Methodology to assess the radiological impact of a repository for uranium mill tailings after remediation (short-term impact).

Anne Christine SERVANT Actes du congrès "International Conference Uranium Mining and Hydrogeology III 2002" Freiberg (Allemagne) 15/09/2002 au 21/09/2002 "Uranium in the Aquatic Environment" (un recueil ainsi qu'un CD-ROM). p 907 à 914.

In France the current public dose limit for the radiological impact of repositories for uranium mill tailings is 5 mSv.y-1. Transcription into French regulation of the Euratom 96/29 European directive will induce a reduction of this limit to 1 mSv.y-1and therefore a questioning about the methodology used to assess the radiological impact of repositories for uranium mill tailings. Repositories for the uranium mill tailings are the subject of remediation so as to ensure lasting protection for individuals and the environment. Long-term effectiveness of the remediation has to be demonstrated as well as short-term effectiveness, but our study only concerns short term. The approach followed to demonstrate that short-term impact is acceptable consists of several steps : - description and understanding of the environment of the repository ( hydrogeology, climate, agriculture, demographic environment…) ; - description and behaviour of the various structures making up the repository (host cavities, dikes, top covering…) ; - selection of homogeneous (age, location) population groups around the site through a rational method ; - elaboration of a conceptual model representing the various exposure pathways ; - selection of a realistic exposure scenario for each population group, derived from the actual local ways of life (lifestyle, dietary habits, degree of self-sufficiency) ; - measurements in the environment linked with the location of the population groups and the identified exposure pathways (monitoring network) ; - assessment of the radiological consequences of the exposure scenarios selected ; these assessments must be supported by geometrical simplifications and/or simplifications of phenomena adopted, sensitivity studies, estimations of the uncertainty ranges… Wherever possible, the radiological consequences resulting from the presence of the repository is evaluated in relation to the doses that would have been received on the site without a repository. The group(s) of population for which the calculated impact is maximal is (are) considered as the critical group(s). Critical groups are monitored during all the surveillance period to check that the impact of the site remains acceptable.