Theoretical and experimental investigation of local concentration processes in PWR steam generators

The accumulation of non-volatile impurities in PWR Steam Generators (SG) has resulted in the accelerated corrosion of SG materials. Local thermal hydraulic and mass transfer processes concentrate impurities from the bulk water by several orders of magnitude under porous corrosion product deposits. The resulting solutions are aggressive and corrode the SG\u27s. Diffusion within the pore solution of the deposits is an important transport process in this problem. In this work, the effective diffusion coefficient for sodium chloride in simulated porous corrosion products was measured. The measurements were made at temperatures up to 280$\sp\circ$C and pressures slightly above the saturation pressure of water. The effect of the porous corrosion product on the measured diffusion coefficient was correlated with temperature and the properties of the deposit.^ A detailed model of the heat, mass and momentum transfer processes within porous deposits of SG\u27s was also developed. The model is used to predict the concentration of a given specie in the crevice as a function of SG design and operating parameters. The model considers two-phase countercurrent flow of water and steam within a porous deposit, driven by capillary forces. Volatilization, convection and diffusion processes are considered in the model. Both transient and steady-state behavior were investigated. The model predictions are compared with experimental data from other investigators.