Step 1: Drilling into selected emplacement chambers

Date

15/09/2011

Depiction of the sealing construction to an emplacement chamber

When drilling into selected emplacement chambers, the following issues will be examined:

1. What is the set-up of the construction the emplacement chambers are sealed with?
2. What are the conditions behind the sealing construction? Can cavities be found with the help of which it will be possible to find out more about the atmospheric conditions in the emplacement chambers?
3. What is the atmosphere in the emplacement chambers like? To what extent has radioactivity spread in the emplacement chambers?
4. Will it be possible to find first indications as to the state the waste packages in the emplacement chambers are in? This is of particular importance for the planning of the machines required for retrieval that are used for the remote-controlled recovery and packaging of the waste.
5. How stable are chambers, roofs and pillars? Can conclusions be drawn as to health and safety during retrieval operations?
6. Are there saline solutions in the chambers?

In this step no samples are taken yet from waste packages and no packages are taken out. Before the chambers are drilled into it must be ensured that the radiation protection provisions for the safety of the staff will be complied with, even under worst-case conditions. For this purpose a radiation protection area will be established and a filter device and a so-called preventer will be installed. The filter device cleans the air of the radiation protection area. The preventer sits directly in front of the bore hole and seals the drillings during the drilling process in order to prevent gases or liquids from escaping from the bore hole.

Cold trial

Drilling device with preventer for drilling into a chamber

Before the first chamber will be drilled into the BfS carried out a “cold trial”: With drillings into a mine area where no radioactive waste has been stored the handling of the drilling equipment, the safety equipment and the examination devices were tested. Thus the best possible safety will be ensured later on when the emplacement chambers will be drilled into.

In the cold trial also deflected drilling and the handling of the geo-physical measuring methods were tested which are to provide information about cavities and the state of the rock.The cold trial concluded successfully in spring 2011. With the help of experiences gained it was possible to improve some technical details and to acquaint the staff with the essential works relating to step 1 of the trial phase (fact finding). You will find more about the course of works in the article "Cold trial – current status of works".

Drilling into emplacement chamber 7 on the 750-m-level

Planned drilling through the sealing construction into chamber 7

Drilling into chamber 7 on the 750-m level which was backfilled with salt grit will involve drilling at first through the chamber sealing and then into the roof, into the chamber floor (level) and into the pillars (walls between the chambers). Parallel to this, examinations will be carried out, e. g. for contamination.

By means of radar measurements in the bore holes, cavities in the chamber are to be detected, which have possibly remained after the chamber was closed at the end of the 1970s. These cavities are then to be drilled into. After this has been done, more information will be available about the atmosphere prevailing in the chamber, the radiological exposure and the state of the chamber. It will also be possible to draw conclusions about the state of the emplaced waste packages.

Set-up measurement containers and setting-up of tarpaulins to separate the work area

During this process it is to be prevented with the help of geo-physical measurements that drums containing radioactive waste are accidentally drilled into. In order for the drilling device and the radiation protection area to be erected on the sloping terrain in front of the chamber, foundations and base plates made from a special type of concrete had to be produced. Decontaminable floor covering was then applied to the floor. Following this, measurement containers, locks and the housing the radiation protection area is separated with from the residual mine were set up.

Drilling into emplacement chamber 12 on the 750-m level

Other than in emplacement chamber 7 on the 750-m level, the residual cavities in chamber 12 on the 750-m level were not backfilled after the radioactive waste had been emplaced. Therefore it is assumed that there are still larger cavities in the chamber. After this chamber has been drilled into, gas samples from the chamber atmosphere can then be taken. Furthermore one reckons with a first impression of the chamber’s interior and the state of single packages gained from video recordings.

However, there is currently still a so-called brine sump (a depression where saline solution accumulates) directly in front of the emplacement chamber. The solution in the sump is radiologically contaminated. Before it will be possible to drill into the chamber the area in front of it must therefore be decontaminated and remediated. On account of these necessary preparations, chamber 7 will thus be the first one to be drilled into.