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 117
s
IMPLICATIONS OF OUR CONCLUSIONS
Early in this study' we were asked by EPA to provide a description
of how the form of the standard that we recommend differs from that of the
current EPA stanciard for high-level raciioactive waste in 40 CFR 191 and,
where there were significant differences, to provide an explanation of the
basis for the differences. We have tried to do so in the detailed discussions
of Chapters 2, 3, ant] 4. The purpose of this chapter is to provide a
comparison of our recommended approach with 40 CFR 191, including
both common elements ant! differences. It is our intention that this chapter
provide a concise summary of what we propose should be done differently
ant] what elements of the 40 CFR 191 approach we recommenc! be retained.
In adclition, we discuss the approach recommended here and that
of technology-based standards such as the USNRC's 10 CFR 60. Because
our approach is risk-based, it is not useful to make a direct comparison
with 10 CFR 60. We do discuss here some aspects of technology-based
standards, including ALARA and technology requirements to minimize
early releases. Finally, we note some possible administrative consequences
of our recommendations.
COMPARISON WITH 40 CFR 191
40 CFR 191 applies to the Waste Isolation Pilot Plant (WIPP) not
to the proposed Yucca Mountain repository. Whether some other future
repository would be subject to 40 CFR 191 depends on the legislative
means taken to initiate it. The 40 CFR 191 standard has three major
elements: containment requirements, individual dose limits, and grouncI-
water protection requirements. Section X01 of the Energy Policy Act of
1992 directs EPA to issue a standard to protect the public from
radionuclide releases at Yucca Mountain, and requires that the standard be
stated in terms of the maximum annual dose equivalent to individual
members of the public.
117
OCR for page 118
118
YUCCA MOUNTAIN STANDARDS
Considerations
We believe that there are two major considerations that give rise
to differences between our recommendations and 40 CFR 191.
Generic vs. site-specif c standards
By law, EPA is charger] with issuing generally applicable standar(ls
for protection of health and the environment, and for that reason, 40 CFR
191 is a generic standard. This means that 40 CFR 191 contains provisions
applicable for all conceivable terrestrial deep geologic repository sites and
types. In adclition, at the time that 40 CFR 191 was drafted, the major
effort towards establishing a repository was site selection, and 40 CFR 191
was developer! to give guidance regarding the feasibility of different types
of sites. In contrast, our recommendations concern a standard for the
proposed repository at Yucca Mountain. Consequently, we have not
addressed site selection, nor have we emphasizer! potential elements of a
standard that would be operationally insignificant at Yucca Mountain. For
example, our fancying that a containment requirement or release limit is
inappropriate is a finding specific to a Yucca Mountain repository, for
another geologic setting, we might or might not have reached a different
conclusion. The ctistinction between a generic stanciard and a site-specific
one should be noted as our recommendations are compared with 40 CFR
191.
Dose vs. risk
40 CFR ~ 91 limits individual closes from the undisturbed
performance of a repository to 0. ~ 5 mSv per year (15 mrem per year). In
contrast, we have recommended an approach based on individual-risk
limits. Among the reasons why we have chosen risk as the regulatory basis
rather than dose, two are important for this discussion. The first is that
changes in our understanding of radiation health risks can be
accommodates! without revision of the level of the standard. If, in the
future, scientific evidence becomes available in(licating that radiation is
OCR for page 119
IMPLICATIONS OF OUR CONCLUSIONS
119
more or less hazardous than our current scientific understanding suggests,
the framework we propose wouic] incorporate that new information without
a required revision to the level of the standard. The second reason that we
have recommended a risk basis is that the probabilities associated with
various elements of the exposure calculation can be considered. Our
recommended approach is a risk limit based on the probabilistic
distribution of a dose and the probability of health effects associated with
that dose.
