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

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6.1.4.2 System and Facility Description<br />

System Options<br />

6.63<br />

The reference concept for the initial subseabed disposal <strong>of</strong> nuclear waste has been de-<br />

veloped from a number <strong>of</strong> options available at each step from the reactor to disposal in the<br />

subseabed repository.<br />

Various options to be considered for the subseabed concept are summarized in Figure<br />

6.1.12. The bases for selection <strong>of</strong> options for the reference concept are detailed in sources<br />

cited in Appendix M.<br />

<strong>Waste</strong>-Type Compatibility<br />

It is assumed for the reference case that subseabed disposal is limited to disposing <strong>of</strong><br />

spent fuel, HLW and cladding hulls. Other wastes are assumed to be disposed <strong>of</strong> in a mined<br />

geologic repository. However, it should be noted that these wastes may also be appropriate<br />

for subseabed disposal if there are sufficient economic incentives.<br />

<strong>Waste</strong>-System Description<br />

The reference concept design was selected as a feasible approach based on available in-<br />

formation and data and is not supported by a detailed system engineering or cost analysis.<br />

The waste-management system, including the fuel cycle and process flow, for the reference<br />

concept is shown in Figure 6.1.13.<br />

Subseabed disposal has as its foundation a set <strong>of</strong> multiple barriers, both natural and<br />

man-made, that would be employed to ensure the safe isolation <strong>of</strong> nuclear waste. These bar-<br />

riers are (Bechtel 1979a):<br />

* The waste form<br />

* The waste canister<br />

* The emplacement medium (i.e., sediment)<br />

* The benthic boundary layer<br />

* The water column.<br />

The water column is a barrier primarily to intrusion by man, although it would provide dilu-<br />

tion and dispersion for radioactive species.<br />

The waste form (leach-resistant solid) and the metallic waste canister or overpack would<br />

be man-made barriers. It is assumed that they could be engineered as a multibarrier system<br />

to contain the waste for a period during which the heat-generation rate due to fission pro-<br />

duct decay would decrease to low levels.<br />

The emplacement medium (clay sediment) shows evidence that it could provide long-term<br />

containment <strong>of</strong> the nuclides through its sorptive qualities, ion-exchange characteristics, and<br />

very low permeability.

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