Wedoany.com Report-May 10, Teollisuuden Voima Oyj (TVO), a Finnish power company, announced that electricity production has resumed at Olkiluoto Nuclear Power Plant Unit 3 (OL3) in Finland following its annual maintenance outage. The outage involved approximately 2,000 tasks and 6,000 work phases, including refueling, a containment leak-tightness test, maintenance of reactor coolant system pumps, steam generator cleaning and inspection, and warranty work by the plant supplier.

The maintenance effort engaged around 1,000 subcontractor employees, half of whom traveled to Olkiluoto from abroad, alongside TVO’s staff. This outage, the first after an 18-month operating cycle, aligns with OL3’s flexible refueling schedule of 12–24 months. Originally planned for 63 days and set to conclude on May 2, the outage was completed in 59 days and 10 hours. The shorter duration resulted from lessons learned during the previous outage and a schedule that accounted for potential unexpected repairs, which were minimal this year.

Heikki Lukkari, OL3’s Plant Manager, said: “At Olkiluoto 3, the fuel assemblies are removed from the reactor at the start of the annual outage into fuel pools located in a separate fuel building. They undergo a meticulous inspection before a large part of them is transferred back into the reactor together with fresh fuel. We managed to complete this process much more smoothly than last year. We also brought the containment leak test, now carried out for the first time during the annual outage, to a conclusion ahead of the schedule.”

Some challenges were identified during the outage. Early in the process, reactor coolant water entered containment rooms and the floor drain system during reactor pool filling. TVO stated: “The necessary action has been taken to avoid similar incidents in the future.” Additionally, defective seals in certain measurement instrument connectors were found. These connectors, previously inspected in 2023 and 2024, function normally but may not meet accident condition requirements. The Radiation and Nuclear Safety Authority of Finland rated this issue as level 1 on the INES scale. TVO’s further inspections confirmed compliance with safety standards.

Fuel inspections revealed small, fragile pieces of foreign material in some assemblies. TVO addressed these findings and continues to investigate, ensuring the material does not affect safe operation. The company noted: “These findings were dealt with appropriately. TVO continues to carry out investigations and take action regarding the foreign material detected in the fuel of OL3. The detected foreign material does not prevent the safe and reliable operation of the fuel during the upcoming operating cycle.”

The successful outage underscores TVO’s commitment to operational safety and efficiency, ensuring OL3’s reliability while addressing maintenance challenges to support Finland’s energy needs.