Evaluation of alternate power conversion unit designs for the GT-MHR

Analyses of the Load Following Capabilities of Brayton Helium Gas Turbine Cycles for Generation IV Nuclear Power Plants

The control system for generation IV nuclear power plant (NPP) design must ensure load variation when changes to critical parameters affect grid demand, plant efficiency, and component integrity. The objective of this study is to assess the load following capabilities of cycles when inventory pressure control is utilized. Cycles of interest are simple cycle recuperated (SCR), intercooled cycle recuperated (ICR), and intercooled cycle without recuperation (IC). First, part power performance of the IC is compared to results of the SCR and ICR. Subsequently, the load following capabilities are assessed when the cycle inlet temperatures are varied. This was carried out using a tool designed for this study. Results show that the IC takes ∼2.7% longer than the ICR to reduce the power output to 50% when operating in design point (DP) for similar valve flows, which correlates to the volumetric increase for the IC inventory storage tank. However, the ability of the IC to match the ICR's load following capabilities is severely hindered because the IC is most susceptible to temperature variation. Furthermore, the IC takes longer than the SCR and ICR to regulate the reactor power by a factor of 51 but this is severely reduced, when regulating NPP power output. However, the IC is the only cycle that does not compromise reactor integrity and cycle efficiency when regulating the power. The analyses intend to aid the development of cycles specifically gas-cooled fast reactors (GFRs) and very high temperature reactors (VHTRs), where helium is the coolant.

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. First, results explaining the performance and load limiting factors of the inventory control method are documented; subsequently, the transient part power performances are also documented. The load versus efficiency curves were also derived from varying the load to understand the efficiency penalties. This is carried out using a modeling 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 with 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.

A Review of the Turbine Cooling Fraction for Very High Turbine Entry Temperature Helium Gas Turbine Cycles for Generation IV Reactor Power Plants

The potential for high turbine entry temperature (TETs) turbines for nuclear power plants (NPPs) requires improved materials and sophisticated cooling. Cooling is critical for maintaining mechanical integrity of the turbine for temperatures >1000 °C. Increasing TET is one of the solutions for improving efficiency after cycle optimum pressure ratios have been achieved but cooling as a percentage of mass flow will have to increase, resulting in cycle efficiency penalties. To limit this effect, it is necessary to know the maximum allowable blade metal temperature to ensure that the minimum cooling fraction is used. The main objective of this study is to analyze the thermal efficiencies of four cycles in the 300–700 MW class for generation IV NPPs, using two different turbines with optimum cooling for TETs between 950 and 1200 °C. The cycles analyzed are simple cycle (SC), simple cycle recuperated (SCR), intercooled cycle (IC), and intercooled cycle recuperated (ICR). Although results showed that deterioration of cycle performance is lower when using improved turbine material, the justification to use optimum cooling improves the cycle significantly when a recuperator is used. Furthermore, optimized cooling flow and the introduction of an intercooler improve cycle efficiency by >3%, which is >1% more than previous studies. Finally, the study highlights the potential of cycle performance beyond 1200 °C for IC. This is based on the IC showing the least performance deterioration. The analyses intend to aid development of cycles for deployment in gas-cooled fast reactors (GFRs) and very high-temperature reactors (VHTRs).

Analyses of Simple and Intercooled Recuperated Direct Brayton Helium Gas Turbine Cycles for Generation IV Reactor Power Plants

As a nongreenhouse gas-emitting source, the benefits of nuclear as a main power-generation alternative are yet to be fully explored; part of the reason is due to the significant implementation costs. However, with cycle efficiencies of 45–50% in current studies, it can be argued that the long-term benefits outweigh the initial costs, if developed under the Generation-IV (Gen-IV) framework. The main objective of this study is to analyze the effects of pressure and temperature ratios (TRs) including sensitivity analyses of component efficiencies, ambient temperature, component losses and pressure losses on cycle efficiency and specific work. The results obtained indicate that pressure losses and recuperator effectiveness have the greatest impact on cycle efficiency and specific work. The analyses intend to aid development of the simple cycle recuperated (SCR) and intercooled cycle recuperated (ICR) cycles, applicable to gas-cooled fast reactors (GFRs) and very-high-temperature reactors (VHTRs), in which helium is the coolant.