Finland's Teollisuuden Voima Oyj has said that inspections conducted in November and December 2023 have revealed defective seals in connectors used for level and pressure measurements. The inspections were conducted as a result of the seal defects detected in the spring. Defective seals were detected in seven of the eight inspected connectors, and in one connector the seal was missing completely. All the inspected connectors were fitted with new seals.

Connectors with defective seals are fully operable in normal conditions but they will not necessarily fulfil requirements specified for accident conditions. “Failure of these measurements in the event of a loss of cooling accident could hamper operator operations but would still not jeopardise the management of the accident. Situations in which the measurements now being processed would be needed are unlikely,” TVO noted.

In May 2023, a total of 108 connectors were inspected and missing seals were detected in 29 of them. All the inspected connectors have now been provided with new seals. The degree of severity of the event was rated at level 1 on the International Nuclear & Radiological Event Scale (INES). Although the basic rating of the event was 0, it was increased to 1, because deficiencies in procedures have contributed to the occurrence of a common cause failure.

OL3 began regular electricity production in April following the completion of trial operation. Construction of OL3 began in 2005 and various setbacks and delays mean the plant is 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 what was initially estimated. OL3 attained first criticality in December 2021 and was connected to the grid on in March 2022. The 1600 MWe 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.

Image: Finland’s Olkiluoto unit 3 (courtesy of TVO)