Transport Theory Evaluation of the Release of Short-Lived Fission Products from Fuel Grains

Abstract

The first barrier to the release of fission products from reactor fuel elements is the U02 matrix. An assessment of the fraction of a particular fission product being released from the fuel grains is necessary to assess subsequent release mechanisms and pathways. Although the movement of fission products within the fuel lattice is assumed to be by a concentration gradient driven diffusion process, the modelling of this process by diffusion theory requires some approximations to be made when applied to short-lived fission products. This paper applies the more rigorous conditions of transport theory to evaluate the probability of fission product release from a fuel grain as a function of the fission product mean free path and the size of the fuel grain.