Modeling of an air cooler with finned heat transfer tube banks using the RELAP5-3D code

The present paper proposes a calculation model of an air cooler using the RELAP5-3D code. Up to now, the modeling of an air cooler using RELAP5-3D was not described in detail, and there was a problem when calculating the decay heat removal system with the air cooler. Above all, the study of the heat transfer model for an air cooler with finned heat transfer tube banks is few. Since a decay heat removal system with air coolers is essential in liquid metal cooled fast nuclear reactors, it is anticipated how to model the air cooler using implemented heat transfer models in the RELAP5-3D code. The finned heat transfer tube is simulated with multiple bare tubes which have the equivalent heat transfer characteristics considering fin efficiency. Two kinds of simulations have been compared to the measured results of the "Monju" reactor under the forced and natural convection conditions in order to confirm the applicability of the proposed model. The simulation result under the forced convection condition is in good agreement with the test result except the operation mode under the natural convection. Since the simulation result under the natural convection condition overpredicts the test result, the surface area is lessened in order to decrease the heat transfer. As a result, good agreement has been obtained between the simulation and the test result under the natural convection condition. Sensitivity analysis has been performed for the cases where the outside diameter and the number of the simulated heat transfer tubes, and number of divisions of the calculation meshes are changed. It has been confirmed that there is almost no change in the total heat transfer rate even if various diameter tubes are used and the number of divisions is changed. The number of heat transfer tubes has a non-linear sensitivity to the removal heat rate.