Deformational rock mass response during a nuclear waste repository simulation experiment at the Asse salt mine.

A joint US/FRG simulation experiment was performed from 1983-1985. For the installation of four individual test sites an underground test room was excavated at the 800 m-level. At two of the test sites the HLW disposal was simulated by the emplacement of heaters. At the two remaining test sites, cobalt-60-sources of 18 000 Curies each were also emplaced in the boreholes to simulate photon-emitting HLW. In order to observe the rock mass response, room closure measurements at the different test sites were started during the excavation period. Later, horizontal extensometers were installed to monitor the rock mass disintegration in the vicinity of the test room. Vertical room closure measurements were only started after equipment installation, simultaneously with start-up of heating