聚变包层混合增殖球床热机械特性研究

Compared with traditional unitary pebble beds (Li2TiO3 or Li4SiO4), the Li2TiO3&Be12Ti mixed pebble beds, which have the advantage of the higher packing factor, the higher tritium breeding ratio and the higher thermal conductivity, is being concerned by the blanket community and employed in conceptual design of the ceramic breeder blanket. However, for this kind of new mixed pebble bed, there is no currently enough thermo-mechanical experimental database and there is no reliable theories/models available to accurately simulate its thermo-mechanical performace. Especially, it is still unclear for the physical mechanism that the packing rearrangement induced by pebble movement, deformation, crack, and sintering impacts the pebble bed thermo-mechanical performance. These facts cause a great uncertainties for design of blanket thermal-hydraulics and assessment of its safety. Therefore, the study on thermo-mechanical performance of Li2TiO3&Be12 mixed pebble beds by a series of out of pile experiments need to be carried out under different load modes (load/unload/periodical load) and different temperature fields (steady-state/pulse) measurement. And the physical mechanisms of packing rearrangement due to different issues need to be explained. Furthermore, the integrated modeling methods and simulation model for Li2TiO3&Be12 mixed pebble beds will be developed based on experimental results above mentioned and individual breeder pebble irradiation database obtained by experiments in the fission reactor , and are applied to analyze and evaluate the thermo-mechanical performance of Li2TiO3&Be12 mixed pebble beds assembled in complicated geometry of blanket, and are employed to identify safety criteria related to mixed breeder pebble bed. It is of great importance to enrich the thermo-mechanical database of mixed pebble bed and technology development of the water-cooled ceramic breeder (WCCB) blanket for Chinese fusion engineering test reactor (CFETR).

两元混合增殖球床（Li2TiO3&Be12Ti）因具有较高的填充率、氚增殖率和导热率的优势，目前被聚变包层领域关注并应用于包层概念设计中。作为一种新型增殖球床，其热机械特性仍然缺乏充足实验数据和可靠计算模型，对于两种材料微球发生移位、变形、破碎和结块等现象引起的球床重构对球床热机械性能的影响机制尚不明确，给混合增殖球床包层热工设计与安全评价造成很大的不确定性隐患。因此，本项目开展Li2TiO3&Be12Ti混合增殖球床在不同加载模式和不同温度场下的热机械实验研究，解明填充结构改变（颗粒球移位、变形、破碎和结块等）对球床热机械性能的影响机制;基于实验结果并结合现有增殖小球在裂变堆辐照数据，发展混合球床的热机械特性综合建模方法和分析模型，应用于包层原型复杂几何混合球床的热机械特性预测，确定安全判据，对丰富混合增殖球床数据库和中国聚变工程实验堆水冷陶瓷包层技术发展有重要意义。

混合氚增殖球床具有较高的填充率、氚增殖率和热导率，已被应用于中国聚变工程试验堆（CFETR）水冷陶瓷增殖剂（WCCB）包层设计中。作为一种新型增殖球床，其热机械特性仍然缺乏充足实验数据和可靠计算模型。因此，本项目从三个方面开展了研究。首先，设计并搭建了球床热机械实验装置，测量了Li2TiO3、Li4SiO4及玻璃模拟混合球床有效热导率，实验获得了钛酸锂球床在循环加载/卸载条件下的应力-应变曲线及微球力学特性曲线；基于原有氚吹扫模拟实验平台补充测量了Li2TiO3球床和玻璃混合球床的吹扫气压差；同时，基于工业CT测试手段测试并获得了Li2TiO3球床、玻璃混合球床及破碎锂陶瓷球床填充率分布特征及破碎特征，为包层设计分析提供基础数据支持，也为发展球床热机械模型及热工水力学提供参照。其次，发展了基于DEM方法的多元球床传热接触理论及热机械耦合模型，考虑了颗粒接触导热、气隙导热及颗粒辐射换热等传热机制，以及热膨胀引起的热-力双向耦合过程，基于上述实验进行了验证。此外，发展了基于多孔介质方法的大尺度球床CFD模型，结合DEM与CFD方法分析了一元/两元球床内吹扫气流场分布和对流传热的影响，初步验证了模型正确性。与德国KIT合作开发了球床非线性本构关系模型，发展了固态包层大尺度床FEM热机械模型，并成功应用在EU DEMO氦冷包层球床热机械分析中。最后，应用上述球床多孔介质CFD模型，模拟分析了Be12Ti&Li2TiO3混合球床在水冷包层几何下的热工水力学特性，初步评估了其在稳态中子核热条件下的流场、压力场、温度场分布特征；基于以上DEM模型重点开展了水冷包层混合球床的稳态、瞬态热机械特性，获得了球床在准静态加载/卸载过程中的应力-应变曲线，给出了不同配比混合球床在不同机械载荷下的有效热导率，研究了不同传热机制对颗粒球床传热的贡献，分析了一元Li2TiO3球床和两元Be12Ti&Li2TiO3混合球床在热循环载荷条件下的瞬态热机械响应，为CFETR WCCB混合球床优化设计提供了参照。