Eddy Current Effect Analysis of a New Self-sensing Rod Position Detector for Reactor

Currently, coded rod position detectors have many problems such as a large number of coils, complex structure, rough measurement accuracy and poor reliability, which seriously hinder the development of reactor miniaturization. Therefore, we propose a new self-sensing rod position detector in this paper, which employs a double-winding structure with four equal-length A and B coils, where the two sets of coils are independent of each other, and the linear variation of the coil inductance with the motion of the driving rod enables continuous rod position measurement. By quantifying the magnetic skin effect on the rod, the mathematical model of self-sensing rod position detector based on eddy current effect is derived. The finite element simulation model is built to verify the accuracy of the mathematical model, and the influence of the temperature rise of the rod and the key structure parameters of the detection coil on the measurement accuracy of the detector is studied. It is found that the inductance variation of the coil under different temperatures is influenced by the relative permeability and conductivity of the rod. The increase of coil turns is conducive to the increase of inductance variation, and the increase of coil spacing first increases and then decreases the inductance sensitivity. And then the detector structure is optimized considering the above change rules. The prototype is tested and verified. The results show that both coils have an inductance resolution of 0.14 mH/10 mm, and the displacement identification accuracy of 10 mm can be achieved. This study can provide reference for the application of self-sensing rod position detectors in small nuclear reactors.