| ITER provides the heat energy of neutrons produced by thermonuclear fusion. However, neutrons hit the peripheral structures and devices, and activate its materials. In this situation, radiation doses should be less than the safety criterion at the biological shielding. The neutral beam injection supplies high-energy neutral particles to the plasma. We need larger scale ports, in principle, for this reason. A structural port design is required so that the leakage of neutrons from the ports is less than the maximum permissible dose. A horizontal view of ITER is shown in Fig. 2-15. We use a three-dimensional Monte Carlo Nuclear Particle Transport (MCNP) code for shielding calculations. However, the computer calculation times are unrealistically long with this code for the case of the large complex structure. We planned to obtain radiation doses at the biological shielding using the MCNP code only for neutron behavior, and to employ a two-dimensional finite element method for the calculation of induced radioactivity and gamma rays (Fig. 2-16). As a result, we obtained the technical specifications of the shielding structure including the ports, which satisfied the provisional safety criterion. |
