b'Modeling andA first-of-its-kind method to create a more physics-based model for measurement of gasaxial gas transport in nuclear fuel rods accelerates fuel qualification.transport in nuclear fuels A ccelerated fuel qualification relies on developing approaches that combine physics-based modeling and experiments. One of the less understood phenomena associated with gas behavior in fuel rods is axial gas transport, which is important in spent fuel storage of light water reactor fuel rods, loss of coolant accidents, and helium bonded fast reactor fuel rods. Prior to this project, the permeability of gas flow was computed after experiment completion and existing modeling approaches assumed instantaneous equilibration of the pressure PROJECT NUMBER: in the fuel rod. Neither existing experimental measurement or models accounted21A1050-028FP for the fragmented state of the fuel or the size of the fuel-to-clad gap. To overcome TOTAL APPROVED AMOUNT:these limitations, a methodology was developed to use advanced modeling and $885,000 over 3 years simulation to inform experiment design and use the experimental measurements and characterization techniques to develop more physics-based models to describe PRINCIPAL INVESTIGATOR:axial gas transport. First, the scalability of the axial gas transport phenomena was Kyle Gamble studied using the Multiphysics Object Oriented Simulation Environment (MOOSE) CO-INVESTIGATORS: framework and BISON nuclear fuel performance code. It was found that small 5 to 6 Chase Christen, INL inch specimens would still allow for the measurement of pressure decay. The small Fabiola Cappia, INL samples enabled the use of x-ray computed tomography to generated hundreds Kaustubh Bawane, INL of two-dimensional images that use digital image analysis to obtain important Seongtae Kwon, INL characteristics of the fragmented status of the surrogate fuel (alumina) such as crack tortuosity, specific surface, and porosity distribution. Full three-dimensional COLLABORATOR: reconstruction of the experimental specimens was also possible. Surrogate materials Politecnico di Milano were selected because gas transport only depends upon the available pathways for gas flow. Temperature and viscosity effects were considered in the modeling activities. Two approaches to specimen fabrication were considered, thermal quenching and mechanical crushing. It was observed that thermal quenching provided more representative fracture patterns and mechanical crushing resulted in much larger pathways for gas flow. An experimental apparatus was commissioned at the Research Collaboration Building at the Materials and Fuels Complex to test the samples. The experiments conducted as part of the project were characterized, and digital image correlation was performed to develop a new model for the permeability through fragmented fuel pellets as a function of smeared porosity. The project also determined that pressure equilibration is not instantaneous and gas flow is turbulent for shorter decay times.28'