Because the individual dose requirements of 40 CFR ~ 9 ~ have not
been implemented, it is not possible to tell whether or how probabilities
would be incorporated into estimation of dose. Because the effort at EPA
with 40 CFR 191 implementation is now focused on WIPP, and because
the individual dose limit is not a particularly important component of the
standard for WIPP, it is not clear to us how EPA will interpret its dose
limit. In any event, our proposal is clear with respect to our intention that
the standard should include consideration of the probabilistic aspect of
future exposures.
Differences From 40 CFR 191
What follows is a brief summary of the differences between our
recommendations and 40 CFR 191.
Time periods
Perhaps the most significant difference between our
recommendations and 40 CFR 191 concerns the time period! over which the
standard is applicable. In 40 CFR 191, the standard applies for a period of
10,000 years. In our proposal, we have specified that the basis for the
standard should be the peak risk, whenever it occurs. Based on
performance assessment calculations provided to us, it appears that for
some reasonable combinations of parameters, peak risks are likely to occur
after 10,000 years.
Within the limits imposed by the long-term stability of the geologic
environment.
OCR for page 120
120
Population health effects and release limits
YUCCA MOUNTAIN STANDARDS
A major element of 40 CFR 191 is its containment requirement,
which limits releases of radionuclides to the accessible environment during
the first ~ 0,000 years of operation. The stated goal of the release limit was
to limit cancer deaths to the general population to 1,000 over 10,000 years.
This requirement was to be implemented through a comparison of
calculateci releases of radionuclides with a table of allowable release limits
for each radionuclide. For reasons stated in Chapter 2, we do not think that
such a requirement would provide aciciitional protection over that provided
by the inctividual-risk limit for a repository at Yucca Mountain, and we do
not recommend that a release limit be adopted.
A related topic is our recommendation in Chapter 2 to employ the
concept of a negligible incremental risk, which is the level of risk that can,
for radiation protection purposes, be dismissed from consideration.
Persons in some local populations outside of the critical group at Yucca
Mountain might be exposer! to risk from repository releases in excess of
the level of negligible incremental risk. However, as individuals, these
persons wouIc] be exposed to less risk than the risk limit established by the
standard for the critical group. On a collective basis, the risks to future
local populations are unknowable. We conclude that there is no technical
basis for establishing a collective population-risk standard that would limit
risk to the nearby population of the proposed Yucca Mountain repository.
Radiation releases from a Yucca Mountain repository can, in
principle, be clistributed beyond! a local population to a global population.
In general, the risks of radiation produced by such wide dispersion are
likely to be several orders of magnitude below those to a local critical
group.
Human intrusion
Under 40 CFR 191, an assessment must be made of the frequency
and consequences of human intrusion for purposes of demonstrating
compliance with the containment requirements. Human intrusion is not a
consideration for compliance with the indiviclual dose limits of ground-
water protection requirements. In recognition of the substantial
uncertainties involved, EPA has provicled detailed guidance for analysis of
OCR for page 121
IMPLICATIONS OF OUR CONCLUSIONS
121
human intrusion risks and is proposing a reference biosphere be used for
the implementation of 40 CFR 191 at WIPP that incorporates an
assumption that the future biosphere is much like the present. The EPA
requirement includes releases due to drilling cuttings brought to the surface
and also includes increases in other radionuclide releases that might occur,
for example, through accelerated releases to grounc] water.
In contrast, we conclude that it is not possible to assess the
probability of human intrusion into a repository over the long term, and we
do not believe that it is scientifically justifieci to incorporate alternative
scenarios of human intrusion into a risk-based compliance assessment. We
clo, however, conclude that it is possible to carry out calculations of the
consequences for particular types of intrusion events. The key
performance issue is whether repository performance would be
substantially clegraded as a consequence of an inadvertent intrusion for
which the intruder does not recognize that a hazardous situation has been
created. This consequence assessment is to be clone separately from the
calculation of compliance with the risk limit from other events and
processes, and is to exclude exposures to drillers or to members of the
public due to cuttings. We recommend that EPA should require that the
conditional risk as a result of the assumed intrusion scenario be no greater
than the risk limits adopter) for the undisturbed-repository case.
