Studies of S-CO₂ Power Plant Pipe Design

Further development of nuclear energy is required to address the global warming issue while overcoming the difficulty of meeting the constantly growing demand of energy. As the nuclear energy does not only reduce the carbon dioxide emission but also attain sufficient and stable electricity supply, this is considered as one of the most clean and sustainable energy sources. The Sodium-cooled Fast Reactor (SFR) is a strong candidate among the next generation nuclear reactors. However, current SFR design may face difficulty in public acceptance due to the potential hazard from sodium-water reaction (SWR) when the current conventional steam Rankine cycle is utilized as a power conversion system for SFR. In order to eliminate SWR, the Supercritical CO₂ (S-CO₂) cycle has been proposed. Although many S-CO₂ cycle concepts are being suggested by many research organizations, pipe selection criteria for S-CO₂ cycle are one of the areas that are not clearly established. As one of the most important parts of the plant design is economical fluid transfer, this paper will discuss how to select a suitable pipe for the S-CO₂ power plant compared to steam Rankine cycle. The main advantages of S-CO₂ cycle are: prevention of no SWR by changing the working fluid, relatively high efficiency with 450∼750 .deg. C turbine inlet temperature, physically compact size. Additional study for larger system such as 300MW class system in MIT report will be conducted. From the preliminary estimation when the S-CO₂ system becomes large than the pipe diameter may exceed the current ASME standard. This means that more innovative approach will be needed for the S-CO₂ pipe design. To economically design the pipe of S-CO₂ recompressing cycle, optimal flow velocity for S-CO₂ that can be obtained through the process engineering should exist. Although the Ronald W. Capps equation offers an optimal flow velocity while considering safety, capital cost, operating cost and life-cycle cost, this equation is optimized for water or steam system. As S-CO₂ cycle is not commercialized yet and it is being developed actively at present, procedure for the S-CO₂ pipe design is not fully established. Thus, further study and accumulation of operating experiences are salient for the further development and realization of the S-CO₂ cycle