Ruthenium transport experiments in air ingress accident conditions

In this study the release, transport and speciation of ruthenium in conditions simulating an air ingress accident was studied. Ruthenium dioxide was exposed to oxidising environment at high temperature (1100-1700 K) in a tubular flow furnace. At these conditions volatile ruthenium species were formed. A large fraction of the released ruthenium was deposited in the tube as RuO2. Depending on the experimental conditions 1-26 wt% of the released ruthenium was trapped in the outlet filter as RuO2 particles. In stainless steel tube 0-8.8 wt% of the released ruthenium reached the trapping bottle as gaseous RuO4. A few experiments were carried out, in which revaporization of ruthenium deposited on the tube walls was studied. In these experiments, oxidation of RuO2 took place at a lower temperature. During revaporization experiments 35-65 % of ruthenium was transported as gaseous RuO4. In order to close mass balance and achieve better time resolution 4 experiments were carried out using a radioactive tracer. In these experiments ruthenium profiles were measured. These experiments showed that the most important retention mechanism was decomposition of gaseous RuO3 into RuO2 as the temperature of the furnace was decreasing. In these experiments the transport rate of gaseous ruthenium was decreasing while the release rate was constant