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

6.105
would permit different isolation practices to be adopted for the high-heat-generating, rela-
tively short-lived isotopes (half-lives about 30 years) and the remainder of the waste con-
taining the much longer lived, lower heat generating isotopes.
The liquid waste would be diluted with water or chemically neutralized and pumped from
the reprocessing facility to the injection facility or to interim storage in holding tanks.
Site. Deep well injection would require natural, intergranular fracture porosity or
solution porosity formations, overlain by impermeable cap rock, such as shale. A minimum ac-
ceptable depth for disposal would be about 1,000 m (3,300 ft) (EPA 1973). The injection site
must not conflict with either present or future resource development.
Synclinal basins would be particularly favorable sites for deep well liquid injection
since they consist of relatively thick sequences of sedimentary rocks frequently containing
saline ground water (Warner 1968). Ground-water movement within the injection fornation
would have to be limited, however, particularly vertical movement.
The lithological and geochemical properties of the isolation formation would have to be
stable so that the behavior of the waste could be accurately predicted. In general, sand-
stone would be the most suitable rock type because it combines an acceptable porosity and
permeability with chemically inert characteristics relative to the acid waste form.
The overall site area has not been determined yet, but would be greater than the 1270 ha
(3140 acres) initial injection area and would depend on the maximum horizontal dimension of
the injection area, the size of control zone required around the repository, and the total
amount and type of waste to be injected.
Drilling System. The drilling rigs would be similar to those used in the gas and petro-
leum industries and would be portable for movement from one location to another on the site.
Each complete rig would require a clear, relatively flat area, approximately 120 m x 120 m
(400 ft x 400 ft) at each hole location (see Section 6.1.1).
Repository Facilities. The processing plant would be located on site as an integral part
of the overall injection system. The basic repository facilities would be similar to those
required for the very deep hole concept, as discussed in Section 6.1.1 (Bechtel 1979a).
Interim storage tanks similar to those described for the rock melt concept (Section
6.1.2) would be provided for surge capacity. The stainless steel tanks would have a combined
capacity of about 106 liters (2.8 x 105 gal) which equals 3 months production. The tanks
would be similar in design to those at the AGNS plant in Barnwell, South Carolina, which are
contained in underground concrete vaults and provided with internal cooling coils and heat
exchangers to prevent the waste from boiling.
An underground pipeway system would connect the reprocessing facility to the storage
tanks and the injection facility. The pipe would be double cased and protected by a concrete
shielding tunnel with leak detectors provided in the annulus of the pipe. The pipeway design
would provide containment, monitoring, decontamination, maintenance, and decommissioning