The reverse flow among parallel U-tubes in steam generator under natural circulation condition: A review

Under natural circulation conditions, the reverse flow will occur among parallel U-tubes of the steam generator, which lessens the natural circulation capacity and affects the passive safety of the reactor. First, this paper analyzes the experimental discovery of the reverse flow, and points out the characteristics of the reverse flow's happening and disappearing, as well as the space distribution of the reverse flow U-tubes. Then, the paper introduces the theory model of the reverse flow, explains the reverse flow influencing factors and influencing rules, and discusses the effect of reverse flow on natural circulation. Existing studies have shown that the reverse flow's criterion is affected by the U-tube features, primary side inlet conditions of steam generator, secondary side features and environment conditions. Researches on the influence of the reverse flow on the natural circulation ability have showed the reverse flow rate accounted for a relatively high proportion, which has significantly reduced the natural circulation ability. Although Reducing the ascending section and setting the non-heat transfer section could effectively to solve the problem of reverse flow, however their feasibility will need to be investigated in further studies.