Jožef Stefan Institute, as one of the TSO organizations in Slovenia, is currently involved in support of the Slovenian Nuclear Safety Administration activities during the unplanned Krško Nuclear Power plant outage.

The Krško Nuclear Power plant was on October 6 preventively shut down upon an indication of a water leak from the primary system. Even though the coolant leakage was below the limits of the Technical Specifications, the power plant was on the principle of conservative decision-making shut down as a precaution to enable the detection of the source of the leakage and to eliminate the deviation. A hole of the size of a sewing needle at the weld of the reducing part of the piping connection system to the primary system, one meter from the penetration into the reactor vessel was detected. All water was collected in containment systems and will be processed with an evaporator according to established procedures.

As part of the analyses and preparations for the repair of a leak in the 4-inch pipeline, the Krško NPP carried out additional investigations using non-destructive methods. With one of them, an indication of an additional anomaly in the pipeline material was identified in the leaking pipe, which led the Krško NPP to decide to completely replace the pipeline segment – from the connection to the reactor vessel to the first valve. For a safe long-term and as soon as possible plant operation, the Krško NPP, in cooperation with the original equipment supplier Westinghouse, decided to replace the pipeline on the other line of the system to the same extent.

Westinghouse will repair the pipelines and the domestic industry will provide support. Roughly 100 contractors will participate, who will first undergo the necessary training. The Slovenian Nuclear Safety Administration together with authorized organizations is monitoring all work.