Development of Engenvalue Separation Monitor for Nuclear Reactor by Using Position Sensitive Proportional Counter

特征值分离是评价核反应堆稳定性的重要指标。我们打算利用位置灵敏正比计数器(PSPC)测量的中子通量的空间积分来研制一种本征值分离监测器。通过这项研究，得到了以下结果：(1)在京都大学临界大会上的实验证实，可以从PSPC测量的中子通量估计本征值分离，并且必须通过数值计算来校正沿未测量方向的高阶模式的影响。(2)实验还证实，通过求解多个PSPC测量的中子通量分布的耦合方程，可以在不进行数值修正的情况下估计本征值分离。但是，为了排除初始磁通失真的影响，估计特征值分离需要依赖于次临界的多次实验。(3)我们准备了同时记录PSPC的位置信号及其到达时间的系统，并考察了时空相关测量能力。(4)通过在以前的高阶模式数值编码中加入节点法，我们可以高精度地估计简并的特征值。(5)我们证实了探测器效率的空间相关性是由阳极线支承的制造工艺的变化引起的。因此，基于PSPC测量的通量的特征值分离监测器是可以开发的。但未来还需要对实际核反应堆的适用性进行更多的研究。时空相关测量有望成为反应堆动力学参数测量的一种新方法。

The eigenvalue separation is important as an index for evaluating the degree of stability of nuclear reactors. We intend to develop an eigenvalue separation monitor by using spatial integral of neutron flux measured by the position sensitive proportional counter (PSPC). Through this study, the following results were obtained.(1) It was confirmed from experiments at Kyoto University Critical Assembly that the engenvalue separation can be estimated from the neutron flux measured with a PSPC.The effect of higher modes along the directions not measured must be corrected by numerical calculations.(2) It was confirmed also from experiments that the eigenvalue separation can be estimated without numerical corrections by solving the coupled equations of neutron flux distributions measured by multiple PSPCs. But, to estimate the engenvalue separations excluding an effect of initial flux distortion, multiple experiments depending on subcriticalities are necessary.(3) We prepared the system registering simultaneously both a position signal of the PSPC and its arrival time, and investigated ability of time-space correlation measurement.(4) By adding the nodal method to the previous numerical code on higher modes, we can estimate degenerate eigenvalues with high accuracy.(5) We confirmed that the spatial dependence of detector efficiency is caused by the variety about manufacturing of anode wire supports.It was concluded that the eigenvalue separation monitor based on the flux measured with the PSPC can be developed. But more investigations on the applicability to actual nuclear reactors are needed in future. The time-space correlation measurement is expected to be a new method for measuring parameters of reactor dynamics.