Study on inventory recovery system design of supercritical $CO_2$ power cycle for sodium-cooled fast reactor

Abstract

Current Sodium-cooled Fast Reactor (SFR) design may face difficulty in public acceptance due to the potential risk from sodium-water reaction (SWR) when the current conventional steam Rankine cycle is utilized as a power conversion system for a sodium-cooled fast reactor (SFR). In order to eliminate SWR, a concept of coupling the Supercritical $CO_2$ ($S-CO_2$) cycle with SFR has been proposed. Controlling the $CO_2$ inventory of any power systems is important for stable operation and achieving high efficiency. To design an inventory control system for the $S-CO_2$ power cycle, the total $CO_2$ mass in the system should be known first. This means that not only $CO_2$ in turbo-machinery and heat exchangers is important but also $CO_2$ in piping system is important. Furthermore, pressure drop in the pipes should be considered when designing a realistic $S-CO_2$ power system. For these reasons, pipe design of a $S-CO_2$ power plant is pre-requisite to the conceptual design of the inventory control system and overall power system concept as well. Because the $S-CO_2$ power cycle is a highly pressurized system, certain amount of leakage flow is inevitable in the rotating turbo-machinery via seals. The parasitic loss caused by the leakage flow should be minimized since this is directly connected to the cycle efficiency. A model for estimating critical flow in a turbo-machinery seal is essential to predict the leakage flow rate and calculate the required total mass of working fluid in a S-$CO_2$ power system for minimizing the parasitic loss. In this work, how to select a suitable pipe of the $S-CO_2$ power plant is first discussed. This is followed by showing a conceptual design of the $S-CO_2$ power cycle for a small modular reactor (SMR) type SFR application. A computational critical flow model is described next and experiments were conducted for the critical flow calculation validation. Study on a $CO_2$ recovery system design was conducted by finding the suitable recovery point and sensitivity analysis was performed on the power system performance with respect to multiple $CO_2$ recovery process options.