Very Long-term Storage of Fission Products.

The authors present a new strategy for the management of very high-level liquid effluents produced at reprocessing plants. The strategy involves: solidification, immediately after reprocessing, by a reversible process; retrieval of the products after 20 or 30 years; separation of the transuranics and, possibly, recovery of the noble metals; and separate storage, in an appropriate geological formation, of the fission products and transuranics. The strategy is based on the fact that the rare earths will have fully decayed by that time and that the much lower activity will facilitate the operations. Very long-lived fission products do not present any long-term problems, although it might perhaps be of advantage to store iodine-129 separately, especially in geoloformations from which any possible transfer would be towards the sea. The authors evaluate the potentially adverse effects of storge in geological formations. Study of diffusion effects in the soil shows that the main feature of radiological safety of the storge system is the adsorption capacity of the soils; the time taken to cross the geological barrier, when there is no adsorption, is small compared with the very long half-lives. Conversely, the geological barrier, when there is no adsorption, is small compared with the very long half-lives. Conversely, the geological barrier itself ensures dilution of the radionuclides and could, of its own accord, lead to acceptable concentrations in terms of radiological protection standards. Lastly, the authors compare the potentially adverse effects of storage in geological formations, especially granite, to that of natural rock, while concluding that under certain conditions the comparison is very favorable.