Analyses of the failed impulsion lines of NPP Dukovany steam generator

Three fractured segments of the impulsion piping were analyzed and the root cause was identified. One segment had been fractured due to smaller wall thickness and wrong geometry. The other two segments had been fractured due to stress corrosion cracking. Chloride was present at the inner surface of the tubes, presumably as a residue from the manufacturing phase. Several possible countermeasures were proposed: prevent mechanical deformation of the tubing; proceed with tightness testing, analyze and clean the inner surface of all newly installed tubes, perform non-destructive testing of important segments and pressurize the piping