Influence of fission products on ruthenium oxidation and transport in air ingress nuclear accidents

Abstract In separate effect tests at 1000–1200 °C Ru oxidation rate and content of Ru in escaping air flow have been studied with special emphasis on effects of other fission product elements on the Ru oxidation and transport. The results showed that in the decreasing temperature section (1100–600 °C) most of the RuO 3 and RuO 4 (≈95%) decomposed and formed RuO 2 crystals; while the partial pressure of RuO 4 in the escaping air was in the range of 10 −6 bar. The re-evaporation of deposited RuO 2 resulted in about 10 −6 bar partial pressure in the outlet gas as well. Measurements demonstrated the importance of surface quality in the decreasing temperature area on the heterogeneous phase decomposition of ruthenium oxides to RuO 2 . On the other hand water or molybdenum oxide vapour in air appears to decrease the surface catalyzed decomposition of RuO x to RuO 2 and increases RuO 4 concentration in the escaping air. High temperature reaction with caesium changed the form of the released ruthenium and caused a time delay in appearance of maximum concentration of ruthenium oxides in the ambient temperature escaping gas, while reaction with barium and rare earth oxides extended Ru escape from the high temperature area.