Investigation of Plugging and Wastage of Narrow Sodium Channels by Sodium and Carbon Dioxide Interaction

− We investigated the physical/chemical phenomena that a slow loss of CO 2 inventory into sodium after the sodium-CO 2 boundary failure in printed circuit heat exchangers (PCHEs), which is considered for the supercritical CO 2 Brayton cycle power conversion system of a sodium-cooled fast reactor (SFR). The first phenomenon is plugging inside narrow sodium channels by micro cracks and the other one is damage propagation referred to as wastage combined with the corrosion/ erosion effect. Experimental results of plugging shows that sodium flow immediately stopped as CO 2 was injected through the nozzle at 300~400 C in 3 mmID sodium channels, whereas sodium flow stopped about 60 min after CO 2 injection in 5 mmID sodium channels. These results imply that if pressure boundary of sodium-CO 2 fails a narrow sodium channel would be plugged by reaction products in a short time whereas a relatively wider sodium channel would be plugged with higher concentration of reaction products. Wastage by the erosion effect of CO 2 (200~250 bar) hardly occurred regardless of the kinds of materials (stainless steel 316, Inconel 600, and 9Cr-1Mo steel), temperature (400~500 C), or the diameter of the CO 2 nozzle (0.2~0.8 mm). Velocities at the CO 2 nozzle were specified as Mach 0.4~0.7. Our experimental results are expected to be used for determining the design parameters of PCHEs for their safeties.