Improvement of Indication Signal Evaluation in Control Rods In-service Inspection

Considering that an indication signal may not be evaluated certainly in Rod Cluster Control Assembly in-service eddy current test, the test specimen with artificial flaws were fabricated, the magnet core was installed in coil assembly to produce magnetic saturation coils in order to eliminate possible magnetic impact on the control rods, and 3-point centre aligned device was changed with 6-point center aligned device in coil assembly to improve the examination condition and enhance the inspection reliability. Test and examination results showed that the current inspection technique can detect the axial and circumferential flaws for both bobbin and pancake coils; for pancake coils, it can distinguish single or multiple flaws, but not for bobbin coils; and the eddy current signal was signified by axial flaws. However, structure signals sometimes were similar with circumferential flaw signals.