Analyses of the control system strategies and methodology for part power control of the simple and intercooled recuperated Brayton helium gas turbine cycles for generation IV nuclear power plants

An important requirement for Generation IV Nuclear Power Plant (NPP) design is the control system, which enables part power operability. The choices of control system methods must ensure variation of load without severe drawbacks on cycle performance. The objective of this study is to assess the control of the NPP under part power operations. The cycles of interest are the Simple Cycle Recuperated (SCR) and the Intercooled Cycle Recuperated (ICR). Control strategies are proposed for NPPs but the focus is on the strategies that result in part power operation using the inventory control method. Firstly, results explaining the performance and load limiting factors of the inventory control method are documented; subsequently, the transient part power performances. The load versus efficiency curves were also derived from varying the load to understand the efficiency penalties. This is carried out using a modelling and performance simulation tool designed for this study. Results show that the ICR takes ~102% longer than the SCR to reduce the load to 50% in Design Point (DP) performance conditions for similar valve flows, which correlates to the volumetric increase for the ICR inventory tank. The efficiency penalties are comparable for both cycles at 50% part power, whereby a 22% drop in cycle efficiency was observed and indicates limiting time at very low part power. The analyses intend to aid the development of cycles for Generation IV NPPs specifically Gas Cooled Fast Reactors (GFRs) and Very High Temperature Reactors (VHTRs), where helium is the coolant.