EVALUATION OF WALL THINNING OF PWR FEED WATER PIPING WITH THE COUPLED MODEL OF STATIC ELECTROCHEMICAL ANALYSIS AND DYNAMIC DOUBLE OXIDE LAYER ANALYSIS

摘要

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 ID and 2D CFD codes and corrosive conditions were calculated with a N_2H_4-O_2 reaction analysis code. Precise flow turbulence at major parts of the system was analyzed with the 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.Flow distribution calculated with the 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. Wall thinning rates calculated by applying the obtained mass transfer coefficients agreed with the measured rates within a factor of 2.From demonstration of the FAC evaluation model, the effects of water chemistry improvement on FAC mitigation on feed water piping and its adverse effects on steam generator have been calculated, and then, sufficient mitigation effects of suitable oxygen injection into the feed water line on FAC without any serious adverse effect on SG have been confirmed.