ML20197A954
| ML20197A954 | |
| Person / Time | |
|---|---|
| Issue date: | 12/18/1997 |
| From: | NRC COMMISSION (OCM) |
| To: | |
| References | |
| REF-10CFR9.7 NUDOCS 9712230257 | |
| Download: ML20197A954 (105) | |
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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION
Title:
AIEETING WITII ADVISORY COhihirfTEE ON NUCLEAR WASTE (ACNW) -- PUBLIC MEETING Location:
Rockville, Alaryland Date:
Thursday, December 18,1997 Pages:
1 - 55
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l DISCLAIMER This is'an unofficia1' transcript of a meeting of the United States Nuclear Regulatory Commission held on
[
Decenber 18, 1997 in the Commission's office at one White Flint. North, Rockville, Maryland.
The meeting was open to l
public attendance and observation.
This transcript has not l
.been reviewed, corrected or edited, and it may contain inaccuracieu.
The transcript is intended solely for general informational purposes.
As provided by 10 CFR 9.103, it is not part of the formal or informal record of decision of the matters discussed.
Expressions of opinion in this transcript do not necessarily reflect final determination or beliefs.
No pleading or other paper may be filed with the Commission in any proceeding as the result of, or addressed to, any statement or argument contained herein, except as the commission may authorize.
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1 UNITED STATES OF AMERICA 2
NUCLEAR REGULATORY COMMISSION 3
-4 MEETING WITH ADVISORY COMMITTEE 5
ON NUCLEAR WASTE (ACIN) 6 7
PUBLIC MEETING 8
9 10 liuclear Regulatory Commission 11 Commission Hearing Room 12 11555 Rockville Pike 13 Rockville, Maryland 14 15 Thursday, December 18, 1997 16 17 The Commission met in open session, pursuant to 18 notice, at 10:07 a.m.,
the Honorable SHIRLEY A. JACKSON, 19 Chairman of the Commission, presiding.
20 21 COMMISSIONERS PRESENT:
22 SHIRLEY A. JACKSON, Chairman of the Commission 23 GRETA J. DICUS, Member of tae Commission 24 NILS J. DIAZ, Member of the Commission 25 EDWARD McGAFFIGAN, JR., Member of the Commission ANN RILEY & ASSOCIATES, LTD.
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STAFF AND-LPRESENTERS SEATED AT THE COMMISSION TABLE:
2 JOHN C._' HOYLE, Secretary 1
3 --
. KAREN D._CYR,: General Counsel-l.
4
=DR.-B.l JOHN GARRICK, Chairman, ACNW-5 DR. CHARLES HORNBERGER, Vice Chairman, ACNW 6
-DR._ CHARLES-FAIRHURST,-Member, ACNW 7
DR. RAYMOND WYMER, Member, ACNW
'8=
DR. - JOHN T. IARKINS, Executive Director, ACNW 9
10 :-
'll 12 13 14
-15 16 17 18 19 20
-21
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'1l P R O C E E DLI'N-G S-2.
[10:07 a.m.)
3
-CHAIRMAN-JACKSON:- Good morning, ladies and
+
4-
- gentlemen.
Today the--Commission will be briefed by the 5
Advisory Committee.on Nuclear Waste on several technical 6
issues related to'the management and disposal of radioactive 7
waste.
6-The Commission always looks forward to the ACNW to 9
provide it with its technical advice to assure the safe 10 management ar.d disposal of this country's radioactive waste.
11 Today's briefing by the ACNW will-include 12 discussions on three technical issues that are of great 13 incerest to the Commission.
These topics include the 14 application of probabilistic risk assessment or PRA to 15 performance assessment in the NRC High Level Waste Program, 16 performance assessment capability in the NRC itself in the 17 NRC High Level Waste Program,-and the implementation of a 18 defense-in-depth concept in High Level Waste.
19 In addition to these technical discussions, the 20 Commission will also discuss its priorities for the next.
21-year.
The Commission looks forward to your presentation and 22 unless any of my fellow Commissioners have opening comments, 23 Dr. Garrick, Please proceed.
24-DR. GARRICK:
Thank you.
Perhaps before we start, 25
~ Chairman Jackson, I would-like to recognize two new members q
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of the Committee -- Dr. Raymond Wymer and Dr. Charles 2
Fairhurst, and we're delighted to have them and put them to 3
work as quickly as possible.
4 We have taken the liberty to restructure the 5
agenda a little bit from what you described, and in 6
particular, in order to establish a framework within which 7
we can identify the relevance of the issues we are going to 8
talk to you about, we are planning to talk a little bit 9
about the priorities first.
10 CHAIRMAN JACKSON:
Sounds good.
11 DR. GARRICK:
And I think that one of the things 32 that we have attempted to do with the presentation is to 13 create somewhat of a theme, starting with the priorities or 14 starting with the Strategic Plan as a proposed structure 15 within which we opera.e, and getting into the performance 16 acsessment issue as a discipline and our comments regarding 17 that, and then moving from there to, well, what capabilities 18 exist within the NRC to deal with this subject, and then 19 somewhat in the context of an example address the icsue of 20 defense in-depth.
21 We hope that that theme is logical and appeals to 22 you, so with that I will lead off the discussion, talking 23 about the Strategic Plan.
24 What we have done here is pick up on your 25 leadership for developing a Strategic Plan for the Agency ANN RILEY & ASSOCIATES, LTD.
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and root our plan in that plan and ask ourselves along the 2
way-about its relevancy to the overall plan of the Nuclear 3
Regulatory Commission -- so we hope that that occurs. -We 4
hope also that this can become a benchmark, if you wish, 5
with which we can measure our perfermance, and of coursa we 6
expect to do this each year.
7 So if I could, I would like to proceed to the 8-Plan.
We have chosen to take a top-down approach just as 9
the NkC Plan did, and to get into the whole arena of 10 mission, vision, goals, objectives, and then finally the 11 product that we want out of the Plan was priorities.
12 Our first exhibit here is what is the mission of 13 the ACNW.
Our characterization of that mission is that we 14 are to provide independent and timely technical advice on 15 waste management issues to support the NRC in conducting an 16 efficient regulatory program that enables the nation to 17 safely use nuclear materials.
18 Now with respect to our vision,-the Advisory 19 Committee on Nuclear Waste strives to provide advice and 20 recommend solutions that are forward-looking, that are based 21 upon the best available science and technology, and that can 22 be implemented and reflect the needs and balance risk, 23 benefit and cost to society to enable the safe use of 24 nuclear materials.
25 As far as goals are concerned, we have identified ANN RILEY & ASSOCIATES, LTD.
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several goals.
One of the goals of course is to position 2
ourselves to be effective in our response to change and the 3
attendant uncertainty that surrcunds us in the management of 4
nuclear waste, to provide assurance to the Commission that 5
the best science is being employed in resolving key safety 6
issues, and of course when we talk about that science we are 7
talking about consistent with the constraints that we all 8
have to work under; to provide advice to the NRC on how to 9
increase its reliance on risk as a basis for 10 decision-making, including risk assessment methods for 11 waste, radioactive waste management; to support and assist 12 the NRC in improving public involvement; and to optimize the 13 effectiveness and efficiency of the ACNW operations.
14 CHAIRMAN JACKSON:
.es, please.
15 COMMISSIONER DICUS:
On the fourth bullet, in 16 assisting and improving public involvement, what are some of 17 your ideas that you would be doing to help us improve public 18 involvement that we are not already doing?
19 DR. GARRICK:
All right.
Well, I am not 20 suggesting that we aren't doing some of these things, but a 21 couple of things that come to our mind and that we have 22 talked about a little bit is that we could probably be a 23 little more deliberate in our outreaching for public 24 involvement, in giving ourselvea confidence that the public 25 is well-represented on key issues.
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1-Weiare in a position of anticipating these issues-2J much further in advance than the~ announcement accommodates,
'3 -
and so I think that one aspect of this that we have been 4-thinking about is:perhaps there.are some things we can do in I-5 the. sense,~in the context of an outreach program.
6_
The other thing that I think is very fundamental
'7 to the whole notion of a transition towards a risk-informed 8-regulation is that many of us believe very strongly that one 9
of the most important mechanisms, one of the most important L10 tools for reaching to the public.is to have a framework 4
' 11 within which issues are consistently.and systematically 12 addressed, including issues, comments,-or input that might 13 come'from the public -- so those are a couple of thoughts, 14 COMMISSIONER DICUS:
That's good.
Thank you.
15 DR. GARRICK:
Criteria -- obviously if you are 16 going to have as an _cd gcal of a strategic plan and 17 development of priorities you need some sort of process that 4
18 gives you some confidence that these priorities are properly 19-connected to our vision and our mission.
20 The priorities that we have listed here are very 21
-consistent with the priorities that we have seen in the Plan 2
22 for-the Agency.
23 It's clearly protection of public health, workers,
- 24:
and the environment.
We want-certainly to be responsive to 25 issues that the Commission is most interested in.
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Timeline.ss is always a matter that is important in 2
the effectiveness of-any advisory effort.
3 We have also tried to measure the relationship of 4
the issues to the Strategic Plan of the Agency, the 5
potential for an issue to pose undue risk or surprises or 6
things that would affect the reasonableness of the solution 7
to that issue -- such as cost; issues arising from 8
strategies and activities of licensees -- it seems that if 9
you are going to be an effective advisor you need to 10 understand the depth and breadth of the issues as viewed by 11 the people that you are trying to regulate; and finally 12 issues arising from technical basis for safety assessments.
13 So what this all led to was a set of priorities.
14 We chose to divide these priorities into two categories, one 15 that we chose to call the First Tier priorities, and of 16 course a major consideration in something being First Tier 17 is that it is something that needs to be addressed now, 18
- 1998, 19 We have also tried to cut these at a level where 20 they convey some sort of an image that is less than generic 21 that people in our business in the Agency identify something 22 with, and so we have been rather sensitive to the labels 23 here.
24 So the priorities, not necessarily in order of 25 priority, that we have listed under the First Tier are the AIO! RILEY & ASSOCIATES, LTD Court Reporters 1250 I Street, N.W.,
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12
. viability' ass'essment.
We realize that this is not an'
'2-officialiNuclear Regulatory Commission requirement, but we-3 also realize that as-the Agency moves _and positions itself 4
to be increasingly effective in the licensing of repository-
. for high level waste that this'is an.-important. opportunity 6
for us to get-involved,-to see issues,.to.get a sense'of
-7 what.the licensee or the applicant is doing, and so we view; 8.
this as a vary important activity.
9 Risk-informed performance-based regulation -- I 10 don't think we need to elaborate much on that.
It's 11:
becoming an across-the-board issuelof considerable 12 importance to the Agency. -We will be addressing it some 13 more in our subsequent presentations.
14 We all know also that as the Site Characterization 15 Program proceeds with respect to Yucca Mountain and as we 16 learn more about the characteristics and the properties of 17 that site, we learn a great deal more about what we are-18 going to have to do in the way of modifying that site to
-19 give us confidence that it can comply with the standards and 20 the regulations that are to follow.
21 One of those issues that has surfaced-that is
-22 beccming. increasingly ^important is that there is 23 considerable evidence that perhaps there is going to have to 24_
-be-a greater-dependence on engineered systems than maybe the 2 5 --
way we were thinking a few years ago, and so we have moved ANN RILEY & ASSOCIATES, LTD.
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that up as a high priority.
2 Decommissioning is judged to be also a First Tier 3
priority and it crosses a lot of activities and disciplines 4
in the whole arena of waste management.
5 Then, of course, research -- this is an issue that 6
has increased in importance for a few reasons.
One is that 7
this is a function that was handled to some extent by the 8
previous Nuclear Safety Research Review Committee and the 9
activities of that committee are having to be spared by the l
10 Advisory Committee on Reactor Safeguards and the Advisory 11 Committee on Nuclear Waste and we want to be darn sure that 12 we are forward-looking with respect to this research.
13 CHAIRMAN JACKSON:
I think Commissioner McGaffigan 14 has a question for you.
15 COMMISSIONER McGAFFIGAN:
This may be more a 16 statement than a question.
17 I just want you to be aware on the risk-informed, 18 performance-based regulation, we had a meeting yesterday 19 where we talked in reactor space about how far we can push, 20 how rapidly we can push towards risk-informed regulation in 21 that context and I believe the Strategic Plan says that 22 risk-informed and as appropriate performance-based.
We are 23 still trying to define when it is appropriate and I think in 24 the waste area I think we believe it is appropriate but we 25 don't have a lot of guidance at the moment as to when it is ANN RILEY & ASSOCIATES, LTD.
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- appropriate to use a performance-based rule as opposed to a 2
more prescriptive rule,.and I think.we-are still. struggling
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32 toscome up.with:the' criteria for when one does'that,_so it-4-
- isL an ongoing _--.we have made a= commitment to try to make a 5
transition to more risk-informed and to more 6
performance-based or lesu prescriptive, but the words in the 7:
Strategic Plan were struggled over, ar.d_ so I just point out 8
the_ nuances to you.
