Investigation Of Nuclear Radiation Dose Field In EAST Experimental Site

The large amount of neutrons and ?-rayss ionizing radiation generated by the EAST device during deuterium plasma discharge are closely related to the plasma parameters,which are the important factors affecting the performance and lifetime of the instruments,the activation level of structural materials and the radiation safety of the experimenters,and they are also the important parameter bases for the study of plasma performance.The study on the radiation behaviors and dose spatial distribution characteristics of neutrons and ?-rayss in the EAST hall during operation are the important premise to ensure the radiation safety of personnel and environment,and they are also the key contents of radiation protection research.In this paper,the study of the nuclear radiation dose field in the experimental site of the EAST device was carried out,focusing on the online calibration of radiation dose monitoring probes,radiation behaviors of neutrons and ?-rayss under different heating modes,as well as the dose distribution monitoring in the experimental hall.In order to obtain more accurate experimental monitoring data,the three groups of neutrons and ?-rays ionization chamber monitoring probes in the EAST hall were calibrated online by using 252Cf neutron source and 137Cs ?-rays source.Combined with the on-site environment of the experimental site,the three-dimensional neutron model of the detectors were established,and the simulation calculation was carried out by using the MCNP program.By comparing and analyzing the experimental values,theoretical values and simulated values,the calibration coefficients of the detectors were corrected,which narrowed the difference between the neutron accumulated monitoring results of the online monitoring system and the offline dosimeters to some extent.This calibration experiment also laid a good foundation for checking the working state of the detectors and the regular calibration and maintenance of the detectors before and after the discharge experiment of EAST device.Using the online radiation dose monitoring system,combined with the plasma operating parameters and the monitoring data of the relevant diagnostic system on the EAST device,the radiation intensity and accumulated doses of neutrons and y(X)-rays under ohmic heating,lower hybrid waves heating,neutral beam injection heating and collaborative heating were analyzed and studied.Through further statistical analysis,the radiation behaviors and various sources of neutrons and ?(X)-rays under different experimental conditions were grasped.Based on thermoluminescence detection technology,the dose distribution monitoring experiment in the EAST hall was carried out.Through the analysis of the monitoring results,the spatial distribution characteristics of neutrons and ?-rays accumulated doses in the EAST radiation field,the variation trend of accumulated doses with radial distances,and the approximate linear relationship between neutrons accumulated doses and ?-rayss accumulated doses during the pulse operation of the EAST device were obtained for the first time.In addition,a portable survey instrument was used to obtain the distribution of the ?-rays dose rates in the discharge gap and shutdown phase of the EAST device,which provided the basic data for evaluating the effects of ionizing radiation on experimenters and visitors during different periods.