Development of Chemical Decontamination Process Based on Ozone for System Surfaces with Chromium Containing Oxides

Abstract

Chromite or chromium containing oxides are formed as a protective oxide film on the stainless steel surface of heat transport systems. The chemical dissolution of these passive oxide films forms an important step in decontamination formulation development for water-cooled nuclear reactor systems. Dissolved ozone as a reagent was tested for effective chemical dissolution of Fe3+ substituted in nickel chromite and individual component oxides. The study showed the importance of the solution pH and temperature on the dissolution kinetics of Cr2O3, NiO, and NiFexCr2-xO4. Neutral water pH or 0.04 mM OH− were better for achieving a high dissolution rate for chromium containing oxides compared to acidic (2.5 mM H+) or alkaline conditions. In an acidic condition, the release of nickel from NiO or nickel chromite was more in the ozone medium compared to a high pH condition. Substitution of Fe3+ in nickel chromite affected the dissolution behavior in the ozone medium. The dissolution of Fe3+ substituted in nickel chromite showed a small increase in the dissolution rate constant with up to composition x = 0.4, and further increase in the Fe3+ composition in the oxide lattice decreased the dissolution rate constant.