**Coupled Neutron Diffusion and Porous Media Heat Transfer Model**

This model couples multi-group neutron diffusion and finite element heat transfer. The neutron energy spectrum is divided into eight energy groups. The group boundaries are chosen to capture the cross-section changes in heavy metals and in isotopes in the FLiBe salt. Multi-group cross-sections and diffusion coefficients are generated using the Monte Carlo code Serpent and defined as input in COMSOL 5.0. The data are calculated at different fuel temperatures and different FLiBe densities. As part of the project, a MATLAB package has been developed to automatically read data from Serpent output files and produce temperature and density dependent group constants for as many neutron energy groups as deemed necessary. Figures 6-7 show results from a steady state simulation.