-9
.DR. GAF. RICK:
Yes.
10 CHAIRMAN JACKSON:
I actually believe that that is 11-
-in-fact an opportunity.
12 DR. GARRICK:
Yes.
13 CHAIRMAN JACKSON:
For our advisory committees.
14' DR. GARRICK:- Yes -- and we agree with that.
15 As far as the Second Tier --
16 CHAIRMAN JACKSON:
Excuse me --
t 17 DR. GARRICK:
Oh, excuse me.
18 CHAIRMAN JACKSON:
Commissioner?
19 COMMISSIONER DICUS:
Well, this could be for First 20 Tier or second-Tier questions or slides rather.
Have you 21 within your First Tier -- did I hear you say you haven't 22 really prioritized within the First Tier priorities.-
Is it 23 as the issue comes up or as.you may to discuss it?
24
.DR. GARRICK:
Well, we-have not really fine-tuned 25 it that much.
I think each-member of the committee has.
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- their:own preferences'as to:which isitheitop. priority.
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-I-suspect that the; events-will determine that as.
-2:
-3l we_ proceed in 1998.and they.take on a little different-4 context:'becauseEsome of-these issues will--continuesfor sure:
5 way beyond 1998.-.Others are going to-be much more:
6-
- short-lived.
. 7.
' COMMISSIONER-DICUS:
I-don't=know whether I:should 8~
ask-thisLquestion-or not, but I guess lE will.
Even-just-9 looking=at the First Tier priorities that you read,-some of the-items in the Second Tier psiorities, it is a lot of work 11=
- for a relatively small group.
12 That's:more a statement than a question.
11 3 DR. GARRICK:
You're absolutely correct, 14 Commissioner Dic_s --
15-CHAIRMAN JACKSON:
Don't set him up to ask for 16 more --
17-(Laughter.]
18 COMMISSIONER DICUS:- When I asked the question, I 19-thought I know I am going-to get in trouble with this 20 question.
t 21 CHAIRMAN-JACK 3ON:
You are.
t 22
[ Laughter.)
23 DR. GARRICK:- The only answer lE can give is yes.
24 CHAIRMAN JACKSON:
Thank you.
Very good answer.
25 LDR, HORNBERGER:-
I think in part, if I could just r
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1 interject, it's clear that we arei not. going to exhaustively -
2 approach all of these topics and the viability asse'ssment we
-- 3 '
will-do.what.we:can when the' products.come through:later-in 4.
the year.
- 5 CHAIRMAN JACKSON:
It's a triage, yes.
6-DR. GARRICK:
Triage, yes.
I think we are short 7
of time and I don't think I want to-dwell much-on the Second 8
- Tier :except to recognize'them and to indicate that-these not 9
only_ reflect the application of our criteria but have-10 involved a number of reviews-of neetings we-have had.
j
- 11 Commissioner Dicus made a major contribution to 12 this when she attended part of:our retreat.
13 We have received a lot of information from the 14 NMSS as to what they believe are the priorities, so this is 15 something that has come from a wioe band of resource bases.
16 COMMISSIONER McGAFFIGAN:
A question about just 17 how the Advisory Committee with limits compared to ACRS 18 operates.
19 We involved ACRS quite often in lots of Staff 20 proposals, generic letters, whatever.
We have in this long 21 list of priort u 2 items-that come up.
22 One that comes to mind-at the moment we and the 23-State of Washington are struggling with is the Trojan 4
-24 reactor, vessel _with internals intact and whether it should 25 be-disposed of at'Richland.
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Do you see a role for yourself in advising the 2
Staff and the Commission on these cases?
I guess it's more 3
casework.
The ACRS I think does more casework.
4 You have thus far stayed at a higher policy level.
5 How do you see that in your committee's work?
6 DR. G3RRICK:
Well, I guess I would say first that 7
we are here principally to respond to issues raised by the 8
Commission, and if the Commission sees us as having an 9
effective role in that arena we would, I think the committee 10 would be delighted to do so.
11 I don't think that we see ourselves as fenced in 12 on any particular way of operation.
I would hope that we 13 would have the flexibility to do that.
14 COMMISSIONER McGAFFIGAN:
And this gets back to a 35 fundamental question, I have noticed reading Nucleonics 16 Week and other publications recently that there is a 17 movement afoot or in France for example to question whether 18 repositories are the appropriate role or if there may be a 19 technology out there and some sort of interim approach, and 20 then some technology comes along in 100 years, and that 21 obviously -- my old Los Alamos sometimes -- cells 22 accelerated transmutation of waste -- is that technology 23 that may come along.
24 I know there is a big Academy report on that 25 subject, but is there a role for you all in continuing tc ANN RILEY & ASSOCIATES, LTD.
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inform'us aslto -- I know on the viability of the repository-2-
-approach bution these alternatives that. occasionally get.
3 talked about, whether_they are indeed viable intyour view?
i 4-DR._GARRICK:
Well,1 Commissioner McGaffigan, I 5.
surely hope there.is.
Speaking for myself, this is what 6-makes this job interesting is to be in a position to address-7 broader issues than maybe we see in trying to set up our.
8 agendas and what have you.-
9 I think that it is clear in our conversations 10 among the committee that we have a-very-deep interest in 11
. alternatives, in interim solutions, in methods of timeliness 12 with respect to when we get to a particular type of 13 solution, and in the technologies that are involved, so I 14 think that we would be very interested in that kind of 15 involvement.
16 CHAIRMAN JACKSON:
Actually, that leads to two 17 comments.
18 One is that having recently been in France, I 19 think the issue for the French is not rejecting the idea 20 because I actually had a meeting with all of the nuclear 21 players.
It's not rejecting per se the idea of a repository 22 but having a repository built in a way where it can either 23 be permanently sealed or what is put into it being 24 retrievable if a technology is developed that llows for
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25 disposition of the high level waste by some alternative ANN RILEY & ASSOCIATES, LTD.
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mechanism, and so we want to be careful in terms of how it 2
is reported versus what the players are really'saying.
3 DR GARRICK:
Yes.
As a matter of fact, when we 4
put the priority repository design on here, we were. thinking 5
of just those kinds of issues and the retrievability issue 6
is a particularly important one that we sometimes think is 7
not adequately addressed, and from a reality standpoint from 8
an operational standpoint, and that is a very good example.
9 CHAIRMAN JACKSON:
Go ahead, please.
10.
COMMISSIONER DICUS:
So it would cover, if I can 11-change the terminology a little bit, the closed repository 12 designs as well as maybe an open repository design?
13 DR GARRICK:
Yes.
It's no question that our 14 focus has been on a closed repository and post-closure but 15 there is strong interest in alternatives and some of those 16 alternatives involve modifications of -- interface that goes 17 from open to closed.
18 CHAIRMAN JACKSON:
Right. Exactly.
19 COMMISSIONER DICUS:
How does your Strategic Plan 20 track with the Agency's Strategic Plan?
21 DR. GARRICK:
Well, I think -- and one of the 22 things we are going to do is send you a copy of it -- and we 23 have agreed on a letter to do that and you will be receiving 24 that within the next few days.
I think the attachment to 25 our letter will be very apparent with respect to its ANN RILEY & ASSOCIATES, LTD.
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. connection with the--NRC Plan.
1 I would like to iove-on to the next topic, l
2 i
3 application of probabilistic risk assessment. methods to 4
-performance assessment in the NRC High' Level' Waste Program,-
=5 and 6'
You have received a letter on this.
As'you 7
observed from our letter, the primary issues that we 8
identified had to do with the committee feeling very 9
strongly'that the true spirit and intent of the concept and 10 the philosophy of risk assessment be suatained.
Whenever we 11 use it and apply it that it is a technology, a discipline 12 that was sought out as an alternative to simplirled 13 calculations, to bounding calculations, to worst case 14 analysis.
It was intended to provide-us more insight into 15 the reality of what was going on with the system-that we-16 were interested in.
17 The issue here is that the-committee wants to have 18 a high degree of confidence that that quality is preserved 19 in_its application so this is more in the context of a 20 caution and a consciousness, a concern than anything in
-21 particular.
22 The approach to performance assessment should 23 clearly allow an exposure or a manifestation of those things 24 that are driving the risk because that is what gives you the 25 information you.need'to implement any kind of sensible risk ANN RILEY & ASSOCIATES, LTD.
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management-program.-
2
. CHAIRMAN JACKSON:
Yes, Commissioner.-
3l COMMISSIONER McGAFFIGAN - On the first_ caution,--
4 you'said there-is nothing specific:there, but is the fearL 5
that' bounding. calculations and worst case calculations have 6
a way of. creeping into'so-called realistic --
i 7
DR.'GARRICK:
Yes.
8~
COMMISSIONER McGAFFIGAN:
-- models?
i 9-DR GARRICK:
Yes, that's true, and the fear that 10 we;are really doing a disservice to the public because in 11 the way they-are presented sometimes the public interprets 12 them as being the real world-and the real analysis and I 13 think we need to be very cautious about that.
14 CHAIRMAN JACKSON:
Yes?
15 COMMISSIONER DICUS:
Maybe you are going to 16 address this in the other slides, but given the fact that 17 what we are doing is to review what DOE is doing, how would 18 something like this track with what DOE is doing?
19 DR. GARRICK:
Yes, I realize the roles-are 120 different.
21 I realize that the purpose of the Agency with
- 22 respect to performance assessment-is, first, to gain an 23 understanding and increase knowledge about the facility or 24 the site that they are trying to evaluate,.and then-second,_
4 25-
=to use it as.a mechanism for giving them an independent ANN.RILEY &: ASSOCIATES, LTD.
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perspective, the independent ability to review what LOE 2
does, so I think the point is well-taken and it is important
'3 to realize that our interest, the Nuclear Regulatory 4
Commission's interest in the performance assessment is a 5
different one than the licensee, and I think those are the 6
two primary differences.
7 One of the things that we were briefed on last 8
summer was the progress that the Commission has made with 9
respect *.o performance assessment, the tools that have been 10 developed, and we were very pleased to see that a great deal 11 of progress has been made.
12 Revised NRC total performance assessment code 13 Version 3.1 in our judgment represents a major step forward.
14 We are very aware that it has been a longstanding 15 effort on the part of the Staff to collect the evidence to 16 package the information that supports any analysis in an 17 effective manner and that the Staff has continued to be 18 interested in trying to gain this understanding that I spoke 19 to of the processes that affect repository performance.
20 We think they have made a lot of progress in that 21 regard.
22 CHAIRMAN JACKSON:
I think Commissioner McGaffigan 23 has a question.
24 COMMISSIONER McGAFFIGAN:
Well, it really relates 25 to -- you are praising _on this page but on the page you are ANN RILEY & ASSOCIATES, LTD.
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going to suggest that 2
DR. GARRICK:
The good news and the bad news.
3 (Laughter.)
4 COMMISSIONER McGAFFIGAN:
That there may be a need 5
for TPA 3.2, which would get rid of what you call 6
unrealistic results that arise from bounding calculations 7
embedded in the code.
8 Is that in fact -- it's a pivotal effort but it 9
isn't quite there yet, if I try to put these two thoughts 30 together?
11 DR. GARRICK:
Yes.
I think that obviously we in 12 our briefings and in the documentation we received don't 13 always have a full view of everything that is going on, and 14 we recognize that, and as a mat *.er of fact, between the 15 briefing in July and this meeting, we have had things 16 brought to our attention that illuminate some of the issues 17 that we were concerned about and in fact there is less 18 concern, but one of the things that we were triggered on a 19 little bit during our meeting and the basis for this letter 20 was that it was the impression of some of the committee 21 members that maybe not as much attention to detail was being 22 given as could be with respect to some critical assumptions.
23 I think that we were especially focused in that 24 meeting on the engineered barriers -- that was sort of a 25 theme of that meeting -- and so we were looking very ANN RILEY & ASSOCIATES, LTD.
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-21 1-strongly at a component of the~ repository design chat 2
perhaps the TPA-3.1 in its evolution had not quite caught _up 3
with in: terms of its-importance.
4-So, yes, we'made some judgments that perhaps there 51 were some assumptions having to do with the representation.
~
6 of'the-degradation of the wacte package that were more 7
conservative than we would have liked to.have seen, but 8
still in the context of my opening comment-here, the 9
approach we were taking was one of caution more.than one of 10~
necessarily being unduly critical and re. minding ourselves of 1
- 11 what this discipline can do for us and what its underlying 12 capability is.
13 DR. HORNBERGER:
I would point out too that I
' 14 don't think it is inconsistent with the Staff's position.
15 That is, I don't believe that they see this as a fixed 16 immutable instrument -- that they really do want to test 17 things out-and improve it in areas where they see 18 improvement is needed, whether it is called 3.2 or just a 19 revision of TPA 3.
20 CHAIRMAN JACKSON:
Let me ask you this question.
21 In terms of trying to get at what you called some 22 of the ultra-conservative model assumptions --
23' DR. GARRICK:
That word --
24 (Laughter.)
