Copyright 2000 Federal News Service, Inc.
Federal News Service
June 23, 2000, Friday
SECTION: PREPARED TESTIMONY
LENGTH: 2043 words
HEADLINE:
PREPARED TESTIMONY OF DR. DEBRA KNOPMAN U.S. NUCLEAR WASTE TECHNICAL REVIEW
BOARD
BEFORE THE HOUSE COMMITTEE ON COMMERCE
SUBCOMMITTEE ON ENERGY AND POWER
SUBJECT - HIGH-LEVEL WASTE
MANAGEMENT
BODY:
Mr. Chairman and members of
the Subcommittee. I am Debra Knopman, a member of the Nuclear Waste Technical
Board. My full-time job is Director of the Center for Innovation and the
Environment of the Progressive Policy Institute. It is my pleasure to act as the
Board's representative this morning and to express the views of the Board on
progress in the Yucca Mountain site-characterization program.
The Board's Chairman, Dr. Jared L. Cohon, sends his regrets at not being able to
be here today.
With your permission, Mr. Chairman, I will make some
brief summary remarks and ask that my full statement be entered into the hearing
record.
The Board's Mandate Mr. Chairman, when Congress created the
Nuclear Waste Technical ReviGw Board in the 1987 amendments to the Nuclear Waste
Policy Act (NWPA), it gave the Board a very important--and unique mandate. That
mandate is to conduct an independent review of the technical and scientific
validity of activities conducted by the Secretary of Energy in implementing the
NWPA, including characterization of the Yucca Mountain site and
packaging and transportation of spent nuclear fuel and high-level radioactive
waste. Congress intended the Board to communicate its findings and
recommendations to the Secretary and to Congress in a timely fashion before
important decisions are made, not after the fact. The Board takes its charge
very seriously, Mr. Chairman, and we are pleased to have this opportunity to
update the Subcommittee on the Board's view of the Yucca
Mountain program before the release of the Department of Energy's (DOE)
site recommendation consideration report, or SRCR, which currently is scheduled
for the end of this year. In particular, I would like to update the Subcommittee
briefly on some of the Board's most recent recommendations on the DOE's safety
strategy for the Yucca Mountain site, methods for predicting
repository performance, and scientific studies of Yucca
Mountain.
The DOE's Site Recommendation Consideration Report
As I mentioned, Mr. Chairman, the DOE intends to issue a site
recommendation consideration report on Yucca Mountain at the
end of this calendar year. The DOE plans to update the SRCR and use it along
with other information called for in the Nuclear Waste Policy Act as the basis
of a site recommendation, currently scheduled for mid-2001.
According to
the DOE, the SRCR will include four elements: a comprehensive computer model
called the "total system performance assessment," or TSPA; a qualitative
description of the attributes of the Yucca Mountain site; a
repository design and safety case; and an outline of future research needs. Over
the last few months, the Board has commented to the DOE on some of these issues.
I will briefly summarize some of our most recent comments. Representation of
uncertainties about the Yucca Mountain site. The Board
continues to endorse the use of performance assessment, or PA, supplemented by
other lines of evidence, for making a site-suitability determination' While the
numerical models in a PA help us understand and estimate how a repository might
perform at the Yucca Mountain site, the models are based on
many assumptions. For example, underlying the models are assumptions about the
natural environment, including climate, water movement, chemistry, seismicity,
and volcanism, and about the engineered system, including corrosion and other
processes. The assumptions may be based on field and laboratory data, on the
results of expert judgment, or on detailed conceptual and numerical analyses.
The Board believes that explaining the uncertainties inherent in the PA
and the underlying assumptions as clearly and fully as possible is essential for
technical credibility and sound decision-making. The Board is concerned that a
PA without such an explanation could deprive policy-makers of critical
information on possible trade-offs between projected performance and the
uncertainty in those projections. For example, one policy-maker might be willing
to accept development of a repository that would release half of the permitted
dose and have only a 1 in 1,000 chance of exceeding the permitted dose. However,
that same policymaker might decline to develop a repository that is expected to
release only a tenth of the permitted dose but that has a 1 in 4 chance of
exceeding the permitted dose. Another policymaker's preferences might be the
opposite. Because the uncertainties about repository system performance may be
substantial, estimates of uncertainty about doses are at least as important as
estimates of performance.To help decision-makers better understand estimates of
repository performance in the PA, the Board recommends that the DOE include in a
site recommendation document a description of critical assumptions, an
explanation of why particular parameter ranges were chosen, a discussion of data
limitations, an explanation of the basis and justification for using expert
judgments, and an assessment of confidence in the conceptual models used.
In addition, the Board recommends that the uncertainties associated with
the performance estimates be identified and quantified well enough so that the
performance estimates can be put in the context of what is well known, what is
less well known, and what is unknown (or unknowable) about Yucca
Mountain. The DOE and the Board have had numerous exchanges on this
point, and we understand that the program is making an effort to respond to the
Board's concerns.
