b'Figure 1. The effect of sintering time and atmosphere on grain size in undoped fuel.fabrication of large grained undopedinstrument profiles were conducting UO 2fuel that could serve as referencein an STA to monitor the stoichiom-fuels for fission gas behavior studies inetry during the sintering schedule to enhanced UO 2accident tolerant fuel.inform the role that crystalline defects Such experiments would provide thehave on sintering kinetics in UO 2 . The data necessary for decoupling dopantinitial UO 2feedstock had an oxygen effects vs microstructural effects (i.e.,to metal (O/M) ratio of 2.16 and a large grains) and further enhance thepressing pressure of 200 MPa was used understanding of the mechanisms thatto prepare green pellets. control grain growth in UO 2 . A 4 hour sintering time at 1550 C Accomplishments: in an inert (Ar) or oxidizing (CO 2 ) Sintering studies were performed in aatmosphere with a 5 C/minute dilatometer to investigate the densifica- heating/cooling rate produced pellets tion behavior in a variety of gas condi- with an average density of 94% tions, ramp rates, and holds. The same 2020|AFC ACCOMPLISHMENTS 55'