Effect of burn-up on the thermal conductivity of uranium–gadolinium dioxide up to 100 GWd/tHM

The thermal diffusivity of reactor irradiated (U,Gd)O₂ fuels has been measured, for burn-ups from 33 to 97 GWd tHM⁻¹ and for irradiation temperatures from 670 to 1580 K. Measurements under thermal annealing cycles were performed in order to investigate the recovery of the thermal conductivity as a function of temperature. The analysis of the results showed a lower thermal conductivity for (U,Gd)O₂ when compared to UO₂, with similar effects of the burn-up and irradiation temperature. A correlation for the thermal conductivity could be proposed on the basis of that for UO₂ presented in an earlier work, which describes the separate effects of soluble fission products, of fission gas frozen in dynamical solution and of radiation damage