Future problems relating to real time display system of measured results at monitoring stations and posts

The monitoring stations and monitoring posts surveying the spatial dose around nuclear plants have not been able to detect low level radiation dose in the past, and it is recommended now that the NaI (Tl)-DBM is adequate owing to the easiness of maintenance and the development to energy information collection. The present system to be used for monitoring in Japan is presented as reference. But the NaI (Tl)-DBM is much affected by temperature and for example, snow contributes 1 mR, rain contributes 1 mR, and no rain and calm condition 0.6 mR to environmental dose in one year. This delicate phenomena are explained with the special behavior of Rn nuclide in raining time and thereafter, the measured fluctuation of average dose rate and the change of exposure rate due to wind velocity. The problems to be considered for the measuring equipments and installation are the locations of monitoring stations and posts, the structures and materials of monitoring stations and the aquisition of informations and the equipments. The rising of exposure rate in Urasoko owing to the discharge of gaseous radioactive waste from the Tsuruga Nuclear Power Plant and the exposure rate measured with various detectors are presented. Concerning the maintenance management, the characteristic behavior of the detectors, and the calibration, inspection and adjustment are very important, and have to be checked up frequently. The dose has to be evaluated by the distorsion of histograms, the usual background, the natural concentration of Rn nuclide in the air and so on. The profile of a monitoring station and the prospective monitoring method are presented. (Nakai, Y.)