Computer modeling of thermal processes involving calcium, strontium and cesium during radioactive graphite heating in the carbon dioxide atmosphere

Abstract

The design of nuclear reactors did not provide for decommissioning solutions, and there were no safe technologies to handle irradiated reactor graphite. Decommissioning of uranium–graphite reactors is a combination of complex tasks involving the selection of appropriate methods and techniques for the radioactive graphite handling. Computer modeling of the reactor graphite reprocessing by heating in a carbon dioxide environment makes it possible to determine the behavior of radioactive elements. The behavior of Ca, Sr and Cs during radioactive graphite heating in the carbon dioxide atmosphere was studied through computer modeling. It has been found that calcium is present as vapors of Ca, CaO, CaCl and CaCl2, as Ca+ and CaO+ ions, and as condensed forms of CaCO3, CaCl2 and CaO. Strontium is present as vapors of Sr, SrO, SrCl and SrCl2, as Sr+ and SrO+ ions, and as condensed forms of SrCl2, SrCO3 and SrO. Cesium is present as vapors of Cs and CsCl, as Cs+ ions, and as a condensed phase of CsCl2. Basic reactions have been identified and their respective equilibrium constants have been determined. The data obtained has shown that formation of calcium, strontium and cesium chloride vapors takes place at temperatures of 573 to 973K. A temperature increase to 1373K leads to thermal ionization of cesium chloride and to formation of ionized cesium. As the temperature increases to 2273K, thermal ionization of strontium and cesium is observed and ionized calcium and strontium form.