A Study on the Long-Term Variation of Signal Current in Rhodium Self-Powered Neutron Detectors Under In-Core Burnup Conditions

摘要: As a key instrument for measuring neutron flux within a reactor core, the signal current of a Self-Powered Neutron Detector (SPND) is subject to change due to continuous material burnup.Accurately accounting for the long-term evolution of SPND signals is essential for reliable power monitoring and safe reactor operation. This study focuses on the Rhodium Self-Powered Neutron Detector (Rh-SPND) and, within the context of a typical Pressurized Water Reactor (PWR), develops a predictive model for signal current variation using a Back Propagation Neural Network (BPNN). The model incorporates changes in emitter material composition due to burnup and utilizes a layered approach to calculate the radial distribution of burnup. Key parameters such as beta electron generation rate, escape probability, gamma photon generation, and gamma-induced electron escape rate are all taken into account. Results show that over a 10-year period at a neutron flux of 1×10¹⁴ n/(cm²•s), the smaller the radius of the rhodium wire, the greater the variation in detector sensitivity. Specifically, a 0.1 mm wire radius results in a 51.3% sensitivity reduction, while a 1 mm wire radius yields a 25.2% reduction. The proposed model enables accurate sensitivity compensation for Rh-SPNDs over time, thereby minimizing neutron flux measurement errors and enhancing reactor safety and stability.