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

5.35
Contaminated assemblies are first cleaned, then sealed in a canister; damaged assemblies
are returned to their casks, transferred to the overpack cell, and encased in canisters and
appropriately sized overpack canisters. The canisters are then transported to the
canistered waste shaft and lowered into the repository. All spent fuel handling is done
remotely.
The spent fuel canisters are received at subsurface transfer stations where shielded
transporters remotely remove the canisters from the transfer stations for delivery to an
emplacement room.
In addition to the thermal restrictions discussed in Section 5.3.1.1, room capacity is
limited by the minimum allowable hole spacing of 1.8 m (6 ft) center to center. This is a
mechanical limit that prevents weakening of the floor by holes spaced too closely together.
The conceptual repositories in salt and shale emplace both PWR and BWR canisters in holes,
while repositories in granite and basalt emplace PWR canisters in holes and BWR canisters
in trenches. Trenches allow the relatively low heat-generating BWR canisters to be spaced
more closely together (trenches are not economical for the higher heat-generating PWR can-
isters). The trenches run the length of emplacement rooms and contain steel racks to main-
tain the canisters in an upright position. They are backfilled after emplacement sleeves
are installed.
Table 5.3.3 lists the contents of the conceptual spent fuel repositories in salt,
granite, shale, and basalt formations at the end of emplacement.
TABLE 5.3.3. Contents of the Conceptual Spent Fuel Repositories When Full
PWR BWR Total
Canisters MTHM Canisters MTHM MTHM
Salt 68,200 31,500 104,000 19,600 51,100
Granite 162,700 75,100 246,300 46,500 121,600
Shale 86,300 39,800 131,000 24,700 64,500
Basalt 162,700 75,100 246,300 46,500 121,600
Two separate repository design concepts were also developed for the limited quantities
of spent fuel, 10,000 MTHM and 48,000 MTHM, produced in the two cases (Cases 1 and 2 in
Section 3.2.2) where the nuclear industry is assumed to be severely constrained. Surface
facilities are reduced in size and capacity for these reduced requirements and the mined
area is reduced in proportion to the quantity of spent fuel sent to disposal.
5.3.1.5 Retrievability
Actions necessary to remove emplaced wastes from a geologic repository depend on the
period of repository operations during which removal takes place. Initially, wastes are
emplaced in holes lined with steel sleeves and sealed with removable concrete plugs. The
sleeves and plugs ensure the canisters remain accessible and minimize corrosion or other
damage. During this period the wastes are considered readily retrievable in that they are
removable from the repository at about the same rate and with about the same effort as for