Study on Hydrogen Induced Delayed Cracking Behavior of Zirconium Alloys Caused by Surface Defects

Zirconium alloy components used in nuclear reactors maybe occur to fail due to hydrogen induced delayed cracking (HIDC) during service. Whether the microdefects on the surface of the components will cause HIDC is worth studying. In this paper, samples with microcrack defects on the surface of zirconium alloy were prepared by vacuum electron beam welding method, and the corrosion behavior of these microcrack defects during thermal cycling treatment in high-pressure water at 350℃ after corrosion in superheated steam at 400℃ was studied. As the formation of a wedge-like oxide film embedded in the metal at such defects, a tensile stress concentration and stress gradient zone will be formed at the front end of the wedge-like oxide film, resulting in the diffusion and enrichment of hydrogen, and the precipitation of hydrides. In this case, even if the samples are not subjected to external stress and have no residual stresses, these defects will also cause HIDC, leading to defect extension and cracking. Therefore, when designing and manufacturing various zirconium alloy components used in the nuclear reactor core, attention should be paid to how to avoid such defects formed on the surface of such components.