A new methodology for structural reliability assessment of the heat exchanger tubes of WWER steam generators

Abstract

A physically and statistically based method for steam generator (SG) heat exchanger tubes (HET) integrity assessment is proposed. The method based is on the stochastic laws of crack dimensions distribution with taking into account its growth, limit load-model of cracked tube, and SG plugging statistics. Based on the history of the tubes, plugging of the specific SG three statistical parameters has to be found: initial number of defects, stochastic parameter of defect depth, and the defect growth rate. The developed method was used for the prediction of HET failure for all Ukrainian SG. It is also used for the justification of pressure reduction of hydrostatic test (HT) for primary circuit of WWER NPPs. It is shown that the pressure reduction from 24.5 to 19.6 MPa for WWER-1000 s and from 19.1 to 15.7 MPa for the WWER-440 s does not practically increase the HET failure probability during operation.