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The control rod position is an important factor that affects the power of nuclear reactors. The unique real rod position of nuclear reactors is indicated by the control rod position sensor, which is the key measuring equipment of nuclear reactors. The capacitance control rod position sensor (CCRPS) is designed for the 200 MW Nuclear Heating Reactor (NHR-200) developed by Tsinghua University. The CCRPS has the advantages of simple structure, high reliability, long life-time, and high precision. The research progresses of static performance of the CCRPS are reviewed in this paper, including the research method, error characteristics, and methods for enhancing the measuring precision. The static performance of various types of the CCRPS are summarized. The optimum design of the CCRPS is determined. As a result, it is hoped that the information presented in this paper can provide a foundation for the follow-up studies of the CCRPS. [ABSTRACT FROM AUTHOR]

• The control rod position measurement method of double capacitance values is proposed. • The structure of array electrode capacitance control rod position measurement sensor is proposed. • The static characteristic experiments and finite element model analyses are carried out. • The maximum measurement error can be limited to ± 4 mm within the measurement range of 840 mm. Control rod position measurement sensor is the key measurement component of the nuclear reactor. For the capacitance control rod position measurement sensor (CCRPMS), a new method of measuring the control rod position with double capacitance values is proposed. In order to realize this method, the array electrode CCRPMS is designed. For the array electrode CCRPMS, the static characteristic experiments are carried out, the finite element model is established. The relationship between the electrode arrangement method and the "eccentricity inconsistency" effect is analyzed. The function between double capacitance values with rod positions is fitted. For tilt states and different deflection angles of the measuring rod, the applicability of the function is evaluated. Static measurement errors of the sensor are systematically analyzed. Results show that the maximum measurement error of the array electrode CCRPMS can be limited within ±4 mm. [ABSTRACT FROM AUTHOR]

Control rod position sensors are the core measuring components of the control rod drive system. For the capacitance control rod position sensor with protection electrodes, the sensitivity of the sensor is obtained by experiments. The calculated model of the sensor is established, and it is verified by experimental results. Based on the calculated model, the regulation method of protection electrodes on the unevenness of the sensitivity field of the sensor is systematically studied. Performance analysis of the sensitivity field, the structure design, and error analysis of the sensor are carried out. The results show that the sensor sensitivity is 0.007 563 pF/mm and the maximum measuring error can be limited within ±0.5 mm, which can meet the actual use demands. The results provide a new technical scheme for the subsequent research of capacitance control rod position sensors. [ABSTRACT FROM AUTHOR]

• The experiments of capacitance rod position measurement sensor with and without protection electrodes are carried out. • The theoretical model of the sensor is established by using finite element method and verified. • The shielding effect on sensitivity and maximum eccentricity error of FHE-CRPMS-PE is analyzed. • The design of two-section FHE-CRPMS-PE is proposed and can realize control rod position measurement without losing step in NHR200. Capacitance rod position measurement sensor (CRPMS) is the key measurement equipment of control rod hydraulic drive system (CRHDS). For four-helix electrodes CRPMS with protection electrodes (FHE-CRPMS-PE), the static characteristic experiments are carried out and the sensitivity functions of FHE-CRPMS-PE are fitted. The shielding effect experiment is carried out. The computational model of FHE-CRPMS-PE is established by using finite element method, and the experimental results are in good agreement with the model calculation results. The maximum eccentricity error of FHE-CRPMS-PE is analyzed by using the computational model, the influence of shielding radius on sensitivity and maximum eccentricity error of FHE-CRPMS-PE is analyzed. The design of two-section FHE-CRPMS-PE is proposed. The static characteristic experiment and model calculation of the two-section FHE-CRPMS-PE are carried out. The results show that the two-section FHE-CRPMS-PE can meet the measurement error limit and realize control rod position measurement without losing steps. [ABSTRACT FROM AUTHOR]

• The measurement errors are classified, different solutions are proposed. • The multi-electrode capacitance rod position measurement sensor is designed. • The maximum measurement error of the sensor is 6.25 mm. Rod position measurement sensor is the key equipment of control rod stepping and scram measurement, its accuracy is directly related to the safety and reliability of NHR-200. The nonlinear errors of capacitance rod position measurement sensor (CRPMS) were classified, and the experiments of sensor edge effect and measuring rod eccentricity effect were carried out. The calculation model of CRPMS was established, the results of the model agree well with the experimental results. The relationship between eccentricity error and rod position depth was analyzed, and the design of multiple unequal length helix electrodes CRPMS based on the eccentricity error zeroing method was proposed. The static characteristic experiment of the CRPMS with suspending electrodes was carried out and the model was verified. The edge effect and eccentricity effect nonlinear errors were analyzed by using the model. The results show that the nonlinear errors can meet the requirement of rod position measurement accuracy. [ABSTRACT FROM AUTHOR]

• A capacitance rod position measurement sensor with protection electrode for measuring grounding metal rod is proposed. • The finite element model of the sensor is established, the static characteristic experiment of the sensor is carried out to verify the finite element model. • The sensor is optimized, the maximum eccentricity error can be reduced from 664.96 mm to 6.36 mm. • It can realize the rod position measurement without losing step in NHR. Control rod step and scram measurement is performed by control rod position measurement sensor. For winding wire capacitance rod position measurement sensor, the static experiments were carried out and the sensor sensitivity was obtained, the finite element model was established and the results of the model were verified by experiment. The influence of wire pitch, winding method and wire number on the eccentricity performance was analyzed, and the design method of installing grounding protection electrodes was proposed. The optimized combination of parameters of the sensor was obtained. The results show that increasing wire pitch, evenly arranging the wires into two electrodes when the wire pitch is fixed, and reducing the wire number are helpful to reduce the maximum eccentricity error. Furthermore, the maximum eccentricity error can be greatly reduced by adding protection electrodes, and the optimized design can meet the requirement of rod position measurement without losing step. [ABSTRACT FROM AUTHOR]

The application object of capacitance control rod position measurement sensor (CCRPMS) is the control rod hydraulic drive system (CRHDS). CRHDS can be applied to integrated water-cooled nuclear reactors. The design of straight electrodes CCRPMS with protection electrodes is proposed in this paper. The regulation method of protection electrodes on static characteristics of the sensor is studied. The structure optimization design of the sensor is conducted. Static calibration experiments are carried out for the sensor, which include 366 experimental points. The reference sensitivity function of the sensor is fitted by experimental results, and measurement errors of the sensor are analyzed. The results show that measurement errors can be limited within the range of ±4 mm, which can meet the accuracy requirements of CRHDS. • Straight electrodes capacitance control rod position measurement sensor with protection electrodes is proposed. • The static calibration experiments of the sensor are conducted. • The maximum measurement error of the sensor can be limited within ± 4 mm. [ABSTRACT FROM AUTHOR]