Research and Application of Single-Point Calibration Method for Ex-core Nuclear Instrument System of PWRs

The ex-core detector is used to indicate the reactor power and axial-power difference in commercial PWRs, and it needs to be calibrated regularly to ensure the accuracy. The conventional multi-point calibration method needs to move the control rods and measure the flux-mapping several times, which influences the economy and safety of power plants. Therefore, the single-point calibration method for the ex-core nuclear instrument system has been proposed in this paper, which combines both the theoretical calculation and measurement data. The axial offset correction factor and the ex-core detector sensitivity are introduced in this method. And the core-analysis code is utilized to simulate the movement of control rods. Eventually, the calibration coefficients could be determined. Based on the single-point calibration method, the function development has been achieved in the core-analysis code SPARK, and it has been verified by the multiple cycles’ measurement data from M310 reactor. The verification results indicate that the single-point calibration method proposed in this research has higher calibration accuracy. Compared with the measured power level and axial power difference, the average biases of calibration results are 0.31% and 0.16%, repectively. Therefore, the single-point calibration method is capable to determine the calibration coefficients accurately, and save calibration time without control rod movement. This method could improve the economy and safety of power plants and has the engineering application and popularization value.