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中国物理学会期刊

两个系列铍反射层临界基准实验的一致性分析与核数据检验

CSTR: 32037.14.aps.74.20241685

Consistency analysis and nuclear data validation for two series of beryllium reflector critical benchmark experiments

CSTR: 32037.14.aps.74.20241685
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  • 铍金属与氧化铍都是重要核材料, 铍的中子核反应数据对核能研发具有重大意义. 宏观检验是核数据评价过程的重要环节, 对确保核数据的可靠性与精确度至关重要. 临界基准实验是目前核数据宏观检验最重要的标准. 但此前研究发现, 两个高度相似的铍反射层临界基准实验系列HMF-058与HMF-066在检验铍的中子反应数据时给出了矛盾的结论, 不能指出铍相关数据的改进方向, 导致这两个系列共14个实验无法被用于高精度的核数据检验. 出射中子角分布是反应堆物理计算中的关键物理量, 但核数据宏观检验中对其的关注度较低. 本文通过改进铍(n, n)与(n, 2n)反应的出射中子角分布数据提升了两个系列的理论计算与实验测量值的一致性. 基于改进的核数据, 所有计算与实验测量值的偏差均在1σ实验不确定度范围内, 因此无法在此不确定度内拒绝两个系列实验的一致性. 结合最新的整套铀核数据, 两者的一致性还有少许提升. 若要得出两个系列期望值系统性差异的结论, 仍需降低实验不确定度或开展更高精度的实验.

     

    Beryllium metal and beryllium oxide are important nuclear materials, with neutron-induced nuclear reaction data on beryllium playing a crucial role in nuclear energy research and development. Macroscopic validation is an essential step in the nuclear data evaluation process, providing a means to assess the reliability and accuracy of such data. Critical benchmark experiments serve as the most important references for this validation. However, discrepancies have been observed in two closely related series of beryllium-reflector fast-spectrum critical benchmark experiments, HMF-058 and HMF-066, which are widely used in current nuclear data validation. A previous systematic study indicates that these two series of experiments reache contradictory conclusions in validating the neutron-induced nuclear reaction data of beryllium, creating ambiguity in improving beryllium nuclear data. As a result, the total of 14 experiments in these two series cannot currently support high-accuracy validation of nuclear data. Although most researches on nuclear data validation and adjustment mainly focus on cross sections, the angular distribution of emitted neutrons is a key factor in reactor physics calculations. In this work, we address these inconsistencies by improving the secondary angular distributions of the (n, n) and (n, 2n) reactions of beryllium, thereby making the theoretical calculations (C) and experimental results (E) of these two series more consistent, and reducing the cumulative χ2 value from 7.58 using the ENDF/B-VII.1 evaluation to 4.52. All calculations based on the improved nuclear data agree with the experimental measurements within 1σ experimental uncertainty. With these enhancements, the consistency between the HMF-058 and HMF-066 series cannot be rejected within the 1σ experimental uncertainty. Based on the latest comprehensive evaluation of uranium nuclear data, this consistency is slightly improved, and the cumulative χ2 value decreases to 4.36 once again. Despite these advances, systematic differences in the expected values of C/E between the two series still exist. The C/E values of the HMF-066 series are generally 230–330 pcm lower than those of the HMF-058 series, comparable to their experimental uncertainties of 200–400 pcm. Therefore, drawing a definitive conclusion about this systematic difference remains challenging. If the current improvement of differential nuclear data based on experimental data of 9Be is accurate, then the HMF-058 series experiments seem to be more reliable than the HMF-066 series. Ultimately, to achieve this goal, either reducing experimental uncertainty or designing and executing higher-precision integral experiments is required.

     

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