Development of 16N monitoring system for real-time detection of small leakage in reactor coolant systems

Abstract

This paper introduces a16N monitoring system designed for the real-time detection of minor coolant leaks in nuclear reactors. Conventional coolant leak detection methods in nuclear power plants rely on observing changes in sump tank water levels, as guided by Nuclear Regulatory Commission standards. However, these methods are slow and often inaccurate, particularly for detecting small leakages of less than 0.5 gallons per minute (gpm). Such delays pose risks of corrosion from boric acid and potential safety hazards due to mechanical or thermal fatigue at critical junctions. To address these challenges, we have developed a Reactor Coolant System (RCS) leakage detection system that can swiftly identify small coolant leaks. This system employs beta-ray emissions from 16N, a nuclide predominantly produced during reactor operation and accounting for 90.4% of the total radioactivity in the APR1400 RCS coolant. High-energy beta-rays emitted by 16N are ideal for monitoring due to their significant energy levels, which distinguish them from other nuclides. This system is specifically designed for installation within the annulus zone of the reactor containment, where it captures air near reactor pipes to measure 16N beta-rays. Given the short half-life of 16N (7.13 s), direct measurement is challenging; hence, we use an indirect method to determine calibration factors between dose rate with count rate and estimate radioactivity concentrations based on simulation data and experimental measurements with a surrogate 90Sr/Y source. This system can enhance the safety protocols of nuclear plants by enabling early detection of leaks. Our findings demonstrate that this system can detect leaks as small as 0.01 gpm within seconds, significantly improving response times compared to conventional methods.