EFFECTS OF A SPACER ON THREE-DIMENSIONAL VOID FRACTION DISTRIBUTIONS IN GAS-LIQUID TWO-PHASE FLOW IN A BUNDLE

水冷反应堆中的燃料棒是由一个隔离物支撑的。隔板内部及其附近冷却剂的行为是复杂的，从核反应堆安全考虑，了解隔板周围的两相流是重要的。本研究的目的是通过中子射线照相CT方法测量三维空隙率分布，阐明隔板对棒束内稳定两相流的影响。空气-水两相流的实验结果表明，隔板对棒束内稳定两相流的影响是显著的。在具有环形套圈型间隔件的4 × 4棒束中进行了相流实验，并进行了空间分辨率为0.18mm的CT重建。通过CT重建，沿管道进行两个321 × 321点的水平分层，沿着管道。水平分布用空隙率的亮度和曲面图表示，三维分布的所有切片用动画表示，从而发展了理解三维分布的方法，通过得到的三维分布可以明确间隔物对空隙率分布的影响。结果表明，在环形流区，隔片对含气率分布影响较大，隔片内的水在四个拐角处聚集，其影响在隔片下游仍然存在。

Fuel rods in water cooled reactors are supported by a spacer. The behaviors of the coolant inside and near the spacer are comlex and they are important from safety considerations of nuclear reactor to understand the two-phase flow around the spacer.The purpose of this research is to clarify the effects of the spacer on the steady two-phase flow in the rod bundle by measuring the three-dimensional void fraction distribution by a neutron dadiography CT method.Air-water two-phase flow experiments in a 4x4 rod bundle with circular ferrule type spacers were carried out and CT reconstructions with 0.18 mm in the spatial resolution were made. By the CT reconstructions, two handreds horizontal slices with 321x321 points along the conduit were carried out. The horizontal distributions were expressed by the brightness and the surface plot of the void fraction and animations were made to show the all slices for the three-dimensional distributions to develop the methods to understand well the three-dimensional distributions.The effects of the spacer on the void fraction distributions could be clarified by the obtained three-dimensional distributions. It was shown that the void fraction distribution was affected much by the spacer in annular flow region and the water gathered at four cornners in the spacer the effects of which remained downstream of the spacer.