ABSTRACT

To judge whether an application system is a subcritical state or not based on numerical results of the effective neutron multiplication factor ${\mathrm{k}}_{\mathrm{e}\mathrm{f}\mathrm{f}}$, an evaluation method of the estimated criticality lower-limit multiplication factor (ECLLMF) using the bootstrap method is newly proposed. By utilizing numerical results of ${\mathrm{k}}_{\mathrm{e}\mathrm{f}\mathrm{f}}$ for critical benchmark-problems that are selected depending on neutronic similarity to the application system, the ECLLMF should be carefully and conservatively estimated based on uncertainties of ${\mathrm{k}}_{\mathrm{e}\mathrm{f}\mathrm{f}}$ due to a criticality safety analysis code, experimental uncertainty, and covariance matrix of the nuclear data library. Furthermore, the frequency distribution of ${\mathrm{k}}_{\mathrm{e}\mathrm{f}\mathrm{f}}$ for these problems does not necessarily obey an ideal normal distribution. Using a resampling technique called ‘bootstrap method,’ the proposed method can reasonably estimate the ECLLMF considering the uncertainties and nuclear data-induced correlation between each critical benchmark-problem without the assumption of normality. To investigate the applicability of the proposed method, the approach-to-criticality experiment was carried out at the Kyoto University Critical Assembly (KUCA). Comparison of numerical results of ${\mathrm{k}}_{\mathrm{e}\mathrm{f}\mathrm{f}}$ and the ECLLMF using the bootstrap method indicated that the proposed method was able to judge an actual subcritical core as subcritical state.

摘要

根据有效中子倍增因子的数值结果判断应用系统是否处于亚临界状态 ${\mathrm{克}}_{\mathrm{电子}\mathrm{F}\mathrm{F}}$, 新提出了一种使用 bootstrap 方法的估计临界下限乘法因子 (ECLLMF) 的评估方法。通过利用数值结果${\mathrm{克}}_{\mathrm{电子}\mathrm{F}\mathrm{F}}$ 对于根据与应用系统的中子相似性选择的关键基准问题，ECLLMF 应根据不确定性进行仔细和保守的估计 ${\mathrm{克}}_{\mathrm{电子}\mathrm{F}\mathrm{F}}$由于临界安全分析代码、实验不确定性和核数据库的协方差矩阵。此外，频率分布${\mathrm{克}}_{\mathrm{电子}\mathrm{F}\mathrm{F}}$因为这些问题不一定服从理想的正态分布。使用称为“引导法”的重采样技术，所提出的方法可以在不假设正态性的情况下，考虑每个关键基准问题之间的不确定性和核数据引起的相关性，合理地估计 ECLLMF。为了研究所提出方法的适用性，在京都大学临界大会（KUCA）进行了临界方法实验。数值结果的比较${\mathrm{克}}_{\mathrm{电子}\mathrm{F}\mathrm{F}}$ 使用自举法的 ECLLMF 表明，所提出的方法能够将实际的亚临界岩心判断为亚临界状态。