The impact of key design parameters on 14-MeV neutron wall load in a D-T tokamak

Eighty percent of the energy released in a D-T fusion reaction is in 14-MeV neutrons. These neutrons heat the surrounding media, damage and activate material, and can be used to breed additional tritium. The 14-MeV neutron wall load is a measure of the local energy flux due to uncollided neutrons.

The choice of key design parameters can have a marked effect on the 14-MeV neutron wall load. A sensitivity study was performed to determine the impact of several key design parameters on the 14-MeV neutron wall load. Parameters considered in the study included elongation, maximum field at the TF coil, safety factor, ignition parameter, aspect ratio, toroidal field enhancement, and inboard shield thickness. System effects due to variations of the design parameters were determined using the Fusion Engineering Design Center Systems Code. Poloidal variations in the 14-MeV neutron wall were determined using the MCNP Code. It was determined that peak-to-peak poloidal variations in the 14-MeV neutron wall load can exceed 50% of the nominal value at the plasma edge. The poloidal variation in neutron wall load observed for the reference case appeared characteristic of the other study points as well. The 14-MeV neutron wall load was most sensitive to the maximum field at the TF coil. More modest sensitivities were observed for field enhancement, safety factor, elongation, and aspect ratio. The sensitivity of the 14-MeV neutron wall load to changes in ignition parameter or inboard shield thickness was much less pronounced than for the other parameters.