Numerical simulation of boiling two-phase flow in tight-lattice rod bundle by 3-dimensional two-fluid model code ACE-3D

Yoshida, Hiroyuki  ; Misawa, Takeharu; Takase, Kazuyuki

Japan Atomic Energy Agency (JAEA) develops a three dimensional two-fluid model analysis code ACE-3D, which adopts boundary fitted coordinate system in order to simulate complex shape channel flow. In this paper, boiling two-phase flow analysis in a tight lattice rod bundle is performed by ACE-3D code. The parallel computation using 126CPUs is applied to this analysis. In the results, the void fraction, which distributes in outermost region of rod bundle, is lower than that in center region of rod bundle. At the height of z=0.5m, void fraction in gap region is higher in comparison with that in center region of the subchannel. However, at the height of z=1.1m, higher void fraction distribution exists in center region of the subchannel in comparison with gap region. The tendency of void fraction to concentrate in gap region at vicinity of boiling starting point, and to move into subchannel as water goes through rod bundle, is qualitatively agreement with the measurement results by neutron radiography. And the predicted pressure loss of test section almost agreed with experimental results. To evaluate effects of two-phase flow model used in ACE-3D code, numerical simulation of boiling two-phase in tight lattice rod bundle with no lift force model is also performed. From the comparison of numerical results, it is concluded that the effects of lift force model are not so large on void fraction distribution in tight lattice rod bundle.