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Control rod hydraulic drive system (CRHDS) is the key power control equipment of 200 MW Nuclear Heating Reactor (NHR-200), and the capacitance rod position measurement sensor (CRPMS) is the key measurement equipment of CRHDS. For the measurement error caused by the eccentricity of the measuring rod, a new measurement method which can separate the capacitance variation caused by the stepping and eccentricity of the measuring rod was proposed (eccentricity-stepping separation method). Based on this method, a design of four-helix electrodes CRPMS was proposed. For the sensor, the theoretical model was established by finite element method, and the static characteristic experiment was carried out. The calculation results of the theoretical model are in good agreement with the experimental results. Based on the theoretical model, the function between capacitance values and rod positions was established, and the measurement error of the sensor was systematically analyzed. The structure optimization of the sensor was conducted. The results show that for the four-helix electrodes CRPMS with eccentricity-stepping separation method, the maximum measurement error is -3.11 mm under the calculation conditions, which can meet the requirements of rod position measurement without losing step. The results provide guidance for the improvement of CRPMS.

Capacitance sensors are frequently applied for dielectric objects measurements. However, the study on the ungrounded/grounded control rod position measurements with capacitance sensor is limited. In this connection, a system based on the helix-electrode capacitance sensor is applied to measure the rod position in NHR. Based on the variations of equivalent electrical permittivity with different control rod positions in NHR, the helix-electrode capacitance sensor has been successfully used for the ungrounded/grounded control rod position measurement due to its advantages of non-invasion, low-cost, high reliability and non-radiation. The finite element method is used to calculate the sensor capacitance and the sensor sensitivity is also presented. Then, the ungrounded/grounded control rod position experiment is carried out to measure the response of the helix-electrode capacitance sensor, in which a novel method is proposed to calibrate the helix-electrode capacitance sensor based on the grating linear displacement measuring probe. The capacitances obtained by simulations were compared with experiment results to verify the proposed models. The subsequent quantitative analyses on the data indicate the reliability and accuracy of the apparatus for monitoring control rod position. It is demonstrated that such a system shows promising applications for measurements of the control rod position in NHR. [ABSTRACT FROM AUTHOR]

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]

• 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]

Highlights • PEEK are introduced as the control rod guide rod material. • Measurement resolution of the BCRMS is as high as ±7.09 mm. • The built models and BCRMS are proved to be an efficient solution to measure the control rod position in NHR-200. Abstract The accurate control rod position measurement is crucial to ensure the reactor safety and reliability. Based on the variations of equivalent electrical permittivity with different control rod positions in NHR-200, the built-in capacitance control rod position measurement system (BCRMS) has been successfully used for the PEEK material control rod guide rod due to its advantages of non-invasion, low-cost, high reliability and non-radiation. And a novel method is proposed to calibrate the built-in capacitance control rod position sensor (BCRS) based on the grating linear displacement measuring probe. The BRCMS was experimentally tested on the horizontal test facilities. In addition, Capacitances obtained by the built electric theoretical model and FEM analysis were compared with experiment results to verify the built models. Meanwhile, measurement resolution of the newly designed BCRMS is as high as ±7.09 mm. Errors caused by the eccentricity and sensor end effects are analyzed to be in the reasonable range. The built models and newly designed BCRMS are proved to be an effective solution to measure the control rod position in NHR-200. [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]

• The established dynamic mathematical model of the CCRMS were verified. • The CCRMS is basically realized the dynamic process measurement function. • The dynamic characteristics of the CCRMS system were obtained. In this paper, the dynamic mathematical model of the capacitance control rod position measurement sensor (CCRMS) were established. The experimental research, numerical calculation, and model validation were carried out for the case of the velocity dynamic response calculation, scramming dynamic response calculation, scramming time test and scramming performance measurement test of the CCRMS. The results show that the validity of the proposed model is verified and the CCRMS is basically realized the dynamic process measurement function with one step display measurement requirement. Furthermore, the dynamic characteristics of the double-helix structure CCRMS system were obtained based on the proposed model and experimental research. Moreover, the dynamic measuring error of the CCRMS is less than ±1.20 mm, the delay time of the CCRMS is t = 3 τ which is less than 0.84 ms, and the dynamic response time of the capacitance measuring instrument is about 8 ms. [ABSTRACT FROM AUTHOR]

• The established model of the capacitance control rod position measurement sensor (CCRMS) were verified. • The CCRMS is basically realized the one-step display measurement requirement. • The static characteristics of the CCRMS were obtained based on the proposed model. The accurate and reliable measurement of the control rod position concerns the operation and safety of the 200 MW nuclear heating reactor (NHR-200). In this paper, the static mathematical model of the capacitance control rod position measurement sensor (CCRMS) were established. The experimental research, finite element method (FEM) simulation, and model validation were carried out for the case of the ungrounded metal medium, grounded metal medium, dielectric medium control rod measured rod and eccentricity. The results show that the validity of the proposed model is verified and the CCRMS is basically realized the one-step display measurement requirement. Furthermore, the eccentricity inconsistency of the measured rod is solved. In addition, the end effect of the CCRMS can be reduced reasonably but the eccentricity of the measured rod still have some influences to a certain extent. Moreover, the static characteristics of the double-helix structure CCRMS were obtained based on the proposed model. [ABSTRACT FROM AUTHOR]