After passing through a security gate, the van descends into a tunnel that burrows under the forests of Olkiluoto, an island off Finland’s west coast. The wheels crunch on crushed stone as a gray, wet October day gives way to darkness.
“Welcome to Onkalo,” deadpans Antti Mustonen, a geologist here. Onkalo—“cavity” or “pit” in Finnish—will be the world’s first permanent disposal site for high-level nuclear waste, and a triumph for Finland.