Shutdown dose evaluation experiment for ITER

A shutdown dose experiment was conducted by using the FNS at JAERI under the ITER R&D Task T-426, in order to evaluate the accuracy of the shutdown dose evaluation method. The activation and the delayed gamma-ray distribution after passing through the straight duct were simulated in the experiment. The experiment was conducted at the 80° beam line of the FNS and the irradiation was carried out over 6 days. The experimental analyses were carried out by using the new direct one step Monte Carlo method that is used as the design tool to estimate shutdown dose of the ITER/FEAT. The nuclear data packages, FENDL-2/MC and FENDL-2/A, were compared through the analysis of the experiment. As a result, the following facts were found for the accuracy of the shutdown dose evaluation: (1) the C/E values of the shutdown dose at around 106 s after the irradiation were 0.92–1.07; (2) the shutdown dose rate could be evaluated by the new direct one-step Monte Carlo method within the experimental error, and the accuracy of the method is sufficient for shielding design of the International Thermonuclear Experimental Reactor (ITER).