发表机构
Massachusetts Institute of Technology; Tennessee Tech University; Stony Brook University; Commonwealth Fusion Systems; Brookhaven National Laboratory; Oak Ridge National Laboratory; University of Massachusetts Lowell（麻省理工学院; 田纳西科技大学; 石溪大学; 联邦聚变系统; 布鲁克海文国家实验室; 橡树岭国家实验室; 马萨诸塞大学洛威尔分校）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究结合全散射实验与分子动力学模拟，探究FLiBe中5mol% CsF的结构效应，明确Cs团簇及对氟铍酸盐网络的影响，为相关原子模型提供实验基准。
AI 中文摘要
数种下一代裂变反应堆设计采用FLiBe（2LiF-BeF₂）等熔融盐，部分方案将燃料直接溶解于盐中。运行期间，铯等裂变产物会在盐混合物中积累，可能引发原子结构支撑的热物理性质演变。为理解含5mol% CsF的FLiBe中的结构扰动，本研究开展了X射线与中子衍射测量，基于实验数据优化了经验势结构精修（EPSR）模型，并将所得结构与神经网络分子动力学（NNMD）模拟结果进行对比。通过对比EPSR与NNMD结构，区分出受散射数据约束的特征与仍依赖模型的特征。含Cs的新关联关系解释了总结构因子与对分布函数的变化，而FLiBe的关联关系几乎未发生改变。研究发现，Cs会轻微破坏中程氟铍酸盐网络，增加游离氟离子的比例，而局部配位基本保持不变。FLiBe中的Cs离子会大量团簇，BeF₄²⁻四面体桥接相邻的铯环境。与液体中微小的结构扰动形成对比，添加5mol% CsF在室温下抑制了晶态Li₂BeF₄相的形成，该相仅在加热至180℃以上时出现。这些经实验约束的结构特征为预测含裂变产物的FLiBe行为与性质的原子模型提供了基准。
英文摘要
Several next-generation fission reactor designs employ molten salts such as FLiBe (2LiF-BeF$_2$), with some concepts using fuel dissolved directly in the salt. During operation, fission products such as cesium will accumulate in the salt mixture, potentially leading to an evolution of the thermophysical properties underpinned by the atomic structure. To understand the structural perturbations in FLiBe with 5 mol% CsF, we conducted X-ray and neutron diffraction measurements, refined empirical potential structure refinement (EPSR) models against the experimental data, and compared the resulting structure with neural network molecular dynamics (NNMD) simulations. Comparisons of the EPSR and NNMD structures distinguishes features constrained by the scattering data from those that remain model dependent. The new Cs-bearing correlations account for the changes in the total structure factor and pair-distribution function, while the FLiBe correlations remain minimally altered. We find that Cs slightly disrupts the intermediate-range fluoroberyllate network, increasing the fraction of free fluorine ions, while the local coordination remains largely unchanged. The Cs ions within FLiBe cluster extensively, with BeF$_4^{2-}$ tetrahedra bridging neighboring cesium environments. In contrast to the minor structural perturbations in the liquid, the addition of 5 mol% CsF suppressed the formation of the crystalline Li2BeF4 phase at room temperature, with the phase appearing only above 180C upon heating. These experimentally constrained structural features provide a benchmark for atomistic models used to predict the behavior and properties of fission-product-containing FLiBe.
