An investigation of the Pu migration phenomena during irradiation in fast reactor

The phenomenon of radial plutonium migration in fast reactor MOX fuel is one of the important performance issues. In this study, mechanisms of this phenomenon were modeled for vapor transport concurrently occurring with thermal diffusion. Further improvement was modeled by accounting for the effects of the oxygen to metal ratio. Additionally, to evaluate more precisely the fuel temperature history during irradiation, the thermal conductivity in the fuel-cladding gap was evaluated by including the thermal effects of fission-product (FP) compounds. The calculated plutonium distribution in MOX fuel irradiation tests, with the linear heat rate (LHR) gradually decreasing with irradiation, agreed well with the measured data. Improvement by considering the effect of the oxygen to metal ratio was considered to be effective and indispensable for the evaluation of plutonium migration in the MOX fuel.