Finland has spent decades building a tunnel 430 metres into 1.9-billion-year-old bedrock to store nuclear waste for 100,000 years — and the current plan is to seal it, leave no marker, and hope no fut

Key Points:

• Finland's Onkalo facility on Olkiluoto Island is the world's first deep geological repository designed to store spent nuclear fuel safely for about 100,000 years, using multiple engineered barriers including copper canisters, bentonite clay, and stable granite bedrock.
• The project, managed by Posiva, has progressed since the 1980s with construction starting in 2004 and operational disposal expected in the mid-2020s, despite some timeline delays.
• A key challenge is the “marker question”: after sealing the site, Finland plans to leave no warning markers on the surface, believing that any signs might attract future humans rather than deter them, due to the difficulty of communicating danger across such vast time spans.
• Onkalo addresses only Finland’s existing spent fuel and does not solve global nuclear waste issues or the political debates around nuclear power; other countries are at earlier stages of similar disposal projects.
• The immediate focus is on beginning the emplacement of spent fuel canisters, while decisions about surface marking and final site closure remain decades away.