Another production-filled year behind us

Energy sector in a transition

The Finnish energy sector has for quite some time already been going through a strong period of transition. The overall picture of electricity production is very different from what it was a decade ago, for example. The most obvious change has been the significant increase in weather-dependent production forms, particularly wind power. In terms of capacity, wind power has exceeded nuclear power for quite some time already. However, with stable all-year-round production, nuclear power still stays in the front position as far as the amount of electricity produced is concerned.

For the climate goals of Finland, the energy transition has been beneficial. The completion of Olkiluoto 3 as well as the significant increase in wind and solar power have already made Finnish electricity production fossil-free to a large extent. On the global scale, Finland and the other Nordic countries are, indeed, commendable spearheads in this respect. A large part of the world is only just envisioning what has already been achieved here. This has attracted international interest in the example set by Finland, which is also seen in the Olkiluoto visitor calendar.

With such a large share of energy production dependent on weather, we are facing a new kind of a challenge. Since production and consumption must always go hand in hand, this has in practice meant that the flexibility of production has become ever more important. This is reflected also in the day-to-day operations in Olkiluoto.

The times when nuclear plants were always operated at 100 percent power whenever possible are behind us. Of the Olkiluoto plant units, output regulation was actually one of the design bases of OL3. And for a good reason. In the past year, for example, the output power of the OL3 plant unit was regulated approximately 700 times. This means that in practice, our production was also based on wind conditions.

Powerful operation at OL3

OL3 literally became TVO’s own plant unit in 2025, when the takeover agreement was signed in June, after the two-year period of regular electricity production stipulated in the delivery contract.

The first production years of OL3 have been very strong. And 2025 was no exception. The power level of the plant unit did undergo regulation according to plans, but there was not a single unplanned disruption in production due to a technical fault. This is nothing less than a remarkable result for a new unit that is the first of its type in Europe. Naturally, this would not have been possible without our excellent personnel and cooperation partners – across all the stakeholders of the entire organisation.

The second annual outage in the history of OL3 was also carried out successfully. This year we completed the outage several days ahead of the original schedule. The lessons learned from the first service outage played a crucial role in this. In addition to TVO’s own personnel, a shout-out for the successful outage goes also to the subcontractors as well as excellent cooperation with authorities.

In 2025, the total production of Olkiluoto 3 was 10.38 TWh, showing an increase over the previous year (9.69 TWh). Even such a massive volume still leaves room for improvement. It is most certainly also possible to significantly reduce the duration of the annual outage even more as we gain more experience.

Another wish we hope will come true is that we do not have to operate the plant at reduced power levels due to system protection restrictions. At the present, unfortunately, we are still required to reduce the output power at times, not due to technical factors but because of these other reasons. Negotiations with Fingrid about this are still ongoing, however. Resolving this issue would benefit Finland as a whole, including the consumers.

Nuclear Power is a marathon

The only unplanned production breaks during the production year took place our older plant units and were both caused by faults in the turbine island. At OL1, the disruption due to a fault only lasted a little over a day, but OL2 suffered greater production losses. The unit was off production for several days as a result of technical issues. OL2 is still operated at a reduced power level. This is based on a conservative approach where the reliable and safe long-term operation of the plant unit is prioritised over production maximisation. Quick wins have no place in the nuclear industry – not now or in the future.

Annual service outages are crucial in allowing us to secure the reliable and safe operation of the plant units, not only during the next operating cycle, but also over the long term. For TVO, the starting point has from the very beginning been to keep the plant units in as good as new condition and we have not wavered from this. This is also the key reason for an extension of the service life of the OL1 and OL2 plant units being even considered in the first place. We are pondering on pushing the end of their operational life from the current 2038 to as far as 2058. This would give OL1 a total service life of up to 80 years.

No decisions have been made yet, but technical analyses show that there are no obstacles to doing it. Without carefully executed annual outages it would not be possible, of course. Speaking of annual outages: this year’s outages are already on the horizon. In 2026, the outage season in Olkiluoto starts in April at OL2. But more about them later.

Wishing everyone an energetic year 2026, with thanks,
Marjo Mustonen