Study on the relationship between Fe3O4 fouling and NiFe2O4 oxide layer in the secondary circuit of nuclear steam generator

Abstract

Fouling is one of the most significant problem in the steam generator (SG) of pressurized water reactor (PWR) nuclear power plant (NPP). To figure out the deposition process, through changing the Fe2+concentration and temperature in the simulated configurations (523 K–603 K), adsorption mechanism of fouling Fe3O4 on steam generator (SG) tube in secondary circuit of pressurized water reactor (PWR) nuclear power plant was investigated by molecular dynamic simulation. The ion concentration distribution, the mean square displacement (MSD), the radial distribution function (RDF), and the energy change before and after adsorption were compared. The influence of the change of temperature and Fe2+ concentration on the corrosion of the SG tube was discussed. Due to the negative surface charge of NiFe2O4, the Fe2+ in the solution did not bond with OH−, but agglomerated with high-pressure high-temperature H2O in the form of triangular bipyramid and octahedron. The diffusion coefficient of OH− increases linearly with the increase of temperature (from 15.28 × 10−5 cm2/s to 18.59 × 10−5 cm2/s) and concentration (from 14.40 × 10−5 cm2/s to 16.06 × 10−5 cm2/s). While the diffusion coefficient of Fe2+reduces, the diffusion coefficient of H2O changes. Simultaneously, Fe3O4 fouling formed on the surface of NiFe2O4 dense oxide layer due to the ion adsorption and interface charges. This work can provide an atomic-scale basis for fouling inhibition in the SG of PWR nuclear power plant.