Corrosion Product Generation Processes in the Circuits of Nuclear Power Facilities

The problem of improving the corrosion conditions during operation of a nuclear power facility (NPF) is directly connected with increasing the corrosion resistance of structural steels to general (uniform) corrosion, chemical transformation and mass transfer of corrosion products in water coolant in conducting different water chemistry (WC) versions. The article gives a description of the generation processes and chemical transformations of the initial ionic forms of structural steel corrosion products at the initial stage of the general corrosion process followed by the generation of the precursors of solid phase oxide-hydroxide particles (sludge and crud) dispersed in coolant and generation of final solid phase forms of corrosion products such as suspensions, deposits, and corrosion oxide films in the nuclear power facility circuits under the conditions of reduction and oxidative water chemistries. The article proposes a physicochemical model of mass exchange and mass transfer of corrosion products in the steel–water coolant system with taking into account the chemical transformations of corrosion product ionic forms up to the generation of solid phase products in water coolant and on the corroding steel surface, on which a two-layer (with topotaxic and epitaxic layers) oxide film of a local origin is produced. On this film, dense corrosion product deposits from the coolant are formed along with loose (dissipative, weakly fixed) corrosion product deposits that are in equilibrium between the circuit surfaces and coolant. The chemical composition of all product existence forms is determined by the compounds of iron with admixtures of structural steel alloying elements, and the radionuclide composition is determined by the activation products of reactor materials (58Co, 60Co, 54Mn, 59Fe, and 51Cr) and other, more short-lived radionuclides. The proposed body of mathematics can be used for determining the numerical values of the indicators characterizing different corrosion process stages – from metal ionization to generation of final corrosion products on the surfaces and in the coolant of the nuclear power facility circuits under the conditions of different water chemistries.