An investigation of sodium-CO2 interaction byproduct cleaning agent for SFR coupled with S-CO2 Brayton cycle

Abstract

One of the promising future nuclear energy systems, the Sodium-cooled Fast Reactor (SFR) has been actively developed internationally. Recently, to improve safety and economics of a SFR further, coupling supercritical CO2 power cycle was suggested. However, there can be a chemical reaction between sodium and CO2 at high temperature (more than 400 degrees C) when the pressure boundary fails in a sodium-CO2 heat exchanger. To ensure the performance of such a system, it is important to employ a cleaning agent to recover the system back to normal condition after the reaction. When sodium and CO2 react, solid and gaseous reaction products such as sodium carbonate (Na2CO3) and carbon monoxide (CO) appear. Since most of solid reaction products are hard and can deteriorate system performance, quick removal of solid reaction products becomes very important for economic performance of the system. Thus, the authors propose the conceptual method to remove the byproducts with a chemical reaction at high temperature. The chemical reaction will take place between the reaction byproducts and a cleaning agent while the cleaning agent is inert with sodium. Thus, various sodium-based compounds were first investigated and three candidate substances satisfying several criteria were selected; sodium bromate (NaBrO3), sodium chlorate (NaClO3), and sodium tetrafluoroborate (NaBF4). The selected substances were thermally analyzed with the TG/DTA studies. Unfortunately, it was revealed that all candidate substances did not react with Na2CO3 and decomposed before 600 degrees C. However, since no study has been performed on the issue of cleaning byproducts of Na-CO2 reaction so far, this study provides the basic guideline for the future study and suggests the future research direction and preferred characteristics of cleaning agent of sodium CO2 reaction byproducts.