Finland's Onkalo, expected to be the world’s first permanent repository for spent nuclear fuel, is almost ready. Located about 430 metres underground in 1.9-billion-year-old bedrock, it will seal radioactive fuel in copper canisters surrounded by bentonite clay. The facility can store 6,500 tonnes of spent fuel and is designed to isolate waste for 1,00,000 years after official approval is granted.