THE PRIME RECIPIENT IN PARTNERSHIP WITH SUBRECIPIENTS AND INDUSTRY ADVISORS WILL DELIVER A PRE-LIMINARY DESIGN OF A SUPERCRITICAL CARBON-DIOX¬IDE (SCO2) POWER BLOCK FOR GEN3/GEN3++ CONCENTRATING SOLAR POWER (CSP) APPLICATIONS. THE WORK SCOPE HAS THREE HIGH-LEVEL OBJECTIVES: 1. A BROAD-TEMPERATURE RANGE SCO2 POWER CYCLE TO INTEGRATE SOLID PARTICLE-BASED PRIMARY HEAT EXCHANGER WITH SCO2 POWER BLOCK TO ACHIEVE $0.05/KWHR LCOE (END OF BP1 OBJECTIVE). 2. A PRELIMINARY DESIGN OF THE POWER BLOCK COMPRISING NOVEL TURBOMACHINERY LAYOUTS, ELECTRICAL GENERATORS, ALONG WITH PRACTICAL ASPECTS OF THE POWER BLOCK DESIGN SUCH AS THE PLANT PIPING LAYOUT AND INVENTORY MANAGEMENT SYSTEM. A COST-OPTIMIZED CONFIGURATION OF THE SOLID-PARTICLE BASED THERMAL SYSTEM INCLUDING THE HELIOSTAT FIELD, PARTICLE THER¬MAL STORAGE SYSTEM, CONVEYANCE SYSTEM, PARTICLE-BASED PRIMARY HEAT EXCHANGER, AND THE SOLAR RECEIVER (END OF BP1 OBJECTIVE). 3.TEST DATA ON THRUST GAS BEARINGS OPERATING IN RELEVANT SCO2 ENVIRONMENT FOLLOWED BY TECHNICAL GAP AND RISK ASSESSMENT FOR ADVANCING TO HIGHER FUTURE TIER EFFORTS.