Calculation method for diffusional gas release with grain boundary resolution

The problem of diffusional release of stable fission gas atoms in nuclear fuel including grain boundary resolution is described. A numerical method for solving the set of resulting non-linear differential equations in time varying conditions is presented. The method is an extension to the locally accurate method (LOAM) published earlier. The extended LOAM accounts for the kinetic evolution of the gas content in the grain boundary. The fission gas release and the time to reach the saturation concentration at the grain boundaries by the extended method are compared to analytical solutions under steady state conditions. The results of this comparison show the excellent capability of the extended LOAM. The performance of the extended method in time varying conditions is tested by calculating the fission gas release for hundreds of complicated temperature-power histories. The extended LOAM is found to be able to calculate the fission gas release with +/- 1% accuracy in time varying conditions by using only three equal volume nodes. The computing time of the extended LOAM is less than twice the time needed by the LOAM without grain boundary resolution. (C) 2000 Elsevier Science S.A. All rights reserved.