Corrosion of EP-823 STEEL (16Kh12MVSFBR) under conditions of high-temperature processing of spent nuclear fuel

The corrosion behavior of EP-823 steel was studied during high-temperature treatment (HTT) with nitrogen. It was found that in nitrogen at temperatures of 650–800°C, the steel is subject to only slight surface corrosion. It is shown that there is a slight change in the surface composition and structure of steel, which does not have a significant effect on the reprocessing of model SNF. It is shown that on the surface of the material, processes of interaction of some electronegative components of ferritic-martensitic steel with components of the gas phase – nitrogen and impurity oxygen – occur with the formation of inclusions of nitride and oxide compounds of chromium and manganese of different stoichiometric compositions. The process is limited by the diffusion of these components from the volume of the alloy to the surface. The corrosion rates of EP-823 steel at temperatures of 650 and 800 ° C were 0.104 and 0.241 mm / year for 12 hours of exposure, and 0.013 and 0.02 mm/year for 84 hours of exposure, respectively. The nature of the destruction of the surface of the samples is continuous and uneven, localization of corrosion at the boundaries of steel grains is clearly observed, which is associated with the formation of secondary phases along the grain boundaries. At the temperature of the treatment, significant sensitization of steel occurs, chain-like precipitation of secondary phases is observed along the grain boundaries, which leads to the development of intercrystalline corrosion. Conclusions are made about the change in the structure of the material during high-temperature exposure and the nature of the corrosion damage of the material is determined; based on the results of X-ray fluorescence analysis, conclusions are made about the composition of the corrosion products of EP-823 steel.