Switzerland relies on the deep disposal of nuclear waste, in clay.

The deposit hundreds of meters underground is a huge project not without challenges.

Sweden and Finland will bury the waste in granite.

Switzerland opts for Opalinus clay which was formed in the Jurassic period, some 175 million years ago, when the north of the country was covered by a shallow sea.

Why clay?

This clay is very waterproof.

And, in contact with humidity, a large part of the clay minerals will swell, sealing any cracks.

Experts consider that it can be practically excluded that harmful substances are transported by water.

On the other hand, in waste, most radionuclides (radioactive substances) have a positive charge and attach themselves to clay minerals.

The few negative radionuclides move extremely slowly in clay.

Which therefore has the property of confining radioactive substances effectively and over long periods of time.

As this clay is a rock of low hardness, it presents challenges in terms of construction, but technical solutions exist.

In addition, during the placement of high-level waste which still initially releases considerable heat, care must be taken that this is not transferred to the clay, in order to maintain its confinement properties.

Close to Germany

It is in a strip in the north-east of Switzerland near the German border that the requirements relating to the thickness and depth of the clay are best met, according to the experts.

It is in this zone that the three potential sites for a deep repository are located, called Jura-East, North of the Lägern and Zurich North-East.

In these regions, the clay layer is found at a depth ranging from about 400 to 1,000 meters.

To protect it from the consequences of glaciation and erosion, the repository will be located several hundred meters deep.

Just before being transported to the deep repository, the waste will be transferred to storage containers, which will themselves be sealed off with bentonite aggregate, a type of clay which, in the event of moisture infiltration, swells and seal the cracks.

During the site selection process, collective discussions were held with representatives of civil society and of the cantons and municipalities concerned, including from Germany due to their proximity.

These discussions made it possible to establish that the German participants were in principle opposed to any landfill project near their homes, according to Uelli Müller, who led the Jura-Est discussion group.

Referendum?

“All sites are technically and geologically adequate.

We must now see which one offers the greatest margin in terms of safety, ”explained Felix Glauser, spokesman for Nagra, in charge of radioactive waste management.

Nagra will announce in the fall, probably in mid-September, which site is in its opinion the most suitable.

The final decision will be taken by the Federal Council.

To this end, Nagra will have to submit a request for general authorization by 2024. The Federal Council will probably make its decision in 2029 and will submit it to the Federal Assembly for approval in 2030. The Swiss will also have to decide in a referendum on the subject if the opponents collect 50,000 signatures.

The authorities estimate the costs of phasing out nuclear power at 23 billion Swiss francs (about 22.6 billion euros), including 19 billion Swiss francs (18.7 billion euros) for the management of radioactive waste, which will be stored on an area estimated at 2 km².

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