A simple operational gas release and swelling model. Pt. 2

The model described in this paper is intended for use in fuel behaviour codes and extends work given in an earlier paper to include the behaviour of fission gas on grain boundaries. The model includes: a description of the configuration of porosity on the grain faces and edges, both before and after interlinkage: a rate theory treatment of the flow of vacancies between the grain faces and the various types of porosity; a treatment of the distribution of fission gas between the grain faces and edges; and the interlinkage of both types of pores, leading to the release of gas from the fuel. In addition to reproducing experimentally measured gas release and swelling well, the model allows a quantitative understanding of the observation of interlinked face porosity in large-grained material and the dominance of the growth of edge porosity in small-grained material. (orig.)