Autocatalytic decomposition of tributyl phosphate in the spent extractant of the PUREX process for safe disposal of radioactive impurities

The possibility of processing the spent extractant of the PUREX-process by thermochemical decomposition of tributyl phosphate (TBP) to hydrocarbons and phosphoric acid was investigated. It was shown that the main condition for the intensive and complete decomposition of TBP is the presence of free phosphoric acid in the system, which ensures the course of the process in an autocatalytic mode. This is observed at a molar ratio of H3PO4: TBP > 2: 1 and can be achieved in the technological process using recycled phosphoric acid. Under these conditions, at a temperature of 190–200 °C, the decomposition of TBP proceeds quantitatively within 5–10 min. It was found that the process proceeds with the formation of butene and a large amount of alkanes and alkenes of various molecular weights, which is caused by secondary processes of polymerization and cyclization of decomposition products catalyzed by excess phosphoric acid. During the decomposition of TBP, radioactive impurities pass into the phosphoric acid phase, which creates the possibility of their neutralization and disposal in the form of phosphate glasses. •Tributyl phosphate is decomposed by the reaction product, phosphoric acid.•Hydrocarbons are formed.•Radioactive impurities pass into phosphoric acid.