(Original Finnish text from 2019)

Viite – Finnish Greens for Science and Technology visited the Posiva Onkalo in Olkiluoto on August 19th, 2019. Onkalo is the world’s first disposal site for spent nuclear fuel from civilian nuclear power plants, and it’s almost completed. The site consists of a network of tunnels 450 meters under Finnish bedrock and smaller vertical holes which serve as the final resting places of nuclear waste capsules.

Finland has decided to dispose of its nuclear waste by itself, and its legislation forbids the export of nuclear waste. As such, Finland is a forerunner. When the first Finnish nuclear power plants were completed, the companies running the plants were obligated to plan for the disposal of their waste. As the Finnish bedrock is highly stable, there are multiple areas in Finland that are well-suited for long-term nuclear waste disposal.

Most of the refuse produced by nuclear power plants can be recycled normally. Fuel rods comprise only 5 % of all waste, and most of the radioactive waste produced during the plant’s life cycle consists of radiation-exposed cover-alls and the final remains of the eventually-decommissioned reactor. Waste disposal will start in the 2020s, and the premises will be sealed sometime in the 22nd century. Onkalo will fit all the waste produced by the existing Olkiluoto and Loviisa plants. There is also additional space to accommodate waste from Olkiluoto 4 and Loviisa 3 if they are ever constructed.

Nuclear waste life cycle

When depleted fuel rods are removed from the nuclear reactor, they are moved to pools of water where they will cool for the next 30-40 years. During that time, radiation will decrease a thousand-fold from its levels at  removal. Once there is enough waste to fill a tunnel, the cooled rods are moved to the encapsulation plant. The rods are encased in a capsule of spherical graphite, which in turn are encased in an external capsule made out of copper. The capsules do not stop radiation, as their purpose is to protect the fuel from the elements. The capsule will still be a light source of radiation, producing as much heat as a regular sauna stove.

The capsules are then lowered into Onkalo, where they are remotely transferred to the storage slot set aside for the capsule. The capsules are then encased in bentonite. Once all the slots in a tunnel are filled, the entire tunnel is then filled with bentonite. Within a few years, the bentonite will have absorbed enough water to seal the entire cave tightly enough to prevent running water from reaching the capsules. Stored this way, the capsules will remain untouched for hundreds of thousands of years – even through new ice ages. By the next ice age, the capsules’ radiation will have been reduced enough to be indistinguishable from background radiation anyway.

Threats during storage

Once Onkalo has been filled sometime in the 22nd century, the area will be landscaped, and the capsules left alone. However, one can imagine several threat scenarios involving the nuclear waste capsules. In principle, the waste could be dug up and used for nuclear weapons. However, once Onkalo has been filled and sealed, it would take years to reach the capsules. Hardly an endeavour that can be done in secret.

An unprecedented earthquake or other seismic phenomena strong enough to break both capsule layers would also be a threat. This would enable the radioactive substance to reach water, which would, in turn seep towards the surface and its food chains. However, the tunnels are located 450 metres below the surface, where water flows extremely slowly. Even if water contamination occurred, it would take a very long time for the water to reach the surface. The radiation would weaken all the time, and simulations indicate the radiation would be indistinguishable from natural background radiation. In any case, the effects would only impact the immediate Onkalo surroundings. The probability of an event like this is extremely low, as Finnish bedrock is some of the most stable in the world.

We can conclude that Finnish nuclear waste disposal is almost ready for duty, lacking just a few final tests. Onkalo and its surrounding bedrock have been studied exhaustively to determine and prepare for geological risks. There are several similar areas in Finland, meaning that there’s potential to expand our nuclear power generation capacity safely. However, the situation is not at all the same in many other countries, creating global demand for nuclear waste disposal solution know-how. Posiva Solutions was founded in 2016 to export the Onkalo know-how.

Posiva’s mission is to implement its legal obligations to dispose of nuclear waste. Of course, one hopes that fourth-generation breeder reactors will be commercialised before Onkalo is sealed. Breeder reactors can re-utilize the waste from earlier-generation reactors, extending its life cycle and limiting the need for long-term disposal to a thousand years.

Nuclear power and climate change

The visitor centre had a beautiful view of the Olkiluoto reactors across the bay. OL1 and OL2 had already been there a while, and OL3’s superstructure was also complete. At the time of writing, OL3 is producing energy to the grid as part of its commissioning tests. OL3 has been used – with perfect justification – to say that nuclear power is not a fast enough solution to combat climate change. Inevitably, we also started to think about additional nuclear power.

Despite its rough road to completion, OL3 is turning out to be a fast-ish way to increase emissions-free electricity production. In light of technical constraints, renewables’ variable output makes them, joule-for-joule, roughly as fast as OL3. Wind power is fickle and needs either backup power or electricity storage for around 5,000 h per year. Using current technologies, a fully renewable power grid would be very costly. Finnish nuclear power runs for around 8,500 hours per year, that is, around the clock (excluding maintenance).

To produce an equivalent amount of energy as a large nuclear power plant, one would need around 4,500 MW of wind power. Finnish feed tariffs have enabled around 2,000 MW of wind power over the last seven years. As there are those who oppose wind power, administrative complaints slow down the building process. At the time of writing, building out 5,000 MW of wind capacity will take around 15 years.

It’s also important to bear in mind that no amount of increase in renewables will help to combat climate change by itself. We need to reduce energy consumption or ramp up emissions-free energy production at an unprecedented rate. Fossil fuels produce over 80 % of our current energy needs. Wind and solar account for barely a few percentage points, while nuclear power produces around 4 %.

As for sea-level rise, the existing reactor floors are around 4 m above the surface. Even the wildest forecasts do not foresee a rise of this magnitude during OL4’s lifetime. It’s also essential to bear in mind that nuclear power itself will help mitigate climate change and sea-level rise. In any case, sea levels will rise slowly enough to give us time to react and follow Netherlands’ example in flood mitigation. We have also written extensively about nuclear power and its role in climate change prevention in the past.


Four members of our group boarded a Tesla Model 3 right next to Olkiluoto 3. The battery had been filled with nuclear electricity, so we had an opportune moment for some range testing. We drove all the way from Olkiluoto past Turku to Viikki via Tikkurila. There was no need to recharge, as we still had an estimated 169 km in the tank after 308 kilometres. A range of 500 km at highway speeds would have been unthinkable a year ago and it gives us faith in an electric future.

The one big thing in energy production is to replace fossil fuels with electricity. At the same time, we need to make electricity production emissions-free, even if it costs more.

Our visit to Onkalo convinced us that nuclear waste in Finland is in capable hands.

Written by: Peppi Seppälä, Antti Van Wonterghem and Jonni Lehtiranta

Volunteers in Viite national and local chapters