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UNITED STATES OF AMERICA
NUCLEAR REGULATORY COMMISSION
- - -
BRIEFING ON STATUS OF ACTIVITIES WITH
CNWRA AND HLW PROGRAM
- - -
PUBLIC MEETING
Nuclear Regulatory Commission
One White Flint North
Rockville, Maryland
Thursday, April 4, 1996
The Commission met in open session, pursuant to
notice, at 2:00 p.m., Shirley A. Jackson, Chairman,
presiding.
COMMISSIONERS PRESENT:
SHIRLEY A. JACKSON, Chairman of the Commission
KENNETH C. ROGERS, Commissioner
GRETA J. DICUS, Commissioner
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STAFF SEATED AT THE COMMISSION TABLE:
KENNETH HART, Technical Coordinator, Office of the
Secretary
WILLIAM J. OLMSTEAD, Associate General Counsel for
Licensing and Regulation
PRESENTERS:
HUGH THOMPSON, Deputy EDO
CARL PAPERIELLO, Director, NMSS
MARGARET FEDERLINE, Acting Director, Division of
Waste Management, NMSS
WESLEY PATRICK, President, CNWRA
BUDHI SAGAR, Technical Director, CNWRA
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P R O C E E D I N G S
CHAIRMAN JACKSON: Good afternoon. The purpose of
this afternoon's meeting is for the NRC staff and the Center
for Nuclear Waste Regulatory Analysis to provide the
Commission with a periodic briefing on the status of the NRC
high-level waste program and the activities at the Center.
The Commission is pleased to welcome Dr. Wesley
Patrick and the other members from our staff who will be
presenting the briefing this afternoon.
I understand that this briefing will cover several
factors influencing the high-level waste repository program,
a revised NRC high-level waste program, and several key
technical issues facing the program and the issue resolution
process which, of course, you know I am always interested
in.
Since the last briefing legislative initiatives
and budgetary reductions have had a significant impact on
the overall high-level waste program and the NRC's ability
to maintain its present level of activity in this program.
As a result, I understand that you have revised the NRC
program objectives and focused on several key technical
issues, as I mentioned earlier. We are here to listen.
Dr. Patrick, I am introducing you and Dr. Sagar
publicly to Commissioner Dicus.
MR. PATRICK: Pleased to meet you.
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CHAIRMAN JACKSON: Do my fellow commissioners have
any additional comments?
COMMISSIONER ROGERS: Nothing, thank you.
COMMISSIONER DICUS: No, thank you.
CHAIRMAN JACKSON: You may proceed, Mr. Thompson.
MR. THOMPSON: Dr. Jackson, commissioners, this
has been a year of significant changes in the high-level
waste program. In particular, Congress continues to look at
this area frequently. They do more looking than they do
acting.
CHAIRMAN JACKSON: Let the record show that
Mr. Thompson made that comment.
[Laughter.]
MR. THOMPSON: In the high-level waste program.
It is important that we continue to maintain our
focus on the ultimate disposal as the focus of our program
and in fact the national program. We don't want to lose
sight of that.
The significant budget reductions as well as the
recognition that we have to make some modifications to the
regulations themselves to make things more predictable, more
reasonable, more implementable on our regulations, pose some
additional challenges to the staff. That is what we are
going to be touching on today.
This is kind of a unique briefing where we bring
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both the Center and the staff together. We hope that this
is one the Commission will find both informative as well as
a useful approach, and if it is, we may be considering doing
this in the future.
Margaret Federline, who is the acting director for
the Division of Waste Management, will make the presentation
for the staff, and Dr. Patrick, who is the president of the
Center for Nuclear Waste Regulatory Analysis, will make the
presentation on some of the detailed activities in the
Center.
Margaret.
MS. FEDERLINE: Chairman Jackson, Commissioner
Dicus, Commissioner Rogers, we appreciate the opportunity to
be with you here today. I hope you will forgive me. I have
my normal spring cold. I will do my best.
As Hugh indicated, there have been significant
changes in the high-level waste program over the past year.
Dr. Dreyfus met with you in January and discussed the
perspective on DOE's program. Since then, in March, just a
few weeks ago, DOE introduced some additional changes in
their program in the appropriations hearing for the DOE
program.
We have not had an opportunity to review those
changes in detail, but in looking at them in an overview
fashion, we believe that we have put a program in place that
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has the flexibility at a sustained funding level to be able
to address the changes in their program. So today I will be
talking just briefly about the factors that influence the
program and our revised program to address the revised DOE
program. Dr. Patrick will address our formatting of the
most important technical issues for repository performance
and our approach for dealing with them.
Slide four, please.
[Slide.]
MS. FEDERLINE: As Hugh said, several legislative
initiatives are under way in the Congress. On March 13 the
Senate Energy and Natural Resources Committee passed amended
S. 1271; the House Commerce Committee early in the year had
passed H.R. 1020. Both of these pieces of legislation
envision an enlarged role for NRC, particularly in the
standard setting aspect as well as the licensing.
A couple of other key parameters. They do
establish a basis for the waste confidence in the bills
themselves and they know all the siting guidelines and the
suitability process that DOE has put in place under the
Nuclear Waste Policy Amendments Act.
Another significant factor has been the
publication in August 1995 of National Academy of Sciences
recommendations on the technical basis for a Yucca Mountain
standard. These recommendations raise significant policy
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questions. We are spending time doing analysis, working
with EPA to interpret the National Academy report.
As you are painfully aware, our fiscal year 1996
budget was reduced from $22 million to $11 million, and
DOE's budget was also reduced, from $400 million to $250
million for the repository program. Now DOE's program is
about half of their fiscal year 1996 request and it is 40
percent below the 1995 percent levels. They have already
eliminated approximately 1,000 contractor positions.
I have listed on this slide the key changes that
have occurred in the DOE program. Since we are focusing
today on the repository program, I will touch on the bottom
one.
In response to congressional direction, they have
refocused their program on design and performance issues,
really focusing on the core science which underlies each of
these issues.
Slide five, please.
[Slide.]
MS. FEDERLINE: The next slide depicts the key
milestones in DOE's program. I wanted to illustrate these
milestones because for each of these milestones there is a
significant responsibility for NRC. Of course we are all
familiar with the licensing responsibility. Currently,
under the existing program they are planning to make a
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recommendation to the President in 2001, and NRC by virtue
of the Nuclear Waste Policy Act would be required to comment
on that.
Also, in the latest information we have received,
the draft EIS, which had been previously deferred, is back
on the list, and they are planning to complete that by 1999
with a final in the year 2000. We are obliged to adopt
DOE's environmental impact statement to the extent that we
can.
