Lanthanides migration and immobilization in U–Zr nuclear fuels

Redistribution of lanthanides fission products during irradiation and migration to the surface of U–Zr based metallic fuels is a concern due to their interaction with the cladding. The existing remedy for preventing this effect is the introduction of diffusion barriers on the cladding inner surface or by adding thermodynamically stable compound-forming elements to the fuel. Exploring this second option, in this work atomistic modeling with the Bozzolo–Ferrante–Smith (BFS) method for alloys is used to study the formation of lanthanide-rich precipitates in U–Zr fuel and the segregation patterns of all constituents to the surface. Surface energies for all elements were computed and, together with the underlying concepts of the computational methodology and large scale simulations, the migration of lanthanides to the surface region in U–Zr fuels is explained. The role of additions to the fuel such as In, Ga, and Tl for immobilization of lanthanides is discussed.