35 CHAIRMAN JACKSON:
How much is this related to a e
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conservatism that is cultural versus a conservatism that $s 2
based on lack of inforuation?
3 DR. GARRICK:
Yes.
Well, I guess the way -- I 4
know what you are saying.
I guess u way that I would like 5
to address that is that I think as technical people, and we 6
certainly have to be sensitive to cultural conditions, but 7
as technical people I think it is very important for us when a
we are talking about a parameter or a performance measure to 9
do the best job we can of characterizing the full range of 10 values of that measure.
11 Now by that we are not suggesting that we ought 12 not to be conservative.
On the contrary, the committee has 13 been outspoken on that issue.
We should be conservativa, 14 but if you do the former and you do it systematically and 15 visibly, then the opportunity exists when you have decided 16 to regulate on the basis of a value, the opportunity exists 17 to see what the context is of that value based on reality, 18 so that is the thought here.
19 CHAIRMAN JACKSON:
But that is a key phrase you 20 just used.
Yce said based on reality, and that gets to my 21 question about the informational base that is being drawn 22 on.
23 DR. GARRICK:
Yes.
24 CHAIRMAN JACKSON:
And so if you could answer the 25 question in that context, in terms of how can the Staff or ANN RILEY & ASSOCIATES, LTD.
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?
.1-what needs.to happen to haveLthe models become more 2
-realistic?~
3
-DR~.
GARRICK:
I think the one. thing-_that is very-4 important to do just what youfare talking aboutuis-to make' 5
sure.that'when you present a calculation or a distribut'.on
]
6 that the evidence supporting that is very--clear.--
7 -
One of the things.we also recommended strongly in 8
'that letter is that a lot of attention be given-to'packagi.ng 9
the supporting information such that one could-make a 4
10 connection between the values and the information base, and 11 it reflects a philosophy I think that it's maybe not so 12 important what the analyst does as it is what the analyst 4
13 does on what basis -- what is the evidence, what is the 14 information base that the analyst uses.
15 So what we have tried.to do is put a little focus 16 and emphasis on the source material, on the evidence base
-17 for the calculations.
18 CHAIRMAN JACKSON:
Yes, Commissioner Diaz, 19 COMMISSIONER DIAZ:
Just following up on the same 20 issue, do you think it might be possible in some period of 21 time to define what conservative means?
4 22 DR GARRICK:
Well, Commissioner Diaz.
I am not 23-
-sure, but I do ---this is one of the great attractions that 24
-the probabilistic-thought process has to me is namely 25:
context,-namely. perspective, namely-the full range of values ANN RILEY & ASSOCIATES, LTD.
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24 IL that you might_ associate with a particular-analysis.
2 iThe key _is whether1or not'you-have sufficient-3
- supporting evidence to make that a reality.
4
_There is always going to be. uncertainty.
5-COMMISSIONER DIAZ:
I-understand, but in old-time.
-_ 6 _
engineering we used to take these safety _ factors and
-7' sometimes a safety factor of two was fine and sometimes a 8-safety factor of four was fine.
-9 DR. GARRICK:
Right.
10.
COMMISSIONER DIAZ:
You know, at one point we have 11 --
to maybe decide is it a factor of 10 what being conservative 12 is.
13 DR. GARRICK:
Yes.
14 CHAIRMAN JACKSON:
Commissioner McGaffigan.
You 15 had a question?
(;o response.)
N
~16 17 DR. GARRICK:
So I am going to move to the 18 interpretation of results.
19 I think we have been talking about -- and I am not 20 going to say much about that because key similarities of PRA 21.
and PA we did discuss at the last Commission meeting.
22 They have a great deal of similarity.
They both 23 can be scenario-based.-
If-you talk about a scenario-based
.24-approach, you are talking about initial conditions and end
~
25 conditions.
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In the reactor game we talk about initiating 2
events.
In our game we talk about initial conditions, 3
end-states.
4 We have an advantage in the waste field in that 5
the end states that are the most likely going to be defined, 6
and we are looking forward to EPA doing rnat, is a health 7
standard of some sort, a dose standard, and so we don't have 8
to have a surrogate for health effect, we can calculate it, 9
so it lends itself very nicely to a risk-based approach.
10 There are some dissimilarities.
11 One of the things we talked about in this letter 12 is the need for a mechanism, a tool for analyzing the 13 results, for being able to take the results and take 14 advantage of how those results were assembled and unravel 15 them in such a way that one can see the effect of 16 intermediate results on the bottom lines.
17 We know Staff is working on that.
We are going to 18 continue to push for that because we think that that is f
19 absolutely key to making this process an acceptable process.
20 We talked about specific methods that are employed 21 to do this.
We mentioned the event tree.
We are not 22 religious about that.
There are other methods and we are 23 open to those kinds of suggestions, so our conclusions 24 relative to probabilistic performance assessment, we do 25 believe that sustaining the properties of risk analysis, of ANN RILEY & ASSOCIATES, LTD.
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4 26 1
doing realistic analysis is important.
2 We want to make a contribution to having that be a 3
conscious thing on the part of the people doing the work, 4
tuid we are suggesting that, in conclusion, that the Staff 5
look very hard at some sort of a post-processor that makes 6
this whole issue of interpreting the results of the PA a 7
more manageable one, and we are convinced, especially 8
following our meeting, that they are working on this.
9 CRAIRMAN JACKSON:
Thank you.
Commissioner?
10 COMMISSIONER DICUS:
A couple of questions.
11 One, on the use of the post-processor, you said 12 the Staff is working on this, that they seem to be agreeable 13 to do this, that this is the right direction to go?
14 DR. GARRICK:
Yes,' they are agreeable.
15 I think that as most of the problems in life are 16 communication problems, everybody has their own language as 17 to -- in this field when they practice this, and they become 18 strongly identified with that language and the images that 19 come out of that, and I am certainly no exception to that 20 and the committee is no exception to that, so we have had a 21 little bit of difficulty understanding each other on how we 22 are doing this ani I think we need a lot more briefings and 23 interaction, especially with respect to developing a more 24 in-depth understanding of TPA 3.1 before we can rehlly say 25 we are getting together on this.
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So-I think therefis work to-be_done, but_I-suspect-2:
a-lot-of that work-Lis_ understanding.eachiother.
3 COMMISSIONER DICUS:
What about',.again' thinking.
4 about DOE, is DOE--doing anything like this, are_you aware?-
t 5-1[ don't know if we know.
-6 DR. GARRICK:
DOE needs this.: There is no 7-question in our mind that they need it.
We' understand ~that 8
_they are doing some things.
We don't know for sure what 9
they are.
10 They attended the same meeting where this was L
-11 discussed.
They-did comment at the end of that meeting they 12~
thought they were doing-most of what we were talking about.
13 Based on what we have seen, what we have heard, we 14 --
are not convinced of that, and also down the road i; 2he 15 licensing process it's going to take a lot more interec :icn.
16-CHAIRMAN JACKSON:
Is this being done within a 17-laboratory, DOE laboratory, or is it done by other DOE --
p 18 you knoa, staff?
19-DR. GARRICK:
The team that is doing the TSPA, the 20
. Total Systems Performance Assessment, is made up of -- that 21 is one of the things that' concerns us.
22 There's a lot of laboratories, universities, M&O
-23
_ contractors, DOE staff that are involved.
I think that one
- 24 lof the biggest challenges they have is the integration of 25 the' inputs that they are --
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n 28 21-CHAIRMAN JACKSON: 'Well, you~know,_ I told-them 2-thatetwo-years ago.
3; DR. GARRICK:- Yes.
Well,: you were right on.
4-CHAIRMAN JACKSON - Yes, actually -- I mean-it was i
.5 clear then in terms.of-how the work was tracking and who 15
_ was, you know, wno was pulling it all together.
7 COMMISSIONER DICUS:
And one more just quick' 8
question.. Making these shifts a little bit with the staff 9_
and more realistic models and all, have you thought about 10 resource implications for the Commission?
~ 1'l.
-DR. GARRICK:
Yes.
Yes, and-we know --
-12 COMMISSIONER DICUS:
Do you have them?
13 DR. GARRICK:
There are resource problems.
The 14 NRC Staff clearly does not have-the resources that DOE has 15 to work on performance assessment and so they have to be 16 much more selective in what they do, and it is a constraint.
17 No question.
18 COMMISSIONER DICUS:
Thank you.
19 CHAIRMAN JACKSON:
Part of the reason I asked the 20 question also had to do with -- about information bases --
21 is the input-to this process from the Center, the Nuclear 22 Waste Regulatory Analysis.
23 Do you have a sense of how the work that that 24 center is doing is being integrated into --
25_
DR. GARRICK:
I am not sure we completely 4
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understand that.
2 I know one thing that the committee is in 3
agreement on is that the Center has a very import-~* rule 4
and that we feel that their involvement is extremely 5
important and there's some integration problem there too.
6 It's a little simpler.
7 CHAIRMAN JACKSON:
Right.
8 DR. GARRICK:
Than DOE's.
9 CHAIRMAN JACYSON:
Commissiont.r?
10 COMMISSIONER DIAZ:
Yes.
Going back to something 11 you said a while ago and to this you aaid that when you do 12 your PA analysis it's different than reactor because your 13 end point is better known.
14 What is the implication of the recent, you know, 15 Chairman of ICRB suggesting that we go to a 30 millirem per 16 ar and back off collective dose if that -- what I am 17 king is tfould that knowledge make the process of analyzing 18 these things, if you really know what dose you are going to, 19 easier and lese resource intensive?
20 DR. GARRICK:
Commissioner, you have just touched 21 on a subject that will take us 10 meetings.
22 (Laughter.)
23 DR. GARRICK:
There is no questions that some 24 decisions on collective dose and thresholds would have a 25 major impact on end states and how we deal with them.
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'This is a very critical issue.
If I had to guess 2
an issue that might find itself on the top tier next year, 3
it would be that one.
It would be the whole issue of 4
thresholds and --
5 COMMISSIONER DIAZ:
And so would you recommend-
~
6 some time that the Commission makes this an issue that needs 7
to be resolv6d with whatever means we have to address it?
8 DR. GARRICK:
Yes, I would.
Very much so.
9 All right.
Wnat I would like te (o now.ts move 10 into our third presentation actually -- Dr. Wymer.
11 DR. WYMER:
Thank you.
We heve passed over into 12 some cf my areas in some of these questions and responses.
13 I would like to take just a minute to put this in 14 context a little bit and to explain some of what I will say, 15 which may diffar somewhat from the viewgraphs in a few minor 16 ways.
17 We have prepared three letters on this subject of 18 performance assessments spaced rcughly at three year 19 intervals.
I think the pace will quicken as we get closer 20 and closer to the repository licensing action and I will 21 add, too, what we are embarked on here in the performance 22 assessment for the Yucca Mountain Reposito.y is very large, 23 very costly, and probably more import antly from the point of 24 view of our considerations is in many ways unique with as respect to the knowledge base required and with respect to ANN RILEY & ASSOCIATES, LTD.
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31 j
1 what the input to the performance assessment has-to be.
2 That to a large extent has set the stage for much 3
of what the NRC has had to do.
4 So with that little introduction, I would like to 5
get into it.
Now since we wrote the letter-to the G
Commission on the eighth of October and subsequent to that, 7
toward the latter end of Hovember, we got a very detailed
{
8 response from the Executive Director of Operations that-j 9
dealt with a lot of our suggestions'and in fact pointed out t
10 that not only had they been considering these suggestions 11
'that we made, we'd like to think it's based on our previous 12 communications and discussions, but also largely to their 13 own initiative, and had in fact planned to deal with many of r
14 these issues that we have raised, which is very gratifying, 15 and in some cases had actually acted on them.
16 So with that little background, I'll move on to 17 the first viewgraph.
18 We thought we would start off on a positive note 19' and -- and it will stay pretty positive -- r.nd point out the l
20 accomplishments that the NRC Staff with the support of the i
21 Center have achieved.
22 One of the things we were particularly concerned 23 about was in light of budget cuts and reduction and the 24 ability to carry out soma of the support for the key.
25'
'technidal issues,.of which'10 have been identified, whether i
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-1 or not the NRC would be able to go' ahead-and do-what it 2
needed to do in a timely enough way to meet the needs for 3
the review of the total system performance assessment l
t 4
viability assessment and the licenme application and what we-5 have-ler.gned is that in fact the Staff has been very clever-T 6
and has managed ~to reassign some of the-key parts of some of 7
the key technical issues to other; better' supported-key f
8 technical issues in order to keep things alive and make sure i
9-that-the. essential things are moving,-so that has happened, 10 How as you know, the-key technical issues and the l'i' Issue Resolution Status Reports are the mechanism by which 12 this whole process is carried forward. As the 'tey techr,1 cal j
13 issues are addressed and the technical requirements use 14 established, the input then is fed into the performance 15 assessment people and there is a necessity for a close 16 symbiosis there and that is well-integrated as far as we can 17 see and takes place quite well.