Dr. Dreyfus, when he spoke with you in January,
indicated a need to revise their regulatory structure. We
have since learned that they do have plans underway to
revise their Part 960, which are the rules against which
they would evaluate site suitability under the Nuclear Waste
Policy Act. The Commission has a concurrence role in that.
This was a very public process the last time we went through
this.
DOE is using their total system performance
assessment to focus their safety case. You can see at the
bottom of this slide that they will be completing site
process models and we will be seeing modules on a yearly
basis of their total system performance assessment.
Also, the ESF -- I will touch on what is going on
at the site in just a minute -- there are key experiments
going on in thermal response and coupled processes that we
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need to stay tuned into and make sure that the information
is forthcoming.
Slide six, please.
[Slide.]
MS. FEDERLINE: The centerpiece of DOE's revised
program strategy is the viability assessment. It is
scheduled to be complete in 1998. This is not licensing and
it is not suitability.
As Dr. Dreyfus has indicated in his presentations,
this is intended to provide a technical basis for making
decisions about continuing with the repository development.
So we would expect that there would be a lot of information
that would be collected after the viability assessment was
completed for licensing.
Key elements of the assessment are listed here on
this slide. We have emphasized continually in the past that
a design of the critical elements of the repository are
essential for us to be able to review DOE's program. So we
were pleased to see that that was in the package.
They have also indicated that they will present a
preliminary performance assessment which will predict
repository behavior and will provide a basis for planning
and cost estimating for licensing work.
We believe that it is critical for us to be
involved in commenting on this document. We believe that
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this will be the critical decision-making document by
Congress. So our program is structured to identify
agreements and disagreements with DOE on the most critical
issues for performance as a basis for making our comments in
1998.
Slide seven, please.
[Slide.]
MS. FEDERLINE: Dr. Dreyfus gave you a perspective
on where we stood with site characterization. There have
been some updates that I wanted to mention.
DOE is about three miles into the mountain at this
point in time. They are back in good ground as of this
morning. We receive a routine morning update from DOE on
the tunneling operations.
Four test alcoves have been completed at the site
and they are currently working at the bottom of the slide on
alcove five, which will be used for in situ thermal testing.
That is scheduled to begin in October of 1997.
The thermal testing will be particularly critical,
because that will be the testing that will give us
information on how the repository behaves under heat loads.
We are very anxious to see that and we are very anxious to
interact with DOE on the adequacy of the design of that
experiment.
Site investigations have been scaled back, as I
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note here on the slide. They are focused on testing the
hypotheses of DOE's waste isolation strategy. This mainly
focuses on bounding of hydrologic parameters in the vicinity
of the repository. They are also doing some pump tests to
determine the origin of the northern gradient just above the
Yucca Mountain site.
I think it is important to observe at this point
that no direct observations in the ESF have indicated that
there are any fatal flaws with the Yucca Mountain site, but
of course it is important to continue those investigations
and to probe the vulnerabilities.
DOE's emphasis on testing their waste isolation
strategy seems a very positive perspective to us. We have
urged them for a number of years to integrate site
characterization and performance assessment. We believe
that that is a very positive aspect of their program.
If there were a weakness in the program that we
have seen, it is that DOE is focusing on the positive
aspects of performance and not testing perhaps extensively
alternate concepts. That is going to make the regulator's
role even more important as we try to probe the underlying
vulnerabilities in the assumptions that they make.
Slide 9, please.
[Slide.]
MS. FEDERLINE: As a result of the budget
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reductions, NRC and the Center have already made significant
cuts in the program. There have been a total of 16
full-time equivalents reduced from the NRC program, as you
can see on the slide. This involves loss of some critical
skills such as materials and nuclear engineering, geology,
quality assurance, and hydrology. There has also been a
loss of eight FTEs, as you can see, between 1995 and 1996 at
the Center.
Our program is funded at a $17 million level in
fiscal year 1996. We were able to do this as a result of
some previous year money that was available to us.
Our fiscal year 1997 request is at the $14 million
level. There will be $3 million in previous year money
available at that point. So we will be able to sustain the
program, assuming that we obtain the requested amount in
fiscal year 1997 through the year fiscal year 1997, but in
1998 there will be no remaining carryover funds. So we
believe it will be critical to request the full amount to
sustain the program at a $17 million level.
[Slide.]
MS. FEDERLINE: Let me chat for a few minutes
about our concerns stemming from the budget reductions.
We believe that the program we are at now, which
is the $17 million level, is the minimally acceptable
regulatory program. Even prior to the fiscal year 1996
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budget reductions we recognized the need to focus the
program. We were getting behind in our pre-licensing work
and we felt it was important to reconfigure the program to
look at the issues that posed the greatest risk to the
repository.
We believe that any additional reductions that are
taken would result in having to cut into the core skills
that deal with those key scientific issues, and if new
issues are raised at the time of licensing as a result of
our not being able to probe them in pre-licensing, we
believe that licensing could be untimely and could be
jeopardized.
We also believe one of the most important things
that we are doing at this point in time is working with EPA
on the development of implementable high-level waste
standards. The Center analyses have been absolutely
critical. As we work with EPA, we have been doing real time
analyses as they formulate their strategy for the standard,
and we have been providing these analyses to EPA so that
they would have some measure of whether the standards are
implementable when they put them into place.
We also feel that the level of program that we are
at now is essential to provide us a strong technical basis
for commenting on the viability assessment. If we eliminate
from consideration some of the issues which we feel to be
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key at this point in time, the licensing costs and schedules
that are predicted may not have input from the NRC.
I also mention on here that if the viability
assessment is found to be negative, this could also trigger
an early waste confidence decision which is scheduled for
the year 2000. We want to avoid introducing unnecessary
conservatisms in the process.
At the bottom of the slide, we believe that a
sustained funding level, the $17 million level, is needed to
continue the credible regulatory program and the development
of implementable standards.
[Slide.]
MS. FEDERLINE: Let me turn to our program and
talk for a minute about what we have done to refocus our
efforts.
Of course the backbone of our program is our
program objectives. As a result of budget constraints, we
have been looking at these objectives and the assumptions
which underlie these objectives almost on a daily basis.
The most important activity that we have going at
this point in time is our cooperation with EPA in the
development of the standards. We formed a formal liaison
with EPA. We have a representative who deals with the EPA
staff on a weekly basis. We have been conducting meetings.
We have had four meetings at the management and staff level
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to discuss the development of the standards. As I said, the
Center has been critical in helping us to do some technical
analyses which have provided support to EPA.
