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

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 Zr-2(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 Zr-2(Ni,Fe)-type particles will trap the migrating H until these are dissolved or fully oxidised. (C) 2012 Elsevier Ltd. All rights reserved.