LWR Fission Gas Behavior Modeling Using OpenFOAM Based Fuel Performance Solver OFFBEAT

Fission gas release is one of the most important limitations in reactor fuel designs. Low soluble Xenon and Krypton gas generated in fission events may either retained in the fuel pellet, leading to fuel swelling and causes Pellet-Cladding Mechanistic Interaction (PCMI), or releases to fuel gas gap and results in a higher fuel temperature even crack of the cladding due to their relative low conductivities. The behavior of fission gas is mechanistically complicated and hard to model as it is coupled to fuel neutronic and thermal responses. Therefore, the capability of fission gas behavior modeling is one of the top-ranked criteria while evaluating the reliability of a fuel performance code. The OFFBEAT code is a multi-dimensional fuel performance code based on the OpenFOAM@ C++ library. It contains models that are required by LWR fuel analysis and can build from 1.5-D to 3-D. By coupling with the 0-D fission gas solver SCIANTIX, the code can offer mechanistic modeling of fission gas behavior. However, the performance of the coupled code has not yet been fully validated. In this work, preliminary validation of the OFFBEAT code in fission gas modeling is conducted. From open literature, Halden experiment IFA-716 rod 1&6, IFA-677 rod 1&5 are modeled and analyzed. These experiments indicate the capability of the OFFBEAT solver in modeling large grain size. The capability of the code in modeling high burnup fuel is validated against HBEP BK365 rod. The results show that the OFFBEAT code has quite good accuracy in modeling regular grain fission gas release as well as high burnup fuel. However, while dealing with doped large grain fuel, the code overestimates the release at low burnup but underestimates it for relatively high burnup. Nevertheless, the cluster dynamic model applied in SCIANTIX shows a better result than the Speight model normally applied in fuel performances codes.