Đorđe Lazarević

An overview of the technical and operational characteristics of modern nuclear power plants (NPPs) relevant for their integration into the power system, with particular emphasis on Generation III+ reactors and small modular reactors (SMRs). The analysis covers technologies such as EPR, AP1000, VVER-1200 (VVER-TOI), APR1400 and HPR1000 (Hualong One), and the NuScale VOYGR SMR concept, considered from the perspective of their behavior within the power system. Particular focus is placed on the parameters defining the interaction between nuclear power plants and the grid, including unit size and its relation to total system capacity, minimum stable operating power, load-following capabilities, and the speed and characteristics of the plant’s response to grid disturbances. The role of nuclear power plants as base load units is also considered, together with limitations in terms of operational flexibility arising from design and safety requirements. Additional attention is given to the contribution of nuclear power plants to power system stability, including the inertial response of synchronous generators and their potential role in frequency and voltage control, as well as in the provision of reactive power. Particular emphasis is placed on the importance of reliable off-site power supply as a key requirement for nuclear safety, highlighting the strong interdependence between the power plant and the power system. In this context, the requirements imposed by the power system on generating units are also considered, including the ability to operate within specified ranges of frequency and voltage, participation in system control, and performance under grid disturbances (fault ride-through). These aspects are relevant for aligning the technical characteristics of NPPs with the requirements of the transmission system operator. A comparative analysis of large nuclear power units and SMR technologies highlights differences in their integration into the power system. The lower power of SMRs may represent an advantage in terms of reduced system impact in the event of a unit trip and potentially greater operational flexibility, while at the same time introducing specific requirements regarding generation planning and grid interaction. The objective is to identify similarities and differences in the behavior of these technologies from the perspective of power system integration, and to emphasize the need for these characteristics to be explicitly considered in analyses conducted within Phase 1 of a nuclear power programme, in line with the IAEA Milestones Approach. Such an overview is of particular relevance for Serbia in the context of assessing the technical conditions and constraints for integrating nuclear capacity into the national power system.

Keywords: NPPs, power system, Generation III+ reactors, SMRs, grid integration, off-site power