THERMO-FLUID DYNAMIC RESEARCH ON THE CHARACTERISTICS OF HEAT REMOVAL FROM THE NUCLEAR FUEL RODS NEAR THE SPACER

采用两种不同的支撑棒，研究了支撑棒的支撑棒的几何形状对支撑棒附近热流现象的影响。一种是环形，另一种是网格型间隔件。特别关注的是（a）引起干斑休眠的机制，（B）干斑形成的频率和（c）间隔物下侧附近的温度分布。结果总结如下。(1)即使在间隔件和加热管表面之间存在间隙，冷却水也由于表面张力而滞留在间隔件之间。因此，在使用具有差距的间隔件的本实验的情况下，主要是排水导致恰好在间隔件下方形成干斑。特别是在栅格型间隔件的情况下，差距在周向上不是均匀的，并且表面张力也在周向上起作用。然后水是 ...更多信息 比环形间隔件更紧密地保持在最小间隙区域内，并且如同固体一样起作用。因此，干斑的形成仅限于最西边的间隔间隙区域之下的区域，并且在网格间隔的情况下比环形间隔的情况下更频繁。虽然已经在实验中清楚地表明，在网格间隔的情况下的临界热流密度小于环形间隔的情况，但是其原因仍处于争论之中。本研究所得到的结果是迄今为止最可能的机理。(2)温度分布表明，（a）在有间隔物的情况下，间隔物底侧附近的温度比没有间隔物的情况下低，因为热边界层被间隔物内生长的气泡干扰。气泡可以自由移动的差距空间在栅格型间隔物的情况下被限制为较宽的间隙区域，但在环型间隔物的情况下不受限制。环形隔板对加热棒冷却的混合作用强于格栅隔板。这一实验事实也为环型隔离片上级栅型隔离片提供了依据。(3)目前的实验结果表明，即使在环形流的情况下，液膜的排出也是导致加热棒热临界情况的更合理的控制因素，即，燃尽，而不是夹带沉积理论，这是传统上被认为是导致燃尽的机制。少

The effects of the geometry of the spacer, which supports the nuclear rods, on the thermo-fluid phenomena near the spacer were investigated by using two different types of the spacers. One is the ring type and the other is the grid type spacers. The special attention was focused on (a) the mechanism to cause the drypatch dormation, (b) the frequency of the drypatch formation and (c) the temperature distribution near the down side of the spacer. The results are summarized as follows.(1) Even if there is a gap between the spacer and the heating tube surface, the coolant water stagnates in between the spacer due to the surface tension force. Therefore it is mainly the drainage that causes the drypatche formation just underneath the spacer in the case of the present experiment where the spacer with the gap is used. Especially in the case of the grid type spacer the gap is not circumferentially uniform, and the surface tension acts in the circumferential direction as well. Then the water is … More kept more tightly within the smallest gap region than the ring type spacer and acts as if it is solid body. And accordingly the drypatch formation is limited in the region just beneath of the narrowest spacer gap region and more frequent in the grid spacer case than the ring type spacer.Although it has been made experimentally clear that the critical heat flux is smaller in the case of the grid type spacer than the ring type spacer, the reason of it is in the midst of a dispute. The result obtained in the present research is the most probable mechanism so far.(2) The temperature distribution shows that (a) the temperature near the bottom side of the spacer becomes lower in the case with the spacer than without the spacer because the thermal boundary layr is disturbed by the growing bubbles within the spacer. The gap space where the bubbles can move freely is limited to the wider gap region in the case of the grid type spacer but is not limited in the case of the ring type spacer. Then the mixing effect on the cooling of the heating rods is stronger in the case of thr ring type spacer than the grid type. This experimental fact also gives a ground That the ring type spacer is superior to the grid type.(3) The present experimental results show that the drainage of the liquid film even in the case of the annular flow is the more reasonable controlling factor to cause the thermally critical situation of the heating rods, i.e., the burnout, rather than the entrainment deposition theory, which is conventionally supposed to be the mechanism to cause the burnout. Less