Reactor design is the academic field and engineering discipline focused on the conceptualization, analysis, and specification of systems that initiate, control, and utilize nuclear reactions. This research area investigates the complex interplay of nuclear physics, thermal hydraulics, material science, and safety engineering principles necessary to achieve efficient energy conversion and secure containment. Its key characteristics include optimizing reaction parameters, ensuring structural integrity under extreme conditions, managing heat transfer, and implementing robust control and safety mechanisms, underscoring its critical significance in advancing nuclear energy generation and scientific research.