Preliminary investigation of the shutdown radioactivity for EAST based on gamma ray spectrometry.

• The HPGe spectrometer system was placed inside the vacuum vessel to measure the characteristic γ-rays emission from radionuclides after EAST shutdown. • The identification and pathway analysis of radionuclides were discussed based on structural materials and radiation sources of EAST. • Activity of radionuclides and time evolution of dose rate, preliminary activation results, were discussed. Experimental Advanced Superconducting Tokamak (EAST) is capable of operating with long-pulse deuterium plasma, which will generate a lot of radiation such as fusion neutrons, gamma rays and hard X-rays. Since the structure material of the device was activated, work around and inside the tokamak would be limited from a radiation protection point of view after shutdown. Identification of radionuclides and evaluation of dose rate inside the vacuum vessel are needed to develop a guiding principle for radiation protection during maintenance. In this paper, a gamma ray spectrometer based on high purity germanium (HPGe) detector and digitizer was placed inside the vacuum vessel to measure the characteristic gamma ray emission from radionuclides. 7Be, 46Sc, 51Cr, 54Mn, 58Co, 60Co, 59Fe, 88Y, 91Y, 91mNb, 99Mo, 124Sb and 110mAg produced by photonuclear reactions and neutron-induced reactions were identified. The activities of radionuclides was calculated respectively with the uncertainty not exceed 6.05 %. The dose rate for 10 days after shutdown was mainly contributed by 60Co, 58Co, 54Mn, 110mAg, 59Fe, 51Cr, 88Y, 99Mo, 7Be and 124Sb, total dose rate were 3.62 × 10−9 Sv/h(Port E) and 3.40 × 10−9 Sv/h(Port I). [ABSTRACT FROM AUTHOR]