EPA has told us they are going to send the
standard to OMB in the May-June time frame. Our plan is to
prepare comments for the Commission's consideration on the
proposed standard, but at the same time we want to develop a
paper on what we believe a conceptual outline of our
implementing regulations would be so when you are commenting
on the EPA standards you have an opportunity to visualize
what our standards would look like. It is quite a tall
order, given the amount of time that was taken to put
standards in place the last time we had a go-around. We are
working very hard on this.
We have also set our program priorities on key
technical issues that are most important to repository
performance. We are working hard to achieve agreement with
DOE on these issues. At the current time there are two
issues, the volcanism issue and the seismic activity issue
where there are some differences with DOE. We continue to
pursue those.
Our goal is to resolve or narrow our differences
with DOE so that both organizations are focusing resources
on the areas of clear uncertainty and dispute.
I would just note that we have recently closed the
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erosion issue. You probably recall that the National
Academy of Sciences issued a report on the erosion issue.
We have taken a slightly different approach. We considered
all the data that was available to us, not just the data
that was available from DOE. We looked at that issue and
determined it would not be significant for repository
performance and advised DOE that if they had adequate data
in their license application that we would be able to close
that issue at that time.
Slide 12, please.
[Slide.]
MS. FEDERLINE: Another of our major objectives is
to provide early feedback to DOE on potentially significant
flaws in the design or the performance of the repository.
We think this will have the advantage of focusing our
interactions. We have established a new practice in the
division. We don't have any meeting without an objective.
Once we complete the meeting, we review our objectives and
critique it to determine if we have met our objectives.
Time is so valuable to us at this point in time that we
don't want to waste time if it is not clear what we are
trying to achieve.
It is also important for DOE. We want to have
interaction with DOE when site data can most feasibly be
collected. It won't do any good if we get to 1999 or the
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year 2000 and all of a sudden raise some concern that should
have been addressed as the ESF was being constructed in
fiscal year 1996.
In the face of constrained resources, we are
always interested in improving our program efficiency. On
the next slide I will discuss a number of ways that we have
attempted to streamline our program.
Of course our bottom line goal is always
developing our capability for licensing, and we are
dedicated to developing the methods as well as the staff
capability to do that.
Slide 13, please.
[Slide.]
MS. FEDERLINE: The focus of our technical program
is to independently evaluate the ten key issues which are
specific for a Yucca Mountain site. These issues have been
identified based on our understanding of the site. NRC has
been involved in this program as long as DOE has and we have
some extensive experience both on staff and at the Center.
We also are conducting our own performance
analysis. We call it iterative performance assessment where
we continually confirm the significance of the key technical
issues. We have also done a systematic assessment of our
regulation to ensure that we haven't forgotten anything.
Our key issues are consistent with DOE's waste
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isolation strategy, but as a regulator we have the
appropriate role of probing vulnerabilities and DOE has the
role of proving the positive aspects. So there will be
slight differences in the key technical issues as we go
along. We believe that this will allow us to evaluate the
vulnerabilities in DOE's assumptions.
In order to improve the efficiency of our program,
we have recently reorganized in the Division of Waste
Management and we have consolidated the high-level waste
work into two branches. We feel this will have enhanced
management oversight at the branch chief level as well as
facilitating communications.
We have also established a management board. I
participate in that board, the Center participates, and each
of the branch chiefs that are involved in overseeing the
activities.
We also have multidisciplinary issue teams focused
on bringing all the requisite skills to the solution of each
of these independent issues.
We have developed implementation plans which have
laid out all the activities necessary to conduct between now
and 1999. We have prioritized those activities and we are
moving ahead with those activities which are most
significant in the 1996 time frame. That does include
specifying a path possible for resolution.
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I would just note that the focus of our 1996
program is on using sensitivity analyses to independently
assess the relevant importance of KTIs. We want to ensure
that we are not spending our resources on some aspect of an
issue which overall will not be important for repository
performance.
With this as a backdrop, I would like to turn it
over to Dr. Patrick, who is president of the Center for
Nuclear Waste Regulatory Analysis. He will discuss the
relationship between our issues and DOE's waste isolation
strategy and our management approach for narrowing our
differences with DOE on key issues.
Wes.
MR. PATRICK: Thank you.
Slide 15, please.
[Slide.]
MR. PATRICK: As part of its response to the
budgetary and programmatic changes that have just been
described, DOE has proposed a strategy for evaluating how
well the repository at Yucca Mountain would contain and
isolate waste. This is their waste isolation and
containment strategy.
It focuses on two primary objectives. One is
limiting the annual dose to the public for the period of
time to be specified in the EPA standard, and second,
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providing containment of the waste within the waste
packages.
The strategy comprises five basic assertions or
assumptions that underlie the safety case that they would
intend to make in their license application, and, by
implication, what they would intend to focus their
activities on during the viability assessment.
You can see those five enumerated here. I would
just point out a couple of key features about them.
Most importantly, and you will see this theme
running throughout the remainder of this presentation and
showing up in a variety of the documents that we produce
over the next several years, groundwater is the principal
path of release for radionuclides. With the exception of
just a few radionuclides that exist in gaseous form, those
are the most likely nuclides that will be the focus of
uptake in future populations. Consequently, both DOE's
strategy and also the key technical issues that we are
examining are focused on groundwater, potential disruptions
to those groundwater flow paths, and related sort of events.
Sixteen, please.
[Slide.]
MR. PATRICK: We have identified a total of ten
key technical issues, or KTIs. Those span the entire range
of concerns that must be addressed in testing those five
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hypotheses or assumptions that comprise DOE's waste
isolation and containment strategy.
In contrast to the basic strategy that DOE has
proposed, several of our key technical issues go beyond the
basic performance, the so-called undisturbed performance of
the repository, and they explicitly identify potentially
disruptive processes and events that could occur. A couple
of those have already been alluded to: volcanism, which is
indicated here on the top; and then part way down the chart,
the structural deformation processes and related seismicity,
earthquakes, and so forth.
For low probability events, our focus of attention
is going to be on the consequences of those events in terms
of risk to the public.
You will note down the side of chart 16 a number
of priorities that are indicated. The first level of
focusing of the resources that are available was to identify
these ten key technical issues. As an adjunct to that, to
further focus our attention, we have also assigned these
priorities, as indicated here.
There is always a question as to whether we have
identified the right KTIs and whether we have assigned the
right priorities to those. It is always a good question and
it doesn't always have a good answer. Consequently, we use
the sensitivity analyses that have been alluded to earlier
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and the iterative performance assessment process, those two
things together with the continual acquisition of data by
the Department of energy and the focused acquisition of data
in a confirmatory sense and an exploratory sense from the
staff side to probe whether those are indeed the issues that
we need to focus our attention on and whether we have
assigned them appropriate priorities and given them
appropriate resources within the constraints that exist.
