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Information on unusual event: Krško NPP (NEK), Slovenia, 4. June 2008

The plant operated at full power for 210 days in the 23rd fuel cycle without any limitation. At 15:07 of June 4, 2008 an increase on primary leakage was noted by the shift crew.

The crew entered the abnormal operating procedure trying to identify and isolate the leak. In the meantime the leakage increased above the Technical Specifications limitation which requires shutdown of the plant to Cold Shutdown Condition. At 15:56 an Unusual Event was declared. Power reduction was started at 16:50 with the rate of 5MW/min per General Operating Procedures for normal plant shutdown. The plant was disconnected from the grid at 19:31. The entire time leak rate was stable and amounted to about 3 m3/hr. There was no additional malfunction or failure. There was no protection system actuation and no need for the operation of safety systems. The reactor was manually shutdown with insertion of all control rods and it was subcritical at 19:50. At 19:55 entrance to the reactor building started. Leakage was located on the primary system isolation valve on one of the temperature measurement 2 inch line. Plant cooldown to Cold Shutdown condition started at 21:00. Unusual event was cancelled on June 05, 2008 at 12:40 when the plant was brought to Cold Shutdown condition. State and local authorities were provided by all required information on the plant throughout the event. 

Detailed inspection confirmed that the leakage had been caused by the failure of the manual isolation valve on temperature measurement line (RTD manifold line - second isolation valve from the hot leg side). Water leaked through the valve steam seal pack. Complete valve will be replaced. Detailed root cause of the valve failure will be performed. 

After completion of the repair work, the plant will be brought back on line in the middle of the next week. 

High publicity in the public all around Europe was created due to the fact that the European Community Urgent Radiological Information Exchange ( ECURIE ) warning system was activated. 

There were no impacts on the general public or workers health and there was no release into the environment. 

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