b'previous years, the current modelscollaboration with NEAMS via lower- metallic fuel modeling are appro-utilized in BISON have some successlength scale information such aspriately implemented, verified, and in matching EBR-II data, but fail tofission gas diffusivity and fundamentaldocumented. In addition, extensive capture cladding strain when varyingmaterial parameters, leading to a trulyframework development by Alex rod parameters such as plenum heightmulti-scale solution to fuel behavior. Lindsay and Daniel Schwen from INL and pellet radius. Consequently,In addition to the new coupledlead to the implementation of Auto-tuning parameters for the currentlyplastic strain model, a new multi- matic Differentiation and Automatic implemented empirical models thatscale model for cladding creep hasScaling, increasing the robustness of impact cladding strain (i.e., internalbeen implemented. Again, workingthe MOOSE-based simulations when plenum pressure, fuel swelling, andwith NEAMS, primarily throughusing complex models. We have cladding creep) will have limitedLaurent Capolungo and his team, aconverted all metallic fuel BISON applicability to off-normal fuellower-length scale informed modelmodels to the new system, allowing pin designs, high burnup fuel,has been implemented in BISON viacomplex coupled behavior such as and accident scenarios. In a movea reduced-order model that rapidlythe fuel strain model discussed above away from empirical formulationscalculates creep strain using anto be feasible in production runs.and mechanistically capture theextensive set of previously calculatedCitations: behavior of the fuel, a new coupledruns from the LANL code Visco-Plastic[1.] Matthews, C., Bieberdorf, N., fuel swelling, fission gas release,Self-Consistent (VCPS). LeveragingCapolungo, L., Andersson, D., porosity, and creep model has beenour BISON modeling experience withCombined Visco-Plasticity and implemented in BISON. The modelCapolungos constituent modelingSwelling in Metallic Nuclear Fuel, was employed following collaborationexpertise allowed rapid implementa- LA-UR-19-25483, (2019).with a LANL team lead by Laurenttion of creep models for HT-9 and Capolungo, and will allow BISON toSS316 cladding. [2.] Prakash, Naveen, Matthews, capture the behavior of fuel outsideChristopher, Versino, Daniele, and the EBR-II operational experienceFinally, in order to be applicable toUnal, Cetin. A general constitu-envelope such as slotted or annularthe greater scientific community,tive framework for thecombined fuel [1,2]. In addition, fission gasBISON needs to not only calculatecreep, plasticity and swelling release of the fuel will be calculatedvalues that match historical data, butbehavior of nuclear fuels in an using physically based models ratherit must be robust and easy to useimplicit hypoelastic formulation. than the currently implementedfor non-MOOSE experts. Part of this2019. doi:10.2172/1493517.curve-fit from EBR-II data. The modelFY was spent ensuring the models will also benefit from continuingthat are in place that are used for 228 2019|AFC ACCOMPLISHMENTS'