Decommissioning options assessed

The Federal Office for Radiation Protection (BfS) examined different approaches for decommissioning and filed a plan-approval application for the best suitable option.

Alternative procedures

Other options that have been examined but have not been pursued any further are the following ones:

Flooding

In potash mining targeted flooding is a well-established practice for concluding operation. The safety concept for the Morsleben repository applied for is superior to flooding

• because the supporting effect is greater and thus the pressing of radioactive solution will be lower,
• because solution processes of potash salts that would be accepted in the case of flooding will be minimised.

Hydraulic backfilling

When using this method from salt mining, salt material is washed into the cavities with saline solution. Compared to this option, the backfilling of the Morsleben repository with salt concrete as it has been planned by the BfS has the benefit that, on account of the flow behaviour of the salt concrete, the backfilling of the cavities will be more complete, the stability will be larger and, at the same time, the movement of saline solutions in the mine will be significantly more restricted once the decommissioning process has concluded.

Encapsulation in the near vicinity of the emplacement areas

This concept provided for

• filling porous material into the emplacement areas to store the gases forming,
• constructing high-end sealing constructions to the individual emplacement areas with bentonite and
• carefully sealing weak points on the uppermost level in order to safely prevent inflow of water.

For this purpose constructions should be built for which no technical experience existed at that time. Due to further uncertainties associated with anhydrite layers and non-calculable solution processes in the potash deposits, this concept was given up.

Pore storage facility concept

According to this concept the transport of possible radioactive solutions was supposed to be channelled and delayed by long transport routes filled with porous material. On account of realisation risks and problems in verification the concept was dropped. Thus the necessary complete filling of delay sections and keeping them open for the long term cannot be documented.

Pneumatic stowing

When applying this procedure, as it has already been done for example in the Asse mine, salt material is blown into the cavities with an air flow. Pneumatic stowing has the benefit that the porosity is high, the material settles and the supporting effect occurs a long time after backfilling has taken place. Thus cracks can form and leakages may occur in the surrounding rock. Furthermore, solution processes may occur in the re-forming cavities, in particular those of potash salts.

Discarded options

Further discarded options are:

Retrieval of the waste

The feasibility of retrieving the waste emplaced in the Morsleben repository, the required funds and efforts and the radiation exposure to the Morsleben repository staff and to the population that is associated with retrieval was evaluated by experts.

According to the submitted long-term safety analysis, retrieval of the waste is neither appropriate nor necessary from the BfS point of view. Relocation, removal and interim storage of the recovered waste would be associated with additional radiation exposure to the staff of the Morsleben repository and the population and would thus not lead to a quantifiable increase in safety.

Continuation of operation with later decommissioning

As the BfS irrevocably waived the emplacement of additional waste in Morsleben because this was no longer justifiable, the basis for an optional continuation of operation of Morsleben has ceased to exist.