Experience with Eddy Current Imaging for the Detection of Cracks Within and Under the Clad in a Pressure Vessel

摘要

Typical reactor pressure vessel (RPV) inspections focus on performing ultrasonic volumetric inspections of the welds and their heat affected zone (HAZ). The clad region is not considered part of the pressure boundary by the ASME code and so traditionally has not been inspected. Recently there has been an increased interest in the condition of the clad and un-derclad regions of RPVs. One of the primary issues driving this interest is pressurized thermal shock (PTS). PTS would occur during a loss of coolant accident (LOCA) when the relatively cold water from the emergency core cooling system (ECCS) is pumped into the RPV. This quenching results in significant stress being applied to the RPV. If an RPV contains defects within or under the clad, the stress of a PTS could cause these defects to grow significantly, resulting in significant vessel damage and possibly even failure.