Transport and Containment Chemistry of Ruthenium under Severe Accident Conditions in a Nuclear Power Plant.

Doktorsavhandling, 2016

During a severe nuclear accident volatile elements and elements readily forming volatile compounds are the main concern regarding the release of radioactive material to the environment. As ruthenium is prone to form volatile oxides under severe nuclear accident conditions as well as having radiotoxic isotopes, it is one of the more important elements during such an accident. In this work the chemical behavior of ruthenium during the transport in the reactor cooling system and the chemistry of ruthenium within the containment was studied. Studies on ruthenium transport included the effect of temperature, air-radiolysis products and aerosols on the quantity and chemical form of transported ruthenium during an accident. During the experiments the temperature had significant effect both release and transport of ruthenium. Different air radiolysis products affected both quantity and physical form of the transported ruthenium. The other part of the studies was focused on the chemistry of ruthenium within the containment. These experiments aimed at the interaction of ruthenium tetroxide with metallic (Al, Cu, Zn) and epoxy paint covered surfaces within the containment. Ruthenium had great affinity towards these surfaces that led to the formation of ruthenium rich deposits and thus a clear retention. Chemical characterization as well as quantification of these deposits was obtained. The effect of gamma radiation on the formed ruthenium deposits was shown and re-volatilized fractions of ruthenium under different atmospheres and received doses were determined decreasing the retention significantly.  Studies focused on interaction of ruthenium tetroxide with iodine-covered surfaces showed its ability to oxidize iodine deposit and re-volatilize iodine from the aluminum and zinc metals. Iodine covered surfaces were also proved to be an effective trap of ruthenium within the containment. Data obtained from these studies can be utilized for the better understanding of severe accident phenomenology and behavior of radionuclides during an accident.