SAINT-URSANNE, SWITZERLAND (AFP) – Above-ground storage of radioactive waste is a risky business, but the Swiss believe they have found the solution: burying spent nuclear fuel in clay deep underground.

The Mont Terri International Laboratory was built to study the effects of burying radioactive waste in clay located 300m below the surface near Saint-Ursanne in the northwestern Jura region.

The underground laboratory stretches over 1.2 km of tunnels.

Niches along the way, each about 5m high, are filled with various storage simulations containing small amounts of radioactive material monitored by thousands of sensors.

More than 170 experiments were conducted to simulate the different phases of the process – waste positioning, tunnel closure, surveillance – and to reproduce every physical and chemical effect imaginable.

According to experts, it takes 200,000 years for radioactivity in the most toxic wastes to return to natural levels.

Geologist Christophe Nussbaum, who heads the lab, said the researchers wanted to determine what the possible effects might be “on storage, which must last nearly a million years.”

That “is the length of time we need to ensure secure detention,” he said, adding that “the results so far are positive.”

Three potential sites in the northeast, near the German border, have been identified to host such radioactive waste.

The Swiss nuclear power plant operators are expected to decide on their preferred option in September.

The Swiss government won’t make the final decision until 2029, but that probably won’t be the last word as the matter would likely end up in a referendum under Switzerland’s famous system of direct democracy.

Despite the lengthy process, the environmentalist Greenpeace is moving too fast.

“There are countless technical issues that remain unresolved,” Mr. Florian Kasser, in charge of nuclear issues at the environmental activist group, told AFP.