Fuel-cladding chemical interaction in uranium-plutonium oxide fast reactor fuel pins

Abstract

A model of cladding attack is developed based on the formation of a cesium chromate on the cladding inner surface and the formation of a cesium-fuel compound at the cooler, outer edge of the fuel. These compounds are assumed to be in equilibrium via the gas-phase transport of cesium and/or cesium hydroxide across the fuel-cladding gap. Using thermochemical and kinetic data for the species involved, the model successfully predicts: 1.(a) the observed temperature dependency of cladding attack in EBR-II, DFR, Rapsodie, and Phenix pins; (b) the observed in-pile threshold temperature for cladding attack;2.(c) the decreased incidence and decreased severity of cladding attack for sphere-pac fuel and for pellet fuel irradiated at low power levels; and3.(d) the large difference in the temperature dependency of cladding attack between out-of-pile versus in-pile experiments. Furthermore, the model identifies the local temperature difference between the fuel outer surface and the cladding inner surface to be the single most important parameter governing cladding attack.