27.11.2009 08:43

A new research niche in ONKALO

A new research niche has been completed this fall in the underground characterisation facility ONKALO. The research niche, which is the third in total, has been excavated at the tunnel length of 3620 metres and is in effect a side tunnel which reaches circa 60 metres sideways from the main tunnel. The experiences and knowledge obtained from the excavation of the research niche (the EDZ research niche) can be utilised in the future when the excavation of the actual final disposal tunnels will commence.


ONKALO-geologist Kimmo Kemppainen, why has the EDZ research niche been excavated?

– EDZ stands for 'excavation disturbed zone', and these zones develop on the walls of the tunnel as a result of the excavation. Thus, the EDZ research niche serves the purpose of examining which kinds of drilling and charging methods produce the least amount of disturbance to the tunnel walls. This experimentation will help increase the quality of the excavation methods so as to cause as little disturbance to the bedrock as possible. The implementation of the research niche was done by applying different working methods and a detailed plan was followed to ensure no oversights would occur during the process.


What exactly does the research conducted in the EDZ research niche entail?

– Before the excavation begun two drill holes were made, one into the tunnel profile and the other approximately a metre outside of the profile. Similar measurements to those from other drill holes of ONKALO were made, namely geophysical and hydrogeological measurements. After the excavation was completed, new measurements were made from the drill hole outside of the tunnel profile to compare the before and after results. A seismological measurement of the research niche has also been undertaken - to locate the disturbance zone - coupled with ground radar scanning. The research was concluded at the beginning of November. In the future, the research niche in question will be transformed into a research niche for bedrock mechanics. More excavation of the tunnel will therefore be made to ensure favourable conditions for the upcoming research. Additional research will begin immediately and the excavation will be continued after the installation of measurement equipment.


How will the research results be utilised in the future?

The EDZ research niche is smaller than the regular tunnel in its measurements. The experience acquired now will be put to use with the implementation of the final disposal tunnels, when the quality of the excavation must be of a very high quality to ensure safe final disposal of spent nuclear fuel.

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