Release of fission cesium from irradiated UO6 powder

The amount of Cs released from irradiated UO2 powder in a range of temperature between 820° and 980°C was measured by sweeping with H2-1%HCl mixture. This mixed gas proved effectively to carry off the released Cs from the UO2 surface, as verified by observation of the characteristics of CsCl adsorption on UO2 and desorption therefrom. In addition, the amount of Cs released by knock-out during irradiation was measured. The chemical form of Cs adsorbed on the UO2 surface after release by knock-out, is considered to be elemental. The activation energy for Cs migration in UO2 is discussed, with account taken of the difference in behavior between single-crystals and poly-crystals.