THE INFLUENCE OF THE OXIDATION-REDUCTION POTENTIAL OF THE ENVIRONMENT ON THE CORROSION OF 12Cr18Ni10Ti STEEL IN THE MELT (LiCl-KCl)-UCl/UCl

Currently, high-temperature technology for processing spent nuclear fuel using molten salts is being actively developed. One of the key stages of this technology is electro-refining using a salt composition based on LiCl-KCl as an electrolyte. High operating temperatures and changes in the composition of salt electrolytes as a result of ongoing technological processes cause increased aggressiveness of the melt with respect to structural materials. The work investigated the effect of changing the oxidation-reduction potential of the medium, set by introducing uranium chlorides into the salt electrolyte (the proportion of trivalent uranium chlorides in the additive 2 wt.% UCl/UCl from 5 to 95%) on the corrosion characteristics of 12Cr18Ni10Ti stainless steel in a melt of lithium and potassium chlorides. Corrosion tests lasting 100 hours were carried out at a temperature of 550°C in an inert gas environment of argon with a water content of less than 0.1 ppm and oxygen content of less than 10 ppm. The oxidation-reduction potential of the environment was determined both relative to the chlorine and relative to the lithium dynamic reference electrode (Li/Li). With the predominant introduction of UCl into the melt, a decrease in the corrosion rate is observed (up to 0.005 g/(m•h)). In the same time with the introduction of the tetravalent form of uranium chloride a significant increase in the corrosion rate of 12Cr18Ni10Ti steel (up to 0.703 g/(m•h)) relative to the corrosion rates obtained as a result of corrosion tests in the eutectic melt of LiCl-KCl without additives (0.062 g/(m•h)). With an experimentally measured value of the ORP of the melt (LiCl-KCl)-UCl/UCl (relative to the lithium dynamic reference electrode) from 1.78 to 2.08 V, the corrosion rate of 12Cr18Ni10Ti steel is lower than the value of the corrosion rate of this steel in the eutectic melt of lithium and potassium chlorides.