An approach to the assessment of transuranic speciation in the geosphere

Investigations of the behaviour of transuranic radionuclides and long-lived fission products in geological media are being undertaken to study their potential mobility. Such information is necessary for the assessment of the feasibility of storage of nuclear wastes in geological formations. The major difficulties in such assessments are the identification of the chemical species and the knowledge of their stability under realistic environmental conditions. In view of existing time constraints and the limitations of present analytical techniques for in situ measurements, the assessment of the potential mobility of physico-chemical species of radionuclides in a number of different geological options may depend on the development of an indirect approach. This will involve two aspects. Firstly, the identification of a number of characteristic classes of physico-chemical species which may be expected to occur in both liquid and solid phases of different geological media. Secondly, the identification of the geochemical parameters that will require in situ measurement to delimit the probable chemical forms at a given site of interest. A working methodology employed by the J.R.C., Ispra Establishment is described. Two examples are given concerning americium and technetium. (orig.)