Integrated Systems Test (IST) Supercritical CO2 Brayton Loop Transient Model Description & Initial Results

by Mike J. Hexemer, H. T. Hoang, Kevin D. Rahner, Brett W. Siebert, & Greg D. Wahl
Knolls Atomic Power Laboratory

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This paper provides the initial transient analysis for operation of the supercritical carbon dioxide (S-CO2) Brayton cycle being constructed at the Bettis Atomic Power Laboratory. A preliminary model of the Integrated System Test (IST) is documented and initial results presented for use in thermal hydraulic, mechanical, instrumentation and control system designs.

The IST provides a test bed to evaluate a wide range of control strategies that could be applied to a future S-CO2 closed loop Brayton power plant. A transient computer model of the Brayton loop is required to determine how each control strategy would influence the IST design and testing. A wide range of control features are available on the IST to evaluate three major control strategies; SPEED, T/H LEAD and LOAD FOLLOW. These three strategies incorporate the flexibility to control the compressor and power turbine shafts using either a motor/generator or control valve(s). Testing these three strategies will provide the operational understanding to optimize a control system for a future application. The IST will also provide data needed to validate the code and models used for this report. Validated models are needed to support the next generation test design.

This paper documents functional requirements for mechanical system components (turbomachinery, heat exchangers and cooling system), including control valves. Control system descriptions and functional requirements and controller settings are also provided. Control system strategies are discussed and transient results for each are presented for a range of power maneuvers. The first transient analysis of a two shaft Brayton loop startup and heatup is provided. Model documentation and analysis results provide a starting point for component structural analysis, further control system development, as well as future as-built model upgrades.