b'Figure 2. Selected EBSD maps at different radial locations: a) pellet intermediate radial position b)pellet rim.Project Description:appearances developed along the It is known that fuel pelletradius. These zones are referred to fragmentation appears to be largelyas the high-burnup structure (HBS) driven by a rapid expansion of fissionor the rim zone, the central zone of gas bubbles along grain boundaries,the fuel, and the intermediate zone but quantitative assessment of thebetween the rim and center, generally local gas inventory and relatedreferred to as the dark zone which microstructural factors playing acan contain several sub- regions major role in fuel fragmentation iswith variable bubble concentration. still incomplete. The project focusesIt is postulated that a significant on the characterization of the initialamount of gas is retained in the local fission gas inventory and graindark zone and at intermediate radial structure at different radial positionspositions, making these areas prone in high-burnup fuel. This informationto fine fragmentation. The fission gas is crucial to better interpret resultsmeasurement experiment will utilize from future integral Loss of Coolantfocused ion beam techniques to Accident (LOCA) tests planned on theremove samples in radial increments same mother rod. so that the fission gas within each Fission gas measurement experimentszone can be compared.will be used to assess the retainedThe fuel will also be characterized fission gas at different regions withinusing scanning electron microscopy the fuel. As UO 2is irradiated within(SEM) techniques including imaging a reactor, the material forms threeand electron backscatter diffraction concentric zones with different 2019|AFC ACCOMPLISHMENTS 135'