Fission product gas and aerosol particle control (FIKSU). Ruthenium behaviour in severe accident condition

In this project the transport and speciation or ruthenium in conditions simulating an air ingress accident was studied. Ruthenium dioxide was exposed to oxidising environment at high temperatures (>1200 deg C) in a tubular flow furnace. At these conditions volatile ruthenium species were formed. A major part of the released ruthenium was deposited in the tube as RuO2. Depending on the experimental conditions 12-35 wt-% of the released ruthenium was trapped in the outlet filter as RuO2 particles. At completely dry conditions using stainless steel tubes only 0.1-0.2 wt-% of the released ruthenium reached the trapping bottle as gaseous RuO4. However, when alumina was applied as tube material or the atmosphere contained some water vapour the fraction of RuO4 reaching the trapping bottle increased to 5 wt-%, which is close to thermodynamic equilibrium at the temperature of the furnace. This indicates that RuO4 was not decomposed in these experiments. (orig.)