A Detection Method for the Fuel Balls Passing Through the Pipeline of Pebble-bed High Temperature Gas Cooled Reactor

摘要

The fuel handling system for fuel elements is an important part in the pebble-bed high temperature gas cooled reactors (HTGR). It is significant for the reliability and safety of the reactor to exactly detect the fuel elements passing through stainless steel pipeline of fuel handling system. In view of the shortages of sensors fixed inside the pipeline and sensors fixed in the side hole of pipeline, a new detection device is designed, which is installed outside the pipeline and doesn?ˉt destroy the pipeline in the sensors installation and maintenance. The detection fundamentals, sensor structure, signal handling system and ball-passing judgment method are described in detail. The detection system includes two parts: detection sensor and signal handling unit. The sensor is composed of two semicircular parts, each part consists of one exciter coil and two detector coils connected differentially. The signal handling unit utilizes direct digital synthesis (DDS) technique, ultrahigh speed phase/frequency discriminator and amplitude detector, so the ball-passing signal can be clearly picked-up. Base on amplitude detector and phase detector, a ball-passing detection method combining threshold judgment with wave shape judgment is putted forward, which can easily distinguish real ball-passing signal from interfere. The influence of exciting frequency on detecting sensitivity is also studied and the optimal exciting frequency is determined. Experiments are carried out to verify the validity and reliability of the detection device. The results show that designed detection system can accurately inspect the discrete and continuous ball-pass when its speed is between 0.3m/s and 10m/s.