Thermal conductivity degradation analyses of LWR MOX fuel by the quasi-two phase material model

Abstract

The temperature measurements of mixed oxide (MOX) and UO 2 fuels during irradiation suggested that the thermal conductivity degradation rate of the MOX fuel with burnup should be slower than that of the UO 2 fuel. In order to explain the difference of the degradation rates, the quasi-two phase material model is proposed to assess the thermal conductivity degradation of the MIMAS MOX fuel, which takes into account the Pu agglomerate distributions in the MOX fuel matrix as fabricated. As a result, the quasi-two phase model calculation shows the gradual increase of the difference with burnup and may expect more than 10% higher thermal conductivity values around 75 GWd/t. While these results are not fully suitable for thermal conductivity degradation models implemented by some industrial fuel manufacturers, they are consistent with the results from the irradiation tests and indicate that the inhomogeneity of Pu content in the MOX fuel can be one of the major reasons for the moderation of the thermal conductivity degradation of the MOX fuel.

Recent activities in the field of nuclear materials and nuclear fuels

“…To explain the difference in the thermal conductivity degradation between mixed oxide (MOX) fuel and UO 2 fuel after burnup [16], the quasi-two phase material model was proposed [17]. The numerical result showed the gradual increase of the difference with burnup which was consistent with the results from the irradiation tests.…”