This lecture covers the analysis of heterogeneous reactors, including reflector savings, infinite slab reactor analysis, heterogeneous lattices, and practical reactor calculations. It delves into topics such as multi-group diffusion equations, neutron kinetics, reactor technology, and neutron moderation. The lecture also explores the derivation of multi-group diffusion equations, the k-eigenvalue problem, and the determination of group constants. Additionally, it discusses the energy group structure, applications of the multi-group diffusion model, and the criticality condition for reflected systems.