Ground-water protection
40 CFR 191 inclucles a provision to protect ground water from
contamination with radioactive materials that is separate from the 40 CFR
191 inclividual-dose limits. These provisions have been adcled to 40 CFR
191 to bring it into conformity with the Safe Drinking Water Act, and have
the goal of protecting ground water as a resource. We make no such
recommendation, and have baser! our recommendations on those
requirements necessary to limit risks to indivicluals.
Common Elements With 40 CFR 191
Although our recommendations differ from 40 CFR 191, there are
also important similarities in approach.
OCR for page 122
122
Dose apportionment
YUCCA MOUNTAIN STANDARDS
In the recently revised 40 CFR 191, EPA has enciorsec} the dose
limit anti dose-apportionment recommendations of the ICRP. We support
this approach.
Reference biosphere
In view of the almost unlimited possible future states of society
ant! of the significance of these states to future risk and dose, both EPA and
we have recommended that a particular set of assumptions be used about
the biosphere (including, for example, how anti from where people get their
foot! and water) for compliance calculations. Both EPA and we
recommence the use of assumptions that reflect current technologies and
living patterns.
Exclusion zone
The original standarcI, 40 CFR 191, container! a provision for an
exclusion zone in the immediate vicinity of the repository. The purpose
was to provide a boundary for calculating releases. The zone was
presumably to be protected! from human activity.
In light of our conclusion in Chapter 4 that it is not reasonable to
assume that institutional controls can be maintained for more than a few
centuries, we also conclude that there is no scientific basis for assuming
that human activity can be prevented from occurring in an exclusion zone
or that defining such a zone will provicle protection to future generations
from exposures in the vicinity of the repository. If, as we recommend,
human intrusion is treated separately from the performance of an
undisturbed repository, it is reasonable in our view to define a region in
which human activities are to be regarded as intrusion and to exclude that
region from calculation of the undisturbed repository performance.
Beyond the repository footprint, however, there seems to be no practical
purpose for deEning a larger exclusion zone for the form of the standard!
we recommend. Without either a release limit or a time limit for the
OCR for page 123
IMPLICATIONS OF OUR CONCLUSIONS
123
standarc! for undisturbed performance, an arbitrary boundary serves no
purpose.
Use of mean values
We recommend that the mean values of calculations be the basis
for comparison with our recommended standards.
LIMITS OF THE SCIENTIFIC BASIS
Our assignment has been to assess the scientific bases for a
standard to protect the public health from radiation exposures that might
result from radionuclicle releases associated with a high-level waste
repository at Yucca Mountain. In so cloing, we have conclucled that for
some decisions there presently exists a limited scientific basis required to
set and administer such a standard. We have explicitly noted these issues
in the preceding chapters, and have indicated that they must be decided on
a policy, rather than a scientific, basis. This interplay of scientific ant]
policy issues in the standard! has two major implications.
First, where we have iclentified policy issues, we have
recommencled that sounc! public policy would have these issues addresses!
in rulemaking by the appropriate federal agency, EPA or USNRC. The
process of addressing these issues by rulemaking or an equivalent
procedure must provide a full opportunity for public participation,
especially by the citizens of the affected jurisdictions, an(l allow the agency
the flexibility to take a broad range of public opinion into account in its
final public policy judgments. We regard these characteristics as essential
for the policy judgments that are required in formulating the standard. In
contrast, the licensing process is not suited to this policy-making role, but
rather is the arena in which compliance with the standard can be tested.
Several times we have identified possible positions that could be
used by the responsible agency in formulating a proposed rule, which is
often the initial step in the process. Other starting positions are possible,
and of course the final rule might differ markedly from the one proposed.
We have tried only to illustrate by reference to other authorities or by
OCR for page 124
124
YUCCA MOUNTAIN STANDARDS
example that there seems to be a reasonable policy position from which to
begin.
