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OCR for page 13
FINDINGS
The Limitations of Analysis
Overview
Engineers are unable to anticipate all of the potential problems that might
arise in trying to site, build, and operate a repository. Nor can science
prove that a repository will be absolutely "safe." This is so for two reasons.
First, proof in the conventional sense cannot be available until we have
experience with the behavior of an engineered repository system precisely
what we are trying to predict ahead of time. And second, safety is in part a
social judgment, not just a technical one. While technical analyses can
greatly illuminate the judgment of whether a repository is safe, technical
analysis alone cannot substitute for decisions about the degree of risk that is
acceptable. These decisions belong to the citizenry of a democratic society.
Both of these important limitations of technical analysis have been understated,
a lapse that feeds the concern and magnifies the public's distrust of nuclear
waste managment when these limitations are pointed out by the program's
. .
cntlcs.
Uncertainty and Significant Risks
A principal source of concern over Be U.S. program is the uncertainty in
estimating the risks from a radioactive waste repository. Technical approaches
are available to reduce or at least bound these uncertainties. Yet in focusing
on ways to improve the analysis, public discussion has often overlooked a
more important question: whether the uncertainty matters. This is, in
principle, the domain of performance assessment, which draws together the
different portions of the technical analysis so that one can see which parts
of the waste confinement system may pose environmental hazards during or
after the time when the repository receives waste.
Performance assessment of a repository system is necessarily a task for
computer modeling. The waste management system, which starts at the
reactor and continues into the distant future of a sealed repository, includes
many different parts and processes that are described through different kinds
of data (with different levels of quality), and different kinds of analysis
(with different levels of accuracy). It is a practical consequence of the
complexity of high-level radioactive waste (HLW) disposal, together with
the fact that no one has ever operated a repository, that performance assessment
is, in the end, a matter of technical judgment.
13
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14
The traditional approach in such cases, where an important social deci-
sion hinges on uncertain scientific data and projections, is to inform the
political decision through a consensus of the appropriate technical commu-
nity. Such consensus is difficult to reach in this case, however, given the
political controversy, conflicting value systems, and overlapping technical
specialties involved in assessing repository performance. Indeed, the allowable
residual risk associated with a permissible repository site is a political choice;
EPA has taken the position that the implementation of their guidelines constitutes
the exercise of this choice. Unfortunately, the number and magnitude of the
uncertainties in the probabilistic approach may be expected to reintroduce
political controversy. This was recognized by the High-Level Radioactive
Waste Disposal Subcommittee of EPA's Science Advisory Board in their
January 1984 report reviewing EPA Draft Standard 40 CFR 191. That
subcommittee concluded there was
insufficient basis for agreeing with the EPA staff that the proposed release
criterion with its probabilistic corollary can be demonstrated to have been met
with reasonable assurance, and that this could be argued definitively in a legal
setting.
The subcommittee strongly affirmed the validity of EPA's probabilistic
approach, but warned that
if EPA cannot have high confidence in the adequacy and workability of a
quantitative, probabilistic standard, [it should] use qualitative criteria, such as
recommended by [the US]NRC.
Specifically, with regard to the first major topic of the Science Advisory
Board's findings and recommendations, "Uncertainty and the Standard," the
subcommittee recommended relaxing the nuclide release limits by a factor
of 10, modifying the probabilistic release criteria so that
analysis of repository performance shall demonstrate that there is less than a
So-so chance of exceeding the Table 2 release limits, modified as is appropriate.
Events whose median frequency is less than one in one-thousand in 10,000
years need not be considered,
and, finally
that use of a quantitative probabilistic condition on the modified Table 2
release limits be made dependent on EPA's ability to provide convincing
evidence that such a condition is practical to meet and will not lead to serious
impediments, legal or otherwise, to the licensing of high-level-waste geologic
repositories. If such evidence cannot be provided, we recommend that EPA
adopt qualitative criteria, such as those suggested by the [US]NRC.l
Unfortunately none of these recommendations was adopted.
The USNRC staff, in commenting on the EPA Draft Standard, strongly
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15
questioned the workability of quantitative probabilistic requirements for the
defined releases stating, in part
numerical estimates of Me probabilities or frequencies of some future events
may not be meaningful. The [US]NRC considers Mat identification arid evaluation
of such events arid processes will require considerable judgment and therefore
will not be amenable to quantification by stansiica~ alyses without the in-
clusion of very broad Garages of uncertainty. These uncertainty ranges will
make it difficult, if not impossible, to combine the probabilities of such events
wide enough precision to make a meaningful contribution to a licensing proceeding.2
The problem is compounded when the adequacy of the performance as-
sessment to determine if the allowable residual risk is achieved is judged
by its political impact (i.e., the effect of reopening the discussion of what is
allowable residual risk) as well as its technical accuracy.
The difficulty of evaluating performance assessments is compounded by
the fact that there is no actual experience in the disposal of HEW on which
to base estimates of the risk. Some risk scenarios include low-probability/
high-consequence events. Others are based on explicit or implicit assump-
tions that cannot be plausibly proved or disproved for example, the consequences
of climatic changes that could increase rainfall and groundwater flows at a
repository site. The data and methodologies for modeling of repository
isolation performance are still under development.
The actual performance of a repository is difficult to predict for many
reasons. Geologists often disagree about the interpretation of data in analyzing
the history of a site or geological structure. Long-term predictions are even
more uncertain. Releases may occur thousands of years in the future, and
they are likely to be diffuse and hard to detect. The potential for (and
effects of) human exposure will be further shaped by unpredictable changes
in demographics and technology.
