5. Behavior of Fuels in Reactor

This chapter is devoted to describe the behavior of fuels (D and T) in a reactor vessel. As given in Chap. 3, D and T are fueled in a reactor vessel with gas-puffing, pellet injection, or NBI. Among the total fuel throughput, only a few % are going into burning plasma, confined with the particle confinement time of a few second and exhausted or recycled. While the remaining part of the throughput is transported through scrape-off layers surrounding the burning plasma to evacuation pumps. Hence, all surfaces of the reactor vessel are exposed to neutral fuel gas with a pressure of a few Pa at the first wall and a few tens to a few hundreds Pa at the divertor. In addition, plasma facing surfaces are exposed to energetic particles, both ions and charge exchanged neutrals escaping from the plasma. The interaction of the gas with the surface is not special but just those occurring in a container with hydrogen gas inside. However, the interactions with the energetic particles and the plasma facing surfaces give significant effect both to the plasma and to the surfaces. A terminology “plasma wall interaction or plasma surface interaction” is often used for the interactions of energetic particles with surface but seldom to include the interactions of thermalized or residual gas with surface. Accordingly, the fuel retention in the plasma facing wall, which is quite important for T safety and fuel self-efficiency, is not understood well and quite difficult to evaluate, as already discussed in Chap 3.