“Onkalo will outlast every human institution that has ever existed — and it must.” — Posiva Oy, on designing a 100,000-year solution
Finland is on the verge of commencing operations at Onkalo — the world’s first permanent deep geological repository (DGR) for highly radioactive spent nuclear fuel. Located on Olkiluoto Island in the municipality of Eurajoki, western Finland, the facility has been under construction since 2004. Finland’s nuclear safety authority is expected to grant the operating licence within months of April 2026. The name Onkalo means “small cave” or “cavity” in Finnish.
Built 400–450 metres underground inside bedrock that is 1.9 billion years old, Onkalo is designed to isolate spent nuclear fuel for up to 100,000 years — entirely without human supervision. Once sealed, it relies solely on geological and engineered barriers. Finland’s model is now closely watched by governments and energy planners worldwide as nuclear power experiences a global resurgence.
☢️ The Nuclear Waste Problem: Scale and Stakes
Since commercial nuclear power began in the 1950s, reactors worldwide have generated approximately 430,000 tonnes of spent nuclear fuel, according to the IAEA. While this fuel can no longer sustain a fission reaction, it remains intensely radioactive — emitting harmful gamma radiation, alpha particles, and heat — for thousands to hundreds of thousands of years.
Currently, most countries store spent fuel in temporary water-cooled pools (to dissipate residual heat) and then in dry cask storage on the surface. Both methods are safe only for limited periods — decades, not geological timescales. The United States alone faces an estimated USD 44.5 billion liability from accumulated spent fuel with no permanent storage in sight.
The risks of continued temporary storage include radiation leakage from ageing containment, groundwater contamination, vulnerability to surface weather events, and the challenge of maintaining institutional memory across generations. This unresolved waste question has been one of the strongest objections against expanding nuclear power globally.
Think of spent nuclear fuel like the ash from a fire — except this ash stays dangerously hot for 100,000 years. You can’t just leave it in a bucket forever. Most countries have been doing exactly that for 70 years. Onkalo is the world’s first serious attempt to put the ash somewhere permanently safe — deep inside ancient rock that has been geologically stable for nearly 2 billion years.
📜 How Finland Solved Its Nuclear Waste Problem
Finland’s path to Onkalo was shaped by deliberate policy choices over four decades. The Nuclear Energy Act of 1987 established a dedicated nuclear waste management fund, with charges levied on nuclear electricity production. A pivotal 1994 amendment mandated that all nuclear waste produced in Finland must be treated, stored, and permanently disposed of within Finland — prohibiting both exports and imports. This legal obligation forced Finnish operators to fund and implement a long-term domestic solution.
In 1995, the two Finnish nuclear utilities — Teollisuuden Voima Oyj (TVO) and Fortum Power and Heat Oy — established Posiva Oy as a joint company for final disposal. Posiva surveyed over 100 candidate sites from 1987 to 1999, shortlisting five. Olkiluoto in Eurajoki was selected in 2000, following municipal consultations and the “Vuojoki Agreement” — which included economic benefits for local communities, a globally cited model of transparent public engagement.
The construction licence was granted in 2015 — the first time any country had issued such a licence for a DGR. By 2014, Finnish operators had already accumulated €2.38 billion in the State Nuclear Waste Management Fund. Operating and sealing the facility over a century is estimated to cost an additional €4 billion.
⚙️ Engineering the Repository: The KBS-3 Multi-Barrier System
Onkalo uses the KBS-3 method (kärnbränslesäkerhet — nuclear fuel safety), developed by Sweden’s SKB (Svensk Kärnbränslehantering AB) in close cooperation with Posiva. The method was inspired by natural analogues — including the Oklo natural nuclear reactor in Gabon and the Cigar Lake uranium mine in Saskatchewan, Canada — where radioactive material remained geologically contained for billions of years without human intervention.
| Barrier Layer | Material | Role / Function |
|---|---|---|
| 1st — Inner Insert | Boron steel canister with cast-iron insert | Structural support; holds 12 fuel assemblies |
| 2nd — Outer Shell | Copper capsule (corrosion-resistant) | Resists oxidation under low-oxygen deep bedrock conditions for millennia |
| 3rd — Buffer | Bentonite clay | Swells when wet, sealing gaps and blocking groundwater movement around capsule |
| 4th — Final Barrier | 1.9-billion-year-old crystalline granite (400–450m depth) | Protection against seismic activity, ice ages, glacial erosion, and surface events |
Mnemonic “SCBG”: Steel canister → Copper capsule → Bentonite clay → Granite bedrock. “Some Countries Bury Garbage.”
