Main coolant pump resistance influence on single phase water reverse flow in the inverted U-tubes under natural circulation

Based on nuclear power plant (NPP) best-estimate transient analysis with RELAP5/MOD3 code, the reactor point kinetics model in RELAP5/MOD3 code is replaced by the two-group, 3-D space and time dependent neutron kinetic model, and two-fluid model is replaced by drift flux model. A coupled three-dimensional physics and thermal-hydrodynamics model is used to develop its corresponding computing code, thus simulating natural circulation of single-phase flow for the PWR. In this paper, we report the forward and reverse flow distribution in the inverted U-tubes of the steam generator (SG) under some typical operating conditions in the natural circulation case, and analyze the influence of main coolant pump resistance on the forward and reverse flow distribution. The calculation results show that, the pressure drop between SG inlet and outlet plenum decreases, and the SG inlet and outlet mass flow decrease with an increased main coolant pump resistance, but net mass flux of reverse flow in inverted U-tubes, and the ratio of mass flow in all reverse flow tubes to that of main coolant pipeline increase, meanwhile, the secondary steam load is invariable in this process. (authors)