|
Items in cart [1] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 105
4
HUMAN INTRUSION AND INSTITUTIONAL
CONTROLS
INTRODUCTION
In Section 801(a)(2) of the Energy Policy Act of 1992, Congress
asked three specific questions. The first question, about the use of
incliviciual dose as a criterion for protecting the public, was addressed in
Chapter 2. The second en c! third questions concern the potential that at
some future time people might intrude into the repository, thereby
defeating its geologic and engineered barriers. We were asker! to examine
the scientific basis for predicting human intrusion and the potential for
protecting against it, specifically:
Question 2. Whether it is reasonable to assume that a system for
post-closure oversight of the repository can be cieveloped, based
on active institutional controls, that will prevent an unreasonable
risk of breaching the repository's engineered barriers or increasing
the exposure of individual members of the public to radiation
beyonc! allowable limits.
Question 3. Whether it is reasonable to make scientifically
supportable predictions of the probability that a repository's
engineered! or geologic barriers will be breaches! as a result of
human intrusion over a period of 10,000 years.
Briefly, we conclude that the answer to both questions is "no" for the
reasons outlined below.
Human activity that penetrates the repository, such as by drilling
into it from the surface, can cause or accelerate the release of
radionuclicles. Waste material might be brought to the surface and expose
the intruder to high radiation doses, or the material might disperse into the
biosphere. Even if this does not occur, a borehole could go through the
105
OCR for page 106
106
YUCCA MOUNTAIN STANDARDS
repository and open a pathway by which radionuclides more readily reach
the ground water.
Over the years, DOE has developed a considerable literature on
human intrusion and on active and passive controls to prevent it (von
Winterfeldt, 19941. For example, some studies have examined resource
potential and historical exploration activity and used current understanding
and rates of drilling to project future activity. Other studies have detailed
examples of monuments and inscriptions that have survived from long ago.
Still others have speculated on the characteristics of signs and markers that
might improve their long-term effectiveness at delivering a message to
future generations. Basec! on our understanding of this literature, however,
we conclude that there is no technical basis for predicting either the nature
or the frequency of occurrence of intrusions.
For some initial period, human intrusion could be managed through
active or passive controls. As long as they are in place, active institutional
controls such as guards could prevent intruders from coming near the
repository. We conclude, however, that there is no scientific basis for
making projections over the long term of either the social, institutional, or
technological status of future societies. Relying on active controls implies
requiring future generations to dedicate resources to the effort. There is,
however, no scientific basis from which to project the durability of
governmental institutions over the period of interest, which exceeds that of
all recorder! human history. On this time scale, human institutions have
come and gone. We might expect some degree of continuity of
institutions, and hence of the potential for active institutional controls, into
the future, but there is no basis in experience for such an assumption
beyond a time scale of centuries.
Similarly, there is no scientific basis for assuming the long-term
effectiveness of active institutional controls to protect against human
intrusion. Although it may be reasonable to assume that a system of post-
closure oversight can be developer! and relied on for some initial period of
time, there is no defensible basis for assuming that such a system can be
relied on for times far into the future. Between these limits, the ability to
rely on such active institutional systems presumably diminishes in a way
that is intrinsically unknowable. We have seen no evidence to support a
claim to the contrary. People might disagree, of course, on their
predictions for how long into the future active institutional controls might
survive and remain effective.
OCR for page 107
HUMAN INTR USION AND INSTITUTIONAL CONTROLS 10 7
The situation is not qualitatively different for passive institutional
controls. As long as they are recognized and heeded, passive controls such
as markers, barriers, and archival records could serve to warn potential
intruders away. Passive controls, too, may be of limited duration, requiring
future generations to renew them. While many historical markers,
monuments, and recorcis have survived for long periods of time, up to
thousands of years, most presumably have not. Those records that have
survived might not represent records for which the local social knowledge
was continuous. We cannot know those that did not survive to our time.
