Research and development of safe and efficient nuclear energy systems is imperative, since nuclear safety is the key issue in the development of nuclear energy, and it is also the premise of nuclear energy development learned from the painful lessons in history. Advanced numerical simulation can restore the complex physical processes as much as possible and predict system behavior and safety performance, and it facilitates accurate design and assessment. International research in nuclear safety simulation has developed from single physical phenomena simulation to coupling simulation with digital reactor and to comprehensive simulation with virtual nuclear power plant by integrating environmental and social information. Compared with digital reactor, virtual nuclear power plant pays more attention to the evolution of reactor accidents, such as large-scale physical and social behavior simulation, which concerned the relationship between nuclear safety and environment, as well as the relationship between the nuclear safety and the public. FDS Team proposed "nuclear informatics" firstly by combining nuclear science and informatics and has developed the virtual nuclear power plant in digital society environment Virtual4DS, where many key technologies are developed under the guidance of nuclear informatics, such as integration cloud architecture, automatic accurate modeling, multiphysics coupling simulation, multidimensional information visualization and virtual simulation, and nuclear big data. Virtual4DS has been widely used in the nuclear power plant, nuclear weapons, well logging, etc.