Supercritical carbon dioxide and liquid sodium chemical reaction experiments

Development of the sCO2 Brayton cycle as an advanced power converter for use with Sodium-Cooled Fast Reactors (SFRs) as well as other advanced reactors and power systems has been underway within the U.S. Department of Energy (DOE) and at Argonne National Laboratory since the early 2000’s. The main benefits of supercritical carbon dioxide (sCO2) power conversion for SFRs are improved economics (reduction of the nuclear power plant overnight capital cost per unit output electrical power, $/kWe, or, alternately, the levelized cost of electricity, LCOE) and the elimination of the need to accommodate potential sodium-water reactions. However, sodium and carbon dioxide (CO2) interact chemically such that there is a need to understand and accommodate potential sodium-CO2 interactions, if a leak were to occur in the heat exchanger boundary between the two fluids. This paper presents the results of sCO2-sodium tests performed under prototypic SFR conditions and builds on previous sCO2-sodium studies. The two main ways this paper differs from those previous studies is as follows: 1) The current work focused on leak sizes of 0.062–0.115 mm, smaller than performed in past studies, which were typically in the 0.3–1.0 mm in size. While the leak size of a typical DBHE failure is not currently known, the leak size is postulated to be small, on the order of microns, due to the crack forming in robust, diffusion- bonded material. 2) We report this is the first known study of the injection of supercritical CO2 into sodium, since gas injection pressures in the current study where as high as 200 bar, where previous work, performed injections in the range of 1.0–55 bar. The expected operating pressure of sCO2 at the sodium-to-sCO2 heat exchanger in an SFR is just under 200 bar in the reference SFR.