Mineralogical and geochemical constraints on maximum admissible repository temperatures

In choosing a suitable host rock for the disposal of high-level radioactive wastes many geological factors must be taken into account. This paper deals with one of these factors: the geochemical and mineralogical constraints imposed by the thermal loading of the wastes. Using a combination of data on stabilities of component minerals and their predicted behaviour under the physicochemical conditions at depth in a backfilled repository, the three main proposed rock types (granites, evaporites and clays) are examined. Where data permit, arguments are made for imposing a maximum admissible temperature rise during the thermally active life of a repository for each of these rock types. The resultant discussion emphasizes the need for a low-temperature-disposal policy. The implications of such an imposed temperature limit for pre-disposal waste management are briefly outlined. (author)