These uncertainties do not necessarily mean that the risks are significant,
nor that the public should reject efforts to site the repository. Rather, they
simply mean that there are certain irreducible uncertainties about future
risk. An essential part of any successful management plan is how to operate
with large residual uncertainties, and how to maintain full public accountability
as information about the risks changes with experience. This is not an
impossible task: public policy is made every day under these conditions,
and private firms undertake all sorts of activities in the face of uncertainty.
What is clear, however, is that a management plan that promises that
every problem has been anticipated, or assumes that science will provide all
the answers, is almost certainly doomed to fail. There have been many
cases where attempts to understate uncertainty have damaged an agency's
credibility and subverted its mission. For this reason, experienced regulatory
agencies like EPA now pay careful attention to describing the uncertainties
associated with their risk assessments.
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Perceptions of Risk
Studies have linked the high public perceptions of the risk from nuclear
power plants to certain qualities of that risk, in particular to perceptions that
the risks are catastrophic, new, uncertain, and involuntary (i.e., beyond
individual control). Radioactive waste poses risks with many of the same
technical characteristics: the principal health risks (chiefly cancer and genetic
defects) originate in the hazards of ionizing radiation. The risks from radioactive
waste also have some of the same social characteristics as risks from nuclear
reactors: a long time may pass before the hazards become apparent, dangers
may be imposed involuntarily on populations, and there is a perceived pos-
sibility of catastrophe. The last perception, in particular, is qualitatively
incorrect for HLW, since radioactive waste materials have far lower energy
levels in comparison to those of reactors, thereby limiting the risk associated
with HLW to much lower levels in virtually all accident scenarios.
Given the complexity of the potential risks from HLW, most people will
transfer the judgment of the safety of geologic disposal to the experts. The
key question is which experts they will listen to. The answer depends on
who seems more trustworthy: citizens may have little experience with radioactive
waste, but they have considerable experience in evaluating people.
The perception of integrity and competence in risk managers depends not
only on their personal attributes but also on the character of the policies
they implement and the institutions they represent. The current decision
process is structured in a way that does not promote trust in those who are
implementing the waste management program. The current situation in
Nevada, for example, demonstrates the importance of local input in the
acceptance of risk. The political leadership of Nevada is fighting the proposed
repository and portraying their State as a victim, reinforcing the perception
on the part of the broader public that the program is beyond local control.
The Department of Energy (DOE) should recognize that communications
about the program will be ineffective so long as Nevadans believe they have
no voice in the process. To the extent that DOE can share power, however,
the increased perception of local control is likely to improve acceptance of
a repository. The funding of a technical review group whose members are
selected by the State government would be one positive step in this direction.
In order to encourage rigorous technical analysis, it should be required that
the findings of this review group include a statement of the technical evidence
and reasoning behind the conclusions, as is done now by the State of New
Mexico's Environmental Evaluation Group for the Waste Isolation Pilot
Plant.
Given the highly polarized reactions to radioactive waste disposal, it is
reasonable to anticipate criticisms and challenges to the technical competence
and integrity of the program and its participants. Critics of the program
OCR for page 17
17
point to the perceived incentives to find the proposed site and technology
suitable, the motivation to meet schedules and budgets, and the resulting
incentive to disregard or play down troubling findings. Claims to predict
accurately events like earthquakes and climatic change are guaranteed to be
challenged. These concerns have been addressed through a regulatory re-
view process that is carefully designed to reveal errors, optimistic assump-
tions, and omissions; but the perceived credibility of that process can be
bolstered if state and local groups and individuals have an opportunity to
participate, not only in the formal review process but also through informal
working relationships with project staff.
Those involved in HEW management must also avoid the trap of promising
to reduce uncertainties to levels that are unattainable. Uncertainties are
certain to persist. Whether the uncertainties in geologic disposal are too
great to allow proceeding can only be judged in comparison to the projected
risks and uncertainties for the alternatives, such as delayed implementation
of disposal or surface storage of spent fuel. As a rule, the values determined
from models should only be used for comparative purposes. Confidence in
the disposal techniques must come from a combination of remoteness, engineering
design, mathematical modeling, performance assessment, natural analogues,
and the possibility of remedial action in the event of unforeseen events.
There may be public desire or political pressure on implementing agencies
to provide absolute guarantees, but a more realistic and attainable goal
is to assure that the likelihood of unforeseen events is minimal, and that the
consequences of such events are of limited magnitude.
Technical program managers may ask whether it is better for the public
to know too much or not enough. When unforeseen events occur, for example,
the public can raise questions about the validity of the technical approach,
as well as the competence of the risk analysis that was used to justify it.
Conversely, when foreseen events occur, they lead to questions about why
they were not prevented. The technical credibility of the project team
suffers in either case, but it probably suffers more when the organization
has understated the risk or uncertainty.
Moral and Value Issues
Overview
The foregoing discussion suggests that, in the area of radioactive waste,
ethical issues are as important as management and technical decisions. In-
terested parties approach the issues with different views about the right way
to proceed, often due to differences in moral and value perspectives. As a
result, an exploration of ethical issues can illuminate the fundamental policy
debates in this field by showing the technical issues in their political and
OCR for page 18
18
social context. Such an exploration also provides scientists with an oppor-
tunity to explore their own ethical responsibilities as they provide society
with technical advice on controversial subjects. During its 1988 study ses-
sion, the Board examined recent work on ethical questions in radioactive
waste management conducted by scholars from a variety of disciplines.
These ethical concerns fall into two principal areas: (1) questions concerning
the professional responsibility of scientists and engineers; and (2) questions
concerning the appropriate uses of science in the decision-making process.
Science and engineering are part of broader human activities, and as science
enters the public arena, decisions can no longer be purely scientific; good
science is not enough. Science has also become an important source of
information and analysis for the public policy process, and scientists find
themselves being called to account for, and to justify the results of, those
decisions. Is this responsible, good, or desirable? How can the process be
improved and the parties satisfied? Scientists have been sheltered from
such questions in the past, but the increasing scale, sophistication, and per-
vasiveness of technical information require a corresponding increase in the
sophistication with which these value judgments are made.
