Hydrogen redistribution in non-irradiated and irradiated duplex zirconium claddings by high-resolution neutron imaging

Duplex claddings, a concept with an outer layer on Zircaloy-4 substrate, have been employed in Swiss pressurized water reactors for decades. A significant amount of spent fuel encapsulated within this cladding type is currently stored in interim dry storage facilities before relocation to deep geological repositories. Duplex claddings exhibit different hydrogen distribution behaviour compared to single material claddings. This behaviour has been previously observed in non-irradiated duplex claddings. In this study, we extended the investigation to reactor-irradiated duplex cladding with an average burnup of 71.6 MWd/kg (HM). The results show that chemical potential and terminal solid solubility influence hydrogen distribution in both non-irradiated and reactor-irradiated cladding. However, the initial distribution of hydrogen plays a significant role in its subsequent redistribution. The formation of a dense hydride accumulation zone in the liner (DHAZ_liner) is evident and arises from differences in hydrogen solubility between the liner and substrate. Irradiated claddings demonstrate higher hydrogen mobility within the cladding, making them more responsive to external stresses in comparison to non-irradiated claddings.<br /><br />