Evaluation Method for Flow Accelerated Corrosion of Components by Corrosion Analysis Coupled with Flow Dynamics Analysis

摘要

The troubles of major components and structural materials in nuclear power plants have often been caused by flow-induced vibration, corrosion, and their overlapping effects. In order to establish safe and reliable plant operation, it is required to forecast future troubles based on combined analyses of flow dynamics and corrosion and prevent them at very early stages. Corrosion analysis models have been combined with three-dimensional flow dynamics and heat transfer analysis models to evaluate corrosion damage (e.g., stress corrosion cracking [SCC] and flow-accelerated corrosion [FAC]) of major components and structural materials. The models are divided into the following two parts. First is a prediction model of future trouble on materials. The distribution of oxidant concentrations along the flow path are obtained by solving water radiolysis reactions in the boiling water reactor primary cooling water and hydrazine and oxygen reactions in pressurized water reactor secondary cooling water. Then, the distribution of electrochemical corrosion potential (ECP) along the flow path is obtained by oxidant concentration based on a mixed potential model. Higher ECP enhances the possibility of SCC, while lower ECP accelerates FAC. Second is an evaluation model of wall thinning caused by FAC. At the location with a higher possibility for FAC occurrence, a trend of wall thinning is evaluated, and the lifetime is estimated for preventive maintenance.