Research on backflow characteristics in U-tube of forced circulation steam generator under ocean conditions

Abstract

The reverse flow phenomenon may occur in the primary loop of steam generator (SG) at low flow rate. The reverse flow will increase the flow resistance in the heat transfer pipe, reduce the heat transfer efficiency and reduce the ability of the primary loop to take away the core heat. When the ship encounters the ocean conditions during traveling, the additional force of the ocean conditions will change with time, which will make the occurrence and evolution mechanism of reverse flow be more complicated. Unfortunately, most of the existing researches regarding the reverse flow are focused on the steady-state conditions, and the transient variations of SG System under the ocean conditions are rarely studied.In this paper, a dynamic simulation model of typical ocean conditions was established and the correctness of the model was verified based on RELAP5/MOD3 program. On the basis of the improved RELAP5/MOD3 program, the influence of different rolling conditions on the flow rate in low flow forced circulation was studied. The results indicated that rolling amplitude and the rolling period had significant influence on the reverse flow, but had little effect on pitching; if SG outlet is higher than inlet during rolling, the reverse flow will be inhibited, while SG inlet in symmetrical position is higher than outlet, the reverse flow will occur more easily; after 45 s of rolling, two SGS will be reverse flow at the same time.