The second implication of the limitations that we have identified
is that since they represent current gaps in scientific knowledge, it might
be possible that some of these gaps and uncertainties might be reduced by
additional research. It seems reasonable, therefore, to ask what gaps could
be closed by taking time to obtain more scientific and technical knowledge
on such matters as the nature of the waste, its potential use, the health
effects of radionuclides, the value of waste products for later generations,
and the security of retrievable storage containers. New information in
these and other areas could improve the basis for setting the standards if,
for example, this information reduced the uncertainty about the effects of
very low doses of radiation.
Whether the benefit of new information would be worth the
additional time and resources required to obtain it is a matter of judgment.
This judgment would be strengthened by a careful appraisal of the probable
costs and risks of continuing the present temporary waste disposal practices
and use of storage facilities as compared with those attaching to the
proposed repository. No such comprehensive appraisal is now available.
Conducting such an appraisal, however, should not be seen as a reason to
slow down ongoing research and development programs, including
geologic site characterization or the process of establishing a standard to
protect public health.
TECHNOLOGY-BASED STANDARDS
Technology-based standards play an important role in regulations
designed to protect the public health from the risks associated with nuclear
facilities. The purpose of these standards is typically to help ensure
protection by employing the best available technology, considering cost
and other factors. Three issues involving technological approaches have
been raised in our study, and we comment on them below.
OCR for page 125
IMPLICATIONS OF OUR CONCLUSIONS
The ALARM Principle
125
The "as low as reasonably achievable" (ALARA) principle has
been a basic feature of racliation protection for nearly 30 years. It is
intended to be applied after threshold regulatory limits have been met, and
calls for additional measures to be taken to achieve further reduction in the
calculated health effects resulting from radiation exposure of workers or
of a population so that final exposures are "as low as reasonably achievable
taking account of economic and social factors." ALARA requires a
balancing of costs ant! benefits.
While ALARA continues to be widely recommended as a
philosophically desirable goal, its applicability to geologic disposal of
high-level wastes is limited at best because the technological alternatives
available for designing a geologic repository are quite limited (IAEA,
1989~. Further, the difficulties of demonstrating technical or legal
compliance with any such requirement for the post-closure phase could
well prove insuperable even if it were restricted] to engineering ant! design
issues. We conclude that there is no scientific basis for incorporating the
ALARA principle into the EPA stanciarct or USNRC regulations for the
repository. However, it is nothing other than sound] engineering practice
to consider whether reductions in radiation close or risk can be achiever!
through engineering measures that can be implemented in a cost-effective
manner.
10 CFR 60
If EPA issues a standard based on individual risk, USNRC is
required to revise its current regulations embodies] in 10 CFR 60 to be
consistent with such a stanciard. One purpose of the existing USNRC
regulations is to help ensure multiple barriers within the repository system.
The concept of multiple barriers, implemented through subsystem
requirements, has its origin in the Nuclear Waste Policy Act of 1982.
Recognizing this origin, we nonetheless conclude that because it is the
performance of the total system in light of the risk-based standard that is
crucial, imposing subsystem performance requirements might result in a
suboptimal repository design. Care shouIc] be taken to ensure that any
OCR for page 126
126
YUCCA MOUNTAIN STANDARDS
subsystem requirements for Yucca Mountain do not foreclose design
options that ensure the best long-term repository performance.
For example, in 10 CFR GO, there is a subsystem requirement that
''the geologic repository shall be located so that the preemplacement
ground water travel time along the fastest path of likely radionuclicle travel
from the disturbed zone to the accessible environment shall be at least
1,000 years. . ." This regulation was written with the presumption that the
repository would be located in a saturated zone. At Yucca Mountain, the
repository is being considered! for location in the unsaturated zone where
there is a direct pathway to the atmosphere. This subsystem requirement
has focuses] attention on the grounc! water and away from the gaseous
pathway.