Further, languages have changed over periods of centuries so that fill
documents and inscriptions might be clifficult for any but scholars to
interpret. Even though technologies for making markers and monuments
will improve and even though modern global telecommunications might
slow the rate of change of languages, the time span of concern for a high-
leve! waste repository far exceeds experience, so there is no technical basis
for making forecasts about the reliability of such passive institutional
controls.
Just as there is no basis for assuming the effectiveness of either
active or passive institutional controls to reduce the risk of human
intrusion, we also conclude that there is no scientific basis for estimating
the probability of intrusion at far-future times. Several types of intrusion
can be considered: inadvertent intrusion into the repository in the process
of exploring for or producing other resources in the vicinity, intrusion
driven by curiosity about the markers and what might lie below them, or
intentional intrusion for malicious purposes or to recover the repository
contents. (The malicious intrusion might be by a hostile nation or
subnational group assuming a societal or institutional presence.) In our
view, there is simply no scientific basis for estimating the probability of
inadvertent, willful, or malicious human action.
Estimating the probability of inadvertent intrusion as a
consequence of exploration or production of resources might seem more
plausible than for the cases of willful or malicious intrusion. Doing so,
however, requires knowledge of which materials at or near the site will be
regarded as resources in the future and the technologies that will exist for
exploration and production. We cannot predict fixture economic conditions
that help to define what is a valuable resource nor can we forecast future
exploration technology, although we can observe that, if the past is an
aciequate guide, economic conditions and technology will change rapidly
OCR for page 108
108
YUCCA MOUNTAIN STANDARDS
in the future. It might very well be, for example, that subsurface
exploration technology in the future could be based on remote sensing so
that penetration of the surface is no longer required. We therefore do not
think that it is feasible to make meaningful predictions about the
probability of advertent or inadvertent intrusion.
Based on these findings, we make two observations about how to
deal with human intrusion in the Yucca Mountain standard. First, although
there is no scientific basis for judging whether active institutional controls
can prevent an unreasonable risk from human intrusion, we think that if the
repository is built such controls ant] other activities can be helpful in
reducing the risk of intrusion' at least for some initial period of time after
a repository is closed. Therefore, although it cannot be proven, we believe
that if a repository is built at Yucca Mountain, a collection of prescriptive
requirements, inclucling active institutional controls, record-keeping, ant]
passive barriers and markers, will help to reduce the risk of human
intrusion, at least in the near term. The degree of benefit is likely to
decrease over time. Further, once other knowledge of the repository is lost,
passive markers could attract the curious and actually increase the risk of
intrusion. Nonetheless, we conclude that the benefits of passive markers
outweigh their clisadvantages, at least in the near tertn.
Second, because it is not technically feasible to assess the
probability of human intrusion into a repository over the long term, we do
not believe that it is scientifically justified to incorporate alternative
scenarios of human intrusion into a fully risk-based compliance assessment
that requires knowledge of the character and frequency of various intrusion
scenarios. We clo however conclucle that it is possible to carry out
calculations of the consequences for particular types of intrusion events,
for example drilling one or more boreholes into and through the repository.
We also believe that calculations of this type might be informative in the
sense that they can provide useful insight into the degree to which the
ability of a repository to protect public health would be degraded by
intrusion.
For these reasons, to address the human intrusion issue on an
adequate basis, we recommence that the repository developer should be
required to provide a reasonable system of active and passive controls to
reduce the risk of intrusion in the near term and that EPA should specify
in its standard a typical intrusion scenario to be analyzed for its
consequences on the performance of the repository. Such an analysis will
OCR for page 109
HUMAN INTR USION AND INSTITUTIONAL CONTROLS 109
provide useful quantitative information that can be meaningful in the
licensing process, as ciescribe~i later in this chapter. Because the assumed
intrusion scenario is arbitrary and the probability of its occurrence cannot
be assessed, the result of the analysis should not be integrated into an
assessment of repository performance based on risk, but rather should be
considered separately. The purpose of this consequence analysis is to
evaluate the resilience of the repository to intrusion.
