Effects of irradiation on the multi-field coupling delayed hydride cracking behavior of zirconium alloys

Abstract

With high mechanical strength, good corrosion resistance and small thermal neutron absorption cross-section, zirconium based alloys are widely used as the nuclear structural materials. Stress concentration usually appears in zirconium-based-alloy components during their reactor service phase or the storage stage of spent fuels, which could induce the delayed hydride cracking (DHC) behavior to seriously threaten the nuclear safety. In this study, an innovative multi-field coupling theoretical frame is developed, with the effects of texture factor, with the irradiation hardening and embrittlement effects as well as the hydride orientation contributions involved in the cohesive model, with the hydrogen diffusion affected by the irradiation-induced variations of Nb concentration. The multi-field coupling simulation results indicate that (1) the predictions of the DHC velocities for different irradiation doses are in good agreement with the experimental data, and the subcritical cracking traits can be captured, which validates the effectiveness of the newly developed models; (2) the irradiation-enhanced hydrogen diffusion coefficient plays a dominant role in the increase of DHC velocity with the radiation dose; (3) the irradiation hardening leads to the increases of hydrostatic stress gradient and the concentration gradient of solid-soluted hydrogen atoms, which accelerates the diffusion flux of hydrogen atoms towards the crack tip region; (4) essentially, it is the irradiation hardening that shortens the required length of hydrided zone to initiate new fracture, and quicken the multi-coupling cracking process. This work lays a foundation for the further study of delayed hydride cracking behavior.