possibly just rely on the numbers to 17 say we don't need in-service inspection.
18 DR. POWERS:
Could I understand better why you 19 want to appeal the defense-in-depth here?
Why ita't this 20 just completely and adequately resolved on a probabilistic 21 basis?
22 MR. SULLIVAN:
I guess there might be others that 23 might care to answer from the staff, but I would say I don't 24 think that we want to see failures occurring in piping just 25 because the risk numbers say that we can handle those ANN RILEY & ASSOCIATES, LTD.
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failures.
()
2 DR. POWERS:
Thou shalt not have pipe failures.
3 MR. SULLIVAN:
I think that's the whole 4
defense-in-depth approach, which may sound circular.
5 DR. SHACK:
The general design criteria call for 6
the integrity of the reactor coolant system.
7 DR. POWERS:
Yes, but it does not say thou shalt 8
never have a pipe failure.
9 DR. SHACK:
It's embedded in the whole regulatory 10 system.
11 MR. SULLIVAN:
There are places in the GDC that 12 say extremely low probability.
13 DR. POWERS:
I don't know, ten-to-the-minus-four, 14 ten-to-the-minus-five is certainly what I would call
()
15 extremely low.
16 DR. APOSTOLAKIS:
But, also, let's make it clear 17 that their conclusion is not based on the numbers alone.
I 18 mean, it's the whole report and analysis that supports all 19 that and the judgments and so on.
It's not that they got 20 the number of ten-to-the-minus-five and say, my god, you 21 know, this is insignificant.
It's the whole process that 22 has led --
I 23 DR. POWERS:
I will grant that.
What I want to j
24 understand is why -- I mean, very specific here.
We say we 25 should look at and think about defense-in-depth, a very 1
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important concept in reactor safety.
Yet, this seems to be
)
2 a topic that's susceptible to probabilistic analysis and I'm 3
trying to understand why.
4 MR. DINSMORE:
This is Steve Dinsmore, from the 5
staff.
I guess I have to review a lt'- of this probabilistic 6
analysis that come in regarding this stuff and the numbers 7
are actually quite uncertain and one of the problems is when 8
they say from experience data, they haven't seen much, there 9
isn t that much experience to get ten-to-the-minus-seven, 10 ten-to-the-minus-eight, statistical numbers from the 11 experience data.
So they have to do some type of 12 interpretations and Bayesian updates and engineering 13 judgments to get the numbers which they are using to support 14 this process.
O)
(
15 And even though you could say that the numbers 16 indicate that if we stopped inspecting, there would be no 17 great increase in CDF or LERF, the numbers that they're 18 using, again, there is a lot of judgment in those numbers i
i 19 and there is not enough data to support them really at a 20 statistical pace.
21 DR. APOSTOLAKIS:
There are two things that come 22 to mind from this comment.
First of all, I think if you 23 want to defend defense-in-depth in this context, you have to 24 tell us where the big uncertainties are that you just 25 mentioned that perhaps could invalidate this conclusion.
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But second, I will come back to Carl's comment,
()
2 that for most of these failures, you don't have enough 3
warning time to catch them by inspection, which doesn't 4
sound like a PRA argument, to me.
5 That's really the physics of the problem.
So I 6
inspect just to feel better.
That's really what is going 7
on.
In the name of defense-in-depth.
8 MR. ALI:
Syed Ali, from the staff.
Carl, correct 9
me if I'm wrong, but I think the kind of mechanism that he 10 was referring to that do not give you warning are loading 11 type mechanisms, such as water hammer or fatigue.
But the 12 mechanisms which are time-related, degradation type 13 mechanisms, they do give you time and augmented, like IGSCC, j
14 erosion / corrosion.
()
15 DR. APOSTOLAKIS:
But we're not referring to all 16 the augmented programs.
Just this one.
We're not saying 17 that we should drop other programs, right?
18 MR. MITMAN:
First of all, I want to make 19 something clear.
EPRI has not recommended that we drop all 20 Section 11 inspections.
21 DR. APOSTOLAKIS:
That's fine.
Other people 22 might.
23 MR. MITMAN:
You asked an opinion --
24 MR. BARTON:
We'll deal with them when they come 25 before us.
1 O
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MR. MITMAN:
You asked an opinion --
()
2 DR. APOSTOLAKIS:
Let me tell you what's going on, 3
because probably you think this is a discussion that
{
-- we 4
are facing a major problem now as to what the role of 5
defense-in-depth should be in a risk-informed regulatory 6
system.
That's why you're getting all this.
7 That makes more sense now to you probably.
8 MR. DINSMORE:
Could I just quickly respond to 9
something?
When you asked me if the uncertainty doesn't or 10 why we can't accept the results because of uncertainty, I 11 would say we can accept the results of what EPRI is doing in 12 spite of the uncertainty.
It's because of the uncertainty 13 that we are -- that we can accept what they're trying to do 14 and not s.y, well, you have to do even more or even less.
)
15 DR. APOSTOLAKIS:
So what you're saying l
16 essentially is that their numerical assessment of the impact 17 of this, which led them to the conclusion that it doesn't 18 matter, is really not correct.
19 MR. DINSMORE:
Probably not supportable.
20 DR. SEALE:
Tney're not sure about that.
21 MR. DINSMORE:
Not supportable from the 22 statistical data.
4 23 DR. APOS10LAKIS:
But anyway, I think we've 24 covered this enough.
At least for me.
25 DR. POWERS:
I still haven't gotten an answer.
I
(}
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may never get an answer.
()
2 DR. APOSTOLAKIS:
That's my bet.
3 MR. MITMAN:
I've put up a slide that's not in 4
your package and it looks at each of the damage mechanisms 5
and --
6 DR. APOSTOLAKIS:
It's in the report, though.
7 MR. MITMAN:
It's in the report, if I remember 8
correctly.
9 DR. APOSTOLAKIS:
Yes.
10 MR. MITMAN:
But it's not in the presentation.
It 11 shows each of the damage mechanisms and our calculated 12 rupture frequency per the damage mechanisms.
There are two 13 categories of those damage mechanisms, the dark ones and the 14 light ones.
The light ones are those that we feel are not
()
15 amenable to inspection, things like they include vibration, 16 water hammer, unknown and other causes.
17 DR. WALLIS:
Just for clarification.
Your rupture 18 frequency is based on how many reactors?
19 MR. MITMAN:
It's based on over 2,000 operating 20 years of reactor.
21 DR. WALLIS:
This is the total rupture frequency 22 of all the reactor population.
23 MR. MITMAN:
In the United States.
Yes.
24 DR. WALLIS:
Otherwise, it looks pretty lousy.
If 25 you multiply it by a hundred, it gets scary.
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MR. MITMAN:
Right.
r) 2 MR. FLEMING:
But these are on a per reactor year (s-s 3
basis.
These are on a per reactor year basis.
4 DR. WALLIS:
Per reactor year?
5 MR. FLEMING:
Yes.
6 DR. WALLIS:
No, it's not.
It's per a hundred 7
reactor years.
8 DR. APOSTOLAKIS:
Anywhere in the population.
9 DR. WALLIS:
Anywhere in the population.
So I 10 don't multiply by a hundred.
11 DR. APOSTOLAKIS:
No, you shouldn't.
That's 12 correct.
This is per calendar year anywhere in the United 13 States.
14 MR. FLEMING:
No.
This is per reactor year.
)
15 DR. WALLIS:
So I multiply it by a hundred.
16 MR. FLEMING:
This is for each reactor, on the 17 average for each reactor, but it covers the entire plant.
18 It covers all the piping systems in the entire plant.
Only 19 a small portion of this is in the safety-related systems.
20 DR. APOSTOLAKIS:
You're right., because you had 21 1,511 total number.
22 MR. FLEMING:
That's right.
23 DR. APOSTOLAKIS:
Now it makes sense.
24 DR. WALLIS:
So this is per reactor year.
25 MR. FLEMING:
These are per reactor year, yes.
So O
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you do multiply by a hundred.
l 1
2 DR. WALLIS:
So I do multiply.
1 \\_J 3
MR. FLEMING:
Yes.
4 DR. WALLIS:
Thank you.
5 DR. APOSTOLAKIS:
But this is all pipes.
6 MS. DIMITRIJEVIC:
All pipes, all sizes.
7 DR. APOSTOLAKIS:
By the way, this number, which 8
is in several places in the report, ultimately is not used.
9 Is that correct?
The ten-to-the-minus-two, I was looking l
l 10 very hard to find a place where you actually use it.
It's l
11 just an indication, but you don't really use it.
12 MR. MITMAN:
It's part of the design basis of the 13 degradation categorization and it is available to us if we 14 need it to do the risk impact analysis.
()
15 DR. APOSTOLAKIS:
Well, you can't really use it, 16 though, because this is anywhere in the plant.
I mean, if 17 you go to your pages 3-1 and 3-2, then you have to 18 specialize it.
l 19 MR. MITMAN:
You're right.
l 20 MR. FLEMING:
It requires further analysis.
21 DR. APOSTOLAKIS:
Further analysis, right.
So 22 right now it's not used.
In your calculations, ultimately, 23 the ten-to-the-minus-two from there is not used and I think 24 that should be made clear in the report.
25 MR. FLEMING:
At this level, they are not used.
l l
{s/
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DR. APOSTOLAKIS:
It is not.
/x) 2 MR. FLEMING:
This is just a presentation of
(_./
3 general experience.
4 DR. APOSTOLAKIS:
I understand.
It took me a 5
while to figure it out.
It's not stated in the report that 6
it's not used.
7 MR. FLEMING:
But I think it's worthwhile -- it's 8
just an intermediate step along the way towards breaking the 9
data down so that we could confirm that these high, medium 10 and low categories that were developed on the deterministic 11 degradation mechanism basis do correlate to order of 12 magnitude estimates of pipe rupture frequency, and that's --
13 DR. APOSTOLAKIS:
I think in your viewgraphs you 14 have the equations.
So maybe you can go to.them right now.
I ))
f 15 Equations 3-1 and 3-2, on page 3-8.
You didn't expect that, 16 Jeff?
17 MR. MITMAN:
We're ready.
18 DR. APOSTOLAKIS:
Okay.
It says pipe break 19 frequency, is that what it is, PBF?
20 MR. FLEMING:
Yes.
21 DR. APOSTOLAKIS:
This is page 3-8.
This is what 22 you would -- you would need this number, which is really now 23 segment-specific, to do the calculations.
24 MR. FLEMING:
Yes.
25 DR. APOSTOLAKIS:
Do you actually get a number f'/}
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like that?
In principal, I know you can get something.
(}
2 MR. FLEMING:
Yes.
3 CHAIRMAN JACKSON:
You do?
4 MR. FLEMING:
We had developed a number, 5
segment-specific.
6 DR. APOSTOLAKIS:
And it's discussed in the report 7
how you do that?
8 MR. MITMAN:
It's not discussed in this report.
9 It's discussed in a supporting document.
10 DR. APOSTOLAKIS:
Can I have a copy of the 11 supporting document?
12 MR. MITMAN:
The staff already has a copy of it.
13 DR. APOSTOLAKIS:
Okay.
We might have it already.
14 MR. MARKLEY:
Which document are you talking
()
15 about, Jeff?
16 MR. MITMAN:
TR111880, which is in the references.
17 It's currently in a final draft, but the staff does have
]
18 copies of that.
19 DR. APOSTOLAKIS:
So then what you do is you take I
20 tne ten-to-the-minus-two and you can see that the number of 21 systems and you judge subjectively then, like we specialize 22 the fire frequencies for critical locations.
You start with 23 a building and slowly go down to the location.
24 MR. FLEMING:
Yes.
And very briefly, what we do 25 is we break the whole population of piping failure O
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statistics up into PWR and BWR vendor groups.
We break the
(~')
2 system populations into several system sizes and then we V
3 look at all the different failure mechanisms.
So we can 1
4 look at it on a conditional segment base type of analysis.
5 DR. APOSTOLAKIS:
So this is one of the major 6
uncertainties that Steve Dinsmore probably referred to.
Say 7
yes, Steve.
8 MR. DINSMORE:
Yes.
