Studies on the cause of damage and measures against small leaks in Elbe water charged cooling water systems

During the operational duty cycle 2005/2006 tubing of auxiliary cooling water systems in a German NPP experienced leakages that were caused by corrosive attacks of the Elbe water. Extensive investigations included the safety relevant consequences, clarification of the cause of damage and measures concerning repair and prevention in the future including an improved test program. The study revealed local pitting corrosion that started as subsurface corrosion. There was no risk for flooding. Material investigations showed that the used coating scheme for long-term protection at the inside of the piping is appropriate with respect to the cooling water. Concerning aging the important properties of the coating have not changed over the operational time. During the revision in 2006 extensive visual inspection of the piping inner wall was performed, defects were repaired.