REACTION KINETICS OF RARE EARTH AND ACTINIDE MATERIALS by

This dissertation presents the effects of atmosphere, time, and energy input (thermal and mechanical) on the kinetics of gas-solid and solid-solid reactions in systems of dysprosium, uranium, oxygen, and nitrogen. Accordingly, Chapter Two presents a novel synthesis technique used to form DyN via a gas-solid reaction between dysprosium and nitrogen. DyN was rapidly formed through a mechanochemical process in a high energy ball mill at ambient temperatures. The progress of the reaction was quantified using in situ temperature and pressure measurements coupled with microscopy and x-ray diffraction. It was found that the rate of the nitridation reaction is controlled by the creation of fresh dysprosium surfaces, which is a function of milling intensity and the number of milling media. Chapter Three describes how UN was synthesized prior to mixing with UO2 in the fabrication of accident tolerant nitride fuels for nuclear reactor applications. High purity and carbon free UN was synthesized using a hydride-dehydride-nitride thermal synthesis route. In order to fabricate an accident tolerant nitride fuel, it is postulated that the addition of small amounts of UO2 (up to 10 w%) to UN will significantly increase its corrosion resistance. UN-UO2 composite pellets were sintered in Ar-(0-1 at%) N2 to study the effects of nitrogen concentration on the evolved phases and microstructures. Further studies were conducted where UN and UN-UO2 composites were sintered in Ar100 ppm N2 for five hours at various temperatures (1700-2000 °C) and the final grain