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

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areas occupy 650 to 730 ha, with the remaining 80 to 160 ha occupied by shafts, general ser-
vice areas, main corridors and unmined areas within the repository.
5.3.1.3 Construction
In the process of excavating repository subsurface areas, all mined rock is brought to
the surface and stored onsite. The storage pile is constructed using standard earth-moving
equipment. Standard dust control procedures (water sprays, etc.) are employed during con-
struction at all repositories; salt and shale storage piles are also provided with water
run-off control. When retrievable emplacement operations are complete, a portion of the
rock will be returned to the mine as backfill. Present plans call for rock not used for
backfill to remain piled on the surface. While in the case of a salt repository, excess
salt may be disposed of by placing it in an abandoned salt mine or by selling the salt for
commercial use, these options depend heavily upon the nature of specific sites. (If mined
salt were to be used in commerce, the salt could be moved off site before any radioactive
waste arrives onsite. Thus there would be no potential for radioactive contamination of
the salt.) Quantities of rock removed and stored are described in Table 5.3.2.
TABLE 5.3.2. Mining and Rock Handling Requirements at the Reference Spent Fuel Repository
Mined Room Total Permanent Onsite
Quantity Backfill Backfill Surface Storage
(MT x 106) (MT x 10 6 ) (MT x 106) (MT x 10 6 ) m 3 x 106
Salt 30 14 17 13 6.1
Granite 77 29 38 39 15
Shale 35 15 21 14 5.5
Basalt 90 32 46 44 15
Although a repository in any of the four rock media occupies an overall area of 800 ha,
larger amounts of rock are removed in constructing repositories in granite and basalt.
This is due in part to larger mining extraction ratios (ratio of mined to intact volume).
The increased extraction ratios are possible because of greater rock strength that allows
the pillar widths to be decreased, resulting in more emplacement rooms and consequently more
waste storage per given repository area.
5.3.1.4 Operations
Spent fuel packaging facilities are here assumed to be incorporated in the repository
surface facilities but could be a separate facility nearby. Spent fuel elements arrive at
the repository's surface facilities by rail or truck in shipping casks designed for fuel
transport. These casks are lifted by crane from the rail cars or trailers to shielded
transfer cells for remote removal of the spent fuel assemblies. At this point, the assem-
blies are examined for external contamination, signs of damage, and compatibility with
other acceptance criteria. Acceptable assemblies are encased in helium-filled canisters.
The helium atmosphere in the canister provides a means for canister leak testing.