Three Issues of Equity
To see how questions of equity apply to radioactive waste management,
consider first a study by Roger E. Kasperson and Samuel Ratick.3 This project
identified three sets of equity concerns, each of which raises questions of
differential impact, public values, and moral accountability:
· Labor. Who does the work and who pays for it? Congress has determined
that DOE will be responsible for the work and that the beneficiaries of
nuclear power will pay for it through a surcharge on their electric rates.
· Legacy. What do we owe to future generations? Moral intuition tells
us that our descendants deserve a world that we have tried to make better.4
Posterity matters to us, independent of economic trade-offs; policy should
therefore take that interest into account. The EPA regulation requiring
evidence that radioactive waste releases will be limited for 10,000 years and
more is an illustration of such a concern for the distant future.
· Locus. Who benefits, and who is exposed to risk? A repository is the
final resting place for the waste from nuclear power plants that provide
benefits spread over the whole nation for a short time; but it also concentrates
risks and burdens along transportation routes and, for a much longer time,
at the disposal site. A radioactive waste repository poses additional complications:
it will be the first facility of its kind; the risks it poses are uncertain and, to
the extent they exist at all, are likely to emerge over very long time spans;
public fears are unusually high; and the history of federal action has raised
OCR for page 19
19
concerns about whether the interests of local populations will be treated
equitably.
These ethical questions, when applied to radioactive waste management,
demonstrate that once science enters the policymaking arena, good science
is no longer enough, because technical decisions are no longer simply sci-
entific. When the questions are no longer scientific, scientists alone cannot
be expected to answer them. Sheldon Reaven suggests that the Nuclear
Waste Policy Act POPPA) creates a "scientific trap," in which citizens are
encouraged to expect certainty from flawless science, and in which scientists
and engineers are encouraged to believe or pretend that they can supply it.5
Sheila Jasanoff makes the same point: the political need for accountabil-
ity in the United States pressures regulators to seek a "scientifically correct"
answer, even when there is none.6 The attempt is doomed to scientific and
political failure. It is therefore critical to recognize the boundaries of scientific
understanding as it can be applied to a societal problem.
Five Issues of Policy
These ethical considerations have been applied to the current HEW situa-
tion by an interdisciplinary team led by E. William Colglazier.7 For each
of five key policy issues, the study discusses the "fairness" and appropriateness
of the procedures for making decisions, the distribution of costs and benefits,
and the type of evidence that is considered sufficient and admissible. The
study places special emphasis on the role of scientific evidence because of
the large scientific uncertainties and the continuing controversy, even among
experts, on what is known and not known. The study's observations include
the following:
· The need for the repository. The core policy dispute concerns the
choice between permanent disposal in a geologic repository and long-term
monitored storage in an engineered facility (including at-reactor storage) at
or near the surface. The controversy has been over the distribution of costs
and benefits to current and future generations and to various stakeholder
groups:
Pro-nuclear groups feel that the federal government promoted nuclear
power and therefore has a special responsibility (spelled out in contractual
obligations) to accept spent fuel in a timely manner for permanent disposal.
Many environmental groups, on the other hand, view radioactive
waste as a special threat to people and the environment; they also favor
permanent disposal in order to fulfill this generation's responsibility, and
view interim storage as an unfair "legacy" to future generations.
Some proponents of interim storage, however, argue that this gen-
eration should not make decisions that would be costly to correct in the
OCR for page 20
20
future; new technological developments may occur over the next century
that could change our view of how to handle nuclear waste.
In short, all stakeholder groups agree that this generation should ful-
fill its responsibility to future generations, but they disagree on how to turn
this value principle into policy.
· Siting. In making politically difficult siting decisions, political lead-
ers have two basic options: make the choice internally and impose it on a
weak constituency; or set up and follow a selection process perceived as
objective, scientifically credible, and procedurally fair. When NWPA was
passed in l9X2, the latter course appeared necessary for both technical and
political reasons. However, critics soon claimed that DOE was being political
rather than objective in its decisions, citing as evidence DOE's choice of
first-round sites and its decision to defer the second round of site selection.
This perception led to a stalemate: DOE lacked credibility, and credibility
is essential to implement the siting approach set forth in the NWPA. This
stalemate was broken by Congress win the 1987 NWPA amendments, which
designated Yucca Mountain, Nevada (one of DOE's first-round choices), as
the initial site to be characterized and, if acceptable, to be licensed.
· Intergovernmental sharing of power. Procedural values were also
important in NWPA, which established rules for sharing power among the
affected governmental entities. However, the states feel that federal agencies,
and especially DOE, have generally chosen to try to meet milestones rather
than slow down the process to live up to the spirit of "consultation and
cooperation." DOE, for its part, feels that it has a mandate to move forward
expeditiously; it has tried to accommodate the states, which (in DOE's
view) seek delays to throw obstacles in the way of efficient implementation.
Nevada, in particular, interprets the 1987 NWPA amendments as unfair on
procedural (as well as distributional and evidential) grounds.
· Safer. The fundamental safety issue is the determination of a fair
evidential process and standard of proof for showing that the repository is
acceptably safe for the thousands of years over which the waste will remain
dangerously radioactive. The United States has adopted a set of licensing
criteria (e.g., groundwater flow time, package lifetime, waste release limits,
and so on) that require considerable certainty. As is often the case with
frontier science, however, knowing more may actually increase rather than
decrease the uncertainties, at least in the near term. The evidential uncertainties
in assessing repository safety may point to a more flexible and evolutionary
approach (see below); but this conflicts with the concerns to keep to a fixed
schedule, so as to limit costs, discharge obligations to future generations,
and meet contractual commitments to utilities holding spent fuel.