Building a case for repository safety. Although we
endorse the use of PA, the Board believes that PA modeling should not be used as
the sole source of guidance about the features, events, and processes that might
affect the long-term performance of the repository system. Therefore, the Board
supports the DOE's use of multiple and independent lines of argument and
evidence, including defense-in- depth, safety margin, natural analogs, and
performance confirmation testing, to supplement the TSPA in its case regarding
Yucca Mountain site suitability. These additional elements,
combined with a clear description of uncertainty as described above, will
present a more technically defensible demonstration of repository safety than
would any element by itself In other words, this is a matter of not putting all
the scientific eggs in one basket of computer modeling. The Board believes that
the program is making an effort to develop these additional lines of evidence,
but it is unclear at this time how far along DOE will be in their development at
the time of the SRCR.
Connections between repository design and
uncertainties in the safety case. One way to address uncertainties is to reduce
them by modifying repository design. In early 1999, the Board recommended to the
DOE that it analyze alternatives to the repository and waste package designs
included in the DOE's 1998 viability assessment. In particular, the Board
suggested that the DOE investigate the effects of heat on the waste packages,
repository tunnels, and hydrologic and hydrogeochemical processes at the site.
The Board made this suggestion because higher temperatures, especially if water
is present in repository tunnels, appear to carry additional uncertainties in
estimating repository system performance in comparison to lower- temperature,
below-boiling conditions in the rock surrounding the tunnels. In the past, the
DOE has maintained that above-boiling repository designs have the potential to
vaporize water in the rock surrounding the repository tunnels, thereby keeping
the waste packages essentially dry for up to a thousand years.
Understanding the differences in estimated performance and associated
uncertainties under different temperature conditions is an important component
of our overall understanding of potential repository performance at the
Yucca Mountain site. However, the Board is concerned that PA
may not in its current state of development capture adequately how the thermal,
hydrologic, mechanical, and chemical processes in the mountain interact. If this
is the case, then the PA model may not accurately represent the uncertainty
associated with above-boiling designs. A below-boiling design may have the
potential to reduce concerns about these "coupled processes." Nonetheless, more
thorough analysis is needed before any judgment is made about the optimal
thermal conditions for repository operation.
In any case, Mr. Chairman,
the Board believes that an analysis of the tradeoffs between estimates of
performance and the uncertainties in those estimates is essential before a
technically defensible decision can be made on repository design. The Board is
pleased that the DOE has begun preliminary work in this area.
Important
scientific studies continue at Yucca Mountain. An important
aspect of reducing uncertainties is obtaining relevant data. For example, the
Board believes, on the basis of current knowledge, that the DOE has chosen the
best materials available for the waste package. However, experience with the
materials extends over only a few decades---a short time relative to the tens of
thousands of years in their intended life in a repository. The Board is closely
following the DOE's efforts to address questions about stress corrosion cracking
and about dissolution of the passive layer that acts as a corrosion barrier in
the alloy that has been selected for the exterior of the waste package.
Answering these questions should help reduce uncertainties and increase
confidence in predictions of waste package performance that are extrapolated
from present-day experience.
The east-west cross drift recommended by
the Board and completed in October 1998 by the DOE continues to yield dividends
in scientific information that help to address some of the current questions
about the properties of the layer of rock where most of the waste would be
placed and about how liquid water and water vapor will move within that layer.
In addition, the ongoing drift-scale heater test, now in its third year, should
provide important information on the general effects of heat on the mountain.
Conclusion
In conclusion, Mr. Chairman, on the basis of what we
know at this time, the SRCR will provide an important analysis of key issues
that are likely to be included in a final technical document accompanying a site
recommendation. Although the Board cannot say whether the SRCR itself will be
sufficient for determining site suitability, the Board believes that the DOE's
efforts to develop the SRCR have been very useful in helping the DOE identify
issues that would have to be resolved or clarified in a final site
recommendation report.
At this point, the DOE has not encountered any
issue in characterizing the Yucca Mountain site that
automatically eliminates it from consideration as the location of a permanent
repository for spent nuclear fuel and high-level radioactive waste. However,
important technical questions remain about Yucca Mountain,
especially about the effects of heat on the movement of water in the mountain
and on the associated transport of radionuclides. The DOE is taking steps to
address these questions, but some uncertainty will inevitably continue about
predictions of the performance of a potential repository system. This may be
true to some extent at any site. At the time a decision is made on site
recommendation, the Board and the scientific community are likely to be asked at
least two questions:
(1) Is the underlying science broadly regarded as
technically credible and sound? and
(2) Are the uncertainties in
estimates of performance displayed clearly and openly, especially about the
major factors that may lead to a potential radioactive release? A major question
for policy-makers at that point may be whether the site is suitable, given the
level of uncertainty associated with the DOE's site-suitability determination.
The Board believes it is critical that the DOE not only offer estimates of
performance but also clarify the extent and significance of the technical and
scientific uncertainties. Understanding uncertainties is vital for sound
decision-making.
Thank you very much for this opportunity to provide the
Board's views. I will be happy to respond to questions.
END
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