Lanthanide migration and immobilization in metallic fuels

It is recognized that the lanthanide fission products can enhance the fuel-cladding chemical interaction (FCCI), which is a key concern of using metallic fuels such as U-Zr in a sodium-cooled fast reactor. The present work conducts a critical review on the analysis of lanthanide functions in FCCIs. Available in-pile and out-of-pile data are first collected and analyzed, then the theories for lanthanide migration and redistribution in the fuel in operation are analyzed. For mitigating FCCIs, one of the effective method is applying fuel additives for immobilizing lanthanides. The review investigates four candidates of fuel additives (Pd, Sn, Sb and In), and it is concluded that Sb can be the best candidate among the four elements based on current available thermodynamic data and microstructure characterizations. Considering that FCCIs lead to formation of metallic alloys/compounds between lanthanides and steel cladding constituents (Fe, Cr, and Ni), the review also analyzes the thermodynamic data such as enthalpy of formation of the alloys and/or metallic compounds and identify the solidus temperature of each alloy.