In the case of principal waste streams from nuclear power plants and reprocessing plants, the characterization of some critical long-lived isotopes by ICP-MS is markedly affected by the complexity of sample composition.

This paper gives a few indications on a French approach presently under study to ensure the safety of surface repository sites, from which it might be possible to assess a ranking of the principal isotopes and their desirable detection level. On this basis, the discussion concentrates on the methods currently under development in our laboratory to improve ICP-MS determination of ¹²⁹I and ⁹⁹Tc.

In view of difficulties encountered during the dissolution of solid waste and selective extraction of the species into an organic phase, a new preparative procedure is being developed. It consists of a direct pyrohydrolysis applied with no prerequisite: after fixation into an alkaline solution, the volatile species can be directly measured by ICP-MS. The sensitivity and range of applicability of this method are discussed.