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

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5.3 DESCRIPTION OF THE CONCEPTUAL GEOLOGIC REPOSITORY FACILITIES
In this section, descriptions are given of a conceptual repository for spent fuel in
the once-through cycle and a repository for wastes from the reprocessing cycle. The concep-
tual repositories are described independent of geologic media with specific design and oper-
ational features that may be affected by geology detailed separately. Geologic media
considered representative of formations available for location of a repository and that are
described in this Statement are bedded salt, granite, shale, and basalt (other media may
also be acceptable). The concept of siting repository facilities on a regional basis is
also described in this section.
5.3.1 Once-Through Fuel Cycle Repository
Conceptually, a repository operating in the reference once-through fuel cycle is
required to receive PWR and BWR spent fuel elements. The characteristics of these wastes
are described in Section 4.2.
5.3.1.1 Design Bases
Waste emplacement at the conceptual repository is controlled by thermal criteria. The
thermal criteria used here specify both areal thermal loadings, which control canister spac-
ing, and canister thermal loadings, which limit the heat output of individual waste pack-
ages. The criteria were developed from an analysis of the thermal stresses that accumulate
in the geologic formation and in the waste canisters. The criteria are designed to limit
these stresses to values that will not compromise the integrity of the formation, the mine
area or the waste canisters. Development of these criteria is discussed in Appendix K.
The design areal thermal loadings for the conceptual repositories for this Statement
were limited to two-thirds of the calculated allowable thermal loadings. This was done to
ensure a conservative estimate of capacity. These design basis thermal limits for spent
fuel are shown in Table 5.3.1.
The criteria for granite and basalt, 320 kilowatts/hectare,(a) indicate that 2.6 times
more heat-generating waste may be stored in a hectare of granite or basalt than in a hectare
of salt. This means that with equal areas a repository in granite or basalt would contain
approximately 2.6 times more spent fuel than a repository in salt. This ratio is actually
2.4 for the conceptual repositories because of differences in the mining extraction ratios
and room arrangements between the hard rocks and salt. Another parameter, discussed further
in a later subsection, that affects the repository waste capacity is waste age.
We assume here that spent fuel may be sent to a geologic repository after five years
of cooling. However, a large portion of the spent fuel will be considerably older and
cooler. This is because of the large inventory that will accumulate before a repository is
available and because of the time required to dispose of this inventory. For a 1990
(a) One hectare equals approximately 2.47 acres.