Abstract
The capability of eddy current testing (ECT) for the bottom mounted instrumentation (BMI) weld area of reactor vessel in a pressurized water reactor was demonstrated by the developed ECT system and procedure. It is difficult to position and move the probe on the BMI weld area because the area has complexly curved surfaces. The space coordinates and the normal vectors at the scanning points were calculated as the scanning trajectory of probe based on the measured results of surface shape on the BMI mock-up. The multi-axis robot was used to move the probe on the mock-up. Each motion-axis position of the robot corresponding to each scanning point was calculated by the inverse kinematic algorithm. In the mock-up test, the probe was properly contacted with most of the weld surfaces. The artificial stress corrosion cracking of approximately 6 mm in length and the electrical-discharge machining slit of 0.5 mm in length, 1 mm in depth and 0.2 mm in width given on the weld surface were detected. From the probe output voltage, it was estimated that the average probe tilt angle on the surface under scanning was 2.6°.
Highlights
Eddy current testing (ECT) techniques to detect a defect, especially a stress corrosion cracking (SCC), on a reactor vessel (RV) and reactor internals have been developed as one of the surface inspection methods for nuclear power plants [1,2,3,4,5,6,7]
In order to provide faster services, the defect detection capability of the ECT probe using the cross coil has been estimated for the inspection before and/or after the underwater laser beam welding for the dissimilar metal welding area at the RV nozzle in pressurized water reactors (PWRs) [12,13,14]
We describe the procedure of bottom mounted instrumentation (BMI) mock-up test; the results of measuring weld surface shape and defect detection tests
Summary
Eddy current testing (ECT) techniques to detect a defect, especially a stress corrosion cracking (SCC), on a reactor vessel (RV) and reactor internals have been developed as one of the surface inspection methods for nuclear power plants [1,2,3,4,5,6,7]. As a part of maintenance methods for the RV and reactor internals, laser peening and underwater laser beam welding techniques to prevent and repair from the SCC have been developed [8,9,10,11]. We describe the procedure of BMI mock-up test; the results of measuring weld surface shape and defect detection tests.
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