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

Abstract

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.

Experimental study of ruthenium volatilization from boiling nitric solution

“…So, this work highlights same tendencies observed before by Ishio et al [14]. For more complete information, a recent literature review is available [6].…”

“…Even if the probability of occurrence of such an accident remains low, several mitigation systems have already been developed since the design of the process and can still be improved. A review of the studies carried out on this accident scenario in the design stage confirmed the lack of reliable data on the behaviour of ruthenium [6]. It also highlighted the limits of the models used at the time to evaluate the source term.…”

“…The review of literature indicate that the chemistry of ruthenium in a concentrated nitric acid appears to be very complex, with the existence of ruthenium nitrates -hydrated complexes with many oxidation states [1][2] [5] [6]. Faced with such complexity, no mechanistic chemical model could be successfully developed.…”

Capture and immobilization of gaseous ruthenium tetroxide RuO4 in the UiO-66-NH2 metal–organic framework

“…Other experiments realized on the same experimental setup and under the same conditions with sand, silver-doped zeolites, and activated charcoal showed a very low decontamination below 4. 7,41 So, UiO-66-NH 2 is a much more promising material for the filtration of RuO 4 .…”

Ruthenium behavior in the reactor cooling system in case of a PWR severe accident: study of oxidative conditions with stainless steel tube

“…Second, nitrogen oxides are of special interest regarding ruthenium chemistry. RuO4 is known for its ability to form different nitroso and nitrosyl compounds after reacting with nitric acid, NO2 or NO gases [5][6][7]. RuO4 can also be trapped into the water phase after reacting with NO2 or NO gases [8].…”