Nathan Jerred

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.

The feasibility of the fabrication of tungsten based nuclear fuel cermets via Spark Plasma Sintering (SPS) is investigated in this work. CeO₂ is used to simulate fuel loadings of UO₂ or Mixed-Oxide (MOX) fuels within tungsten-based cermets due to the similar properties of these materials. This study shows that after a short time sintering, greater than 90 % density can be achieved, which is suitable to possess good strength as well as the ability to contain fission products. The mechanical properties and the densities of the samples are also investigated as functions of the applied pressures during the sintering.

The overall scope of this article is to develop and investigate different heat exchanger concepts for a closed CO₂ Brayton power cycle with regeneration that is part of the fission to surface power system (FSPS) concept from NASA, designed to function as a lunar outpost. The heat exchangers investigated are designed with the goal of utilizing ‘off the shelf technology’ and a sub-goal to ensure the heat exchangers designed are integrated into the FSPS as a whole. The FSP system utilizes two streams as the hot and cold sources: 850K sodium and potassium eutectic (NaK) stream from a nuclear reactor and 375K water stream cooled in titanium radiator piping as the cold source, which must be kept as a liquid. The thermodynamics and heat exchanger parameters were modelled and calculated using chemical process simulation software. The power delivered is 10kW electric per power conversion unit. There are three heat exchangers investigated as possible options for the NaK—CO₂ hot side heat exchanger. When compared with a shell-and-tube heat exchanger, the compact heat exchangers are a better choice because they provide a lower mass system and a smaller footprint.