Fission product retention of fuelled beryllium oxide spheres and urania-thoria fuel particles in post-irradiation annealing experiments.

Abstract

The post-activation diffusion technique has been used to measure the release of Xe-133 from beryllium oxide based, spherical fuel elements and the urania-thoria fuel particles from which they were prepared. Release rate parameters (apparent diffusion coefficients, D') for bare fuel particles were of the order 10-8 sec-1 to 10-10 sec-1 at 1400ºC, whereas most spheres tested gave parameters of 10-16 sec-1 or less, indicating that the beryllia matrix and cladding were having a marked effect in retaining fission gases. Mid-anneal changes in release rates from bare fuel particles were observed at 1200ºC and 1400ºC, This behaviour is tentatively attributed to slight pore growth and the release of trapped gas from pores which open to the surface during annealing.