Microstructural characterization of as-cast U-20Pu-10Zr-3.86Pd and U-20Pu-10Zr-3.86Pd-4.3Ln

Palladium is being investigated as a potential additive to metallic fuel to bind fission product lanthanides, with the goal of reducing or preventing fuel-cladding chemical interactions (FCCI). A primary cause of FCCI is the lanthanide fission products moving to the fuel periphery and interacting with the cladding. This interaction will lead to wastage of the cladding and eventually to a cladding breach. The current study is a scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigation of as-cast U-20Pu-10Zr-3.86Pd and U-20Pu-10Zr-3.86Pd-4.3Ln in wt. %, where Ln = 53Nd-25Ce-16Pr-6La. In U-20Pu-10Zr-3.86Pd, PdZr2 is forming, along with a possible ternary phase between Pu, Zr, and Pd. Pu is also present in the Pd-Ln precipitates formed in U-20Pu-10Zr-3.86Pd-4.3Ln. In the LnPd phase, Pu appears to be substitutional, forming (Ln,Pu)Pd. The other prominent phase, which appears to be Ln7Pd3, has a fine, lamellar structure. The lanthanides remain essentially constant across this fine structure, but Pu and Pd alternate as to which has the higher concentration.