Modelling of fission gas release and gaseous swelling of light water reactor fuels

Abstract

Modelling to investigate the behavior of fission gas atoms of light water reactor fuels is elaborated. The model features the treatment of the grain boundary assumed to consist of two zones for solute gas atoms and intergranular bubbles. This, along with the athermal diffusion of fission gas atoms, enables the retention of gas during the base irradiation and the instantaneous release at temperature rise. The number density of intergranular bubbles varies upon interlinkage to express the saturation of the gaseous swelling after the gas release. Gas release at power reduction is dealt with considering the effective tensile stress acting on the grain boundary. The model is verified with four kinds of data from the irradiated fuels with known temperatures and confirmed to simulate fission gas release in a wide range of burnup, the time-dependency of gas release and porosity change in pellet, the decrease of gas release onset temperature with burnup, and the gas release at the power reduction.