Developing Technologies for Protective Oxidation of Equipment in the Third Circuit of a BN-800 Reactor Unit

The results of the development of alternative technologies for directional protective oxidation of working surfaces of equipment made of pearlitic steels for the evaporating and superheating modules of the N-272 vertical steam generator (SG) of the BN-800 reactor unit (RU), operated under the conditions of an oxygen-ammonia water-chemical regime, are presented. The formation of protective oxide films of magnetite with desired properties occurs during the thermolysis of aqueous solutions of complexonates and iron complexes with various ligands in contact with the surface of pearlite-class steels. Two-stage technologies of directional oxidation are based on the use of solutions of ammonium acetate or Trilon B. The chemical forms of iron compounds in working solutions for the formation of high-quality protective films have been established. At the first stage, associates of “oxidizing” Fe(III) complexes with elemental iron atoms in active centers of metal dissolution are formed. At the second stage, the thermal decomposition of the associates occurs with the formation of nuclei of magnetite crystals, which retain the chemical bonds that have arisen in the associates between the metal atoms in the crystal lattice of steel and in the dissolved Fe(III) complex. The temperature range of thermal decomposition of associates of primary Fe(III) complexes in contact with iron atoms on the steel surface for the implementation of the formation of oxide films has been established. The compositions of the solutions and the parameters of the protective oxidation process by acetate and complex technologies have been substantiated, and the protective properties of the formed oxide films have been established. A combined technology of complex oxidation with the transformation of the washing solution into a solution of directional oxidation has been developed, which makes it possible to drastically reduce the volume of generated liquid waste. Recommendations are given for choosing the optimal variant of the oxidation technology, taking into account the thermal characteristics of the equipment.