9 MR. FLEMING:
And by the way, I wanted to respond 10 to what Steve said earlier about the uncertainties, because 11 I agree in his comment to some extent, but I also wanted to 12 clarify that.
We have done a detailed Bayesian uncertainty 13 analysis of the attempts to make pipe failure rates and 14 rupture frequencies from the service data and when you look
( )'
15 at -- if you look at these results on an order of magnitude 16 basis, on a logarithmic basis, you have very, very broad 17 distributions that characterize large uncertainties, and 18 it's a true statement, what Steve said.
19 But if you try to take that and then develop a 20 conclusion about what do those uncertainties say about the 21 impact on risk, it's still possible to develop very robust 22 conclusions that in spite of the large uncertainty, it's 23 still a very, very small fraction of the risk.
24 But there is one other -- but I think coming 25 around to support what I think the -- and the concern about
//)
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defense-in-depth is that these PRA calculations that we can
(-)
2 do today based on looking at historical data, I think, are 3
good for making current estimates of what we think the 4
rupture frequencies are today, but we'd be on very shaky 5
ground if we tried to project these 20, 30 or 40 years out 6
into the future, and I think therein would lie the 7
difficulty in trying to make conclusions about life 8
extension without having some kind of way to keep monitoring 9
possible trends in performance.
10 Because we can't see the future in yesterday's 11 data.
12 DR. APOSTOLAKIS:
Now, in the report, you say 13 something that's not quite the same as what Carl said a few 14 minutes ago.
Right under equations 3.1 and 3.2, you say
()
15 based on the expressions, they're using a conservative 16 estimate of the total PBF frequency of ten-to-the-minus-two, 17 where it calculates the CCDP and so on.
18 So that's why I raise the issue.
When I read 19 this, I thought, my god, they're using something that is a 20 frequency of type of break anywhere to make judgments, and 21 so the report perhaps is not written very well on that 22 point.
23 MR. FLEMING:
The sections you're looking at right 24 now explain the logic in deriving the original matrix to 25 start with and then back in Section 2, with the benefit of O
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42 g
)
1 more detailed analysis of the service data, we took another 2
look at that question and confirmed that the order of 3
magnitude assessments were --
4 DR. APOSTOLAKIS:
That's not here.
5 MR. FLEMING:
If you get to Section 3-7, for 6
example, you finally -- if a pipe is classified as having a 7
medium rupture potential, it's 8
one-times-ten-to-the-minus-four per year.
9 DR. APOSTOLAKIS:
Right.
10 DR. SHACK:
They sort of assign conservative pipe 11 break frequencies based on essentially degradation l
i 12 mechanisms.
If it's got a high degradation mechanism, 1
13 medium or low.
I 14 MR. FLEMING:
But in Section 2 of the report, this j
15 other more detailed look at applying the service data to 16 look at these calculations is presented and it confirms the 17 order of magnitude assumptions that were originally made.
18 DR. APOSTOLAKIS:
I'm talking about the 19 specialization.
Section 2 is very general.
It doesn't say 20 how you go down the system.
Section 2 is an analysis of the 21 existing failures.
22 MR. FLEMING:
Right.
23 DR. APOSTOLAKIS:
I would have covered that.
And 24 there is equation 2-1 that bothers me, too, on page 2-8.
25 The probability of rupture given failure.
I don't know what O
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that means.
Page 2-8.
()
2 MR. FLEMING:
That was a simple model that we used 3
to analyze the service data for those failure mechanisms 4
that have a strong leak-before-break characteristic.
We 5
define failure as the whole package of failure modes, 6
including small leaks and ruptures.
7 So the model basically says we have a rupture 8
frequency which is equal to the failure frequency times the 9
conditional probability that it's a large failure.
10 DR. APOSTOLAKIS:
So that's what is missing from 11 the report, though.
I didn't see that.
So it wasn't clear 12 to me what the difference between the rupture and the 13 failure.
14 MR. FLEMING:
The way we defined it --
()
15 DR. APOSTOLAKIS:
A leak is a failure?
16 MR. FLEMING:
A failure is any fluid going through 17 the boundary, including a leak.
A rupture we defined at 50 18 gpm and larger flow areas.
19 DR. APOSTOLAKIS:
That would have saved me a lot 20 of time.
21 MR. FLEMING:
Sorry.
22 DR. APOSTOLAKIS:
Back to your presentation.
23 MR. MITMAN:
Next, the next slide is on the pipe 24 service experience, which we've already talked a little bit 25 about.
There is over 2,000 reactor operating years of O'
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experience --
[JD 2
DR. WALLIS:
You bet"Gr put in the word reactor 3
there, too.
4 MR. MITMAN:
Fair enough.
In that database, there 5
is 1,145 events, 1,145 failures.
Here, failures are defined 6
as either leaks or ruptures.
The vast majority, 1,076 of 7
those were leaks.
Most of those were less than five gpm and 8
most are due to corrosion mechanisms.
9 Out of the total database, there are 69 events 10 that were categorized as ruptures.
The failure mechanisms i
11 are well understood and the conditions necessary to produce l
12 the failures are generally known.
13 DR. APOSTOLAKIS:
Now, where are the numbers, on 1
14 another table?
n
(
15 MR. MITMAN:
Which?
16 DR. APOSTOLAKIS:
Table 2-2 and 2-1.
17 MR. FLEMING:
They're consistent.
18 DR. APOSTOLAKIS:
You said 1,100-something total 19 failures and I don't see that here.
I see 1,500.
20 MR. MITMAN:
If I remember correctly --
21 DR. APOSTOLAKIS:
Oh, 1,145.
I'm sorry.
In the 22 database.
Okay.
You have to look elsewhere.
23 MR. FLEMING:
It's consistent.
It's confusingly 24 presented, but it's consistent.
25 DR. APOSTOLAKIS:
Speaking of that, what's the O
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difference between the degradation mechanism and severe 2
loading?
3 4
MR. FLEMING:
Degradation mechanisms are 5
degradation mechanisms like thermal fatigue, stress 6
corrosion cracking that occur over long periods of time due 7
to physical degradation mechanisms, where severe loading 8
conditions are the imposition of loads in excess of the 9
capacity of the pipe due to water hammer, impact, external 10 impact on the pipe, frozen pipes, over-pressurization of the 11 pipe beyond its design capacity and things like that.
12 DR. APOSTOLAKIS:
So what you're saying is that in 13 the severe mechanism, there was no aging mechanism acting.
14 It's just that you had the load that exceeded the design 15 capacity.
16 MR. FLEMING:
In the vast majority of cases.
- Now, 17 in principal, you can have a failure due to a combination of 18 degradation.
19 DR. APOSTOLAKIS:
That was my next question.
20 MR. FLEMING:
But in the analysis of the service 21 data, this was not evident.
22 DR. APOSTOLAKIS:
So when you had the degradation 23 mechanism, you didn't see any failures because there was 24 degradation and then there was a load.
25 MR. FLEMING:
We didn't see'any evidence of that, O.
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although in principal, we know it's possible.
We didn't see
(
)
2 any evidence of that.
The severe loading condition failures 3
were, according to the reports that we analyzed, the loads 4
were sufficient to cause the failure.
5 DR. APOSTOLAKIS:
So let's look at the rupture.
6 You say erosion / corrosion or flow accelerated corrosion, 7
there were 18 ruptures, on table 2-1.
8 MR. FLEMING:
Right, in large pipes.
9 DR. APOSTOLAKIS:
So you're saying that these were 10 due to the steady-state pressure in the pipe and you simply 11 had deterioration.
12 MR. FLEMING:
Yes.
13 DR. APOSTOLAKIS:
Wow.
14 MR. FLEMING:
Or if there was any variation --
D)
(
15 DR. SHACK:
EC will do that to you.
16 MR. FLEMING:
Or if there was any variation to the 17 loading, it was not of any -- it wasn't of any significance 18 that was noted in the report.
There might have been some 19 small pressure transient.
20 MR. MITMAN:
Keep in mind this is Class I,
II and 21 III piping, not just Class I.
22 MR. FLEMING:
It's the whole plant.
I 23 DR. BONACA:
Do you make an analysis of the i
24 difference between the systems that normally run and systems 1
25 that don't run?
The reason why that's an important question i
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47 1
is that most safety systems are standby.
They don't run.
2 MR. MITMAN:
Well, some of the damage mechanisms N-3 behave differently whether the system is running or not.
In 4
our analysis, we go ahead and we look at operating 5
conditions of the plant or of the system and of the portion 6
of the system, and that helps us decide whether that segment 7
is subject to the damage mechanism.
8 DR. SEALE:
Could I ask a somewhat different l
9 question?
My impression is that one of the things that gets 10 us off the hook on a lot of our concerns is the validity of 11 the idea of leak-before-break.
Is that equally valid for 12 what I will call degradation versus load-induced failures?
13 MR. MITMAN:
It's true for some of the damage 14 mechanisms.
IGSCC, it is.
It's not true for FAC.
So it
()
15 depends upon the damage mechanism, whether leak-before-break 16 is valid.
17 DR. SEALE:
But in general, you can't make a 18 generalization that would say that load-induced failures are 19 less likely to exhibit leak-before-break.
20 MR. FLEMING:
That's correct.
21 MR. RICCARDELLA:
I think that's a true statement.
22 DR. SEALE:
So the ones you're not -- that 23 inspection doesn't help you with are the ones that are most 24 likely to be severe immediately on occurrence.
25 MR. FLEMING:
That's right.
f*
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DR. SEALE:
Okay.
()
2 MR. FLEMING:
And looking at your question from 3
the service data standpoint is that we can look at this 4
second parameter in that one equation, given the failure, 5
what's the conditional probability that it's a rupture given 6
a failure.
And looking at that parameter for the 7
degradation mechanisms other than FAC, that number tends to 8
be very low, on the order of a few percent, but for flow 9
accelerated corrosion and the severe loading conditions, it 10 tends to be much higher, water hammer events, over pressure 11 events, which stands to reason, I think.
12 DR. WALLIS:
I'm wondering if it's true that if 13 inspection doesn't help you, I'm thinking of the fire-line 14 break in Washington, where they had something like 17 water
()
15 hammers they didn't pay any attention to and then the 18th 16 broke the pipe, and probably this is because it's a loosened 17 thing.
The other water hammers have loosened things up.
So 18 paying attention to the history and inspecting would perhaps 19 have prevented the failure due to sudden loading.
20 MR. MITMAN I don't think we're trying to say 21 that you should ignore what's going on in the system, but 22 doing an ultrasonic inspection or volumetric inspection of a 23 weld probably isn't going to keep you out of trouble with a 24 water hammer.
)
25 DR. WALLIS:
Something like a water hammer, minor O-ANN RILEY & ASSOCIATES, LTD.
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{
1 water hammers have happened before in that component and no 2
one has paid much attention maybe and the2 there is a big 3
one.
4 MR. MITMAN:
And that's one of the things we will 5
discuss a little it later, is that we do take into 6
consideration water hammer in our categorization of the 7
degradation mechanisms.
8 DR. BONACA:
Just to complete my thought.
I had a 9
question before.
So you feel that that statement, failure 10 mechanism, well understood, it's still applicable also for 11 those piping by systems that don't run.
12 MR. MITMAN:
Absolutely.
13 DR. BONACA:
That's fully understood.
14 MR. MITMAN:
Yes.
15 DR. BONACA:
And for those, also, inspections 16 doesn't have preferential value.
17 MR. MITMAN:
That is correct.
In the database, 18 there are 69 rupture events where rupture is defined as 19 greater than 50 gpm. Again, the failure mechanisms are 20 understood.
Some of the mechanisms are not amenable to j
21 inspection.
There is only one event in the RCS and several 22 events in steam water and feed water systems.
i 23 EPRI has a program to periodically update the 24 database, keep an eye on what's going on in the industry, 25 and make sure that the methodology doesn't need to be f)
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revised.
1 2
The next slide is an example of the deterministic criteria that we used to do the damage mechanism analysis.
3 4
In this particular example, we're looking at thermal --
5 DR. APOSTOLAKIS:
Can I interrupt?
Because I have 6
to go somewhere at 10:00 and I have a couple of questions 7
that jump ahead and I wanted to ask them.
