Fuel-cladding mechanical interaction in fast breeder fuel pins; observations and analysis

The problems of fuel-cladding mechanical interaction are considered, and a survey is given of the causal processes in oxide fuel pins. Their importance is judged by relevant results from irradiation experiments in thermal and fast test reactors, and by corresponding modelling computations. It is demonstrated that critical cladding strain has to be expected only in case of large, fast rod power increase, primarily from reduced power to full power, and maybe also in case of serious cesium accumulation at the fuel/blanket interface. Steady-state fuel swelling does not make any considerable contribution to cladding strain by thermal creep or plastic flow.