Xianggang Kong

The alloy element Nb plays an important role in improving the performance of zirconium alloys in nuclear reactors. The effect mechanism of Nb doping on mechanical and thermodynamic properties was investigated using experimental and theoretical methods. The results of this study showed us that Nb doping refines grains and enhances hardness. The hardness increases from 2.67 GPa of pure Zr to 2.99 GPa of Zr1.5Nb. Depending on the first-principles calculations, the hardness decreases with the increase in the Nb concentration in the Zr matrix, namely from 2.45 Gpa of pure Zr to 1.78 GPa of Zr1.5Nb. If the first-principles calculations indicate that the hardness decreases with the increase in the Nb concentration in the Zr matrix, grain refinement or defects could play a major role in the increase in hardness. Furthermore, regarding the effect of Nb doping on thermal expansion coefficients, the increase in Nb content causes the thermal expansion coefficients to decrease, which might stem from the strong binding energy between Nb and Zr atoms. The thermal conductivities of three samples show similar changing trends, indicating that thermal conductivity begins to decrease at room temperature and reaches a minimum value of around 400 °C. The thermal conductivity of pure zirconium samples is consistently higher, is more obvious than that of Nb-doped samples in the test range, and decreases with an increase in the doping concentration. The possible reasons for this might stem from the distortion of the Zr matrix due to Nb substitution doping and grain refinement, both of which cause phonon propagation scattering and thus hinder the propagation of phonons. The results obtained herein may be useful for the development of advanced nuclear fuels and waste forms that utilize zirconium in applications beyond their current usage.

Co-adsorption of multi-components in ZrCo-based hydrogen storage materials can lead to a number of synergistic effects, such as the modification of adsorption sites, and further worsen the hydrogen storage capability. In this work, we explore the co-adsorption of H and CO on the ZrCo(110) surface and find that the molecular CO can be adsorbed on the clean alloy surface and thus decrease the hydrogen storage ability of the alloy. Moreover, CO occupies the adsorption site of H and therefore prevents the adsorption and diffusion into the interior of the lattice. Fortunately, the Hf dopant reduces the number of adsorption sites of the CO molecule and inhibits the formation of carbides to a certain extent. In addition, the partial density of states (PDOS) result shows that there is almost no interaction between the s orbital of H and the s orbital of Co on the pure surface of pre-adsorbed CO, while on the Hf-doped surface of pre-adsorbed CO, the s orbital of H overlapped greatly with the s orbital of Co, indicating that Hf doping inhibits CO toxicity in the interaction between H and the surface. Hence, the doping of Hf has the effect of giving resistance to CO toxicity and is conducive to the adsorption of H.

The addition of the Hf atom favors He accumulation in the surrounding of Hf, improving the ability of helium retention.

Hydrogen molecules in a purge gas are known to enhance the release of tritium from lithium ceramic materials, which has been demonstrated in numerous in-pile experiments. The static computational results suggest that the molecular adsorption of H₂ on the “ideal” Li₂O/hydrogenated-Li₂O (111) surface encounters high dissociation barriers in various entrance channels. The surface chemical inertness of the plane can be broken by introducing vacancy defects. In the present work, a combination of static DFT calculations and ab initio molecular dynamics has been performed to investigate the H₂ dissociative mechanism. Our theoretical results, that the end-on oriented H₂ could dissociate on the hydrogen monomer vacancy surface with one hydrogen atom ejected into the gas phase by the abstraction channel and the parallel H₂ molecule dissociates on the hydrogen dimer vacancy surface with two hydroxyls forming, suggest that hydrogen vacancy defects facilitate the adsorption and dissociation of H₂ molecule. The presence of the O²⁻ ion induced by the hydrogen vacancy provides some low energy states in which the H₂ electrons can be accommodated. This is very instructive for the comprehension of phenomena that occur during the operation of a thermonuclear reactor.