As an explicit example of suboptimization, it could be that in a
specific geologic setting the requirement to keep grounci water travel times
to the accessible environment above 1,000 years, as required by 10 CFR
60, might have next to no effect on future indiviclual risks. However, such
· . . ~ ~ .. · . . · . . .. .. · ~
a requirement COU10 force the repository design team to alter the specific
location ofthe emplaces] waste to a location that, although it could meet the
travel-time requirement, would be less optimal. That is, it could imply
greater future incliviclual risks clue to other factors such as, for example,
a less optimal gaseous pathway or a different geochemical setting that
wouIcI leac} to higher raclionuclide solubilities or lower retardation.
Minimum Early Release
Several persons suggested to our committee the use of a
technology-basec] standard that would specify a strict release limit from an
engineered barrier system during the early life of the repository. A
representative proposal of this type would permit the release of less than
1 part in 100,000 per year of the radionuclides present at 1,000 years after
repository closure. It was suggested that this proposal would be consistent
with the essentially complete containment concept of 10 CFR 60, and
would result in essentially no public health impact for an initial period of
time of 300 to 1,000 years, cluring which the integrity of the engineered
barrier system conic} be assurer! with a high level of confidence.
We find that such a limitation on early releases from the repository
would have no effect on the results of compliance analysis over the long
OCR for page 127
IMPLICATIONS OF OUR CONCLUSIONS
127
term. Nevertheless, some members of the committee believe that such a
limitation might provide adclec! assurance of safety in the near term.
Whether to provide such assurance by using a limitation on early releases
is a policy decision that EPA might wish to consider.
ADMINISTRATIVE CONSEQUENCES FOR EPA, USNRC, AND
DOE
Our recommenciations, if adopted, will imply the development of
regulatory and analytical approaches for Yucca Mountain that are different
from those employed in the past and from some approaches currently user]
elsewhere by EPA. We further note that several parameters important in
risk-based assessment require determination by rulemaking. Both the
change in approach and the time required to develop a thorough and
consistent regulatory proposal anti to provide for full public participation
in the rulemaking process, particularly in devising the biosphere models,
identifying the critical groups, and clefining intrusion scenarios, will
require considerable effort by EPA.
Incleed, this process probably will take more than the year, that is
currently provided for in the statute, for EPA to complete development of
a Yucca Mountain standard in a technically competent way. Although it
is important to obtain a timely result, we also believe it is important that
EPA take sufficient time to produce a thorough, competent, and consistent
standard. A similar duty is imposed on USNRC to assure that its
regulation implementing the EPA standard] is not compromiser! by time
constraints.
Although a new standard ant] its implementing regulations might
not be available within the two years envisioned in the Energy Policy Act
of 1992, that floes not mean that DOE's Yucca Mountain Site
Characterization Project cannot proceed usefully in the interim. The site-
characterization ant} iterative-performance assessment efforts can continue
in the absence of a promulgated standar~i. DOE has, in fact, been making
progress consistent with our recommendations with its series of
total-system performance assessments (TSPAs) anti we hope that progress
will continue. For example, the TSPA-1993 reports from the Sandia
National Laboratory (Wilson et al., 1994) and Intera, Inc. (Anctrews et al.,
1994) examined the performance measure of radiation close to a maximally
OCR for page 128
128
YUCCA MO~TAINSTANDA=S
exposed individual, in addition to consideration of normalizeci cumulative
releases as dei inert by EPA in 40 CFR 191.13. The TSPA has also reporter}
on repository performance for a period of one million years as well as for
the ~ 0,000-year period. Both the dose calculation anti extension of the
time perioc} move in the direction of our recommendations. On the other
hanci, progress for some aspects of DOE's program might depencl on the
nature of EPA's promulgates! standard. For example, the potential risks to
a critical group living near Yucca Mountain cannot reaclily be assesses!
until the rules for identifying the critical group are defined.
Representative terms from entire chapter:
human intrusion
