Calculation of the signal current of self-powered neutron detectors in a nuclear reactor

[Background] Self-powered neutron detectors (SPNDs) are critical devices in the monitoring and protection systems of nuclear reactors, and their signal current directly reflects the value and distribution of the core power. Insulators play an essential role in the design of SPNDs and are the main factor affecting the calculation accuracy of the signal current.[Purpose] This study aims to improve the accuracy of the calculation method of the SPND signal current, ensuring that the measured currents accurately reflect the reactor conditions and meet the highest industrial standards. [Methods] Firstly, the signal generation mechanism of the SPND was thoroughly discussed, and three independent calculation methods of the current based on the inherent physical characteristics of the space electric field of an insulator were proposed. Then, high-fidelity simulations of the SPND were performed using the Monte Carlo code, and the three methods were validated based on the simulation results. In addition to the current caused by the neutrons, the current caused by the photons inside the reactor was quantitatively analyzed. Meanwhile, extensive radiation experiments on the various reactors have been performed to verify these three current calculation methods. [Results] The difference between the results obtained by using the three methods is less than 1%, demonstrating a considerable accuracy. In addition, the current of the rhodium SPND is primarily owing to the neutrons, whereas the photon-induced current is generally less than 5%. Experimental verification results on the several operating reactors show that the difference between the theoretical and experimental results is less than 3%, which also proves its effectiveness and accuracy. [Conclusions] This method has been applied to the large Chinese Gen-III advanced pressurized water reactor (HPR1000) and is universal. It can be used for the signal analysis of different types of SPNDs, as well as for providing valuable references for core monitoring systems in other reactors, such as the Gen-IV fast reactor as well as future fusion reactors. © 2024 Science Press. All rights reserved.