Control system of environmental radiation monitoring

On the operation of nuclear power station, monitoring of environmental radiation by continuous measurement to ensure the health and safety of public is the responsibility of the operation side. Monitoring of environmental radiation covers various measurement. Among them, the continuous measurement of spatial γ-ray rate is thought to be an effective method because this measurement is possible to detect the fluctuation of the level of environmental radiation quickly and is effective to find out abnormal condition in early stage. The monitoring system of spatial γ-ray rate is composed of low range monitoring equipment and high range monitoring equipment, signal transmitting system and monitoring station. NaI(Tl) scintillator, which can measure the background radiation and the radiation from power station separately, is used for the former monitoring, and is able to identify the source of radiation. For the monitoring of high range radiation, pressurized spherical scintillator is used to catch the spatial γ-ray in the occasion of emergency. Those equipments were installed in stations of ALC plate construction, and signals are transmitted to monitoring center by optical fiber cable. The monitoring panel of monitoring center is equipped with output terminals making provisions for future computerization. Though present system is attaining high evaluation, efforts are being made to reach higher reliability by improving the signal transmitting system and by developing new materials for radiation detecting device. (Ishimitsu, A.)