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MEASUREMENT OF NEUTRON AND GAMMA-RAY NOISE IN LARGE SUBCRITICAL CONDITION FOR CRITICALITY SAFETY

机译:大型亚临界条件下的中子和伽马射线噪声的测量

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Various experimental methods have been proposed for subcriticality measurement and neutron noise analysis method is one of important experimental techniques for this purpose. The variance to mean value method, called Feynman-alpha method, is one of well-known noise analysis methods. In this method, variation of neutron count rate distribution from the Poisson distribution caused by fission chain reactions, which is called Y-value, is measured, however, it is difficult to measure the Y-value in large subcritical state such as nuclear fuel facility, because number of emitted neutrons by fission chain reaction is small, which causes large statistical error. We developed new experimental technique based on Feynman-alpha method combined with pulsed neutron source, called Delayed Neutron Noise Analysis (DNNA) method, to monitor the change of subcriticality. In this new method, neutron and gamma-ray counts measured only appeared in the delayed neutron region after injection of pulsed neutron are analyzed, and the prompt neutron region is completely ignored. The advantage of DNNA compared with conventional method is that spatial dependency of detector positions on measured results can be greatly decreased, which result in increase of accuracy of measured subcriticality. The validity of the DNNA method was experimentally investigated in the Kyoto University Critical Assembly (KUCA) at Kyoto University Research Reactor Institute. In the experiments, pulsed neutrons by D-T reactions are injected into the core and we used ~3He detectors to measure neutron noise signals and BGO scintillation detectors to measure gamma-ray noise signals, and all data in the delayed neutron region were analyzed based on Feynman-alpha method. From the experimental results, it was found that the Y-values are clearly larger than zero in the case of existence of fuel assemblies and this method can be applied to detection of hidden special nuclear materials for example in a cargo container.
机译:已经提出了各种实验方法,用于子临时测量和中子噪声分析方法是此目的重要的实验技术之一。均值的均值法方法的差异方法是众所周知的噪声分析方法之一。在该方法中,测量了由裂变链反应引起的泊松分布的中子计数分布的变化,其被称为Y值,然而,难以测量大型亚临界状态(如核燃料设施)的Y值,因为通过裂变链反应的发射中子的数量很小,这导致大的统计误差。我们开发了基于Feynman-alpha方法的新实验技术与脉冲中子源相结合,称为延迟中子噪声分析(DNNA)方法,监测子临界性的变化。在这种新方法中,分析了在注射脉冲中子喷射后仅出现在延迟中子区域中的中子和伽马射线计数,并且迅速忽略迅速的中子区域。与常规方法相比DNNA的优点是检测器位置对测量结果的空间依赖性可以大大降低,这导致测量的子尺度的精度增加。在京都大学研究反应堆研究所在京都大学临界大会(KUCA)实验研究了DNNA方法的有效性。在实验中,通过DT反应的脉冲中子注入核心,我们使用了〜3HE检测器来测量中子噪声信号和BGO闪烁探测器来测量伽马射线噪声信号,并且基于Feynman分析延迟中子区域中的所有数据-alpha方法。从实验结果中发现,在燃料组件存在的情况下,Y值明显大于零,并且该方法可以应用于例如在货物容器中检测隐藏的特殊核材料。

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