Design of gamma-ray and neutron area monitoring system for the IFMIF/EVEDA accelerator building

In the IFMIF/EVEDA accelerator, the engineering validation of the personnel protection system (PPS) is planned at the BA site in Rokkasho, Aomori, Japan. The PPS inhibits the beam by receiving the interlock signal from the gamma-ray and neutron monitoring system. The gamma-ray and neutron monitors for IFMIF/EVEDA have detection ranges of 80 keV–1.5 MeV (gamma-ray) and 0.025 eV–15MeV (neutron). For the present shielding design, it is imperative to validate the shielding performance which has to be within the detection ranges for gamma-ray and neutron detectors. For this purpose, the energy reduction performance of a shielding for neutrons and photons with the shielding materials of water and concrete has been evaluated by PHITS code. From the calculating results, it is found that the photon energy range can be suppressed up to 10 MeV by water and concrete employed shielding, but still some optimization to suppress the photons with energy below 1.5 MeV is indispensable.