Predicting growth rate of wall thinning for severely degraded SG tubes using a statistical methodology

Abstract

Based on the requirements of TSTF-449 or NEI 97-06, operational assessment (OA) should be performed to guarantee the steam generator (SG) tube integrity. OA is a forward looking evaluation of the SG tube conditions. One of main evaluations for the OA is to estimate the growth rate of tube degradation prior to the next SG tube inspection. Therefore, the majority of this paper is to predict the growth rate of wall thinning for the SG tubes by way of a statistical methodology. The wall thinning of degraded SG tubes predicted by the present model agrees well with the plant measured one. The relative errors between the predictions and measurements are less than 10%. In addition, the present model would over-predict the wall thinning in most cases, revealing that this methodology could provide a useful and conservative tool for the PWR plant staff to execute the OA for SG tubes.