Corrosion Behavior of High-Chromium Alloys in Molten LiCl-KCl Eutectic

doi:10.1007/s40195-024-01742-9

Abstract

Abstract:

Pyrochemical reprocessing utilizing a molten LiCl-KCl eutectic medium is regarded as the most promising approach for recovering uranium and transuranic elements from spent metallic nuclear fuels. However, the harsh corrosiveness of molten chloride poses a significant challenge to the durability of structural materials. Herein, we report the corrosion behavior of 304 SS, 316H SS and Inconel 800H in LiCl-KCl eutectic salt at 550 °C for 100 h under an argon atmosphere. Experimental results indicate that all three materials can form a rather continuous Cr₂O₃-based scale through oxidation reaction at the beginning, but only the scale developed on 800H maintains excellent protection against corrosion throughout the entire exposure period. In contrast, both 304 SS and 316H SS experience considerable active dissolution on the bare substrate under a detached scale. We suggest that the primary reasons for the outstanding resistance of 800H to molten salt corrosion are the high concentration of noble Ni in the system, which lowers the inclination for active dissolution, and the beneficial addition of Al, which accelerates the formation of a less defective Cr₂O₃-based scale. Our work offers an in-depth understanding on the corrosion performance of high-Cr alloys in molten chloride, insights critical for the selection and subsequent development of structural materials for pyrochemical reprocessing applications.

Key words: Corrosion, High-chromium alloys, Molten salt

Mengmeng Ji, Xin Li, Zihe Liu, Xiaoguang Yang, Xue Zhang, Ying Li. Corrosion Behavior of High-Chromium Alloys in Molten LiCl-KCl Eutectic[J]. Acta Metallurgica Sinica (English Letters), 2024, 37(10): 1809-1818.

Figures/Tables 9

Table 1 Chemical compositions of the tested materials (in wt%)

Alloy	Fe	Cr	Ni	Mo	Mn	Si	Al	Ti
304	Bal.	18.5	9.5	-	0.16	0.45	-	-
316H	Bal.	18.0	12.0	2.6	1.50	0.40	-	-
800H	Bal.	21.0	30.8	-	-	-	0.46	0.42

Fig. 1 Optical metallographic structures and average grain sizes of 304 SS a, 316H SS b, Inconel 800H c

Fig. 2 Cross-sectional morphologies and corresponding EDS analyses of 304 SS after immersion in LiCl-KCl eutectic at 550 °C for 100 h under argon atmosphere: a region with an adhesive scale a, a region with a detached scale b

Fig. 3 SEM/EDS measurements of 316H SS post exposure to LiCl-KCl eutectic at 550 °C for 100 h under argon atmosphere. A low magnification cross-sectional image of a typical region with an almost fully detached scale a. EDS line-scan measurements performed on regions with representative oxides b, c

Fig. 4 SEM/EDS measurements of Inconel 800H after exposure at 550 °C for a period of 100 h in the LiCl-KCl melt. A low magnification cross-sectional image that inserted with a histogram comprising the averaged scale thickness and GB oxidation depth a. EDS line-scan measurement of a region with typical GB oxides b. EDS mappings of a near-surface region crowded with oxides c

Fig. 5 Phase equilibrium diagram of oxygen partial pressure versus temperature of Fe-18.5Cr-9.5Ni-0.16Mn-0.45Si (in wt%)

Fig. 6 Phase equilibrium diagram of oxygen partial pressure versus temperature of Fe-18Cr-12Ni-2.6Mo-1.5Mn-0.4Si (in wt%)

Fig. 7 Phase equilibrium diagram of oxygen partial pressure versus temperature of Fe-21Cr-30.8Ni-0.46Al-0.42Ti (in wt%)

Fig. 8 Schematic diagram for the corrosion evolution processes of 304 SS, 316H SS and 800H in molten chloride

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