Although we believe that a requirement baser! on analyses of
intrusion consequences is useful in assessing repository performance at
Yucca Mountain, such analyses are likely to be more meaningful in
selecting among alternative sites (such as by avoiding sites that have
potentially valuable mineral, energy, or ground-water resources) than in
assessing the performance of a particular site and design. However, Yucca
Mountain has already been selected for evaluation as a potential repository
site, so the value of analyses of the consequences of human intrusion at
Yucca Mountain is limited. Consideration of analytic approaches that
would discriminate among alternative sites with greater or lesser likelihood!
or consequences of intrusion is beyond our charge.
In the remainder of this chapter, we present our argument for the
usefulness of an analysis of consequences of a simple intrusion scenario;
ant! provide additional cletai] on the factors we consiclerec] in arriving at our
conclusions.
The Consequences of Intrusion
As noted earlier, the consideration of human intrusion cannot be
integrated into a fully risk-based standard] because the results of any
analysis of increaser] risk as a consequence of intrusion events would be
driven mainly by unknowable factors. We reach this conclusion
specifically because the numerical value of the risk of Diverse health
effects due to intrusion is always the product of two factors, the frequency
of an intrusion scenario and the measure of consequence. However, the
frequency of an intrusion scenario in the distant future is indeterminate.
OCR for page 110
110
Technical basis
YUCCA MOUNTAIN STANDARDS
Some factors affecting an analysis of the consequences of human
intrusion can be assesses! from a technical base, and some cannot. The
historical record of intrusion in the region of the site, inclucling both rate
and characteristics (drill depth, hole size, etc.) and the characterization of
known mineral and other current resources near the site, can be assesses!
very well. However, the relevance of the historical recorc} is doubting. The
physical consequences, in terms of the release and probable dispersion of
radioactive materials, which is conditional on a cleaner! intrusion scenario
either benevolent or malevolent in purpose (such as the timing ant}
physical characteristics of the intrusion ant! whether the intrusion is
recognizes! and remecliated), can be assesses! moderately well within limits
imposer! by the level of detail contained in the modeling. Aciverse
consequences from a specified type of intrusion to a specified local society
can also be assesses! moclerately well, but this assessment for the distant
future requires making assumptions about many aspects of the future
society, including its sources anti technologies for distributing drinking
water and food, the ability to detect contamination of food or water,
locations of future populations, etc. which cannot be accurately predicted.
These assumptions, discusser! in Chapters 2 and 3, are inherent in any
health-based standard, and we have recommended that for the purposes of
compliance analysis they be made explicit through the rulemaking process.
Factors that cannot be technically assessed include the likelihood
that institutional controls will persist and succeed over time, or that
markers or barriers would persist, be understood, and deter intrusion; the
probability that a future intrusion would occur in a given future time period
such as in any one year; and the probability that a future intrusion would
be detectecI and remediated, either when it occurs or later. In addition, we
cannot predict which resources will be discovered or will become valuable
enough to be the objective of an intruder's activity. We cannot predict the
characteristics of future technologies for resource exploration and
extraction or whether future practice will include sealing of physical
intrusions such as boreholes. Continued developments in current non-
invasive geophysical techniques, for example, could substantially reduce
the frequency of exploratory boreholes.
OCR for page 111
HUMAN INTR USION AND INSTITUTIONAL CONTROLS I 1 1
Consequence-based analysis
Although it would be desirable if the risks associated with the
disturbances to a repository by human intrusion could be integrated into a
risk assessment of the undisturbed repository performance, technically it
is not appropriate to do so. Rather than a complete risk analysis, one
alternative is to examine the site- and design-related aspects of repository
performance under an assumed intrusion scenario to inform a qualitative
judgment. In this approach, the objective would be to perform a
consequences-only analysis without attempting to determine an associated
probability for the analyzed scenario. We recommend that the Yucca
Mountain standard require such an analysis.
We considered at some length the question of whether the
calculation of consequences for one or more specified human intrusion
scenarios, absent their associated probabilities, could form a useful basis
for evaluating a proposed repository site and design. We conclude that the
calculations of consequences would provide useful information about how
well a repository might perform after an intrusion occurs. The key
performance issue is whether the repository would continue to be able to
isolate wastes from the biosphere, or if its performance would be
substantially degraded as a consequence of an intrusion of the type
postulated.
