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TREAT Test E8 Simulating a Liquid-Metal Fast Breeder Reactor $3/s Overpower Accident with Irradiated Fast Test Reactor Type Fuel

Richard Simms, Robert K. LO, William F. Murphy, Alan B. Rothman, George S. Stanford

Nuclear Technology

Volume 50 / Number 3 / October 1980 / Pages 225-241


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In a transient overpower (TOP) accident, the fuel element failure threshold is a function of the rate of reactivity increase and the fuel microstructure. Test E8 simulated a hypothetical $3/s TOP accident in a liquid-metal fast breeder reactor using seven (Pu,U)O2 fuel elements of the fast test reactor (FTR) type. The test elements were pre-irradiated at 30 kW/m in the Experimental Breeder Reactor II to 5 at.% burnup, leading to a low-to-moderate power micro structure typical of FTR fuel Data from test vehicle sensors, hodoscope, and post-test examinations were used to deduce the sequence of events occurring within the test zone. The initial fuel failure event occurred abruptly at ∼29 times the nominal power level at an estimated average enthalpy of ∼925 kJ/kg relative to 20°C, with 50% of the fuel cross-sectional area above the solidus at the suspected failure site. After the initial failure, ∼2% of the fuel was ejected above the top of the active fuel region. Sodium voiding occurred rapidly. An upper blockage was formed that apparently prevented further fuel dispersal. Inherent test vehicle limitations, loss of flow tube geometry, and nontypical power generation after fuel element failure may have caused a departure from the fuel motion predicted for the FTR conditions. No violent fuel-coolant interactions were observed in the test.

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