Ageing monitoring and management for WWER steam generator and secondary circuit piping of WWER/213 NPPs

In Dukovany NPP the evaluation and prediction system of the flow accelerated corrosion was introduced. The CHECMATE software was used to predict the wear in model components. Feedwater system, steam lines, condensate, high pressure extractions were investigated. It was shown that the equivalent components in the same trains have the same or similar chromium contents and there are similarities in the wear of these components. The structural integrity of WWER steam generator tubes is affected by pitting and stress corrosion cracking. The tube main corrosion damage results from through-wall-deep (TWD) cracks and partial through-wall-deep cracks. The correlation between defect size and indications of eddy current test (ECT) was investigated. This correlation has a large scatter of data when the actual wall thinning is less than 60 %. The stability of TWD cracks was evaluated by burst test method. The critical pressures for unstable propagation of TWD cracks were found for tubes with electric discharge machining flaws. Lower conservative estimations of critical lengths of TWD axial cracks were determined for WWER-440 operational and accident conditions. (author). 5 tabs., 26 figs., 6 refs