Continuous beta monitoring technology for uncontrolled radiological release in underwater using integrated beta and gamma detection system

A monitoring system capable of in-situ beta detection has been developed to address the potential risks associated with radioactive releases from nuclear sites. Although releases are controlled within permissible limits and follow strict protocols to minimize environmental and public health impacts, incidents of uncontrolled releases due to human or mechanical failures have occurred, resulting in contamination of underground water sources. To improve response capabilities, transitioning from traditional sample-based monitoring to real-time monitoring of underground water is crucial. The system utilized an NaI(Tl) detector for gamma nuclides and two plastic scintillation detectors for beta nuclides. Beta detection was facilitated through a coincidence method involving the two plastic scintillators, with any influence from gamma radiation effectively mitigated using data from the NaI(Tl) detector. This configuration ensured accurate measurement of beta radiation by removing gamma contributions from the coincidence counts. The system, which was evaluated using detection experiments for beta nuclides 3 H and 90 Sr, achieved a minimum detectable activity that satisfied the criteria for restricting the intake, distribution, or consumption of 90 Sr and 3 H to 0.1 and 100 Bq/g, respectively, within 20 minutes.