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.

Refractory oxide dispersion strengthened 13Cr-2Mo steel powder was successfully consolidated to near theoretical density using high voltage electric discharge compaction. Cylindrical samples with relative density from 90% to 97% and dimensions of 10 mm in diameter and 10–15 mm in height were obtained. Consolidation conditions such as pressure and voltage were varied in some ranges to determine the optimal compaction regime. Three different concentrations of yttria were used to identify its effect on the properties of the samples. It is shown that the utilized ultra-rapid consolidation process in combination with high transmitted energy allows obtaining high density compacts, retaining the initial structure with minimal grain growth. The experimental results indicate some heterogeneity of the structure which may occur in the external layers of the tested samples due to various thermal and electromagnetic in-processing effects. The choice of the optimal parameters of the consolidation enables obtaining samples of acceptable quality.

This article gives a brief overview of the development of vanadium alloys as structural materials for fast and fusion reactors in future. The most important properties of vanadium alloys are considered with respect to the properties of austenitic and ferritic-martensitic steels. Vanadium is sufficiently spread in nature metal, and series alloys have good processability. Short-term strength properties of vanadium alloys remain at a high level up to the temperature of 970 K. In the high-temperature strength properties (thermal creep, long-term strength) vanadium alloys significantly exceed similar characteristics of austenitic and ferritic-martensitic reactor steels. Vanadium-base alloys are characterized by higher melting point and lower density than steels, and have a lower linear thermal expansion and higher thermal conductivity. At the same time, vanadium alloys are able to withstand higher heat loads due to better thermal and physical properties than steels. Analysis of the nuclear physical properties shows that the helium production rate is 2–3 times lower in vanadium alloys than the one in austenitic and ferritic-martensitic steels (as well as hydrogen production). At the same time nuclear heating rates are lower for the vanadium alloys compared to both steels. These effects provide a significant advantage to vanadium alloys as compared with steels. Alloys V – (4–5) Cr – (4–10) Ti have the highest potential in long-term radioactivity and show the advantages over low activation steels. From the point of view of radiation embrittlement, it is concluded that the temperature of 700 K should be taken as the lower limit of the operating temperature for vanadium alloys when they are used as a reactor structural materials. The data on radiation creep of vanadium alloys are extremely limited and contradictory. The ways are noted of solving the existing problems: helium and hydrogen by corresponding alloying, the sensitivity to impurities using high-purity vanadium and/or special alloying, compatibility with liquid sodium using the composite material “steel – vanadium alloy – steel”.

Hydrogen retention in vanadium and its binary alloys with titanium are investigated by means of hydrogen thermal desorption spectrometry. The samples are saturated with hydrogen for 2000 h at a temperature of 620 K in an autoclave, where hydrogen is fed at a pressure of 16.8 MPa. It is shown that in V-Ti alloys there are two main types of traps for hydrogen and from which the hydrogen release occurs in the temperature range of 780–790 (peak I) and 870–880 K (peak II) The position of peak I on the temperature scale does not depend on the alloy composition, and the intensity and position of peak II on the temperature scale are determined by the alloy composition. Titanium non-monotonically affects the amount of hydrogen retained: an addition of 0.5% Ti decreases, 1 and 5% Ti increases, and 10% Ti again decreases the amount of hydrogen in the alloy. A physical explanation of the appearance of two peaks of hydrogen thermal desorption and nonmonotonic influence of titanium on the amount of hydrogen in vanadium is proposed.

The microstructure and mechanical properties of 18Cr10NiTi austenitic steel were studied after high-temperature neutron irradiation of samples in a helium atmosphere. It was revealed during irradiation, helium penetrates into steel samples forming bubbles distributed on dislocations and along grain boundaries. Character of the temperature dependence of the mechanical characteristics of irradiated steel indicates a high-temperature radiation embrittlement of steel. The character of the mechanical properties temperature dependence change of irradiated steel points to its high-temperature radiation embrittlement.

The temperature dependences of the internal friction, Q ⁻¹, of vanadium and of V-(0.3–10%) Ti alloys are measured in the range from room temperature to 900°C. Three peaks at 227, 295, and 375°C attributed to the O-V, O-Ti, and Ti-V complexes are detected for the alloys with a low content (<5%) of titanium. In the alloys containing 5–10% titanium, these peaks disappear, but a new peak attributed to the V-O-Ti complex arises at 475°C. The binary complexes are found to make the main contribution to retardation of dislocations in the V-Ti alloys with a low content of titanium and, consequently, to strengthening and embrittlement of these alloys.