Overview of Supercritical CO2 Brayton Cycle Integrated System Test (IST) Turbomachinery Development

by Kenneth Kimball
Knolls Atomic Power Laboratory

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Turbomachinery fabricated by Barber Nichols Inc (BNI) specifically for installation in the Naval Nuclear Propulsion Program (NNPP) S-CO2 Brayton Cycle Integrated System Test (IST) was tested and refined prior to installation in the IST. This testing was conducted in the Sandia National Laboratory (SNL) S-CO2 Brayton cycle test loop located at BNI. The test program was methodically performed in three phases. Phase One consisted of combined bearing friction and rotor windage measurements. Phase One testing was performed prior to installation of the turbine or compressor wheels via a series of coast down tests from shaft speeds up to 75,000 rpm. Phase 2 consisted of axially loading the thrust bearing up to 110 lbs over a speed range of 25,000 rpm to 45,000 rpm. Phase 3 consisted of optimizing turbo-compressor start-up procedures, compressor surge control demonstration, operation under simulated IST cold and hot idle conditions, and ultimately generation of electric power. During all phases of testing, shaft seal leakage and bearing heating were measured. Pre-test and post-test analytical modeling of shaft seal leakage, windage, thrust, turbomachinery performance, and system heat balance was performed. This series of testing supported design refinements to both the turbomachinery and associated motor-controller and will help to ensure successful conduct of the IST test program.