Modes of Failure of Fast Reactor Fuel Pins Irradiated Under Loss-of-Coolant-Flow Conditions

Capsule irradiations have been performed on single fast reactor fuel pins in a sodium environment under simulated loss-of-coolant-flow conditions. The main objectives were to determine the thresholds, modes, and mechanisms of fuel pin failures. The parameters were canning temperature and internal pin pressure. The loss-of-coolant-flow condition was simulated by adjusting midwall canning temperatures of ∼850 and ∼1000°C. The results indicated that creep rupture is the predominant failure mechanism at canning temperatures of 1000°C and gas pressures of above 40 bars. The failure mechanism of fuel pins tested at ∼850°C and gas pressures lower than 60 bars is probably cladding strain due to differential expansion of fuel and canning.