A Photothermal Line-Scanning System for NDT of Plasma-Sprayed Coatings of Nuclear Power Plant Components

Abstract The main pump of the nuclear power plant primary circulation system is one of the most important and critical components of the pressurized water reactor type nuclear power plant. For instance, the failure of plasma-sprayed coatings on the pump's shaft seal rings leads to shutdown of the entire reactor. However, suitable methods for NDT of these coatings have not been found in spite of the obvious need. In this study, a photothermal NDT technique based on line-scanning laser heating and infrared radiation detection was applied. The measurements were modelled numerically and then performed in four series. First, a newly coated seal ring pair was inspected; two adhesion defects were found. The defective pair was subjected to a trial run emulating the real conditions of use and after that was re-inspected. Twenty new adhesion defects were found. Another newly coated seal ring pair was inspected and found to be faultless, and it was installed in the nuclear power plant for a year. During the next maintenance stop the pair was inspected again, and a group of three adhesion defects was found. The detecting of adhesion defects in both the unused and stressed coatings demonstrates the applicability of the photothermal method.