The nature of interstitial sites, their spatial correlations as well as their occupation probabilities by H (or D) have been investigated in random bcc binary alloys. Sites of both octahedral and tetrahedral types have been taken into account assuming they were distinguishable one another on the basis of either the chemical composition of their first shell of neigbouring atoms or of the distribution of the two metallic species within this shell. Short-range repulsive interactions among H atoms

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... ave been accounted for in terms of the hard core model and expressions have been derived for the so-called selective blocking factors. The results of calculations have been used to predict the occurrence of anelastic relaxations due to H. A comparison of the theoretical predictions with experimental data available in the literature is presented. Article published online by EDP Sciences and available at http://dx.