Thermal conductivity of UO_2+x and U₄O_9-y

Stoichiometries of UO₂ specimens ranging from 2.000 to 2.210 were prepared in situ at 1673 K within thermoanalytical equipment. Thermal conductivities were analyzed according to Klemens-Callaway defect model. Analysis of the data sets allows for extraction of the fundamental phonon-phonon and phonon-defect scattering contributions for the materials investigated. Low temperature thermal conductivity data was modeled using sigmoidal averaging to calculate the dual phase field UO_2+x-U₄O_9-y. This allowed the thermal conductivity of U₄O_9-y to be calculated as a function of temperature up to 873 K. This fundamental dataset provides a key contribution to ongoing efforts in the modeling and simulation communities in the areas of both light water reactor fuel performance and accident evolution.