Mechanisms of tritium retention in, and the removal of tritium from plasma facing materials of the Fusion Devices

摘要

In the next step D/T fusion device, the accurate predictions of tritium retention m Plasma Facing Component is important both from the point of view of the safety and the physics performance. However, for reliable prediction of T-retention, a detailed knowledge and understanding on the mechanisms, which are responsible for T-retention are essential. The mechanisms are quite complex, for example, in fusion devices; the PFC is in contact with plasma and PFC surface exposed to large flux of ion and neutral particles. The large flux of ions may be retained in the PFC materials by implantation in the depth of ion range, the particles will diffuse to the bulk of materials and eventually, the particles are trapped. In addition, the ion and neutral particles cause the sputtering of surface. The sputtered particles are ionized in plasma and redeposited somewhere on the surface within the fusion devices. The sputtering and deposition lead to T-retention via co-deposition. After a decade experimental investigation and theoretical study on D/T plasma wall interaction, D/T transport in materials as well as neutron effects, the progress on understanding of the complex of T-retention is significant, so that the prediction of T-retention can be performed more accurate. In this paper, a detailed analysis on the mechanisms of tritium retention has been performed, based on: /. Tritium retention via implantation, 2. Bulk retention via bulk diffusion, 3. Tritium retention via neutron transmutation, 4. Tritium retention via co- deposition, 5. Tritium retention via neutron damage induced trapping sites and 6. Tritium retention in dust and flakes, To assure an optimum plasma performance, to meet physics and engineering goals, it seems necessary to remove effectively the tritium and co-deposited layers as well. To develop effective in situ removal technique, an extensive R & D in framework of EU Fusion Program have been initiated. In this paper, the recent results of EU R & D on Mechanisms and removal of tritium as well as co-deposited layers are presented. The results, implications and consequences for next step fusion devices are discussed.