Prediction of Materials Damage History From Stress Corrosion Cracking in Boiling Water Reactors

Abstract

Over the past decade, we have developed deterministic models for predicting materials damage due to stress corrosion cracking (SCC) in boiling water reactor (BWR) primary coolant circuits. These steady-state models have been applied to fixed state points of reactor operation to yield electrochemical corrosion potential (ECP) and crack growth rate (CGR) predictions. However, damage is cumulative, so that prediction of the extent of damage at any given time must integrate crack growth rate over the history of the plant. In this paper, we describe the use of the REMAIN code to predict the accumulated damage functions for major components in the coolant circuit of a typical BWR that employs internal coolant pumps. As an example, the effect of relatively small amounts of hydrogen added to the feedwater (e.g., 0.5 ppm) on the development of damage from a 0.197-in. (0.5-cm) intergranular crack located at the exit of an internal pump was analyzed. It is predicted that hydrogen additions to the feedwater will effectively suppress further growth of the crack. We also report the first predictions of the accumulation of damage from SCC for a variable power operating cycle. We predict that the benefits of hydrogen water chemistry (HWC), as indicated by the behavior of a single crack under constant environmental conditions, are significantly muted by changes in reactor power. [S0094-9930(00)01301-9]