New methods and approaches to development of nuclear power plant unit imitation models development. An imitation model is proposed for nuclear power plant unit developed on the basis of oriented graph applied to unit flow diagram description logic-numerical operators for calculation of parameters and characteristics determining its operation efficiency, reliability and safety. Automatic system is described developed on the basis of imitation model for decision-making support, applied to analysis of VVER nuclear power plant unit operation efficiency with due consideration of equipment operation reliability and safety indices.