Approximately 100 cubic metres of radioactive coolant leaked from Olkiluoto 3, the largest nuclear reactor in Europe, during a maintenance outage, as confirmed by the operator, Teollisuuden Voima Oyj (TVO).

The incident took place on a Friday and was linked to the filling of the reactor pool.

TVO reported that the leak occurred in containment rooms, which are designed to be sealed off from the external environment, and that the coolant entered the facility's floor drain system.

TVO emphasized that there was no risk posed to personnel, the environment, or overall nuclear safety due to the leak.

The company identified human error as the cause, citing that a hatch for the reactor pool had not been secured properly prior to the incident.

An assessment conducted by TVO determined that the significance of the leak in relation to radiation safety was low, attributed to existing safety measures.

Despite the incident, TVO stated that the leak would not impact the duration of the reactor's annual outage, which is scheduled to continue until May. Olkiluoto 3 utilizes next-generation European pressurised water reactor (EPR) technology, developed by a consortium including Areva and Siemens, and is responsible for over 10 percent of Finland's electricity supply.

Olkiluoto 3 has previously encountered multiple challenges, including construction delays and significant cost overruns, similar to other EPR projects worldwide.

While Olkiluoto 3 is recognized as the largest nuclear reactor in Europe, the Zaporizhzhia nuclear power plant in Ukraine, containing six reactors, is acknowledged as the largest nuclear power plant on the continent.