Nuclear Engineering and Design 241 (2011) 95–100 Contents lists available at ScienceDirect Nuclear Engineering and Design journal homepage: www.elsevier.com/locate/nucengdes Numerical model for estimation of corrosion location in nuclear power plant steam generators S. Tashakor a,∗ , G. Jahanfarnia a , A. Kebriaee b a Science and Research Branch, Islamic Azad University, Tehran, Iran b Mechanical Engineering School, Sharif University of Technology, Tehran, Iran article info Article history: Received 16 March 2010 Received in revised form 15 October 2010 Accepted 22 October 2010 abstract Deposition of dissolved impurities and corrosion in steam generators is a significant problem in the operation of nuclear power plants. Impurities and corrosion products usually accumulate in the secondary sides of steam generators (SG) and form deposits on the SG surfaces. A high level of impurity concentration close to the SG heating surface causes the corrosion process to occur with more intensity. The aim of this study is to estimate the most probable locations of impurity concentration and deposition in a SG. Equations representing the convection and diffusion in the liquid phase close to the heated surface (the viscous sub layer) are derived. Based on the mass balance of impurities in the viscous sub layer as the boundary condition, the derived differential equations are solved by the finite volume (upwind) methods. The distribution of impurities, sediment formation rate and the location of the depositions in the viscous sub layer at different heat flux values are studied in steady and unsteady states. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction Steam generators (SGs) are key components of Pressurized Water Reactors (PWR). Their reliability affects greatly the overall plant performance and availability. World-wide experience shows that a significant number of operating PWRs have now corro- sion or mechanical degradation problems in their SGs (EPRI Steam Generator, 2000). The impurities have their origin in the secondary side systems. The corrosion products generally accumulate in the SG and form deposits on the surfaces of the tube sheet and tube support plates. Corrosion product fouling in the SGs has been identified as a major cause of heat transfer degradation in PWR plants, with the power output at some plants being reduced to as low as 80% of full power (Odar, 2004). The intensity of sediment formation depends on heat flux and impurity concentration close to the heating surface. The variation of impurities concentration in the bulk stream and viscous sub layer due to changes of system parameters is referred to as hide out and return. Hide out is a complex process, which depends on the local geometry, applied thermo-hydraulic conditions and the solubility characteristics of dissolved impurities. These phenom- ena lead to the escalation of impurity concentration to corrosive levels. The rise in impurity concentration levels increases the SG hide-out behavior. ∗ Corresponding author. Tel.: +98 917 1073160; fax: +98 214 4869656. E-mail address: saman.tashakor@yahoo.com (S. Tashakor). Turbulent boundary layers are characterized by the occurrence of a thin viscous sub layer adjacent to the channel surface where the flow behavior is essentially laminar. The viscous sub layer in the applications of interest to this investigation are typically very thin (10–100 m), making experimental investigation of dissolved impurity concentration in the viscous layer very difficult. A new mathematical method has been developed for the inves- tigation of the behavior of impurities in viscous sub layers. The central idea of this study is to numerically solve coupled con- vection and diffusion equations in the viscous layer and calculate the corrosion location in steam generator heating surfaces. The result of proposed model will be compared with other experimental method. 2. Methods and materials After onset of boiling in the heated channel and with regards to solubility of impurities in water, which is much more than in vapor, some part of impurities remain in the liquid phase due to evaporation in the viscous sub layer. The impurities concentration increases in the liquid phase (viscous layer) and only small amounts or more of impurities exit with the vapor. Convection and diffusion are the two phenomena, which have major effects on changing of impurities concentrations. The continuity equation for the liquid phase in the viscous sub layer can be expressed as (Jahanfarnia et al., 2005): ∂ ∂t ((1 - ˛) f ) + ∇((1 - ˛)  W f ) + (1 - ˛) f g = 0 (1) 0029-5493/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2010.10.020