Experts debated realisation options for the planned Asse recovery shaft

According to knowledge gained so far and in spite of the existing complex geological conditions, the realisation of the planned recovery shaft is not questioned. However, for a concrete and safe planning, more exploration work is necessary. Those are the central results from a professional workshop to which the Federal Office for Radiation Protection (BfS) had invited about 50 experts from different areas on 13 October 2015.

Incorrect maps and assumptions of the previous operator require careful exploration works

To check the maps and data of the previous operator to see if they are correct, the BfS is exploring the underground of the Asse mountain range. The findings are necessary to guarantee safe shaft planning.

According to initial analyses it became clear that part of the available exploration results deviate from original assumptions. This is consistent with the experiences gained in nearly all sub-projects of the Asse decommissioning.

In the case of an unprecedented task such as the recovery of the Asse wastes which involves many imponderables and uncertainties, the discovery of new facts and conditions is part of the daily job.

Exploration works also form the basis for the construction of infrastructure rooms

There was a strong consensus amongst the experts that the available findings did not question the construction of a recovery shaft. In the opinion of all experts, further explorations ought to be conducted, however. This is also essential to clarify how additional infrastructure rooms can be built underground. Infrastructure rooms are places inside the mine openings where e.g. devices and machines can be kept.

Wide exchange amongst experts from universities, authorities, institutes and shaft construction companies

The meeting treated the crucial question as to how the planned second shaft can be constructed under the geological and technical conditions. The approach selected by the BfS of initially carrying out exploration drillings to determine safe planning data for the construction of the recovery shaft, was considered reasonable in the workshop.

Apart from the BfS and the Asse-GmbH, further, project-independent experts from universities, authorities, institutes and shaft construction companies took part in the debates:

• Working Group Options Retrieval Comparison of Options (AGO)
• Federal Environment Ministry
• Federal Institute for Geosciences and Natural Resources (BGR)
• DMT GmbH & Co. KG
• ERCOSPLAN - Ingenieurgesellschaft Geotechnik und Bergbau mbH
• Institut für Gebirgsmechanik GmbH (IfG)
• K-UTEC AG Salt Technologies
• Landesamt für Bergbau, Energie und Geologie
• Lower Saxon Environment Ministry
• Clausthal University of Technology
• TU Bergakademie Freiberg The University of Resources
• Thyssen Schachtbau Corporation

With this meeting, the BfS has continued the proven practice to debate central topics relating to the decommissioning of the Asse mine on a wide technical basis. The BfS already organised similar meetings (in German) on the topics "emergency preparedness" or "speeding up retrieval".

Background

Shaft 5 is a vital component of the Asse mine’s decommissioning. It is planned to recover the wastes via an additional second shaft.

The new connection between mine openings and surface guarantees more safety in radiation protection. On the other hand, the additional shaft helps more people and machines simultaneously working for retrieval than is now permitted by the existing infrastructure with one main shaft only.

Status of exploration work for the recovery shaft

So far drill cores and measured data is available from one surface, vertical exploration drilling that reached a depth of 900 metres. Also first data is available from two further, underground drillings.

In a depth of 574 metres, one drilled horizontally from the mine openings towards the planned shaft. Further drillings in a depth of 700 metres are currently in preparation.