Experimental study of DRACS thermal performance in a low-temperature test facility

Direct Reactor Auxiliary Cooling System (DRACS) is a passive decay heat removal system proposed for the Fluoride-salt-cooled High-temperature Reactor (FHR) that combines coated particle fuel and a graphite moderator with a liquid fluoride salt as the coolant. The DRACS features three coupled natural circulation/convection loops, relying completely on buoyancy as the driving force. These loops are coupled through two heat exchangers, namely, the DRACS heat exchanger and the natural draft heat exchanger. To experimentally investigate the thermal performance of the DRACS, a scaled-down low- Temperature DRACS test facility (LTDF) has been constructed. The design of the LTDF is obtained through a detailed scaling analysis based on a 200-kW prototypic DRACS design developed at The Ohio State University. The LTDF has a nominal power capacity of 6 kW. It uses 1.0-MPa water as the primary coolant, 0.1-MPa water as the secondary coolant, and ambient air as the ultimate heat sink. Two accident scenarios simulated in the LTDF are discussed in this paper. In the first scenario, the DRACS startup scenario occurs with no initial flow in either the LTDF primary or secondary loop, and the system is launched from a cold state. In the second scenario, a reactor coolant pump trip process is studied, during which a flow reversal phenomenon in the DRACS primary loop occurs. In both scenarios, natural circulation flows are developed as the transients approach to their quasi steady states.