Evaluation of iodine pressure in oxide fuel pins under irradiation

This review summarizes the published theoretical and experimental studies of CsI radiolysis in an operating fuel pin. The calculation method, which has been developed based on gas kinetic theory, is effective for the evaluation of the radiation effect on iodine pressure. The iodine partial pressures, which were calculated by the above method, are high enough to cause FCCI in FBR fuel pins and SCC in LWR fuel rods. The literature data of experiments exhibit that the iodine is liberated through r-radiolysis of solid CsI, and the CsI vapor irradiated by electron beam also produced high iodine pressures. It has been also confirmed that the radiation effect in gas phase is still significant even in the case of existence of Cs pressure, which causes decrease of the iodine pressure by recombination. This review concludes that the radiation effect is important for understanding the chemical behavior of iodine in operating fuel pins.