Stabilisation of the mine by backfilling of cavities no longer required

The objective of remediating the Asse mine is its safe decommissioning. According to the present state of knowledge, this can only be ensured if the radioactive waste is retrieved from the mine. The Bundestag also decided to retrieve the waste unless there are imperative reasons against it. Various preparatory and planning works for retrieval are currently underway, such as

• those relating to the variants to access the emplacement chambers to retrieve the waste,
• works carried out during the fact-finding process,
• those relating to the recovery technique,
• those relating to shaft sinking and the conditioning plant as well as
• those relating to the interim storage facility for the retrieved waste.

At the same time, precautionary measures need to be taken for the event of an uncontrollable inflow of water – which cannot be ruled out – and to stabilise the mine. The precautionary measures have been pursued since 2010 and have been subject to public discussion since. The BfS has continuously informed the Asse II Accompanying Group about these plans, has laid itself open to the group's criticism and has incorporated suggestions in the concept of precautionary measures.

The necessary precautionary and stabilisation measures include the backfilling of mine cavities where no radioactive waste has been stored and that are no longer required. This is to stabilise the entire mine and reduce the probability of an uncontrollable inflow of water and its consequences. Carrying out these measures is therefore key for the implementation of retrieval. Based on the current status, it will take until about 2021 to complete these works.

Stabilisation of the 750-m level and of the 725-m level planned

As part of the precautionary and stabilising measures, it is also planned to backfill cavities on the 750-m level and the 725-m level, where a major part of the waste has been stored. For safety reasons, these works need to be carried out to protect the population and the staff. The mine area is dilapidated and needs to be stabilised before the waste is retrieved. Moreover, the supervisory authorities demand that the BfS implement these works. The supervisory body has approved the first part of these works.

Stabilisation with concrete

The BfS had initially postponed the works in order to discuss the procedure again with the accompanying bodies of the Asse mine, who had criticised the works. Expert talks relating to the planned works started to take place in 2010. They were resumed at the workshop on radiation protection in 2012 and, since April 2013, matters have been discussed with the bodies involved. The BfS has also incorporated suggestions especially by the Comparison of Options – Retrieval - Working Group. Furthermore, the BfS had reported to its technical and legal supervisory board, the Federal Environment Ministry, about the status of planning and had requested the BMU to give its approval to the planned works.

In co-ordination with the Federal Environment Ministry, the stabilisation measures in front of chamber 10 on the 750-m level started on 13 August 2013. The works do not include the backfilling of emplacement chambers. Once the works in front of chamber 10 have concluded, it is planned to backfill the area in front of chamber 12, too. This is because these areas have been particularly stressed over the decades of keeping the mine open and have to be stabilised first. Beside chamber 12 there is additionally a so-called blind shaft which is also to be backfilled within the framework of stabilisation. Before stabilising the blind shaft, the area in front of chamber 12 needs to be backfilled.

Retrieval works are not impaired

The retrieval works are not impaired by the planned works on the 750-m level. Currently a concept on possible variants to access the emplacement chambers for the purpose of retrieving the waste are being developed with the objective to find different options for an optimal access to the waste stored in the emplacement chambers. This includes access variants via the 750-m level and via levels underneath the 750-m level.

All variants require the prior stabilisation of the currently existing areas on the 750-m level and on the 725-m level. Should the option of retrieving the waste from the 750-m level work, this area would anyway have to be stabilised with concrete and be driven in a larger crosscut than the present one.