Preliminary Results of Optimal Pressure Ratio for Supercritical CO2 Brayton Cycle Coupled with Small Modular Water Cooled Reactor

by Ho Joon Yoon1,2, Yoonhan Ahn1, Jeong Ik Lee1,2, & Yacine Addad2
1Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology (KAIST)
2Department of Nuclear Engineering, Khalifa University of Science, Technology & Research (KUSTAR)

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The Supercritical carbon dioxide (S-CO2) Brayton cycle is being considered as a favorable candidate for the next generation nuclear reactors power conversion systems. Major benefits of the S-CO2 Brayton cycle compared to other Brayton cycles are: (1) high thermal efficiency in relatively low turbine inlet temperature, (2) compactness of the turbomachineries and heat exchangers and (3) simpler cycle layout at an equivalent or superior thermal efficiency. However, these benefits can be still utilized even in the water-cooled reactor technologies under special circumstances. A small and medium size water-cooled nuclear reactor (SMR) has been gaining interest due to its wide range of application such as electricity generation, seawater desalination, district heating and propulsion. Another key advantage of a SMR is that they can be transported from one place to another mostly by maritime transport due to their small size, and sometimes even through a railway system. Therefore, the combination of a S-CO2 Brayton cycle with a SMR can reinforce any advantages coming from its small size if the S-CO2 Brayton cycle has much smaller size components, and simpler cycle layout compared to the currently considered steam Rankine cycle. In this paper, SMART (System-integrated Modular Advanced ReacTor), a 330MW th integral reactor developed by KAERI (Korea Atomic Energy Institute) for multipurpose utilization, is considered as a potential candidate for applying the S-CO2 Brayton cycle and advantages and disadvantages of the proposed system will be discussed in detail. In consideration of SMART condition, the turbine inlet pressure and size of heat exchangers are analyzed by using in-house code developed by KAIST-Khalifa University Joint research team. Since the current optimized S-CO2 cycle operates at the maximum pressure of 20MPa which is higher than the primary side pressure (15MPa), thermal efficiency and component size variation for lower pressure ratio will be evaluated to minimize any impacts on the primary side design. All the obtained results will be compared to the existing SMART system along with its implication to other existing or conceptual SMRs in terms of overall performance.