ABSTRACT
This chapter reviews the thermodynamic behaviour of ruthenium at high temperatures. A simple thermodynamic/mass-transport model is proposed to explain the release behaviour of ruthenium in a steam atmosphere. In irradiated fuel, ruthenium is not found as Ru(s) but is alloyed with other metals. The major components of this metallic alloy are ruthenium and molybdenum, and the minor components are technetium, palladium and rhenium. Both the experimental and theoretical results suggest that the rate of ruthenium release is proportional to the vapour pressure of the ruthenium gases in the boundary layer surrounding the fuel. At high temperatures, chemical reactions are generally fast and chemical equilibrium should be rapidly attained after the fission products are released into the primary heat transport system. Fission product releases from irradiated UO2 fuel were measured under various high-temperature conditions at Chalk River Nuclear Laboratories.
