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

Abstract

• 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. 7 Be, 46 Sc, 51 Cr, 54 Mn, 58 Co, 60 Co, 59 Fe, 88 Y, 91 Y, 91m Nb, 99 Mo, 124 Sb and 110m Ag 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 60 Co, 58 Co, 54 Mn, 110m Ag, 59 Fe, 51 Cr, 88 Y, 99 Mo, 7 Be and 124 Sb, total dose rate were 3.62 × 10 −9 Sv/h(Port E) and 3.40 × 10 −9 Sv/h(Port I).