Evaluation Methods for Corrosion Damage of Components in Cooling Systems of Nuclear Power Plants by Coupling Analysis of Corrosion and Flow Dynamics (IV) Comparison of Wall Thinning Rates Calculated with the Coupled Model of Static Electrochemical Analysis and Dynamic Double Oxide Layer Analysis and Their Values Measured at a PWR Plant

Abstract

In order to confirm applicability and accuracy of FAC evaluation methods based on the coupled FAC model of static electrochemical analysis and dynamic oxide layer growth analysis, wall thinning rates calculated with the proposed methods were compared with those measured for the secondary piping of a PWR plant. Distributions of flow velocity and temperature along the whole system were calculated with 1D and 2D computational flow dynamics (CFD) codes and corrosive conditions were calculated with a N2H4-O2 reaction analysis code. Precise flow turbulence at major parts of the system was analyzed with 3D CFD codes to obtain mass transfer coefficients at structure surfaces. Then, wall thinning rates were calculated with the coupled FAC model by applying the mass transfer coefficients. Comparison of the calculated and measured results led to the following conclusions. 1) Structures with complicated geometry in the plant, e.g., the pair of a bend pipe and a valve, could be simplified as a combination of pipes for the calculation. 2) Flow distribution calculated with 3D CFD codes for a large-scale piping system could be extrapolated to those at the very surface of the piping to obtain a precise distribution of mass transfer coefficients at the region of interest. 3) Wall thinning rates calculated by applying the obtained mass transfer coefficients agreed with the measured rates within a factor of 2. 4) The effects of flow turbulence were transferred through a distance of more than 5 times the pipe diameter from the original turbulent point, but the effects on wall thinning rate were negligibly small.