Analysis of Inorganic Selenium Species Using HPLC and ICP-MS for Monitoring Mobility of Selenium in Engineering Barriers of Stored Nuclear Waste

To prevent spreading of radioactive 79Se, a decay product of 238U, engineering barriers with bentonite are used. To predict the behaviour of 79Se, speciation of Se is considered. The interconversions of non-radioactive Se species were studied in aqueous suspensions of bentonite at various pH using HPLC, ion-pair reversed-phase and anion-exchange chromatographies as well as ICP-MS. Some chromatographic parameters were optimized to improve the separation of the species. The limit of Se detection was determined and the linearity of calibration curves was verified. In alkaline medium, a fair amount of selenite in contact with bentonite was oxidized to selenate within two weeks. As the retention of selenate in the barrier is lower than that of selenite, Se could easily spread.