en.Wedoany.com Reported - On June 16, Finland's Teollisuuden Voima Oyj (TVO) announced the completion of annual maintenance for Units 1 and 2 of the Olkiluoto Nuclear Power Plant. The Finnish Radiation and Nuclear Safety Authority (STUK) supervised the maintenance process and confirmed during post-maintenance inspections that the startup and operation of the units are safe.

Unit 2 underwent short-term annual maintenance from April 6 to April 17, 2026, while Unit 1 underwent comprehensive maintenance from April 19 to June 16, including major modifications and inspections, with a shutdown period longer than the normal fuel replacement cycle. The most significant change during Unit 1's maintenance was the update of the reactor automation system. Additionally, detailed inspections were conducted on the reactor's primary circuit and its main structures, and an updated nuclear fuel loading machine was commissioned. To facilitate primary circuit inspections and pressure testing, all fuel from Unit 1 was removed from the reactor and inspected, and a faulty fuel assembly discovered in October 2025 was replaced.

STUK Operations Control Manager Tomi Koskiniemi stated that the annual maintenance was carried out safely as planned. During the maintenance, the radiation doses received by workers involved in the operations were significantly below the annual limit of 20 millisieverts, with the highest individual dose in both maintenance periods being approximately 8.5 millisieverts.

Two incidents occurred during the maintenance. On April 8, a false trip occurred during modification work on the reactor water level measurement system for Unit 2, causing the startup of the makeup water pump and the shutdown of the residual heat removal pump, violating safety technical operating conditions. TVO quickly controlled the situation and restored normal procedures. On April 11, two doors in the reactor building transport hall of Unit 2 were found open during fuel transfer operations, violating relevant safety regulations. STUK's preliminary assessment indicated that both incidents were rated Level 0 on the International Nuclear and Radiological Event Scale (INES), posing no significant impact on nuclear safety or radiation safety.

The annual maintenance for Unit 3 of the Olkiluoto Nuclear Power Plant is planned for September this year. TVO plans to update the reactor automation system for Unit 2 next year.

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