ADS无窗散裂靶中两相流动和腐蚀问题研究

The windowless spallation target is at the 'heart' of the accelerator driven system (ADS) which connects the proton accelerator and the subcritical reactor core. The heavy liquid metal (HLM) lead-bismuth eutectic is not only intended to serve as target material for the spallation reaction but also as coolant in the target. Typical scientific multiphase flow and heat and mass transfer problems during the liquid lead-bismuth eutectic flowing process, such as accurate capturing of the two phase free interface between HLM and its vapor with cavitation, turbulent transferring of the extreme large power density of volumetric heat sources at high temperature, the diffusive mass transfer to the structural steel resulting in corrosion and erosion under irradiation of the intense neutron field, require comprehensive study. All these important issues which belong to the engineering thermophysics research field determine whether the ADS can operate in the long-term, stable and safe condition. Accordingly, more accurate　volume of fluid(VOF) interface capturing method with larger ratio between the two phases' thermophysical properties including the phase change (containing experimental verification on the liquid metal GaInSn at normal temperature) and HLM turbulent transferring of the extreme large power density of volumetric heat sources with low Prandtl number at high temperature will be studied. Simultaneously, the numerical simulation of the atomic interdiffusion between lead-bismuth eutectic and FeCr under the irradiation and its evolution process using microscale and multiscale coupling algorithm will be performed in this proposed project. The above research will develop innovative numerical methods and softwares correspondingly, obtain new perspective and laws about the physical processes in the windowless spallation target and deep understanding on the key factors which influence safe operation of the ADS. Furthermore, it will enrich the knowledge of the mutiphase flow, the fluid dynamics of liquid metal and microscale and nanoscale heat and mass transfer and provide theoretical foundation for the design, optimization and construction of the ADS windowless spallation target in China. Therefore, this research project has important academic value and significant application prospect.

散裂靶在加速器驱动次临界堆系统中连接加速器和反应堆，是核心装置。液态重金属铅铋合金在无窗散裂靶中流动过程包含多相流和传热传质科学问题，主要有与蒸汽间含气蚀相变的自由界面精确捕获、对极大功率密度体积热源的湍流输运、强中子辐照下在结构钢材料中腐蚀的扩散传质过程等，这些都是关系到系统能否长期、稳定、安全运行的关键工程热物理科学问题。针对这些问题，本项目拟开展两相大物性比、含相变的高效精确界面捕获算法及常温液态金属验证性模拟实验研究，高温、低Pr数金属流体湍流对极大功率密度体积热的输运模拟，强辐照下铅铋与结构钢原子互扩散及其演化过程的微尺度和多尺度耦合算法研究等。预期发展相关算法与软件，获得相关过程的新知识、新规律，深入认识影响系统运行的关键因素，丰富多相流、金属流体力学和微尺度传热传质等学科知识，并为我国加速器驱动次临界堆散裂靶的设计、优化和研制提供理论依据，因此具有重要学术价值和重大应用前景。

散裂靶在加速器驱动次临界堆系统中连接加速器和反应堆，是核心装置。液态重金属铅铋合金在无窗散裂靶中流动过程包含多相流和传热传质科学问题，主要有与蒸汽间含气蚀相变的自由界面精确捕获、对极大功率密度体积热源的湍流输运、结构钢材料中腐蚀的扩散传质过程等。针对这些问题，本项目拟开展两相大物性比、含相变的高效精确界面捕获算法，高温、低 Pr 数金属流体湍流对极大功率密度体积热的输运模拟，结构钢原子互扩散及其演化过程的分子动力学研究等。.通过在流动入口加入从 1.0rad/s 到 2.0rad/s 的旋转速度发现加入一定数值的旋转速度可以改变铅铋合金（ LBE） 的流型。随着旋转速度的增大，在汇聚点下方会逐渐形成不断增大的新气蚀区，且回流区逐渐减小直至旋转速度达到 2.0rad/s 时最终消失。 通过改变质子束的流强，模拟得到了小流强下的瞬态温度场和大流强下的稳态温度场，得到了如断翅蝴蝶状分布的温度场。. 铅铋合金自由面高度随下部出口压强增大而升高，随压强减小而降低，主流区速度随压强增大而减小；在异常底部出口压强下铅铋合金溅射增强，回流区高度增加，使更多的铅铋合金蒸汽进入真空管，影响系统正常运行。温度场随入射质子束能量改变，并且能量越高，最高温度越大。在 600 MeV 能量 50 mA 流强质子束作用下，最高温度已达到 1670 K，而铅铋合金沸点为 1943 K，需要优化散裂靶结构以满足继续加大质子束能量或流。. 上述回流区优化、流型及热输运过程研究的数值模拟结果为 ADS 无窗散裂靶的设计和优化提供了可靠的依据，特别是对未来中国 ADS 的研究和应用具有重要的学术和应用参考价值。. 铁在液态铅铋合金中的分子动力学模拟发现随着温度的升高，铁被腐蚀的程度逐渐增加，但是在铅铋合金中中加入氧原子后，铁被腐蚀的程度明显减少；与此同时，在铁中分别加入不同比例的金属Cr、Ni，铁受腐蚀的程度随着加入Cr、Ni比例的增加而减少。在铅铋合金中加入氧气和在铁中分别加入的金属Cr、Ni都会使铁被腐蚀程度减小，从而有利于ADS系统的长期稳定运行。