Research on the Radiation Monitoring Methods in the Reactor Coolant Pressure Boundary Leakage of Nuclear Power Plant

Reactor coolant pressure boundary is one of the important protection barriers in nuclear power plant. The weak parts of reactor coolant pressure boundary, such as crack or fissure of the process pipeline, can present hidden troubles, and it can cause coolant leak and can produce a great threat to the safe operation for nuclear power plant, so it is necessary to pay attention to monitor the reactor coolant pressure boundary leakage. With the increasing requirements on the quantitative monitoring level of reactor coolant pressure boundary coolant leakage, many kinds of radiation monitor methods (including the particulate iodine and noble gas radiation methods, N-13 monitoring method and F-18 monitoring method), have been conducted for the researchers. In this paper, the traditional particulate, iodine and noble gas radiation methods (short for PING monitoring methods) will be introduced in brief, including the basal principle, system design flow and so on. Because the monitoring objects of PING monitoring methods are corrosion products and fission products, it can only achieve qualitative monitor. The nuclear power plant operators pay more attention to the quantitative leakage condition, so 13N and 18F has attracted the attention of many researchers due to their existence form and their characteristic of positron-electron annihilation. Based on the advantages of 13N and 18F, the key technologies research has been carried out in Nuclear Power Institute of China. A full-range measurement method is proposed. More specifically, the radioactive activity measurement has been studied when nuclear power is greater than or equal to the set value (for example, 20%FP). In order to improve the accuracy of measurement, the coincidence detection and digital coincidence measurement technique has been adopted. By measuring the charge and time of the detectors' output signals, the effective coincidence events based on time-to-digital converter (TDC) and high-speed ADC technology can be measured. In addition, the total gamma measurement method has been studied when nuclear power is less than the set value (for example, 20%FP). The digital multi-channel pulse height analysis method has been studied. The energy spectra and linear fitting parameters are tested, the test results indicate that the measurement system has a good energy linearity. Through the above research, 13N and 18F monitoring methods have been proven to have advantages of quantitative monitoring compared with PING monitoring methods. At last, the recommended radiation monitoring methods of the reactor coolant pressure boundary leakage in nuclear power plant is given considering the advantages and disadvantages of different monitoring method.