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02.11.2011 09:46

Researchers process the results of a decade-long final disposal experiment

A full-scale final disposal experiment has been conducted in Äspö's rock laboratory in Sweden for ten years now. The processing of the first parts of the experiment, managed by SKB, responsible for the final disposal project in Sweden, started in December 2010. After this, many different samples have been taken in Äspö to obtain more information about how the final disposal system designed in Sweden and Finland will function in actual rock conditions.

What kind of experiment is this?

”The installation of the inner parts of the experiment commenced at the Äspö rock laboratory in 2011 and that of the outer parts in 2003. Six final disposal holes were drilled in the tunnel located deep in the rock, and six full-scale final disposal canisters were placed in the holes. However, the copper iron canisters do not contain any spent nuclear fuel.


The canisters have thermal resistors that have heated the canisters in a similar way as the spent fuel will heat the final disposal canisters. There is a bentonite barrier around the canisters. Prior to launching the experiment, the tunnel was filled with a mixture of swelling bentonite clay and rock material, and the tunnel was sealed with a concrete plug," says Johanna Hansen, R&D Coordinator at Posiva.

Äspö koe2
Here is the Äspö Prototype Repository (final disposal experiment). Its outer part, i.e., the plug, tunnel filling and two final disposal holes are currently being disassembled. One hole still has the canister in place. (Photo: SKB)
 


What is the goal of the experiment?


"The goal is to obtain information about how the final disposal system and all its components function together in actual conditions. The experiment indicates the full-scale function of the canister, the bentonite barrier, the tunnel filling, plug and the rock."

 

When and how will the experiment be disassembled?


"It will be disassembled in two stages. The inner part with four final disposal canisters will still be left where it is. The outer part of the experiment is being disassembled.  The outer part comprises two final disposal holes located at a six-metre distance from each other in the tunnel, which is over 20 metres long.


The disassembly of the outer part commenced in December 2010, and the disassembly and sampling will take about 12 months. While disassembling, several samples have been taken from the tunnel filling material and the bentonite. They investigate how the groundwater that comes from the surrounding rock to the final disposal tunnel has been distributed in the filling material and the barrier and whether there are signs of erosion. In addition, the chemistry of the bentonite barrier is investigated and it is verified that the barrier functions as expected. Usually, bentonite is investigated at a laboratory and its behaviour is assessed with mathematical models. Now it will be verified that the initial assumptions used in the models also apply to nature.


The first canister was removed in July 2011. The removal of the second canister is scheduled for early December. Based on the canisters, it can be seen if the bentonite has affected the shape of the canister."

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Sampling in the eight-metre-deep hole requires precision, and boring the bentonite is time-consuming. Bentonite has sealed the surrounding space of the canister. (Photo: SKB)
 


How has Posiva contributed to the experiment? What advantages does Posiva gain from it?


"Several experts from Posiva have been monitoring the experiment. I myself coordinate the international cooperation in the disassembly project. In addition to Sweden and Finland, the disassembly involves international nuclear waste organisations from France, Switzerland, the UK, Germany, Canada and Japan.

Äspö's experiment provides us with information for our own experiments. For example, we can select the best sensors for our upcoming experiments.

We have participated in planning the disassembly of the experiment and we will utilise the experiment information for preparing demonstrations in ONKALO, for example. Some analyses related to the experiment are prepared at Finnish laboratories."

Johanna Hansen äspö-juttuun web
"The international final disposal experiment can be monitored from Vuojoki manor, but,at times, I must go on site to see how the work is progressing," says Johanna Hansen of Posiva.


What is the Äspö rock laboratory like?


"It is a location for conducting final disposal research in crystalline bedrock more than 400 metres deep. The behaviour of materials in rock conditions can be investigated there, along with factors related to the bedrock, the technical implementation of final disposal, and to long-term safety.


Äspö is situated in the archipelago of the eastern coast of southeastern Sweden, near Oskarshamn. The distance between Äspö and Stockholm is slightly over 300 kilometres. The rock laboratory had about 7,000 visitors in 2010."


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