A pile of questions

Date

02/10/2009

As from 1 January 2009, the federal government transferred the responsibility for Asse II from the Federal Ministry of Education and Research to the Federal Environment Ministry. Since then, the Federal Office for Radiation Protection (BfS) has been the operator of the mine and operates the Asse II mine according to the strict rules applying to a nuclear facility.

In the mine there exist big problems with stability and the associated risks of an increased inflow of saline solutions. This is due to the numerous cavities caused by extraction that are located close together at the mine’s southern flank. On account of the rock pressure the damaged flank gives in. The adjoining rock and the rock salt between the chambers and the adjoining rock, which is only some metres thick, are damaged by the rock movement. The consequences: About 12,000 litres of saline solutions per day enter the mine through the clefts in the adjoining rock and the loosened salt rock. The entered solution is collected and directed to the collecting basin (on the 658-m level) or, respectively, collected in swamps (725-m and 750-m level).

Furthermore, until 1925, the chambers at the northern flank were backfilled with moist residues from the potash factory. This humidity spreads and has already come into contact with the radioactive waste in chamber 12. Additionally, there is the risk that rock pieces break down from the partially loosened roofs of the chambers.

Retrieval, Relocation, or Complete Backfilling?

In a so-called comparison of options, BfS investigated different options how to decommission Asse II: One option is to retrieve the waste from the mine and to emplace it somewhere else (retrieval). Another option provides for creating new cavities in a deeper part of the salt dome and relocating the waste to this area (relocation). The third option consists of completely backfilling the cavities in the mine with concrete (complete backfilling). The result of the evaluation of the three decommissioning options was published by BfS in January 2010: According to the present state of knowledge, the best variant of how to further deal with the radioactive waste emplaced in the Asse II mine is retrieving the waste.

The closure concept of the former operator Helmholtz Zentrum München (backfilling with a liquid) can be part of an emergency option if there is not enough time for a structured decommissioning as a result of an uncontrollable inflow of brine.

The comparison and evaluation of the decommissioning options is done according to previously established criteria. BfS has developed these criteria, put them up for discussion, and published them in a criteria report. Among the most important fields of evaluation are the safety during the operation of the repository, the long-term safety, the technical feasibility, and the time required for the decommissioning options to be investigated.

To be able to apply the criteria to the individual options, BfS ordered out feasibility studies for each decommissioning option. These studies were introduced in a public workshop in October 2009 and published in the internet. The result of this decision-making process was published in January 2010.