Thermal diffusivity measurements on oxidised irradiated urania fuel up to 900 deg. C

There is a limited amount of available data on the thermal conductivity of oxidised fuel, and none on oxidised irradiated fuel. In this work oxidised samples of irradiated fuel have been prepared and out-of-pile thermal diffusivity measurements have been performed. The usual way to prepare oxidised samples is to anneal at high temperature in a controlled oxygen potential, typically at temperatures ≥ 200 deg. C in CO/CO2 atmospheres. However, such conditions are not suitable for irradiated UO2 because of the restructuring processes that occur above ∼900 deg. C and which could confound the thermal diffusivity measurement results. Therefore a low temperature anneal in air at 460 deg. C for 5 minutes was used to oxidise fragments of irradiated UO2. The results are be reported and compared with oxidation data from different sources and as these cannot be reconciled solely on stoichiometry variation, it is suggested that the method used to produce oxidised samples may be an important contributor. This could explain the difficulty in reconciling Conductivity Integral to Melt data with low temperature measurements. Plans to perform integral oxidation and thermal diffusivity measurements to investigate this phenomenon are being considered. (author)