Chemical interactions between neodymium and advanced stainless steels

During the burnup of U–Zr based metal fuels, lanthanide fission products migrate to fuel periphery and deposit on cladding inner surface, resulting in fuel-cladding chemical interaction (FCCI). Of the lanthanide fission products contained in irradiated U-Zr based fuels, neodymium (Nd) has the highest concentration. In this study, we performed out-of-pile diffusion couple testing to investigate the chemical interactions between neodymium (Nd) and four types of stainless steels (SSs), aiming at elucidating the effects of composition and microstructure on the chemical interactions. The four types of steels are Fe-Cr based oxide dispersion-strengthened (ODS) steel (ODS-1), Fe-Cr-Ni based ODS steel (ODS-2), additively manufactured (AM) 316L SS (A316), and wrought 316L SS (W316). The results show that the interdiffusion between the major constituents in ODS-1 (Fe and Cr) and Nd is suppressed, while nickel was the most active element during diffusion between ODS-2/A316/W316 and Nd, leaving a relatively large depletion area in ODS-2/A316/W316. Compared to W316, the 200-nm pores in the A316 assisted the interdiffusion between the steel constituents and Nd, while the large grain size resulted in slower diffusivity. The kinetics of chemical interaction between Nd and SSs is strongly dependent on the microstructure, including pore structure and grain size.