Engineering geological investigations for planning and construction of an underground repository for low-level radioactive wastes

Abstract

The necessary safety of permanent repository for radioactive wastes can be demonstrated only by a site analysis, in which the entire system, “the geological situation, the repository, and the form of the wastes” and their inter-relationships are taken into consideration. Technical, geotechnical and geological data are the basis of this site analysis. The site analysis has three essential tasks: (a) assessment of the load capacity of the host rock, so that deposition strategies can be determined for the site; (b) determination of the safe dimensions of the mine (e.g. stability of the caverns and safety of the operations); (c) evaluation of the barriers and the long-term safety analysis for the authorization procedure. The Konrad iron ore mine, near Salzgitter—Lebenstedt in the Federal Republic of Germany, has been selected as a potential repository for radioactive waste that does not generate heat. Advantages of the Konrad site are the mine stratum thickness of several hundred metres and the low permeability of the geological formations. Subsidence measurements were started even before ore extraction began, providing current investigations with data collected over the 20 yr extraction period. The measurements show that the mine has been stable since it was opened and the overlying strata, consisting of marlstone formations, have undergone deformations without exhibiting any failure. Stability evaluation of the planned repository was carried out using finite element analysis with the ADINA computer program. It is demonstrated that despite the existence of local plasticization zones no particular stability problems occur. The mining experience gained shows the feasibility of the planned repository with regard to the excavation of the disposal rooms.