Announcement - Asse II mine
19 July 2017: Diverted borehole started in context of fact finding
On 10 July 2017, borehole B-7/750-BA was started in the context of fact finding in storage chamber 7 on the 750m level. This borehole is a sidetracked well, which is to be further developed from borehole B-7/750-B5 (one of several fan shaped boreholes above the chamber). Through the additional use of “drill collars” following the force of gravity, the borehole will take an arc-shaped course directly to the storage chamber. With the help of this borehole coming from above, any available cavities should be located. So as to reduce the probability of missing any available cavities, the highest point of the storage chamber will be used as an approximate target; this has been calculated using (georadar) measurements taken from previous boreholes. When complete, the borehole will have a total length of around 45 metres. The aim of the borehole is:
- to obtain samples from the chamber atmosphere so as to further investigate this for radiologically and conventionally hazardous materials and any potential capacity for explosion and
- to obtain confirmed statements about the presence and (if possible) the dimensions of cavities in the storage chamber.
If larger cavities are located, these are to be measured with an optical measurement process if possible and their structural stability investigated.
In the context of fact finding, storage chamber 7 is currently being investigated as regards the following issues:
- What is the condition of the storage chamber in terms of mining?
- How high is the level of radioactive exposure in the chamber atmosphere?
- Does the chamber atmosphere contain hazardous or explosive gases?
Since June 2012, the investigative boreholes have run to storage chamber 7. The results of the boreholes drilled so far show that to date no explosive gas mixes have been ascertained; nor are there radioactivity levels that would warrant any retrieval. Tears in the chamber ceiling show however that the chamber is subjected to powerful mechanical forces in the rocks.
In the context of further fact finding measures, chamber-specific investigation programmes are to be compiled for each of the 13 storage chambers. These programmes must consider that the available knowledge about the individual chambers varies greatly in its depth.
Facts and figures from storage chamber 7
Storage chamber 7 was established in 1919 and 1920 through salt mining. It is around 33 metres wide, 59 metres long and around 10 metres high in the middle. The original chamber volume was estimated to be 18,800 cubic metres. The chamber is separated from the salt mining chambers at the 725 metre level by a strong 14-metre layer of halite (suspended).
Between 1977 and 1978, the storage chamber was filled with 4,356 waste containers. This amounts to a waste volume of 3,993 cubic metres. Stored here are 1,079 200l barrels, 139 400l barrels and 3,138 concrete-encased waste containers (lost concrete shielding). Firstly, waste in lost concrete shielding was stacked in the chamber in such as way that a defined space was formed in the chamber. The 200l and 400l barrels were then tipped into this and covered with salt. Lost concrete shielding was then once again stacked right to the chamber ceiling.
The remaining cavity of the chamber was then filled as far as possible with salt with the help of an air current (pneumatic backfill).
A glimpse into the working area for fact finding