Application of Multifunctional Systems with Latent Heat Thermal Energy Storages: A Way to Improve NPP Safety and Efficiency

— Growth in the number of nuclear reactors in power systems and their involvement in controlling the electricity consumption schedule call for the need to impose more stringent requirements for their safety. It is shown that the safety of NPPs can be enhanced, and their participation in variable power-consumption schedules can be implemented by combining them with latent heat thermal energy storages (LHTES) and an additional small-capacity steam turbine. A scheme is proposed for combining a two-loop nuclear power plant with a multifunctional thermal energy storage system (TESS) on the basis of an LHTES, with means for heating feedwater above the nominal temperature in the LHTES discharging period. With such a solution, it becomes possible to increase the live steam flowrate without changing the reactor plant output power. The proposed scheme features high thermodynamic efficiency. In addition, doing away with the steam generation system in the LHTES results in that its design becomes significantly simpler and cheaper. Thus, due to increasing the feedwater temperature in a power unit with a VVER-1000 reactor from 215 to 260°С, the additional turbine can produce up to 140 MW of electric power. A distinguishing feature of the proposed scheme is that it allows uninterrupted power supply for the NPP auxiliaries to be provided in an emergency involving loss of power supply by using the steam generated due to the decay heat produced by the shutdown reactor. This makes it possible to enhance the NPP safety level in compliance with the growing requirements set forth by the International Atomic Energy Agency (IAEA) and ensure the possibility of power unit participation in controlling the electric load schedule without changing the reactor plant’s power output. Assessments of accrued net present value (ANPV) carried out with taking into account the multifunctional properties of the system being developed have shown that it has a positive value in the entire adopted range of the difference between the day and night electricity tariffs.