$Sodium-CO_2$ interaction in a supercritical $CO_2$ power cycle for a Sodium-cooled Fast Reactor

Abstract

The supercritical $CO_2$ Brayton cycle option for energy conversion in a Sodium-cooled Fast Reactor (SFR) recently received a great deal of attention due to highly reliable system design features that make it essentially free from risk of a sodium-water reaction in a traditional Rankine cycle power conversion. Although the novel approach will yield significant improvements in overall plant energy utilization, it raises the risk of a potential pressure boundary failure and consequential sodium-$CO_2$ interaction. For this reason, kinetic behaviors should be assessed to confirm its impact upon plant safety. In the present study, fundamental surface reaction tests for a sodium-$CO_2$ interaction were carried out and its kinetics was investigated. The tests were performed for sodium temperatures ranging from $200\degC$ to $600\degC$. Based on the test results, it was found out that the reaction kinetics over the sodium temperature range of $300\degC$ to $550\degC$ depends heavily on the temperature but is not sensitive to the velocity of $CO_2$ flowing over the gas-liquid reacting interface. Gaseous and non-gaseous reaction products were sampled and analyzed quantitatively. The rate of the chemical reaction was determined by measuring the gas concentration of the CO/$CO_2$ mixture. Then, a two-zone reaction model with a threshold temperature of $460\degC$ was proposed. The kinetic parameters for each reaction zone were experimentally obtained and the corresponding model parameters were identified. It was also observed that the self-ignition of sodium took place if the sodium temperature exceeds $590\degC$, regardless of any other reaction conditions like supplied $CO_2$ temperatures and flow rates. Based on the fundamental investigation results for sodium-$CO_2$ interaction mechanism, two major design issues were investigated in regard to the $CO_2$ ingress accident into liquid sodium: i) a wastage phenomenon in regard to a structural damage adjacent to the leaki...