Doctor of Philosophy

dissertationControlling combined sewer overflows (CSOs) is one of the greatest urban drainage challenges in more than 700 communities in the United States. Traditional drainage design typically leads to centralized, costly and energy-intensive infrastructure solutions. Recently, however, application of decentralized techniques to reduce the costs and environmental impacts is gaining popularity. Rainwater harvesting (RWH) is a decentralized technique being used more often today, but its sustainability evaluation has been limited to a building scale, without considering hydrologic implications at the watershed scale. Therefore, the goal of this research is to study watershed-scale life cycle effects of RWH on controlling CSOs. To achieve this goal, (i) the life cycle costs (LCC) and long-term hydrologic performance are combined to evaluate the cost-effectiveness of control plans, (ii) the life cycle assessment (LCA) and hydrologic analysis were integrated into a framework to evaluate environmental sustainability of control plans, and (iii) the major sources of uncertainty in the integrated framework with relative impacts were identified and quantified, respectively. A case study of the City of Toledo, Ohio serves as the platform to investigate these approaches and to compare RWH with centralized infrastructure strategies. LCC evaluation shows that incorporating RWH into centralized control plans could noticeably improve the cost-effectiveness over the life cycle of drainage infrastructure. According to the results of the integrated framework, incorporating RWH could reduce Eco-toxicity Water (ETW) impacts, but caused an increase in the Global Warming Potential (GWP). In fact, incorporating RWH contributes to avoidance of untreated discharges into water bodies (thus reducing ETW) and additional combined sewage delivered to treatment facilities (thus increasing GWP). The uncertainty analysis suggests that rainfall data (as a hydrologic parameter) could be a significant source of the uncertainty in outputs of the integrated framework. Conversely, parameters of LCIA (life cycle impact assessment) could have trivial impacts on the outputs. This supports the need for robust hydrologic data and associated analyses to increase the reliability of LCA-based urban drainage design. In addition, results suggest that such an uncertainty analysis is capable of rendering optimal RWH system capacity as a function of annual rainfall depth to lead to minimized life cycle impacts. Capacities smaller than the optimal size would likely result in loss of RWH potable water savings and CSO control benefits, while capacities larger than optimal would probably incur excessive wastewater treatment burden and construction phase impacts

Multiphysics Assessment of Accident Tolerant Fuel, Cladding, and Core Structural Material Concepts

The severe accident at the Fukushima-Daiichi nuclear power plant in 2011 ignited a global research and development effort to replace traditionally-used materials in Light Water Reactors (LWRs) with Accident Tolerant Fuel (ATF) materials. These materials are intended to extend the coping time of nuclear power plants during severe accident scenarios, but must undergo thorough safety and performance evaluations before being implemented. Four ATF concepts are analyzed in this dissertation using state-of-the-art computer modeling tools: (1) iron-chromium-aluminum (FeCrAl) fuel rod cladding, (2) silicon carbide (SiC) fiber-reinforced, SiC matrix composite (SiC/SiC) boiling water reactor (BWR) channel boxes, (3) mixed thorium mononitride (ThN) and uranium mononitride (UN) fuel, (4) and UO2 [uranium dioxide] with embedded high thermal conductivity Mo inserts. The goals and approaches used for each study differed, and portions of this dissertation focused on verifying the accuracy of advanced modeling tools. Although each ATF evaluation is distinct, the underlying theme is the enhancement of safety, efficiency, and economic competitiveness of nuclear power through the use of advanced modeling techniques applied to material characterization studies. Results from the evaluations show the pros and cons of each ATF concept and highlight areas of needed modeling development. Comparisons of simulated and experimental critical heat flux (CHF) data for FeCrAl cladding and subsequent sensitivity analyses emphasized differences between real-world and simulated post-CHF phenomena. The Virtual Environment for Reactor Applications (VERA) multiphysics modeling suite was verified against other widely-used modeling tools for BWR application, and its advanced features were used to generate boundary conditions in SiC/SiC channel boxes used for deformation analyses. Several ThN-UN mixtures were analyzed using reactor physics and thermal hydraulic techniques and were shown to significantly increase the margin to fuel melt compared with UO2 [uranium dioxide] in LWRs. Mo inserts for UO2 [uranium dioxide] were optimized using sensitivity regression techniques and were also shown to significantly increase the margin to fuel melt compared with traditional UO2 [uranium dioxide]