18 I have the next list of accomplishments here.
19 With respect to the total system performance 20 assessment viability. assessments, there have been a number 21 of communications between the NRC Staff and the Department 22 of. Energy staff on the code development und on the 23 resolution of issues and on the convergence of what the key 12 4 technical-issues in fact are.
25
.That has been very important_in-leading toward t
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preparing for this review.
We don't expect, based on what
)
2 we have heard, that the Department of Energy will receive 3
any great surprises downstream, that in fact there will have l
4 been enough discourse that while there may be a i
5 disagreement, there may not be any surprises -- or certainly 6
not many.
I think that is a very positive thing the Staff 7
has accomplished.
8 With respect to the code, which is in many senses 9
the proof of the pudding, it is the tool that will be used 10 in assessing DOE's license application and capabilities, one 11 of the most important tools, we have been gratified to see, 12 and this came up in the previous comments, that the code has 13 been upgraded.
14 It's recognized as a living document, something 15 that will be continually upgraded as sensitivity studies are 16 made and shortcomings in it or deficiencies in it are 17 unearthed.
18 It's my understanding that the code was completed 19 in September and right now there have been some sensitivity 20 tesco performed on mcdules of this code and there will be a 21 user's manual.
22 This gets to the point that was raised of what is 23 the backup information, what is the documentation, how do 24 you know really what the code has in it and what it will do, 25' how well-based, how well-founded it is.
There will be a i
l l
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-l user's manual we understand, produced in early 1998, which 2
will-detail what the input is, what the assumptions are, 3
what in fact the code consists of, and we are looking 4
forward to seeing that just to see how well it does meet 5
this advertised goal, G
We'll' move on to the next viewgraph then.
One of 7'
the things that we have sort of honed in on is the issue of 8
the engineered barriers.
What we have observed is that as 9
_ time goes on, DOE has more and more come to recognize-that 4
10 geology alone is not going to'be the whole answer or not 11 enough will be known for that to be the whole answer, and in 12 complying with the response to the' defense-in-depth concept 13 which they are obliged to correspond to, that they are 14 getting closer and cloccr to the waste package with respect l
15 to doing analyses of retention of radionuclides and what i
r 16 this means to the final dose.
17 So that gets into the issue,-the whole question of f
18 engineered barriers as it relates to the defence-in-depth 19
_ concept, which George Hornberger will address here next.
20 CHAIRMANiJACKSON:
Let me ask you a question here.
21 You mentioned the reduction of the Center's i
22 efforts,on the_KTIs related to engineered barriers and 23 radionuclide transport.
24
'The question is, are you suggesting that the KTIs 25 need to be reprioritized in some way?
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DR. WYMERs No.
What in fact has happened is 2
since we wrote our-letter we have learned that there has 3
been-a few additional people brought on to deal with these 4
specific areas, in the areas that we have suggested, 5
specifically, and there has been an increased level of i
6 funding associated with the KTI on radionuclide transport 7
and particularly near-field.
8 CHAIRMAN JACKSON:
And when you ta.*s about the 9
specific needs dn engineering analysis, material science, 10 and chemistry, are you saying that the staffing level in 11 inadequate or that there is an absence of these disciplines?
12 DR. WYMER:
It depends.
I think more staffing 13 could be used to advantage.
14 There is not a total' absence in any of these 15 areas, but because of the increased stress and emphasis on 16 engineered barriers, enhancement would certainly be 17 desirable.
i 18 CRAIRMAN JACKSON:
- 7. see.
19 DR. GARRICK:
I think that when we heard the 20 presentations in July, one of the senses of the committee 21 was that if there was an area where we had not seen as much 22 capability and expertise as perhaps we would like, it was 23 the area of analyzing the containment capability integrity 24 of the. engineered systems, so I think that this was a 25 particular point that we were focusing on in view of what l
1
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has happened at DOE in their TSPA over the last two years 2
and the growing dependence on engineered systems to 3
demonstrate the kind of performance they want to achieve.
4 So we were really suggesting that it is not to say 5
the'NRC doesn't have that kind of capability.
It was'only 6
to say that we hadn't seen it.
7 It was not as visible in the presentation and in 8
the documentation.
As we learn more about TPA 3.1, we are 9
seeing more and more.
10 CHAIRMAN JACKSON:
I see.
Commissioner 11 McGaffigan, did you have a question?
12 COMMISSIONER McGAFFIGAN:
No.
t 13 DR WYMER:
Okay.
We have attached enough 14 importance to this whole issue of engineered barriers that 15 we are in fact going to convene a workshop on this subject 16 we hope in March or no later than April of this coming year.
17 CHAIRMAN JACKSON:
Will it be a workshop to which 18 you will invite international participants?
19 DR. WYMER:
We will do our best to invite the best 20 people.
There is a lot of work going on.
31 CHAIRMAN JACKSON:
That's right.
22 DR. WYMER:
That's right.
23-International -- there's a recent meeting that's 24 directed in part toward this topic, and there are some very 25 good people working in the field outside of this country, ANN RILEY-& ASSOCIATES, LTD.
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and we hope that the outcome cf the workshop will be a
]
2' focusing of attention on this area and a highlighting of l
3 some of the needs which } <. haps haven't reslly emerged as 4
clearly as they should up to th.ls point.
5 DR. GARRICK:
Just a quick observation on that, f
6 because I think it's an important point, namely the i
7 international.
8 The committee is fortunate that Dr. Fairhurst is 9
on the committee, because he has been extremely active in-10-the international community and probably knows every 11 rock-hound --
l 12
[ Laughter.)
in Europe-and other places on 13 DR GARRICK:
14 this topic, so we take that question very seriously.
j 15 Can we go to the next viewgraph?
i 16 This is -- this is not meant to do any more than j
i 17
-- it is not meant to do any more than to give you an idea 18 of what the near-field looks like in one of the -- or will 19 look like in one of the drifts in the Yucca Mountain 20 Repository.
21 And the point I wanted to make on this viewgraph 22 is.that it is an extraordinary complex system, starting in u
23-the middle with the fuel, which has its own barriers to 24 release, and inside the canister there could be additional L
25 barriers:provided if that were found to make a positive s
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benefit.
And then's there the cask itself which provides 2
not only containment, but a potentially chemically reducing 3
environment, which further complicates the issue maybe with 4
renpect to transport of thing like technetium and neptunium, 5
which move rapidly in their common valent states, but which, 6
if reduced, might behave very differently.
7 And then that shows a drip shield which is another 8
-- another engineered barrier feature.
And then surrounding 9
the entire thing, but within the concrete liner, wall liner, 10 there can be another filler material which can either be 11 chemically reactive or not, depending on the value of 12 providing that kind of reactivity.
13 So the general point I wanted to make is that, 14 just within that drift, we have an extraordinarily 15 complicated system that requires analysis and it remains to 16 be seen how important each one of the features, or changes 17 in those features inside that drift can be to the ultimate 18 retention of radionuclides and whether or not it is 19 effective in the 10-year, 100-year, or 1,000-year time 20 frame.
These are things which need to be ferreted out, and 21 that's all I wanted to do with that.
22 CHAIRMAN JACKSON:
Yes.
23 COMMISSIONER McGAFFIGAN:
Just on the picture, is 24 the idea at DOE that they will add these barriers over time?
25 The issue we talked about earlier, retrieveability for 100 ANN RILEY & ASSOCIATES, LTD.
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years, or whatever.
2 DR. WYMER:
Yes.
3 COMMISSIONER McGAFFIGAN:
If you have backfilled 4
with a lot of rock, that may or may not be chemically 5
active, it looked like it would be pretty hard to take --
6 DR. WYMER:
7t's kind of hard, yeah.
What we 7
understand is that they plan to not backfill for about 50 8
years.
In order to give time to see-how things play out.
l 9
And then if things look pretty good, and there is no real 10 problems and no objections, then they would -- then they 11 would go in and backfill, and then it does get difficult to 12 do anything after that.
But they -- they see it 50-year, 13 give or take.
14 DR. HORNBERGER:
Our understanding is that most of 15 the things on that diagram are not p-.t of DOE's reference 16 design.
17 DR. WYMER:
Well, the things that aren't -- if we 18 could have it up there again.
Are the things that are in 19 yellow.
Like' ceramic coatil.g is not.
They are not taking 20 credit for the cladding and the backfill is not in the 21 reference design.
But this is the design, I was told by 22 Jack Bailey, the man in charge of thic, that they hie lu 25 fact working to, even though it is not cheir, quote, 24
" reference design."
25 DR. GARRICK:
Well, the reference design for the ANN RILEY & ASSOCIATES, LTD.
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1 viability assessment-is this minus --
l 2'
DR. WYMER:
Minus what is in yellow.
.f t
3 DR. GARRICK:- Minus the thing that is in yellow.
4 Yes.-
l 5
DR. WYMER:
That's right.
That's correct.
6 These other things in yellow are things that could 7
conceivably add to the integrity of the system.
8 CHAIRMAN JACKSON:
Well, this is a clear case l
r 9
where the technical decisions are policies.
10 DR. WYMER:
Yes.
That is absolutely right.
. 11 I wanted to, in the interest of time, to pass on 12 the next viewgraph called Requirements of Realistic 13 Performance because a lot of that has been covered one way 14 or another already.
And go on the conclusions.
Our 15 conclusions by and large are favorable.
We think that there 16 has been substantial and good work done on the EPA 3 Code.
17-
- We have a few concerns.
We would like to see the 18 code verified and benchmarked.
So far what has been done is 19 has been measured against DOE's corresponding code.
DOE's 20~
is much more complex because they have the burden of 31 providing a license application.
The NRC has the burden 22 cnly nf checking themfsud. making sure that we agrs6 with 33 what they say on whether it is right, i
34 We do think that it would be good to get the code-
-t 25 out for peer review as soon and as thoroughly as possible, t
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The unique aspects of the situation do mean that 2
benchmarking is. difficult because it can't -- there is 3
nothing to benchmark it against in some cases, although 4
certain modules can be benchmarked.
5 And, quite important, we think this whole thing of 6
maintaining computer -- adequate computer capability is 7
central, because the code is central, and the code is a 8
computer code.
Therefore, you must be able to have the 9
resources at hand to run the thing, and to adequately carry 10 out the calculations in a timely manner.
11 COMMISSIONER DICUS:
Excuse me.
12
-CHAIRMAN JACKSON:
Yes, Commissioner.
Go ahead.
13 COMMISSIO!!ER DICUS:
Yes.
We may have the same 14 question.
15 CHAIRMAN JACKSON:
Well, go ahead, Commissioner 16 Dicus.
17 COMMISSIONER DICUS:
We are talking about the 18 computer capability.
I think I heard you say resources.
So 19 are you talking about expertise, or are you talking about 20 software and hardware, and expertise?
21 DR. WYMER:
To a large -- hardware is sort of 22 centfhl.
1 r.hink that ths== there could be more manpower 23 put on it for analyzing the code and doing the sensitivity 24 analyses, those are very important.
And, as a matter of 25 fact, I could mention, I guess, to a certain extent, the ANN RILEY & ASSOCIATES, LTD.
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42 1
information is not available, and in other ways, it is not 2
sought for doing the actual probabilistic risk assessment, 3
or the code, but rather their sensitivity analyses are done i
4 on individual modules, which in fact cover a range and allow 5
you to establish what the -- what the swings are in 6
performance under various parameters, and so.
7 COMMISSIONdR McGAFFIGAN:
To follow up, what is 8
the hardware capability at the moment that you are finding 9
locking or potentially locking?
Do we not have powerful 10 enough hardware either here or at the Center to run the 11 codes as they develop?
12 DR. WYMER:
Well, I am little bit like Roy Rogers, 13 all I know is what I read in the newspapers.
All we know is 14 what the -- what the staff tell us.
I, personally, do not 15 have the capability, the background to evaluate it.
But we 16 are -- we are told that they would like to somewhat increase 17 their capability and it might be that some sort of a 18 separate presentation on that specific point might be 19 desirable.
20 DR. HORNBERGER:
There was a concern they would be 21 unable to maintain the current capability in terms of 22 hardware.
And so the first worry is not take a step 23
- onckward, 24 COMMISSIGNER McGAFFIGAN:
The other question that 25 really follows -- you have talked about most of the other ANN RILEY & ASSGCIATES, LTD.
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suggestions previously.
The thrust of these is to add, 2
although the staff has clearly responded on the KTIs with 3
regard to engineered barriers and radionuclide transport, 4
but are there any areas that the staff is working on at the 5
moment that perhaps we could scale back the effort in order 6
to make room for some of these things that you are 7
suggesting we work more on?
8 DR. WYMER:
That is hooked directly to the KTIs, 9
and in some of those, like the vulcanism and tectonic areas, 10 they are farther along than they are in others.
And so 11 there probably is some grounds for discussion of how near 12 complete they are and what the relative importance of these 13 are, but we have been told and there are pieces of paper 14 that support the feeling that some of these areas are 15 nearing completion.
