核反应堆屏蔽计算堆芯中子源强生成方法研究

Core neutron source generation method for nuclear reactor shielding calculation

中子源强作为输运计算的重要输入参数,数值结果直接影响反应堆屏蔽计算精度。源强受几何模型、燃耗和功率分布的影响,其分布趋势存在明显差异。通过研究源强径向分布特点,基于中子价值生成堆芯各组件几何权重,对权重高的外围组件与径向功率分布梯度较大区域的网格源强进行精细计算。轴向不同高度位置采用分层处理,降低轴向功率峰因子对结果稳定性影响。采用体积权重法进行源强网格与几何网格映射,保证总源强守恒。NUREG/CR-6115基准题的数值验证结果表明:多权重源强网格映射算法与平均源强计算方法输运结果相比,快中子注量率相对误差均方根降低了18.46%。多权重源强网格映射算法可获得准确的源强分布,提高屏蔽计算精度,满足工程应用需求。

[Background]The numerical results from a neutron source,as the important input parameter for the transport calculation,directly affect the accuracy of shielding calculations for reactor.The apparent differences between core sources are related to their geometric model,burnup,and power distribution.[Purpose]This study aims to improve the calculation accuracy of the core neutron source for nuclear reactor shielding.[Methods]Firstly,the geometric weight of each component in the core was generated by analyzing the characteristics of the radial source distribution on the basis of neutron importance,and the fine source mesh calculation was conducted for the peripheral components with high geometric weight and the region with a large power gradient.Then,a layered approach for different axial height positions was employed to reduce the influence of the axial power peak factor to achieve stable transport calculation results,and the source and geometry meshes were mapped according to the volume weight method to ensure the conservation of total source.Finally,the NUREG/CR-6115 core as a benchmark model was used for numerical verification.[Results]Numerical verification results indicate that,compared with the average source calculation,the multi-weight source mesh mapping algorithm reduces the root mean square of the relative error in the fast neutron fluence by 18.46%between the transport calculation results and the reference value.[Conclusions]The multi-weight source mesh mapping algorithm can be employed to obtain an accurate source distribution,improve the accuracy of the shielding calculation,and satisfy the requirements of engineering applications.