Abstract: The aim of this work is to prepare a neutron noise calculator based on the second order of average current nodal expansion method (ACNEM). Generally, nodal methods have the ability to fulfill the neutronic analysis with adequate precision using coarse meshes as large as a fuel assembly size. But, for the zeroth order of ACNEM, the accuracy of neutronic simulations may not be sufficient when coarse meshes are employed in the reactor core modeling. In this work, the capability of second order ACNEM is extended for solving the neutron diffusion equation in the frequency domain using coarse meshes. For this purpose, two problems are modeled and checked including a slab reactor and 2D BIBLIS PWR. For validating of results, a semi-analytical solution is utilized for 1D test case, and for 2D problem, the results of both forward and adjoint neutron noise calculations are exploited. Numerical results indicate that by increasing the order of method, the errors of frequency dependent coarse mesh solutions are considerably decreased in comparison to the reference. Accordingly, the accuracy of second order ACNEM can be acceptable for the neutron noise calculations by using coarse meshes in the nuclear reactor core.

中文翻译：

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中子噪声模拟的二阶平均电流节点展开法

摘要：这项工作的目的是准备一个基于二阶平均电流节点展开法（ACNEM）的中子噪声计算器。通常，节点方法能够使用与燃料组件尺寸一样大的粗网格以足够的精度完成中子分析。但是，对于 ACNEM 的零阶，在反应堆堆芯建模中使用粗网格时，中子模拟的精度可能不够。在这项工作中，二阶 ACNEM 的能力扩展到使用粗网格求解频域中的中子扩散方程。为此，对两个问题进行了建模和检查，包括板式反应器和 2D BIBLIS PWR。为了验证结果，对一维测试用例和二维问题使用半解析解决方案，利用了前向和伴随中子噪声计算的结果。数值结果表明，通过增加方法的阶数，与参考相比，频率相关粗网格解的误差显着降低。因此，通过在核反应堆堆芯中使用粗网格进行中子噪声计算，二阶 ACNEM 的精度是可以接受的。