Problems with seals detected in connectors at OL3 plant unit in November-December

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 provided with new seals.

Connectors with defective seals are fully operable in normal conditions but they will not necessarily fulfil requirements specified for accident conditions.

The failure of these measurements during a loss of coolant accident could impede operator actions, but would not be a risk to accident management, however. The probability that conditions in which these measurements are needed would occur is low.

TVO submitted the operating event report addressing this event to the Radiation and Nuclear Safety Authority of Finland (STUK) on 12 January 2024. STUK provided TVO with a preliminary assessment of the INES rating on 17 January 2024.

The preliminary rating of the degree of severity of the event is level 1* on the international INES scale. Although the basic rating of the event is 0, the rating of the event is upgraded by one taking the possibility of a common cause failure into account.

* The events occurring at a nuclear power plant are classified on the international INES scale according to their degree of severity. The INES scale has seven categories of severity. Category 4–7 events are classified as accidents, category 1–3 events as incidents or anomalies with a negative effect on safety, and category 0 events as deviations with no significance for safety.