Confinement of Ruthenium Oxides Volatilized During Nuclear Fuels Reprocessing

While many materials have been suggested and employed as trapping agents for gaseous oxides of fission product ruthenium volatilized during nuclear fuels reprocessing, none that is known to form thermodynamically stable compounds with ruthenium has been utilized. We have employed alkaline earth metal compounds for this purpose because of their ability to form stable mixed metal oxide phases with ruthenium. Results of experiments in which RuO₄ was volatilized from either a solid source (RuO₂·xH₂O) or from solution {[Ru(NO)(NO₃)₃] in HNO₃} and passed through beds of alkaline earth metal carbonates and calcium oxide held at 600 to 750°C have demonstrated that compounds of formulation MRuO₃ (M = calcium, strontium, barium) are formed. Under oxidizing conditions, these materials exist as stable ceramic phases, whereas under reducing conditions, they are transformed into intimate mixtures of the alkaline earth metal oxide and nonvolatile ruthenium metal.