ABSTRACT For a highly enriched uranium subcritical core driven by an inherent or an external Am-Be source in Kyoto University Critical Assembly (KUCA), a series of the source multiplication measurements, the Feynman-α and the Rossi-α neutron correlation analyses was carried out to demonstrate quantitatively that the use of the former inherent source had some advantages over that of the latter external source. Under a reactor drive by the external source, the subcriticality obtained by the neutron source multiplication method (NSM) significantly depended on neutron counter position and was consequently in very poor agreement with that calculated by the continuous-energy Monte Carlo code MVP (version 3) with the nuclear data library JENDL-4.0. In contrast to the above drive, the other drive by the inherent source spectacularly reduced the counter-position dependence and lead to a good agreement with the calculation by the MVP. The prompt-neutron decay constant determined from the Feynman-α analysis under the external source was also significantly dependent on the counter position. The Rossi-α analysis had a relatively slight counter-position dependence of the decay constant to the Feynman-α analysis but had a very low S/N ratio, which indicated an inferior applicability of the Rossi-α analysis to the reactor drive and enlarged a statistical uncertainty of the decay constant. On the other hand, the reactor drive by the inherent source considerably reduced the counter-position dependence of the Feynman-α analysis and spectacularly enhanced the S/N ratio of the Rossi-α analysis. An effective strength of the inherent source could be also determined from the S/N ratio. When the prompt-neutron decay constant obtained under this reactor drive was transformed into each subcriticality by the Simmons and King method, where a subcritical dependence of the generation time and the effective delayed-neutron fraction was neglected, the subcriticality transformed seemed to agree well with that calculated by the MVP. When the decay constant was transformed by the inhour method, where the subcritical dependence of these kinetic parameters was considered, a systematic disagreement between the transformed and the calculated subcriticality appeared.

中文翻译：

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京都大学临界组件固有源驱动的高浓缩铀次临界堆芯的源倍增测量和中子相关分析

摘要 对于京都大学临界装置（KUCA）中由固有或外部 Am-Be 源驱动的高浓缩铀亚临界堆芯，进行了一系列源倍增测量、Feynman-α 和 Rossi-α 中子相关分析以定量证明使用前者的固有来源比使用后者的外部来源具有一些​​优势。在外源驱动的反应堆驱动下，中子源倍增法 (NSM) 获得的亚临界度显着取决于中子计数器位置，因此与连续能蒙特卡罗代码 MVP（版本 3）计算的结果不一致与核数据库JENDL-4.0。与上述驱动相比，内在源的另一个驱动极大地减少了对位依赖，并与 MVP 的计算非常吻合。外源下费曼α分析确定的瞬发中子衰变常数也显着依赖于计数器位置。Rossi-α 分析的衰变常数与 Feynman-α 分析具有相对轻微的反位置依赖性，但信噪比非常低，这表明 Rossi-α 分析对反应堆驱动的适用性较差，并扩大了衰减常数的统计不确定性。另一方面，由固有源驱动的反应堆大大降低了 Feynman-α 分析的反位置依赖性，并显着提高了 Rossi-α 分析的 S/N 比。也可以从 S/N 比确定固有源的有效强度。当在该反应堆驱动下获得的瞬发中子衰变常数通过 Simmons 和 King 方法转换为每个亚临界时，忽略产生时间和有效延迟中子分数的亚临界依赖性，转换后的亚临界似乎与由MVP计算。当衰减常数通过 inhour 方法转换时，其中考虑了这些动力学参数的亚临界依赖性，转换后的亚临界与计算的亚临界之间出现了系统性不一致。在忽略产生时间和有效延迟中子分数的亚临界依赖性的情况下，转换的亚临界似乎与 MVP 计算的结果非常吻合。当衰减常数通过 inhour 方法转换时，其中考虑了这些动力学参数的亚临界依赖性，转换后的亚临界与计算的亚临界之间出现了系统性不一致。在忽略产生时间和有效延迟中子分数的亚临界依赖性的情况下，转换的亚临界似乎与 MVP 计算的结果非常吻合。当衰减常数通过 inhour 方法转换时，其中考虑了这些动力学参数的亚临界依赖性，转换后的亚临界与计算的亚临界之间出现了系统性不一致。