The paper presents operating principles of passive safety systems used in modern nuclear power plants with AP1000 reactor. Paper describes in detail the passive residual heat removal system and the passive containment cooling system in above-mentioned power plant. Furthermore, the paper consists thermo-hydraulic analysis of a scenario, in which power plant loss off-site power, reactor is shut-down and the active elements (especially Diesel generators) failed. Considerations and calculations present the role of passive safety systems in nuclear power plant. In particular described phenomena concerns two above-mentioned systems, which are responsible for residual heat removal. Change of the few of the most important parameters, like reactor coolant temperature, medium flow or heat exchange in the refuelling water storage tank, were simulated, presented and described. Mathematical model also includes the role of passive systems and its impact on the main parameters in nuclear power plant with AP1000 reactor.

Due to the necessity of decarbonising and transforming the Polish energy mix, topic of using nuclear power plants as one of the key low-carbon generation sources is returning to the public debate. This paper compares a large, system-wide AP1000 nuclear power plant with a new concept based on small modular reactors (SMRs), specifically NuScale 60 MW_e. Computer models of secondary loops of the generating units were used for the analysis, and basic operating parameters were determined. A consistent modelling approach was used to evaluate technical, thermodynamic, and economic indicators. As a result, a relationship between total capital expenditures and unit electricity generation cost was developed. For example, if the investment outlays, taking into account the freeze, for a large-scale nuclear power plant are USD 8 billion, then the investment outlays for an SMR power plant should be below USD 0.4 billion in order to ultimately ensure a lower or equal unit discounted cost of electric energy generation. Assuming stable power demand, the AP1000 reactor power plant remains the most cost-effective technology, offering favourable economies of scale. However, modular units are characterised by shorter lead times and greater flexibility of application in different areas of the energy industry. Therefore, in the decarbonisation process, it is essential to develop both analysed technologies in parallel.