To the release of fission products from spherical fuel elements

The release from a sphere doped with fission products into a flowing gas medium is dealt with theoretically, taking into account Fick's diffusion and introducing an α-parameter, which describes the characteristic of the release kinetics at the surface of the sphere. The theoretical statements are compared with experiments, which refer to the system: caesium-matrix-graphite-helium. For the experimental investigations a testing facility especially adjusted to the subject was built. This testing facility is described. Due to our results performed in the temperature range between 9000C and 11000C we can conclude that the desorption of fission products can be described with the proposed model. In this connection the experimentally determined data of the diffusion constant (D), the α-parameter (α), the evaporation coefficient (αsub(v)) and the Henry-constant (K) are indicated for the considered system. (orig.)