Proposal of simplified model of radionuclide release from fuel under severe accident conditions considering pressure effect

Hidaka, Akihide  ; Kudo, Tamotsu ; Ishigami, Tsutomu; Ishikawa, Jun ; Fuketa, Toyoshi

An experimental program VEGA is being performed at JAERI to understand mechanisms of radionuclides release from fuel during severe accidents and to improve source term predictability. The VEGA tests showed that the Cs release rate at 1.0MPa decreased by about 30% compared with that at 0.1MPa. To explain this pressure effect, a numerical release model on 2-stage diffusion that considers the lattice diffusion in grains followed by gaseous diffusion in open pores was newly developed and a simplified model 1/ CORSOR-M was derived from the numerical model. The effect of pressure on source term was also estimated for a transient sequence at BWR with JAERI's THALES-2 code in which the simplified model was incorporated. Since the adequacy and applicability of 1/ CORSOR-M model were confirmed for the pressures up to 16 MPa through comparison with the VEGA tests and mechanistic models, it is proposed that the model be used for source term analyses.