Last November and December, Teollisuuden Voima found incorrect connector seals in the inspections of third unit (OL3) of the Olkiluoto nuclear power plant. The incorrect seals have not compromised plant safety.
Connectors, whose seals were now replaced with new and functional seals, would be needed in some measurements carried out in unlikely accident situations. Faults in the seals could have affected the measurement results, but they could not have compromised the containment of the accident.
Incorrect seals could have affected the functionality of many connectors, in other words, they posed a risk of common mode failure. For this reason, the Radiation and Nuclear Safety Authority (STUK) initially placed the incident in category 1 on the International Nuclear and Radiological Event Scale (INES). Category 1 events are anomalies affecting safety.
TVO also found faults that required repairs in the seals of the third unit of Olkiluoto last spring (TVO identified faults in OL3 connectors | Radiation and Nuclear Safety Authority STUK). After that, TVO continued to inspect the connectors together with the plant provider. The deficiencies detected in November–December were in different types of connectors than those detected in the spring. TVO and the plant provider have inspected the most important connectors in terms of safety and checked that they have the right seals.
The inspection of the seals is still continuing and TVO has announced that all the connectors will be inspected by the end of the annual maintenance starting in March.
