  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.
