SPENT NUCLEAR FUEL DISSOLVING SOLUTION BY METHOD FOR SUPERCRITICAL CARBON DIOXIDE EXTRACTION AND METHOD FOR DENITRIFYING HIGH LEVEL RADIOACTIVE WASTE LIQUID

摘要

PROBLEM TO BE SOLVED: To make it possible to simplify a denitrifying method by the reduction in nitric acid concentration of high level radioactive waste liquid by heating and pressurizing liquefied carbon dioxide mixed with tributyl phosphate(TBP) to specific temperature and pressure to supercritical fluid, and denitrifying the spent nuclear fuel dissolved solution during the reprocessing step. SOLUTION: Liquefied carbon dioxide mixed with tributyl phosphate(TBP) is heated and pressurized to 60 to 80 deg.C and 10 to 26Mpa to supercritical liquid, supercritical carbon dioxide fluid fed via the solution collected in an extraction vessel 1 is returned to the normal pressure at the pressure via a restrictor 8, and then introduced to a capturing vessel 10. After metal element such as uranium separated at the initial stage of the extraction is recovered into the vessel 10, then further supercritical carbon dioxide fluid is continuously fed, nitric acid in the sample solution is extracted, and recovered to another capturing vessel. The extracting operation is conducted for a predetermined time to denitrify the nitric acid solution.