Verification of Transient Modeling of FRTAC Supercritical Carbon Dioxide Brayton Cycle

Supercritical carbon dioxide (SCO₂), with its good heat transfer capability, stability, safety and economy, is a good energy conversion workhorse with broad application prospects. The application of supercritical carbon dioxide Brayton cycle to nuclear energy systems not only improves thermal efficiency, but also facilitates miniaturization. Sodium-cooled fast reactors and lead-cooled fast reactors, among six generation Ⅳ systems proposed by the Generation Ⅳ Nuclear Energy Forum (GENERAF), also recommend the use of SCO₂ as a Brayton cycle workhorse. So SCO₂ power cycle systems have been widely noticed in advanced reactor design. Fast reactor transient analysis code (FRTAC) is a system analysis program developed independently by China Institute of Atomic Energy, which can be used for steady-state and transient simulations of liquid metal cooled reactors. In order to further satisfy the needs of the program, a corresponding calculation module for the SCO₂ power cycle system was developed in the FRTAC program, which used the interpolation method to obtain the CO₂ physical property library, the quasi-steady-state method to predict the mechanical behavior of the turbine, and the assumptions such as the uniform distribution of the flow in the flow channel to model the printed-circuit plate heat exchanger, and empirical relational formulas to calculate the frictional heat transfer of SCO₂. In order to verify the reliability and accuracy of the model calculation, FRTAC was used to test the steady-state and transient modeling of the key components and systems in the SCO₂ cycle system, such as the turbine, compressor, and printed circuit plate heat exchanger. For single-module testing of key components, steady-state testing of one turbine, two compressors, and three return heaters was performed, and flow reduction transient calculations were performed for one of the return heaters. For system testing of the recompression Brayton cycle circuit, steady-state, 5% load increase and decrease, and 5% cooling water flow increase and decrease transient calculations were performed. Comparing the FRTAC program calculation results with those of SCTRAN program, data with good agreement with SCTRAN program were obtained, and the deviation of the steady-state test of key equipment such as the turbine and the recirculation loop was no more than 1% compared with that of SCTRAN program, and the relative deviation is within the acceptable range. The change trend of each transient test key parameter is highly consistent with SCTRAN program, and the deviation of parameters before and after the transient change is small, which basically verifies the correctness of the transient model of FRTAC program SCO₂ Brayton cycle. It is demonstrated that FRTAC program is primed to analyze steady-state and transient conditions in the SCO₂ Brayton cycle.