Application of Supercritical Carbon Dioxide to Extraction of Uranium and Plutonium from Their Mixed Oxide

摘要

Application of supercritical carbon dioxide (SF-CO_2) is a relatively new technology for processing ofrnnuclear materials. A few years ago it was no more than scientific curiosities, but now seems to be promising. We foundrnmineral and organic acids can be introduced in SF-CO_2 as complexes with tri-n-butylphosphate (TBP). Among them, therncomplex with nitric acid is most useful to extract metals from their oxides. Uranium andplutonium extraction from nuclearrnfuel consisting of the mixed oxide where PuO_2 forms a solid solution was successfully demonstrated under a high pressurerncondition at the Chemical Processing Facility in Japan Nuclear Cycle Development Institute (JNC). This experiment wasrnperformed as a part of a collaboration work by JNC, Mitsubishi Heavy Industries and Nagoya University. Main advantagernof using SF-CO_2 to treat nuclear materials is waste minimization, which leads to reduction of the escalated cost for treatmentrnof radioactive materials. In this demonstration, a chemical complex of TBP with HNO_3 and H_2O was used as a reactingrnagent for the mixed oxide, and uranium andplutonium were extracted congruently from the solid matrix.