Nuclear reactor engineering is an interdisciplinary field concerned with the scientific and technical principles governing the design, construction, operation, and decommissioning of nuclear reactors. This field investigates the physics of controlled nuclear chain reactions, thermal energy transfer, radiation transport and shielding, reactor materials science, safety analysis, and fuel cycle management. Characterized by its integration of nuclear physics, thermal-hydraulics, materials engineering, and systems control, its significance lies in enabling the safe and efficient conversion of nuclear energy, predominantly from fission, for power generation and other applications.