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

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The ocean's benthic boundary layer extends from less than 1 m below the sediment-water
interface to 100 m above that interface. This layer results from the turbidity induced by
natural flow processes and by the biological activity at, or just below, the sediment-water
interface. Particulate matter, which would act to sorb radionuclides escaping the sedi-
ments, is temporarily suspended in this layer and then returns to the sediment surface.
The water column extends from the benthic boundary layer to the surface of the water. It
would provide dilutional mitigation to the release of radionuclides. It would also be a bar-
rier to man's intrusion.
Predisposal Treatment. The predisposal treatment of waste for the subseabed concept
would be identical in many respects to the predisposal treatment of waste for the mined geo-
logic repository concept. Chapter 4 of this document discusses the predisposal systems for
both spent fuel and HLW common to all of the disposal concept alternatives.
Ocean Environment. Analysis of ocean regimes has shown that the most appropriate areas
for subseabed waste containment would be clay-covered abyssal hill regions away from the
edges of subocean tectonic plates underlying large ocean-surface currents known as gyres.
These vast abyssal hill regions are remote from human activities, have few resources known to
man, are relatively biologically unproductive, have weak and variable bottom currents, and
are covered with red clay layers hundreds of meters deep.
These clay sediments are soft and pliable near the sediment-water interface and become
increasingly rigid with depth. Tests have shown that they have high sorption coefficients
(radionuclide retention) and low natural pore-water movement. Surface acoustic profiling
indicates that such sediments are uniformly distributed over large areas (tens of thousands
of square kilometers) of the ocean floor. As shown by core analysis, they have been contin-
uously deposited and stable for millions of years, giving confidence that they would remain
stable long enough for radionuclides to decay to innocuous levels (DOE 1979).
Transportation Features. The overland transportation features of the subseabed disposal
concept would be essentially identical to those of the mined geologic disposal concept. In
addition, subseabed disposal would require transportation of the waste from the mainland to
the subseabed repository. The principal transportation requirements would be for seaport
facilities and seagoing vessels.
a. Seaport Facilities. The subseabed reference concept assumes that seaport facili-
ties would be used only for waste disposal activities and would not share services with other
commercial endeavors (Bechtel 1979a).
The seaport would have facilities for receiving railway casks containing the waste can-
isters and for storing them in a water pool until shipment to the repository site. All re-
quired handling equipment, including that needed to load the canisters into seagoing vessels,
would be available at the port.
The port facility could receive and handle 10,200 spent fuel canisters a year (Bechtel
1979b). For handling high-level reprocessing waste, the total annual throughput would be: