Modeling the Influence of Boiling in the Core of WWER-1200 on Uniform Corrosion of the Outer Surface of Fuel Elements

The parameters of the coolant moving in the channel between the fuel elements in the WWER-1200 core with a design steam content of 0.1 at the outlet are determined. The corrosion of the outer surface of these elements is modeled taking into account the heat and mass exchange between the near-wall layer of the coolant flow (with a thickness of the order of the thickness of the evaporating microlayer under the steam bubble) and its core. It is found that the concentration of ammonia in the near-wall layer of the flow is 0.35 of its concentration in the flow core, and this concentration level is typical of the upper half of the core. A formula is proposed for calculating the thickness of the oxidized layer of the outer surface of the fuel elements taking into account the concentration of oxidizers in the near-wall layer of the coolant flow. An increase in the thickness of the oxidized layer due to the effect of boiling is estimated at 30% compared to the thickness observed upon completion of operation during four annual cycles without boiling.