8 You didn't really expect that we would let you 9
finish your presentation the way you have prepared it.
10 Would you go to your slide 19?
Consequence 11 ranking criteria.
Now, the conditional core damage 12 probability, this is calculated as shown in one of the 13 equations here as the new CDF, assuming the system is down, 14 minus the baseline, times the exposure of time, and the
()
15 exposure of time can be anywhere from a year to maybe a few 16 days.
17 Now, as far as I know, the NRC does not have and 18 nor does the industry criteria as to what's high or low with 19 respect to the conditional core damage probability, except 20 for temporary outages, where they give a 21 ten-to-the-minus-seven number.
22 So where did the ten-to-the-minus-four come from?
)
23 The ten-to-the-minus-four is used for the core damage l
24 frequency, not the core damage probability over a period of 25 three months.
i O
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51 1
MS. DIMITRIJEVIC:
This was this equation three
()
2 you just asked us about, CDP.
3 DR. APOSTOLAKIS:
Yes.
4 MS. DIMITRIJEVIC:
Where as that equation?
5 DR. APOSTOLAKIS:
There were two equations on page 6
3-8.
7 MS. DIMITRIJEVIC:
Yes.
8 DR. APOSTOLAKIS:
But it doesn't --
9 MS. DIMITRIJEVIC:
It tells you that that was very 10 conservative, assuming the --
11 DR. APOSTOLAKIS:
But I don't know whether it's 12 conservative, is it?
13 MS. DIMITRIJEVIC:
If you look in the explanation 14 after, because if you assume that we are going to look in
()
15 every location and segment, if we assume that we're going to 16 have a thousand segments at the top of a plant, it's 17 ten-to-the-minus-two, which we think is a conservative 18 estimate.
Then ten-to-the-minus-two for pipe failure 19 frequency, times ten-to-the-minus-four, will give you 20 ten-to-the-minus-six CDF, which corresponds to that failure 21 for CDF.
22 MR. FLEMING:
So it was derived from a CDF limit 23 and working backwards to come up with a conservative 24 estimate of what that would mean.
25 DR. APOSTOLAKIS:
So if I don't do anything for a
(}
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year, then you say the NRC's goal of ten-to-the-minus-four
()
2 per year times one year becomes a probability.
3 MR. FLEMING:
No, no, no, no, no.
4 MS. DIMITRIJEVIC:
The frequency CCDP here is 5
conditional given pipe failure.
6 DR. APOSTOLAKIS:
I understand that.
That's why 7
I'm --
8 MS. DIMITRIJEVIC:
So we take the five FAC yearly 9
frequency and we say the worst we can have is five yearly 10 frequency of ten-to-the-minus-two if every segment is in the 11 high risk area.
12 DR. APOSTOLAKIS:
Okay.
13 MS. DIMITRIJEVIC:
And then ten-to-the-minus-two 14 per year times ten-to-the-minus-four is ten-to-the-minus-six 15 per year.
16 DR. APOSTOLAKIS:
But where did the 17 ten-to-the-minus-four come from?
That's my question.
18 MS. DIMITRIJEVIC:
Well, we selected that so that 19 we get that ten-to-the-minus-six per year.
20 DR. APOSTOLAKIS:
You selected it.
21 DR. SHACK:
Took ten-to-the-minus-six and divided 22 by ten-to-the-minus-two.
23 MS. DIMITRIJEVIC:
That's it.
We took the 24 ten-to-the-minus-six and divided it by ten --
25 DR. APOSTOLAKIS:
And they did it correctly.
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Where did the ten-to-the-minus-six come from?
()
2 MS. D1MITRIJEVIC:
That came from the NRC criteria 3
of ten-to-the-minus-six not allowing any changes and things 4
like this, Reg Guide 1.174.
5 MR. FLEMING:
Which we anticipated before it was 6
published.
7 MS. DIMITRIJEVIC:
It's very conservative because 8
that means they actually accept changes, but we still have a 9
medium region.
10 DR. APOSTOLAKIS:
So the delta CDF -- actually, it 11 ten-to-the-minus-six is negligible.
Ten-to-the-minus-five 12 was even allowed.
13 MS. DIMITRIJEVIC:
So that's why I say we are very 14 conservative, because of uncertainty, we said, okay, 15 everything which is ten-to-the-minus-six we're going to look 16 at, that's our basis.
And we say even in 17 ten-to-the-minus-six, we're still going to take a little 18 look.
19 DR. APOSTOLAKIS:
The report could have been 20 written a much better way.
I really tried to understand it 21 and, boy, every sentence is loaded with --
22 MS. DIMITRIJEVIC:
Meaning.
23 DR. APOSTOLAKIS:
With meaning, yes.
I mean, Carl 24 had to explain a few things, you had to explain a few 25 things.
Anyway, that makes sense.
What you just said makes O
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sense.
But it's not easy to understand that from this.
2 DR. WALLIS:
Are you suggesting a report in which
(
3 the sentences were loaded with less meaning would be better?
4 DR. APOSTOLAKIS:
Yes, because then you would have 5
more of those and it would be easier.
The total sum would 6
be the same.
7 If I have to spend three-quarters of an hour 8
understanding each sentence, that's a pretty thick report, 9
that doesn't help.
There was a whole rationale that Vesna 10 just gave us that is not evident from this paragraph.
11 That's what I'm saying.
12 DR. SHACK:
Right.
13 MR. MITMAN:
You wanted to ask additional 14 questions?
m 15 DR. APOSTOLAKIS:
Gee, now you're catching me.
16 Oh, yes.
A general question.
You used the word " easy" 17 earlier.
Now, I must say this business of the trains and 18 giving a worth of one-half and all that, why is that easier 19 from having your PRA, your PC, and saying, you know, put 20 this down, get the new number, 21 I mean, we have the software now that does these 22 calculations very quickly and get conditional core damage 23 frequencies.
And to go through this exercise of deciding 24 the worth of each train and going through -- in other words, 25 you are redoing part of the PRA.
What is the reason for i
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1 that?
()
2 MS. DIMITRIJEVIC:
I will tell you why it was 3
designed.
It was designed so that people who are not PRA 4
analysts can come up with --
5 DR. APOSTOLAKIS:
But they have to do PRA-type 6
analysis, Vesna, anyway, because they have to look for 7
trains that will save you.
8 MS. DIMITRIJEVIC:
That's true, but they have to 9
-- and they can be provided with them in the beginning and l
10 then they can do the analysis.
But if you really know PRA, 11 which can be done fast, if you know something --
12 DR. APOSTOLAKIS:
You don't really have to know 13 PRA, you don't have to be a PRA analyst to use it.
You have 14 your PC and you do your sensitivity calculations.
()
15 Otherwise, if you know nothing --
l 16 MS. DIMITRIJEVIC:
Let me give you two reasons to i
17 let you even forgetting that PRA, in my opinion, really 18 don't run them fast yet.
It always takes some time.
19 But independent of that, let me tell you what's 20 the main reason.
When you run the PRA, you come with a 21 number.
It gives you a number, but it doesn't tell you what 22 it is and why it.is.
l 23 When you look in this, you know exactly why and 24 what's happening and it really helps you to understand the l
25 heart of this.
We went in the heart of the PRA.
So they O
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know that this is -- if they have this pipe failure, that J
()
2 this is because they are HPSI is going to know how --
3 instead of getting the number three times putting 4
four-times-ten-to-the-minus-four.
I 5
We thought they would be more valuable for 6
analysts to understand why are some failures and the other 7
thing is also we have to rank the initiating events.
So we 8
can really use importance measures for that.
9 We thought that it will give more insight and will 10 help people who are not PRA analysts do this estimate.
11 DR. APOSTOLAKIS:
That's the right word.
- But, i
12 Vesna, I think you have a valid point there, that you 13 shouldn't really get a number alone.
But it seems to me you i
14 can easily get those insights from a good PRA, because a
()
15 good PRA doesn't give you numbers only.
16 MS. DIMITRIJEVIC:
You can look at sequences 17 DR. APOSTOLAKIS:
It gives you the sequences, the 18 minimal cut sets and so on.
19 MS. DIMITRIJEVIC:
Yes.
20 DR. APOSTOLAKIS:
And maybe you can develop a 21 small software package to compliment what you already have 22 to get these insights.
But this reluctance on the part of 23 the industry to say PRA is useful and we will do things 24 using the PRA is a mystery to me.
It's mystifying.
25 MS. DIMITRIJEVIC:
The one thing which I have to i
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say is the misconception that this method doesn't use PRA,
(
2 it uses it very well.
3 DR. APOSTOLAKIS:
Of course it does.
4 MS. DIMITRIJEVIC:
And uses it perfectly, in my 5
opinion, because it's break is what actually PRA is all 6
about and shows exactly.
So it shows the safety function, 7
it shows you backup trains, it shows you the sequences.
So 8
it's basically really uses PRA.
9 It doesn't use it as being -- it gives you the 10 importance measures and things like that, but that is what 11 PRA is all about.
So, therefore, PRA is very -- and I did a 12 lot of analysis.
You can believe me that this really makes 13 it very easy and clean-cut. You look in the PRA, you see 14 there the success criteria, you put the safety functions 15 diagrams, you look in there, the ability of the trains and 16 their initiating events and there you are.
17 Then you have ten pages and you can just run 18 through the events very nicely.
19 DR. APOSTOLAKIS:
Who did that?
Did a guy with no 20' experience with a PRA actually figure out what are the 21
. trains that are available and gave the weights?
22 MS. DIMITRIJEVIC:
No.
That was -- that's done 23 with the PRA specialist.
But once when you have them, 24 everybody can do the analysis.
25 DR. APOSTOLAKIS:
And this is an analysis you do O
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only once, right?
()
2 MS. DIMITRIJEVIC:
Yes.
3 DR. APOSTOLAKIS:
It could be done off-line by 4
somebody who knows something about the PRA.
It's not that 5
you are asking your average --
6 MS. DIMITRIJEVIC:
No.
7 DR. APOSTOLAKIS:
-- doing this every month.
8 MS. DIMITRIJEVIC:
It's always done with the 9
people who know PRA.
10 DR. APOSTOLAKIS:
I am really mystified by this 11 reluctance to say we now have the PRA, here is what you can 12 do with it, here is what you need for this kind of analysis, 13 here is a way to get it.
Instead of doing that, we're 14 saying we'll develop these mysterious tables, that give a
()
15 wroth of
.5.
I don't know how to do that.
16 MS. DIMITRIJEVIC:
Well, because we are working in 17 actually in the intervals, not with the actual number.
We 18 do have a section on --
19 DR. APOSTOLAKIS:
And I don't even know what the j
20 train is sometimes.
You're asking a poor guy to make all 21 these judgments when the PRA has already provided you with 22 answers.
I'm not saying that what you did was incorrect, 23 but I'm just mystified by this reluctance on the part of the 24 industry to say here is a tool that's useful, let's use it, 25 and not try to dance around it all the time.
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And, my god, if we ever demand a PRA, it's a major
()
2 crime.
3 MS. DIMITRIJEVIC:
We added it --
4 DR. APOSTOLAKIS:
I've made my case.
5 MS. DIMITRIJEVIC:
But we did it add it in our 6
report section 3.36, which tells you really how PRA --
7 DR. APOSTOLAKIS:
Page?
I always give you the 8
page.
9 MS. DIMITRIJEVIC:
Page 3.32.
10 DR. APOSTOLAKIS:
3.32.
11 MS. DIMITRIJEVIC:
Yes.
12 MR. FLEMING:
I want to just augment something, if 13 I may, on what Vesna just said.
I think there may be a 14 little bit of misunderstanding here.
()
15 It is the role of the PSA analyst to figure out i
16 these train relationships and that is only for a qualified 17 PRA analyst to do. But the idea here was to give the piping 18 engineer a tool that he could put segments on the risk 19 matrix without himself doing the PRA calculations to put 20 them on the matrix.
l 21 And since it didn't require him to come up with a 22 numerical estimate, just to figure out which of the bins to 23 put it in, which are four decades wide, there was a question 24 of whether you want to use a surgical instrument or a 25 screwdriver to do the appropriate tests, f' )
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DR. APOSTOLAKIS:
Well, all right.
2 DR. SEALE:
Can I ask a related question?