· Impacts. The debate over the distributional impacts of the repository
program include such issues as who should pay for the program, how the
impacts can be fairly calculated, and what is fair compensation for negative
OCR for page 21
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1
impacts. NWPA determined that the costs should be paid by the beneficia-
ries of nuclear-generated electricity through fees, initially, of one mill per
kilowatt-hour. An evidential dispute concerns the potential "stigma effect,"
including lost jobs and lost tax revenues, due to nuclear waste; the social
science methodologies for assessing this effect are still controversial. An-
other issue concerns the use of incentives and compensation: in the 1987
NWPA amendments, Congress authorized special payments for the host
state, provided it forgoes its right to object. This runs the risk of being
perceived by opponents as a bribe, offered in exchange for taking otherwise
unacceptable risks. Congress also sought a procedural solution to these distri-
butional impacts through creation of the Office of Special Negotiator, hoping
that the negotiator might find an acceptable arrangement with the host state.
Consideration of these policy debates regarding the disposal of radioactive
waste leads to three important conclusions:
· no interested party has an exclusive claim to be rational or to articulate
the public interest;
· what is considered fair or unfair is subjective and can change over
time;
· and with regard to repository safety, the issue is acceptability rather
than certainty acceptability being what is acceptable to society, given the
evidential uncertainties, perceptions of risk, and contentious stakeholder
debates.
These conclusions highlight the advantage of an empirical approach one
that examines fairness in process, outcomes, and evidence; one that reflects
an understanding of the values as well as the interests of the stakeholders.
Such an approach may lead to policies that have a greater chance of surviving
over time because they are more widely perceived as fair.
Modeling and Its Validity
Overview
Models based on geological principles play a central role in the design
and licensing of a waste repository. Because this is where science enters
into the design and evaluation process, the Board discusses the appropriate
use of models at some length, including the following topics: the purposes
for which models are used; the relationship among modeling, treatment of
uncertainties, and regulation; and supplements to the use of models in the
current program.
The role of models in the design and licensing of the repository should
properly be understood to be different from the use of models in designing
airplanes or licensing nuclear reactors. There are major sources of uncertainty
OCR for page 22
22
in quantitative geophysical modeling even geohydrology, the best developed,
can provide only approximate answers. Geoscientists will need more time to
learn how to do more reliable predictive modeling of near-term events, and
some events may prove to be chaotic—that is, impossible to predict in
detail.
In particular, there is a critical need for (1) better communication between
modelers and geological experts, in order to improve model prediction; and
(2) a more open, quality-reinforcing process such as could be obtained
through a peer-reviewed research program at universities and elsewhere.
This would do much to improve technical and public confidence in models.
DOE could support such an effort by allocating R&D funds, possibly through
or in cooperation with the National Science Foundation, for model improvements.
In the meantime, however, models can be useful in identifying and evaluating
significant contributors to risk and uncertainty. Models are not well suited
to describe the risk and uncertainties to lay audiences, however. Natural
analogues, if they can be found, are far more useful for this purpose (see
below).
Problems of repository performance assessment, according to the scheme
shown in Figure 1, belong in Region 2 or at the border between Regions 4
and 2. However, there is a general tendency to assume that we can address
them using a Region 3 approach: that is, start with a deterministic model
that incorporates all "relevant" contributors to overall behavior, and then
attempt to collect enough data to move the problem from Region 2 into
Region 3. In reality, however, this approach leads to increasingly complex
models and increasingly expensive site evaluations, without a concomitant
improvement in either understanding or design. Anthony M. Starfield and
More Data
Figure 1. Types of modeling problems.
Region 1 Region 3
Region 4 Region 2
More Understanding
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23
P. A. Cundall have suggested that we sometimes demand answers that the
model is incapable of providing because of complexity or input demands.
The design of the model should be driven by the questions that the model is
supposed to answer, rather than by the details of the system that is being
modeled. Under the present HEW program, geophysical models are being
asked to provide answers to questions that they were not designed to tackle.8
Models and Modeling Problems
Figure 1 illustrates a general classification of the types of modeling problems
taken from C. S. Holling.9 In Region 1 there are good data but little under-
standing; this is where statistics is the appropriate analytic tool. In Region
3 there are both data and understanding; this is where models can be built,
validated, and used with conviction. The use of finite-element models in
structural design is a good example of Region 3 models. Regions 2 and 4
contain problems that are data-limited in the sense that the relevant data are
unavailable or cannot be placed in a rigorous theoretical framework. In
Region 2 the understanding of basic mechanisms is good; it is the detailed
information that is unobtainable. In Region 4 there is not even a sound
understanding of the basic mechanisms and interactions.
Appropriate Uses for Geophysical Models
In the Board's judgment, a scientifically sound objective of geophysical
modeling is learning, over time, how to achieve the long-term isolation of
radioactive waste. That is a profoundly different objective from predicting
the detailed structure and behavior of a site before, or even after, it is
probed in detail. Yet, in the face of public concerns about safety, it is the
latter use to which models have been put. The Board believes that this is
scientifically unsound. This conclusion is based on review of the modeling
approach used by DOE and the regulatory agencies in order to implement
the NWPA.
In order to support the regulatory and political argument that a site will
be safe, it is necessary to make detailed, expensive, and extended extrapolations.
These are informed speculations based on existing knowledge. In many
instances the guesses are likely to be correct. The geotechnical models
used to assure that the foundations of a building or bridge will be secure in
the event of earthquakes provide an example of a well-founded predictive
use of geophysical modeling. But to predict accurately the response of a
complex mass of rock and groundwater as it reacts over thousands of years
to the insertion of highly radioactive materials is not possible.
