Finland is making history as Posiva advances towards starting the world’s first industrial-scale geological final disposal facility for spent nuclear fuel. Through a decades-long partnership, VTT has provided multidisciplinary scientific expertise to Posiva, demonstrating that nuclear waste can be disposed responsibly and safely.
Key facts
The safe disposal of spent nuclear fuel in the bedrock according to International Atomic Energy Agency (IAEA) standards has been a decades-long scientific pursuit.
Posiva’s final disposal solution is based on a passive multi-barrier system. VTT has supported its development and safety demonstration through multidisciplinary expertise in areas including materials research, modelling, monitoring technologies and full-scale testing.
Posiva received a favourable safety assessment from Finland’s Radiation and Nuclear Safety Authority (STUK), taking the world's first industrial-scale final disposal facility closer to an operating licence – a decision on this is expected to be made by the Finnish Government later in 2026.
Posiva Oy is an expert organisation in environmental technology, established in 1995. The company is tasked with handling the final disposal of the spent nuclear fuel generated by its Finnish owners, Teollisuuden Voima (TVO) and Fortum. The company designs, constructs and will operate ONKALO, the encapsulation plant and final disposal facility located on the western coast of Finland at the same site as TVO’s Olkiluoto nuclear power plants.
Solving the global nuclear waste challenge
As the world seeks reliable, low-emission energy to combat climate change, nuclear power remains an important part of the energy mix in many countries. However, expanding nuclear energy has historically been hindered by one central question: what to do with the highly radioactive spent fuel?
No country has yet started industrial-scale geological final disposal of spent nuclear fuel. Supported by a strong national strategy formulated decades ago, consistent funding and transparent public dialogue, Finland is the first to have reached this stage of implementation.
VTT's comprehensive, multidisciplinary research expertise and infrastructure have been key reasons we have chosen to work with them so extensively.
A decades-long, multidisciplinary partnership
VTT's involvement in Finland's nuclear waste programme predates Posiva itself, stretching back nearly 50 years.
“Posiva has used VTT's expertise at every stage, from choosing and modelling potential sites, to conceptual and detailed design, and scaling technology from the lab to full underground scale,” says Erika Holt, Portfolio Lead, Nuclear Energy Back-end at VTT.
Ilkka Poikolainen, President and CEO of Posiva, sees the partnership as a crucial part of the company’s strategy.
“Posiva is a pioneer in this field, and our aim has always been to build a broad network of research institutes, universities and joint projects around us. VTT has comprehensive research expertise and infrastructure that simply doesn't exist anywhere else in Finland. Their multidisciplinary knowledge has been a key reason we have chosen to work with them so extensively,” Poikolainen says.
A historic milestone for the global nuclear sector
In August 2026, Posiva reached a major breakthrough when STUK issued a favourable safety assessment, concluding that the ONKALO facility meets the stringent requirements for an operating licence. The operating licence is now awaiting a final decision by the Finnish Government, with Posiva targeting operational readiness by the end of 2026.
“It's a huge milestone, not just for us but for the entire nuclear sector. It's one of the missing pieces of nuclear power's life cycle, now finally being put in place,” Poikolainen states.
Holt points to a strong national roadmap, accurate investments to the waste management fund and use, and clear roles and responsibilities across the Finland stakeholder ecosystem as the elements for Finland’s success: “Our open, transparent way of working is a big part of why Finland has been able to stay on this path for thirty years without the setbacks other countries have faced.”
Driving innovation for the next century
The key areas of expertise provided by VTT to Posiva include:
Current and future waste inventory and spent fuel calculations, including safety assessment of criticality
Material science: specialised knowledge in the design and performance assessment of engineered barrier materials such as concrete, bentonite clay and canister metals
Long-term safety modelling: mathematical modelling of the geological site, material performance, radionuclide transport and holistic safety case including process scenarios
Sensor technology & AI: development of monitoring sensors coupled with energy-harvesting batteries and the application of AI analysis tools
Microbiology & robotics: insights into microbial impacts on material performance such as canister corrosion, alongside robotic applications for high-precision underground installations
Competence development and knowledge preservation over decades of work.
Reaching a licensed operating facility is not the end of the VTT–Posiva collaboration – both partners describe it as the start of a new phase. ONKALO is expected to remain in operation for more than a hundred years, and Poikolainen emphasises how Posiva has built a strong R&D organisation to support it.
For VTT, this means continuing to work with Posiva on optimising materials, improving monitoring and data systems and managing knowledge across generations. At the same time, VTT is increasingly helping other countries – Sweden, France and Canada are likely next for implementing geological repositories – to leverage Finland’s first-of-a-kind solution for optimising their own programmes.
“With our experience, we can help other countries accelerate their own programmes by adapting Finnish solutions to localised geology and waste streams. But the work with Posiva itself doesn't stop. We'll keep optimising, looking at better materials and improving how the repository is monitored and understood, for as long as it operates, without ever compromising on safety,” Holt concludes.
