SLIMM DECAY HEAT REMOVAL BY NATURAL CIRCULATION OF AMBIENT AIR

摘要

This paper presents the results of 3-D Computational Fluid Dynamic (CFD) and thermal-hydraulic analyses investigating passive decay heat removal for the Scalable Liquid Metal cooled small Modular (SLIMM) reactor by natural circulation of ambient air, in case of a malfunction of the in-vessel helically coiled tubes, Na/Na heat exchanger. Results show that the longitudinal metal fins along the outer surface of the reactor guard vessel effectively increase the heat removal by air natural circulation. The thermal radiation from the guard vessel outer wall and metal fins is a major contributor to the heat removal of the decay heat by ambient air, accounting for 29%-42% of the total rate of heat removal. Results showed that the decay heat removal by ambient air is quite effective, even without metal fins along the outer surface of the guard vessel wall (～ 1.0 MW_th). The metal fins increase the rate of the heat removal by naturally convection of ambient air by an additional 26% to 1.26 MW_th. Without metal fins along the outer surface of the guard vessel wall, the average temperature of the circulating liquid sodium in the reactor primary vessel peaks at ～ 821.7 K, ～ 1.5 hr after reactor shutdown and decreases to 400 K ～ 22.2 hr after reactor shutdown. With metal fins, the higher rate of heat removal (1.26 MW_th), limits the peak temperature of the in-vessel liquid sodium to ～ 806 K, only ～ 40 minutes (or 0.665 hr) after reactor shutdown. These results confirm a large safety margin, ＞ 330 K, from the boiling temperature of liquid sodium (～ 1156 K at 0.1 MPa).