Application of Anticoincidence Technology to Burn-Up Measurement Systems in High-Temperature Gas-Cooled Reactors

Nuclear energy is the focus of sustainable energy development worldwide. A high-temperature gas-cooled reactor (HTGR) plays a vital role in the development of nuclear energy. In a pebble-bed HTGR, the burn-up measurement system is important for ensuring reactor safety and economy. This study optimized a burn-up measurement system by adding anticoincidence technology with bismuth germanium oxide (BGO) crystals and a plastic scintillator used as anticoincidence detectors. Through Monte Carlo simulation, the detection effects of two different anticoincidence detectors on fuel elements were compared and analyzed. The study focused on varying the wall thickness and top thickness of these detectors to optimize the peak-to-Compton ratio (P/C). The results showed that the size of the BGO detector with the best anticoincidence effect (P/C of 727) consists in a diameter of 140 mm and a length of 210 mm. The best plastic scintillator size (P/C of 180) consists in a diameter of 260 mm and a length of 260 mm. Adding the anticoincidence technology lowered the Compton plateau of the measured gamma spectrum and significantly improved the detection performance of the burn-up measurement system. The new burn-up measurement system has improved detection precision not only for Cs-137 but also for low-activity nuclides.