Unidentified leakage from the primary circuit in excess of TS limit
Monday, June 9, 2008
The Krsko NPP was safely shut down on 4 June 2008 at 8:10 p.m. (local time), after a primary circuit leak was detected at 3:07 p.m. on the same day. The leak of about 3 m3/h has exceeded the limit of the plant Technical specifications and required the plant to shut down. The event was classified as an unusual event. There was no demand on the safety systems. The loss of coolant was controlled by the charging flow. There was no need for off-site protective measures since there were no releases to the environment. The shut down was performed in a controlled way by following the general operating procedures. The exact location of the leak was determined on 6 June early in the morning. The stem seal of the isolation valve 8067 B of the RTD manifold on the hot leg loop 2 was found to be leaking. In order to repair the leakage, the plant needed to be brought into a cold shutdown mode and the primary coolant level decreased to cold leg + 50 to 60 cm. Plant personnel performed replacement of the complete tandem of valves 8063 B and 8067 B. After successful inspection of all the RTD manifold valves the plant was on 8 June 2008 afternoon ready for start-up. The further steps to power operation are pending the SNSA regulatory inspection results.