聚变装置中氢同位素在钨灰尘中滞留行为的模拟和实验研究

Due to the radioactivity and special environmental migration characteristics of tritium, tritium safety has become a key issue of future fusion reactors. In fusion devices, there is a large amount of dust whose surface absorbs significant amount of tritium. The escape of tritiated dusts from vacuum chamber in loss of vacuum accident (LOVA) is a serious safety hazard in fusion devices and can even cause tritium leakage. In this project, the molecular dynamics (MD) will be performed to investigate tritium retention in tungsten dust. The relations between dust size/structure/temperature and tritium retention will be illustrated. We will also introduce the influence of plasma environment. Finally we will estimate the total absorption of tritium in future fusion devices. In order to make sure the accuracy of the simulation, the experiment of deuterium retention will be performed due to their similar retention properties. Different parameters will be selected to calculate tritium absorptions. Experimental and simulation results will be compared to figure out the authentic MD parameters. The expectation of this project is to deepen the understanding of tritium retention which contributes to our fusion career.

由于氚的放射性和独特的环境迁移特性，氚安全是未来聚变堆的核心问题之一。聚变装置中存在大量灰尘，其表面会滞留大量的氚。如果携氚灰尘在失真空事故中逃逸出真空室，将成为聚变堆安全运行的重大安全隐患，甚至可能导致严重的氚泄漏。本项目将利用分子动力学，探索氚在钨灰尘中的滞留机制，揭示滞留量与钨灰尘尺寸/结构/温度间的依赖关系，阐明等离子体环境对氚滞留量的影响，评估未来聚变装置中氚在钨灰尘中的滞留总量。为保证模拟的准确，并考虑到氘氚滞留行为的相似性，将进行氘在钨灰尘中滞留的台面实验，同时选取不同参数对氘在钨灰尘中的滞留行为进行模拟并计算滞留量，再对比实验与模拟结果，以选择可信的模拟参数。项目预期结果将加深对氚在钨灰尘中滞留行为的理解，为我国聚变事业做出贡献。

通过模拟方法，研究氚在钨灰尘中的滞留机制。结果表明，灰尘内部的结构对氘/氚在钨材料内部的影响很大，不同方式产生的钨灰尘，其氘氚滞留率差别可以达到一个量级。另一方面，等离子体环境对氘/氚滞留有着重要影响，本课题使用PIC方法给出入射到钨灰尘表面的氘/氚粒子的速度和角度分布，以及表面鞘层电势对粒子流量的影响。结果表明，相同质量的情况下，较小的灰尘尺寸会吸引更多的入射粒子。本课题的实验方面，在韩国KSTAR进行了标记瓦实验，以跟踪氘在再沉积层中的滞留行为。我们得到了面向氘等离子体的瓦块以及氘在钨表面的沉积深度。这对评估氘/氚粒子是否容易从钨灰尘中逃逸（即滞留率的评估）非常重要。最后，我们对装置中氘/氚在钨灰尘中的滞留总量进行了评估。