Computational study of Fe3O4 adsorption behaviour on the secondary side of the heat exchange tube in the steam generator

Abstract

Based on the scaling problem on the outer surface of the steam generator tube in the secondary circuit condition of pressurizedwaterreactor, the molecular dynamic was used to calculate the adsorption characteristics of Fe3O4. The trajectory, mean squared displacement, radial distribution function and adsorption energy of Fe3O4 agglomeration and deposition process were further analyzed through variation of temperature and concentration. When the temperature was between 510 K and 530 K, the diffusion coefficient of Fe2+ and OH− could reach the minimum value of 2.255 × 10-5 cm2/s and 2.638 × 10-5 cm2/s, respectively. During variation of Fe2+ concentration, the size of agglomerate particles increased continuously, and the diffusion coefficient of H2O can reach the minimum value of 3.78 × 10-5 cm2/s. Fe2+ with positive charges can effectively agglomerate with H2O and OH−, forming the tetrahedral and octahedral structures of Fe3O4 crystal. At this time, a small number of OH− were adsorbed at the interface of the matrix, forming the double electrical layer and affecting the deposition of agglomerated Fe3O4. Apart from this, high temperature is beneficial to inhibit scaling deposition in part. Likewise, low concentration of the dissolved Fe2+ and OH− can also lead to weaker deposition of agglomerated Fe3O4 on the outer scaling layer of the secondary side in the steam generator.