Basic Study on Regional Oscillation of Nuclear Reactor by Using Coupled Core from a Neutronics

人们可以在大型核反应堆中观察到功率的区域振荡。为了揭示这一现象的机理，利用京都大学临界组件（KUCA）构建的空间耦合系数接近现有沸水堆（BWR）的耦合堆芯进行了基础研究。系统地改变堆芯分离距离和堆芯内燃料节距，测量与反应堆稳定性密切相关的空间一谐模的特征值分离（ES）。采用费曼- α法、棒降法和磁通倾斜法测量ES值。它们在实验误差范围内是一致的。结果表明，基于光纤闪烁探测器测量中子通量分布的通量倾斜法能够获得精确的ES值。然而，费曼- α方法似乎很难测量强耦合核中的ES，在强耦合核中，第一模比基模小得多。随着堆芯间距和燃料节距的减小，ES增大。在扩散理论和输运理论的基础上对实验结果进行了中子计算分析。输运计算结果比扩散计算结果更符合实验结果，因为在本分析中输运效应较大。对于第一模态的计算，虽然网格效应较小，但三维效应、能量群塌缩效应和输运效应均大于基模态。这一事实表明，与基模计算相比，在第一模计算中需要更大的校正。此外，还进行了应用高阶微扰理论计算通量倾斜度和测量中子通量从一个堆芯到另一个堆芯变化的传输时间的试验。然而，果实还没有得到。少

One can observe a regional oscillation of power in a large sized nuclear reactor. To reveal the mechanism of this phenomenon, a basic study was conducted by using coupled cores constructed in the Kyoto University Critical Assembly (KUCA) of which spatial coupling coefficient was close to that of existing Boiling Water Reactor (BWR).The core separation distance and the fuel pitch in the core were systematically varied to measure the eigenvalue separation (ES) of the spatial first-harmonic mode which is closely related to the reactor stability. The Feynman-alpha, the rod drop and the flux tilt methods were applied to measure the ES values. They were agreed with each other within experimental errors. It was found that the flux tilt method based on the measurement of neutron flux distribution by an optical fiber scintillation detector is powerful to obtain an accurate ES value. Whereas the Feynman-alpha method seems to be difficult to measure ES in strongly coupled core where the first-har … More monic mode is much smaller than the fundamental mode. It was observed that ES becomes larger with decreasing the core separation distance or the fuel pitch.The neutronics calculations were executed to analyze the experimental results on the basis of either diffusion or transport theory. The result of transport calculation agreed better with the experimental result than that of diffusion calculation, since the transport effect was large in the present analysis. For the calculation of the first-mode, although the mesh effect was smaller, the three-dimensional, the energy group collapsing and the transport effects were larger than those for the fundamental-mode. This fact indicates that the larger correction would be necessary in the first-mode calculation compared with the fundamental-mode calculation.Moreover, traials were conducted to apply higher order perturbation theory to calculate the flux tilt and to measure the transmission time of the change in neutron flux from one core to the other core.However, the fruit has not been obtained yet. Less