INTERACTION OF NICKEL IONS WITH MAGNETITE PARTICLES IN HIGH-TEMPERATURE WATER

The current study addresses the needs for deeper understanding of the behavior of iron-nickel based corrosion product systems, particularly the mechanism of ion/oxide interaction, formation and dissolution of n onstoichiometric nickel ferrites, which are believed to be the key tar gets of the activity transport in the primary circuits of light water reactor systems. The interaction of Ni2+ ions with Fe3O4 particles was studied experimentally in the aqueous phase at 423 and 473 K by monit oring the concentrations of nickel and iron ions in the aqueous phase after the injection of nickel ion solutions to the magnetite particle dispersion system. Formations of NiO or NiFe2O4, as initial metastable states, depending on the amount of the injected Ni2+ ions, were obser ved in the experimental series. A systematic understanding of the inte raction mechanism was achieved based on the methods of both the thermo dynamic analyses and solid-state diffusion. A new approach was propose d to treat a set of metastable states of the system tending to reach i ts most stable equilibrium state under a given initial condition. It w as concluded from the experimental results and the thermodynamic analy ses that the formed systems are gradually transforming through changin g their composition and number of solid phases to the most stable stat e defined only by one solid phase, NixFe3-xO4.