16 CRAIRMAN JACKSON:
Do you have a sense that the 17 staff has a plan, a migratory plan to go from a focus in 18 some of these areas to the arean that need more focus?
19 DR. WYMER:
She's looking at you.
20 DR. GARRICK:
- Well, 21 CHAIRMAN JACKSON:
When I, this is only way I know 22 to communicate.
23 DR..GARRICK:
We are assured that they do.
But at 24 the risk of getting in a little trouble, to answer Mr.
25 McGaffigan's question, I think that some of us would ANN RILEY & ASSOCIATES, LTD.
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certainly want the Commission to look at, if they are 2
resource-constrained, the tradeoff of some of the earth 3
science capability for more engineering capability.
Because 4
the whole industry has -- is transitioned from an earth 5
science dominated issue to more and more engineering 6
involvement.
So, as a general statement, I think -- and if 7
I were -- had an organization such as they have, that is 8
probably where I would begin to look.
And I had no more 9
FTEs that I could add -- that is a term I have learned about 10 since coming here.
So --
11 CHAIRMAN JACKSON:
Okay.
Earth sciences versus 12 engineering.
13 DR. GARRICK:
Yes.
14 CHAIRMAN JACKSON:
One E for another.
All right.
15 DR. WYMER:
One fina) point I wanted to make is 16 that we would like to see an enlargement of the -- of the 17 scientific basis for treatment of the near-field 18 radionuclide mobilization.
And there's a lot of information 19 available.
It has not been developed in the context of this 20 problem, but it certainly is directly relevant to this 21 problem.
An enormous information base can be tapped.
It 22 probably should be done r.iore systematically and in more 23 detail than it has been, and I think to this point it hasn't 24 been just because there hasn't been a recognition of the 25 importance of the near-field like there is now, and the ANN-RILEY & ASSOCIATES, LTD.
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resources are -- are bounded.
2 CHAIRMAN JACKSON:
Right.
Okay.
Yes?
3 COMMISSIONER McGAFFIGAN:
Is that an additional 4
KTI or is that scmething that would need to be done within 5
the context of the existing KTIs?
P 6
DR. WYMER:
That is a subissue under the KTIs, 7
yes.
8 COMMISSIONER McGAFFIGAN:
Okay.
9 CHAIRNAN JACKSON:
I think we had better on.
i 10 COMMISSIONER McGAFFIGAN:
Yes.
11 CHAIRMAN JACKSON:
Because we are running out of 12 time here.
13 DR GARRICK:
Dr. Hornberger will talk about 14 defense-in-depth and the letter you have received on that 15 subject.
16 DR. HORNBERG2R:
- Yes, I see we are running out of 17 time.
They tried to kid me that I was batting clean-up.
i l
18 But we all knew.
19 I have some comments that I would like to make on 20 the letter than we sent you on October 31st, 1997.
- And, 21 clearly, the whole issue is the revision of 10 CFR 60, the 22 site-specific revision that is to follow on the heels of the 23 EPA site-specific regulation for or standard for Yucca 24 Mountain.
2f Just a bit of history.
I guess it was last spring ANN RILEY & ASSOCIATES, LTD.
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Janet Kotra gave us a wonderful presentation sort of 2
illuminating for us the thought process that went -- that 3
people went through to come to the current 10 CFR 60.
And 4
Jack Sorenson, this summer, wrote a nice paper for us in 5
which he did a lot of research on where defense-in-depth 6
crops up in the regulations in NRC.
And it is quite 7
interesting that defense-in-depth is something that we all 8
adhere to but --
9 CHAIRMAN JACKSON:
Don't know what it is.
10 DR. HORNBEPGER:
Right.
11
[ Laughter.)
12 DR. HORNBERGER:
It is a nice picture, but it is a 13 little fu :y.
14 CHAIRMAN JACKSON:
We are comfortable with that 15 that we have used for 30 years.
16 DR. HORNBERGER:
That's right.
17 CHAIRMAN JACKSON:
We don't know anything more 18 about it than the concepts, which we may not know about 19 either.
20 DR. HORNBERGER:
And it is good.
And then Charles 21 Fairhurst yesterday showed me the French, the " Defense en 22 Profoundeux" -- I apologize to anyone who actually 'oeaks 23 French.
But the French concept is also quite different ' rom 24 ours.
25 So, at any rate, the first thing that we did is ANN RILEY & ASSOCIATES, LTD.
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we, for ourselves, we said-that defense-in-depth, when we 2
talk about it, was going to refer to methods of design, i
3 construction and operation of a geological repository in 4
ways that ensure safety in the face of considerable 5
uncertainty.
And given that still kind of soft definition 6
of defense-in-depth, we came to the conclusions that this 7
was an opportunity for us to look at our risk-informed 8
approach to -- to the regulation.
And, in fact, we 9
concluded that the specific re- -- subsystem requirements, 10 pr escriptive requirements in terms of the rule, really were 11 unnecessary.
There's more -- this is sort of the bottom 12 line of the whole letter.
~
13 We think that an overall performance-based 14 standard is a superior tool.
15 The next slide, in terms of background, I think, 16 again, perhaps a more logical way, I would go to the tecond 17 bullet for -- first.
We certainly endorse -- I think 18 everybody in the whole business, worldwide, endorses the 19 concept of defense-in-depth, and we recognize this need for 20 the dependence on diverse barriers.
We certainly support 21 the concept in 10 CFR 60 that both the engineered system and 22 the geological system should make contributions to safety.
23 What we -- the conclusion we came to, what we do 24-not support at this timo is the furthering of rule-based 25 prescriptive subsystem requirements in the Yucca Mountain ANN RILEY & ASSOCIATES, LTD.
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.1
-site-specific standard.
2 I threw in --
3 CHAIRMAN JACKSON:
Let me make sure I understand 4
what you said.
l 5
DR. HORNBERGER:
- Sure, f
i 6'
CHAIRMAN JACKSON:
So you are rationalizing
~
7 defense-in-depth with the risk-informed in the following 8-way._
If you want to look at some net system performance 9
that involves both the engineered piece and the natural i
10 piece, and that you recognize that each one makes a
_11 contribution, as you have said, and you can optimize that, 12 but you don't to separately, and within each one, propose L
13 specific requirements, because you are saying in the end you l
14 may not have optimized.
Is that your point?
15 DR HORNBERGER:
That is correct.
Maybe we should l
i 16 write that L-17
[ Laughter.)
18 CHAIRMAN JACKSON:
The transcript will show it.
19 DR. HORNBERGER:
I put in the next slide of the
[
20 Matrunchka because this is -- it is an image that is used 21 quite a bit, in radioactive waste.
22 CHAIRMAN JACKSON:
That's cute.
23
-DR GARRICK:
We were going to bring you each one.
24 We decided that_was pushing it a little.
i 125 CHAIRMAN JACKSON:
I think that's --
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DR. HORNBERGER:
Charles McCombie sent me a nice 2
video that the-Europeans did.
Perhaps you have all sent it.
3 Which is a public information video in which extensive use l
4 is made of this metaphor of the Russian doll.
And I think 5
for public education, it serves a very useful purpose.
It 6
has some limitations carried to the technical extreme, 7
however, and the next slide also comes from -- from Neil 8
Chapman's book.
And we begin to see that -- how we can 9
somehow use this metaphor to say, yes, we have these diverse 10 barriers, each playing a role.
-11 The problem is that we shouldn't get too caught up 12 in the notion that while if one of the -- one component 13 breaks, then we are going to ae saved by the next shell in 14 this Russian doll.
And so I just wanted to point out that i
15 we went through this and had long discussions and -- I 16 shouldn't say that.
We didn't discuss -- we discuss the 17 Russian doll.
18 COMMISSIONER DICUS:
How do you address, and 19 without getting, carrying on too long, an event that would 20 challenge several systems?
I mean how do you -- you have to 21 take that into account.
22 DR. HORNBERGER:
Yos.
23 COMMISSIONER DICUS:
A paving machine can run over 24
_this doll and it is gone.
25 DR. HORNBERGER:
And then -- and then it is gone.
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Right.
2 COMMISSIONER McGAFFIGAN:
This' doll.
3
-[ Laughter.)
j 4
COMMISSIONER DICUS:
And with -- dealing with the j
i 5
public, that's, I mean --
j 6
DR. HORNBERGER:
Yes.
l 7-COMMISSIONER DICUS:
-- that's, as a member, if-I l
8 were a member of the public and this was brought as a way
-9'
.to,.you know, these protective barriers, I would say, well,
-10 I can run over that with a steamroller and I don't have any
-11:
-protective orders.
So you just have-to be careful.
i 12 DR. HORNBERGER:
Yeah.
No, that is correct.
And
[
13 I mean even in the repository context, obviously, if one has 14 a volcano --
i 15 CHAIRMAN JACKSON:
A cataclysmic event.
16 COMMISSIONER DICUS:
Right.
Exactly.
17 DR. FAIRHURST:
It is perhaps a little more 18 appropriate to react to context where there is an external 19 environment that is immediately accessible, where there is 20 an underground geological environment that has got its 21
' limitations.
I o
22 DR. HORNBERGER:
Okay.
Let me go to the 23 recommendations that were part of our letter, because, 24 again, the wholelletter has been summarized very nicely for
-25; us,- Our recommendation is/to use performance assessment to i
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1 quantify the effectiveness of individual barriers.
- Again, f
2 as John said, our whole approach, the way we think about 3
risk-informed decisions is that if we can get in front of us 4
what are our expectation is for the behavior of the system, 5
we can then make informed decisions.
6 DR. GARRICK:
I think an important point on this 7
is that we are -- because it can be misinterpreted, is we 8
are saying put more emphasis on the individual barriers.
9 Put enough emphasis on the individual barriers that you do a 10 better job of quantifying their role in various scenarios, 11 including cataclysmic events or volcanic events, as long as 12 you carry with that the likelihood of the event.
13 DR. HORNBERGER:
Right.
In fact, the second 14 recommendation is that we really think that DOE should, or 15 any license application in the future should be required to 16 demonstrate the contributions, quantitative, including the 17 uncertainties that come out of a PA.
And we also c.'.nk that IS the -- that guidance can be given implementing the DID 19 concept in a revised 10 CFR 60.
In our mind, that feeds 20 back really to the first recommendation, that this guidance 21 would probably take the form of how one would expose the 22 contributions in a rigorous way using a PA effectively.
23 CHAIR!!AN JACKSON:
Go ahead.
24 COMMISSIONER DICUS:
Just, I had this note on his 25 questions.
I almost hate to ask, but this last bullet, "NRC ANN RILEY & ASSOCIATES, LTD.
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should set forth sound principles "
Give us an example of a 2
sound principle.
I mean -- what you mean or define the term 3
a little bit.
4 CHAIRMAN JACK 3ON:
We are back to these 5
adjectives.
6 DR. HORNBERGER:
Yeah, the adjectives.
Yeah.
I 7
wish we had taken that out, right.
8
[ Laughter.)
9 DR. HORNBERGER:
No.
The -- it is very difficult i
10 for me, of course, to -- to give very precise -- a very 11.
precise answer.
And perhaps the wording is a little 12 awkward.
But we think that guidance in terms of the 13 performance to be expected can be given, and should be 14 given.
We don't think that subsystem requirements are 15 appropriate in a rule.
But certainly through guidance, one 16 can set forth ideas on how one would actually go forward in 17 a performance assessment to do what we say in the first 18 bullet there, to expose the contributions.
19 DR. GARRICK:
I think this is clearly an issue we 20 expect to deal with a lot more.
21 DR. HORNBERGER:
Yeah.
32 DR GARRICK:
We expect to interact with the 33 staff, but you have just received a letter, for example, 34 from the ACRS on the characterization of parameters, point 25 values versun uncertainty, where that is a specific example ANN RILEY a ASSOCIATES, LTD.
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of the kind of guidance you might want to give in how you 2
characterize the performance of an individual barrier.
3 CHAIRMAN JACKSON:
I understand.
4 DR.-HORNBERGER:
Let's see, I put in the next 9
slide.
This is a draft from the staff as to how they I
6 envision the -- well, the structure framework for a total system performance, and I think that it-just illustrates 7
8 that there are points at which you could interrogate the 9
analysis to actually get at the contribution of these 10 various processes or the -- and the importance of key 11 technical issues in the staff's framework for how they are 12 going to deal with that.
13 So the conclusion, we think that the approach that 14 we recommend allows to take advantage -- one to take 15 advantage of site-and design-specific properties and 16 features, that it clarifies the degree of dependence of the 17 overall performance of individual barriers, and exemplifies 18 risk-informed performance-based regulation.
19 CHAIRMAN JACKSON:
Thank you.
20 Any further questions?
21 I had one question for you, Dr Larkins.
You know, 22 as I look back at the Committee's outline on its strategic 23 plan, and it laid out its goals and its criteria, for 24 instance, to select the priorities, leaving aride the 25 specific priorities, how much concurrence is there between ANN RILEY & ASSOCIATES, LTD.
