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

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The total seabed area required would be 560 km 2 /yr (215 mi 2 /yr) for HLW and 920
km 2 /yr (354 mi 2 /yr) for spent fuel assemblies, based on an arbitrary spacing of 300 m
(984 ft) between canisters and a waste disposal system of 5,000 MTHM/yr.
Retrievability/Recoverability. Retrievability has not been designed into the system
concept (though during the experimental period all emplaced radioactive material would be de-
signed for retrievability) (DOE 1979c). Postemplacement waste-canister recovery from any of
the four emplacement options (see Figure 6.1.12) would be possible with existing ocean engi-
neering technology, but estimated costs are high.
Monitoring. After the wastes were emplaced, a monitoring ship would use instrumentation
on the ship, on the ocean bottom, and on the canisters to determine information about the
buried canister: e.g., its attitude and its temperature.
This monitoring would continue for as long as necessary to verify the performance of the sub-
seabed isolation system.
6.1.4.3 Status of Technical Development and R&D Needs
Present State of Development
The status of concept design, equipment, and facilities for different facets of a sub-
seabed disposal operation is described below.
Emplacement Medium. Properties of the red clay sediment of the ocean's abyssal hills
have been studied extensively under the Subseabed Disposal Program (SDP) (Talbert 1977,
Sandia 1977, Sandia 1980). The considerable data collected indicate that the sediment is a
very promising emplacement medium. The SDP has collected data on nuclide sorption and migra-
tion, effects of heat and temperature, ecosystems, and other aspects of the subseabed envi-
ronment in these sediment areas. The program was started in 1973, and studies of the
emplacement medium and. of concept feasibility are planned to be completed in 1986. After
that, the program would deal with other engineering problems, such as the handling of waste
during sea transportation and emplacement (Sandia 1980).
Emplacement Methods. The SDP has not yet defined the methods of waste emplacement in the
subseabed. The technical problems associated with this task would be addressed after the
studies on sediment properties are completed. In other words, the required depth of emplace-
ment, spacing of canisters, method for assuming hole closure, etc., would have to be known
before emplacement methods could be developed.
Four possible methods of emplacement are being considered: (1) free-fall penetrometer,
(2) winch-controlled penetrometer descent to a detennined depth and final propulsion (the re-
ference concept), (3) trenching, and (4) drilling. The operations are described in Reference
4. The first two methods that use penetrometers present fewer technical challenges since the
penetrometer is a widely used tool in marine, land, space, and arctic operations.