3 DR. APOSTOLAKIS:
Am I going to say no?
Go ahead.
4 DR. SEALE:
You have here an application of a PRA 5
and it's clear in coming up with your simplified algorithms 6'
that consciously or unconsciously, you're responding to the 7
fact that not all PRAs are equal.
There is another effort 8
going on, quite separate from this, that the Commission has 9
a commitment to, and that is the development of criteria for 10 what constitutes an adequate PRA.
11 I'm going to ask the staff.
Do you guys who find 12 these kinds of applications for PRAs talk to those guys who 13 are worried about what constitutes an adequate PRA?
14 MR. DINSMORE:
This is Steve Dinsmore.
15 DR. SEALE:
You've got your hat in both rings.
16 But you see the question.
I mean, clearly, there are other 17 applications like this where people are using PRAs and there 18 is not necessarily that nexus made to this other effort, 19 which is supposedly graduating the level of the PRA, the 20 product, to what we would hope would be the workable all 21 things for all people version.
It's just a caution.
22 MR. DINSMORE:
Okay.
23 DR. APOSTOLAKIS:
Mr. Fleming, by the way, is 24 intimately involved with that effort.
25 DR. SEALE:
Okay, fine.
Fine.
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DR. APOSTOLAKIS:
But it's a more general comment
()
2 that I wanted to make.
Every time we see something, for 3
heavens sake, let's not ask them to use a PRA.
So we go out 4
of our way to produce tables and things, like the five 5
methodology, again, PRA, my god, no tables.
People are not 6
stupid and finally --
7 DR. SEALE:
You only get there, though, if you 8
make the effort.
9 MR. MITMAN:
Another thing to keep in mind is this 10 methodology was started back in '92 '93 and the capabilities 11 of the machines and the capabilities of the codes and the 12 PRAs isn't what it is today.
And if we started today, we 13 might do it differently.
14 DR. APOSTOLAKIS:
Or you wouldn't do it at all,
[
\\
15 based on your conclusions.
If somebody took 16 defense-in-depth away, you wouldn't do it at all.
17 MR. MITMAN-We would discuss it with the 18 appropriate industry --
19 DR. APOSTOLAKIS:
I understand that, yes.
20 MR. MITMAN:
-- bodies and see what we would come 21 up with.
22 As we were saying at slide 14.
Slide 14 shows 23 some of the damage mechanism attributes that we use to 24 determine whether a weld segment is susceptible to those 25 damage mechanisms.
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What we're looking at here is thermal fatigue and (m) 2 some of those damage mechanisms that are there.
3 Deterministic rules that we apply to determine whether the 4
segments are susceptible or not.
5 DR. WALLIS:
I was looking at the bottom there.
6 You don't often inject cold fluid in the hot pipes, so in 7
infrequent even which will lead to fatigue, but there are 8
sometimes situations where cold is somewhere close to hot 9
and there are circulation patterns set up which are unstable 10 and a piece of piping is bathed in hot, cold, hot, cold, 11 over a long period of time, and that's a classical thermal 12 fatigue mechanisms.
I don't see it here.
13 MR. RICCARDELLA:
That's what we call tasks.
14 DR. WALLIS:
That's what you call tasks?
)
15 MR. RICCARDELLA:
Yes.
Tasks is thermal --
16 DR. WALLIS:
Maybe I didn't -- okay.
17 MR. RICCARDELLA:
-- and stratification --
18 DR. WALLIS:
It's rather hard to figure out, as I 19 remember, and sometimes it happens, sometimes it doesn't.
20 MR. RICCARDELLA:
But we've looked -- EPRI has 21 done a very, very large study on tasks.
They had a task 22 force to put together a large thick report, and we've gone 23 through that and we've attempted to come up with some 24 conservative rules that if you have any of these conditions, I
25 we say it's susceptible to thermal fatigue.
All of these i
O\\
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are very conservative.
)
s~~
)
(
2 It's not often that a delta T of 200 or 150 is
(
)
3 going to cause you a problem.
But if there is even the i
4 potential that a system could get a delta of that much, we 5
say it's potentially thermal fatigue susceptible.
6 Now, we could go in with a finer screen, and 7
sometimes we do.
It's no good to prioritize if everything 8
comes out.
So if we get too many locations, then we'll go 9
in with a finer screen and find out what the actual delta T 10 is.
11 DR. WALLIS:
So this is a case where one could 12 call understanding of the thermal hydraulics is important to 13 risk assessment.
14 MR. RICCARDELLA:
To selecting in-service
()
15 inspection locations.
16 DR. SHACK:
Whether that's important to the risk 17 assessment is another question.
18 DR. WALLIS:
Well, presumably it is.
If you don't 19
-- if there is some physical mechanism which you completely 20 ignored which can break a pipe, then it can seem that that's 21 important to the risk and whether you assess it or not is 22 perhaps up to you as a responsible professional.
)
23 MR. RICCARDELLA:
Yes.
Well, part of what you're 24 getting at is the reason for this performance monitoring 25 feedback loop; that if there is some mechanism that we've
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1 just forgotten about or didn't know about and it occurs in
()
2 one plant, then it's going to work its way into our 3
methodology and will-be picked up.
4 MR. MITMAN:
The outcome of the damage mechanism 5
assessment is categorization into three categories, high, 6
medium and low.
Where we end up is to get into high, you 7
have to have flow accelerated corrosion.
Medium is any 8
other damage mechanism and if there are no damage mechanisms 9
present, then that gets you into low.
10 Now, there is one caveat with this.
It doesn't 11 show on this slide.
It's discussed in the report.
That is, 12 there is another way to get into the high category, which 13 came up in earlier discussions, and that is if you have 14 another damage mechanism, plus water hammer.
(
15 So if you've got some degradation of a pipe due to 16 MIC and you know that the system is subject to -- is 17 susceptible to water hammer, that would also put you into 18 the high category.
19 In practice, what we see happening most of the 20 times is if a system is susceptible to water hammer, most 21 plants will go out and try and resolve the question on water 22 hammer, which would drop it back down into the medium 23 category.
24 DR. SHACK:
I would assume that water hammer would 25
-- if it's susceptible to water hammer, it's high, O
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degradation or no degradation mechanism.
()
2 MR. MITMAN:
It would be high, but you can inspect 3
all you want with volumetric inspections and you're not 4
going to find water hammer.
5 DR. SEALE:
Okay.
These are for leaks then.
6 MR. MITMAN:
This is leak --
7 DR. SEALE:
For inspection, I beg your pardon.
8 MR. MITMAN:
The whole methodology is to help you 9
decide where to do your volumetric inspections per Section 10 11.
11 DR. SEALE:
So in general, that's why load-induced 12 failures don't show up here.
13 MR. MITMAN-That's right.
14 DR. SHACK:
We were scheduled for a break at ten
()
15 and since we're about to go to the consequence, maybe this 16 is a good time to do it.
Does that seem reasonable?
17 MR. MITMAN:
That sounds reasonable.
18 DR. SHACK:
A 15-minute break then.
19
[ Recess.]
20 DR. SHACK:
I guess we have enough members back, 21 so that we can resume the meeting.
22 MR. MITMAN Okay.
We want to start in on the 23 consequence analysis at this point.
The first thing we do 24 is there are four types of -- four considerations that we 25 have when we go into the consequence analysis.
We're I~\\
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looking at initiating events, events that affect the
()
2 mitigating ability of systems and trains, both from a loss 3
of the system or train or degradation of the system or the 4
train.
5 We're looking at containment effects, both loss 6
and degradation of containment, and then we also look at 7
combination events, something that will affect both a 8
mitigating system and containment or could be initiating 9
event and affect a standby safety system also.
10 We've seen this slide already.
The consequence 31 ranking is -- there is a four-tier consequence ranking, 12 high, medium, low, and not shown here is none.
There is --
13 none is the easiest to deal with.
There are a couple of 14 abandoned in-place piping systems that we've found here and
)
15 there that have no consequence whatsoever on the analysis, 16 and that's why they show up on the matrix.
17 The high category is conditional core damage 18 probability greater than le-to-the-minus-four and 19 conditional large early release probability of greater than 20 le-to-the-minus-five.
21 These are severe initiating events or severe loss 22 of mitigation capability or high risk of containment bypass.
23 Medium category is conditional core damage probability, 24 greater -- greater than le-to-the-minus-six, but less than 25 le-to-the-minus-four.
It should be less than or equal to.
()
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Also, conditional large early release probability
()
2 between le-to-the-minus-seven and le-to-the-minus-five, and 3
these are moderate type events.
4 Then on the low side is conditional core damage 5
probability less than le-to-the-minus-six and conditional 6
large early release probably less than 7
le-to-the-minus-seven.
8 These are for mild type events.
9 DR. SHACK:
Again, I guess I asked this question 10 before, I mean, you -- when I look at this guideline for 11 assigning the consequence category, there is some sort of 12 generic PRA that decides that when I have one unaffected 13 backup train, that I'm in the 14 ten-to-the-minus-four/ ten-to-the-minus-five categ' r,
and 15' it's high.
16 The guy doesn't actually do that calcul& tion.
l 17 MR. MITMAN:
Initially, it's generic.
The tables i
18 were set up generically, but the expectation is that the 19 plant will recalibrate those tables with the plant-specific 20 PRA.
21 DR. SHACK:
And they will bend it this way, then.
22 MR. MITMAN:
This is the criteria for bending it 23 and you may -- if you go to South Texas, with a three-train 24 system, you'll probably move everything to the --
25 MS. DIMITRIJEVIC:
Medium.
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MR. MITMAN-Yes.
Everything will drop down to
[Jl 2
medium in: stead of having it in the high category.
But, yes, 3
you do that plant-specific calibration.
4 DR. SHACK:
What it could mean is that for some 5
plants with one and a half backup trains, you could be in 6
the medium instead of the high for some very plant-specific 7
reason.
8 MR. MITMAN:
Yes.
You could have some 9
susceptibilities or come weaknesses in the plant design.
10 MS. DIMITRIJEVIC:
You could have a different 11 number of backup trains and the load would be different.
12 MR. DINSMORE:
This is Steve Dinsmore, from the 13 staff.
Our understanding is that the table won't change, 14 because we're going to be moving the table.
What will A( y) 15 change is the number of trains that they can take credit 16 for.
17 If they have two HPSI trains, but, again, if it 18 was ten-to-the-minus-three, in one plant, they can only 19 credit one and a half trains.
In another plant, maybe 20 because it's better designed, they'd be able to credit it 21 two trains.
22 DR. SHACK:
So the table stays the same.
23 MS. DIMITRIJEVIC:
The same.
24 DR. SHACK:
It's how you credit --
25 MR. MITMAN.
The number of trains.
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DR. SHACK:
-- the number of trains.
()
2 MR. MITMAN:
The remaining tasks in the 3
methodology, we'll go in and do segment risk categorization, 4
selection of inspection locations, selection of the 5
appropriate inspection techniques.
We do a risk impact i
6 assessment.
We document and finalize the project, put 7
together the submittal, and then there is a performance 8
monitoring where we have a long-term process to monitor the 9
plant and also EPRI will continue to monitor the industry to 10 make sure that there is no new mechanism that appears or an 11 increase in the frequency of a degradation mechanism because 12 of aging effects that we haven't seen yet.
13 DR. SHACK:
Now, one of the things that the WOG 14 ASME thing does that doesn't seem to come in here is they h
15 make an effort to estimate the leakage, also, as well as the 16 failure, and their goal was essentially to maintain the 17 leakage rates about what they've observed.
18 That doesn't seem to be -- that's nothing you're 19 addressing here.
20 MR. MITMAN:
We are not trying to calculate any 21 leakage rate.
What we essentially see, if you go back and 22 look at the risk matrix, the medium category tends to be 23 those damage mechanisms, medium category here tends to be 24 those damage mechanisms that typically leak.
25 The only way you're going to get into -- or ANN RILEY & ASSOCIATES, LTD.
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getting into high, you tend to have a damage mechanism that
()
2 can fail on your, can have a large rupture.
So that's 3
probably the only place that the leakage rate figures into 4
the analysis.
But we're not trying to --
5 DR. SHACK:
You don't have a target leak rate for 6
7 MR. MITMAN:
No.
