基于高保真堆芯热工水力与燃料行为耦合模型的快堆金属燃料包壳失效机制研究

In order to meet the demand of energy saving and economic development in China, the utilization of nuclear power, which produces nearly no carbon-dioxide and has lower cost than its renewable counterparts, is imperative. Sodium Fast Reactor (SFR) is thought to be one of the most promising technologies in six generation IV reactor concepts and has a promising prospect in China. Due to the uranium utilization and other advantages, metallic fuel is considered to be very promising in the future SFR. It is an established fact that the thermal creep and the irradiation growth are remarkable in metallic fuel and the mechanism of fuel cladding interaction is complex which is a key factor to ensure the structural integrity of the fuel in the whole lifetime. The conventional fuel performance codes adopted one dimensional stress analysis model and single-channel model which couldn’t obtain the coolant and the fuel cladding surface temperature distribution. Meanwhile fuel and cladding creep are very sensitive to temperature. In order to obtain accurate performance evolution of the metallic fuel in SFR, a thermo-mechanical analysis model based on the finite element method will be developed and a fuel behavior code will be developed. The investigation on the distributed resistance model and CFD method is carried out to develop a comprehensive wire-wrapped model and improve the sub-channel analysis model. A coupled model between the core thermal-hydraulic and the fuel performance will be built; systematic analysis on the fuel and cladding creep will be carried out; and the failure mechanism of metallic fuel cladding affected by the key parameters will be revealed to enhance the understanding of the fuel safety features in SFR. This research could provide reliable input and theoretical support to metallic fuel development in future Chinese SFR.

核电作为低成本的低碳能源，是我国经济发展和节能减排双重需求的必然选择。钠冷快堆作为我国主推的四代堆型，具有广泛应用前景，金属燃料由于中子利用率高等优点，被认为是快堆燃料的未来发展方向。金属燃料蠕变、辐照肿胀显著，燃料与包壳相互作用机理复杂，是确保燃料包壳完整性所面临的挑战。目前的燃料性能分析程序普遍采用一维应力分析模型，冷却剂边界采用单通道模型，未考虑冷却剂和燃料包壳表面周向温度分布，而包壳和芯块蠕变对此非常敏感。为了准确理解金属燃料性能演变进程，本项目拟开展：1）开发燃料棒热力分析二维模型，改进燃料性能分析程序；2）基于分布阻力模型和CFD方法，开发绕丝分析机理模型，并改进子通道分析程序；3）基于堆芯热工水力与燃料行为耦合模型，开发高保真分析平台，系统研究金属燃料包壳和芯块在寿期内的蠕变特性，揭示关键参数对金属燃料包壳失效机制的影响规律，为我国快堆金属燃料的研发提供借鉴和理论支持。

核电作为低成本的低碳能源，是我国经济发展和节能减排双重需求的必然选择。钠堆作为我国主推的四代堆型，具有广泛应用前景，金属燃料由于中子利用率高等优点，被认为是快堆燃料的未来发展方向。金属燃料蠕变、辐照肿胀显著，燃料与包壳相互作用机理复杂，是确保燃料包壳完整性所面临的挑战。目前的燃料性能分析程序普遍采用一维应力分析模型，冷却剂边界采用单通道模型，未考虑冷却剂和燃料包壳表面周向温度分布，而包壳和芯块蠕变对此非常敏感。为了燃料组件安全，利用计算机模拟，精确预测燃料组件温度与力学变形分布，可以有效避免因为芯块与包壳温度过高，发生燃料棒的熔化以及因为芯块包壳力学相互作用发生包壳失效等情况。为了准确获得芯块与包壳的温度分布、变形率和安全裕量，本项目建立了金属燃料的分析模型，开发高精度二维燃料性能分析程序。考虑到冷却剂温度场和绕丝的影响，开发了组件热工水力模型包括：1）建立了快堆子通道模型，并采用先进分布阻力模型模拟绕丝效应；2）开发堵流分析模块，采用局部阻力模型模拟堵块、改进绕丝模型使之适用于横流占优工况、提出综合考虑轴向流动与横掠棒束效应的对流换热模型。.基于堆芯热工水力与燃料行为耦合模型，开发高保真分析平台，X425金属燃料棒为研究对象，对其在有绕丝约束的工况下的燃料行为进行了研究分析，发现：绕丝对温度分布与芯包接触现象影响很小，但由于在接触点的力学约束，绕丝会对包壳的环向应力分布带来较大影响，在绕丝接触点附近出现应力峰值，威胁包壳安全。通过系统研究金属燃料包壳和芯块在寿期内的蠕变特性，揭示关键参数对金属燃料包壳失效机制的影响规律，为我国快堆金属燃料的研发提供借鉴和理论支持。