Statistical evaluation of cross flow in a tight-lattice rod bundle

Zhang, W.; Yoshida, Hiroyuki  ; Ose, Yasuo*; Onuki, Akira; Akimoto, Hajime

In relation to the thermal-hydraulic design of FLWR, this study presents a statistical evaluation of numerical simulation results obtained by a detailed two-phase flow simulation code (named TPFIT). In order to clarify mechanisms of cross flow in such tight lattice rod bundles, the TPFIT was used to simulate water-steam two-phase flow in two modeled subchannels. Attention was focused on instantaneous fluctuation characteristics of cross flow. With the calculation of correlation coefficients between the differential pressure and gas/liquid mixing coefficients, the time scales of cross flow were evaluated, and the effects of mixing section length, flow pattern and gap spacing on correlation coefficients were investigated. The difference in mechanism between gas and liquid cross flows was pointed out.