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

6.33
Drilling/Mining System. The reference concept requires two access shafts for each cav-
ity, each 2 m (6.6 ft) in diameter and approximately 2,000 m (6,560 ft) deep. They would be
drilled using the blind hole boring method (Cohen et al. 1972). A rotating head with cutters
would be turned by electric motors down hole. The entire boring machine would be held fixed
in the hole by a hydraulic gripping arrangement. The shafts would be lined with carbon steel
casings after drilling (Bechtel 1979a). This method would require men in the shaft to oper-
ate the boring machine (DOE 1979).
The cavity would be excavated by conventional mining techniques, although the equipnent
used would be limited by the access shaft diameter (Bechtel 1979a). Any blasting would be
controlled to minimize fracturing of the surrounding rock. The spoil from both drilling and
excavating would be hoisted up the access shafts by cable lift for surface disposal (Bechtel
1979a).
Repository Facilities. If the reprocessing plant were located on site, the reprocessing
facilities would include a processing/packaging facility. If processing and packaging of
wastes for off-site disposal were performed off site, the repository facilities would include
a receiving facility similar to that described for the very deep hole concept (Section
6.1.1.1). The following description assumes that the reprocessing facility would be on site.
Four identical stainless steel tanks would be provided for storing HLLW. These tanks
would have a combined capacity of about 106 liters (2.8 x 10 5 gal), which equals 3
months' production. The tanks, with the same design as those at the commercial reprocessing
plant in Barnwell, South Carolina, would be contained in underground concrete vaults and
provided with internal cooling coils and heat exchangers to prevent the waste from boiling
(Bechtel 1979a).
An underground pipe system would connect the reprocessing facility to the storage tanks
and the three rock melting cavities. The pipe would be double cased and protected by a con-
crete shielding tunnel. The pipe annulus would contain leak detectors. Heavy concrete and
steel confinement buildings over the pipe and cavity shafts would provide for containment,
shielding, monitoring, decontamination, maintenance, and decommissioning activities, primar-
ily by remote control (Bechtel 1979a).
There would be four main pipes in the operating shaft to the rock melting cavity:
* A double-wall, stainless steel waste-addition pipe
* A single-wall, stainless steel water-cooling pipe
* A single-wall, stainless steel steam-return pipe
* A stainless steel instrumentation pipe through which monitoring devices would be inserted
to measure the temperatures and pressures at various points in the system (Bechtel
1979a).
The confinement buildings over the cavities would also house the equipment and systems
needed for filling the cavity and sealing the shaft. Three important process systems would