8 DR. SHACK:
In a general sense, who ends up with 9
more inspection locations following which process?
10 MR. MITMAN:
I think we end up with --
11 DR. SHACK:
With more.
12 MR. MITMAN-No.
We end up about the same.
About 13 the same.
14 MS. DIMITRIJEVIC:
We don't really know.
()
15 MR. MITMAN:
Well, we've looked a little bit at 16 Surry, comparing Surry to the work we've done, and I think 17 if you look at what's done on Surry and what's done on --
18 what's coming out of the ANO-2 analysis and the Fitzpatrick 19 analysis, that they're approximately the same order of i
1 20 magnitude of inspections.
21 MR. ALI:
This is Syed Ali from the staff.
Just 22 to clarify.
Although the comparison is really not valid 23 because one is a PWR, Surry is a PWR, and some of the ones 24 you have done are BWR.
But for Class I, this methodology, 25 the EPRI methodology, the sample size went down from 25
( '/}
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percent in ASME-11 to about ten percent, whereas the
[v) 2 Westinghouse methodology is about six and a half or seven 3
percent.
So that's the order of magnitude difference.
4 MR. MITMAN:
Okay.
The next step in the 5
methodology is to do the risk evaluation.
At this point, we 6
have completed the degradation analysis and the conditional 7
-- or the consequence evaluation and that allows us to bend 8
the segments into the appropriate boxes on the matrix.
9 DR. SHACK:
Another question.
You're also 10 building 0313 into this also, aren't you?
In the sense that 11 that's how you bend things into high, medium and low.
12 MR. MITMAN:
At this point, 0313 is -- we're only 13 building in the category A 0313 welds for IGSCC.
We feel 14 and it's part of the evaluation that's going on now with
)
15 BWRs that with a category A weld, that we can justify that 16 we need no additional inspection beyond what the 17 risk-informed process is requesting.
18 Now, there is a dialogue, a discussion and some 19 analysis going on in the industry to revisit 0313 and that's 20 not part of the methodology right now.
However, the 21 methodology is set up so that if and when that happens, 22 we'll be able to take advantage of it.
23 One of the big concerns that we've addressed in 24 the last year or so was to take a harder look at the risk 25 impact of the analysis and that's -- well, once we've done ON ANN RILEY & ASSOCIATES, LTD.
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the element, the risk-ranking and we go out and do element (Gj 2
selection and then we go ahead and look at inspection for 3
cause and decide what methodology should be looked at in the 4
various segments.
5 One of the questions that was asked earlier in the 6
discussion that we have deferred was what do you do with the
{
7 segments in the low categories and the methodology calls for 8
no inspections in those low risk regions.
I f
9 You should keep in mind here that that's not to 10 say we're not doing any inspections on the systems.
We l
11 continue to do inspections in the medium and the high risk 12 regions of those systems and we haven't found any systems t
13 yet where we're recommending doing no inspection.
14 In addition to that, we continue to do the 15 augmented inspection for FAC, IGSCC and whatnot.
So it's 16 not like we're walking away from large segments of the plant 17 and not performing any assessments for those.
18 DR. SHACK:
And, again, you're doing leak tests.
19 Everything but volumetric inspection.
20 MR. MITMAN:
And we continue to do leak tests on 21 all Class I, II and III.
22 MR. RICCARDELLA:
Another aspect of that, too, is 23 if you look at the lower right-hand corner, things with low 24 or essentially no degradation mechanism identified, we still 25 are inspecting some subset of those, because some of them do O
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fall over into the medium category.
()
2 If they have a high failure consequence potential, 3
then they do get a medium and we see that we do a lot of 4
category four -- there are category four inspections.
So j
5 it's not like we're ignoring things just because we haven't 6
identified any mechanism.
7 MR. MITMAN:
Now, in the earlier -- in the 8
beginning slides, we talked about the two code cases that 9
apply here, N-560 for Class I only and N-578, which applies I
10 to the full plant.
This is the one place where we come up 11 with a slight distinction between how you select welds and 12 elements between the two code cases.
13 In N-578, we do 25 percent of the high risk 14 category elements.
In the medium risk category, we do ten
)
15 percent.
In the low, we do none, no volumetric inspections 16 In N-560, we start at the category one, category 17 here, and start going and applying welds, looking at welds 18 and adding them to our list.
But when we get approximately 19 to ten percent, then we'll pull up and stop.
20 In practice, what we see is we don't do all the 21 high category welds.
We do -- for instance, if we have a 22 BWR with four steam lines and we have four welds on each of 23 the steam lines, we might take half of those welds, so we 24 capture representative inspections for all of the steam 25 lines and then save some of those other inspections for O
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other places in the Class I system, so that we get a more I~'i 2
V representative and a better, broader perspective of what's 3
happening in the Class I system.
4 DR. SHACK:
Now, the description in the report 5
actually says it's considered more prudent, but there is 6
nothing that says you have to do it that way.
7 MR. MITMAN:
To do it?
8 DR. SHACK:
To split your ten percent.
9 MR. MITMAN:
It's a very strong recommendation.
10 To date, EPRI has been involved with all the applications of 11 this methodology and we very carefully ensure that it's not 12 being misapplied.
13 DR. SHACK:
Why isn't there just a step that says 14 do some of them, 25 percent?
()
15 MR. MITMAN:
Didn't want to get too prescriptive, 16 wanted to be able to use engineering judgment and a little 17 bit of flexibility to decide exactly where to get those ten 18 percent.
19 Pat, you wanted to add something?
20 MR. O'REGAN:
Pat O'Regan, EPRI.
One of the 21 reasons we didn't want to be too prescriptive is there are 22 other considerations that go in when you select locations, 23 such as high rad areas and accessibility and stuff like 24 that.
We wanted to make sure that still carried weight when 25 we went through the element selection process.
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MR. MITMAN:
One of the last steps we do is to do I~D 2
a risk impact assessment.
The process itself was designed O
3 as a risk-informed process.
So there are risk 4
considerations taken into account from the beginning.
The 5
risk impacts are -- we see risk impacts in three areas.
6 Allocation of inspections at the high risk 7
locations, we have inspection for cause impacts, and we have 8
impacts from elimination of inspections in the low risk 9
segments.
10 The risk assessment process is a three-tiered 11 process, essentially.
Initially, we want to eliminate as 12 much quantitative analysis as is appropriate and we bring to 13 bear some qualitative tools to do that.
14 If we have regions that are -- if we have low risk O
15 regions, we can qualitatively show that it has no impact on qj 16
-- no unacceptable impact on risk.
If we're doing -- if 17 we're increasing the number of inspections, we can 18 qualitatively show that we have a positive or an improvement 19 in the risk consequences.
20 So first of all, if we want to do the qualitative 21 analysis, and we can do that in most cases.
Where we can't, 22 we want to go ahead and apply some bounding estimates to 23 help us decide that the risk impacts are acceptable.
If the 24 bounding estimates are not sufficient, then we bring to bear 25 realistic quantitative analysis to help us assure ourselves
/
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that we're having appropriate impact on risk
()
2 DR. SHACK:
It seemed to me that it was almost a 3
"gimme" if I believed your -- that 4
one-times-ten-to-the-minus-four was really a bounding CCDP 5
for a medium risk thing, that I was almost set up to get a 6
controllable delta C-P, because I'm looking at the important 7
stuff and I'm neglecting the unimportant stuff, and I'm just 8
going to get the' answer to come out.
9 I guess the question is, can I really be confident 10 that the one-times-ten-to-the-minus-four is a bounding CCDP 11 for a guy with a medium classification, a two-train system 12 with anticipated transients 13 MR. MITMAN:
I think so, yes.
14 DR. SHACK:
For all plants?
I guess that's the
()
15 part'I have a little trouble with.
16 MS. DIMITRIJEVIC:
What's plant-specific is -- you 17 want to --
18 DR. SHACK:
For the plant-specific part is how I 19 credit the two trains.
20 MS. DIMITRIJEVIC:
How many trains you have, yes.
21 Yes.
22 DR. SHACK:
And so I guess the answer is if I have 23 two credited trains, am I always guaranteed that 24 one-times-ten-to-the-minus-four is a bounding estimate.
25 MS. DIMITRIJEVIC:
You're going to be -- yes.
You O
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could be a little -- I mean, we cannot really guarantee
(, ~')
2 always, because sometimes it happens that you're 1.1 because L/
3 of these estimates, ten-to-the-minus-four or something in 4
the medium.
But you are very inside this.
It is not going 5
to be higher than Se-minus-four.
6 DR. SHACK:
Guarantee is a strong word to use in a 7
PRA, right?
8 MS. DIMITRIJEVIC:
That's true.
The best of our 9
knowledge.
The best of our knowledge, yes.
10 MR. MITMAN Pat, you want to add something?
11 MR. O'REGAN:
Yes.
Maybe a point of 12 clarification.
Pat O'Regan, from EPRI.
The methodology is 13 set up that if you assign to medium, you'll always be less t
14 than ten-to-the-minus-four.
If you have two trains in the
,r3
(
)
15 plant, there is no guarantee that you'll always be a medium.
16 DR. SHACK:
If I have two qualified trains and the 17 matrix is approved, then I'm going to be a medium.
18 MR. O'REGAN:
If you have two qualified trains, 19 that's true.
20 MS. DIMITRIJEVIC:
Yes.
21 MR. O'REGAN:
But if you bave two turbine-driven 22 pumps, that may not goalify.
23 DR. SHACK:
That's different, right.
24 MR. O'REGAN:
So you may be a high.
But the 25 criteria always is set -- the criteria is set in stone.
()
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It's just a question of whether the plant could meet the
()
2 criteria or not.
3 MR. MITMAN:
One of the discussions earlier today 4
was a discussion about questions about supporting 5
documentation and where more of the analysis is shown.
6 These are most of the published reports that we've published 7
to date on the methodology.
Most of those are proprietary 8
reports, but we can make the necessary -- we can make them 9
available for the ACRS to look at.
10 MR. FLEMING:
I wanted to reflect back on the last 11 question.
With regard to the potential issue about how 12 robust are these conclusions, the battle lines for this 13 argument really are down at the boundary between medium and 14 low, because the way in which we do our delta risk O(,/
15 evaluations, we entertain the need to do some quantitative 16 bounding estimates if we're in the medium or high risk 1
17 regions and we're suggesting a reduction in the number of 18 locations that are eliminated.
19 So the question about robustness really gets down 20 to between the medium and low region.
That's where the 21 potential issue would exist and at that level, we're another 22 two orders of magnitude down the risk scale.
23 MS. DIMITRIJEVIC:
And an ideal medium region is 24 to escape those boundaries.
This is why we introduced this 25 medium region.
So we don't have to have a clear cut between
\\
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high and low.
()
2 MR. FLEMING:
So what I'm saying is that if, for 3
example, for some error or uncertainty in analysis that a l
l 4
category that belonged in the high region was miscategorized i
5 in the medium region, our delta risk procedure would still i
6 catch that, because if we ended up in this hypothetical 7
location suggesting a reduction in the nunter of locations, j
8 and, therefore, there's a potential risk increase', we would 9
go and do a calculation where we actually go in and do a 10 bounding estimate that would more than cover that 11 uncertainty.
12 DR. SHACK:
Is that clear to me where I have to do 13 the -- that was the point I couldn't quite figure out, is 14 when you had to do the quantification.
There's the
()
15 qualitative estimate and the quantitative.
16 MR. FLEMING:
For any medium or high risk region 17 in which -- or segment in which we're actually suggesting a 18 reduction in the number of locations, we would come in and 19 do bounding estimates.
So we're only relying on the 20 qualitative arguments for the low risk category components.
21 So the robustness issue associated with how we put 22 the things on the matrix really is the -- the central 23 question is have we gotten the lows correct.
The low-medium 24 issue is more important than the high issue.
25 MR. MITMAN:
The second to the last slide that I I'
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have shows some results from the pilot studies.
We're
()
2 showing the number of inspections that were done under the 3
current ASME Section 11 requirements and the number of 4
inspections that we're proposing have been approved by SERs 5
for the pilot plants.