The principle of passive safety is central to the design: once sealed, the repository functions without any maintenance, monitoring, or human action. Even if one barrier fails, the remaining three continue to isolate radiation. The facility’s tunnels will eventually stretch approximately 50 kilometres in total. The repository is expected to operate until the 2120s, after which it will be permanently sealed.
📋 Licensing Process & Current Status (2026)
Posiva submitted its operating licence application in December 2021. Finland’s nuclear safety regulator, STUK (Säteilyturvakeskus), is assessing the application. In December 2024, STUK delayed its safety assessment by one year — citing incomplete technical documentation — with a revised deadline of 31 December 2025. As of April 2026, the final operating licence decision is anticipated within months.
Prior to the full licence grant, Posiva conducted a trial run in late 2024, successfully encapsulating and emplacing the first three canisters containing non-radioactive test elements. This validated the entire encapsulation, transport, and emplacement process. Once the licence is granted, Phase 4 — actual burial of spent nuclear fuel — will commence.
The IAEA Director General has described Onkalo as a “game changer” for the nuclear industry, demonstrating a technically credible and publicly accepted permanent waste disposal solution.
Don’t confuse: Construction licence (granted 2015) with Operating licence (expected 2026). Onkalo has been under construction since 2004 — it is NOT yet operational as of April 2026. The operating licence from STUK is the final step before actual spent fuel burial begins (Phase 4).
🌍 Global Comparison: Where Other Countries Stand
Finland is the first country to implement a DGR for spent nuclear fuel, but several others are in various stages of development.
| Country | Site / Project | Method / Operator | Expected Timeline |
|---|---|---|---|
| Finland 🥇 | Onkalo, Olkiluoto | KBS-3 / Posiva Oy | Operational 2026 (licence pending) |
| Sweden | Forsmark, Östhammar | KBS-3 / SKB | Construction started 2024; operations ~2042 |
| France | Cigéo (Meuse/Haute-Marne) | Andra | Expected commissioning 2035 |
| USA | Yucca Mountain (shelved 2010) | DOE | No active DGR; USD 44.5B liability; deep borehole research funded 2025 |
| India | No DGR programme | DAE (closed fuel cycle) | Spent fuel reprocessed; permanent disposal deferred |
Sweden’s Forsmark DGR was greenlit partly because of a legal rule requiring reactor operators to have a credible disposal plan before receiving operating licences. This “no plan, no permit” approach directly incentivised industry to invest in long-term waste solutions. Could similar regulatory mandates work in India, where the closed fuel cycle strategy currently defers permanent disposal?
🌍 Significance for the Nuclear Energy Renaissance
Nuclear power is experiencing a significant global resurgence, driven by climate commitments and post-2022 energy security concerns. The IAEA and IEA project that global nuclear capacity could more than double by 2050 to meet net-zero targets. New reactor designs — including Small Modular Reactors (SMRs) — are being developed across North America, Europe, and Asia.
However, the unresolved waste question has historically been a major barrier to public acceptance of nuclear expansion. Finland’s Onkalo directly addresses this objection. Finland’s success illustrates four key policy lessons: an early legislative mandate for domestic disposal (1994 Act amendment), sustained multi-decade funding through a dedicated waste fund, transparent public engagement at the local level (Vuojoki Agreement), and rigorous independent regulatory oversight by STUK.
Onkalo raises a profound ethical question: Is it right for one generation to create radioactive waste that lasts 100,000 years, even if we can bury it safely? Finland’s answer — build the best solution available now, with transparent governance and full funding — is one model. Others argue that future generations should not inherit any nuclear burden. This intergenerational equity debate is central to nuclear policy discussions worldwide.
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Onkalo is located on Olkiluoto Island in the municipality of Eurajoki on Finland’s west coast — where the Olkiluoto nuclear power plant also operates.
The four KBS-3 barriers are: steel canister, copper capsule, bentonite clay, and granite bedrock. Concrete is not part of the KBS-3 system — the design relies on natural and passive barriers, not engineered concrete structures.
Onkalo is designed to safely isolate spent nuclear fuel for up to 100,000 years — far longer than any existing temporary storage solution, which is considered safe only for decades.
The KBS-3 method was developed by Sweden’s SKB (Svensk Kärnbränslehantering AB). Posiva Oy adopted and implemented this method for Onkalo in close cooperation with SKB.
Sweden’s Forsmark DGR began construction in late 2024 and is expected to become operational around 2042, using the same KBS-3 method as Onkalo. France’s Cigéo is a different type — for high-level waste, not exclusively spent fuel — and is expected by 2035.
