均匀系统超精细群共振自屏计算组合函数变阶迭代深度学习方法

Composite Function Antiderivative Transformation Iterative Deep Learning Solution Method for Hyper-fine Group Resonance Self-shielding Calculation in Homogeneous System

  • 摘要: 共振自屏计算在反应堆物理分析中发挥着至关重要的作用,传统上超精细群方法是公认的高精度方法,但也存在计算效率不高、几何适应性不强等挑战。当前,深度学习计算方法在求解中子扩散/输运方程等领域已取得了显著成效,这为共振自屏计算提供了新的技术途径。为此,本文针对均匀系统的超精细群共振自屏计算,提出了“组合函数变阶迭代”(简称组合变阶)深度学习方法:将慢化方程中待求的慢化能谱与总截面相乘形成组合函数;同时,将方程包含的所有积分项分别变换为被积函数对应的原函数,从而将积分形式的慢化方程变换为微分方程;然后,用深度神经网络分别表示组合函数及不同的原函数,并构造各种神经网络函数对应的加权损失函数;针对这些神经网络进行交替迭代深度学习,减小损失函数到极小值,从而实现慢化方程的求解。本文针对多个例题进行了数值验证,得到了慢化能谱的连续能量分布,并解决了多个核素的共振干涉问题,从而为超精细群共振自屏计算探索了新的技术途径。

     

    Abstract: Resonance self-shielding calculations are crucial in reactor physics analysis and core design computation, as they serve as a preliminary step for conducting neutron transport or diffusion calculations based on macroscopic cross sections. In resonance self-shielding calculation methods, the equivalence theory and subgroup method are commonly used in engineering for their high efficiency, but they have the problem of insufficient accuracy. While the traditional hyper-fine group method is recognized for its high accuracy, it faces challenges such as low computational efficiency and limited geometric adaptability. At present, with the rapid advancement of artificial intelligence technology, deep learning methods have emerged as effective surrogate models in reactor physics calculations. At the same time, they have demonstrated exceptional performance in directly solving neutron diffusion/transport equations without requiring prior data acquisition, while offering innovative technical methodologies for resonance self-shielding calculations. This paper proposed a composite function antiderivative transformation iterative deep learning solution method (C-AIM) for hyper-fine group resonance self-shielding calculations in homogeneous systems. The C-AIM involved forming composite function by multiplying the slowing-down spectrum by the continuous energy total cross section. It also transformed all integral terms in the equation into antiderivatives of the integrand functions, converting the integral-form slowing-down equation into an exact differential equation. Then, deep neural networks were used to represent the composite function and different antiderivatives, with weighted loss functions constructed for each neural network function. These loss functions included those derived from the neutron slowing-down equation, the antiderivative transformation equation, the antiderivative solution constraints, and the boundary conditions. At last, the C-AIM conducted alternating iterative training to minimize the loss function. When the loss function’s value was below the preset minimal threshold, the numerical solution to the slowing-down equation was obtained. This solution could be used to condense the effective resonance self-shielding cross sections. The paper carried out numerical verification on a number of examples, including single-resonance nuclide problems and multi-nuclide resonance interference problems, leveraging a physics-informed neural network (PINN) deep learning architecture with fully connected neural networks. The continuous-energy slowing-down spectrum was obtained, and the multi-group cross section condensed using this spectrum was accurate compared to the result of the traditional hyper-fine group method. This lays a solid technical foundation for future resonance self-shielding calculations in complex heterogeneous systems. C-AIM represents not only a novel resonance self-shielding computation technique in theory but also demonstrates potential engineering application value in the generation of resonance integrals, subgroup parameters, and interference factors within the framework of traditional equivalence theory and subgroup methods.

     

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