压水堆重反射层堆芯核热耦合高精度计算分析研究

重反射层的应用可提高反应堆中子经济性，其结构和中子吸收特性均与压水堆常规围板/反射层差异较大，因此对核设计程序的计算分析能力提出了新的要求。为分析重反射层建模方案对堆芯中子学计算结果的影响，使用先进中子学程序SCAP N和确定论堆芯高保真模拟程序NECP X对压水堆重反射层问题进行了高保真模拟，分析了5种反射层建模方案下计算结果的差异，并将高精度计算结果与商用核设计程序系统进行了对比。数值结果表明，重反射层水洞内冷却剂温度变化对计算结果影响较小；相较精确建模方案，重反射层铁水打混建模方案造成的反应性计算偏差在±30 pcm以内、组件相对功率分布计算偏差在±2%以内。

Neutronics and Thermal-hydraulics Coupling High Fidelity Simulation of PWR Core with Heavy Reflector

The reflector can reduce the neutron leakage from the reactor core, increase the neutron economy, and improve the fuel utilization. In commercial PWR, light water is usually used as the main body, combined with stainless steel shroud to form radial reflector. The industrial nuclear design code system has rich experience in calculating and verifying the neutron characteristics of the shroud/water reflector. In the design of some small reactors and large PWRs, the use of heavy reflector with better neutron reflection effect can further reduce neutron leakage and critical size, and improve reactor economy. The heavy reflector is usually made of metal materials, and its structure and neutron absorption characteristics are quite different from those of conventional shroud/water reflector. The simulation of heavy reflector core puts forward new requirements and challenges to the calculation and analysis ability of industrial nuclear design code system. The core high fidelity simulation program system can be used to accurately analyze the reflector effect and test the applicability of the design code. The calculation accuracy, simulation resolution and program application scope of high fidelity numerical reactor technology characterized by multi physical field, multi scale coupling and high performance calculation are better than the existing industrial nuclear design code system. It has important application value in design code verification, design result verification and new reactor design analysis. In this paper, the high precision nuclear thermal coupling simulation program system developed based on the coupling of advanced neutronics program SCAP N and subchannel program SAPRE IP was used to calculate and analyze the heavy reflector core of PWR. Firstly, NECP X program and SCAP N program were used to simulate the heavy reflector core problem of PWR. Five reflector models were established. The correctness of the modeling results and the calculation accuracy of SCAP N program were verified by comparing the results. Then, the calculation results of SCAP-N were compared with those of commercial nuclear design code system to analyze the difference of reflector modeling results between core high fidelity simulation program system and industrial nuclear design code system. Compared with the results of NECP X program, the results of NECP X and SCAP N programs are in good agreement. The influence of heavy reflector on the core eigenvalue is about +450 pcm. The change of coolant temperature in the water tunnel of heavy reflector has little effect on the calculation results. Compared with the accurate modeling scheme, the reactivity calculation deviation caused by the water metal mixing modeling scheme of heavy reflector is within ±30 pcm, and the calculation deviation of component relative power distribution is within ±2%, which is within the acceptable range. Compared with the calculation results of SCAP N program of real geometric fine modeling scheme of heavy reflector, the eigenvalue calculation deviation of commercial nuclear design code is -34 pcm, the relative power distribution deviation of the module shows an external positive and internal negative distribution, and the most positive deviation is 553% and the most negative deviation is -7.35%.