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.the ACRS -- does it have a plan and --
~
2 DR. LARKINS:
Yes.
3' CHAIRMAN JACKSON:
-- do its goals and criteria l
4 track with those of the ACNW?
5 DR. LARKINS:
Fairly closely.
Both Committees are 6
revising their operating plans right now to reflect the new 7
priorities that are being developed.
They track pretty 8
closely with the Agency's operating plans and I think they 9
are -- there is consistency betwoon the two.
10 CHAI)U4AN JACKSON:
Okay.
Thaak you.
11 DR. LARKINS:
I can't quantify it.
I mean there's 12 differences, obviously.
13 CHAIRMAN JACKSON:
The Commission would like to 14 thank of all you for a very informative bricCly.
Obviously, 15 you know, even though we are being very careful, we have a 16 keen interest in the use of PRA in the regulation of nuclear 17 fa-ilities and activities, including waste disposal.
In 18 fact, as part of the PRA implementation plan, as you know, 19 Margaret Feuerline has a piece of that relates to looking at 30 the use of PRA and those kinds of approaches in the context 21 of waste management.
32 It. you know, it does seem that it can provide i
23 useful insights into the performance of a repository, and we 24 encourage you, as well as the staff, to continue your 25 explorations along these lines.
Your views are very 1
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l 1
important to the Commission on these matters because you I
2 have the broad-based expertise and the opportunity to stand 3
back and look at these things from a more reasoned point of 4
view.
5 I am intrigued about the idea of the International 6
Conference.
And so the Committees are to be commended for 7
the high quality of today's briefing.
And I really 8
appreciate it and the Commission appreciates it a great 9
deal.
10 So unless there are any further comments, we are 11 adjourned.
12
[Whereupon, at 11:26 a.m., the meeting was 13 concluded.)
14 15 16 17 4
18 19 20 21 2?
23 24 25 ANN RILEY & ASSOCIATES, LTD.
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CERTIFICATE 1
This is to certify that the attached description of a meeting i
of the U.S. huclear Regulatory Commission entitled:
TITLE OF MEETING:
MEETING WITH,@'t.?ORY COMMITTEE ON NUCLEAR WAUTE (ACNW)
PLACE OF MEETING:
Rockville, Maryland DATE OF MEETING:
Thursday, December 18, 1997 was held as herein appears, is a true and accurate record of the meeting, e.nd that this in the original transcript thereof taken stenographically by me, thereafter reduced to typewriting by me or under the direction of the court reporting company Transcriber: LN f
Reporter:
(.
TJ Jon Hundley l
l
[
~
'%,i UNITED STATES 4
NUCLEt,R RE(tULATOPY COMMISSION g,
3 3 ADVISORY COMMITTEE ON NUCLEAR WASTE WASHINGTON. D.C. 20066 4....
December 11,1997 MEMO TO: John C. Hoyle Secretarycf the Co
' sion -,
$ /.N!w FROM:
John T. Larkins, dxecu ive Director Advisory Committee on Nuclerer Waste
SUBJECT:
Aovisory Committee on Nuclear Waste Meeting with the U.S. Nuclear Regulatory Commission, December, 18,1997 - Schedule and Background information The ACNW is scheduled to meet with the NRC Commissioners between 10:00 and 11:30 a.m. on Thursday, December 18,1997 to discuss the items listed below.
Background materials related to these items are attached.
Introduction by NRC Chairman, Dr. Shirley Ann Jackson 10:00-10:05 a.m.
Presentations by Advisory Committee on Nuclear Waste 1.
Pilority issues for the Advisory Committee on Nuclear Waste Dr. B. John Garrick, Chairman ACNW 10:05-10:20 a.m.
2.
The Application of Probabilistic Risk Assessment Methods to Perfom1ance Assessment in the NRC High-level Waste Program (10/31/97)
Dr. B. John Garrick, Chairman ACNW 10:20-10:40 a.m.
3.
Comments on Performance Assessment Capability in the NRC High-Level Radioactive Waste Program (10/08/97)
Dr. Raymond G. Wymer, ACNW 10:40-11:00 a.m.
4.
Recommendations Regarding the implernentaticn of the Defense-in-Depth Concept in the Revised 10 CFR Part 60 (10/31/97)
Dr. George M. Homberger, Vice-Chairman ACNW 11:00-11:20 a.m.
Closing Remarks - NRC Chairman 11:20-11:30 a.m.
Attachments: As stated ec:
^ ~ - ' ' ^ ~ ^ " ^ ^
p nREGuq h)
ADVISORY COMMITTEE ON NUCLEAR WASTE MEETING WITH U.S. NUCLEAR REGULATORY COMMISSION Rockville, MD December 18,1997 e
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I Advisory Committee on Nuclear Waste i
Strategic Planning and Priorities for 1998 i
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Dr. B. John Garrick i
Chairman, ACNW i
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1 ACNW Mission Provide independent and timely technical advice on waste j
management issues to support the NRC in conducting an efficient regulatory program that enables the Nation to safely use l
nuclear materials l
I 2
i 1
.l l
o ACNW Vision t
i The ACNW strives to provide advice and recommend solutions that are forward looking, based upon the best-available science l
and technology, can be implemented, and reflect the need to balance risk, benefit, and cost to society to enable the safe use of nuclear materials
~
5 l
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)
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3 i
s
1 ACNW Goals Assist the NRC in responding to change and uncertainty in the management of nuclear waste e
Provide assurance to the Commission that the best science is being employed in resolving key safety issues 1
e Provide advice to the NRC on how to increase its reliance on risk as a basis for decision-making including risk assessment methods for waste management e
Assist the NRC in improving public involvement Optimize effectiveness and efficiency of ACNW operations e
4
\\
1 Criteria to Select Priorities Protection of public health, workers, and the environment o
issues requested for ACNW review by. Commission e
e Timeliness based on scheduled Commission review Relationship of issue to NRC Strategic Plan e
Potential for an issue to pose undue risk or cost to. society e
issues arising from strategies and activities of licensees e
i issues arising from technical basis for safety assessments e
5
l l
ACNW First Tier Priorities Viability Assessment e
Risk-Informed, Performance-Based Regulation
.e Engineered Barrier System e
i Decommissioning e
e Research 6
i 6
1
i ACNW Second Tier Priorities i
Repository Design
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HLW Interim Storage 1
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a DOE Oversight l
LLW and Agreement States e
1 Radiation Risk Levels for Low-Level lonizing Radiation e
Control and Accountability for Radioactive Devices e
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1 Applications of Probabilistic Risk Assessment Methods to Performance Assessment in the NRC High-Level Waste Program f
i Dr. B. John Garrick Chairman, ACNW 8
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t Primary Issues Performance Assessments should follow'the philosophy of-e i
risk assessment in developing realistic models that display the uncertainties 4
1 The approach to Performance Assessment should allow the o
contributors to the performance of the repository to be transparent and rank-ordered i
9
[
I
NRC Staff Accomplishments Revised NRC Total Performance Assessment code, version e-3.1 (TPA-3), represents e pivotal effort l
i Longstanding staff efforts to ensure:
e l
the collection of appropriate site characterization information, and
[
the understanding of processes affecting repository i
j performance i
l Approaches for abstracting site and design information and e
process models into the TPA-3 model l
l 10 i
i Realistic Models
.i l
l Realistic models and ' parameters should be used so that the results of the pas represent the full range of values that can l
be supported by the evidence i
i Magnitude of the uncertainties is inversely proportional to the l
strength of the evidence i
l e
Bounding analysis and worst-case calculations should be used primanly to screen out issues of little or no concern TPA-3 should be reviewed for unrealistic results that arise from bounding calculatio~ns embedded in the code i
11 l
i Interpretation of Results 1
.j Key similarities of PRA and PA methodologies e
Initial conditions and modular approaches Decompose into logical pinch points
]
Specific performance measures 1
PRA post-processing methodologies allow systematic and e
efficient unraveling of results into specific contributors to performance Identify inputs and outputs of different modules in terms of contributions to overall performance Event tree approaches can make the results more transparent and sharpen understanding of the t'otal system model 12 i
.l
j 1
Interpretation of Results { Cont.)
An event tree or a similar approach should be developed and applied to evaluating TPA-3 model results
\\
i Staff should continue developing appropriate importance measures Performance measures at specific pinch points in the j
analysis should be defined i
i 13
Conclusions More realistic model assumptions and parameters will help.in i
identifying where uncertainties are important to demonstrating compliance and assist in defending staff.
i positions vis-a-vis magnitudes of uncertainties and degree of conservatism in analyses l
Ari event tree postprocessor will help identify the importance of Key Technical Issues to overall performance and in j
prioritizing resources j
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llNITED STATES (NUCLEAR REi3ULATORY COMMISSION'
(
ADVISORY CC MMnTEE oN NUCLEAR WASTE a
f-WAWNGTON. o.C. 20556 -
]
g October 31 1997 v
The Honorable Shirley Ann Jackson l
Chairman U.S. Nuclear Regulatory Commission Washington, D.C. 20555-701
Dear Chairman Jackson:
SUBJECT:
Application of Probsoilistic Risk Assessment Methods to Performance Assessment in the NRC High-Level Wasto Program This letter provides the Commission with the Advisory Committee on Nuclear Waste's (ACNWs) observations and recommendations cn the application of probabilistic risk assessment (PRA) methods to performance assessment (PA) in the High-Level Radioactive Waste (HLW) Program. We believe our recommendations enhance the Commission's policy of y
increasing the use of risk-informed, performance-based approaches in waste management.
The Committee considers this istae a high-priority item because of the need for transparency and clarity' in the decision-making process, not only for the NRC's prelicensing and licensing activities for the proposed HLW rapository at Yucca Mountain, but also for other waste-related activities, such t,s decommissioning, low-level waste management, and management of uranium mill tailings. The complexity of the proposed repository system at Yucca Mountain and the models that are intended to represent its performance over time necessitates some method for presenting the results that clearly indicates to the decision makers and to the public what the expected performance will be and wl'at the main subsystem components are that contribute to that performance. The Committee firmly believes that certain PRA approaches can be successfully applied to the PA results for waste management Summary and Recommendations f
in general, the Committee is impressed with the methods employed by both the NRC and the Department of Energy (DOE) in their work on PA. Analytically characterizing the performance of the proposed Yucca Mountain repository involves an unprecedented application of physical process modeling and probability methods. The progress in abstracting site characterization and facility design information into probabilistic PA (PPA) models has been extensive.
8 By ? transparency" we mean the ability to see hrough the entre process, to understand the process, by "clanty* we mean the ability to discem 0)e key elements in the analyses.
4 4
-. -. -. ~ - -
9 2
Despite this considerable progress, the Committee does have some concems about the staff's PA program. These concems conter around two primary issues. The Committee believes that pas should follow the intent arvJ spirit of the risk-assessment philosophy of developing realistic i
models with uncertainties included, as opposed to developing bounding or worst-case calculations..We also beliete the assessments should enable unraveling the results into rank-ordered contributors to the overall risk or to the performance of the repository. The latter provides a solid basis for developing confidence in the design and meaningful risk-management practices.
' Therefore, we recommend the following:
To as great an exterit as possible, realistic models and parameters should be used so e
i that the rer,ults of the pas represent the full range of values (i.e., upper and lower bounds, central tendency parameters, and the values in between) that realistically can be supported by the evidence.
_ Bounding analysis and worst-case calcu!ations should be used primarily to screen out o
issues of little or no concem, i.e., to scope the analysis, but not to be the basis for generating results that are clearly out of context with reality and, thus, that do not produce a framework forjudging reality.
i e
The NRC Total Performance Assessment code, version 3.1 (TPA-3), should be reviewed for unrealistic results that arise from bounding calculations embedded in the code. Ultraconservative modci assumptions and parameter values should be replaced with more realistic assumptions and probability distributions.
An event tr.ee or a similar approach for evaluating the TPA-3 model results emphasizing the systematic and efficient unraveling of results into specific contributors to performance should be developed and applied.
Appropriate importance measures should be developed. We understand that staff from e-l-
both the NRC and the Center for Nuclear Waste Regulatory Analyses (CNWRA) are currently working on this issue. The Committee encotrages the continuation of this effort.
Subsystem performance measures at specific pinch points in the analysis, such as the 8
flux of radionuclides released from the repository into the geosphere, should be defined. These performance measures might include the integrated release of j
radionuclides over time, or the release rate as a function of time..Both the NRC and DOE have indicated that their respective models are capable of providing intermediate results (e.g., source term output to the geosphere). Hence, the approach can take advantage of the existing model subsystem output capabilities.
- Pmch poets occurwhere outputs (material, energy, or information flow) fmm one module of the total system model become the inputs to another module.
