b'Assessment of Viability of Scaled AnnularPellet Fabrication Technologies Principal Investigator: Chris Grote, LANLF abrication of annular pelletsfaster rate, the fuel is likely going to and/or scaled traditionalbe subject to thermal effects commis-pellets has potential to supporterate with the increased heat by more accelerated burn-up testing concepts.fission. In a normal fuel pellet, this To this end, a variety of geometriesincreased temperature would operate have been proposed that supportless efficiently because the thermal the accelerated fuel qualificationdiffusivity of the pellet only allows program within the Department ofit to transfer heat so quickly, thus Energy Nuclear Energy Advancedcausing a high centerline tempera-Fuels Campaign. (DOE-NE AFC)ture and noticeable stress along the Figure 1. Polished microstructure ofThis includes the traditional soliddiameter of the pellet. Solutions could 3mm radius annular pellet. monolithic cylindrical geometriesinclude smaller pellet radii or annular with diameters down to 2 mm, asdesigns, which would have a greater well as annular pellet designs withsurface area giving off heat relative to sizes ranging from 10 to 3 mm withtheir volume, or shaped fuel designs annular holes that scale with pelletmodifying the thermal behavior.diameter. Work this year has centered High-density pelletson the development of pellets usingThe concept that drives the annular can successfully bethese unique geometries and ispellet design is reduction of the manufactured withdemonstrated for CeO 2 , UO 2 , andthermal gradient caused from the high geometries of interest toU 3 Si 2 . Polished microstructures arecenterline temperature at the center accelerated fuel testingshown detailing the defects present inof a normal pellet to its surface. By and qualification. specific geometries/designs as well asremoving the center of the pellet, the methods to mitigate these features innew centerline will instead be closer to future fabrications. an edge (whether that be the inner or outer edge), allowing cooling to wick Project Description: away more heat than the traditional Irradiation testing to high burnupdesign. This increase in heat removal fuel (to ~60G Wd/MTU) requireswould allow the pellet to be subjected significant time in current test reactorsto higher energy output, and thus limiting the ability to effectivelyaccelerate the burn-up process.model how the fuel will behaveAccomplishments:when it approaches long durationIn an effort to develop methodology, energy generation. While reachingCeria was used as a non-radiological this point conventionally is achievablematerial surrogate for both testing the in test reactors, it requires a decadepunch and die sets outside of a glovebox to achieve using current irradiationtesting the viability of fabricating testing schemes. Accelerated burnupannular pellets on a well-known system. would be approaching the thresholdFor this reason, only the largest and of high burnup more quickly, onsmallest annular designs were tested. the order of 1-2 years. To achieve this 176 2019|AFC ACCOMPLISHMENTS'