This point is important to the public concerns that have surrounded the
U.S. radioactive waste program. Use of complex computer models is neces-
OCR for page 24
24
sary to apply well-known geophysical principles in order to estimate or to
set bounds on the behavior of a site, so that its likely suitability for a waste
repository can be evaluated. But it is impossible to stretch the almost
always incomplete understanding of a site into an accurate quantitative pro-
jection of whether a repository will be safe if constructed and operated
there. Even after a detailed and costly examination of the site itself, only
an informed judgment can be reached, and even then there will be uncertainties.
As modelers have become more aware of the processes they are attempt-
ing to model, they are also recognizing that the geological environment is
more complex than originally thought and that quantitative prediction is
correspondingly more difficult and uncertain. Many computer simulation
models of geological environments are based on deterministic models that
have been used successfully in branches of mechanics such as aerospace
engineering, where the basic phenomena are much better defined. Such
models are of limited value for the ill-defined, data-limited, long-term situations
such as the repository isolation problem. It is illusory to expect accurate
quantitative estimates of radionuclide releases from them.
Sources of Uncertainty in Geophysical Models
Performance assessments—estimates of the repository's ability to isolate
HEW are based on current computer simulations and parameters derived
from laboratory and field measurements. As a consequence, they will have
large uncertainties associated with the predicted performance. These uncertainties
could pose serious obstacles in demonstrating compliance with licensing
requirements. Discussions at BROOM's 1988 study session identified four
principal causes of uncertainty:
1. Structural uncertainty. Do the equations adequately represent the
operative physical processes? Do we in fact understand the system well
enough to model it mathematically? Modeling will be most successful in
solving Region 3 problems (see Figure 1), where we have a great deal of
data and a good understanding of how the system works.
2. Parametric uncertainty. Have we chosen the right values for the
variables (e.g., permeability) in the equations? Have we in fact chosen the
right variables to represent the behavior of the system? Are our measurement
techniques valid? Will they produce enough, and good enough, data?
3. Uncertainties in initial arid boundary conditions. Have we inter-
polated adequately from a few spatially isolated point measurements to a
broad three-dimensional domain (e.g., groundwater, heat, in situ stress)?
4. Uncertainties in forcing functions. How well can we characterize
past and future events that might play a part in the fate of the repository
(e.g., climate, tectonics, human intrusion)?
OCR for page 25
25
Urgent attention should be given to examining these and other causes of
uncertainty, but even with continuing research along the present lines, im-
provement will come slowly. It may even turn out to be appropriate to delay
permanent closure of a waste repository until adequate assurances concern-
ing its long-term behavior can be obtained through geophysical studies.
Judgments of whether enough is known to proceed with placement of waste
in a repository are needed throughout the life of the project. But to repeat
the Board's earlier point: these judgments should be based on a comparison
of the available alternatives, rather than just a simplistic debate over whether,
given current uncertainties, a repository site is "safe." Even when the
detailed behavior of an underground repository is still under study, it may
well be safer to put waste there, in a way that permits retrieval if necessary,
rather than leaving it at reactors or in storage at, or near, the surface of the
earth.
Modeling Limitations An Example
The inherent diff~culdes of modeling are illustrated by the case of Groundwater
flow, which is used as an example precisely because it the best developed in
terms of modeling. Groundwater flow has been extensively modeled for a
broad range of engineering problems, and it consequently has a richer base
from which to draw than do many other aspects of repository isolation.
Groundwater flow is also generally accepted as the primary mechanism by
which radionuclides could move from the repository to the biosphere, so it
has been emphasized in modeling studies of repository isolation. Several
experts, however, have commented on the difficulty of applying classical
hydrology models to the problem of radioactive waste isolation.
Groundwater hydrologists are becoming increasingly aware that inadequate
and insufficient data limit the reliability of traditional deterministic [distributed-
parameter] Groundwater models. The data may be inadequate because aquifer
heterogeneities occur on a scale smaller than can be defined on the basis of
available data, time-dependent variables are monitored too infrequently, and
measurement errors exist.10
To carry out these [repository flow] calculations, hydrogeologists are apply-
ing geostatistical models and stochastic simulation methods originally developed
to assess piezometric response in near-surface unconsolidated aquifers over
limited spatial distances and short time frames with relatively abundant data.
. . . These techniques may not be as valuable when applied to the assessment
of radionuclide transport in deep rock formations, over large distances and
long time frames, under conditions of sparse data availability.... [The
authors] have repeatedly drawn attention to the potential problems associated
with the geostatistical methods (Bayesian and otherwise) when data networks
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are sparse and sample sizes small. Id our opinion, this is the potential Achil-
les heel for Me application of geostatistics at nuclear repository sites.
With regard to repository isolation modeling, increased study has thus
far resulted in the identification of greater complexity. Progress is being
made toward including some of this complexity in the models, at least in
terms of groundwater studies; but other geotechnical aspects of repository
isolation (such as constitutive properties of rock joints, excavation and repository
scale deformation behavior, and regional in situ stress) are far less developed.
It will take years of additional research to represent them adequately in the
models. As a result, the prospects are poor, especially in the short term, for
models that can produce reliable quantitative measures of isolation performance.
Appropriate Objectives for Modeling
Repository performance assessments are unlikely to prove beyond doubt
that risks are below established limits. Nor do the regulations require it-
EPA requires only a "reasonable assurance." The problem is that in a case
without clear precedents, it is unclear what is "reasonable." The Board's
point is that unsound use of technical information is not a proper substitute
for the political reasoning that, in a democratic society, must in the end win
consent for taking reasonable steps to advance public health and safety.
