Jet pump inspection device has developed to inspect circumferential weld of BWR Jet Pump inlet mixer and diffuser, which is important for the structural integrity of Jet Pump and also plant safety. Figure 1 and 2 shows the weld lines and the configuration of the Inspection device. In order to inspect all length of the circumferential weld of the Jet Pump for more optimized evaluation, this inspection tool aims to inspect from the inside the Jet pump, which has no obstruction of the inspection.

In order to inspect the inner weld line without dismount the jet pump inlet mixer, the inspection probe scanner has been designed slim enough to pass through the narrow opening of the jet pump nozzle. Then the inspection probe scanner can be remotely positioned inside the jet pump transported by the wheeled platform with a telescopic guide. The inspection probe scanner can use not only UT sensor but eddy current test (ECT) sensor. In order to perform the inspection in short time, the inspection probe is not positioned to each weld line. Along the inner surface of the pipe, rotary scan is continuously carried out up from the bottom in the direction of a circumference. The scanning result is reconstructed using the position information on a welding line, and is evaluated later. The platform moves roundly on the top of the shroud, and set the tip of the telescopic guide to the opening of the jet pump nozzle. The inspection probe scanner is inserted through the gap of the nozzle. Then rotating the sensor arm, the probe scanner is pulled up by the cable, and the continuous rotary scan is performed spirally.

As mentioned above, this device is intended to realize non-critical inspection work of the Jet pump, by achieving parallel work with Fuel Loading or the other in-vessel work, without decomposing Jet pump assembly.

Fig. 1 Access method of the jet pump inspection Device

Fig. 2 System configuration of jet pump inspection device

1. (1) Components: Jet Pump (circumferential weld of inlet mixer and diffuser)

1. (2) Material: Stainless Steel and weld, nickel based alloy and weld

1. (4) Condition: In-vessel underwater environment

1. (1) The inspection device is composed of the probe scanner and the platform. This system enables the fast and easy installation, inspection and removal.
   
   - The platform has three-stage telescopic guide to be used to introduce the probe scanner into the Jet pump. This system enables fast and easy prove scanner installation.
   
   -The inspection probe scanner is light in weight and the diameter is 40 mm, to make the installation easier. Also a slip ring is arranged between the expansion arms and the sensor arms to enable the consecutive turns of the sensor arm. The drive air cylinder of the expansion arm will be arranged to the downside with the actual equipment. Moreover the tip of a cylinder rod will be separated from the part which opens the expansion arm, and the arm closes by its own weight.

1. (2) Using UT sensor, both inside and outside of the weld portion can be inspected. This lead to more precise SCC growth evaluation and then lead to longer inspection interval, compared to visual inspection from outside.

1. (3) This device is intended to achieve non-critical inspection work of the Jet pump, by achieving parallel work with Fuel Loading or the other in-vessel work.

Fig. 3 External view of the jet pump inspection device

Basic functional test using prototype device were conducted.

1. (1)Installation into the jet pump inlet mixer. (Fig.4 (a))
   
   The bottom end of the telescopic guide was positioned to the opening of the jet pump nozzle, and insertion/recovery of the probe scanner was performed.

1. (2)Scanning of the probe scanner. (Fig.4 (b))
   
   It was confirmed that the simulated UT sensor could move along the inner surface of the pipe by 75 mm/s, having attached the simulated UT sensor pushed by 3N. And the center of the probe scanner was adjusted focusing on pipe and the probe scanner could scan the UT sensor around the center of the pipe.

1. [1]M.Shimamura, Y.Togasawa, H.Hozumi, N.Mukai, Y.Yuguchi ; "Development of Remotely Operated Inspection Devices for BWR Internals", ICONE18, May 17-21,2010, Xi’an, China

Japan Society of Maintenology (ejam@jsm.or.jp)