The determination of diffusion coefficients of Cs and Ag in pyrocarbon and silicon carbide by post irradiation annealing of coated particle fuels

Diffusion co-efficients for Cs in methane and in propylene derived coatings of low enriched UO2 coated particle fuel, have been determined at 15000C. The results obtained using irradiated coated fuel particles and an annealing and a grinding technique are as follows:- methane derived pyrocarbon: (1) (by annealing) D = 2 x 10-12 cm2 sec-1; (2) (by grinding) D = 1 x 10-12 cm2 sec-1: propylene derived pyrocarbon: (1) (by annealing) D = 5 x 10-12 cm2 sec-1; (2) (by grinding) D = 3 x 10-12 cm2 sec-1. During the course of this work it was found that pyrocarbon afforded no delay at 15000C to Ag release from the coated fuel particle, but there was some delay when silicon carbide was incorporated in the coating layers. (author)