Thermodynamic modeling and experimental tests of irradiated graphite molten salt decontamination

Abstract

ABSTRACTMolten salt flameless oxidation of graphite is one of the prospective methods of irradiated graphite waste processing. Molten salts are capable to retain a considerable part of radionuclides, to neutralize acidic off gases, moreover spent salts could be vitrified on completion of the process. We have used thermodynamic modelling to assess the efficiency of molten salt oxidation of graphite. Equilibrium compositions of both the melt and the off gas were calculated depending on graphite content and temperature. The feasibility of decontaminating the irradiated graphite of its near-surface layers using complete molten salt oxidation was investigated in a series of laboratory experiments. As the molten salt medium used to oxidize irradiated graphite we have investigated lithium, potassium and sodium carbonates. Sodium sulphate, boron oxide, barium and potassium chromates were also used as oxidizers. Tests were carried out at 870–1270 К. The efficiency of decontamination of graphite blocks has been assessed based on the activity of 137Cs and 60Со in the samples before and after molten salt oxidation. Data obtained demonstrated the feasibility of decontamination by molten salt removal of near surface layers on irradiated graphite blocks. Decontamination rate and efficiency depend on oxidizers used and temperature of process.