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

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4.19<br />

Another variation considered in ONWI-39 (Section 10.6) involves disassembly prior to<br />

packaging so that the canisters contain spent fuel rods only, instead <strong>of</strong> complete assem-<br />

blies. In this option the end fittings are removed from the fuel elements, the elements are<br />

disassembled, and the fuel rods are bundled together and sealed into canisters.<br />

4.3.1.2 Chop Fuel Assembly, Voloxidize Fuel, and Encapsulate<br />

A process for chopping the fuel assemblies, removing volatile components through<br />

voloxidation, and encapsulating the spent fuel is described in 0NWI-39 (Appendix C). The<br />

end fittings <strong>of</strong> the spent fuel are first cut <strong>of</strong>f and encapsulated. The remaining portions<br />

<strong>of</strong> the fuel assemblies are then chopped and voloxidized, and encapsulated in canisters. A<br />

flow diagram for the process is shown in Figure 4.3.2.<br />

The voloxidation process, which is in the development stage (Groenier 1977), promotes<br />

the release <strong>of</strong> gaseous fission products from the fuel by oxidizing UO 2 to U 30 8 at 4000to<br />

500 0 C in air. This oxidation results in disintegration <strong>of</strong> the fuel, which provides an<br />

easier escape path for the gaseous fission products. Removal <strong>of</strong> the gaseous fission pro-<br />

ducts from the <strong>of</strong>f-gas stream is addressed in Section 4.3.4.<br />

The processed spent fuel is encapsulated in cylindrical steel canisters that are<br />

helium-filled, sealed by welding, and leak tested. Any leaking canisters are overpacked in<br />

a second larger canister. The primary canister size is 0.30 x 3.0 m (12 x 120 in.).<br />

Sixty-one canisters per GWe-yr are estimated to be required to contain the chopped and<br />

voloxidized fuel.<br />

The end fittings sheared from the fuel-bearing portions <strong>of</strong> spent fuel are packaged<br />

without further processing in 0.5 x 3.0 m cylindrical canisters. One canister holds the<br />

ends <strong>of</strong> either three PWR or six BWR assemblies; for the mixture <strong>of</strong> fuel used in this generic<br />

study, 11.6 canisters are filled per GWe-yr.<br />

VOLATILE F.P.<br />

RECOVERY<br />

OFF GASES<br />

PACKAGED<br />

VOLATILE VOLTIL<br />

F.P.<br />

HARDWARE REMOVAL<br />

SPENT FUEL WATER BASIN ASSEMBLY AND VOLOXDATION ENCAPSULATION<br />

ASSEMBLIES STORAGE DRYING FUEL CHOPPING<br />

TRU WASTES<br />

CANISTERED MISCELLANEOUS TRU CANISTERED<br />

HARDWARE WASTETREATMENT POWDERED<br />

FUEL<br />

PACKAGED<br />

MISCELLANEOUS<br />

TRU WASTES<br />

FIGURE 4.3.2. Flow Diagram for Encapsulation <strong>of</strong> Chopped and Voloxidized Spent Fuel

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