Study on eddy current technique for detection of defects in steam generator tubing in nuclear power plant

Defects in a steam generator tubings are one of the major problems in operation of a nuclear power plant. Eddy current multi-frequency technique has been used for evaluation of the various type of defects, which is not sufficient to solve the problems. Failure of the tubings near the tubesheet, defects in the free length region due to pitting, and the defects due to fretting wear in anti-vibration bar, have been difficult problems in detection and quantitative analysis. In this research, various artificial defects were machined on the steam generator tubings, with electro-discharge machining technique. Combining the defects to the simulated tubesheet or support plate, detectability and ability to eliminate the tubesheet signal were investigated using frequency mixing technique. The effect on the tubesheet in multi-frequency method was studied. The results were analyzed with the interaction terms of the mixed frequency signals. By measuring the smallest detectable defects, it will be used as a basis for the eddy current technique of detection and evaluation of the flaws due to the pitting in Kori Unit 1. The results on the effect of the support plate or subesheet are directly related to the flaws on the top of the tubesheet in Kori Unit 2. (Author)