Abstract
Phase-stability in a U-Zr-Te-Nd multi-component metallic fuel for advanced nuclear reactors is systematically investigated by taking into account binary, ternary and quaternary interactions between elements involved. Historically, the onset of fuel-cladding chemical interactions (FCCI) greatly limits the burnup potential of U-Zr fuels primarily due to interactions between lanthanide fission products and cladding constituents. Tellurium (Te) is evaluated as a potential additive for U-Zr fuels to bind with lanthanide fission products, e.g. neodymium (Nd), negating or mitigating the FCCI effect. Potential fresh fuel alloy compositions with the Te additive, U-Zr-Te, are characterized. Te is found to completely bind with Zr within the U-Zr matrix. Alloys simulating the formation of the lanthanide element Nd within U-Zr-Te are also evaluated, where the Te-Nd binary interaction dominates and NdTe is found to form as a high temperature stable compound. The experimental observations agree well with the trends obtained from density functional theory calculations. According to the calculated enthalpy of mixing, Zr-Te compound formation is favored in the U-Zr-Te alloy whereas NdTe compound formation is favored in the U-Zr-Te-Nd alloy. Further, the calculated charge density distribution and density of states provide sound understanding of the mutual chemical interactions between elements and phase-stability within the multi-component fuel.
Highlights
Phase stability in a multi-component alloy is determined by a complex set of mutual chemical, elastic and other energetic interactions between elements of the alloy
The Te addition is based on the anticipated amount needed to bind all of the lanthanides that form in the fuel at the respective concentrations
The concentration of neodymium in the alloys represents the anticipated total lanthanide amount to form within the fuel at both 8 and 16 at.% burnups based on fission product concentrations reported by Mariani et al.[6]
Summary
Phase stability in a multi-component alloy is determined by a complex set of mutual chemical, elastic and other energetic interactions between elements of the alloy. As opposed to acting as a diffusion barrier, i.e. liners and coatings, fuel additives are alloyed with the fuel to form high-temperature, stable compounds with lanthanide fission products as they form within the fuel during irradiation, stabilizing them within the fuel meat and limiting their interaction with cladding constituents at the fuel – cladding interface. It is worth noting that in their characterization of the U-10Zr-Te-Ce alloy, their results indicate Te and Ce primarily form the stable compound CeTe. In the present study, the microstructure of potential fuel compositions that may be resistant to FCCI are characterized, followed by a characterization of fuel compositions that contain Nd to simulate the formation of lanthanide fission products through fuel burnup. This research focuses on the mutual interactions between elements in the U-Zr-Te and U-Zr-Te-Nd multi-component alloys, which lead to stable phase formations within the U-Zr matrix
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