Evaluation of biological dose rates around the ITER NBI ports by 2-D Sn/activation and 3-D Monte Carlo analyses

Shielding analyses for the International Thermonuclear Experimental Reactor (ITER) neutral beam injector (NBI) ports have been performed using two-dimensional discrete ordinates S n method with activation analyses and three-dimensional Monte Carlo method. From the two-dimensional S n /activation analyses, it was found that a conversion ratio relating fast neutron flux to the biological dose rates at 10 6 s after reactor shutdown is 1.5–2.0×10 −5 μSv/h per (cm −2 s −1 ) for the fast neutron flux with energies above 0.1 MeV. From the results of three-dimensional Monte Carlo analyses, the fast neutron flux above 0.1 MeV at the cryostat is about 3.6×10 6 cm −2 s −1 for the case of a 50–60 cm thick NBI port wall (thin case), and 5.2×10 5 cm −2 s −1 for a 60–65 cm thick port wall (thick case). The corresponding biological dose-rates at the cryostat are about 7 and 2×10 1 μSv/h for the thin and thick cases, respectively. These dose rate levels satisfy the tentative design target of 100 μSv/h specified for the ITER Engineering Design Activity (EDA).