Because the form ant! frequency of intrusions cannot be predicted,
certain assumptions must be made in order to assess the resilience of the
repository to intrusion. As in the case of adopting a mode] of the biosphere
ant! identifying critical groups, selecting an intrusion scenario for analysis
entails judgment. To provide for the broadest consideration of what
scenario or scenarios might be most appropriate, we recommend that EPA
make this determination in its rulemaking to adopt a standard. In this
regard, we suggest the following starting point.
For simplicity, we considered a stylized intrusion scenario
consisting of one borehole of a specified diameter drilled from the surface
through a canister of waste to the underlying aquifer. One can always
conceive of worse cases, such as multiple boreholes with each penetrating
a canister, but this single-borehole scenario seems to us to hold the promise
OCR for page 112
112
of providing consiclerable
minimum complication.
YUCCA MOUNTAIN STANDARDS
.
Insight into repository performance with the
An example of a scenario that we believe provides a reasonable
basis for evaluation would postulate current drilling technology but assume
sloppy practice, such as not plugging the hole carefully when abandoning
it, after which natural processes would gradually modify the hole.
Although the time at which the intrusion occurs in the future is arbitrary in
any hypothetical scenario, we believe it is useful to assume that the
intrusion occurs during a period when some of the canisters will have
failed but the released materials would not otherwise have had time to
reach the grounc! water. This assumption places emphasis in the
consequence analysis on the creation of enhancer! pathways to the
environment (both to the atmosphere and to the aquifer) as opposed to
emphasis on the intrusion's breaching of the canister, which will happen
eventually even without human intrusion.
Having definer! the reference scenario, the principal questions are
what consequence should be assesses} and how the result should be
interpreted. In our view, the performance of the repository, having been
intruded upon, should be assessed using the same analytical methods and
assumptions, including those about the biosphere and critical groups, used
in the assessment of the performance for the undisturbed case. This
analysis should be carried out to determine how the hypothesized intrusion
event affects the risk to the appropriate critical groups. We propose that
the figure-of-merit for this calculation should be the same as in the
undisturbecI case, because a repository that is suitable for safe, long-term
disposal should be able to continue to provide acceptable waste isolation
after some type of intrusion.
The result ofthis calculation, however, would be a conditional risk:
that is, a risk assuming that the hypothesized intrusion occurs. Because the
probability is inherently unknowable, we are led to the conclusion that the
most useful purpose of this type of analysis is to identi fy the incremental
effects from the assumed scenario. As indicated earlier, we believe that
Under many conditions, the effect of multiple boreholes presumably would be
the sum of the effects of each taken separately, but circumstances when this
assumption is invalid can easily be conceived. Because construction of
scenarios is arbitrary, we would argue for the simplest case that tests the
repository.
OCR for page 113
HUMAN INTRUSION AND INSTITUTIONAL CONTROLS 113
since human intrusion of some type might be likely at some time in the
future, a repository should be resilient to at least modest inadvertent
intrusions. Because whether and how frequently intrusion events might
occur are unknowable, how important these effects are for our expectation
that the repository will protect the public can also only be a matter of
judgment. Our recommendation is that EPA should require that the
conditional risk as a result of the assumed intrusion scenario should be no
greater than the risk levels that would be acceptable for the undisturbed-
repository case. The conditional risk calculation would not include risks
to the intruder or those arising from the material brought directly to the
surface as a consequence of the intrusion. As with other policy-related
aspects of our recommendations, we note that EPA might decicle that some
other risk level is appropriate.
Finally, we wish to reiterate that the single borehole scenario that
we have discussed should not be interpreter} as an estimate of the likely
form or frequency of intrusion. A calculation of consequences for such an
intrusion removes from consideration a number of imponderables, each of
which would otherwise need to be treated separately, including the
probability that an intrusion borehole would intersect a waste canister, the
probabilities of detection and remediation, and the effectiveness of
institutional controls and markers to prevent intrusion. This scenario
should not be interpreter! as either an optimistic or pessimistic estimate of
what might actually occur, because there might be no boreholes that
intercept canisters, or there might be more than one. We believe that the
simplest scenario that provides a measure of the ability of the repository to
isolate waste ant! thereby protect the public health is the most appropriate
scenario to use for this purpose.
