Comparison of the leaching behaviour of irradiated fuel, SIMFUEL, and non-irradiated UO2 under oxic conditions

The aim of this study was to compare the leaching behaviour of irradiated UO2 and MOX and non-irradiated UO2 and SIMFUEL. Direct comparisons using the very large amount of experimental data available in the literature are often difficult, not only because of the differences existing between SIMFUEL or non-irradiated UO2 and spent fuel (i.e. the presence of intense radiation fields surrounding irradiated fuel, hence radiolysis effects, or the formation of cracks and pores due to the volatile fission products, hence larger surface area), but also because of different experimental procedures used by different authors. In the case of MOX, the possible effects due to the different initial composition and microstructure also affect the leaching behaviour. This work presents results of sequential leaching experiments in deionized water at room temperature under oxic conditions using irradiated and non-irradiated fuel. The experimental conditions and procedure for all types of fuel were kept similar as much as possible. The SIMFUEL and UO2 samples underwent a more extensive characterisation due to easier handling. The specimens used were UO2 (54 GWd/tU) and mixed oxide (MOX, 30 GWd/tU) LWR spent fuels, and UO2 and SIMFUEL (30 and 50 GWd/tU) as non-irradiated chemical analogues. The highest fractional release of uranium was measured for UO2 spent fuel. The uranium release data for MOX fuel showed behaviour closer to non-irradiated fuels. Comparison of fission products release between SIMFUEL and irradiated fuel was also performed. (orig.)