Nuclear reactor design is the academic and engineering discipline concerned with the principles, methods, and technologies required to conceive, analyze, and develop systems that utilize controlled nuclear fission reactions to generate thermal energy or achieve other specific nuclear objectives. This field investigates reactor physics, thermal-hydraulics, materials science, safety engineering, and control systems to optimize performance, ensure safety, and manage the nuclear fuel cycle, enabling the controlled harnessing of nuclear energy for power generation, research, and other applications.