Lanthanide-induced fuel-cladding chemical interaction (FCCI) is the key concern of U-Zr fuel. Unlike UO2 where lanthanides are stabilized by oxygen, the lanthanides are free atoms and can migrate along the gradients of temperature and concentration in U-Zr. There are three theories to describe the FCCI process, which are solid phase diffusion, vapor phase transport, and liquid-like transport. The liquid-like transport theory is opposite to the other two and better explains the distribution, precipitation and rapid migration process. HT-9 is the leading cladding candidate for U-Zr fuel. To investigate the effects of composition and microstructure of cladding on FCCI, out-of-pile diffusion couple testing were carried out with a focus of chemical interaction zones formed by between lanthanides and different types of stainless steels, including HT-9, Fe-Cr oxide dispersion-strengthened (ODS), Fe-Cr-Ni ODS, wrought 316L, and additively manufactured 316L. Doping additives in the U-Zr fuel was found to stabilize lanthanides and mitigate FCCI.