Hydrogen accommodation in Zr second phase particles: Implications for H pick-up and hydriding of Zircaloy-2 and Zircaloy-4

TL;DR

This study uses ab-initio simulations to explore how different second phase particles in Zircaloy alloys influence hydrogen trapping and migration, impacting hydrogen pick-up and hydriding behavior.

Contribution

It reveals that Zr2(Ni,Fe) particles favor hydrogen trapping, while Zr(Cr,Fe)2 particles may facilitate hydrogen migration, providing new insights into hydrogen behavior in Zircaloy alloys.

Findings

Zr2(Ni,Fe) particles have favorable solution enthalpies for H.

Zr(Cr,Fe)2 particles may act as pathways for H migration.

Zr(Cr,Fe)2) particles do not trap H effectively.

Abstract

Ab-initio computer simulations have been used to predict the energies associated with the accommodation of H atoms at interstitial sites in {\alpha}, {\beta}-Zr and Zr.M intermetallics formed with common alloying additions (M = Cr, Fe, Ni). Intermetallics that relate to the Zr2(Ni,Fe) second phase particles (SPPs) found in Zircaloy-2 exhibit favourable solution enthalpies for H. The intermetallic phases that relate to the Zr(Cr,Fe)2 SPPs, found predominantly in Zircaloy-4, do not offer favourable sites for interstitial H. It is proposed that Zr(Cr,Fe)2 particles may act as bridges for the migration of H through the oxide layer, whilst the Zr2(Ni,Fe)-type particles will trap the migrating H until these are dissolved or fully oxidised.