Evaluation of Flow Accelerated Corrosion of PWR Secondary Piping by Coupling Analysis of Corrosion and Flow Dynamics

Flow accelerated corrosion (FAC) is divided into two processes: a corrosion (chemical) process and a flow dynamics (physical) process.  The former is the essential process to cause FAC and the latter is the accelerating process to enhance FAC occurrence.  The chemical process in the surface boundary layer is analyzed to evaluate FAC rate. 
Precise flow patterns and mass transfer coefficients at the structure surface were calculated with 3D computational flow dynamics codes. Wall thinning rates were calculated with the coupled models of static electrochemical analysis and dynamic double oxide layer analysis.  Anodic current density and electrochemical corrosion potential (ECP) were calculated with the static electrochemistry model based on an Evans diagram and ferrous ion release rate determined by the anodic current density was applied as input for the dynamic double oxide layer model.  Some of the dissolved ferrous ion was removed to the bulk water and others precipitated on the surface as magnetite particles.  Conversion factor from magnetite to hematite was expressed as a function of ECP.  The thickness of oxide layer was applied for the electrochemistry model. 
It was confirmed that the calculated results of the coupled models resulted good agreement with the measured ones.