In light of the limitations of technical knowledge, the Board concludes
that it makes sense to conduct the assessments through an iterative process,
in which the assessment provides direction to those characterizing a repository
site and developing the repository engineering features. As further information
is developed about the candidate site, it is also used in the performance
assessment.
Many of the uncertainties associated with a candidate repository site will
be technically interesting but irrelevant to overall repository performance.
Conversely, the issues that are analytically tractable are not necessarily the
most important. A key task for performance modeling is to separate the
significant uncertainties and risks from the trivial. Similarly, when there
are technical disputes over characteristics and processes that affect calcula-
tions of waste transport, sensitivity analysis with alternative models and
parameters can indicate where further analysis is required and where enough
is known to move on to other concerns.
Using Models to Reduce Uncertainty
Models do have an indispensable role in developing understanding of
such problems, provided that the models are developed and used within the
proper limitations. In other words, modeling can be used to improve models.
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The following quotations from those concerned with such problems illustrate
this point:
. . . much time can be saved in the early stages of hypothesis formulation by
Me explarai~on of these hypotheses Trough mathematical models. Similarly,
mathematical models cart be used to investigate phenomena from the view-
point of existing theories, by the integration of disparate theories into a single
working hypothesis, for example. Such models may quickly reveal inadequacies
in the current theory and indicate gaps where new theory is required.
The updating properties of Me Bayesian approach . . . are well suited to Me
iterative approach we espouse for die model~ng/data ga~er~ng sequence at a
site. We feel that the first modeling efforts should precede or accompany
initial site investigations.13
A good example of this general approach is the "regionalized sensitivity
analysis" approach, by which G. M. Hornberger and his collaborators have
been able to identify the "critical uncertainties" in applying a particular
model to several data-sparse ecological problems and, thereby, to define
programs of investigations to reduce those uncertainties.~4
In summary, models should be qualitatively sensible, robust to sensitivity
analysis, and independent of minor effects or processes, and they should
include acceptable levels of uncertainty. However, models cannot prove
that the repository is safe, nor can they resolve public concerns about the
repository.
Supplements to Modeling
Natural Analogues. Because models cannot be conclusive with regard to
the safety of a repository site, it is important to think carefully about natural
analogues. These are natural "test cases," geological settings in which
naturally occurring radioactive materials have been subjected to environmental
forces for millions of years. These natural experiments demonstrate the
action of transport processes that are similar to those that will govern the
release of man-made radionuclides from a repository in a similar setting.
The natural analogue approach depends, of course, on whether the natu-
ral case is in fact an analogue for a repository situation. Where there is
scientific agreement that the analogy applies, however, the approach is powerful
because it allows us to predict processes with confidence over many millennia.
And natural analogues can serve two additional roles: (1) they can provide
a check on performance assessment methodology, and (2) they may be more
meaningful than sophisticated numerical predictions to the lay public. The
alternative management strategy described in the following section would
make substantial use of natural analogues, such as undisturbed natural de-
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posits of radioactive elements and groundwater systems, in order to illumi
nate the behavior of the geologic environment.
Professional Judgment. A second approach is to use the professional judg-
ment of technical experts as an input to modeling in areas where there is
uncertainty as to parameters, structures, or even future events. Such judgments,
which may differ from those of DOE program managers and their staffs,
should be incorporated early in the process. A model created by this process
can redirect the DOE program substantially.
It is important to bear in mind that all uses of technical information
entail judgments of what is important and what is less so. If the technical
community is to learn from the successes and failures of the DOE program,
it is essential that these technical judgments be documented. Setting out the
reasoning of DOE staff and of independent outside experts contributes to
learning and builds credibility in the process even when the experts disagree
with DOE staff and among themselves.
Implications for Program Management
The Board has concluded that geological models, and indeed scientific
knowledge generally, are being inappropriately applied in the U.S. radioac-
tive waste repository program. That misapplication prompts this Board to
outline an alternative management strategy. The next section describes an
alternative management approach that employs natural analogues and professional
judgment in a program design that uses science appropriately in the search
for a safe disposal system. Putting such an approach into effect, however,
would require major changes in the way Congress, the regulatory agencies,
and DOE conduct their business. Such changes will be difficult to achieve,
but the Board has reluctantly concluded that nothing else will put to rest the
problems that plague the national program today.
Strategic Planning
Overview
There is no scientific reason to think that an acceptable HEW repository
cannot be built and licensed. For historic and institutional reasons, however,
DOE managers often feel compelled to "get it right the first time." This
management strategy runs the risk of encountering "show-stopping" problems
that may delay licensing and will certainly cause further deterioration of
public and scientific trust.
The alternative would be a more flexible, experimental strategy that em-
bodies the following principles:
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· respond with conservative design changes as site attributes are discovered;
· use modeling to identify areas where more information is needed; and
· allow for remediation if things do not turn out as planned.
Implicit in this approach is the need to revise both technical design and
regulatory criteria as more information is discovered. This is difficult to
achieve in a governmental structure that disperses authority among legisla-
tive and executive agencies and separates regulation from implementation.
When presented with intense controversy, such an institutional arrangement
breeds disgust among governmental units and the public. In that setting,
partial remedies further entangle the procedural morass.
More practically, however, DOE can enhance the credibility of the program
and reduce the likelihood of late-stage surprises by (1) encouraging effective
communication within its complex management structure; and (2) providing
incentives for field personnel to identify and solve problems. DOE and the
USNRC can also enhance credibility by encouraging periodic external reviews
of the repository design, construction, and licensing requirements and associated
processes.
Policy Context
The present U.S. approach to HLW disposal is increasingly vulnerable to
being derailed by minor surprises. This vulnerability does not arise from a
lack of talent or effort among the federal agencies and private contractors
working on the program. Nor does the design or construction of the repository
represent an unusually difficult technical undertaking. Instead, the program
is at risk because it is following the wrong approach to implementation.
