Hydrogen migration in monoclinic ZrO₂ and the effects of defects and dopants assessed by first-principles calculations

Abstract

Zirconium-based alloys, which have been employed as cladding materials in nuclear industry, pick up hydrogen during service because of corrosion in water. This is one of the degradation processes that challenge the safe operation of nuclear reactors. Composition of commercial zirconium-based alloys has been developed experimentally, aiming to improve corrosion and hydrogen resistance. The empirical testing process is costly, time-consuming and can provide little knowledge on the underlying mechanisms. In order to understand the critical step of hydrogen entering zirconium-based alloys, we study hydrogen migration in monoclinic zirconium dioxide (m-ZrO2 ), the oxide phase, which is present in the outer protective oxide layer contacting the cooling water. First principles calculations are casted to study hydrogen migration at atom-istic scale. All possible stable sites for hydrogen to take in the structure are determined based on energy minimization. Barriers and saddle point configurations of elemental diffusion paths are obtained using the nudged elastic band method. Each extended diffusion path can be constructed from these elemental migration steps ...