Toward a better understanding of the hydrogen impact on the radiation induced growth of zirconium alloys

Under neutron irradiation, recrystallized zirconium alloys, used as structural materials for Pressurized Water Reactor fuel assemblies, undergo stress-free growth which accelerates for high irradiation doses. This acceleration is correlated to the formation of c-component vacancy dislocation loops. Some feedbacks from neutron irradiations show that the in-service hydrogen pick-up could influence the fuel assembly radiation-induced elongation. 2 MeV proton irradiations were performed on as fabricated materials in M5®, recrystallized Zircaloy-4 and 350 wppm pre-hydrided M5®. The irradiations were conducted on a Tandem Accelerator (MIBL/University of Michigan) at 623 K up to four doses. For both grades, the c-component loops evolution with dose is examined and compared to the neutron irradiated microstructures. As observed under neutron irradiation, the c-loop density in Zy-4 is higher than in M5®. Moreover, TEM observations on 350 wppm pre-hydrided M5® show that c-loop density is higher than without pre-hydriding. It is also seen that c-loops are preferentially located in the surrounding of some delta-hydrides partially or fully dissolved. The role played by hydrogen in solid solution and as precipitated hydrides is discussed