DEVELOPMENT OF RADIOACTIVE WASTE TREATMENT SYSTEM USING SUPERCRITICAL WATER

In nuclear facilities, there is some organic waste containing radioactive material. In the future, it is desired that this waste will be decomposed to reduce the volume and become stable. Toshiba has developed a waste treatment system using supercritical water. First, supercritical water was applied to the decomposition of used ion exchange resin for water purification in a nuclear power plant. Actual plant size apparatus was constructed with a treatment capacity of 1 kg ion exchange resin an hour. A kinetic model that can predict the ion exchange resin decomposition yield was also developed, and treatment conditions were determined using this model. Test revealed that 99.9% or more ion-exchange resin was decomposed at 723K and 30MPa. This decomposition yield predicted by the kinetic model fitted with the observed ion exchange resin decomposition yield. Moreover, compact equipment with a treatment amount of 33g /h was developed for decomposing organic solvents such as the liquid scintillation counter cocktail that is used for analyzing radionuclides. Test revealed that 99.9% or more liquid scintillation counter cocktail was decomposed at 773K and 30MPa. The equipment dimensions are about 2mL×1mW×1mH. It can even be installed in the glove box in nuclear facilities. Various types of organic liquid waste, for example, tributyl phosphate, turbine oil, silicone oil, etc. can be treated with this equipment. One such type of equipment has already been installed in a nuclear facility in Japan to treat organic liquid waste such as the liquid scintillation counter cocktail and has been operating well.