Monte Carlo simulation of activity concentration measurement of primary coolant of high-temperature gas-cooled pebble-bed modular reactor

Abstract The real-time and prompt determination of the radioactive level in the primary coolant of the first demonstration high-temperature gas-cooled pebble-bed modular reactor (HTR-PM) in China is essential for establishing its radiation safety since it can reflect the radiological status of the fuel elements in the core. This paper presents the design of the activity concentration measurement of the primary coolant of HTR-PM and focuses on the detection efficiency simulation of the on-line gross γ monitoring instrument. The purpose of this instrument, which was set in place at the entrance of the helium purification system of HTR-PM, is to provide continuous, real-time, prompt, and reliable activity concentration monitoring of the gaseous fission products in the primary coolant. The Monte Carlo method is used to simulate the detection efficiency of the instrument. A sensitivity analysis with the variations in the source terms of the primary coolant of HTR-PM is presented and discussed.