Corrosion of Austenitic Steels and Their Components in Molten Nacl–Kcl–UCl₃

The fused halides can be used for nuclear fuel reprocessing and as working media for molten salt nuclear reactors. However practical implementation of such technologies is limited by the problem of finding suitable corrosion resistant materials capable of long-term working in contact with molten salts. From the economical point of view the application of stainless steels as construction materials for the molten salt media is one of the most prospective ways. In the present study the corrosion behaviour of metallic iron, nickel, chromium, molybdenum, AISI 316L and 12Kh18N10T (analogue of AISI 321) austenitic steels was studied in NaCl–KCl–UCl 3 (1 wt.% U) melts at 750 ºC. Gravimetric measurements served as a basis for estimating corrosion resistance of studied materials. Quenched melts were analyzed using ICP-AES method. The surface of the alloy samples after corrosion tests was characterised using XRD, SEM and Х-ray microanalysis. The foils of corroded materials were examined by TEM. The corrosion rates of studied metals in NaCl–KCl–UCl 3 melt decrease in the following order: Cr>Fe>Ni>Mo, which correlates well with the formal standard potentials of metals in chloride melts indicating electrochemical nature of the corrosion processes. Molybdenum is the only corrosion resistant metal in the uranium-containing chloride melts and it can be used as a construction material for molten salt reactors. The major products of stainless steel corrosion in chloride melts are iron, chromium and manganese species. The surface of the corroded samples of austenitic stainless steels was depleted in manganese and chromium and enriched in nickel and molybdenum. Intergranular corrosion was observed for all types of austenitic steels. In terms of intensity and depth of the corrosion layer in NaCl–KCl–UCl 3 the studied steels can be ranged in the order AISI 321>AISI 316L that correlates with the amount of excessive phases formed (figure). Figure 1