6 What we see is in the high risk regions, we have 7
some increases in the number of inspections, some decreases, 8
but essentially about the same number of inspections.
9 For the medium risk regions, we show usually a 10 decrease in the number of inspections.
The one exception to 11 that is on ANO-2, we were actually showing an increase in 12 the medium risks.
Then in the low risk regions, we're 13 showing a decrease in the number of volumetric inspections.
14 DR. SEALE:
A couple of questions.
First of all,
()
15 what percentage of the sites that wind up in the high i
16 category are actually identified for an inspection, in the 17 medium?
18 MS. DIMITRIJEVIC:
In high?
19 DR. SEALE:
What fraction of the highs --
20 MS. DIMITRIJEVIC:
Twenty-five percent.
21 DR. SEALE:
-- are -- what fraction of the ones 22 that are qualified as high actually wind up candidates for 23 inspection?
24 MS. DIMITRIJEVIC:
Twenty-five percent.
25 DR. SEALE:
Okay.
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MS. DIMITRIJEVIC:
Twenty-five and ten percent,
()
2 and that's for the full scope.
3 DR. SEALE:
For the full scope.
4 MS. DIMITRIJEVIC:
Yes.
5 DR. SEALE:
What about when you do it with your 6
CI-1, Class I?
7 MS. DIMITRIJEVIC:
Class I, we select ten percent 8
total and most of them are from high risk.
9 MR. RICCARDELLA:
It comes out to be about 25 10 percent of the high risk.
11 MS. DIMITRIJEVIC:
The same.
12 MR. RICCARDELLA:
It's just the way the numbers 13 work out.
And all three of these examples, it's essentially 14
-- in fact --
()
15 DR. SEALE:
Old Arkansas-2 really inspects the 16 devil out of things, don't they?
17 DR. SHACK:
Just a question on Vermont Yankee.
18 What is their IGSCC fix?
Have they replaced piping?
19 MR. RICCARDELLA:
Vermont Yankee replaced piping.
20 DR. SHACK:
So basically all their recirc piping 21 is Class A then.
22 MR. RICCARDELLA:
Yes.
23 MR. MITMAN:
We did put together a backup slide 24 that you do not have and it is not in the report that shows 25 comparisons between what we end up with or what we would end O
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up with if we did -- depending if we did an N-578 or an
[~ )\\
2 N-560 analysis.
These are all --
3 MS. DIMITRIJEVIC:
N-578 selection criteria.
4 MR. MITMAN:
And this is for Class I only.
5 MS. DIMITRIJEVIC:
This is just for Class I.
It 6
shows you that actually when you apply N-578 criterion to 7
Class I, you always are around ten percent total.
You are 1
8 either 9.4, 10.6, 13 or 9.8.
So basically even if you use 9
again 578 criteria on Class I, because of the division 10 between high and medium categories, then it's around ten 11 percent of total, which is the same as N-560 criteria.
12 And we keep that in mind with this percentage and 13 we were not surprised at that.
14 DR. BONACA:
I have a question.
Maybe I should
()
15 ask the NRC.
But if I look at the whole logic, you have 16 some high degradation category, piping in the high 17 degradation category, with no consequence.
For those, 18 essentially, you're recommending elimination of inspection 19 in many cases.
20 MS. DIMITRIJEVIC:
Actually, ten percent of 21 inspection in medium.
22 MR. MITMAN:
No.
You're over-hearing the none.
23 MS. DIMITRIJEVIC:
None.
Are you saying low or 24 none?
25 DR. BONACA:
None.
Just taking an extreme case.
Q(_/
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That tells me that you are going to have failures at some
()
2 point of some of the piping.
3 MR. MITMAN:
The only thing that we've seen 4
' categorized with no consequence are those abandoned in place 5
piping.
6 MS. DIMITRIJEVIC:
So we never saw high 7
degradation in none.
8 MR. MITMAN:
Now, if you have low consequence, 9
which could be extremely low, le-to-the-minus-ten or 10 whatever, we're still bending that in a medium risk 11 category.
12 DR. BONACA:
And that is fine.
I just was worried 13 more about the corner, because simply you're going to see 14 more failure.
From a regulatory standpoint, a utility that
()
15 commits t this program and then has failures in the field, 16 you get a black eye anyway ultimately.
17 So I understand now that that box on the top left 18 corner is not really one that should be of concern.
19 MR. MITMAN:
If we started to see a lot of pipe 20 segments falling into that segment, we'd have to ask a lot 21 of questions about whether that's appropriate or whether we 22 should take a harder look at it.
23 DR. BONACA:
Because although you have -- from a 24 risk standpoint, it's fully convincing to me that there are 25 other issues that have to do with how do you deal with 1
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actual failures there and how are they classified and is it
[d\\
2 part of corrective action programs and how is that going to 3
fit back into the adequacy of a program of this nature that 4
you implement.
5 It will raise all kinds of issues within a power i
6 plant if you begin to have those kind of failures.
7 MR. RICCARDELLA:
I know for the Class I programs, 8
which is most of the pilot studies we did, nothing has ever 9
fallen in that category.
Every Class I -- all the Class I 10 piping has either low, medium or high failure consequence.
11 MR. MITMAN:
Carl?
12 MR. FLEMING:
Carl Fleming, from ERIN.
With 13 regard to the earlier discussion we had about the insights 14 from service experience and the different kinds of loading
()
15 mechanisms and degradation mechanisms responsible for 16 service data, those insights are responsible for both leaks 17 and ruptures.
18 So the concern that reducing volumetric 19 inspections might result in an increase in the frequency of 20 leaks in piping does not seem to be supported by the 21 insights from in-service data.
It indicates that they'll 22 probably occur at about the same rate as we're seeing now, 23 because they're due to mechanisms that are just not being 24 captured by the inspection process.
25 DR. BONACA:
Thank you.
[
}
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MR. MITMAN:
My summary and concluding slide.
The
()
2 revised topical has been submitted recently.
It addresses 3
questions and concerns, lessons learned that we've learned 4
along the way in the application of the pilot process, the 5
methodologies and compliance with Reg Guide 1.174 and Reg 6
Guide 1.178.
7 The methodology has been applied to a diverse and 8
extensive group of plants, GE BWRs, Westinghouse, B&W, and 9
CE PWRs, multiple AEs, and both full and partial scope, 10 So we've got a very broad, diverse, I think a very 11 good distribution of the pilots and there has been a lot of 12 feedback into the methodology from that.
We are seeing 13 significant rem reductions out of the application and the 14 pilots and research support the conclusions of negligible
()
15 risk impacts by application of the methodology.
16 DR. SEALE:
You mentioned earlier that you had a 1
17 process by which you did some follow-up to find out if there I
18 are any changes or wild trends that might show up in the 19 results of the application of this.
20 Is there any systematics to that follow-up and if I
21 so, what are they?
22 MR. MITMAN.
The final step in the process is this 23 performance monitoring that hangs out to the side here on 24 the_ feedback loop.
EPRI has been doing database analysis.
25 We continue to watch the industry and the LERs and the O
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reports from the industry.
That's all part of the process.
()
2 The pro est really isn't formalized at this point, but it's 3
there.
4 There is a discussion about setting up something 5
that might be equivalent to a user's group that would be j
6 also fed into the monitoring process and we're also 7
expecting each individual plant that applies the methodology 8
to watch what's happening in their plant and in the industry 9
and to go back and revise, change, correct their own 10 application of the methodology.
11 DR. SEALE:
I noticed you mentioned that the 12 owners groups for the different vendors have been 13 participants.
14 MR. MITMAN:
Well, the CE owners group has not, D)
(
15 per se, been part of this.
The vast majority of the CE 16 plants have been part of an EPRI tailored collaboration, but 17 not, per se, the CE owners group.
18 DR. SEALE:
Okay.
But in the other cases, the 19 owners groups may have their own impromptu groupings or 20 reviews, as well, I guess.
21 MR. MITMAN:
Obviously, Westinghouse and the WOG 22 have their own methodology and their own process there.
23 There is no discussion at this point with either the BWR 24 owners group or the B&W owners group about having any kind 25 of feedback loop between the owners groups and EPRI.
There h(_/
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is -- it's on a plant by plant basis.
I~'\\
2 That's all I had.
V 3
DR. SHACK:
Any more questions?
They're not 4
scheduled to start until 11:15.
Can we go ahead with them?
5 MR. MARKLEY:
Yes, we can.
We're not changing 6
subject here.
So that's fine.
7 DR. SHACK:
Thank you.
8 MR. ALI:
My name is Syed Ali, I am from the 9
Division of Engineering in NRR.
With me is Steve Dinsmore, 10 who is from the Division of DSSA in NRR.
11 What we are going to try to do in the short time 12 that we have is to basically give an overview of the status 13 of the review of the topical report and also the associated 14 pilot plants, and a little bit of the changes that EPRI has
()
15 made in their topical report since we approved some of their 16 pilots.
17 Some of these items EPRI may have already 18 discussed this morning or may have been discussed as a 19 result of questions or just to complete the picture, we will 20 go over the status of what we have done so far, again.
21 EPRI submitted its draft topical report back in 22
'96.
At that time, we were also in the process of 23 developing the regulatory guide and the standard review plan 24 for the risk-informed ISI.
25 We issued some questions and requests for ANN RILEY & ASSOCIATES, LTD.
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additional information the middle of
'97.
Subsequent to
}
2 that, EPRI was involved in developing the pilot applications 3
and submitting the pilots, so their priority was more toward 4
the pilot submittals. So they came back with their responses 5
to the RAIs and the questions and comments that we had sent 6
near the end of last year.
7 That was also about the time that we had finished 8
basically the regulatory guide and the standard review plan 9
and also some of the pilots.
So they were able to utilize 10 the lessons learned not only from the pilot study they had j
11 done, but also from the regulatory documents that we had 12 issued.
13 I think since then, this process has picked up and 14 our interface with EPRI has become much more significant.
()
15 We had a meeting back in March to discuss the responses and 16 there were a few additional issue.
EPRI responded to those 17 additional issues and then submitted their current report or 18 their new version of the topical report 11267, which is the 19 one that you are reviewing and that we have been reviewing.
i 1
20 Those are the items that have been completed.
We 21 are having the ACRS subcommittee meeting today.
We intend 22 to have a follow-up meeting with EPRI sometime in July.
23 In addition to that, since right now we are 24 actively reviewing the EPRI report and some of their backup 25 reports, we have a weekly telephone sort of update as to the
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issues and the items that are ongoing.
)
2 We plan another meeting or another presentation to t
3 ACRS in their September meeting and that's when we will be 4
able to present our SER.
One thing that you see different S
here is that since the ACRS meeting is in September, we 6
think that we will be able to issue the final report by the 7
end of October and not the end of September, as you saw in 8
some of the EPRI slides.
9 That schedule was based on having an ACRS 10 presentation in August, which is not on schedule at this 11 time.
12 DR. SHACK:
Are you still going to have a draft 13 SER in June?
14 MR. ALI:
We still plan to have a draft SER in
(
15 June.
So we should be able to give you a draft SER.
- Now, 16 whether that draft SER will be a clean SER in the sense that 17 it may have some open items, we don't know.
But probably it 18 will have some open items, but we will have a draft SER.
19 If we proceed the same way that we did with the 20 Westinghouse, then we will probably have a draft SER with 21 maybe a few open items and then have the meeting with EPRI 22 to try to resolve those open items and then have a final SER 23 by the time you have your September meeting.
24 The next slide was just a listing of the pilots.
25 EPRI talked about those already.
Also, we have completed t
(~)
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two pilots, Vermont Yankee, which is a GE BWR, and on that 2
it was applied only to Class I utilizing the code case 3
N-560.
We have also completed the review of ANO-1 Unit 2, 4'
which is a CE PWR, and we are currently reviewing the 5
submittal for ANO Unit 1.
6 DR. SHACK:
Now, those two pilots, the application 7
basically followe'd this topical, although this topical 8
didn't show up until April.
9 MR. ALI:
It followed the topical that they 10 initially submitted.
11 DR. SHACK:
The old topical.
12 MR. ALI:
Old topical, but then there were 13 additional things done as a result of that review.
So a lot 14 of that is reflected in the changes that were made in this 15 topical.
