A Fan-Controlled Sodium-to-Air Heat Exchanger Configuration for Failsafe Decay Heat Removal in Sodium-Cooled Fast Reactors

Passive safety systems help to improve overall plant safety, reliability, and resilience. However, the real gain in the use of passive systems depends on the robustness of the design utilizing the passive process and the role of active elements, if any. In this paper, we propose a fan-controlled sodium-to-air heat exchanger (AHX) system design for a failsafe and passive decay heat removal (DHR) function in a pool-type sodium-cooled fast reactor. The proposed system uses a fan to control air flow and minimize heat loss during normal operation, and when the fan trips due to loss of power or a trip signal, DHR gets enabled in a failsafe mode. The system is analyzed with the help of a simplified one-dimensional model as well as with detailed computational fluid dynamics software. It is found from analysis that it is possible to control and maintain the air flow to about 4% to 5% of full flow, as in the case of conventional dampers, to minimize heat loss during normal reactor operation. The reliability of the proposed system is also analyzed and shows that the fan-controlled AHX-based decay heat removal system (DHRS) has a much better reliability compared to the conventional passive DHRS with active damper-dependent operation.