Design optimization of real-time in-containment 16N beta detection system

Abstract

The design process for optimizing a real-time 16N beta monitoring system inside a containment building was developed in this study. The purpose of the system is to detect the unidentified small leaks (less than 0.5 gpm/h) of the primary and secondary coolant system of a pressurized water reactor, based on radiation measurements. The system is located at the annulus zone of the reactor containment building, away from the high radiation background, and detects the 16N beta particles that are transported to the system after collection at the leakage points of the reactor coolant system. The specifications of the overall system were determined using Monte Carlo and computational fluid dynamics simulations. In particular, the optimization process for the shielding and collection cavity geometry has been described. A 5 cm lead shielding was determined considering the efficient weight reduction of the system and the radiation tolerance of the detector system over the reactor life. Assuming a 16N concentration of 1000 Bq/cc in the designed air collection cavity (2000 cc volume), the signal-to-noise ratio was evaluated to be approximately 2.2, and the leakage could be confirmed in the background radiation environment in the annulus zone. Based on the derived specifications, a system prototype was manufactured considering structural safety.