Statistical Modelling of Pressure Tube Diametral Creep

Abstract

This paper presents the development of a weighted least squares (WLS) regression model for predicting pressure tube diametral creep over time, using in-service inspection data from 328 different pressure tubes from Bruce B and Darlington stations. The proposed model is linear in time as a function of flux and temperature, with a temperature dependent variance function. The model predicts the shape of the observed diametral creep profiles very well, and is useful not only for prediction, but also for assessing tube-to-tube variability and manufacturing properties among the inspected tubes.