Calculated Evaluation of Mass Transfer of Corrosive Hydrogen in a Steam Generator of a Sodium Water Type during Chemical Washing and in Operation

For timely and prompt detection of depressurization of the "sodium-water" type steam generator in the second circuit, the hydrogen content as a product of the interaction of sodium with water is continuously monitored. During the operation of the steam generator, corrosion products accumulate on the surface of the structural material. Removal of deposits is carried out using operational chemical flushing (OCF). However, during the OCF, the corrosion rate increases significantly, which leads to an increase in the concentration of hydrogen in water and sodium. Diffusion of hydrogen from the water circuit to the sodium circuit through the walls of the steam generator tubes can affect the material (steel) of the steam generator by hydrogenation of the steel. If the established limits for hydrogen content in steel are exceeded, it becomes embrittled, which can lead to a leak in the steam generator. This problem raises concerns due to the regular OCF (one steam generator is washed every year). However, rejection of OCF is unacceptable. In order to answer the question of whether the contribution of OCF to the hydrogenation of steel is critical, it is necessary to assess the contribution of the mass transfer of corrosive hydrogen to the operating mode of the steam generator. The article presents the results of the analysis of the operational data of the BN-600 reactor plant on the hydrogen content in the washing solution and sodium in the secondary circuit during chemical washing, passivation, and start-up of the power unit. A computational and analytical assessment of the behavior of corrosive hydrogen and its mass transfer to the steam generator during chemical washes has been carried out. Estimating the hydrogenation of the pipes' metal in the steam generator is carried out.