Crop - a project for comparative description of national concepts for disposal of radioactive waste

Nine partners representing Sweden (SKB), Belgium (SCK-CEN). Finland (POSIVA). France (Andra). Germany (GRS), Switzerland (NAGRA), Spain (ENRESA). Canada (OPG), and the US (DOECBFO) participate in the EC-supported project CROP, which is the synonym for Cluster Repository Project and aims at describing the various repository concepts for identifying similarities and differences. The ambition is to assist designers and modelers in the development of the respective concepts. Design, construction and instrumentation of underground laboratories (URLs) and forthcoming repositories as well as modeling the engineered performance of national repository concepts in crystalline rock, salt and clay are defined and compared. The depth of location of the repositories is different - 250 to 1000 m- and also the design: the multi-barrier philosophy is proposed for disposal in all types of rock but for salt the geological medium is considered to be the major barrier. The minimum time for effective isolation of the waste differs among national programs (E4 to E6 years) and so is the effort of modeling physical and chemical degradation of the engineered barrier system (EBS), which consists of canisters, embedding buffer and backfill, and plugs. CROP is focusing on the buffer and backfill and shaft, tunnel and borehole seals including plugs. The temperature in the near-field is a most important factor for the repository performance. It will be in the interval 90-110 deg C for crystalline rock and clay, and up to 200 deg C for salt in the close vicinity of the waste according to the concepts, attenuating with increased distance from it. The heat and temperature gradient affects the groundwater flow and rock strain and thereby the evolution of the EBS in the first few hundred years and they are determinants of the chemical stability and hence required dimensions of the engineered barriers. Both the short- and long-term performance of the EBS are significantly affected by the groundwater chemistry. (authors)