Effect of alpha self irradiation on helium migration in (U,Pu)O2 samples

The helium behavior and its migration mechanisms in nuclear spent fuel (UOX and MOX) significantly impact the possible evolution of the spent fuel matrix in a closed system during interim storage or during a disposal repository. An experimental study has been conducted on (U,Pu)O2 samples in order to investigate the impact of defects created by alpha decay on helium diffusion. One large part is devoted to thermal atomic diffusion and applied on 3He implanted samples, annealed at 850 and 1000 deg. C. The He profiles, as implanted and after annealing, were investigated with the 3He(d,p)4He nuclear reaction. Another part deals with the thermal release of 4He amassed in the samples. The measured thermal diffusion coefficients are compared with previously published values, thereby highlighting the effect of the alpha self-irradiation on helium behavior. (authors)