2018 | AFC ACCOMPLISHMENTS 168 The BISON fuel performance code is well underway to being extended to model zirconium based metallic fuel.The challenges presented by the advanced U-Zr and U-Pu-Zr fuel types have resulted in a coupled thermo-mechanical-species diffusion simulation required to describe historical observations, as well as predict future performance.Advances in fundamental models such as swelling and zirconium diffusion will help provide the necessary foundation for advanced models such as fuel cracking and fuel-cladding chemical interaction (FCCI). Benchmark comparisons to past post irradiation examinations are utilized to assess model performance, with advanced calibration techniques playing a role when data is sparse or unavailable. Project Description: The objective of this research is to provide a code that can predict behavior of zirconium based metallic fuel for use in future advanced Gen IV commercial or test reactors such as theVersatileTest Reactor (VTR) currently under development.The favorable thermal conductivity and proven safety record of metallic fuel experienced during operation of the Experimental Breeder Reactor (EBR-II) lends U-Zr and U-Pu-Zr fuel naturally to the requirements of enhanced safety in next generation reactors.With fuel-cladding chemical interaction as the primary limiting factor of metallic fuels, enhancements in understanding and modeling of the key phenomena involved in FCCI can help bolster the economic viability of metallic fuel through extending the fuel lifetime. Simultaneously, the coupled nature of nuclear fuel requires the implementation of many fundamental models in order to provide a baseline capability for advanced concepts and off-normal behavior. Due to the sparse availability of modern data, historical EBR-II data is used as a primary source of information for model formulation and comparison. Previous codes have been limited to heavily empirical models due limited resources, understanding, and data. By leveraging many of the capabili- ties within BISON, advanced models that capture complex behavior can be implemented in a viable way. In addition, on-going work within the Advanced Fuels Campaign (AFC) has helped bolster the limited data set with new irradiations and higher fidelity data collection. Modern computational tools such as Bayesian calibration have been implemented to help bridge over limited data. In general, metallic fuel modeling in BISON aims to create a tool that is predictive in order to provide confidence for core designers in the safe, reliable, and efficient use of metallic nuclear fuel. Metallic Fuel Modeling Principal Investigator: Cetin Unal (LANL) and Christopher Matthews (LANL) Collaborators: Naveen Prakash (LANL), Jacob Hirschhorn (LANL, UF), Garrison Stevens (LANL), Blake Wilkerson (LANL) Through the development, implementation, and calibration of mechanistic models can BISON is quickly becoming a useful tool for predicting metallic fuel behavior for future applications.