Abstract Monte Carlo (MC) codes are widely used for the accurate modeling of nuclear reactors. However, efficient inclusion of thermal-hydraulic (TH) feedback within the MC calculation sequence is still an open problem. The issue is emphasized when coupled MC-TH calculations are needed to model the burnup evolution using multiple depletion steps. Among the techniques proposed to solve this problem is the utilization of stabilized Picard iteration in conjunction with a low-order prediction step. The latter is composed of a prediction block for cross sections and a fast deterministic solver that uses the cross sections to obtain a prediction of the power profile. The predicted power is then used as an improved guess for the next MC calculation, therefore leading to faster convergence for the overall algorithm. In this paper, we propose a new prediction block in which one-group cross sections are calculated through convolution of the TH scalar fields with MC-generated generalized transfer functions (GTFs). First-order perturbation theory is then utilized to calculate the power profile from the updated cross sections. A version of this prediction block using a simple fast Fourier transform–based approximation of the GTF is tested against a boiling water reactor unit-cell with realistic density profile and axial reflectors. The analysis was limited to the feedback between neutronics and coolant density variation. Good agreement was observed for both the spatial power and the one-group macroscopic cross-section profiles, which were compared to the reference MC results. This agreement was also preserved near the boundary, where the spatial flux gradients are maximum due to proximity to the axial reflectors.

中文翻译：

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通过传递函数实时预测对 TH 扰动的宏观横截面空间响应：理论和初步结果

摘要 Monte Carlo (MC) 代码广泛用于核反应堆的精确建模。然而，在 MC 计算序列中有效地包含热液 (TH) 反馈仍然是一个悬而未决的问题。当需要耦合 MC-TH 计算来模拟使用多个耗尽步骤的燃耗演变时，这个问题就会得到强调。为解决这个问题而提出的技术之一是将稳定的 Picard 迭代与低阶预测​​步骤结合使用。后者由横截面预测块和使用横截面获得功率分布预测的快速确定性求解器组成。然后将预测功率用作下一次 MC 计算的改进猜测，从而使整个算法更快收敛。在本文中，我们提出了一个新的预测块，其中一组横截面是通过 TH 标量场与 MC 生成的广义传递函数 (GTF) 的卷积来计算的。然后利用一阶微扰理论从更新的横截面计算功率分布。使用基于简单快速傅立叶变换的 GTF 近似值的该预测块的一个版本针对具有真实密度剖面和轴向反射器的沸水反应堆单元进行了测试。分析仅限于中子学和冷却剂密度变化之间的反馈。观察到空间功率和一组宏观横截面轮廓具有良好的一致性，并将其与参考 MC 结果进行比较。这个约定也保存在边界附近，