Evaluation of single-phase CFD applicability to estimate fluid hot spot locations by comparing water DNB data

For the development of PWR spacer grids, it is necessary to confirm mechanical strength and thermal-hydraulic characteristics. Mitsubishi has applied Computational Fluid Dynamics (CFD) to thermal-hydraulic design of spacer grids. In this study, CFD under single-phase condition, which takes into account heat generation from rods, is performed to simulate flow conditions of water DNB test. 3 conclusions can be drawn. First, the simulation shows that the energy flux is distributed mainly by mixing vane effect in the upstream, and that enthalpy around the rod surface is increased where velocity is down. Secondly, the estimated rod where the possibility of DNB occurrence is high agrees with the rod of DNB indication in the test. And thirdly, CFD is possible to model the complicated flow field involving spacer grid and a rod bundle and to evaluate local velocity and enthalpy distribution around the rod surface