Evaluation of Wall Thinning of PWR Feed Water Piping With the Coupled Model of Static Electrochemical Analysis and Dynamic Double Oxide Layer Analysis

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. Flow turbulence at major parts of the system was calculated with 3D CFD codes and extrapolated to the very surface of piping wall to obtain mass transfer coefficients at boundary layers of the structure surfaces. Then, wall thinning rates were calculated with the coupled FAC model by applying the mass transfer coefficients. Major conclusions are as follows: 1) Flow distribution calculated with 3D CFD codes could be extrapolated by applying 2/7 power law of turbulence energy as a function of distance from the surface to those at the very surface of the piping to obtain a precise distribution of mass transfer coefficients. 2) Wall thinning rates calculated for large scale piping of a PWR by applying the obtained mass transfer coefficients agreed with the measured rates within a factor of 2. 3) As a result of demonstration of the FAC evaluation model, it was confirmed that suitable amount of oxygen injection into the feed water resulted sufficient mitigation of FAC without any serious adverse effect on steam generator tubing.