This $1.16 billion hole in the ground is humanity's best plan for nuclear waste, and it's opening in the world's happiest country - here's what you need to know

Finland nuclear waste repository: For decades, countries around the world have faced the same difficult question: what should be done with radioactive nuclear waste that remains dangerous for thousands of years?

Finland believes it may finally have an answer.

What Is Onkalo and Why Is the World Watching Finland's Nuclear Waste Project

More than 433 meters beneath the surface in southwestern Finland, a massive underground facility called Onkalo is nearing completion. Built deep inside 1.9-billion-year-old bedrock, the project is expected to become the world's first permanent repository for spent nuclear fuel, as per a report.


After years of planning, construction, and safety reviews, the €1 billion ($1.16 billion) facility could begin operations as early as the end of this year or early next year, as per a Science Alert report.

The journey into Onkalo begins with an elevator ride hundreds of meters below ground. At the bottom sits a vast network of tunnels carved into ancient rock near Eurajoki, not far from the Olkiluoto nuclear power plant.

This underground repository has been designed to permanently store spent nuclear fuel from Finland's five nuclear reactors, three of which are located at Olkiluoto, as per the Science Alert report.

The Finnish Radiation and Nuclear Safety Authority (STUK) is expected to deliver its final assessment in June. Once approved, an operating license can be granted.

Why Finland Built Onkalo - Nuclear Waste Has Been a Global Problem for Decades

Since nuclear power plants first appeared in the 1950s, countries have largely relied on temporary storage solutions for radioactive waste.

Finland is expected to become the first country to open a permanent underground storage facility for spent nuclear fuel.

How Finland Plans to Store Radioactive Waste for 100,000 Years

The waste that will be stored at Onkalo is currently kept in cooling pools at an interim storage site next to the Baltic Sea.

According to TVO Chief Executive Philippe Bordarier, this fuel will be the first to be moved into the repository, as per the Science Alert report.

The scale of the project is difficult to imagine.

Onkalo has enough capacity to store 6,500 tons of uranium and is expected to receive spent fuel for roughly 100 years.

After that, the repository will be sealed.

Why Onkalo Was Built 433 Meters Beneath Ancient Bedrock

The goal is to keep the radioactive material isolated and secure for at least 100,000 years.

As Posiva chemist Lauri Parviainen explained, the waste will remain highly radioactive for tens of thousands of years before gradually declining to levels similar to the uranium ore from which it originally came, as per the Science Alert report.

Before entering the underground repository, spent fuel will be sealed inside highly corrosion-resistant copper canisters. The canisters will then be lowered into holes drilled deep into the bedrock.

Those holes will be packed with bentonite clay, creating another protective barrier around the waste. Once a disposal tunnel is full, it will be closed using a steel-reinforced concrete plug.

The system relies on multiple layers of protection designed to work together for extremely long periods of time.

Safety experts have evaluated scenarios stretching up to one million years into the future. According to STUK expert Jarkko Kyllonen, the first 10,000 years are particularly important because the protective capsules must remain intact during the period when the waste poses the greatest hazard, as per the Science Alert report.

Potential risks include corrosion of the copper canisters and geological activity during future ice ages that could damage the storage system.

Public Support for Onkalo and Finland's Growing Confidence in Nuclear Energy

Despite those concerns, Kyllonen said years of safety assessments have produced positive results.

While similar projects have faced significant opposition elsewhere, support for Onkalo has been relatively strong in Finland.

Researchers say public trust in STUK has played an important role. According to LUT University professor Matti Kojo, many people have become accustomed to the project over time and trust the regulator's assessments, as per the Science Alert report.

Support for nuclear power in Finland is currently at historically high levels.

Why Some Environmental Groups Still Oppose the Onkalo Project

However, not everyone agrees. The Finnish Association for Nature Conservation continues to argue that no one can guarantee the safety of a repository for thousands of years and maintains that nuclear waste remains a serious long-term risk, as per the Science Alert report.

Finnish law requires nuclear waste produced in the country to be stored within Finland.

As the government continues exploring future nuclear projects, including small modular reactors (SMRs), questions remain about how waste from those reactors would eventually be managed.

FAQs

What is Onkalo?
Onkalo is Finland's underground repository for spent nuclear fuel.

Where is Onkalo located?
It is located near Eurajoki in southwestern Finland.