An Experimental Study on the Ignition Temperature of Sodium-CO2 Reaction with an Implication of Safety of a SFR with S-CO2 Brayton Cycle

Abstract

The Sodium-cooled Fast Reactor (SFR), which is one of the most promising Generation IV Reactors, has been actively developed with a configuration of traditional steam Rankine cycle to generate power. But there has been a significant design challenge concerned with the potential sodium-water reaction (SWR) in the SFR. In order to avoid SWR, the supercritical CO2 (S-CO2) Brayton cycle was proposed as a power conversion system for SFR applications. The S-CO2 Brayton cycle with a SFR has several advantages: 1) relatively higher thermal efficiency than the traditional steam Rankine cycle, 2) smaller components such as the turbo-machinery and heat exchangers, 3) milder reaction with sodium. In spite of these advantages, carbon dioxide also reacts with sodium when pressure boundary fails. When CO2 gas leaks into the sodium side of SFR, a reactive process of liquid sodium and CO2 will follow. During the process, heat is also generated which will result in a temperature increase. The reaction was flammable at more than 580~590℃ in our former experiments. Fortunately, it was not explosive below 580~590℃, though the reaction characteristics between sodium and CO2 should be examined prior to the basic design of the SFR coupled with the S-CO2 Brayton cycle. In the beginning of this research, the authors classified the behavior into a variety of subjects and it was found that many interesting phenomena occur in sodium-CO2 interactions from the collaborative researches with Korea Atomic Energy Research Institute (KAERI). During the course of the investigation the ignition temperature of sodium-CO2 reaction was roughly identified but the exact ignition point was remained unknown. In this paper, the necessity of finding the exact ignition point will be discussed and the preparation and process for the experiment will be described. It is expected that our results will play an important role in the development of SFRs in the future.