Impact of alpha-damage and helium production on Heat Capacity of (U, Pu)O2

International audienceThe heat capacity of (U, Pu)O2 samples having cumulated alpha-decay damage was measured during thermal annealing. The excess of heat released from various defect recovery stages was measured. Results from Transmission Electron Microscopy, helium thermal desorption, thermal diffusivity, and XRD post-annealing studies were used to support quantitatively the microscopic origin of radiation damage to heat capacity. It was shown that different defect annealing stages could be singled out. It could also be evidenced that the excess of energy stored by defects tends to saturate at rather low damage levels but, with increasing radiogenic helium production, another contribution of stored energy emerges and that can be attributed to the formation of helium-defect complexes that cannot annihilate until high temperatures are reached. Some correlation will be established with spent nuclear fuel ageing processes