Zirconium-based alloys have served the nuclear industry for several decades due to their acceptable properties for nuclear cores of light water reactors (LWRs). However, severe accidents in LWRs have directed research and development of accident tolerant fuel (ATF) concepts that aim to improve nuclear fuel safety during normal operation, operational transients and possible accident scenarios. This review introduces the latest results in the development of protective coatings for ATF claddings based on Zr alloys, involving their behavior under normal and accident conditions in LWRs. Great attention has been paid to the protection and oxidation mechanisms of coated claddings, as well as to the mutual interdiffusion between coatings and zirconium alloys. An overview of recent developments in barrier coatings is introduced, and possible barrier layers and structure designs for suppressing mutual diffusion are proposed.

In this paper, phase transitions and microstructure evolution in titanium Ti-6Al-4V alloy parts produced by electron beam melting (EBM) under hydrogenation was investigated. Hydrogenation was carried out at the temperature of 650 °C to the absolute hydrogen concentrations in the samples of 0.29, 0.58, and 0.90 wt. %. Comparative analysis of microstructure changes in Ti-6Al-4V alloy parts was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Furthermore, in-situ XRD was used to investigate the phase transitions in the samples during hydrogenation. The structure of Ti-6Al-4V parts produced by EBM is represented by the α phase plates with the transverse length of 0.2 μm, the β phase both in the form of plates and globular grains, and metastable α″ and ω phases. Hydrogenation to the concentration of 0.29 wt. % leads to the formation of intermetallic Ti₃Al phase. The dimensions of intermetallic Ti₃Al plates and their volume fraction increase significantly with hydrogen concentration up to 0.58 wt. % along with precipitation of nano-sized crystals of titanium δ hydrides. Individual Ti₃Al plates decay into nanocrystals with increasing hydrogen concentration up to 0.9 wt. % accompanied by the increase of proportion and size of hydride plates. Hardness of EBM Ti-6Al-4V alloy decreases with hydrogen content.

Influence of manufacturing parameters (beam current from 13 to 17 mA, speed function 98 and 85) on microstructure and hydrogen sorption behavior of electron beam melted (EBM) Ti-6Al-4V parts was investigated. Optical and scanning electron microscopies as well as X-ray diffraction were used to investigate the microstructure and phase composition of EBM Ti-6Al-4V parts. The average α lath width decreases with the increase of the speed function at the fixed beam current (17 mA). Finer microstructure was formed at the beam current 17 mA and speed function 98. The hydrogenation of EBM Ti-6Al-4V parts was performed at the temperatures 500 and 650 °С at the constant pressure of 1 atm up to 0.3 wt %. The correlation between the microstructure and hydrogen sorption kinetics by EBM Ti-6Al-4V parts was demonstrated. Lower average hydrogen sorption rate at 500 °C was in the sample with coarser microstructure manufactured at the beam current 17 mA and speed function 85. The difference of hydrogen sorption kinetics between the manufactured samples at 650 °C was insignificant. The shape of the kinetics curves of hydrogen sorption indicates the phase transition α_H + β_H→β_H.