An approach to constructing effective training data for a classification model to evaluate the reliability of a passive safety system

•Passive system reliability is important for securing the safety of nuclear power plants.•Extensive computations are generally required to evaluate the passive system reliability.•Artificial intelligence (AI) models are useful for reducing the amount of computations but a lot of training data are necessary to develop them.•A method to obtain effective training data is proposed in this study with case studies to clarify its effectiveness.