Pre-training is a methodological approach involving the initial simulation, configuration, or preparation of complex nuclear systems, such as fusion reactions or fission reactors, prior to the initiation of sustained energy generation. As a research concept within nuclear science and engineering, it investigates the foundational states, critical initial conditions, and transient behaviors of these systems, characterized by predictive modeling, state initialization, and parameter tuning. Its significance lies in enabling the safe, efficient, and controlled operational phase by optimizing the system's preparatory state and understanding its response to initial conditions derived from nuclear physics principles.