ADDITIONAL BASES FOR OUR RECOMMENDATION
In this section we discuss two additional aspects of the human
intrusion question that underlie our thinking: the various categories of
future human intrusion scenarios and the categories of hazards that could
result from a typical borehole intrusion.
OCR for page 114
114
YUCCA MOUNTAIN STANDARDS
Categories of Future Human Intrusion Events
For the purposes of considering how to clear with human intrusion
in the context of stantiard-setting and licensing, we have focused on the
particular class of cases in which the intrusion is inadvertent and the
intruder does not recognize that a hazardous situation has been created.
We consiciered several other categories of intrusive events. One
case is when the intrusion is inadvertent, but the intruder recognizes that
a radioactive waste repository has been clisrupted ant! takes corrective
actions. On the assumption that the corrective measures taken are effective
ant! the repository is sealed, this class is not of concern. If, however,
corrective actions are not taken or are ineffective, this type of intrusion is
operationally the same as the inadvertent intrusion that is not recognized
as hazardous, which is the class of cases on which we have focused.
We also considered! intentional intrusion for either beneficial or
malicious purposes, but concluded that it makes no sense indeed! it is
presumptuous to try to protect against the risks arising from the
conscious activities of future human societies. Given the potential energy
value of the wastes intended for Yucca Mountain, however, this category
of intrusion scenarios might be likely.
Categories of Hazards Resulting From an Intrusion
We have identifier] three broad types of hazards from radioactive
material that could occur as a result of an intrusion into the repository of
the type characterizes! by borehole scenarios. The categories are:
Hazards to the intruders themselves (the drillers, miners, or
handlers of material previously in the unclisturbed
repository).
Hazards to the public from any material brought directly to
the surface by the intrusive activity. These hazards would
arise because such material, now no longer at depth within
the repository, would! now be mobile in the biosphere, and
the public (in addition to the intruders) can be exposed to the
material.
OCR for page 115
HUMAN INTR USION AND INSTITUTIONAL CONTROLS 11 5
· Hazards that arise because the integrity of the repository's
engineered! or geologic barriers have been compromiser! by
the intrusion.
In the first and second instances, we concluded that analyzing the
risks to the intrusion crew and the risks from any material brought directly
to the surface as a consequence of intrusion is unlikely to provide useful
information about a specific repository site or design and therefore should
not provicle a basis for judging the resilience of the proposed repository to
intrusion. Whenever highly dangerous materials are gatherer! into one
location ant! an intruder inadvertently breaks in, that intruder runs an
inevitable risk. This is not unique to a cieep geologic repository, and all
deep geologic repositories have this feature. In particular, for inadvertent
human intrusion, we believe that it wouIc! not be feasible to take regulatory
actions today to protect the intrusion crew itself against the risks of its
actions, except that requirements identified above associates! with active
or passive institutional controls might be helpful in this regard.
However, it is possible that an inadvertent intruder would not
recognize or wouIc} irresponsibly ignore the hazard and wouIc! leave the
cuttings on the surface so that further exposures would occur. This is the
second category of hazards listed above. Our view is that the amount of
such future cuttings might not be very different from one repository site or
design to another, especially given the unknown nature of an intrusion.
Analysis of this hazard too, therefore does not provide information that is
useful for judging the ability of the particular repository site ant} design to
protect the public. In this case, we also believe that it is not feasible to take
regulatory actions tociay to alter the repository design to minimize these
risks.
We therefore, recommend that the compliance analysis should
concentrate on the third category of hazard posed by human intrusion, the
one resulting from modification of the repository's barriers and the
consequences of these mollifications for the ability of the repository to
perform its intended function.
OCR for page 116
Representative terms from entire chapter:
institutional controls
