Management of Commercially Generated Radioactive Waste - U.S. ...

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deep hole, island mined repository, subseabed, ice sheet, and space disposal concepts.
Uncertainties, however, are associated with the very'deep hole concept depending on depth
of emplacement and associated conditions of temperature and pressure to which the package
is exposed.
Because the rock melt concept does not provide a system of engineered barriers, and
because of the elevated temperatures, it appears likely that heated water vapor or liquid
could contact, leach and transport waste from the as yet unsolidified rock-waste matrix of
the rock melt concept during the initial 1000-year post-operational period.
Because the well injection concept does not provide a series of engineered barriers,
one thousand year containment could not be assured with either of the well injection pro-
posals. Diffusion of dilute acid injected waste into fractures and discontinuities of for-
mations adjacent to the host formation could be expected.
In conclusion, it appears probable that containment of emplaced waste, as defined,
could be maintained through the period dominated by fission product decay for all concepts
except rock melt and well injection. The containment concept does not apply to
transmutation.
6.2.3.3 Waste Should Be Isolated from the Accessible Environment for a Minimum of
10,000 Years
Ten thousand years has been proposed as a time period during which the radiotoxicity
of properly treated waste would decay to levels comparable with the natural uranium ore
bodies from which the materials were originally derived (Voss 1980). "Isolated" is inter-
preted as "segregation of the waste from the accessible environment within acceptable
limits" (Proposed 10 CFR Part 60) where the accessible environment includes the atmosphere,
the land surface, surface waters, oceans and presently used aquifers (Proposed, 10 CFR
Part 60, 40 CFR Part 146). "Acceptable limits" has been generally interpreted to include
releases resulting in dose rates within the normal variation of naturally occurring radia-
tion dose rates (DOE 1980).
Analysis to date of the mined repository concept suggests no reason to believe that
acceptable isolation could not be maintained by the geologic environment for a 10,000-year
period, with the possible exception of very low probability catastrophic accident situa-
tions. The probability of these occurring is estimated to be small. Similarly, it appears
quite possible that the very deep hole concept could maintain acceptable waste isolation
over the required period if such depths are successfully isolated from ground water.
Maintenance of waste package containment cannot be assumed for the 10,000-year period
for the mined repository, very deep hole, island mined repository, subseabed disposal and
ice sheet disposal concepts. Package failure would expose the waste form to a saturated
hydrologic environment for the subseabed and island disposal concepts and acceptable isola-
tion would be dependent upon stability of the hydrologic environment and the sorptive prop-
erties of the host material and surrounding geologic environment. Available evidence
indicates that acceptable isolation could be maintained using the subseabed concept. Satis-