A leakage of some 100 cubic metres of reactor coolant occurred at unit 3 of Finland’s Olkiluoto NPP (OL3) related to the filling of the reactor pool, plant operator Teollisuuden Voima Oyj’s (TVO) reported. The coolant flowed into containment rooms closed to the environment and into the floor drain system of the containment. The incident did not pose any risk to personnel, the environment, or nuclear safety.
Finland’s Radiation & Nuclear Safety Authority Radiation & Nuclear Safety Authority (STUK – Säteilyturvakeskus) said about 100 cubic metres of primary circuit cooling water had flowed into some of the rooms inside the containment.
TVO said the annual outage at OL3 is planned to continue until early May and the incident will not affect the planned duration of the annual outage. “The leakage occurred as a result of a human error through a hatch of the reactor pool that had not been closed properly,” TVO noted. “The significance of the event to radiation safety was low, in the end, owing to the safety actions taken.” TVO has initiated an event investigation about the incident and will implement necessary actions to prevent any recurrence.
“The reactor coolant that leaked into the containment flowed from the rooms into the drains of the floor drain system which are designed to collect and drain any reactor coolant leakages,” TVO said. “The radioactive wastewater will be handled in accordance with appropriate procedures utilising various systems. Cleaning work was commenced quickly in the containment rooms and personnel instructed about necessary changes in accessible areas.”
STUK said it was informed of the leak as soon as it occurred. “The cooling water flowing into the containment building was slightly radioactive. TVO reacted quickly to the event and began to correct the situation immediately. Radioactive substances were not released from the facility and the incident did not endanger the safety of the facility, the environment or people.”
During the outage, OL3 will be refuelled. Maintenance work will include a containment leak-tightness test, work on the reactor pumps, warranty work carried out by the plant supplier as well as steam generator washes and inspections. In addition to TVO’s own personnel, about 1000 employees of subcontractors are taking part in work.
This is the latest in a series of problems affecting the EPR at OL3. In October 2024, the plant’s power was automatically decreased from 1,600 MWe to approximately 1,220 MWe after one of the EPR’s control rods unexpectedly dropped into the reactor. TVO said the event had no impact on nuclear safety and the issue was resolved after a few hours.
OL3 began regular electricity production in April 2023 following the completion of trial operation. Construction of OL3 began in 2005 and various setbacks and delays resulted in the plant being some 14 years behind the original schedule and significantly over budget. OL3’s final price tag is put at some $11bn ($12bn), some three times the initial estimate.
OL3 attained first criticality in December 2021 and was connected to the grid on in March 2022. The EPR was operated at full capacity for the first time in late September 2022. However, cracks were identified in the impellers of the feedwater pumps located in the turbine island, causing further delays. During its first outage in April, technical problems resulted in delays in restarting the unit after fuel unloading took more time than planned and additional fuel inspections were required.
