29.10.2014 13:21

Countries sparring each other

Cooperation between countries planning final disposal of spent nuclear fuel benefits all parties. Examples of achievements include a bentonite buffer installation vehicle, a canister transfer and installation vehicle, and the deposition tunnel plugging test.

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The development of the bentonite mounting device is a good example of the results of the international cooperation.

The network of international experts plays an important role in successful final disposal operations. According to director Tiina Jalonen from Posiva, the support of the scientific community greatly helps gain general acceptability for the project.

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Director Tiina Jalonen from Posiva.
“International cooperation is vital when selecting a disposal location, developing the overall concept and designing the facilities, as all these phases require extensive research, development and design work. Our work is validated when operators in other parts of the world come to similar conclusions”, Jalonen says.

The bentonite buffer installation vehicle which arrived at Olkiluoto in March 2014 is a good example of the fruits of international cooperation. The vehicle was developed as part of the LUCOEX project partially financed by the EU.

Even though the vehicle was entirely designed and built in Finland, a large number of international specialists followed the development work. The LUCOEX project is a joint effort between Posiva and three other operators currently developing their own final disposal projects: SKB from Sweden, Andra from France, and Nagra from Switzerland.

“Each participant in the LUCOEX project has opened their own work to others and given their input to the others’ projects. External final disposal experts called in to review the projects have also monitored and commented on the work”, says development engineer Keijo Haapala from Posiva.

During the last six months, the 20-tonne vehicle has received software updates and testing in actual operating conditions.

“Based on preliminary tests, the required precision and speed can now be achieved when installing buffer blocks into the deposition hole”, Haapala says.

Canister installation vehicle also completed

The canister transfer and installation vehicle, designed and built in Finland, arrived at Olkiluoto in May 2014. The prototype is the result of four years' work, and will be used to test the installation of final disposal canisters into the deposition hole. The test results will be used to develop the system further, and the final vehicle will be built based on the current prototype.

A prototype of the canister installation device.

The device weighs approximately 103 tonnes when loaded with a canister, but is filled with finely tuned mechanics. The device’s multiple safety features are the result of careful design.

“The design of the vehicle optimally fits the size of the tunnel. Plenty of attention has also been given to easy operation, precision and safety”, says design engineer Jouni Tiainen from Posiva.

The canister installation vehicle is used to place the spent nuclear fuel into the deposition hole lined with bentonite clay. The required accuracy is 10 millimetres. The device will be used to transport canisters from the interim storage facility, located more than 400 metres below ground, to the deposition tunnel.

Posiva leading the plug test project

A plugging test with a massive reinforced steel plug being built at the final disposal depth will also be performed in Olkiluoto.

Development engineer Petri Koho from Posiva says that the plug to be constructed in the front section of a deposition tunnel will be tested by increasing the water pressure in the tunnel to the level of ground water pressure prevailing in the deposition tunnels.

POPLU tunnel under construction Photo Posiva
Demonstrationtunnel 4 under construction September 2013.

The plugging test will be part of the international DOPAS project coordinated by Posiva. The project includes plugging tests of similar magnitude to be performed in Finland, Sweden, France, Germany and the Czech Republic.

“Sweden is proceeding ahead of others. SKB initiated the plugging test in March 2013 and is currently in its follow-up stage. In France, a test tunnel has been constructed above ground. In the Czech Republic, construction will take place this autumn, and in Germany, testing is at the planning stage”, Koho says.

“Joint projects are important to us. Experiences shared by specialists from various countries give us solid information.”

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