DFT study of the fouling deposition process in the steam generator by simulating the absorption of Fe2+ on Fe3O4 (001)

In order to reveal the fouling problem on the outer surface of the steam generator (SG) tube in the secondary circuit condition of pressurized water reactor (PWR) nuclear power plant, based on the density functional theory (DFT) method, the Cambridge sequential total energy program package (CASTEP) is used to simulate seven kinds of highly symmetric adsorption structure models of termination with tetrahedral Fe (A termination) and termination with octahedral Fe (B termination) on Fe3O4 (0 0 1) surface. The adsorption energies and stable adsorption conformations are calculated. The results show that the most stable adsorption structures of the Fe2+/Fe3O4 (0 0 1) configurations are Fe2+ above Fe-O bond of B layer termination (Fe3O4(001) A-b). During the adsorption, the Fe-Fe, Fe-O bond length, and Fe-Fe-O bond angle of (0 0 1) surface change, and the atomic positions parallel and perpendicular to (0 0 1) surface change correspondingly. The change happened to the surface layer is the most drastic one. The calculation of charge population, the density of states (DOS), and electron local function of Fe2+/Fe3O4 (0 0 1) optimal adsorption configuration show that there is electron transfer between Fe2+ and Fe3O4 (0 0 1), and the adsorption type is chemisorption. Among them, Fe (Fe2+)-Fe (Fe3O4) forms a metal bond, and Fe (Fe2+)-O (Fe3O4) forms the ionic bond. The results illustrate the interaction between free Fe2+ and Fe3O4 is the reason of the nucleation and agglomeration of Fe3O4 scale and it provides the foundation for the further research on Fe3O4 scale deposition.