Effects Due to Fission Gas During Unprotected Overpower Transients in a Liquid-Metal Fast Breeder Reactor

A behavior model for fission gas in irradiated liquid-metal fast breeder reactor fuels is applied in a computer code. The subroutine LANGZEIT calculates the “long-time” kinetics processes during steady-state operation. The results are used as initial conditions for the subroutine KURZZEIT, which permits the description of the bubble growth during rapid overpower transients. This model has been applied to the SNR-300-Mark I core. The calculations indicate a prompt precipitation of fission gas during the reactivity excursions, which results in a dampening effect on the reactivity ramps.