ABSTRACT:

The supercritical CO2 Brayton cycle is under consideration for power conversion of VHTR process heat and other energy-related applications because it allows for system simplification and high power conversion efficiencies. A high temperature, high pressure autoclave has been designed and constructed for testing materials corrosion in supercritical CO2 environments at temperatures and pressures of up to 650°C and 20MPa respectively. The system is equipped with a gas chromatography mass spectroscopy (GCMS) unit for measuring inlet and outlet gas compositions. The gas flow rate, composition, pressure, and temperature are monitored automatically and continuously using LabView software. Using this facility, the corrosion behavior of select alloys was studied after exposure to supercritical CO2 at 450°C and 20 MPa for exposure durations of up to 1000hours. Tests were performed using research grade (99.9998%) CO2. The alloys selected for this study were two ferritic steels NF616 and HCM12A, 347 austenitic stainless steel, and advanced concept AFA (aluminaforming austenitic) alloy. The corrosion performance of the alloys was evaluated using weight change measurements and SEM/EDS analyses of the alloy samples after corrosion testing. The test equipment will be first described followed by a discussion of the corrosion behavior of the various alloys.

INTRODUCTION

Supercritical carbon dioxide (SC CO2) is under consideration for Brayton cycle power conversion systems for fast reactors and other energy systems.1-3 Interest in the SC CO2 Brayton cycle stems from its benefits over the traditional Rankine cycle such as increased efficiency and decreased size. Additionally, using CO2 in conjunction with Sodium Fast Reactors (SFR) eliminates the possibility of steam/water interactions that would be present with a more traditional steam cycle. Operation of Brayton cycle systems for high conversion efficiencies may involve temperatures up to 650°C and pressures up to 20 MPa with higher temperatures and pressures anticipated for the future.

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