COMPREHENSIVE INVESTIGATION OF SELECTED ENHANCED ACCIDENT TOLERANT NUCLEAR FUELS

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Nuclear accidents illustrate the risks associated with the present design of reactors based on pure urania (UO2) fuel with its low thermal conductivity that deteriorates at high temperatures and upon further oxidation. Zircaloy cladding reacts rapidly with water at high temperatures and highly explosive hydrogen gas can be released. In the context of developing a sustainable replacement for non-renewable energy sources, innovative research towards enhanced accident-tolerant nuclear fuel (EATF) that can withstand the loss of coolant for a long time is gaining momentum. EATF materials must have higher thermal conductivities (?) to prevent meltdown, a slower rate of hydrogen generation, and improved retention of fission products. We demonstrated that high thermal conductivity nuclear fuel is safer and longer-lasting due to reduced thermal strain. The overall objective of this research is to qualify and develop a fundamental understanding of selected evolutionary and revolutionary fuel concepts. We will investigate ceramic and metallic fuels (with ? increasing with temperature) using the software developed in our research group and advanced ab initio methods with predictive power that are now being conceived through a worldwide collaboration. To prevent errors and make state of the art codes more accessible to engineering students, we have developed an interface, which will be further updated. In this research, we assess the uncharted performance of EATFs under both normal operating conditions and the extreme accident conditions in a reactor. We investigate the effects of structural defects and oxidation on thermal conductivity of new evolutionary (chromia doped urania) and selected revolutionary metallic (uranium nitride (UN)) EATFs. Computational techniques such as density functional theory and classical molecular dynamics (CMD) will be used to account for point defects, large defects, and grain boundaries. The opposite effect of grain sizes on the oxidation rate in UO2 versus UN will be studied. The developed thermal conductivity correlations for fuels, both pure and with defects included, will be used in our software for safety analysis to investigate the temperature profiles and gradients in a fuel rod. The findings will be validated by experimental data. Through a collaboration with Los Alamos National Laboratory, ab initio tight-binding code (Latte) will be used to develop new CMD potentials to help with a qualification of a leading EATF: silicon carbide, which reacts 10000 times slower with steam than zirconium. We will also work with the Canadian Light Source at USask to investigate the electronic structure experimentally. This research will develop a knowledge base to study the properties of nuclear materials and highly qualified personnel to sustain Canada's nuclear industry. EATFs could revive the uranium industry as improved fuels would make reactors safer, more economic and, therefore, the Canadian industry more competitive.