Abstract
A new fast-reactor core model has been developed which allows simulation of the behavior of a multizone core during accidental transients (loss of coolant or external reactivity insertions) leading from steady-state operation to fuel-rod failure and then to gross core damage. The model for the rod failure and for the relocation of the fuel debris is based on an interpretation of the meltdown experiments performed in the TREAT reactor. In the presented core model, the thermal response of the fuel rods is determined using a two-dimensional heat-transfer code in r-z geometry. In addition to the standard kinetics feedback relations, the reactivity effects of the gradual removal of the rod cladding are included. Taking into account the addition and removal of the heat of fusion allows the amount of fuel that resolidifies in the lower core part to be estimated. The presence of rod spacer arrangements is included as additional barriers for the debris relocation. The thermal response of the subassembly walls is calculated taking into account the contact with the high-temperature fuel as well as radiative heat transfer.
Published Version
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