熔盐堆氚输运特性及其与堆物理-热工特性相互作用机制研究

Tritium, as an inherent detrimental byproduct of Molten Salt Reactors (MSR), featured with high corrosivity and permeability, is a key problem in the development of MSR technology. Currently, integrated research on the tritium transport process during the MSR operation is still under the exploration stage at our nation and world-wide. In this project, based on the former MSR research experience, the theoretical study of tritium transport characteristics, including tritium production, tritium solution/diffusion/migration behavior in the fluoride salt, tritium chemical status, tritium absorption and desorption in graphite, tritium-induced corrosion to metallic materials will be conducted combining with molten salt chemistry, chemical kinetics and flow dynamics. The numerical models of tritium transport process will be developed as well as the fine coupling among these models. In addition, considering the strong interaction between tritium transport characteristics and reactor neutronic/thermal-hydraulic characteristics, the multi-physics coupling mechanism and method will be explored. The numerical analysis code for MSR tritium transport simulation will be developed in order to reveal the interaction mechanism between tritium transport characteristics and reactor neutronic/thermal-hydraulic characteristics and obtain the transient distribution of tritium in the MSR system. This project is a multi-disciplinary crossed research. It will provide fundamental understanding of tritium behavior in the MSR. The acquired data will be valuable references for tritium control and removal, safety design and reactor operation for the development of MSR.

氚是熔盐堆运行过程中固有产物，具有强腐蚀性和渗透性，是限制熔盐堆技术发展的关键问题。目前国内外针对氚在熔盐堆系统中复杂的物理化学输运行为综合研究仍处于探索阶段。本项目拟在前期熔盐堆研究基础上，结合熔盐化学、化学动力学和流体动力学，从理论方面探究氚在熔盐堆系统中的输运特性，包括氚的产生、氚在熔盐中的溶解扩散迁移、氚的化学形态转化、氚在石墨中的溶解吸附、氚与金属结构材料的化学腐蚀渗透等，分别建立其数学物理模型，开发多模块精细化耦合联动技术和方法。同时考虑到熔盐堆中氚物理化学行为与反应堆物理-热工特性呈现动态强耦合特征，探索熔盐堆多物理场（化学-材料-物理-热工）动态耦合机制和方法，开发熔盐堆多物理场耦合分析程序，揭示氚输运特性与堆物理-热工特性之间的相互作用机理，阐明氚在系统回路中的瞬态分布规律，这对于熔盐堆氚的控制和消除意义重大。本项目属于多学科交叉，为熔盐堆的安全设计与运行奠定理论基础。

氚是熔盐堆运行过程中固有产物，具有强腐蚀性和渗透性，是限制熔盐堆技术发展的关键问题。目前国内外针对氚在熔盐堆系统中复杂的物理化学输运行为综合研究仍处于探索阶段。本项目在前期熔盐堆研究基础上，结合熔盐化学、化学动力学和流体动力学，从理论方面探究了氚在熔盐堆系统中的输运特性，包括氚的产生、氚在熔盐中的溶解扩散迁移、氚的化学形态转化、氚在石墨中的溶解吸附、氚与金属结构材料的化学腐蚀渗透等，分别建立了数学物理模型，开发多模块精细化耦合联动技术和方法。同时考虑到熔盐堆中氚物理化学行为与反应堆物理-热工特性呈现动态强耦合特征，探索了熔盐堆多物理场（化学-材料-物理-热工）动态耦合机制和方法，开发了熔盐堆多物理场耦合分析程序，预测趋势正确，分模型精度可达20%，揭示了氚输运特性与堆物理-热工特性之间的相互作用机理，阐明了氚在系统回路中的瞬态分布规律，即反应堆稳态运行下一回路主要以氚气形式存在，石墨在很短时间内吸附大量氚，占总产氚量的80%。瞬态事故条件下，对于无保护冷却剂入口过冷事故，石墨对氟化氚的吸附逐渐下降之后达到新的平衡，对氚气的吸附量经过一段时间的波动后有所上升，但是总体来看石墨对氚的总吸附限值呈略微下降的趋势。对于无保护反应性引入事故，石墨对氚总吸附量呈上升趋势是由温度和压力共同作用的结果。对于无保护失流事故，氟化氚吸附限值持续上升，氚气吸附限值有剧烈波动，石墨对氚吸附限值在事故引入期间受氟化氚和氚气吸附限值的共同影响，呈波动上升趋势。此外，针对固态燃料钍基熔盐堆提出了5项氚控策略，1）降低熔盐中Li-6的富集度；2）在线更新石墨；3）在热管段入口处加装在线除氚装置；4）在换热器入口处加装在线除氚装置；5）制作氚渗透窗。本项目对于熔盐堆氚的控制和消除意义重大，属于多学科交叉，为熔盐堆的安全设计与运行奠定理论基础。