Observations of Irradiated Fuel Behavior Under Simulated Accident Heating Conditions

Modifications to the direct electrical heating apparatus have enabled it to be used successfully to heat irradiated mixed-oxide fuel pellets to melting in an α-γ hot cell. For this purpose, a fuel extrusion device was constructed to remove irradiated fuel from its cladding. Proof-testing was successfully conducted using two UO₂-20 wt% PuO₂ pellets irradiated in the Experimental Breeder Reactor II to 3.25 at.% burnup at ∼ 3.05 kW/m (∼10 kW/ft). The sequence of events leading to fuel failure—namely, melting, swelling, and fragmentation—agree with observations from inreactor accident simulations.