Why is the BfS pursuing different decommissioning concepts for Morsleben and Asse?

The crucial point in radioactive waste disposal is guaranteeing long-term safety. Long-term safety analyses are based on observations in nature and of the geological past and provide the option to forecast the future development. Thus, estimations can be made on unfavourable long-term developments (such as an acute inflow of water) and their effects on man and environment.

Due to the hazards emanating from radioactive substances, long-term safety analyses need to be carried out for repositories that are to be licensed under nuclear law, before radioactive waste is emplaced. This was not done for the Asse II mine. Corresponding calculations for the Morsleben repository carried out in the GDR did not comply with today’s requirements.

With the help of later long-term safety analyses the BfS could demonstrate that a safe closure of the Morsleben repository is possible with the decommissioning concept applied for. The required proofs have not been confirmed by the competent licensing authority, however, the Ministry for Agriculture and Environment of the federal state of Saxony-Anhalt.

Comparable calculations for the Asse II mine, however, have ruled out the long-term safe storage of radioactive waste in the mine. According to today’s knowledge, the only way to decommission the Asse mine is retrieving the radioactive waste.

Background

Both mines are very old and have a very large total volume of open drifts and chambers. In contrast to the Asse II mine, there are no major problems relating to the mine’s stability in the Morsleben repository. By timely backfilling 27 chambers in the central part of the mine where no waste has been stored with a special type of concrete, the BfS could establish sufficient stability in order to implement a proper plan-approval procedure under nuclear law for the decommissioning of the repository.

There are also differences in terms of the influent solutions and brines. Water probably originating from the overburden only flow into the Morsleben repository at a place in the Marie mine, which is far away from the stored waste. The volume amounts to about 13 cubic metres per year. For comparison: About 12 cubic metres per day enter into the Asse II mine.

Alternative approaches

Like for the Asse II mine, the BfS also examined alternative decommissioning options for the Morsleben repository. In addition to flooding and delaying brine movements by means of artificial pathways, also various possibilities to backfill the repository were examined. The feasibility of retrieving the stored waste was evaluated by experts. However, this would not result in a verifiably gain in safety.

Solely the major backfilling of the mine and the simultaneous building of sealing structures in the vicinity of the emplacement areas fulfilled the requirements for decommissioning under nuclear and mining law. Accordingly, this concept for a plan-approval decision was applied for.