The Behavior of Palladium as a Getter for Lanthanide Fission Products in U-Mo-Ti-Zr Fast Reactor Fuels

One of the hurdles to extending the life of metallic fast reactor fuel alloys is Fuel-Clad Chemical Interaction (FCCI), a phenomenon which occurs between fuel and cladding resulting in thinning of the cladding. The cause of FCCI is the reaction between cladding constituents (e.g. iron and nickel) and lanthanide fission products generated in the fuel (e.g. lanthanum and cerium). This interaction can produce localized melting of the cladding, reducing its thickness over the life of the fuel element. It has been suggested that FCCI can be hindered by doping the fuel with palladium, a candidate getter for lanthanide fission products. There is therefore interest in demonstrating the efficacy of this particular lanthanide getter for realistic fast reactor fuel analogues.;Work is presented based on the U-M (M = 50Mo-43Ti-7Zr, wt. pct.) alloy system both with, and without, palladium additions. The research was conducted using depleted uranium alloys developed as metallurgical surrogates for real spent fuels. Burnup was simulated using cerium as a mock lanthanide fission product to assess the behavior of palladium with respect to fuel and cladding constituents. The behavior of palladium in terms of microstructural evolution was studied from both as-cast and annealed surrogate fuel specimens as well as diffusion couples between surrogate fuel alloys and type HT-9 stainless steel cladding. Results derived from characterization of these metallurgical surrogate experiments are presented and it is shown that palladium is a promising getter for lanthanide fission products in the given alloy system.