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-Background i
The comments in this letter have been developed, in part, on the basis of a working group ~
meeting on tho application of PRA methods to PA during the g3rd ACNW Meeting at the CNWRA in San Antonio, Texas, on July '4,1997. Part Jpants included representatives from:
the PRA field; the Electric Power Research Institute; the DOE's Yucca Mountain Project; the -
- Waste isolation Pilot Plant PA Project; and the NRC staff. The Committee benefited from
~ detailed NRC staff presentations on the HLW PA program and the NRC's TPA-3 code during
- the previous day's ACNW meeting on HLW PA capability. The Committee members and staff also observed the NRC/ DOE technical exchange on DOE's Total System Performance Assessment activities and NRC's iterative performance assessment (IPA) efforts on July 21-22.
Accomplishments s
The NRC staffs work on the revised TPA 3 code represents a pivotal effort. The staff has
'made longstanding, extraottlinary efforts to ensure that appropriate site characterization information is collected and to understand the processes that ultimately may determine the performance of an HLW repository at Yucca Mountain. As part of the IPA program, the staff has developed approaches for abstracting site and design information and process models that have been incorporated into the TPA-3 model. Tha Committee commends this effort and notes that the recommendations previously presented are aimed primarily at developing more realistic I
modeln, mainly with respect ta assumptions and scope, and improvements in processing the infc r.ation that is the current output of the TPA-3 model, in partcular, the Committee is not suggesting basic changes in the model but is encouraging more realistic assumptions and improvements in the methods for analyzing the results of the pas.
Realistic Models' Probabilistic concepts have their greatest value in communicating confidence in the outcome of an event or process. They provide the tool for analysts to express their full state of knowledge 1
about how likely an event or process is. The introduction of probabilistic analysis does not replace the deterministic models; rather, it allows a richer interpretation of results. Of course, l
'the probabilities must be suppeerted with appropriate evidence, and to the extent that the evidence is weak, the uncertMnties are greater. Such communication is the essence of probabilistic analysis.- Thus, the aim of PPA should be to Neil it like it is* on the basis of all the -
evidence available. The result is what the experts and, with public partmipation, society _
believes is likely to hafpen. A logical framework then exists to make decisions as conservative as desired, but within a framework that defines the level of conservatism.
t internretation of the Results Although there aire clear differences between nuclear power plant PRAs and waste system pas 4
(whleh have beren discussed with the Ccmmission by both the NRC staff and the ACNW), a -
number of key similarities makes it possible to consider the use of PRA methods, such as the top-down event tree approach, to facilitate interpretation of PA results. Both PRAs and pas
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4 begin with a set of initial conditions (in PRAs these are called inibating events). In pas, the initiv conditions may consist of such phenomena as climate conditions, volcanic events,~
seismic events, or human intrusion. Both PRA and pas use a modular approach to the analysis (in PRAs, this includes level-1, -lI, and -Ill analyses; in pas this includes snalyses for 1
!nfiltration, engineered barriers, source term, geosphere transport, biosphere uptake, and dose to the critical group). Both methodologies can be decomposed irdo logical pinch points for which specific performance measures can W developed (such as core damage for PRA and integrated release of radionuclides into the geosphere for PA). The goal is to develop a
. systematic and of'icient method for identifying different inputs and outputs of the various modules that make up the full PA model in terms of their individual contribution to the overall performance of the repository. To do this may require a different approach in the way that scenarios are structured for PA.
At our workshop, rendedate methods were presented for systematically and efficiently -
intrerpreting the results from pas using a post-processing tool, such as an event tree approach.
The pestprecessor could make the results more transparent and sharpen our understanding of the total system mWI. The Committee believes that these techniques should be explored for TPA-3.
An important benefit of the proposed approach to interpreting PA results should be with respect to the program for evaluating key technical issues (KTis). The postprocessor should greatly facilitate the task of determining the importance of individual KTis to the overall performance of the repository. This will allow staff to allocate already scarce resources to the KTl program so that the focus is on the most important KTis and subissue areas. The approach will also prove useful in determining where uruttainties are important to demonstrating compliance and where they do not really matter, even if they are large. Sometimes there is a tendency to focus only on the relative magnitude of the uncertainty in a model or parameter (large uncertainty is considered bad and small uncertainty is considered good), rather than on whether that uncertainty makes any significant difference to the bottom-line result, which is ultimately the health and safety of the public. The goalin the near term would be to avoid spending large resources on trying to reduce uncertainties that do not matter to the result. In the longer term, the goal is to be able to defend in a licensing hearing the specific staff positions in the safety evaluation report vis+vis the magnitudes of the uncertainties for different subsystems and for total system performance.
j The Committee looks forward to following the staffs program in PA, and we are particularly interested in its progress on the t~o 'ssues of transparency of results and the use of realistic models.
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As B. John Garrick Chaiman t
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Performance Assessment Capability in the NRC High-Level Radioactive Waste Program i
1 Dr. Raymond G. Wymer ACNW 15 i
NRC Staff Accomplishments l
Upgrading and preserving a dedicated H'LW PA team e
l Organizing the HLW Program around KTis -- focusing staff's
{
e efforts on issues most important to performance of the 1
repository i
l Integrating across disciplines in KTls and setting priorities e
Developing sound, near-term plans for prelicensing activities, e
including resolving outstanding issues i
16 l
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i NRC Staff Accomplishments (Cont.}
l Preparing for review of DOE's total system performance i
e assessment -- viability assessment (TSPA-VA)
Revising and updating TPA-3 code to increase staff's j
o capability in performing assessment modeling Evaluating the importance of site characteristics Evaluating the contribution of engineered barriers i
17 I
i
Engineered Barrier System
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Concerns Reduction of CNWRA efforts on KTis related to engineered-barriers and radionuclide transport Sufficiency of the PA effort, including TPA-3 code, to i
adequately assess DOE activities t
e Needs i~
- General l
Staff capability to analyze the design of long-term, passive, high-integrity systems
- Specific l
engineering analysis materials science I
chemistry 18
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'ngineering Features Being Considered by "9E for Yucca Mountain HLW Repository Design Ohtions for Waste Isolation (Design Features Evaluation)
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Requirements of i
Realistic Performance Assessment Models PA models should be structured to represent repository performance as realistically as possible Supporting evidence should be collected, organized, and e
documented Abstracting process models into probabilistic models should e
be clear and transparent The scientific basis for treatment of phenomena leading to e
mobilization of radionuclides in the near field should be enhanced 20
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Conclusions Staff's work on the TPA-3 code represents a solid effort and e
ACNW is pleased that a working code has been implemented i
t i
e Further needs include:
t Verification and benchmarking of TPA-3 Obtaining extensive and timely peer review of codes i
Maintaining adequate computer capability Selected capabilities should be added to the program to help assess the containment capacity of the engineered systems
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The ACNW is glad to see the restoration of support at i
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CNWRA for radionuclide transport and engineered barrier KTis j,
21 5
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UNITO STATES
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NUCLEAR REGULATORY CSMMISSION l
ADVisoAY coMMITT;E ot tvuCLEAR WASTE i
wAsHmofow, o.c. asses '
- ...e October 8,1997 4
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l The Honorable Shiriey Ann Jackson Chairman U.S. Nucisar Regulatory Commiss6on Washington, D.C. 20555-0001 f
Dear Chairman Jackson:
SUBJECT:
Comments on Performance Assessment Capabilty in the NRC High-Level Radioactive Waste Program.
The purpose of this letter is to advise she Commission about the NRC staffs performance assessment (PA) capabilty in the High-Level Radioactive Waste (HLW) Program. Performance assessment is an important tool in NRC's prelicensing activities, including the following:
i i
understandmg the importance of specific site characteristes and the design of engineered features j
to the performance of an HLW repository at Yucca Mountain, str&k g key technical issues (KTis) l and staff activities, developing revised standards and regulations for licensing, and preparing for review of the Department of Energy's (DOE's) viability assessment (VA) of the proposed repository, The evaluation of staff HLW PA capability continues to be a priority issue of the Advisory i
Committee on Nuclear Weste (ACNW),
\\
The ob6en-tions and comments in this letter have been developed, in part, on the basis of the 93rd ACNW Meeting at the Center for Nuclear Weste Regulatory Analyses (hereafter the Center) in San Antonio, Texas, on July 23-24,1997. The ACNW previously reviewed and commented on i
staff HLW PA capability in letters dated December 2,1991, and May 27,1994.
Recomspendations The Committee makes the following recommendations:
i Selected ca'pabilities should be added to the program to pnwide further assurance that the i
staff has the abliity to assess the containment capacity of the engineere a systems Support
. for KTis relating to the near field performance of the repository should be restored. Among 4
the disciplines for which the ACNW believes added capability is necessary are engineering analysis, materials science, and chemistry. The crosscutting discipline of corrosion science and eng2neering is also an essential part of the mix.
The PA models should be structured to represent repository performance as realistically
[
. as possible and thereby provide the necessary information for regulators to make decish.M i
la the context of the full state of knowledge about the performance measures of the repository, improved coordination and ::om'nunication betwm the NRC staff and the C.nt.r win b..ss.ntist i
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Greater emphasis should _ be given to collecting, organizing, and documenting the supporting evidence for the performance assessments to enhance scooptance of the results. An important element of this is improvement in communicating the abstraction of f
,wooses models into probabilistic models. Of partcular interest to the Committee is visibility of the treatment of such phenomena as chemical and geolog!:al processes leading to the mobilization of radionuclides in the near field.
i A working version of the NRC's Iotal forformance Assessment code, version 3.1 (TPA 3) should be implemented as soon es practicable.-
(
A program for venfying TPA 3 should be developed. TPA 3 should be benchmarked against other codes for Yucca Mountain. The Committee also encourages exposure of the methods of TPA-3 and associated background information to the scientific community through extensive and timely peer review.
l Accomplishments The Committee comrnends the staff for its many impressive accomplishments in upgrading and l
preserving a dedicated HLW PA team in the face of budget cuts and programmatic uncertainties.
The organtration of the HLW Program around a specific set of KTis and the grouping of expertise and disciplines within the KTis provides an important means of focusing the staffs efforts on issues i
most important to performance of the repository. Performance assessment is important in the-staffs efforts to provide integration across disciplines in the KTis and to set priorities for activities.
The Committee was pleased to see the char integration of PA with other Yucca Mountain activities, i
This effo:t has led to the development of sound, near term plans for prelicensing activities, including resolving outstanding issues and preparing for review of DOE's total system performance
- i assessment supporting the viability assessment (TSPA VA). The rev;swl and updated TPA 3 code increases the statrs capability in performance assessment modeling. The code should facilitate the KTl investigations with its ability to evaluate the importance of specWie site characteristics and 1
the effectiveness of engineered barriors. The ability to conduct waitivity and uncertainty analyses for subsystems and for the total system is improved. The development of the code is a solid effort and we encourage the staff to pursue aggressively the implementation of TPA 3 Many of these staff activities conform to recommendations contained in the ACNWletter of May 27,1994, on PA capability.
Engineered Barrier Syntam The ACNW is concemed about the staffs capability to evaluate quantitatively the engineered
- banier system of the proposed Yucca Mountain repository, This concem is punctuated by lessons
-loomed from PA, including the apparently increasing dependence on engineered barriers to demonstrate compliance with a dose or health-based standard for the repository. With increasing evidence.that engineered systems must be an important part of the waste isolation strategy for Yucca Liountain, it is important that these systems receive extensive scientific and engineering scrutiny.
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- We are concemed about the decision to reduce the effort at the Center on certain KTis, most i
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3 notably those dealing with engineered barriers and radionuclide transport. The shifting emphasis of the DOE to the performance of engineered systems accents the need for the Commission to provide resources to restart work on the KTis most important to an independent assessment of the performance of engineered systems and near field radionuclide transport A concem is that without restarting the work of the NRC staff and the Center, the performance ressessment effort, ir.cluding the TPA 3 code, will not have the scope to assess adequately the DOE work. The Committee urges the Commission 6 act on this issue as soon as practicable.
Beyond the issue of the scope of the engineered systems assessment capability of the NRC staff, the ACNW believes that added capability is necessary to analyze adequately the engineenng design of long Irved, passive high integrity systems. In particular, additional staff effort is required in engineering analysis, materials science, and chemistry (especially corrosion and colloid chemistry) to have the full capaoility to assess the engineered systems.
Realistic Performance Assessment Models The ACNW has three primary points to make regarding the staffs performance assessment modehng activities: (1) the pas should have a risk informed perspective; (2) the pas should be transparent about the supporting evidence (data and information); and (3) the relationship between proccss model and probabilistic calculations needs to be made clear.
Risk informed performance assessment provides the opportunity to assess realistically the performance of an HLW repository. Our concem is that the TPA 3 activity is relying too much on bounding and worst case calculations. Although bounding calculations are a very useful part of any technical investigation in providing insights on what is important to the performance measures of a model, such calculations are often of little value in representing what is likely to happen. In the opinion of the ACNW a much preferred approach is to limit bounding and worst-case calculations to the task of scoping the investigation at:d deciding what may or may not be important to model.
