Outages completed at Olkiluoto 1 and Olkiluoto 2 plant units

The The annual outages of the two Olkiluoto power plant units, each with a power output of approximately 890 MW, went smoothly.

At OL2, this year’s outage was a shorter refuelling outage. It started on 6 April and took a total of 10 days and 18 hours.

For OL1, on the other hand, the annual outage was this year a longer service outage. The most important activities carried out during the outage included repair work on the front chamber of the turbine condenser, upgrading of reactor I&C, maintenance activities on the high-pressure turbine, replacement of electrical penetrations in the containment, as well as a pressure test of the primary circuit.

In addition to TVO's own personnel, about 1,400 employees of subcontractors took part in the annual outage works this spring.

– The OL1 outage was exceptionally significant this year. It was one of the longest annual outages in the unit’s history and involved a substantial amount of extensive work critical to plant safety and reliable electricity generation. The OL1 outage began on April 19 and lasted for 57 days and 9 hours.

The successful completion of the outage demonstrates the strong expertise of TVO’s personnel and partners, as well as their commitment to safety, says Marjo Mustonen, Director of Electricity Production.

The annual outages are designed to guarantee that the operating cycles are as safe and uninterrupted as possible, which makes their implementation to a high standard important for the next cycles.

Areas requiring improvement also identified

When modifications were carried out related to the reactor level measurement system at OL2 on 8 April during the annual outage a protection function was inadvertently activated. The situation was quickly brought under control, the plant restored in normal state and the incident did not cause any risk to the personnel, plant safety, or the environment.

During the annual outage at OL2, on 11 April, a nonconformance was spotted during the transfer of spent fuel, where two doors along the transport route were simultaneously open. The fuel handling process was immediately discontinued and the incident did not affect radiation safety or the environment. The preliminary INES* rating of the incident is 0.

At OL1, on 27 April during the annual outage, water was discharged from a valve onto staff members carrying out maintenance activities, with three employees exposed to reactor cooling water. The employees and the work area were immediately cleaned and the radiation doses caused by the incident remained very low causing no risk to the employees, the plant or the environment.

Annual outages guarantee high and consistent level of production

At nuclear power plants, a significant part of equipment maintenance and repair activities can be carried out with the plant in power operation, but some equipment requires a longer shutdown for servicing. All major modernisation projects are also implemented during service outages. Also, during every annual outage, part of the fuel, about one quarter, is replaced. This ensures that production will be as efficient and stable as possible.

At moment, all three plant units are in normal electricity production after the service outages. For the Olkiluoto 3 plant unit, this year’s annual outage will take place in the autumn.

For more information, please contact

Johanna Aho, Head of Communications, tel. +358 40 7290822.

* The degree of severity of events occurring at a nuclear power plant is classified on the international INES scale. Levels 1–3 describe incidents that have impaired safety and levels 4–7 accidents. Level 0 refers to an abnormal event without safety significance.