CFD simulation of an integrated PCM-based thermal energy storage within a nuclear power plant connected to a grid with constant or variable power demand

The current numerical study investigates the integration of a phase change material (PCM)-based thermal energy storage (TES) system within a nuclear power plant (NPP) to enhance the capability of such proposed plant to better follow the variations of power grid demand especially in countries with a high share of nuclear in their energy mix. This study focuses on the transient behavior of the PCM during the simultaneous charging and discharging (SCD) operation mode during one day. For this, an enthalpy-porosity method is used to simulate the SCD operation mode of PCM within an axisymmetric vertical triplex tube. Hot and cold heat transfer fluids (HTFs) are simultaneously co-circulating within the TES for downward-inner heating and upward-outer cooling. Constant and variable loads are considered to study the load-following ability of the coupled system. During the SCD mode with a constant load, results show that an equilibrium between melting and solidification (charging and discharging) is established and the liquid fraction (20%) is not changing with time. Under the variable load, the suggested TES system is able to follow the daily variation of the grid demand and, hence, fill the gap between reactor supplied energy and grid power demand with the reactor constantly operated at full rated capacity. During the variable load, the liquid fraction within PCM is altering from solid to liquid phases and vice versa depending on the deviations of the grid as expected.