16 So basically this topical utilizes the changes or 17 the lessons learned from the pilot applications and also 18 from the reg guide-and the standard review plan that we 19 issued that was subsequently the first topical report.
20 MR. MITMAN:
This is Jeff Mitman from EPRI.
Both 21 the pilot plants that have been completed, Vermont Yankee 22 and ANO Unit 2, are consistent with the new topical that you 23 have in front of you.
There is nothing that they have done 24 in those pilot plants that is different than what we have 25 proposed in the revised topical.
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MR. DINSMORE:
This is Steve Dinsmore, from the
()
2 staff.
There are more things in the topical than were 3
approved in the pilot plants and I think the next two 4
slides, we're going to go through the differences between 5
what was approved and what's in the current topical.
So 6
there are some differences.
7 MR. ALI:
What we're going to go through are some i
l 8
of the major changes in the topical report rather than l
9 detailed item by item changes subsequent to the approval of 10 the pilots.
11 One change, I would say, an updating of the 12 topical report, is that in looking at the first version of 13 the EPRI topical report and also some of the discussions we 14 had and the questions we had been sending, it was not clear (O,)
15 as to how the augmented programs are integrated with the 16 risk-informed ISI process.
17 So one thing that they have done in this topical 18 report is to clarify as to which of the augmented programs j
19 are, at this point, part of the risk-informed ISI process 20 and which of the augmented programs are still being looked 21 at as the way the licensees had made commitments to the NRC 22 as a result of the degradations found either on an industry 23 basis or on a plant-specific basis.
24 DR. WALLIS:
This augmented part means it's 25 increased, augment is to increase.
[/
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MR. ALI:
What the topical report and the current
()
2 EPRI position is that, for example, for IGSCC, category A i
3 will be most into the risk-informed ISI process, but for j
4 category B through G, the risk-informed ISI process at this 5
time will not change the inspections that are being done for 6
category B to G.
f
{
7 They are not being increased or decreased.
They 8
are just staying the same.
9 DR. WALLIS:
Augmented implies increased.
10 MR. ALI:
Augmented means in addition to what is l
11 in ASME Section 11.
12 DR. WALLIS:
So that's the implication.
It's in 13 addition to that.
I 14 MR. ALI:
In addition to ASME-11 inspections.
)
15 DR. WALLIS:
So on the face of it, it looks as if 16 you're increasing some demands by augmenting inspection.
17 MR. ALI:
No, that's not what is meant.
There 18 were a number of -- there's a number of degradation 19 mechanisms that were found in the plants over the last 20 several years.
As a result of those, the staff had issued 21 generic letters asking the licensees to address those issues 22 and as a result of that, the licensee made certain 23 commitments as to how they will monitor those degradation 24 mechanisms and inspect for those.
25 The second item is --
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DR. SHACK:
Syed?
()
2 MR. ALI:
Yes.
3 DR. SHACK:
An erosion / corrosion, is that 4
augmented inspection program now going to be subsumed into 5
the --
6 MR. ALI:
No.
That, at this point, is going to 7
remain as it is in the generic letter.
So those IGSCC B 8
through G and the erosion / corrosion are the two programs 9
that are not being changed as a result of this program at 10 this time, and other programs are being changed.
11 The second item is that as a result of our issuing 12 the regulatory guide and standard review plan and also 13 reviewing the pilots and issuing the SER, the staff and the 14 industry felt that once we have reviewed the pilots and we
()
15 have reviewed and approved the topical report for these two 16 methodologies, then the industry and the staff should come 17 up with a simplified submittal to the staff so that the 18 review process can be expedited.
19 We had several meetings with the industry to try 20 to come up with the contents of that template.
As a result 21 of those meetings, we agreed to a table of contents and what 22 will go into those templates.
23 The only thing I think that's a little bit 24 different is that as a result of our meetings with NEI and 25 the industry, there were some changes that were made to that
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template, there were some attritions and the template that
(
2 we see in this topical report does not reflect the latest.
3 So I think that's something that we will ask them to do and 4
I don't think that should be a big change.
That can be done 5
easily.
6 DR. SHACK:
Do you have a template for the WOG 7
ASME?
8 MR. ALI:
Yes, we have for both.
Actually, the 9
template is about the same because the high level aspects of 10 the methodologies are really the same.
It's the details.
11 So the template is essentially the same.
12 The third item on this slide is that so far, all 13 of the pilots that we have looked at and approved have been I
14 either the whole plant or Class I.
So we have not been l
l
()
15 asked to review and we have not reviewed any submittals 16 where there was a change in the inspection on a system by 17 system basis.
18 But the topical report presents that as one of the 19 options that the ISI program may be changed on a system by 20 system basis.
They did not talk about that this morning.
21 The criteria, the risk criteria, the risk acceptance 22 criteria on a system by system basis is an order of 23 magnitude more stringent than what it is for the plant 24 basis.
25 This is something that is different than what we
/~'
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have approved at this point and so we are still in the
()
2 process of reviewing that.
3 Steve will now go through the next slide.
4 MR. DINSMORE:
This is Steve Dinsmore from the 5
staff.
I will be talking about some of the differences in 6
the -- I guess most of them are in the delta risk 7
calculations.
Again, these differences are between what was 8
approved in the pilots and what's in the current topical.
9 We talked a lot about those tables, but we haven't 10 been looking at the specific elements in those tables and 11 what those rankings are and the word grade creep comes to 12 mind.
Every pilot has been submitting their own table and 13 the highs and the mediums are kind of drifting off to the 14 left-hand side.
()
15 So we haven't quite approved the table yet.
We're 16 still looking at it.
Some of the elements in there are 17 greater than ten-to-the-minus-four, which are supposed to be 18 mediums, because they say it's a bounding calculation.
So 19 we're still dealing with that.
So if you look in the table 20 and you see numbers which don't seem to fit with the 21 criteria, they don't, and we're working on that.
22 The other big change is these delta risks.
- Again, 23 earlier, when they first started this process, they didn't 24 really look at delta risks and we've been adding that slowly 25 step by step.
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96 1
What's new in the topical, again, is there is a C\\
( j 2
request to do no delta risk calculations if you only do 3
Class I.
EPRI said that they had an argument why ten 4
percent would not increase risk and that there -- if the 5
pilot or if a utility could somehow show that their service 6
experience is similar to generic service experience, then 7
they wouldn't have to do the delta risk calculation.
So 8
we're still looking at that.
9 No delta risk contribution from low safety 10 significant segments.
Carl kind of alluded to that this 11 morning.
They don't want to calculate the change in risk 12 due to low safety significant segments.
They have a 13 reasonable looking argument in the topical where they use 14 bounding calculations, but we're still looking at that, 15 again.
16 They added these screening criteria.
This is 17 actually the first time I've seen those.
We've only had 18 this thing for about two and a half weeks.
The 19 ten-to-the-minus-seven CDF and the ten-to-the-minus-eight 20 LERF, these are all reflected in a flow sheet on the last --
21 there is a flow sheet right in the back of the chapters.
22 Evidently, it's a system by system restriction which you use 23 if you've done either by class or by -- or the whole plant.
24 Then they added on this extra one where they say 25 if you only do one system, then you decrease those by a
(
ANN RILEY & ASSOCIATES, LTD.
\\-/)
Court Reporters 1025 Connecticut Avenue, NW, Suite 1014 Washington, D.C.
20036 (202) 842-0034
)
}
97 1
factor of ten.
In general, with the risk-informed stuff, l
l 2
we've been -- we started out by saying you had to do full 3
scope, everything, and we've been kind of slowly moving 4
back.
Especially if they come in with the argument that 5
it's a risk decrease, it's hard for us not to accept 6
something that's not a risk decrease.
7 Again, these are positive numbers here.
So we're j
8 still kind of looking at that.
9 And the last one that they added was this Markov.
t 10 There was a lot of discussion this morning about this Markov 11 and the data analysis.
We didn't use that in the pilots.
12 We used this bounding option, where they took the highest I
13 possible CDF for each category and the highest possible pipe 14 failure frequency for each category and did some bounding (O,)
15 calculations to show us that without crediting any increase 16 in inspection efficiency, that there would be a very small I
17 risk increase.
If they credited some increase in the 18 inspection frequency, then it would go down.
19 So they've been coming in with minus numbers as 20 their best estimate of the change in risk, which, again, I'm 21 not quite sure what these positive ten-to-the-seven and 22 ten-to-the-minus-eight boundary criteria are.
23 A more mundane problem with the Markov stuff is 24 from Dr. Apostolakis -- it's spread all over about ten 25 reports and we're trying to pull it together.
So we don't
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20036 (202) 842-0034
98 1
really have a good feel for how the whole thing fits
()
2 together with the data.
3 But our current feeling is that the process seems 4
reasonable.
It's just a matter that we have to really get 5
and understand it and say that what we understand is okay.
6 Those are essentially all the differences that 7
we've identified.
8 DR. SHACK:
Questions from the committee?
Do you 9
-need anything from us at the moment?
You're still working 10 on your draft SER.
11 MR. ALI:
We kind of talked about that before.
We 12 usually ask for a letter when we write the SER, but we 13 haven't written the SER.
So I think at this point, it's --
14 DR. SHACK:
Unless we have a major problem.
()
15 MR. ALI:
-- what you write as a result of your 16 meeting or your deliberations.
17 DR. SEALE:
Strictly information.
18 MR. BARTON:
I don't see any big problem that 19 would require a letter.
20 DR. SHACK:
Okay.
21 DR. SEALE:
So you're going to talk again this 22 afternoon?
l 23 MR. ALI:
Yes.
We are on schedule again this 24 afternoon.
I 25 DR. SHACK:
We had some discussion about that, I
O' ANN RILEY & ASSOCIATES, LTD.
Court Reporters 1025 Connecticut Avenue, NW, Suite 1014 Washington, D.C.
20036 (202) 842-0034
l 99 1
since we've got a reasonable segment, we basically sort of
()
2 thought we more or less had to do it, but we would do it in 3
a fairly abbreviated fashion.
4 DR. SEALE:
Yes.
I notice it's just a half-hour.
5 DR. SHACK:
That was more we sort of felt we had 6
to -- you know, since it was noticed, we would have to do 7
it, but it would be an abbreviated session.
8 With that, if there are no other questions or 9
comments, we close the meeting of the subcommittee.
10
[Whereupon, at 11:16 a.m.,
the meeting was 11 concluded.]
12
-13 14
(
\\s 15 16 17 18 19 20 21 22 23 24 25 O
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Court Reporters 1025 Connecticut Avenue, NW, Suite 1014 Washington, D.C.
20036 (202) 842-0034
i REPORTER'S CERTIFICATE This is to certify that the attached proceedings before the United States Nuclear Regulatory Commission in the matter of:
)
NAME OF PROCEEDING:
MEETING:
RELIABILITY AND PROBABLISTIC RISK ASSESSMENT AND MATERIALS AND METALLURGY CASE NUMBER:
PLACE OF PROCEEDING:
Rockville, MD were held as herein appears, and that this is the original b)
(
transcript thereof for the file of the United States Nuclear Regulatory Commission taken by me and thereafter reduced to j
typewriting by me or under the direction of the court reporting company, and that the transcript is a true and accurate record of the foregoing proceedings.
f b IV}lW.
Mark M hon Official Reporter Ann Riley & Associates, Ltd.
4/29/99 O
^ovisoav co==irT== on a=^croa =^reau^aos MEETING OF THE JOINT SUBCOMMITTEES ON RELIABILITY AND PROBABILISTIC RISK ASSESSMENT AND ON MATERIALS AND METALLURGY ROOM T-283,11545 ROCKVILLE PIKE, ROCKVILLE, MD MAY 5,1999 ACRS
Contact:
MichaelT. Markley (301) 415-6885 PROPOSED SCHEDULE -
1 l
TOPlc PRESENTER IlME 1)
Introduction 8:30-8:35 am o
Review goals and objectives W. Shack, ACRS l
for this meeting o
Review previous deliberations and W. Shack, ACRS issues related to risk-informed G. Apostolakis, ACRS inservice inspection (ISI) 2)
Industry Presentation 8:35-10:00 am O
i e
Discussion of EPRI TR-112657, J. Mitman, EPRI
' Revised Risk-Informed Inservice P. O'Regan, EPRI Inspection Procedure' G. Smith, NYPA K. Fleming, ERIN Eng.
