Study on diffusion and migration characteristics of impurities in secondary side of simplified u-tube steam generator

Abstract

During the operation of nuclear power systems, the occurrence of leakage accidents of primary and secondary condensers are a major concern due to the potential threat to safe operation. The entry of seawater into the secondary loop from the condenser, along with impurities such as Cl-, can accumulate near the heat transfer tube, causing wear and corrosion, which can further aggravate the situation. Therefore, it is essential to accurately understand the migration and diffusion process of impurities in the secondary side of the steam generator. This study aims to investigate the three-dimensional multi-tube physical model of fluid–structure coupling heat transfer in the primary and secondary loops of the steam generator, including the heat exchange tube, to gain insights into the migration and diffusion of Cl- and other impurities. The distribution of important thermal parameters, such as volume vapor fraction, temperature, and velocity, in a U-shaped tube bundle were analyzed by numerical simulation of heat transfer and fluid flow. The diffusion and migration of Cl- in a two-phase flow were also studied. Results of this study reveal that impurities concentration is influenced by the effective diffusion coefficient, which is further influenced by the boiling intensity and flow velocity of the coolant. The combined effect of the boiling intensity and flow velocity of the coolant has a synergistic effect on the migration and diffusion of Cl-. In conclusion, this study provides valuable insights into the flow heat transfer impurity migration under a multi-tube coupled heat transfer condition of the steam generator, which can be used as a scientific basis for the design optimization and operation of steam generators.