Slide 17.
[Slide.]
MR. PATRICK: We have identified an approach to
issue resolution which comprises the four points that are
indicated here. There are a number of other programmatic
aspects, of course, that deal with specific aspects of
interacting with the Department of Energy and other
interested parties, but these four basic elements are the
centerpiece of our issue resolution process.
The first two, as you can see, deal primarily with
data. They include the provision for the staff to do
confirmatory testing and evaluations regarding DOE's
assumptions. The staff will also critically evaluate the
conceptual models that DOE has proposed in that waste
containment and isolation strategy. And very importantly,
where appropriate, we will go beyond those conceptual models
and propose alternative conceptual models where we feel that
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perhaps the full range of potential models based on
available data both at this site and at analog sites may not
have been address.
Each of the five elements or hypotheses of DOE's
strategy will be rigorously tested, as indicated in the last
bullet, using independent total system performance
assessment calculations and the associated sensitivity
analyses.
Slide 18, please.
[Slide.]
MR. PATRICK: This issue resolution process has
associated with it a number of specific products or
milestones. Outputs that we will use both to pace our
progress toward resolving issues and, where we have achieved
resolution at the staff level, to document that that
resolution has been attained.
You will note here that one of the key areas deals
with interactions with the EPA regarding the development of
the Yucca Mountain standard. The staff is working very
closely with EPA; NRC is interacting directly with them, and
as Margaret indicated earlier, the Center is involved with
your staff in performing calculations that support
evaluations as to whether what is being proposed in those
standards will in fact be implementable when we move down
the road to developing a revised 10 CFR Part 60.
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Sensitivity analyses play a key role, as we have
mentioned several times. The management board has put a
particular focus on these areas. Between this year and next
we intend to complete sensitivity analyses in all of the
areas involved, as I've indicated here. Many of those will
be conducted during calendar year 1996.
Acceptance criteria and review procedures continue
to be developed. When we briefed you a year or so ago the
focus of those activities was in the context of a license
application review plan. Since that time, with the revision
of the DOE's program, the focus is now not so much on
licensing in the near term but on the viability assessment.
We are examining how those review procedures
should be posed and what criteria are appropriate for that
first phase of evaluation, determining whether the site is
indeed viable and where it should proceed with the
development of a repository at Yucca Mountain through the
licensing process.
One of the major changes that we have seen in the
program this year is that there are relatively few DOE
products that are going to be coming forward, nowhere near
the number of products that we have seen in previous years
where we would be involved in reviewing various study plans
and scientific investigation plans, and so forth.
One of the critical documents that is becoming
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more and more important as we approach viability assessment
as well as the license application that will be anticipated
in the future is their total system performance assessment.
We have just received their TSPA, total system performance
assessment '95. Staff is involved in reviewing and
evaluating that.
We are going to do a two-phase review, first to do
an audit review of that document to try to identify those
areas that are most crucial, that need the most staff
attention, and we are going to focus in on those areas and
do detailed technical review, which may include selected
calculations and sensitivity analyses to determine whether,
number one, we understand the assertions that DOE is making,
whether we can agree at this point with their conclusions,
or whether we ought to be commenting back to them with
respect to either the adequacy of the data, the adequacy of
the conceptual models, or the mathematical formulation of
those models and how they are manifest.
The last item on slide 18 is the culmination of
the year's work under the new program, which will be an
issue resolution report where we will document progress
toward resolving the issues as we have postulated in the
form of these ten key technical issues. That will be done
within the context of the DOE waste isolation and
containment strategy.
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Having looked at the general issue resolution
approach that is anticipated, beginning with slide 19 I
would like to go into a specific example of the resolution
process.
[Slide.]
MR. PATRICK: We have chosen here infiltration,
the percolation, the movement of groundwater from
precipitation down to the repository level, and then on to
the water table and out to the accessible environment where
future generations would be affected by the presence of
radionuclides in that groundwater.
As I indicated earlier, the focus of much of the
program is indeed on every aspect of groundwater flow.
This example mirrors that of many of the others.
Typically we find that there are three fundamental issues
that must be addressed with each of these: the quality of
the data and the sufficiency of that data; the adequacy of
their models, including whether appropriate ranges of
alternative conceptual models have been postulated; and
finally, how they have bounded the potential future events
that could occur at the site.
Those three basic areas we find have to be
addressed in essentially all of the areas that we are
examining and certainly with regard to this specific example
of infiltration.
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[Slide.]
MR. PATRICK: Slide 20 shows the starting point of
this particular issue resolution, dealing with the example
of infiltration. We have constructed a geological framework
model using information that is available about Yucca
Mountain and its vicinities, and we have drawn that data
into a basic model that includes the information we need to
address the two basic parts of infiltration, a shallow
infiltration, the upper 30 meters or so of the area, and
then the deep infiltration.
I would note that the shallow infiltration
requires certain kinds of data that are a little bit
different than the deep infiltration. Of most importance,
and it is displayed here pictorially, are things like
topography, the elevations, hydrologic properties of surface
outcropping units, spatial distributions of rainfall and the
like. Those are the sorts of things that we need to get a
firm understanding of the shallow infiltration processes
which in turn drive deeper infiltration.
The deep infiltration, on the other hand, is
governed more by such matters as the stratigraphy and the
structural geology.
I would note a couple of things about this figure.
With regard to the structural geology, you will notice some
fault zones that are indicated there in cartoon fashion, and
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we have also indicated a tick that shows the general level
at which the repository horizon transects this particular
geological framework model.
[Slide.]
MR. PATRICK: If we were to take a slice through
the top of this geological model, you will see one of the
more critical factors affecting the shallow infiltration,
and that is the spatial distribution of the basic rock units
that exist at that site. We will get into that a little bit
later, in the next slide. Here you can see the outcropping
of the alluvium, the soil-like materials, the welded and
fractured tuff unit, and the non-welded unit indicated there
in blue.
I would also note the outline of the proposed
repository is shown on this figure as well.
[Slide.]
MR. PATRICK: Slide 22 shows two basic models that
we are using to examine the process of shallow infiltration.
You will notice there on the left there is one
indicated in a brownish, reddish hue. That is a good model
for flow through alluvial materials or through non-welded
tuff units. This is a model where the mode of flow is
dominated by matrix processes, flow through the matrix.
The one on the right is a little more complex
model. It's a second model, a separate model that we use.
. 29
It treats the infiltration through an alluvium layer of
variable thickness and then looks at the fracture dominated
flow process.
This is an example of where we are treating two
different conceptualizations of the geological material, one
with a matrix flow process and another one with a fracture
flow process.
