Radiation control in LHD and radiation shielding capability of the torus hall during first campaign of deuterium experiment

摘要

The activities carried out to obtain public consent for deuterium experiments in LHD, which began in 2017, are reviewed in this paper. In addition, the upgrades and the safety management of LHD for deuterium experiments, including neutron yield measurement system, exhaust detritiation system, institutional regulation for radiation control, and other issues, are briefly presented.During the first campaign of the deuterium experiments in LHD, the shielding of gamma-ray and neutron by the concrete wall of the LHD torus hall was evaluated. Also, the confinement of radioactive isotopes in air inside the torus hall was investigated. No increase of radiation dose was measured outside the torus hall, although the high radiation dose field inside the torus hall was found during deuterium experiments. Therefore, almost all gamma-rays and neutrons were shielded by the concrete wall of the torus hall due to its sufficient thickness of 2 m. The radioactive isotopes in air as well as in other components were well confined in the torus hall. In particular, the pressure control inside the torus hall being lower than outside the torus hall effectively prevented the radioactive isotopes in air from diffusing to the unprescribed area.