Development of a seawater radioactivity monitoring system and its preliminary test results

A large amount of radionuclides released into the ocean during the Fukushima accident aroused concerns on the marine radioactivity monitoring. A Seawater Radioactivity Monitoring System based on NaI (Tl) scintillation crystal was developed with its performance being preliminarily tested through simulation and underwater experiment. The detection efficiency of the system for full-energy peak of 137Cs was 2.17 x 10-5 cps/(Bq·m-3), which fully conformed with is calibration result of 2.27 x 10'-5 cps/(Bq·m-3). The system had been also tested underwater in the sea areas near Fujian province with the seawater background being measured in 6 hours. Providing a background spectrum and detection efficiency as above, the minimum detective activity concentration of this system for 137Cs would be 580 Bq/m3. Test results show that the device could be effectively applied in routine monitoring of marine radioactivity or radioactive pollution under accident situation. A further update to the system was also given at last. (authors)