The current predetermined process, in which every step is mandated in
detail as in the more than 6,000-page "Site Characterization Plan,"is is in-
appropriate.
The current policy calls for a sequential process in which EPA and the
USNRC first establish the criteria for safe disposal, and then DOE describes
in detail what steps will be taken to move through site characterization,
licensing, and operation of the facility. The result of this approach is that
any late change, by any of the participating agencies, is taken as an admis-
· ~
slon ot error.
And late changes are bound to happen. One worker was killed and five
injured in an HLW repository under construction in West Germany when a
support ring failed unexpectedly. At the Waste Isolation Pilot Plant (WIPP)
in New Mexico, the discovery of pockets of pressurized brine in formations
below the repository level led to public outcries and a continual National
Research Council review of the suitability of the site.
The United States seems to be the only country that has taken the ap-
proach of writing detailed regulations before all of the data are in. Almost
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all other countries have established limitations on the allowable levels of
radiation dose to individuals or populations resulting from repository estab-
lishment but have taken a "wait and see" approach on design, while collecting
data that may be of use in setting design. The United States, on the other
hand, seems to have felt that detailed regulations can be, in fact must be,
written without regard to any particular geological setting or other circumstance.
As a direct consequence, the U.S. HEW program is bound by requirements
that may be impossible to meet, even though overall dose limits can be
achieved.
Alternative Management Strategies
The preceding sections have shown that there are a number of unresolved
issues in the U.S. radioactive waste disposal program, as well as (and in
part because of) high levels of uncertainty and public unease about the
performance of the repository. The Board's consideration of these subjects
indicates that the proper response to distrust is greater openness in the
process, and that the proper response to uncertainty is greater knowledge
and flexibility, as well as redundancy of barriers to nuclide transport. The
U.S. program will continue to face controversy until it adopts a management
strategy based on these principles.
The current approach to the design, construction, and licensing of the
Nevada site is derived from the philosophy and procedures used for licens-
ing nuclear power plants. The characteristics of the repository and its geological
setting are carefully determined and specified as a basis for a complex set
of calculations that describes the behavior of the system. This model is
used to generate predictions of the migration of radioactive elements into
the biosphere and analyzes the consequences of various events ("scenarios")
that might affect the site over the next 10,000 years, in order to demonstrate
that the repository site meets regulatory requirements (i.e., is "safely. Based
on the model and geologic studies of the site, the construction of the repository
is specified in detail and then carried out under an aggressive quality assurance
program, which is designed to withstand regulatory review and legal challenge.
Within these requirements it is the geological setting that ensures isolation,
not the engineered characteristics of the system; closure aims for complete
entombment and discourages subsequent remediation. For all the reasons
discussed above, a management process based on the regulation of nuclear
power stations (a Region 3 type problem: see Figure 1) is inappropriate to
the development of a waste repository.
A well-documented alternative to this approach is being followed, to
various degrees, by countries such as Canada and Sweden. The exploration
and construction of a geological test facility and a low-level waste repository,
respectively, follow a flexible path, allowing each step in the characterization
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and design to draw on the information and understanding developed during
the prior steps, and from prior experience with similar underground construction
projects. During and subsequent to the closing of the repository, the emphasis
will be on monitoring and on the ability to repair, in order to minimize the
possibility that unplanned or unexpected events will compromise the integ-
rity of the disposal system. Engineered modifications can be incorporated
(e.g., in the waste containers or in the material used to backfill the repository)
if the computer models suggest unacceptable or irreducible uncertainties in
the performance of the unmodified containment system.
The Canadian experience at their Underground Research Laboratory provides
a good example. All of the major rock structures and groundwater conditions
were defined from surface and borehole observations before shaft construction
began. Detailed geological structure can never be totally determined from
surface information, however, and the final details of the facility design
were modified to take account of information gathered during shaft construction.
What are the risks and benefits of the two approaches? The U.S. approach
facilitates rigorous oversight and technical auditing. Its goals and standards
are clear, and, if carried out according to specifications, this approach is
robust in the face of administrative or legal challenge. It is designed to
create a sense of confidence in the planning and operation of the repository,
and it facilitates precise answers to specific technical questions.
However, such an approach is not consistent with normal geologic or
mining practice. It assumes that the properties of the geologic medium can
be determined and specified in advance to a degree analogous to that required
for man-made components, such as reinforcing rods, structural concrete, or
pipes. In reality, geologic exploration and mine construction never proceed
in this way. Most underground construction projects are more qualitative,
using a "design (and improve the design) as you go" principle. New sections
of drill core often reveal surprises that must be incorporated into the geologists'
concept of the site, integrated with past experience, and used to modify the
exploration plan or mine design. In a project where adherence to predeter-
mined specifications is paramount, the inherent variability of the geologic
environment will result in endless changes in the specifications, with resultant
delays, frustration for field personnel, high overhead costs, and loss of
public confidence in both the suitability of the site and the competence of
the professionals working on the project.
The second approach has more in common with research than with con-
ventional engineering practice. This approach continually integrates new
data into the expert judgments of geologists and engineers. It makes heavy
use of natural analogues, such as undisturbed natural deposits of radioactive
elements and groundwater systems, in order to illuminate the behavior of
the geologic environment. It can immediately take advantage of favorable
surprises and compensate for unfavorable ones. That this approach works
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well is evidenced by the enormous number of underground construction
projects in diverse geologic settings that have been completed successfully
around the world. These projects were not designed to contain radioactive
waste for thousands of years, but many of them faced technical problems of
comparable magnitude, such as crossing active faults, sealing out massive
groundwater flows, or stabilizing highly fractured and structurally weak
rock masses.
