Dynamics of the gaseous fission products transport in spherical fuel composites with a combined protective layer

In terms of the defect-trap-diffusion mechanism the problem of gaseous fission product transport in a spherical fuel element, consisting of the fuel kernel, buffer layer and protective layer contaminated with fissible material, is solved. During the whole diffusion process of the gas, its decay and presence of a fission product concentration gradient in the kernel and the protective layer are taken into account. A possibility for the radioactive gas to be trapped on bubbles caught by defect clusters or dislocations both in the kernel and in the protective layer is also taken into consideration. The analytical time dependence of the relative integral gas leakage from the fuel element is described. The transport mechanism described can be experimentally proved by studying the stationary fission product radial distribution or by measuring isothermal leakage of the gases through the outer layer of a fuel element