Loss-of-Flow Transient Reactor Test Facility Tests L6 and L7 with Irradiated Liquid-Metal Fast Breeder Reactor Type Fuel

In Transient Reactor Test Facility tests L6 and L7, a loss-of-flow accident sequence was simulated using three fuel elements containing (Pu, U)O₂. The test fuel had been previously irradiated at 36 kW/m in a thermal-neutron spectrum in the General Electric Test Reactor to 3 at.% burnup. Fuel dispersal rates at 10 and 20 times nominal power were measured using the 1.2-m fast neutron hodoscope. The measured axial fuel density variations were weighted with typical liquid-metal fast breeder reactor fuel-worth distributions so that the significance of the fuel motion could be assessed. Fuel dispersal rates equivalent to 60¢/s per dollar were observed in test L7. The dispersal rate for test L6 was ∼20¢/s per dollar. The dispersive fuel motion in test L7 could have been augmented by fuel vapor pressures. The experimental fuel-worth changes were also compared with the fuel-worth changes computed by fuel motion models SLUMPY and LEVITATE. Of the two models, LEVITATE provided better agreement with the equivalent fuel-worth changes in test L7.