Graduate Defense: Adrianna Lupercio

Dissertation Information

Title: Fracture Behavior Of Advanced Technology Fuels For Light Water Reactors

Program: Doctor of Philosophy in Materials Science and Engineering

Advisor: Dr. Brian Jaques, Materials Science and Engineering

Committee Members: Dr. Andrew T. Nelson, Materials Science and Engineering; Dr. Megan Frary, Materials Science and Engineering; and Dr. Mahmood Mamivand, Mechanical and Biomedical Engineering

Abstract

The urgent call to decarbonize our energy infrastructure, while simultaneously meeting growing energy demands, highlights the need for reliable and clean energy sources. Nuclear energy provides reliable energy while emitting zero greenhouse gases during operation; however, aging infrastructure, regulatory hurdles, and competing energy prices, threaten economic viability. Enhancing nuclear power plant efficiency requires near-term Advanced Technology Fuel (ATF), such as doped UO2, to increase the flexibility of plant operation without impacting safety margins.
The modified microstructure of doped UO2, through metal oxide dopants, is purported to reduce fission gas release, mitigate pellet-cladding interactions, and increase accident tolerance, thereby enhancing fuel performance and safety. Understanding dopant effects on fuel fracture behavior is critical to the qualification of dope UO2 since fuel facture during reactor operation impacts fuel performance, including thermal conductivity. Yet statistical fracture data, such as transverse rupture strength (TRS), are limited. This study aimed to develop and qualify a ball-on-ring (BOR) biaxial flexure technique to determine the effect of dopants on the TRS of UO2.
In this investigation, the BOR technique was validated using technical ceramics with well-known mechanical properties and complemented with a finite element analysis. TRS testing of a non-radioactive surrogate fuel material, specifically undoped and doped CeO2, was performed to refine sample doping and the validated BOR technique for UO2 fuels. Prior to investigating doped UO2, the fracture behavior of undoped UO2 was established using the BOR technique for a comparative analysis.
The refined BOR technique was used to perform a statistical fracture analysis of TiO2- and Cr2O3-doped UO2 to investigate dopant-induced fracture mechanisms. Doped UO2 TRS was reduced when compared to UO2 and indicated increased TRS variability. Enhanced grain size is expected to reduce TRS, yet this study found tensile residual stresses, attributed to dopant-induced defect structures, had a greater impact on TRS. Collectively, the body of this work establishes a BOR test method for the rapid, cost-effective fabrication and mechanical testing of UO2 and ATF concepts. The data presented in this study provide baseline statistical fracture behavior, a valuable contribution to improving the fidelity of fuel performance code predictions. This work provides a robust methodology and foundational fracture behavior study of doped UO2 to assist in the accelerated qualification of ATF concepts for current and advanced nuclear reactors.