Influence of γ-irradiation on the transport kinetics of hydrogen in pre-transition oxidized Zircaloy-4 at room temperature

In a context of nuclear fuel reprocessing, the free-of-fuel hulls and ends of cladding tubes are compacted. The possibility of hydrogen degasing or absorption from/into these tubes has been studied with and without gamma irradiation at 293 K by means of deuterium as isotopic tracer for hydrogen. Under irradiation, as without, the hydrides present in the Zircaloy-4 hulls seem stable. The oxide layer present at the surface of the hulls allows a slow diffusion of deuterium, and the irradiation appeared to have no specific effect on the diffusion process: in both cases, hydrogen diffusion coefficients of the order of 5·10−18 cm2 s−1 have been found. The subsurface activity of deuterium is increased by one order of magnitude at least under irradiation, probably due to an activation of the dissociation/absorption kinetic steps.