CORROSION BEHAVIOR OF 12Cr18Ni10Ti STEEL IN LiCl–KCl MELT CONTAINING ADDITIVES OF f-ELEMENT CHLORIDES

When reprocessing spent nuclear fuel, it is supposed to use LiCl–KCl melt (0.49:0.51) in an inert atmosphere, all metal materials in this salt melt are extremely susceptible to corrosion, besides, during the processing of spent fuel, both the liquid (melt) and the gas phase are saturated with decay products that can act as additional oxidizing agents, increasing the aggressiveness of the environment. The pyrochemical technology of SNF includes operations such as soft chlorination, electrofining and metallization, implying the presence in the melt of compounds of chlorides of rare earth metals lanthanum, cerium and neodymium, as well as uranium(III, IV) chlorides. In this work, the corrosion behavior of 12CR18NI10TI steel in LiCl–KCl melt containing NdCl₃, CeCl₃, LaCl₃, UCl₃ and UCl₄ additives up to 2 wt % was investigated. Corrosion tests lasting 100 hours were performed at a temperature of 500°C in an inert argon atmosphere. It was found that the presence of REM chlorides significantly reduces the degradation of the steel under study. The addition of (REM)Cl₃ leads to the formation of a compound (REM) on the surface of the samples OCl, the thickness and continuity of which increases in the following row: LaCl₃ < NdCl₃ < CeCl₃. The formation of such a compound leads to the inhibition of the corrosion process of steel 12CR18NI10TI due to salt passivation of the surface. The addition of UF4 to the melt causes significant corrosion of 12CR18NI10TI intercrystalline steel. The introduction of UF₃ into the melt leads to a decrease in the corrosion rate, which is associated with the predominant interaction of trivalent uranium chloride with dissolved molecular oxygen contained in the melt, and the formation of a non-stoichiometric compound with the crystal chemical formula U₃O₇ on the surface of samples according to microrentgenospectral analysis.