Finland's plan to bury spent nuclear fuel for 100,000 years

"Onkalo" is a Finnish word for a cave or a hollow. It implies something big and deep: you don't know where an onkalo ends or whether it ends at all.

It's a fitting name for a huge grave made in Finland over the last 20 years. Onkalo, which lies 450m (1,500ft) deep inside the bedrock of Olkiluoto island in the southwest of the country, is the world's first permanent storage site for spent nuclear fuel.

The gently winding road to Olkiluoto is lined with pine trees stretching high up to the sky. Nature has come back to life here after five months of winter. The ground is covered by a carpet of small yellow flowers and the air is filled with birdsong. It's almost too beautiful a setting for a major industrial site.

Olkiluoto is home to three nuclear reactors, which stand side by side on the seaside. The third launched only this year, becoming the first new reactor to provide power in Western Europe in 15 years. These reactors, along with two others in Loviisa on the south coast, produce 33% of Finland's electricity.