Abstract In nuclear Pressurized Water Reactors, fuel assemblies are slender structures composed of many rods held together by regularly spaced grids. Intense in-core conditions may sometimes result in permanent deformations impairing the reactor normal operation or even challenging its safety. Fluid-structure interactions are the central plot of this multiphysical storyline, and the water gaps between adjacent fuel assemblies act as the main character. More specifically, the flow redistribution upstream of grids, from the water gap to the rod bundle or the other way around, affects the force which is exerted by the coolant on the grids. Analytical models accounting for this effect can be found in the literature. The present article describes a simple experiment dedicated to providing validation data to such models. Mock-up grids were 3D printed and disposed in a hydraulic loop with a variable distance between them. For each configuration, the mean axial velocity was probed at hundreds of locations inside the water gap using an LDA acquisition system. The flow rate was then computed with several methods compensating the lack of velocity measures in unreachable areas. This experimental campaign helped to gain insight into the flow behavior across the grids of a fuel assembly. Notably, near proportionality was demonstrated between the water gap width and the flow rate through it. It was also observed that the redistribution cross-flows take place in a very limited region upstream of the grids.

中文翻译：

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由可变间隙分隔的网格状障碍物上游流量再分配的研究

摘要 在核压水反应堆中，燃料组件是细长的结构，由许多由规则间隔的网格连接在一起的棒组成。强烈的堆芯条件有时会导致永久性变形，从而影响反应堆的正常运行，甚至对其安全构成挑战。流体-结构相互作用是这个多物理故事情节的中心情节，相邻燃料组件之间的水隙是主角。更具体地，从水隙到杆束或其他方式的格栅上游的流动重新分布影响由冷却剂施加在格栅上的力。可以在文献中找到解释这种影响的分析模型。本文描述了一个专门为此类模型提供验证数据的简单实验。模型网格被 3D 打印并放置在液压回路中，它们之间的距离可变。对于每种配置，使用 LDA 采集系统在水隙内的数百个位置探测平均轴向速度。然后使用几种方法计算流速，以补偿无法到达区域中速度测量的缺乏。这项实验活动有助于深入了解燃料组件网格中的流动行为。值得注意的是，水隙宽度和通过它的流量之间几乎成比例。还观察到重新分配交叉流发生在网格上游的非常有限的区域中。使用 LDA 采集系统在水隙内的数百个位置探测平均轴向速度。然后使用几种方法计算流速，以补偿无法到达区域中速度测量的缺乏。这项实验活动有助于深入了解燃料组件网格中的流动行为。值得注意的是，水隙宽度和通过它的流量之间几乎成比例。还观察到重新分配交叉流发生在网格上游的非常有限的区域中。使用 LDA 采集系统在水隙内的数百个位置探测平均轴向速度。然后使用几种方法计算流速，以补偿无法到达区域中速度测量的缺乏。这项实验活动有助于深入了解燃料组件网格中的流动行为。值得注意的是，水隙宽度和通过它的流量之间几乎成比例。还观察到重新分配交叉流发生在网格上游的非常有限的区域。在水隙宽度和通过它的流量之间证明了几乎成比例。还观察到重新分配交叉流发生在网格上游的非常有限的区域中。在水隙宽度和通过它的流速之间证明了几乎成比例。还观察到重新分配交叉流发生在网格上游的非常有限的区域中。