V. Dimitrijevic, Duke E&R l
P. Riccardella, Structural l
Integrity Assoc.
" BREAK "
10:00-10:15 am 3)
Industry Presentation - continued 10:15-11:15 am Discussion of EPRI TR-112657, J. Mitman, EPRI l
' Revised Risk-Informed inservice P. O'Regan, EPRI Inspection Procedure' G. Smith, NYPA K. Fleming, ERIN Eng.
V. Dimitrijevic, Duke E&R P. Riccardella, Structural Integrity Assoc.
1 i
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m='
S' M*m4
- B*M es-'
9'@
m 9
4)
NRC Presentation 11:15-11:45 am e
Status of NRC requests for additional S. Ali, NRR information and proposed issues for S. Dinsmore, NRR draft safety evaluation report ISI lasues Risk-informed issues 5)
General Discussion and Adjournment 11:45-12:00 noon e
General discussion and comments W. Shack, ACRS by Members of the Subcommittee, G. Apottolakis, ACRS items for discussion at the May 5, 1999 ACRS meeting N_qtt: Presentation time should not exceed 50% of the total time allocated for a specific item. Number of copies of presentation materials to be provided,to the ACRS - 35.
O I
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UNITED STATES NUCLEAR REGULATORY COMMISSION EPRI METHODOLOGY FOR RISK-INFORMED INSERVICE INSPECTION PROGRAMS FOR l
PIPING l
PRESENTED TO:
O THE ACRS JOINT SUBCOMMITTEES ON RELIABILITY AND PRA AND-MATERIALS AND METALLURGY l
MAY 5,1999 Syed Ali, DE, NRR (415-2776)
Steve Dinsmore, DSSA, NRR (415-8482) l l
O 1
l O
- f... ~,,
S UNITED STATES NUCLEAR REGULATORY COMMISSION STATUS OF EPRI TOPICAL REPORT EPRI Submitted Draft TR-106706 6/30/96 (C)
Staff issued RAls 6/12/97 (C)
EPRI Responses to RAls 11/13/98 (C)
Meeting to Discuss Responses 3/2/99 (C)
EPRI Submitted Revised TR-112657 4/15/99 (C)
^"
8"'
- *'"*** "***'"8 8"
O Follow-up Meeting with EPRI 7/12/99 ACRS/CRGR Meetings 9/99 issue Safety Evaluation Report 10/31/99 O
2
O
(
,1 UNITED STATES NUCLEAR REGULATORY COMMISSION Schedule of EPRI BasedPilot Plant Applications Vermont Yankee 11/9/98 (C)
ANO Unit 2 12/29/98(C)
ANO Unit 1 07/31/99 0
4 0
3
o f.....,
)
UNITED STATES NUCLEAR REGULATORY COMMISSION Maior Changes in EPRI Topical Report Subsequent to Approval of Pilot Plants 1/2 The application of RI-ISI to Augmented Inspection Programs, e.g., IGSCC and Erosion / Corrosion has been addressed Proposed Submittal Template added O
RI-ISI Methodology can be applied on a system-1 by-system basis.
O 4
O f... s,
I 3
UNITED STATES NUCLEAR REGULATORY COMMISSION Major Changes in EPRI Topical Report Subsequent to Approval of Pilot Plants 2/2 Slight changes in matrix safety-significant categories Change in A Risk Calculations / Criteria O
No A risk calculations for Class 1 only (N-560)
No A risk contribution from Low safety-significant segments Added screening criteria on A CDF/LERF 1E-07 CDF,1E-08 LERF 1E-08 CDF,1E-09 LERF system only scope Added Markov option to original qualitative and bounding options O
5
d EPRI Risk Informed -ISI Program to ACRS
?!:
May 5,1999 Vesna Dimitrijevic - DE&S Ilamilton Fish - NYPA Karl Fleming - ERIN Jeff Mitman - EPRI Pat O'Regan - EPRI Pete Riccardella - SIA Glen Smith - NYPA ACRs 5 99 ppt EPEl O
Objectives & Agenda Facilitate ACRS review and concurrence of EPRI RI-ISI methodology to support SER in September 1999 Ac,anda j
I Topical report status Pilot plant status Overview of methodology Summary & conclusions ePei O
1
f 9
Topical Status Submitted to NRC - June 1996 RAI responses - November 1998 Revised topical sent to NRC April 15,1999 incorporating:
Enhanced procedure and basis description Lessons learned from pilots Resolution of questions & comments from NRC RAls Related EPRI research Draft SER expected June 1999 SER expected September 1999 si.* 3
- ggg, O
Code Cases
'9 I
N-560 Approved in 1996 Applies to BJ wolds, excluding socket wold inspection 10% of BJ welds selected by risk Revision started with approval expected in 1999
. N-578 Approved in 1997 Applies to class 1,2, & 3 piping (and may be used for non-code elements)
Inspect 25% of high risk,10% of medium risk,0% of low risk welds Revision started with approval expected in 1999 Risk assessment process is same for both code cases Element selection process is slightly different st* *. Comparable risk results EPEl O
2
O Pilot Plants e Vermont Yankee (N-560)- SER Received
. ANO2 (N-578) - SER Received
. ANO1 (N-560) - Submitted
. Fitzpatrick (N-578) - Submittal in preparation
. Braidwood (N-560) - 80% complete
. STP (N-560) - 75% complete
. Riverbend (N-560) -later in 1999
. Waterford (N-560) -later in 1999 si.*
EPel O
Methodology Overview l Determine Scope l X
N Perform Segment Perform Segment Damage Consequence Analysis Mechanism Analysis l Perform Service Review l l Determine Segment Risk Category (
4 N
Adjust Select Elements for Inspection &
Element Element inspection Methods Performanca
, Selection 4
Monitoring
~*-l Perform Risk Impact Assessment l l Finalize Program f Sh& 9 EPel O
3
O IUSK MATRIX CONCEPT RISK = (CCDP or CLERP given Pipe Rupture) vs (Potential for Pipe Rupture)
Core Damaae or LER Potential Potential for Pipe Rupture Degradation Mechanisms
. PSA & Deterministic Service Experience Impact Groups Rupture Potential Initiating Event Degraded System / Train Ranking High Degraded Containment Combination Medium Low Consequence Ranking High Medium Low None si.* io O1 IUSK EVALUATION Consequence Assessment CONSEQUENCE CATEGORY CCDP and CLERP Potential Failure Potential NONE LOW MEDIUM HIGH Assessment (Degradation gugw:4 Mechanism)
$2
[MEDNM usan 8i
((E5 emm I
$j MEDIUM ae" l#F#KW bb iMEDIUMI she ii
[
k O1 4
3 d
O PIPE SERVICE 7 EXPERIENCE Anaisis of more than 2000 years experience by EPRI, SKI and others yields databose of 1145 pipe failures 1076 Pipe leaks identified Most less than 5 gpm Most due to corrosion mechanisms 69 " Ruptures" identified ( >50 gpm )
Failure mechanisms well understood and conditions necessary to produce failures generally known Some mechanisms not amenable to inspection One RCS event Several events in steam and feedwater systems EPP.I maintains program to periodically update the database 8"* '
- E Pf21 Po DM Attributes & Susceptible Regions -
+
Degradation Criteria Susceptible Mechanism Regions E TF TASCS
- NPS > 1 inch, and Noz2les.
pipe segment has a slope < 45' from horizontal (includes elbow or tee into branch pipe a vertical pipe), and connections,
- potential exists for low flow in a pipe section connected to a component safe ends, allowing mixing of hot and cold fluids, or welds, heat potential exists for leakage flow past a valve (1 e.,in leakage, out4eakage, affected cross leakage) allowing mixing of hot and cold fluids, or zones potential exists for convection heating in desdended pipe sections (HA2s), base connected to a source of hot fluid, or metal, and potential exists for two phase (steam / water) flow, or regions of potential exists for turbulent penetration in branch pipe connected to stress header piping containing hot fluid with turbu'ent flow, and concentrattor$
calculated or measured AT > 50*F, and Richardson number > 4 0 TT operating temperature > 270"F for stainless steel, or operating temperature > 220*F for carbon steel, and potentaal for relatively rapid temperature changes including-cold fluid injection into hot pipe segment, or hot fluid injection into cold pipe segment, and ST
> 200*F for stainless steel, or AT
> 150*F for carbon steel, o, she m AT
> AT a!Iowable (applicable to Soth stainless and carbon) 5
i O
Degradation Mechanism 7 Category Pipe Expected Degradation Mechanisms To Rupture Leak Which The Segment is Potential Conditions Susceptible HIGH Large Flow Accelerated Corrosion (FAC)
Thermal Fatigue Stress Corrosion Cracking (IGSCC, TGSCC, PWSCC, ECSCC)
MEDIUM Small Localized Corrosion (MIC, Crevice Corrosion and Pitting)
Erosion-Cavitation LOW None No Degradation Mechanisms Present su* "
EPel O
Consequence Considerations Initiate event Mitigating ability Loss of system (s) or train (s)
Degradation of system (s) or train (s)
Containment effects Loss of containment integrity Degradation of containment integrity Combination si. i.
- ggg, O
6
O Consequence Ranking 3 Criteria 1
HIGH CCDP >104 or CLERP>10-5 Severe initiating Events Severo Loss of Mitigation High Risk of Containment Bypass MEDIUM 10-8 < CCDP < 104 or 10 7 < CLERP < 10 5 Moderate initiators Moderate Loss of Mitigation Moderate Risk of Containment Bypass LOW CCDP < 104 and CLERP < 10-7 Mild Initiators Minimal Loss of Mitigation Full Containment Slide 19 g
O Remaining Tasks Determine segment risk category Selection of inspection locations Selection of appropriate inspection techniques Risk impact assessment Document & finalize project Submittal Performance monitoring si n
- ggg, O
7
O RiskImpact Assessment
)
EPRI RI-ISI process was designed to maintain or decrease risk level Risk impacts include:
allocation of inspections at high risk locations inspection for cause impacts elimination of inspections at low risk locations Risk impacts assessed using:
qualitative analysis in most cases bounding estimates in some cases realistic estimates where appropriate
- ggg, O
EPRI RI-ISI Reports
~ ~ ~
g" Evaluation of Pipe Failure Potential via g
smiDegradation Mechanism Assessment TR-110157 'ame Application of EPRI RI-ISIGuidelines to CE Plants TR-107531 Application of EPRI RI-ISI Evaluation Procedure to_B W R _ _
TR-107530 Piping Failures in U.S. Nuclear Power Plants:
1961-1997 TR-110102 Piping System Reliability Models and Database for used in Risk Informed inservice inspection Applications TR-110161 Use of Risk informed Inspection Methodology for BWR Class 1 Piping TR-110701 Piping System Failure Rates and Rupture Frequencies for Use in Risk Informed in-Service Inspection Applications _ _DRA,F_T_
.TR-j l1880 Revised EPRI RI-ISI Methodology Procedure TR-112657 (EPEI O
8
O Pilot Results Summary j
l RISK RANKING" 3
i High Med.
- Low lotal Vermont Yaidee
,OldSEEN 37 64 - 25
-~ ~ 126 CEf7430Wsids RASI 33 10 0 ~}]j_~43 ANO'1
- Old Ssd.M 30~-~~ 53i-~~
17 100 Cl.1T394'Wsids RASI 28' 12"- ~ ~ 0
~ ~ '
40 Braidwood jold Sec.N 35 93; 72 203 Cl.~1T723 Wsids
_ [RflSP 43 31 0
74 i
ANO' 2 --
lOld Ssd M 86 120 7 ~ 230 --~ ~436 FUlFScope -7906~WsidslRASI 78 170j 7
255 i
l EPEI O
summary & conciusions Revised topical report submitted Addresses questions & comments raised by NRC It is in compliance with RG 1.174 & 1.178 Methodology has been applied extensively GE, W, B&W & CE Multiple AEs Full / partial scopes Significant REM reduction Pilots & research supports conclusion of negligible risk impact si.* 3 EPel O
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