A Study of Thermal Cycle Circuits of NPPs Combined with Fossil Fueled Power Installations

The need to adapt the world’s industry and economy to constantly tightening climatic standards, as well as a constant growth of energy consumption, facilitate the development of carbon-free electricity generation technologies. Renewable energy and nuclear power plants are referred to energy sources having almost zero carbon dioxide emissions into the atmosphere. However, in view of an insufficient amount of renewable energy resources near large electricity consumers, NPPs play the most important role in the potential transition to the carbon-free economy of Russia. However, they do have certain drawbacks, such as comparatively low energy efficiency, poor maneuverability, and also high specific capital outlays. Combined use of nuclear and fossil fuel may become one of ways for partially removing these drawbacks. The article addresses a thermodynamic analysis of using fossil fuel at an NPP in an external steam superheater with subsequently expanding a part of the steam in a high-temperature turbine. A process circuit solution is proposed whose use makes it possible to obtain an expanded power unit load adjustment range. It has been shown from thermodynamic analysis results that, by subjecting a certain amount of steam from the steam generator to external superheating, it becomes possible to increase the nuclear power unit’s power output and efficiency: the maximal increase in the electric power output can total 338, 382, and 426 MW and that of net electrical efficiency of 0.73, 1.08, and 1.43% at steam superheating temperatures equal to 560, 600, and 640°С, respectively. The hybrid unit employing nuclear and hydrocarbon fuel that operates according to the proposed process cycle circuit includes a smaller amount of main equipment and features wider load adjustment ranges in comparison with standalone NPP and steam turbine thermal power plant: 102.3–132.7, 103.0–136.9, and 103.6–141.2% with respect to the reference process cycle circuit at steam superheating temperatures equal to 560, 600, and 640°С, respectively.