Masters Theses
Date of Award
12-2024
Degree Type
Thesis
Degree Name
Master of Science
Major
Nuclear Engineering
Major Professor
Nicholas Brown
Committee Members
Philip Rack, Lawrence Heilbronn
Abstract
This work optimizes micro-prismatic high-temperature gas reactor (mHTGR) designs to reduce the energy-normalized mass of spent nuclear fuel and high-level waste (SNF&HLW) produced. The optimization was performed for the current graphite moderator and an inert matrix fuel (IMF) concept employing different composite moderators in a prismatic design architecture. The fuel matrix is magnesium oxide (MgO) with entrained tristructural-isotropic (TRISO) fuel. Moderator material including beryllium oxide (MgO-BeO) and beryllium (MgO-Be) at 40 vol. % loading, and yttrium hydride (MgO-YHx=1.9) and zirconium hydride (MgO-ZrHx=1.9) at 15 vol. % loading were entrained within the MgO host matrix. The optimized designs were evaluated and compared on several fuel cycle metrics.
For the mass of spent nuclear fuel and high level waste per unit of energy generated, the composite moderators saw reductions of between 12.6 and 45.0% compared to the graphite reference case. For the volume of low-level waste (LLW) per unit of energy generated, the composite moderators produced between 31.4 and 43.5% less LLW compared to the graphite reference. The last nuclear waste metric is the energy- normalized mass of depleted uranium per unit of energy generated. The composite moderators continued to perform well compared to the graphite reference case, seeing between 12.6 and 45.0% reduction.
In addition to the nuclear waste metrics, the environmental impact of the reactor fuel cycles was evaluated by calculating the energy-normalized mass of natural uranium, the mass of carbon dioxide, the land area, and the volume of water used. Overall the composite moderators produced good reductions in the environmental impact of the fuel cycles. The composite moderator’s designs did not result in significant increases in the activity of the SNF&HLW after 100 to 100,000 years after reactor shutdown. Compared to a graphite reference, composite moderators significantly reduced nuclear waste, environmental impact, and fuel cost. The reduction compared to a graphite reactor makes the mHTGRs an attractive option for micro-reactor designs.
Recommended Citation
Doyle, Donald L., "Composite Inert Matrix Fuel Forms in High-Temperature Gas Cooled Micro-Reactors to Reduce Spent Nuclear Fuel, High Level Waste and Environmental Impact. " Master's Thesis, University of Tennessee, 2024.
https://trace.tennessee.edu/utk_gradthes/12848
