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Rock laboratory seeks safe answer to radioactive waste

Scientists at the Grimsel research laboratory are probing the underground environment

(Keystone Archive)

Scientists at the Grimsel research laboratory in central Switzerland are used to thinking of long-term solutions. After all, the safe disposal of radioactive waste can take tens of thousands of years.

The Grimsel test site lies 450 metres under the Juchlistock in the granite rock of the Bernese Oberland. The tunnel system is about a kilometre long and was opened in 1984.

Organisations from Germany, France, Japan, Spain, Sweden, Taiwan and the USA, as well as the European Union, participate in the programme. The partner organisations either carry out their own experiments or work on projects devised by Switzerland's National Cooperative for the Disposal of Radioactive Waste (Nagra).

"You have to understand the underground environment to build repositories for radioactive waste and ensure their subsequent safety," said Nagra spokesman, Dr Urs Frick.

"Nature does experiments over thousands and thousands of years and a repository has to hold waste for that length of time so you need to investigate natural settings. With the repositories themselves, you can't afford to make mistakes and that's why we have rock laboratories - underground research test sites."

Probing tunnels

The chemical, geological and mechanical properties of the tunnels and caverns are investigated at Grimsel so that the knowledge can be transferred to similar rock sites.

Projects include simulating the heat production of high-level waste; studying how radioactive substances may be released and transported along water-conducting fault zones; evaluating the potential for seismic activity or the effects of underground excavation.

The temperature in the Grimsel laboratory tunnel is a constant 12-13 degrees Centigrade all year round.

"In winter it's dry in here because it's cold outside and in summer it's wet in here because it's warm outside," said Frick. "If you leave a book out here in summer, it turns to pasta."

Lightning underground

One unusual lesson that scientists at Grimsel have learnt through experience is that even 400 metres underground inside a mountain, their experiments are exposed to lightning.

"If lightning strikes the mountain, millions of volts are dispersed through the rock and they come down the water flow zones. If one real mega lightning strikes the ridge above our head, 400 metres up, it can happen that all this electronic equipment is zapped out. We learnt this the hard way."

Switzerland's nuclear power plants and certain materials used in medicine, industry and research account for the country's radioactive waste. Two underground repositories are planned in Switzerland, one for low- and intermediate-level waste and one for high-level and long-lived intermediate-level waste.

"An ideal site has minimum geological disturbance," said Frick. "Then you should have a low conductivity for water. All the rocks are saturated with water in Switzerland but if the water doesn't move, it doesn't transport the radionuclides from a repository.

"I think if you have a large enough, undisturbed rock zone which is really and truly impermeable then you are in a safe spot and if the rock doesn't even crack or fissure, during tectonic movement which is something that might happen over a long time, then it's even better. I'm convinced that there are many places in Switzerland where we could have repositories."

by Vincent Landon

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