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AXSP中热散射截面计算模块ThermalXS的开发与验证

The Development and Verification of the Thermal Scattering Cross Section Calculation Module ThermalXS in AXSP

  • 摘要: 本工作首先基于中子热散射理论,在自主开发的评价核数据处理程序AXSP中开发了中子热散射截面计算模块ThermalXS,基于U、H、Zr等核素的热散射律文件计算出不同类型的中子热散射截面,并与NJOY2016程序中的THERMR模块的计算结果对比,验证了ThermalXS模块热中子计算的正确性。相比于THERMR模块,ThermalXS使用了自适应入射能量网格技术,可以保证金属氢化物热散射截面更精确,并且ThermalXS可以处理一声子修正的热散射律数据。本工作分析对比了ENDF/B-VII.1、ENDF/B-VIII.0、ENDF/B-VIII.1评价核数据库中石墨热散射截面的变化,并与实验值对比发现:ENDF/B-VIII.1中采用一声子模型修正的石墨热散射截面,相比石墨晶体模型截面与实验值符合更好,主要原因是消除了截面计算过程中的非相干近似;计算得到的ENDF/B-VIII.1中反应堆石墨热散射截面具有随孔隙度增大而增大的规律,但是仍远小于具有孔隙度的石墨实验数据。

     

    Abstract: Based on neutron thermal scattering theory, a neutron thermal scattering cross-section calculation module (ThermalXS) was developed independently in the advanced evaluated nuclear cross section processing program AXSP. Different types of neutron thermal scattering cross-sections were calculated using the thermal scattering law files of nuclides such as U, H, and Zr. To verify the reliability of the ThermalXS module for thermal neutron calculations, its results were compared with those obtained from the THERMR module of NJOY2016 program. Compared with the THERMR module, the ThermalXS module employs an adaptive incident energy grid technology, which ensures higher accuracy of thermal scattering cross-sections for metal hydrides. Additionally, it is capable of processing thermal scattering law data incorporating one-phonon corrections. In this study, the variations of the thermal scattering cross-sections of graphite across the ENDF/B-VII.1, ENDF/B-VIII.0, and ENDF/B-VIII.1 evaluated nuclear data libraries were systematically analyzed and validated against experimental values. The results show that the thermal scattering cross section of graphite in ENDF/B-VIII.1, modified using the one-phonon model, shows better agreement with experimental data compared to the graphite crystal model. The primary reason is the elimination of the incoherent approximation in the cross-section calculation. The calculated thermal scattering cross section of reactor graphite in ENDF/B-VIII.1 exhibits a trend of increasing with porosity, yet it remains significantly lower than the experimental data for graphite with porosity.

     

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