RADIATION SAFETY CONSIDERATIONS FOR LHD EXPERIMENTS

For experiments with the Large Helical Device (LHD) which is now under construction at the Toki site in Japan, radiation safety issues were discussed. In the course of plasma experiments, radiations such as X-r ays, induced gamma-rays, and neutrons increase. From a safety point of view, these radiation exposures to the environment should be controll ed to limit the annual dose to less than 50 mu Sv at the site boundary . In order to meet this, an area monitoring system named RMSAFE (Radia tion Monitoring System Applicable to Fusion Experiments) has been deve loped and partly installed. This can discriminate and measure radiatio ns including burst-like emissions due to plasma shots from natural rad iations. For the present period, this system is operating to monitor t he natural radiation levels before the LHD operation. It was observed that the radiation levels strongly depend on rain levels and ground st ate. An indoor area monitoring system has already been implemented on site, to measure radiations from NBI and ECH test shots, and it shows good monitoring ability. Also, thermoluminescence dosimetry has been a pplied. The importance of investigating the radiological behavior unde r natural conditions with continuous monitoring is shown.