Technology of Phased Array Ultrasonic Testing on Jet Pump Beam Installed in Reactor Pressure Vessel

Abstract

Abstract Jet pumps installed inside Reactor Pressure Vessel (RPV) of Boiling Water Reactor (BWR) have a function to circulate cooling water through the core region in RPV. Jet pump beam is one of the parts in the jet pump assembly. Jet pump beam is made of high nickel base alloy and could have potential of Intergranular Stress Corrosion Cracking (IGSCC) in case of high stress and poor material properties. Especially, it was reported that IGSCC occurred in beam bolt hole region (BB-1), transition region (BB-2) and tapered region (BB-3) of BWRs in US and other countries. Due to this reason, it is important to check the soundness of jet pump beam with BB-1, BB-2 and BB-3. In US, jet pump beam is inspected by Ultrasonic Testing (UT). However, there is some difficulty to perform UT because jet pump beams have some complicated shapes and are installed where it is not easily accessible. Since it causes man-hours increase to take out jet pump beams from RPV for inspection, inspection to be implemented in-vessel is preferable. In this study, we developed a Phased Array UT (PAUT) technology for flaw detection of jet pump beam without taking it out from RPV. In order to easily detect flaws, immersion non-contact probe was used. Furthermore, appropriate PAUT technique were applied in accordance with the shape of each region of BB-1, BB-2 and BB-3. Two types of UT equipment for jet pump beams were developed: ultrasonic incidence from lateral surface and ultrasonic incidence from upper surface. The UT equipment was installed on jet pump beam bolt grasping jet pump beam trunnion. The UT equipment can be positioned on the basis of the locations of jet pump beam bolts. We could inspect center cracks that were 5.0 mm length, 1.0 mm depth at BB-2/BB-3, and could inspect corner crack that was 2.5 mm length, 1.0 mm depth at BB-2 by developed PAUT equipment.