[en] Calculations of the binding energy of tritium to helium interstitials, to vacancies, and to vacancies containing ³He in both fcc and bcc materials are presented. The energetics of clustering of small numbers of helium atoms is also described. The results indicate that in an fcc lattice a helium interstitial does not bind a tritium atom but that in a bcc lattice a weak helium interstitial trap may exist which is of the order of the activation energy for tritium interstitial motion. Helium reduces the binding of tritium to a vacancy by approx. 0.25 eV in a bcc lattice. Helium interstitial clustering is found to be an important effect. Small numbers of helium atoms are found to be bound to each other and to significantly reduce the Frenkel pair formation energy: five helium interstitials clustered together will spontaneously drive a metal atom off its lattice site creating a self-interstitial and a vacancy containing the five helium atoms. These atoms are then deeply bound in the vacancy. This suggests an atomistic model of bubble formation in solids in the absence of radiation damage