Potential advantages of coupling supercritical CO ₂ Brayton cycle to water cooled small and medium size reactor

The supercritical carbon dioxide (S-CO ₂) Brayton cycle is being considered as a favorable candidate for the next generation nuclear reactors power conversion systems. Major benefits of the S-CO ₂ 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 it can be transported from one place to another mostly by maritime transport due to its small size, and sometimes even through a railway system. Therefore, the combination of a S-CO ₂ Brayton cycle with a SMR can reinforce any advantages coming from its small size if the S-CO ₂ 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 330 MW _th integral reactor developed by KAERI (Korea Atomic Energy Institute) for multipurpose utilization, is considered as a potential candidate for applying the S-CO ₂ 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. According to the cycle evaluation, the maximum cycle efficiency under 310 °C is 30.05% at 22 MPa of the compressor outlet pressure and 36% of flow split ratio (FSR) with 82 m ³ of total heat exchanger volume while the upper bound of the total cycle efficiency is 37% with ideal components within 310 °C. The total volume of turbomachinery which can afford 330 MW _th of SMR is less than 1.4 m ³ without casing. All the obtained results are compared to the existing SMART system along with its implication to other existing or conceptual SMRs in terms of overall performance in detail.