Interaction between impurity elements (C, N and O) and hydrogen in hcp-Zr: a first-principles study

Abstract

Zirconium (Zr) alloys as cladding materials are widely used in fission reactors. The service life of Zr-based materials cladding is seriously affected by the hydrogen (H) behaviors; while the impurities (C, N and O) in Zr alloys have a great influence on the hydrogen behaviors. In this work, we have investigated the impurity–hydrogen interactions in hexagonal-closed packed Zr (hcp-Zr) by a first-principles approach. It was found that H atom tends to occupy tetrahedral interstitial position in perfect Zr and occupy octahedral interstitial position in Zr with vacancy, while the impurities tend to occupy octahedral interstitial positions in Zr both with and without vacancy. The impurities can trap H atoms. Four possible paths were studied for the diffusion of H atom in hcp-Zr, and it is found that the diffusion barriers of H varied with the presence of impurities.

Crystal Lattice Defects in Deuterated Zr in Presence of O and C Impurities Studied by PAS and XRD for Electron Screening Effect

“…The different mobility of carbon and oxygen vacancies can be then explained by their different binding energies in the Zr crystal lattice. While the carbon atoms should have a large binding energy to the deuteron-produced vacancies (D-C-Vacancy structure) and even increase their binding energy in Zr reducing vacancy diffusion, the oxygen atoms have also a large vacancy binding energy (D-O-V structure) but reduce their binding energy in lattice allowing for easier diffusion, which is in agreement with DFT calculations [16]. However, in both cases, the vacancy conglomerates should have a similar size, as presented in the S vs. W diagrams in Figures 3 and 4.…”

“…This behavior might be explained with a saturation of the vacancy densities, as already observed for carbon ions and diffusion of the defects towards deeper sample layers induced by oxygen irradiation. According to [ 16 ], the oxygen impurity in α-Zr has three times higher binding energy than carbon.…”

“…Lower values (1.5–1.66) observed in the XRD indicates binding of deuterium by vacancies. It has already been shown that up to nine hydrogen atoms can be trapped by a single vacancy [ 16 ].…”

“…This behavior might be explained with a saturation of the vacancy densities, as already observed for carbon ions and diffusion of the defects towards deeper sample layers induced by oxygen irradiation. According to [16], the oxygen impurity in α-Zr has three times higher binding energy than carbon. According to Figures 3a and 4a, a large increase in the vacancy density down to the deuteron range of about 600 nm was visible for all implanted targets.…”

“…Density Functional Theory (DFT) simulations for Ni demonstrate that mono and divacancies complex clusters in which up to twelve hydrogen atom can be segregated are characterized by stable configuration with high total biding energy [ 15 ]. This simulation technique applied to α-phase zirconium revealed that up to nine hydrogen atoms can be trapped in a single vacancy [ 16 ]. Within the same study, the role of carbon or oxygen impurities on hydrogen migration has been investigated.…”