doi: 10.1007/s12540-014-5004-z Met. Mater. Int., Vol. 20, No. 5 (2014), pp. 819~824 Interaction Between Multi-Component Lanthanide Alloy and Ferritic-Martensitic Steel Jun Hwan Kim * , Jin Sik Cheon, June Hyung Kim, Byoung Oon Lee, and Chan Bock Lee Korea Atomic Energy Research Institute, Advanced Fuel Development Division, Daejeon 305-353, Korea (received date: 5 November 2013 / accepted date: 3 February 2014) Studies were carried out to evaluate the effect of lanthanide elements which are generated during the fission process on the interaction between metal fuel and cladding material. Quartenary lanthanide alloy as Nd-Ce- Pr-La and Sm-contained quintenary alloy were manufactured by vacuum arc remelting and a diffusion couple test with HT9 (12Cr1MoWV) alloy was carried out at 660 and 700 ° C for up to 231 h followed by micro- structural analysis. The results showed that interdiffusion between lanthanide element (Nd, Ce) and Fe took place as the diffusion couple test proceeds to form intermetallic compounds as an RE2(Fe,Cr)17 (RE=Nd, Ce, Pr, La) type. As the number of alloying elements increased, the reaction layer thickness increased, but a deviation of the theoretical non-linear relationship as well as an increase in the rate exponent occurred. Instantaneous dif- fusion of Fe into a lanthanide side and its associated Fe depletion beneath the interface acted as the major driving force in forming the reaction layer. The addition of Ce enhanced the Nd diffusion and increased the layer growth when compared to pure Nd alone. Keywords: metals, annealing, diffusion, scanning electron microscope, lanthanide, HT9 1. INTRODUCTION Metal fuel is considered one of the major candidates in next generation reactor fuel used in a Sodium-cooled Fast Reactor (SFR) on account of its high inherent safety and pro- liferation resistance in connection with pyroprocessing [1]. However, actinide elements like U and Pu which mainly con- stitute metal fuel are apt to react with a cladding element like Fe and melt at around the reactor operating temperature which endangers fuel safety (Fuel-Cladding Chemical Interaction, FCCI). Metal fuel is made from spent fuel by a commercial light water reactor (LWR) which contains approximately 1 wt% of lanthanide elements such as La, Ce, Nd, Pr, Sm and so on [2]. In addition, new lanthanide elements will be gener- ated inside the fuel during the operation of a fast reactor and they migrate at the fuel-cladding interface according to the thermal gradient. A recent study reported that these lantha- nide elements will exacerbate the FCCI process by reducing the eutectic temperature [3]. As the majority of components at the outer region of metal fuel during irradiation are lantha- nide elements, it is worthwhile to evaluate FCCI behavior of cladding material using lanthanide alloy alone. A diffusion couple test with mischmetal (70Ce-30La) and cladding mate- rial (9Cr-2W) revealed that interdiffusion and subsequent eutectic reaction occurred at around 660 ° C which corresponds to the SFR operating temperature [4] and similar process was found using Nd [5]. Previous research was limited in terms of a single element, and little research was conducted to investigate the comprehensive effect of the multi-component lanthanide element that closely simulates actual metal fuel [6-9,14-19]. This study aims to investigate the effect of multi-compo- nent lanthanide alloy on the FCCI process, which closely simulates metal fuel formed from spent fuel and its associ- ated pyroprocssing. Quartenary La-Ce-Pr-Nd alloy was fab- ricated using vacuum arc remelting, a diffusion couple test with cladding material was carried out, and a microstructural analysis was conducted. Quintenary lanthanide alloy, which added Sm, was fabricated and the effect of Sm was evaluated. 2. EXPERIMENTAL PROCEDURES 2.1. Materials Quartenary lanthanide alloy was made to simulate metal fuel. A 200 g ingot containing 53 wt% of Nd, 25 wt% of Ce, 16 wt% of Pr, and 6 wt% of La was manufactured using a vacuum arc remelting (VAR) process. Five times of remelting was attempted to keep the homogeneity of the alloy ingot, while the degree of the vacuum was maintained at 5.0×10 5 Torr. A *Corresponding author: junhkim@kaeri.re.kr KIM and Springer