b'Assessment of the Fission Gas ReleaseModel in BISON Applied to UO 2MiniFuelPrincipal Investigator: Amani Cheniour (Oak Ridge National Laboratory)Team Members/ Collaborators: Giovanni Pastore (University of Tennessee, Knoxville), Jason Harp (Oak Ridge National Laboratory), Christian Petrie (Oak Ridge National Laboratory), and Nathan Capps (Oak Ridge National Laboratory)The results of thisT he manuscript provides a(1%) at burnups 62 MWd/kgU. comprehensive assessmentAbove 62 MWd/kgU, FGR will occur analysis have beenof the current BISON fissionat temperatures 800C; however, used to develop a UO 2 gas release model and its ability tofuel sample burnup must exceed MiniFuel irradiationmodel fission gas release in Mini- 100 MWd/kgU before appreciable test matrix is to helpFuel. Furthermore, the model wasFGR is observed at lower tempera-to extend the modelsvalidated to high burnup fissiontures. These results indicate that operational range andgas release experiments to assessMiniFuel irradiations would need to generate new data toits ability to accurately predict highto consider extremely high burnups validate the FGR modelburnup fission gas release. (100 MWd/kgU) or high tempera-capabilities to higherProject Description: tures 800C at 62 MWd/kgU to burnups and transientThe initial MiniFuel fuel perfor- measure FGR under steady-state conditions. mance analysis was designed toconditions. Low-temperature Mini-inform subsequent MiniFuel irradia- Fuel irradiations may still offer the tions campaigns. BISON was usedpossibility to provide microstruc-to model and predict steady-statetural information regarding fission and transient fission gas releasegas (FG) diffusion, bubble nucle-(FGR) for a variety of conditions.ation, bubble growth, and FGR prior A representative BISON model wasto a temperature transient. Further-developed with the appropriatemore, these microstructural features thermal hydraulic boundary condi- could help identify key mechanisms tions to accurately replicate MiniFuelleading to pulverization during a irradiation conditions. The modeltemperature transient. Future work was designed to assess the impactshould consider developing temper-of temperature, sample burnup,ature-transient testing capabilities grain radius, fission rate, andto evaluate transient FGR as well as diffusion constants on FGR. Currentpulverization of MiniFuel samples monolithic MiniFuel experimentsfollowing irradiation in High Flux generally target irradiation of fuelIsotope Reactor (HFIR). The applica-samples at constant temperatures,tion of transient conditions in UO 2ranging from 500 to 600C, and thefuels significantly affects the amount simulated amount of FGR outsideof released FG to the plenum volume of athermal release would not bein a fuel rod. The fuel performance measurable. BISON results indicatecode BISON can model transient that high temperatures 900C areFGR in UO 2and doped UO 2fuels. required to observe appreciable FGRThe BISON FGR model includes physics-based diffusion-controlled 72 2021|AFC ACCOMPLISHMENTS'