Abstract: This paper mainly introduces the research practice of removing radiation hot spots deposited in the primary coolent system lines by ultrasonic on-line decontamination process in NPP. In this study, ultrasonic power of 60 W and 100 W were applied to the decontamination practice of 26.7 mm and 88.9 mm lines, respectively. The practice shows that the efficiency of on-line hot spot removal by ultrasonic can reach 60%-70%, which is more obvious than that by conventional flushing process. At the same time, this research shows that the application of ultrasonic on-line decontamination needs to consider the factors such as on-site working environment, ultrasonic power, medium flow rate and radionuclide deposition mode comprehensively, so as to make it achieve a better application effect.

Key words: ultrasonic, on-line decontamination, nuclear power plant