11239 Application of Coupled Electrochemistry and Oxide Layer Growth Modelsto Water Chemistry Improvement against Flow Accelerated Corrosion in the PWR Secondary System

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Product Number: 51300-11239-SG

ISBN: 2011 11239 CP

Author: Shunsuke Uchida, Masanori Naitoh, Hidetoshi Okada, Seiichi Koshizuka, Derek H. Lister and Taku Ohira

Publication Date: 2011

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Applicability and accuracy of a computer simulation code describing flow accelerated corrosion (FAC) were confirmed based on verification and validation processes. The code will be applied to evaluate the effects of water chemistry improvement on wall thinning of pressurized water reactor (PWR) secondary piping.

In this paper, the validation process of the FAC simulation code, which was based on wall thinning rates measured at a PWR plant was discussed. 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 model of electrochemical analysis and oxide layer growth analysis by applying the corrosive conditions and the mass transfer coefficients. Comparison of the calculated wall thinning rates with hundreds of measured results at the secondary piping of the actual PWR plant confirmed that the calculated wall thinning rates agreed with the measured ones within a factor of 2 and the accuracy of the evaluation model for residual pipe wall thickness was with an error of less than 20 %. Finally, the FAC simulation code was applied to evaluation of the effects of oxygen injection into the feed water line. It was confirmed that a suitable amount of oxygen was injected at a proper location along the feed water line to provide sufficient mitigation of FAC without any serious adverse effects on steam generator tubing.

Keywords: flow accelerated corrosion, corrosive conditions, mass transfer coefficient, oxygen, electrochemical corrosion potential, wall thinning rate