Recoil and transmutation effects in the migration behaviour of actinides

Most actinide nuclides decay by α emission with the formation of kinetically and electronically excited daughters. The behaviour of heavy recoil atoms can be inferred from the observation of rupture of equilibrium in the natural radioactive series, from hot atom chemistry and from computer simulation of collision dynamics. On the basis of these sources of information, a new chemical model is established for α recoil chemistry. It postulates that the chemical state of the daughter atom is determined by redox reactions with oxygen interstitials at the end of the trajectory of the recoil atom. The model predicts that in minerals with low uranium content, 234U tends toward a leachable, oxidized form; on the other hand, in an environment with high uranium content, 234U is less amenable to oxidation, complex formation and leaching. These findings suggest that the disposal of radwaste would be more appropriate in 'reducing' organic solids than in ceramic matter or glassy material. (orig.)