Finland's Nuclear Vault Is Designed to Be Sealed Forever

Finland's Onkalo repository is being prepared for a future in which its tunnels are closed. Depth is only one part of the design: solid fuel, cast iron, copper, bentonite and investigated bedrock have different roles. We examine groundwater pathways, heat, spacing, backfilling and the evidence behind long-term safety assessments. Status is described as of October 2026: a safety assessment, an operating licence and permission to start disposal are separate milestones. This film does not claim that spent-fuel disposal has already begun. Map Motive explores how geography and engineering shape everyday life. Subscribe for more documentary explainers. CHAPTERS 00:00 A facility designed for closure 00:49 What spent fuel still does 02:36 Solid fuel and the canister 03:48 The bentonite buffer 04:37 Investigating the bedrock 06:14 Heat and spacing 07:00 Backfill and future conditions 08:39 Trial operations and licensing 10:17 Protection after closure RESEARCH SOURCES Posiva — Multi-barrier concept: https://www.posiva.fi/en/index/news/p... Posiva — Disposal canister: https://www.posiva.fi/en/index/finald... Posiva — Buffer: https://www.posiva.fi/en/index/finald... VISUAL SOURCES & LICENCES Visual excerpts/photos are cropped, scaled, muted where applicable and combined with original explanation. Adapted CC BY-SA visuals retain the source licence. No source endorsement is implied. Posiva Oy — CC BY 3.0:    • Excavation of final disposal tunnels start...   ;    • Posiva’s Spent Fuel Repository is a "Game ...   ;    • The new jogging buddy inside ONKALO®   ;    • The first in the world – what is the purpo...   ;    • This is how buffer transfer and installati...   ;    • Remote-controlled movers operate between c...   ;    • The final disposal capsule is securely sea...   kallerna — CC BY-SA 4.0: https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... kallerna — Public domain: https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... IAEA Imagebank — CC BY 2.0: https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... Teemu Väisänen — CC BY-SA 4.0: https://commons.wikimedia.org/?curid=... kallerna — CC BY-SA 3.0: https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... IAEA Imagebank — CC BY-SA 2.0: https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... ; https://commons.wikimedia.org/?curid=... Marabu — CC0: https://commons.wikimedia.org/?curid=... Licence terms: http://creativecommons.org/publicdoma... ; https://creativecommons.org/licenses/... ; https://creativecommons.org/licenses/... ; https://creativecommons.org/licenses/... ; https://creativecommons.org/licenses/... ; https://creativecommons.org/licenses/... Maps: Natural Earth (public domain). Original explanatory animation and music: Map Motive. Thumbnail: AI-assisted editorial illustration.