A feedheat-integrated energy storage system for nuclear-powered steam plant

The paper provides thermodynamic analysis of an energy storage concept in which thermal stores are coupled with the feedwater heating train of nuclear-powered steam plant. This allows the electrical output of the plant to be flexed whilst maintaining constant reactor power, thereby providing the equivalent of an electricity storage system and facilitating the adoption of a load-following role for nuclear plant. The concept falls under the umbrella of 'generation-integrated energy storage', which exploits existing hardware required for generation to reduce storage costs, and benefits also from fewer energy transformations when compared to 'electricity-in-electricity-out' forms of storage. This means that a high (effective) round-trip efficiency can be achieved at low cost. An important feature of the proposed system is that the turbine bleed flows (at their various pressures and temperatures) automatically provide good thermal matching with the feedwater temperature profile, so that heat can ultimately be transferred to and from sensible-heat thermal-storage media with high exergetic efficiency. Various options are discussed for the thermal stores, including pressurised water tanks, thermal oils and packed beds. The analysis also includes consideration of the off-design behaviour of cycle components.