The project would make Sweden one of the first countries in the world, along with Finland, to bury its spent atomic fuel for that length of time in a bid to solve the long-running question of what to do with nuclear waste.

The Scandinavian country plans to build a final repository in Forsmark, home to one of Sweden's three nuclear power plants about 130 kilometres (80 miles) north of Stockholm.

It also plans to build a mid-term storage capsule in Oskarshamn in the south.

The Land and Environment Court granted the Swedish Nuclear Fuel and Waste Management Company (SKB) a permit to begin construction at the sites.

That decision could however still be appealed, with critics concerned over the possibility of radioactive leakage.

The court approved storage facilities "for nuclear waste from the 12 reactors that are part of the current Swedish nuclear power programme," it said in a statement.

The country currently has six reactors in operation at three nuclear power plants, having shut down six others since 1999.

The court said the SKB could deposit "around 6,000 capsules with around 12,000 tonnes of nuclear waste".

"Operations are expected to run for around 70 years but can be extended, if for example the reactors' life spans are extended," the court said.

The waste will be buried in tunnels drilled 500 metres (1,640 feet) underground in the bedrock.

The technique used in Sweden consists of storing two tonnes of spent fuel in copper-coated canisters that weigh 25 tonnes each.

Each canister is welded shut using a special technique and then mechanically deposited in a tunnel in the repository.

A buffer of bentonite clay, a volcanic ash that when mixed with water swells to provide a watertight barrier and protect against earthquakes, is then injected to fill the hole in the rock.

Sweden's centre-right government has vowed to increase nuclear power production equivalent to two nuclear reactors by 2035, with a "massive expansion" to follow by 2045.

But the Land and Environmental Court said the approval granted Thursday "does not cover nuclear waste from any future nuclear power programme".