Swelling, densification and creep of (U, Pu) C fuel under irradiation

Abstract In carbide fuel pins for fast breeder reactors, strong mechanical interaction between fuel and cladding is often inevitable, in contrast to oxide fuel pins. The resultant cladding strain depends on swelling, irradiation-induced densification, and irradiation-induced creep of the (U, Pu)C fuel. A survey is given of the present knowledge of these processes. The free swelling rates of carbide and oxide fuel are rather similar, if correlated with the fission rate instead of the burnup. The swelling rate under cladding restraint was estimated from the cladding strain of irradiated carbide fuel pins. It corresponds with the free swelling rate at low fuel temperatures and was found to be (1.4 ± 0.3) vol% per % burnup. Estimations and measurements of irradiation-induced densification of carbide fuel of high porosity allow the conclusion, that the densification proceeds rather fast up to a pellet density of about 90% TD. The irradiation-induced creep rate of (U, Pu)C of high porosity was measured in a special experiment.