New instrumentation of microseismic monitoring system in the asse research mine in Germany.

The former salt mine Asse II, in the ownership of the GSF-National Research Centre for Environment and Health, is a test disposal facility for low and intermediate level radioactive waste. After the research and development activities were completed, the mine was filled with residual salt material. Microseismic measurements have been performed in the Asse Research Mine since 1980. Until the final closure of the mine, which is expected in 2017, it is planned to fill the mine additionally with MgCl2-rich brine. This is necessary to avoid a possible reliquidating process in larger sizes in the mine which would cause instability of its structural system. To enable that the microseismic monitoring system runs reliably in a salt fluid environment, new three components geophone-probes have been constructed. This is important for the ongoing observation of the geomechanical behavior response during the operational phase of the mine and for the safe work in the mine until the final closure. The renewal process has to be performed in stages without any loss of data. Twelve of these new stations, which are about half of the total number of the existing ones, have already been installed during the last year. Some of the new probes operated in parallel to the old stations. The new probes measure the microseismic activities in the mine and its close environment within a few of hundred meters accurately. The evaluation of the data includes source location, analysis and interpretation of the microseismic events. The results show the microcracking activity in the excavation damaged zone and the stabilizing effect of the filling with saline material clearly