Dynamics of fuel vapor pressure buildup in voided lmfbr cores during the transient heating and its effect on the energy release in a core disruptive accident

The core disruptive accident (CDA) analysis of liquid-metal fast breeder reactors is often performed using the saturated vapor pressure equation of state for the fuel. However, during the transient heating of the fuel in a voided core in the disassembly phase of CDAs, the fuel vapor pressure buildup may lag behind the temperature rise and thus may lead to the delayed disassembly of the core and the consequent large energy release. The formulations for such transient vapor pressure buildup and the results on the dynamics of fuel vapor pressure during the transient heating and its influence on the thermal energy release in a CDA are presented. The energy release calculations have been performed by incorporating the present formalism in the disassembly analysis code VENUS-II. In view of the uncertainties in some of the physical parameters, a parametric study was conducted to evaluate the effects of such uncertainties in their values on the results. These results are discussed in detail