Study of the shipborne device for seawater radioactivity monitoring

Combining with the need of the nuclear power developing of China, we have developed a shipborne monitoring and alarm device for seawater radioactivity. The device can monitor seawater radioactivity and give out alarm signals if the activity beyond the standard. It will prevent large time consuming on the journey of sampling the seawater from the sea to laboratory. It takes a short time of 6.5 min averagely for the device to alarm after the monitoring ship enters the sea area with radioactivity beyond the standard. The probability of failing to alarm is <1% for a 20 min monitoring. The alarm device was proved to be less time-consuming, more flexible and scalable to monitor. It is helpful in discovering an accident and activating contingency plans in time. The device can also measure the activities of the nuclides in seawater. The MDA of ¹³⁷Cs in seawater sample is 0.15 Bq/L for a 1 h measurement. The device is centering on 'alarm', instead of the traditional ideas of 'detecting'. By balancing the alarm probability and misreport rate together with the measuring time, we proposed an effective method for the design of alarm devices, which may provide a reference for the designing of fast-alarm devices in future. (authors)