Sequential Separation of Iodine Species in Nitric Acid Media for Speciation Analysis of 129I in a PUREX Process of Spent Nuclear Fuel Reprocessing

For efficient and accurate speciation analysis of I-129 in the nitric acid solution of spent nuclear fuel in its reprocessing process, a sequential procedure for stepwise separation of different iodine species in 3 mol/L HNO3 was proposed based on the solvent extraction using CCl4 and mesitylene. Molecular iodine (I-2) was first separated by solvent extraction using CCl4, and iodide (I-) remaining in the aqueous phase was oxidized to I-2 by adding NaNO2 and then extracted to mesitylene. Finally, iodate (IO3-) was reduced to I-2 using NH2OH center dot HCl and extracted to mesitylene. The separation efficiency of 98-99% for tracer amounts of I-129(2), I-129(-), and (IO3-)-I-129 in 3 mol/L HNO3 and less than 2% crossover among different iodine species were achieved. The extraction process and mechanism of different iodine species in CCl4 and mesitylene were investigated, and the problem of crossover of different iodine species due to the low extraction efficiency of low concentration of iodine in nitric acid solution was solved. A direct transfer of IO3- from HNO3 ( )to the mesitylene phase without conversion to I-2 was observed, which was attributed to the iodination of mesitylene in the HNO3 medium. Addition of a stable iodine species carrier and repeated extraction significantly improved the separation efficiency of iodine species, making their quantitative separation achievable. This method provides an approach for speciation analysis of I-129 in the acidic spent nuclear fuel solution, enabling us to investigate and control the behavior of volatile I-129 in the spent nuclear fuel reprocessing process.