Some problems of hydrogen in reactor structural materials: A review

The review concerns some problems of hydrogen in the main reactor structural materials used in the core of nuclear reactors. Zirconium alloys, steels, and vanadium alloys, as well as the hydrogen and helium synergetic effect exerted on the radiation resistance, are considered. The main sources resulting in the accumulation of hydrogen isotopes in reactor materials are discussed. The causes and consequences of hydride embrittlement of zirconium alloys at relatively low temperatures are analyzed. It is shown that hydrogen can induce the embrittlement of vessel steels through the weakening interatomic bond forces and a stabilization of radiation-induced defects. It is demonstrated that hydrogen in the presence of helium behaves like a gas that enhances the irradiation effect on the microstructure and properties of materials in many cases. The irradiation with simultaneous introduction of hydrogen and helium causes, in particular, a catastrophic swelling of chromium steels and vanadium alloys, whereas in the case of austenitic steel the effect is less pronounced.