Nathan C. Bremer

Development of Process for Cleanup of Sodium-CO 2 Reaction Products

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Description of the First Observed Sodium-C02 Reactions in the Sodium CO2 Interaction Experiment (SNAKE)

One appealing feature of the supercritical carbon dioxide Brayton cycle energy conversion system is the small footprint that the hardware requires, which is in part due to the use of Printed Circuit Heat Exchangers (PCHEs) as the heat source heat exchanger (sodium-to-CO2) as well as the recuperator and cooler modules. Although PCHEs have a high degree of structural integrity, the potential for leaks to develop between the sodium and CO2 coolant channels in the secondary heat exchanger cannot be ruled out, and this would lead to discharge of high pressure CO2 into the secondary coolant circuit. Due to the robustness of the PCHE design, catastrophic failure leading to CO2 jet blowdown into the secondary sodium loop is not deemed likely. Rather, small cracks (or micro-leaks) may develop in which CO2 will bleed into the secondary system at a relatively low rate and chemically react with the sodium. The goal of the sodium-CO2 interaction tests is to gain a fundamental understanding of sodium-CO2 interactions under prototypical conditions of compact diffusion-bonded heat exchanger failure, a fundamental understanding of self-plugging if it occurs, and the development of one-dimensional phenomenological models for the interactions between highpressure CO2 issuing into liquid sodium from a micro-leak across a stainless steel pressure boundary. These models will be validated using experiment data. Therefore, an experiment program at Argonne was initiated in Fiscal Year 2010 to investigate the reaction characteristics between sodium and CO2 under micro-leak conditions. Several reports have described the facility scaling rationale and design. Assembly of the SNAKE (SCO2, Na Kinetics Experiment) began in Fiscal Year 2011 and was completed in July 2012. Approximately 44 lbs (20 kg; ~21 L/5.5 gal) of sodium was transferred into the SNAKE dump tank from a drum of clean sodium in July 2012. The first sodium-CO2 interaction experiment was carried out at SNAKE in September 2012. This test was successful in that supercritical carbon dioxide was sparged into a pool of sodium through a 64 μm diameter nozzle. A series of sodium-CO2 interaction experiments were carried out in Fiscal Year 2013 in the SNAKE experiment. These tests successfully injected supercritical carbon dioxide into a pool of sodium through a 64 μm diameter nozzle. A reaction between the CO2 and sodium was detected. The extent of this reaction was unexpected since the initial sodium temperature was 145 ̊C, a temperature range where previous researchers have detected little or no chemical reaction between these species. The important difference between the SNAKE experiment and previous research is that the SNAKE geometry and conditions promote high-interfacial area and mixing between the CO2 and sodium. These characteristics could be very important in promoting accelerated chemical reactions and will be studied further as the SNAKE test matrix is carried out. Approximately 325 standard liters of CO2 were injected into a 45 cm (15 inch) high column of sodium at a nominal temperature of 150 ̊C over the course of 3 hours. The inlet CO2