In situ beta radiation monitoring system with enhanced efficiency for water samples from decommissioned nuclear environment

A nuclear environment, including decommissioning activity contains various radioactive nuclides such as pure beta emitters. These radionuclides should be monitored to ensure radiological safety. In particular, beta radionuclides, such as 3H and 14C, can cause internal exposures and should be managed more strictly in terms of health physics. For beta radionuclides, the measurement is carried out in a laboratory through sampling rather than on-site because of the short range. This method is time consuming, laborious, and costly and can also generate secondary waste. In this study, a system for the in situ monitoring of beta radionuclides in water samples is proposed for nuclear facilities and decommissioned environments. A plastic scintillator with low sensitivity to gamma rays and good reactivity with beta radionuclides was used. The detection efficiency was increased by using a detection part, whereby the water sample is made to directly contact the scintillator by utilizing the characteristic of plastic scintillators (i.e., they do not react with water). A coincidence circuit was constructed by using multiple photomultiplier tubes (PMTs) and applied to gross beta activity measurements. The values obtained from a single PMT were used in the spectral analysis to determine the effect of each beta radionuclide. Beta radionuclides in water samples in the field can be monitored by using plastic scintillators and multiple PMTs.