Asse II was allegedly used as a research mine since 1965. Between 1967 and 1978 radioactive waste was placed in storage. The mine is operated by the German government, and was executed by the Helmholtz Zentrum München. Research was stopped in 1995; between 1995 and 2004 cavinates were filled with salt. After media reports in 2008 about brine contaminated with radioactive caesium-137, plutonium and strontium politicians accused the operator of not having informed the inspecting authorities.
At Sept. 8th, 2008 the responsible ministers of Lower Saxony and the German government concluded to change the operator. The new one, the Bundesamt für Strahlenschutz (federal office for radiation protection), will close the mine
according to atomic law instead of mining law.
Instability of the pit
No columns and struts are used in a salt mine. The extra stress in the remaining salt structure (the pit building) by constructing the chamber is handled in the capping mass. Plasticity effects are taken into account as they naturally occur in salt domes. Significant mechanical stress is built up between the surrounding diapirs and the artificial construction. The capping mass in Asse II moves 15 cm a year which undermines the strength of the construction.
Because of the high number of tunnel constructions and the decades of use, the deformation in Asse II has reached the state that the pressurised salt is losing its stability:
"The supporting construction is softening by creep deformation, plasticity effects and local fractures from the ground pressure." The Institut für Gebirgsmechanik (IfG) in Leipzig which has been monitoring Asse II since 1996 predicted in 2007 that, from the beginning of 2014, an increase in the loss of the load carrying capacity will result in an increased displacement of the capping mass. The shifts may lead to an uncontrollable increase in water inflow and make the continued operation as a dry pit impossible.
In 1979 a report on the stability of the pit building was released by a working group under the leadership of HH Juergens which describes the now imminent scenario of uncontrolled inflow from the capping mass in the southern flank resulting in the subsequent loss of the load carrying capacity. The manager of Asse II in 1979 and his advisers categorised this report as "unscientific" and declared that there were no stability problems .
Water will always flow into a salt mine where the salt barrier in the surrounding structure is breached. This happens when the salt barrier is damaged in the drilling operation or by plasticity deformation of the salt resulting in cracks. Asse II is particularly threatened by water because the salt barrier is in some places only a few meters thick.
For the period 1906 to 1988 there were 29 documented water breaches. They were sometimes successfully sealed off, partly dry, sometimes negligible (less than 0.5 m³ per day). For the current operational security, they are meaningless.
Between 1988 and 2008 32 new entry points were recorded. Part of the solution is explained as coming from the diapir in the south area. The solution is collected at 658, 725, 750 m and since 2005 at 950 m, the inflow is currently (2008) 11.8 m³/Day. The liquid is tested for radioactivity and if levels are passed pumped into a tank truck and transported to the abandoned K+S AG mines (Bad Salzdetfurth, Adolfsglück and Mariaglück) The brine in Mariaglück was tested again at the end of 2008 with results for caesium-137 and tritium
The German mineral- and table water decree (Mineral- und Tafelwasserverordnung, 24.5.2004) is set at 120 milli-Bq/l U-233 or U-235 for drinking water.