Behaviour of ruthenium in nitric media (HLLW) in reprocessing plants: a review and some perspectives

The reprocessing of spent nuclear fuel produces high level liquid waste (HLLW). Due to the decay heat, the concentrated nitric solutions containing fission products (FP) are stored in cooled tanks. Actually, the loss-of-cooling accident on these HLLW storage tanks could lead to releases of radioactive materials to the environment, especially ruthenium volatile species. After a general presentation on the physico-chemical behaviour of ruthenium in concentrated nitric acid, this paper successively details the different transfer modes of ruthenium reported in the literature, and the available trapping techniques. Based on this review, research perspectives are presented aiming at updating data concerning ruthenium behaviour in this context.