Investigation of CO2 leak accident in SFR coupled with S-CO2 Brayton cycle

Various research organizations have performed feasibility studies for applying the supercritical CO2 (S-CO2) Brayton cycle to the Sodium-cooled Fast Reactor (SFR) system and the studies revealed several technical challenges. The preceding studies are reviewed to identify the current status of overcoming the identified challenges and highlight knowledge gaps. One of the most challenging issues is to comprehend the CO2 leak mechanism initiated from the pressure boundary failure in a Na-CO2 heat exchanger. Thus, an isentropic critical flow model expanding from supercritical phase to gas phase was evaluated. To validate the selected critical flow model, an experiment of CO2 critical flow under supercritical condition was performed and the experimental and numerical results correspond to each other reasonably. Another identified technical issue is removing Na-CO2 reaction product from the system to improve the system economics and plant availability. In this study, candidates that can form eutectic with Na-CO2 reaction product was newly identified. As a result, it was found that Li2CO3-Na2CO3 or Li2CO3-Na2CO3-K2CO3 eutectic systems can act as a potential cleaning agent to eliminate Na-CO2 reaction product within the operating temperature range of SFR. The performance was confirmed with simple experiments.