Abstract: After a long-term operation of the water medium transmission pipeline in the radioactive system of nuclear power plant, some sections of the pipeline will have radioactive material deposition. In order to improve the decontamination effect of pipeline washing, some nuclear power plants in China began to try to introduce online ultrasonic decontamination equipment, which can be installed outside the pipeline, and can peel off the sediment on the inner wall by transmitting ultrasonic vibration into the pipeline, thus improving the decontamination effect of pipeline washing. The application of on-line ultrasonic descaling equipment in nuclear power plants is still in the experimental exploration stage, and its functions need to be further developed and improved. This paper mainly introduces the research on on-line ultrasonic decontamination of pipelines in a CPR1000 reactor type nuclear power plant in China. Tests were carried out on pipelines with diameters of 60.33 mm and 88.9 mm respectively. Two different types of pipelines with loose pollution deposition and fixed pollution deposition were selected in the 88.9mm diameter pipeline test. The test shows that this technology has obvious decontamination effect on the loose pollution deposition pipelines, It has the value of popularization and further research.After long time operation, radioactive materials may be deposited in some sections of the water medium transmission pipeline of radioactive system in nuclear power plants. In order to improve the decontamination effect of pipeline flushing, some nuclear power plants in China began to try to introduce online ultrasonic decontamination equipment, which can be installed on the outside of the pipeline, and by transmitting ultrasonic vibration inward, deposits on the inner wall can be peeled off. While the application of this technology is still in the stage of experimental exploration, and its function needs to be further developed and improved, we have made some efforts at a CPR1000 nuclear power plant. With tests carried out on pipes of 60.33 mm and 88.9 mm diameter respectively, we conclude preliminarily that this technology has obvious effect for non-fixed contamination in pipeline, and it is worth to be popularized and further studied.

Key words: On-line, Pipeline, Flushing, Decontamination, Ultrasonic, CPR1000