Abstract Evaluations of nuclear reaction data for the major uranium isotopes 238U and 235U were performed within the scope of the CIELO Project on the initiative of the OECD/NEA Data Bank under Working Party on Evaluation Co-operation (WPEC) Subgroup 40 coordinated by the IAEA Nuclear Data Section. Both the mean values and covariances are evaluated from 10−5 eV up to 30 MeV. The resonance parameters of 238U and 235U were re-evaluated with the addition of newly available data to the existing experimental database. The evaluations in the fast neutron range are based on nuclear model calculations with the code EMPIRE–3.2 Malta above the resonance range up to 30 MeV. 235U(n,f), 238U(n,f), and 238U(n,γ) cross sections and 235U(nth,f) prompt fission neutron spectrum (PFNS) were evaluated within the Neutron Standards project and are representative of the experimental state-of-the-art measurements. The Standards cross sections were matched in model calculations as closely as possible to guarantee a good predictive power for cross sections of competing neutron scattering channels. 235U(n,γ) cross section includes fluctuations observed in recent experiments. 235U(n,f) PFNS for incident neutron energies from 500 keV to 20 MeV were measured at Los Alamos Chi-Nu facility and re-evaluated using all available experimental data. While respecting the measured differential data, several compensating errors in previous evaluations were identified and removed so that the performance in integral benchmarks was restored or improved. Covariance matrices for 235U and 238U cross sections, angular distributions, spectra and neutron multiplicities were evaluated using the GANDR system that combines experimental data with model uncertainties. Unrecognized systematic uncertainties were considered in the uncertainty quantification for fission and capture cross sections above the thermal range, and for neutron multiplicities. Evaluated files were extensively benchmarked to ensure good performance in reactor calculations and fusion-related systems. New comprehensive evaluations show excellent agreement with available differential data and integral performance better than current evaluated data libraries, and represent a step forward in a quest for better nuclear data for applications.

中文翻译：

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IAEA CIELO 对 235 U 和 238 U 目标的中子诱发反应的评价

摘要 对主要铀同位素 238U 和 235U 的核反应数据的评价是在 CIELO 项目的范围内进行的，该项目是由 IAEA 协调的评价合作工作组（WPEC）40 小组下的 OECD/NEA 数据库倡议的核数据科。平均值和协方差的评估范围为 10-5 eV 至 30 MeV。238U 和 235U 的共振参数通过将新可用数据添加到现有实验数据库进行重新评估。快中子范围内的评估基于核模型计算，代码为 EMPIRE–3.2 Malta，共振范围高于 30 MeV。235U(n,f)、238U(n,f) 和 238U(n,γ) 横截面和 235U(nth, f) 瞬发裂变中子能谱 (PFNS) 在中子标准项目中进行了评估，代表了最先进的实验测量方法。标准横截面在模型计算中尽可能匹配，以保证对竞争中子散射通道的横截面具有良好的预测能力。235U(n,γ) 截面包括在最近的实验中观察到的波动。235U(n,f) PFNS 用于从 500 keV 到 20 MeV 的入射中子能量在洛斯阿拉莫斯奇努设施进行测量，并使用所有可用的实验数据重新评估。在尊重测量的差分数据的同时，识别并消除了先前评估中的几个补偿误差，从而恢复或提高了积分基准的性能。235U 和 238U 横截面的协方差矩阵，使用将实验数据与模型不确定性相结合的 GANDR 系统评估角分布、光谱和中子多重性。在热程以上裂变和俘获截面以及中子多重性的不确定性量化中考虑了未识别的系统不确定性。评估文件进行了广泛的基准测试，以确保反应堆计算和聚变相关系统的良好性能。新的综合评估与现有的差分数据和积分性能表现出良好的一致性，优于当前评估的数据库，代表着在寻求更好的应用核数据方面向前迈进了一步。在热程以上裂变和俘获截面以及中子多重性的不确定性量化中考虑了未识别的系统不确定性。评估文件进行了广泛的基准测试，以确保反应堆计算和聚变相关系统的良好性能。新的综合评估与现有的差分数据和积分性能表现出良好的一致性，优于当前评估的数据库，代表着在寻求更好的应用核数据方面向前迈进了一步。在热程以上裂变和俘获截面以及中子多重性的不确定性量化中考虑了未识别的系统不确定性。评估文件进行了广泛的基准测试，以确保反应堆计算和聚变相关系统的良好性能。新的综合评估与可用的差分数据和积分性能表现出极佳的一致性，优于当前评估的数据库，代表着在寻求更好的应用核数据方面向前迈进了一步。