The use of NRA to study thermal diffusion of helium in (U, Pu)O2

A lot of work has been already done on helium atomic diffusion in UO2 samples, but information is still lacking about the fate of helium in high level damaged UOX and MOX matrices and more precisely their intrinsic evolutions under alpha self irradiation in disposal/storage conditions. The present study deals with helium atomic diffusion in actinide doped samples versus damage level. The presently used samples allow a disposal simulation of about 100 years of a UOX spent fuel with a 60 MW d kg-1 burnup or a storage simulation of a MOX spent fuel with a 47.5 MW d kg-1 burnup. For the first time, nuclear reaction analysis of radioactive samples has been performed in order to obtain diffusion coefficients of helium in (U, Pu)O2. Samples were implanted with 3He+ and then annealed at temperatures ranging from 1123 K to 1273 K. The evolution of the 3He depth profiles was studied by the mean of the non-resonant reaction: 3He(d, p)4He. Using the SIMNRA software and the second Fick's law, thermal diffusion coefficients have been measured and compared to the 3He thermal diffusion coefficients in UO2 found in the literature.