We find that the thickness of the alluvium in that
right-hand model is one of the most important
characteristics that is needed to understand the
infiltration of water down to the fractured area. It is one
of these situations where if the alluvium is very shallow,
in fact nonexistent, there is a potential for greater runoff
and less infiltration. If it is very deep, there is the
potential that the water will be captured long enough that
much more of it will transpire back into the atmosphere.
But there is a middle zone of ranges of thickness of that
alluvium which seem to be very sensitive in driving the
deeper infiltration process.
The arrows up at the top of the diagram, we won't
go into detail, but those are basic processes that take
place at or near the surface of the earth and need to be
included in the model to be able to understand the shallow
infiltration process. So we show the effects of long and
shortwave radiation from sunlight impinging on the surface,
. 30
precipitation, vaporization of the moisture, and so forth.
[Slide.]
MR. PATRICK: We took those two basic models and
the information contained in slide 21, coupled them together
and ran a series of calculations on a 30 by 30 meter grid
spacing across Yucca Mountain's proposed repository area and
the surrounding vicinity. From that we were able to do a
calculation that indicates the range of estimates of shallow
infiltration that could occur based on the information that
is currently available about the Yucca Mountain site.
I just notice broadly here this color band that
starts from very low infiltration rates, on the order of one
centimeter per year or less, and scales up to something in
the range of six to eight centimeters per year.
At most locations, it is important to note, the
shallow infiltration is relatively low, but we do see
critical areas where levels of infiltration much greater
than the average are calculated to occur based on these
models.
We integrated across this entire area and
calculated some average rates of shallow infiltration.
[Slide.]
MR. PATRICK: That brings us to some of the basic
conclusions that we can make even at this early stage with
regard to resolving the issue related to shallow
. 31
infiltration. So far the results of our studies and
comparing them with some of the work that the U.S.
Geological Survey has done are very encouraging. Our
independent calculations are within about a factor of 2 of
what the U.S. Geological Survey has recently reported having
made actual measurements in a number of boreholes in and
around the proposed repository site. As far as hydrology
goes, a factor of 2 is pretty good.
We feel at this point, based on internal
discussions with your staff, that this aspect of the issue
can probably be resolved. We can agree to an average
infiltration rate of on the order of 12 to 25 millimeters
per year. That seems reasonable for this particular site.
The next part of the issue, the deep infiltration,
is where we begin to see some differences in the
conceptualization of the problem in an area where we
anticipate that considerable additional work is going to be
required.
In the same document where the USGS reports these
shallow infiltration results they postulate a model where
they believe that because of differences in material
properties the water will move very rapidly horizontally or
down dip away from the repository site. In a manner of
speaking, shedding the water away from and preventing or
precluding much water infiltrating deeper into the mountain.
. 32
Based on our earlier comments that we have made
here, that is a critical assumption. Repository performance
is going to be directly and vitally affected by how much
water moves into the repository both from an aspect of a
transport mechanism, and before that in time, from the
standpoint of how the containers come in contact with
moisture and corrode as time goes on. So we have got to
focus on this particular area.
[Slide.]
MR. PATRICK: We have run a few preliminary
calculations that highlight the difference between the model
that we are postulating and the model that the U.S.
Geological Survey has noted in their particular case. Here,
unlike the earlier one, I have taken a vertical slice
through an area of Yucca Mountain, one which transects a
fault with properties very much like the Ghost Dance
fault.
We have modeled the stratigraphy, put in
properties as best we know them at this point, and tried to
examine what would happen as water infiltrates from those
shallow models and begins to move. Well, where does it
move?
In this case we show that in an example where the
water can pool or pond up against that fault structure, as
indicted there in the blue and green colors, and can cause
. 33
infiltration to move down deeper into the formation, where
the infiltration from the shallow levels, instead of
skirting off to the right of this diagram and being diverted
from the repository, may in fact form what is called a
trapped or perched water zone along a fault structure,
causing infiltration to occur to deeper levels as time goes
on.
Just to summarize, our study reveals that those
contrasts in permeabilities between the stratigraphic units
and the presence of faults such as the one shown here can
form perched water zones and they could cause the water to
move downward. That is a hypothesis or set of hypotheses,
depending on how one would want to break them down, that has
to be tested, because it is critical to the containment and
isolation strategy that has been proposed.
If we take that a step further and try to a little
more quantitatively understand why we are concerned about
such matters perhaps seemingly esoteric to some about the
perching of groundwater and enhanced deep infiltration, you
can see that in slide 26.
[Slide.]
MR. PATRICK: Here we are showing the most recent
results that NRC and CNWRA staff have developed, iterative
performance assessment 2, which has been completed and
recently published, and the most recent example of the TSPA
. 34
that we thoroughly reviewed and evaluated, TSPA-93. DOE
does TSPAs every two years, and as I indicated earlier, we
have not gotten into TSPA-95 deeply enough right now to make
a comparison of this sort, but we will be in the future.
You will note that the probability distributions
show quite different results. Very critically, if you look
at the Sandia curve, many of the sample infiltrations for
their total system model show zero deep infiltration.
Another way to compare that information is that if you were
to draw a vertical line upward from the 1 millimeter per
year line, you will see that about 90 percent of Sandia's
cases would have infiltrations driving their performance
assessment of less than 1 millimeter per year.
In contrast, our model, our conceptualization of
the problem would show something a little over half of all
the cases would have infiltrations that low.
These higher infiltrations can lead to fracture
flow and can lead to greater movement of groundwater down to
the repository level.
[Slide.]
MR. PATRICK: That difference in infiltration is
in turn reflected in terms of total releases that are
calculated to occur from the repository, based on our
performance assessment calculations, and we just show here
the aqueous release models both from Sandia's performance
. 35
assessment, TSPA-93, and the staff IPA Phase 2.
You will notice there is about a three order of
magnitude difference between those two sets of calculations.
I would point out that there are other differences between
Sandia's model and NRC's model that are being presented
here, but certainly the infiltration aspect of it is a
dominant player in influencing the total system performance
assessment.
I have kind of come full circle now from my
initial assertion of how important groundwater is to now
showing calculationally that it is one of the major factors
that drives the calculated releases of radioactive materials
from a proposed repository area.
Using that as a little bit of a springboard, I
would like to address a question that is often put to us,
and that deals with iterative performance assessment in its
broadest sense. Why does one need to keep iterating? What
kinds of things drive this ongoing process?
[Slide.]
MR. PATRICK: One can come up with a number of
lists. I happen to have a list of four here that we feel
are critical areas that must be addressed and can best be
addressed using total system performance assessments.
