Approximately 100 cubic meters of mildly radioactive water seeped into containment rooms at Olkiluoto unit 3 after workers failed to secure a hatch in the reactor pool prior to filling it. Teollisuuden Voima Oyj (TVO), the facility’s operator, flagged the incident as a significant operational misstep during maintenance on March 7. The coolant spread into portions of the containment structure, though TVO noted that swift safety actions limited any serious radiation concerns and kept potential hazards under control.

In a pressurized water reactor, coolant absorbs heat inside the reactor pressure vessel, travels via piping to the steam generator to transfer energy to the secondary loop, and is then pumped back to its starting point in a continuous process. TVO reported that the escaped coolant flowed into a drainage network engineered to trap and redirect such spills safely, preventing uncontrolled release. The company emphasized that no risks emerged for staff, the surrounding area, or nuclear safety protocols, thanks to the facility’s robust design.

TVO plans to process the contaminated water using established treatment systems built for handling radioactive leaks of this nature. Cleanup operations began promptly within the containment zones, with personnel updated on new access guidelines to maintain safety and prevent further mishaps. Finland’s Radiation and Nuclear Safety Authority (STUK), tasked with supervising the annual upkeep at Olkiluoto 3, received immediate notification of the leak from TVO’s staff. STUK commended TVO’s rapid response in addressing the spill and monitored the cleanup progress and subsequent measures over the weekend to verify proper execution.

The unit’s yearly maintenance outage started on March 1 and is expected to conclude by early May, covering routine checks and upgrades. TVO assured that this coolant leak would not disrupt the planned timeline, and maintenance activities continue on track with no anticipated delays.