Decision making requires more information. The decision maker needs to know the total range of uncertainty of the performance measures. The primary tool for communicating uncertainty, rather than just an upper bound, for example, is to embed the performance measures in probability distributions so that the full range of values and all their supporting evidence are visible. For example, if the value preferred by the regulator is the 90th percentile value, then it is exphertly clear just how consersative the regulator has chosen to be.
The Committee stresses the importance that the evidence (i.e., data and all other information) that is the basis of the PA model be clearly visible, particularly regarding the abstraction from physical process models to probabilistic calculations. We are especially concemed with the abstraction of i
infomiation about the engineered systems, especially under the circumstances of not having a fuced design. In addition, supporting evidence for modeling irnportant phenomena such as the chemistry of redox reactions is weak. Our current impression is that more attention is being given to methods than to the required information to support those met'1ods.
l Analysis CaoabEty The ACNW was impressed with the progress in the development of NRC's TPA-3 cede. We are anxious to follow the development of TPA 3 and look forward to more discussions with the staff.
4 i
The ACNW t rges the staff to implement a working code in an expeditious manner so that the code is fully functional at the TSPA VA analyses are made avaliable to NRC.
The Commisolon has indicated an interest in moving toward a risk-informed, performance based philosophy of regulation. Of conoom to us is whether the TPA 3 effort is keeping pace with the development of methods and ideas on how to implement such a philosophy.
An issue with TPA 3 is how to verify the code. The problem as stated by the staff is that because the code is designed specifically for the Yucca Mountain slte, intomational bench marking is almost impossible itistrue that parts of the code, such as NEFTRAN (Network Elow and IBANsport),
have been tshmarked. The NRC staff must see that TPA 3 is benchmarked against applications of other codes to Yucca Mountain. The ACNW also believes that the NRC staff should pursue other avenues of peer criticism of its codes, such as publication in refereed engineering arid scientifsc joumals.
Although the ACNW believes that it is important to develop a PC compatible version of the code to reach more us6rs, we would not like to see other important activities compromised to reach thit, goal. A PC compatible version should not be created at the risk of oversimplification. Meanwhile, to conduct a full range of analyses in reviewing DOE's TSPA VA, the staff requires the NMSS Advanced Computer System or a suitsNe attemative.
We believe that these comments provide constructive guidance on the future direction of the performance assessment effort and look forward to following NRC staff progress in this important activity.
Sincerely, Q
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B. John Garrick 4
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Defense-in-Depth Concept i
in the Revised 10 CFR 60 i
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Dr. George M. Hornberger j
Vice-Chairman, ACNW l
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Introduction October 31,1997 letter recommends an approach for implementing the defense-in-depth (DID) concept in the revised 10 CFR 60 for Yucca Mountain l
Approach is risk-informed, thus eliminates need for subsystem l
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rates, and waste package lifetime i
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Overall performance-based regulation in the context of a e
risk-based standard is a superior tool for promoting safety relative to imposed subsystem requirements and allows for greater opportunity for public involvement I
23 l
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Background===
ACNW does not support the concept of rule-based, prescriptive subsystem requirements as exist in 10 CFR 60, which can lead to suboptimal design ACNW endorses the concept of DID and recognizes the need e
for reliance on diverse barriers as part of DID e
ACNW supports the concept in 10 CFR 60 that both the engineered portion of repository and the natural setting must each make a definite contribution to waste isolation 24
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Somree: Chapman, N. A. et al. 7he Geological Disposal ofNuclear Waste. J, Wiley & Sons Ltd.1987.
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THE SYSTEM OF SAFETY BARRIERS FOR HIGH-LEVEL WASTE Glass matrix
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- Additional retardation of Settimentary radioactive material transported overburden in water (sorption, matrix diffusion)
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- Geologicallong-term stability Sourre: Chapman, N. A. et al. The Geological Disposal ofNuclear Waste J. Wiley & Sons Ltd.1987.
Recommendations Recommend using performance assessment to quantify the e
effectiveness of individual barriers, relationships between l
barriers, and uncertainties in barrier performance j
L Require DOE to demonstrate that both the geological system e
and the aspects of the engineered system are effective in l
providing waste isolation capacity and how each barrier contributes to meeting the overall safety objective l
NRC should set forth sound principles for guiding the e
irr:plementation of DID in revised 10 CFR 60 l
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i DRAFT REPOSITORY TOTAL PERFORMANCE SYSTEM (Individual
( Dose or Risk) i SUBSYSTEMS
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and exemplifies risk-informed, performance-based regulation f
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UNITED STATES
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NUCLEAR RECULATORY C2MMISSI2N o
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WASHINGTON. D.C. 20066 I
October 31,1997 i
The Honorable Shirley Ann Jackson Chairman U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Chairman Jackson:
SUBJECT:
RECOMMENDATIONS REGARDING THE IMPLEMENTATION OF THE DEFENSE.
IN DEPTH CONCEPT IN THE REVISED 10 CFR PART 60 This letter communicates the recommendations of the Advisory Committee on Nuclear Waste (ACNW) for adopting a revised approach to the existing subsystem performance criteria in 10 CFR Part 60,
- Disposal of High Level Radioactive Wastes in Geologic Repositories," to implement the defense in depth (DID) concept.
RECOMMENDATICNS 1.
The Committee endorses the concept of defense in depth, including institutional as well as structural aspects, in particular, we recognize the benefit of multiple barriers of protection.
The Committee recommends that sound principles be set forth guiding the implementation of the concept of defense in depth. The Committee, however, does not endorse the establishment of rule based subsystem requirements as exist in 10 CFR Part 60.
We helieve that guidance will depend to a large extent on proper construction of a performance assessment (PA) to expose the role of design elements, operational elements, and multiple barriers, including interdependene) of the multiple barriers. The regulations should be clear on how the DID concept should be implemented. The Department of Energy (DOE) (or any future license applicant) should be directed to fumish documentation that shows how the DlD concept has been implemented in meeting the overall performance goal.
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The Committee recommends that NRC performance assessment procedurus be structured so that the effectiveness of individual barriers can be identified explicitly in the total system performance, The PA should clearty expose the effectiveness and role of selected individual barriers suen as the engineered systems and the natural geclogical setting, The assessment of it'.dividual barriers should include a quantification of the uncertainties involved and (ne inter-relationships among barriers. The Committee believes that there are methods for quantifying the role of individual engineered barriers and the containment capability of the natural setting.
To achieve the capability to assess the effectiveness of individual barriers, both geological I
2 and engineered, it may be necessary to modify the analysis methods, including the PA models, and to enhance the database to reveal the performance of individual barriers, The Committee also believes that exposure of the public to a PA process that is sufficiently transparent could lead to improved public confidence in the ability of the repository to isolate waste effectively.
This letter is one in a series of letters to the Commission conveying the ACNWs views on aspects of the NRG statra strategy for revising 10 CFR Part 60. Previous letters on the staff's strategy for revising 10 CFR Part 60 include lssues and NRC Activities Associated with the National Research l
a Councirs Report, Technical Bases for Yucca Mountain Standards,'" February 9,1996; ' Time Span for Compliance of the Proposed High Level Waste Repository at Yucca Mountain, Nevada," June i,1996; and the ' Reference Biosphere and Critical Group issues and Their Application to the Froposed HLW Repository at Yucca Mountain, Nevada,* April 3,1997. Our recommendations are formulated on the basis of presentations made to the Committee during the 90th,91st,92nd, and 93rd meetings by the NRC staff, the DOE staff and its contractors, the State of Nevada, the National Research Council, and representatives from industry, as well as on the basis of the Commission's policy on risk informed, performance based regulation.
The Nuclear Waste Policy Act of 1982, as amended, mandates NRC to develop technical criteria for HLW disposal that are consistent with the Environmental Prefection Agency (EPA) generic standards and provide for a system of multiple barrierc. The Energy Policy Act of 1992 mandates that NRC conform its regulation to the final EPA standards for Yucca Mountain, the latter of which are to be based on and consistent with recommendations made by the National Academy of Sciences' Committee on Technical Bases for Yucca Mountain Standards fTSYMS). As directed by the Comnussion, the NRC staff is currently pursuing development of site specific regulations for Yucca Mountain to implement the forthcoming EPA site rpecific standards for Yucca Mountain.
In this letter, the concept of DlD refers.o the methods of design, construction, and operation of a geological repository for HLW in wgs that aim tu ensure safety in the face of considerable uncertainty in our knowledge of vunous processes. The implementation of DID in the repository context entails an analysis that exposes the contribution of each design element, each process (or set of procnses) in the natural geological setting, and each operational technique to the safety of the repository. The DID concept includes (but is not identical to) the notion of multiple barriers that act to isolate the waste. One of the major issues regarding regulation within the DID framework it whether ar,d how prescriptive rer:uirements (so-called subsystem requirements) should be placed on classes of these barriers. As discussed below, the Committee believes that the adoption of a risk informec approach eliminates the need for prescriptive subsystem requirements for Yucca Mountain.
The present form of 10 CFR Part 60 partlyimplements the DID approach by prescribing performance requirements of particular barriers.' As noted in the Statement of Considerations to 10 CFR Part 60, in addition to the natural barrier provided by the geological setting, this multiple barrier approach identifies two engineered barriers: the waste package and the underground facility The Statemeri' of Considerations notes tMt the multiple barrier concept is implemented b/ the performanca objectives or requirements, as well as by more detailed siting and design criteria. The Committoa
' Paraphrasing the regulation, the performance requirements specify subs'antially complete conta;nment of waste packages fcr 300 to 1,000 years after permanent closure, release rates of radienuclides from the engineered barner less than one pan in 100,000 per year at 1.000 years after closure, and a prewaste-emplacement groundwater travel time of at least 1,000 years.
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3 recognizes that inclusion of the quantitative subsystern performance requirements in the rule was thought to provide additional confidence to compensate for uncertainties associated with predicting the behavior of a reposkory over thousands of years and for the generallack of experience and confidence in analyzing repository performance.
The Committee supports the NRC's view expressed in the Statement of Considerations to 10 CFR Part 60 thut the performance of the engineered portion of the repository and the geological system must each make a definite contnbution to waste isolation. The Committee recognizes the need for reliance on multiple and diverse barriers as part of the DlD concept. However, we do not endorse the implementation of the DID concept through inclusion of prescriptive subsystem criteria in the revised 10 CFR Part 60.
Current thinking, which is supported by much experience and empirical evidence in both probabilistic performance assessment and site characterization is that performance-based regulations are much more efficient and effective in protecting health, safety, and the environment than are
" command and-control" approaches. Focusing on quantitative subsystem requirements for the propot,ed reposrtory at Yucca Mountain would run counter to this thinking because it potentially cou!J force a design that would increase overall risk even though all subsy$ tem requirements were met.
A hypothetical example may clarify: a requirement that backfill in the repository be capable of substantially retaining all radionuclides leached from the waste package for 1000 years might be imposed. Such a requirement, which on the surface could be seen as beneficial, might force a design that would diminish significantly the lifetime of the waste canister by changing geochemical condrtions in the near field The outcome could be an increased risk L ffected populations relative to a repository without backfill. It is this type of potentially soverse effect from subsystem requirements that an overall performance-based regulation would avoid. Consideration of such hyp'thetical examples supports our main conclusion that an overall performance based regulation in thi. context of a nsk based standard is a superior tool for promoting safety relative to imposed subsyvem requirements.
A major poblem with the current version of 10 CFR 60.113,
- Performance of Particular Barners After Permanent Closure 7 which prescribes performance of particular barriers, is that it is not clear just how relevant any subsystem performance requirement is to the overall safety performance of the repository. Funhermore, in the anplysis of repository performance, interdependency of barriers makes it difficult to assess precisely the role of individual barriers. For example, the assumed rate of percolation of water through the repository affects the performance of all subsystems. The connection between barr'er performance and overall performance is very site and design specific.
Prescribing individual barrier performance may create a design that is imbalanced in terms of indivdual bamer effectiveness. Subsystem requirements may also result in very poor designs from on economic standpoint. The ACNWs view is consistent with the TBYMS report, which cautioned against imposing subsystem requirements that may inadvertently result in a suboptimal repository design.
The primacy of an overall performance based regulation does not imply that DOE, as the 1 cense applicant for Yucca Mountain, would not have to demonstrate convincingly to the NRC that both the geological system and multiple aspects of the engineered system were effective in providing waste isolation capacity. The NRC should insist that the applicant's PA clearly and quantitatively indicates how each barner contributes to meeting the overall safety objective. This information should provide the basis for an informed decision on the license application.
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4 The approach that we recommend offers many advantages over prescriptive subsystem requirements. First, M allows taking snaximum advantage of site and design specific properties and features. Second, it is a clear example of risk informed, performance based regulation. The important contributors to risk can be ranked, thus providing a basis for prioritizing design changes and visk management activities. Third, it clarifies the degree of dependence of overall repository performance on indivukal barriers. In a sense, the safety margins of the various barriers are made more explicit through quantification.
Sincerely, e
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- 8. John Garrick Chairman 9
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