Certainly new site data continues to be collected
by the Department of Energy, and we continue through
. 36
programs to get confirmatory data and also to do
investigations that provide us with insights into how to
conceptualize the Yucca Mountain repository, how to develop
conceptual models. Those models, those data, can affect and
directly affect the output of the total system performance
assessments. So as we collect data, as we get new
conceptualizations, we need to fold those back into those
total system performance assessments.
Conducting sensitivity studies is important not
only from the technical aspect of really understanding the
relative importance of the processes and conditions, but
from a management perspective those same sensitivity
analyses help us to identify what the key issues are and to
put proper priorities and proper resources on to each of
those key technical issues.
The third area. We do use performance assessment
to evaluate, to test the adequacy that DOE's bounding
analyses are providing to us, and most specifically, to test
those five key hypotheses that they proposed in their waste
containment and isolation strategy.
The fourth area, which ties in quite tightly to
the first one as well, is to actually incorporate the new
models and the new data into the total system performance
assessment.
The first bullet deals more with getting a basic
. 37
understanding and doing what we call auxiliary analyses to
understand whether this new process or whether these new
data are really going to have an effect. Ultimately, in a
total system performance assessment model we find that we
have to do some simplifications, and that is what we come
down to here in the last bullet.
I am noting there three particular areas that just
in the last 12 to 15 months have been areas where we have
made some changes in our total system performance
assessment.
The focused infiltration, which we spoke to today.
We have looked and are continuing to look much
more critically at an ash dispersion model, which is very
critical to our evaluation of the relative importance of
volcanism, which, as Margaret noted earlier, is one of the
areas that is in discussion between us an DOE as to the
importance of that particular issue.
The third one is an interesting one. Originally
EPA had a release standard, and the TPA code was set up to
calculate releases. When we did our iterative performance
assessment 2, we had begun to get some insights into the
potential move toward a dose-based model. So we introduced
some dose calculation capabilities. Now, with the NAS
recommendation in hand, we are moving another step, to a
risk-based calculation. So the iterative performance
. 38
assessment and the total system performance assessment codes
have to be revised and need to be run again to be able to
incorporate those changes, both technical and regulatory,
into the modeling context that is available to us.
I would like to turn the microphone back over to
Margaret Federline at this point to wrap up.
[Slide.]
MS. FEDERLINE: I would just note we will have an
opportunity to speak to you more in May about our
performance assessment program, both high-level, low-level
and SDMP.
In summary, despite the uncertainties which remain
regarding the legislation and the funding and regulatory
environment, we really believe that we have put in place a
program that has the flexibility to respond to these changes
if a sustained level of funding can be achieved.
We have focused on our issue resolution and
testing of DOE's waste isolation and containment strategy
assumptions. We believe that sustaining the program at $17
million is important to maintaining a credible regulatory
program as a basis for our viability assessment comments.
Thank you.
CHAIRMAN JACKSON: Let me ask you a couple of
questions. Let me go back to you for a second, Dr. Patrick.
Perhaps this will come out more at the later briefing you
. 39
promised where you will talk about the performance
assessment in more detail.
You talked about doing risk-based calculations.
When I think about iteration or iterative processes, I think
of updating. How do you go about doing that? Do you take
some kind of a Monte Carlo type approach? How do you
actually end up doing that in real life?
MR. PATRICK: The basic approach is a Monte Carlo
approach.
Let me back up a little bit further from that.
The code structure that we were wrestling with in the early
years of the program was to try to get something in place
very quickly, to try to get some calculations in hand so we
could try to scope the scale of the problem.
Beginning with iterative performance assessment
phase 2, though, we took a very deliberate approach to
developing a total system performance assessment code, which
we call TPA, that would be modular in form, that would have
a basic executive code and then a variety of modules that
could be called and used as needed.
What we see happening now as time goes on, in some
cases, where it is a matter of new data coming in, we will
feed in a different probability distribution for those
properties. For instance, permeabilities or something of
that nature.
. 40
CHAIRMAN JACKSON: That's how the modularity
helps?
MR. PATRICK: The data input part is we removed
all hard wiring of data from the code as well.
CHAIRMAN JACKSON: I'm talking about where you use
different probability distributions.
MR. PATRICK: The modularity really comes in where
you have a more fundamental change in the model that is
being used. For instance, some of the early calculations,
the volcanism models and the structural geology models,
faulting modules, were very rudimentary. They were based on
rather gross assumptions, particularly with regard to
disruptions of waste containers, assuming that a waste
container was somehow a cantilever beam that was being
shaken back and forth. Not a very good model, but to get an
initial handle on how things were going we chose to do that
within the resources. The modularity really comes in that
now we are going to be able, with additional time,
additional data available, to do a much better
conceptualization of that problem.
Budhi.
MR. SAGAR: I think the main updating is relative
to assumptions. I think all performance assessments,
however complex they are, have underlying assumptions. The
fewer you make the more confidence you have. That is what
. 41
iteration essentially does, that whatever more you have
learned either of the processes that must go into models or
the data, that helps you to understand the site better, or
you know more about design. So long as you can update with
respect to those new things, your final result, I think that
is the updating we are talking about.
CHAIRMAN JACKSON: I see.
MR. SAGAR: We do use Monte Carlo, but that is
primarily to take into consideration the uncertainties in
parameters, in models, in whatever else.
CHAIRMAN JACKSON: If you do this kind of
updating, when is enough enough?
MR. SAGAR: I think that is a very difficult
question to answer. That is not only with respect to the
analyses when it is enough, but also when is data
sufficient. I think you have to make judgments at some
point. I think you have to start saying, can I live with
this amount of uncertainty that I am predicting?
Personally I don't think you can use at the time
of licensing the latest state-of-the-art models, because you
must have something that is proven, that exists in
literature, that other people have tried. So you are always
a few years behind the so-called cutting edge.
But that is a judgment call. I don't think there
is a mathematical expression that we can say, if this, then
. 42
you are done. At least I don't know of any.
MR. PATRICK: But we are finding some specific
areas where we are getting answers to that. For instance,
generally speaking, the repository for at least the low and
intermediate thermal loading conditions is relatively
insensitive to rock mechanical properties, the strength of
the rock, and so forth.
We have done some preliminary calculations. We
have another sequence of those calculations with better
models this year that we intend to run. In the second area,
these models suggest that minor opening and closing of
fractures around the underground openings is relatively
unimportant. They change flow properties by factors of two
and three and four, whereas the natural variability in the
rock is several orders of magnitude. There is an area where
you can apply a judgment and say, well, if I am playing
around with 30 to 50 percent or even 100 percent when my
rock naturally is varying by several orders of magnitude, I
probably know enough at that point.
