The effect of ICRF and LHCD waveguide and launcher location on tritium breeding ratio and radiation damage in fusion reactors

[摘要] In most tokamak fusion reactor designs, ICRF (Ion Cyclotron Range of Frequencies) and LH (Lower Hybrid) radio frequency (RF) waves used to heat the plasma and drive current are launched from the low-field, outboard side where there is more access space. It has recently been proposed to launch these waves from the high-field side [1-3], which increases current-drive efficiency, allows for better wave penetration, and has favorable scrape-off-layer and plasma material interaction characteristics [4]. However the poloidal location and size of RF launchers will also affect important aspects of the neutronics of the tokamak fusion design, i.e. how the 14.1 MeV neutrons born out of the deuterium-tritium (D-T) fusion reaction interact with the surrounding blanket and structures. The goal of this thesis is to assess the dependence of RF launcher poloidal location on the important neutronics parameters of tritium fuel breeding, launcher damage and activation. To determine the effects of waveguide and antenna location on Tritium Breeding Ratio (TBR), damage, and activation, the MCNP Transport Code was used, as well as the EASY 2010 activation package to analyze the activation of the vacuum vessel components. A simple geometry was designed for MCNP, based on the original ARC model [1]. Seven locations for the waveguides and antenna were chosen: the inner and outer midplane, the inner and outer upper corners, two spaces between the midplane (inboard and outboard), and a central location directly above the vacuum vessel. TBR, DPA, and helium concentration were calculated at all seven points to find the optimal location for the waveguides and antenna. Four blanket materials were chosen: two liquid blankets (FliBe and Pb-17Li) and two solid blankets (Li4SiO4 and Li2TiO3). This was to test whether or not blanket material affects the optimal location of the launchers. We find that from the neutronics point of view the overall optimal location is the inboard upper corner, which minimizes DPA and helium concentration in the antenna and waveguide, and maximizes TBR. DPA in the waveguide was minimized when placed in the outboard upper corner, although the difference in DPA between the two locations was small. While TBR was maximized at the top of the vacuum vessel, the differences in TBR between all locations was less than 1%. These results reinforce the choice of inside, upper corner launch as the optimal location for current drive, launcher protection and neutronics. Activation was also assessed for the vacuum vessel, both without and with the waveguides and antenna, assuming irradiation times of one week, one month, and one year. Overall, activation was significant in the vacuum vessel, as expected, due to the use of Inconel 718. The IAEA recycling limit could be achieved, regardless of irradiation time. The dominant isotopes present after irradiation differed when the irradiation time was one week versus one month or one year. Activation was also assessed in the waveguides and antenna for the cases of the launchers being placed at the outboard midplane versus the inboard corner. The activation in the antenna was shown to be reduced by a factor of two and in the waveguides by a factor of four, when the launchers were placed in the inboard corner.

[发布机构] Massachusetts Institute of Technology