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

6.69
Waste Form. The waste form and the canister design required for subseabed disposal of
spent fuel have not been determined. Because of the high hydrostatic pressures at the ocean
bottom, one important characteristic of the waste package would be a filler material with low
compressibility. Generally, metallic fillers would satisfy this requirement, but other solid
materials could be more acceptable because of cost advantages, resource conservation, and
easier process technology.
The waste form required for storage of HLW in a subseabed repository has not been deter-
mined. It is believed that borosilicate glass might be adequate, especially if the tempera-
ture of the canister-sediment interface were maintained below 200 C (392 F). This would
require adjusting the age of the waste and/or the diameter of the canister to provide rapid
heat flow away from the canister. Other waste forms are also being considered.
Waste Containment. Due to the expected effects of high heat and radiation on the pro-
perties of the subseabed sediments, waste containment would have to be maintained for a few
hundred years to delay the release of nuclides. Experimental data on the rate of corrosion
of metallic materials in hot brine and seawater, collected primarily to improve the material
performance in desalinization plants and in geothermal applications, would add to the confi-
dence that this capability can be provided.
The SDP has also included laboratory experiments with metallic materials subjected to a
seawater environment of 200 C (392 F) and 1,000 psi (6.9 x 106 Pa). Plates of Ticode 12
showed the lowest rate of corrosion, as determined by a weight-loss technique (Talbert 1979).
Facilities. The seaport storage facilities and the facilities that would have to be
built aboard ship have not been developed. However, the technology for building them is
available since they would resemble existing facilities, such as spent fuel storage pools and
ordinary port facilities. The seaport location, size, and capabilities are not yet defined
by the SDP.
Technical Issues
The engineering aspects for subseabed disposal have not been established. The transpor-
tation logistics, regulations, and the appropriate transportation "package" have not been
developed. The precise size and type of facilities that would be built are not known, and
the time and motion studies to select the optimum ship size have not been made. In addition,
a large area of uncertainty revolves around the methodology that would be used to emplace the
waste. Techniques to ensure that waste canisters were placed deep enough into the sediment
have not been demonstrated.
If demonstrated, a major attribute of subseabed disposal would be the ability of the
sediments to hold radionuclides until they had decayed to innocuous levels. To determine
whether these sediments could actually do this, the following technical issues would need
resolution.