True, it's a judgment, but I think it is one that
is reasonably well substantiated, particularly if you look
at a risk curve or total system performance assessment
output and find that performance is relatively insensitive
to changes on that order of magnitude.
CHAIRMAN JACKSON: Does that become your de facto
. 43
metric, that is, how much your total system performance
assessment changes as a function of the residual
uncertainties?
MR. PATRICK: I think that is probably, in my mind
anyway, the key factor that comes into play in terms of how
much is enough, which is your basic question, I think.
MR. PAPERIELLO: That is certainly the way I've
always viewed it.
CHAIRMAN JACKSON: I noted that at the last
briefing the staff made to the Commission you indicated that
DOE and the NRC still didn't agree on two issues, having to
do with igneous activity or volcanism and structural
deformation. Where do things stand at this point?
MS. FEDERLINE: The focus of our program this year
in both of those programs is volcanism. We are doing
sensitivity analyses to try and understand for ourselves
where additional data would really make a difference. Those
analyses should be completed towards the end of the summer
and we should be able to have an interaction with DOE and
discuss where we believe additional data would make a
difference, and narrowing those differences.
In the area of seismicity we are primarily
focusing on developing an agreement on the methodology.
That will be the focus of this year's activity. Once we
agree on an appropriate methodology and how it will be
. 44
handled, I think that will go a long way to resolve that
issue.
CHAIRMAN JACKSON: You mentioned that you would be
taking an approach of developing a site-specific standard.
MS. FEDERLINE: Yes.
CHAIRMAN JACKSON: Have you done any resource
estimates associated with doing that vice conforming the
existing Part 60 to the EPA standard?
MS. FEDERLINE: We have done some rough estimates.
We believe that the resource estimate for creating a new
part is about the same as it would be for revising the old
part. It's a question of looking to see what aspects of the
old Part 60 need to be incorporated. The only new pieces
that we would be adding would need to be added to the old
standard as well. It is sort of a sum game.
CHAIRMAN JACKSON: But you think you will end up
with a cleaner rule?
MS. FEDERLINE: Yes.
CHAIRMAN JACKSON: Where you take care of the
implementation as part of that?
MS. FEDERLINE: Yes.
CHAIRMAN JACKSON: Let me ask one last question
and then I will pass the token. I noted that you indicated
that no construction-related disqualifying conditions had
been noted so far during the tunneling. What kind of
. 45
disqualifying conditions might be considered during the
tunneling operations?
MS. FEDERLINE: I will comment and pass it along
to Wes. He can add to it.
As we understand it, the predictions that DOE has
made from the surface about seismicity and faulting are
holding up rather well. As I understand it, their
predictions of the flow system also have been holding up.
Let me ask Wes if he has some things to add.
MR. PATRICK: Personally I think the real answers
to those questions are not to come until the testing in the
alcoves is fully underway. To date most of what you can do
following a tunneling machine has been done, but it is very
observational in nature, with the arguable exception that
the ground tends to be a little more broken up than I think
many people anticipated. That is something that has been
published a number of times in various press accounts.
My own view, speaking as a mining engineer and not
necessarily as the president of the Center now, is that is
the norm for underground. I think the only people who are
surprised by that are people who have never been
underground, frankly.
The Department of Energy seems to be taking a very
prudent and very conservative approach with regard to the
kinds of support that they are placing in the tunnel. I can
. 46
understand why they would do that.
When people do a little bit of cat kicking and
say, well, gee, they have had much more category 4 ground
-- that's one of the four on a scale of 1 to 5 -- than was
anticipated, you have to understand that many of their
decisions seem to me to be driven by programmatic concerns
with regard to worker safety, which I think is a very
prudent way to go.
The testing that will be done in the alcoves is
going to be vital. We have briefed the Commission before;
your staff has; I think the NWTRB interactions -- all of
those have long pointed in the same direction, that the most
important thing DOE could have done was to get underground
and get underground as quickly as possible. They are doing
that now.
My anticipation is within the next year or 18
months or so we are going to see some very critical data,
data that is vital to understanding whether that site is
viable and whether work should continue to progress.
Frankly, I see that many of our questions will be answered
as that work goes on. The thermal testing in alcove 5 is
going to be particularly important in that regard, because
so much of what is being postulated about the performance
and so much about the design is driven by the thermal
processes: What is the heat? What is the emplaced waste
. 47
going to do to the movement of water? What is it going to
do to the rock mechanical response? And so on and so forth.
CHAIRMAN JACKSON: So you are qualifying your
answer about disqualifying conditions?
MR. PATRICK: Yes. I would say it is about as
close to absolutely true as one could state it to say that
nothing has been seen that would disqualify the site. My
qualification on that is that there are things one needs to
measure before one can really make a firm substantive
comment with regard to qualification of the site.
CHAIRMAN JACKSON: Is there an implementation
schedule with milestones and is it tied to the alcove work?
MS. FEDERLINE: DOE's schedule?
CHAIRMAN JACKSON: Yes.
MS. FEDERLINE: Yes. As we understand it, that is
the detail that we have not had an opportunity to look at
yet.
CHAIRMAN JACKSON: I'm saying that would be
driving the schedule and the milestones for resolution of
these key technical issues.
MS. FEDERLINE: That's correct, yes.
CHAIRMAN JACKSON: Commissioner Rogers.
COMMISSIONER ROGERS: We might as well stay on
this topic, because I am very interested in it. I find it
puzzling to visualize how this whole thing is going to come
. 48
together. DOE says that they are going to have their
viability assessment completed by the end of 1998. The
kinds of data that you are talking about from the alcoves,
particularly thermal data, is that going to be available in
any meaningful form before then?
MS. FEDERLINE: If there was an area of concern, I
think that is it. We believe we are going to have one cycle
of heat data before the viability assessment. It would be
desirable to have more than that data by the time of
licensing.
What we are currently looking at is, with a
construction authorization, the question is what determines
reasonable assurance, how many confirmatory items will there
be at the time of construction authorization. Clearly DOE
has indicated that they plan to collect more data beyond
construction authorization.
Wes.
MR. PATRICK: I would agree with that.
COMMISSIONER ROGERS: I know they have said that,
but the viability assessment, if it depends in any critical
way on thermal data, it is hard for me to see how you are
going to have any meaningful thermal data. You really have
to have it right now to be able to wind up that viability
assessment by the end of 1998, which is just around the
corner.
. 49
MR. PATRICK: We have not been part of the
hearings that have been going on downtown and we have not
yet seen DOE's detailed information, but the last that we
have available is that they were looking at one of the lower
parts of the range of thermal loads as what they would come
in with and do their viability assessment on. If that is
true, the thermal loading question may not be as great. It
is at the high end of the thermal loads where they are
counting on very long dry periods that the data become most
critical, at least from our perspective.
As Margaret indicates, one cycle of thermal data
is about what is going to be available.
COMMISSIONER ROGERS: What is a cycle? How do you
define a cycle?
MR. PAPERIELLO: A year.
MS. FEDERLINE: It is actually one heatup of the
mechanical heating device, which will change the temperature
of the rock surrounding the device one time.
MR. PATRICK: Again, we haven't seen the details,
but typically what one does in a heater test like that is
ramp up and either through guard heaters or control of a
main heater get some sort of a plateau in thermal output and
make a series of measurements in terms of how mechanical and
hydrological and perhaps pneumatic flow pathways change or
are altered during that cycle.
. 50
It is a little speculative at this point until we
see the details of their plan. It's more than a little
speculative.
MR. SAGAR: I think we had estimated at one point
a couple of years ago that you probably needed a 10-year
thermal test to get some dependable data.
COMMISSIONER ROGERS: That's what I've heard.
MR. SAGAR: Obviously by 1998 there is no way we
are going to get that kind of data. So it would remain a
large uncertainty in the whole analysis. I think you will
have to deal with it again in making judgments whether the
conclusions that are being drawn can be supported by other
data.
MR. PATRICK: During this time Budhi alludes to,
even then we were counting on the large block tests at Fran
Ridge progressing. That would give many insights into the
performance of these kinds of rocks under those conditions.
That as well is not going forward. So we have lost some
time there, and some data.
COMMISSIONER ROGERS: In your presentation,
Ms. Federline, on slide 10, you emphasized the need for a
sound technical basis for evaluating DOE's viability
assessment -- it is one of the subtopics under the second
bullet -- which could trigger early Commission waste
confidence review.
. 51
What did you have in mind there that would trigger
an NRC waste confidence review other than abandonment of the
high-level waste program?
MS. FEDERLINE: If a negative viability assessment
is found at that point, if DOE goes back to Congress and
there is a conclusion that it is not feasible, licensing
costs are too great, there is too much information that
needs to be obtained, that could cause a triggering of the
waste confidence.
COMMISSIONER ROGERS: You seem to imply here that
we needed a sound technical basis for our evaluating their
assessment, and that assessment might not be a negative
assessment.
MS. FEDERLINE: I guess my point there is that
without an adequate technical basis we would have to make
perhaps unnecessary conservatisms, which would drive our
comments to say far greater time frames or costs would be
involved.
COMMISSIONER ROGERS: I see.
Dr. Patrick, in your key technical issues
priorities list you listed the repository design and
thermo-mechanical effects as priority 3 and total system
performance assessment as priority 1. How do you do a total
system performance assessment if you don't have a repository
design fairly well in hand? They are coupled together,
. 52
aren't they?
MR. PATRICK: They are indeed. An even stranger
one at first glance perhaps is the radionuclide transport
one being priority 3. The reason it is priority 3 is that
our sense from the calculations we have done is that the
performance of the repository is relatively insensitive to
the details of the design.
COMMISSIONER ROGERS: I see.
MR. PATRICK: So we need to have a good ACD,
advanced conceptual design, for the repository to be able to
conduct a total system performance assessment, but we give
it a priority 3 because performance is relatively
insensitive to it, and number two, we believe that DOE is on
track. We spent a lot of time with them and commenting on
their design process in the last couple of years or so and
believe that that process is on track now. We anticipate
getting a good design, so consequently we can downplay that
priority.
MS. FEDERLINE: This sort of reinforces the point
I was making. We are really down to the meat of the
program. We believe priority 1 through 3 are important, but
we had to do some relative prioritization.
COMMISSIONER ROGERS: I understand what you are
saying now. That helped me very much.
That's all I have.
. 53
CHAIRMAN JACKSON: Commissioner Dicus.
COMMISSIONER DICUS: I don't have any questions.
CHAIRMAN JACKSON: Let me ask you this question,
because I want to be sure I understand. DOE does this total
system performance assessment and the approach you are
taking is what you are calling an iterative performance
assessment. You are saying that there is enough in the
linkage between the two that you end up coming to
concurrence and convergence on what would be the key
technical considerations, such as waste package design and
its relative significance, et cetera.
Is that a true statement?
MR. PATRICK: That is correct. I would put one
qualification in there. The implication of part of what you
said is that our models are similar enough.
CHAIRMAN JACKSON: No. There was no implication
implied.
MR. PATRICK: That would be the only thing I would
clarify. Many people believe that one strengthens the case
if by taking a somewhat or maybe even quite different
approach one comes to the same basic understanding.
CHAIRMAN JACKSON: That is what I am asking you.
You were saying something about being comfortable with DOE's
results, and I am saying, so DOE has its way of doing its
total system performance assessment. You, on the other
. 54
hand, do your iterative performance assessment. I guess the
reason I asked the question is, in order for you to have
that comfort, that implies that there is some convergence or
concurrence via your different methodologies on what the
relative importance of these various issues and factors are.
MR. PATRICK: Yes.
MR. SAGAR: I might note that DOE also does
iterative performance assessment. Their TSPA-95 is another
iteration on what they did in 1993.
CHAIRMAN JACKSON: Whatever you call it, PA,
performance assessment, whatever letters you want to put on
it, my point is the reason you have the comfort, so to
speak, in what the DOE is doing is that out of the two
approaches you nonetheless have similar results in terms of
relative importance of the different factors. You are
saying you continue to iterate until your uncertainties
don't affect the overall performance assessment.
MR. PATRICK: From the example you can see a case
where the flip side is true, where their assumptions lead
them to three orders of magnitude less release calculated
than what ours did, and that immediately highlights in our
minds the importance of that.
We and DOE agree. Right now we don't agree with
the different models we are using, but we do both agree now
that performance is so sensitive to that matter of
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infiltration that both organizations need to put concerted
effort into understanding it better. That is really what I
think it is all about, to focus the resources of both
organizations so that we can understand where the problem
areas and uncertainty areas are so that we can resolve those
issues.
CHAIRMAN JACKSON: I would like to thank
Dr. Patrick, Dr. Sagar, and the NRC staff for an informative
briefing. This always enhances our perspective on the NRC
high-level waste management program and the challenges that
it faces. You keep us mindful of the various constraints
that resource constraints place on that.
I commend both the staff and the Center
representatives for working through these issues and for
developing in the face of exigency maintaining a credible
program. Your presentation will, of course, be useful. We
expect you to keep us informed of the progress and look
forward to future briefings on these important issues.
Unless fellow commissioners have any comments, we
are adjourned.
[Whereupon at 3:20 p.m. the meeting was
adjourned.]
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