This book provides engineers with a comprehensive understanding of nuclear reactor physics and neutronics, emphasizing the importance of simple models to validate complex computational results. It explains the rationale behind neutron slowing down and offers a straightforward method to evaluate the resonance escape probability in Fermi's 4-factors formula. The book includes exercises to assess the remaining three factors and demonstrates how to derive the diffusion approximation from the Boltzmann equation. It covers both one-group and two-group diffusion models, applying them to predict...