The second approach, with its reliance on continuous adaptation, would
be much more difficult to document, audit, and defend before a licensing
authority or court of law than is the more prescriptive approach. Some
aspects of quality assurance can work well, such as document and sample
control, the use of standard procedures and tools, and personnel qualifications.
Other quality assurance techniques are likely to be contentious and may be
impossible to implement in the same way they are implemented in nuclear
power plants, including design control, instructions, procedures, drawings,
inspections, and control of nonconforming items. An alternative is to use
an aggressive and independent peer review system to appraise the decisions
made and the competence of the technical personnel and managers responsible.
The legal system is able to accept expert opinion as a basis for action or
assessments of action, but one cannot predict whether a repository could
ever be licensed in the face of the batteries of opposing "experts" who
would inevitably be called on to assess a flexibly designed and constructed
repository for HEW disposal. The debate will hinge in part on a clear
understanding of the alternatives against which a proposed "solution" will
be judged. By contrast, the EPA standards and USNBC regulations define
requirements that, if met, form the basis for the presumption that the facility
is "safe."
Given the unhappy history of radioactive waste disposal in the United
States, however, one very real and likely alternative is that nothing at all
will be done. In judging disposal options, therefore, one should also adopt
inaction or some other likely scenario as a default option, so that comparisons
can be made and progress consistently assessed over time. The combination
of a conservative engineering approach and designed-in maximum flexibil-
ity, to allow unanticipated problems to be corrected, should reassure both
technical experts and concerned nonexperts. The barrier is not logical but
institutional, and the prescriptive approach in the U.S. program is dictated
by a governmental structure that separates regulation from implementation.
Within the present program, for example, "quality assurance" has be-
come the bete noire of frustrated field personnel, who are trying to work
within a system that is hostile to surprises in a world that is full of them.
Because almost any geologic phenomenon has more than one possible cause,
flexibility (including the recognition that uncertainty is inevitable and must
be accommodated) is more likely to lead to the design and construction of a
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safe repository system than are rigid, predetermined protocols. In employ-
ing and evaluating such an adaptive approach to construction, emphasis
focuses on those decisions that have irreversible or noncorrectable consequences
on disposal, rather than on the myriad small adjustments that do not affect
the basic flexibility and robustness of a repository.
The Elements of a More Flexible System
In a program governed by this alternative approach, change would not be
seen as an admission of error; the system would be receptive and responsive
to a continuing stream of information from site characterization. The main
actors would reduce their reliance on detailed preplanning during initial site
characterization, making it possible to debug the preliminary design during
rather than before characterization. But the necessary conditions of the
system are flexibility and resiliency—flexibility to respond rapidly to ongoing
findings in the geology, geohydrology, and geochemistry (within broad
constraints); and resiliency to continuously adjust the performance assessment
to reflect new information, especially where such information indicates possible
precursors of substantial increases in risk. These qualities could be devel-
oped through the following steps:
Iterative performance assessment. The basic approach outlined here
would start with a simplified performance assessment, based on known data
and methods of interpretation. Given the inherent uncertainties and techni-
cal difficulties of the process, the present system may well expend large
efforts on small risks, and vice versa. An iterative approach, on the other
hand, could allow characterization efforts to give priority to major uncertainties
and risks, while there is still time and money left to do something about
them. As in probabilistic risk assessment, analysis focuses on efforts to
reduce the important risks and uncertainties. In this case, that means acquiring
information on the design features and licensing criteria that are most likely
to determine whether the site is suitable or should be abandoned.
· Fixing problems vs. anticipati1lg problems. The underlying concept
of the present, anticipatory U.S. management strategy is "Get it right the
first time." One result is a 6,300-page "Site Characterization Plan" for
Yucca Mountain. For the reasons described above, however, a process
based on getting all of the needed measurements and analysis on the first
pass, with acceptably high quality, is not likely to succeed. The geological
environment will always produce surprises, like the pockets of pressurized
brine at WIPP. No matter what technical approach is initially adopted, the
design can be improved by matching it with specific features of the site.
Experiments are now being conducted at WIPP with backfill material and
other engineered barriers that were not part of the original design. These
~ , _ , _ ~
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are being Died as ways to make the disposal system as a whole robust in the
face of newly discovered uncertainties in the geology.
· Deft ne the problem broadly. As characterization proceeds, especially
if it is done without the guidance of iterative performance assessment, DOE
may eventually find it difficult or impossible to meet some of the criteria
set by the USNRC and/or EPA. This will not mean that Yucca Mountain is
unsuitable for a repository—the problem could be with the detailed criteria.
This is no reason to arbitrarily abandon the release limits it is the more
detailed requirements that may need to be reconsidered, since they ultimately
affect the release limits and the imputed dose. However, one should not
take EPA's release standards or the USNRC's detailed licensing requirements
as immutable constraints. They are roadmarkers to, and surrogates for,
dose limits. Although the EPA standards and the USNRC regulations recognize
and accept a certain level of uncertainty, the discussion to date of the application
of these standards and regulations does not warrant confidence in the acceptance
of uncertainty in licensing procedures.
Some process is needed in order to determine whether DOE's inability to
meet a particular requirement is due to a disqualifying deficiency in the site
or to an unreasonable regulatory demand, one that is unlikely to be met at
any site and is unnecessary to protect public health. And to the extent that
regulatory criteria can be corrected earlier instead of later in the process,
they are more likely to be perceived as technical adjustments rather than as
a diminution of public safety. Given the history of U.S. efforts to dispose
of radioactive waste, current plans for the program have little chance of
progressing without major modification in the 20 years or more that will be
required to get a repository into operation.
Representative terms from entire chapter:
waste repository
