基于统一耦合框架的压水堆堆芯瞬态特性多物理耦合计算方法

Multi-physics Coupling Calculation Method for Transient Characteristic of PWR Core Based on Unified Coupling Framework

  • 摘要: 通过反应堆堆芯行为精准分析,释放传统设计裕量提升核电厂经济性,是当前反应堆设计研发的重点研究方向。本文基于多物理耦合框架MORE开发了堆芯物理热工耦合计算程序,提出Picard迭代做初值的JFNK混合迭代方法对耦合计算过程进行加速,通过相关基准题测试表明,JFNK算法具有显著的加速特性,NEACRP弹棒基准题采用混合迭代算法相对Picard方法收敛速率最大提升超9倍,计算结果与基准值符合较好。利用耦合计算软件开展华龙一号弹棒事故分析计算,寿期初满功率下弹棒事故后功率峰值较传统计算方法下降8.8%以上。本文方法为提升反应堆功率提供理论及工具支撑。

     

    Abstract: Accurate analysis of reactor core behavior to unlock traditional design margins and enhance the economic efficiency of nuclear power plants has become a key research direction in current reactor design and development. Based on advanced multi-physics coupling computational analysis techniques and extensive research experience, this paper develops the MORE multi-physics coupling framework for reactors. MORE enables visual construction of various coupling modes, supports high-precision and high-efficiency mapping between ultra-large-scale multi-type grids, and provides more stable and efficient nonlinear iterative algorithms for strongly coupled complex transient calculations, addressing critical challenges in coupling program development such as complex grid mapping, data transmission, and process control. Using the MORE multi-physics coupling framework, a core physics-thermal hydraulic coupling calculation program was developed. In terms of grid mapping, efficiency is enhanced through multiple technologies including mapping algorithm optimization, stretched grids, and MPI-OpenMP hybrid parallelization. Three-dimensional stretched grids significantly improve mapping efficiency, reducing mapping time by two orders of magnitude. For billion-scale unstructured grids to billion-scale Cartesian grids, the thousand-core mapping time is approximately 70 seconds, with a thousand-core mapping efficiency exceeding 50%. In iterative acceleration, through in-depth research on methods such as JFNK and their key technologies—including core modules like the inexact Newton iteration module, Krylov subspace computation module, Jacobian-Free technology module, global convergence function module, forcing term selection module, and perturbation selection module—a multi-physics coupling iteration algorithm library (MORE-ALGO) was developed, covering mainstream explicit, semi-implicit, and fully implicit coupling methods at home and abroad. A JFNK hybrid iteration method using Picard iteration as the initial value was proposed to accelerate coupling calculations. The coupling program was validated against benchmark problems such as the NEACRP and IAEA rod ejection accidents. Comparisons of parameters including keff, critical boron concentration, steady-state power peaking factor, power peak time, and transient relative power peak demonstrate the accuracy of the calculation results. Tests on the NEACRP rod ejection benchmark problem show that the JFNK method improves the convergence rate by 4-9 times compared to the Picard method, demonstrating superior stability and computational efficiency. Finally, preliminary engineering application analysis was conducted for the HPR1000 reactor. Results show that the power peak in a 100% power rod ejection accident at the beginning of life is reduced by 8.8% compared to traditional analysis methods, providing important support for further exploring safety margins in reactivity insertion accident analysis and evaluation.

     

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