Molecular aspects of the β-decay in Tc clusters

A quantum-chemical tight-binding method has been used in order to investigate the molecular consequences of the spontaneous transmutation of technetium 99Tc into ruthenium 100Ru in spent fuel of nuclear reactors. The Tcn and Run clusters (n=4, 6, 13) in highly symmetrical geometries and some of their mixed Tc/Ru derivatives have been considered. The reactivity of the remaining Tc sites is predicted to be enhanced as regards chemical attacks either on Tc–Ru bonds or specific Tc sites by various types of reagents (e.g. radicals or ions). The main consequences of this electronic mixing effect between two chemically related atoms, albeit different, elements, could be an easier formation of Tc molecular compounds instead of simple clusters during radioactive decay.