Development of a radiochemical separation for selenium with the aim of measuring its isotope 79 in low and intermediate nuclear wastes by ICP-MS
Résumé
Selenium 79 is a beta emitter produced from 235U fission thus occurring as one of the fission products found in nuclear reactors. Due to its long half life (about 105 years), 79Se is one of the radionuclides of interest for the performance of assessment studies of waste storage or disposal. Thus, the National Radioactive Waste Management Agency (Andra, France) requests its monitoring in wastes packages before their disposal in specific sites.Measurement of 79Se is difficult owing to its trace level concentration and its low activity in nuclear wastes. A radiochemical procedure has to be carried out in order to separate selenium from the matrix and to concentrate it before the measurement with a mass spectrometric or a nuclear technique. The beginning of the development is presented in this paper. The optimised protocol firstly developed in view of an ICP-MS measurement, includes 5 steps based on microwave digestion, evaporation and separations on ion exchange resins. It was tested first on synthetic solutions and was optimised in order to be applicable to a large number of sample types. The recoveries of the whole procedure were evaluated using natural 82Se or the gamma emitter 75Se as a radioactive spiker. Then, the protocol was applied to two solid samples spiked with natural selenium, a glass microfiber filter and an ion exchange resin, and two liquid samples spiked with 75Se, a synthetic solution and an effluent. The yields obtained for both samples ranged from 70 up to 80%.