Yasuhiro Yuguchi

Underwater cutting technology of thick stainless steel with YAG laser

In nuclear power plants, irradiated materials like Control Rod (CR) should be stored underwater after service. Due to reducing the storage space, underwater cutting technology is expected. In this study, we developed underwater cutting technology of thick stainless steel with YAG laser in order to cut used CR. Preliminary tests were performed with flat plate test-pieces to optimize the cutting conditions. Due to creating a local dry area between nozzle and test-piece, high-pressure air was blown from the nozzle. Underwater laser cutting was carried out by laser irradiation power of 4 kW, changing the parameters of cutting speed, distance between the nozzle and test-piece, and thickness of the test-piece. We also investigated the wastes like dross and aerosols by laser cutting. Amount of dross was approximately 0.1 kg/m after cutting a 14 mm thick stainless steel plate, which is estimated to be less than other cutting method. Based on these results, we developed underwater cutting system of CR test-piece with YAG laser as a mock-up test. In the cutting torch, there was tracking system was introduced to keep the distance between the nozzle and the test-piece constant, and cutting monitor was also set-in to detect whether the test-piece was successfully cut or not. We have already tried to cut the CR test-piece with this facility and successfully cut in half.

Development of a robotic system for nuclear facility emergency preparedness — observing and work-assisting robot system

YASUHIROYUGUCHI and YOSHIFUMI SATOH 2 1 Automatic Machine System Engineering Group Mechanical Technology and Design Department Isogo Nuclear Engineering Center, Toshiba Corp., 8 Shinsugita-cho Isogo-ku, Yokohama 235-8523, Japan, yasuhiro.yuguchi@toshiba.co.jp 2 Nuclear Mechanics and Systems Technology R&D Department Power and Industrial Systems R&D Center, Toshiba Corp., 8, Shinsugita-cho Isogo-ku, Yokohama 235-8523, Japan, yoshifumi2.sato@ toshiba.co.jp

Underwater Remote Handling Equipment for Reactor Internals Maintenance

More than fifty nuclear reactors generate about thirty-five percent of electricity in Japan. The need to operate these reactors safely and in a stable manner constitutes a very important issue. On the other hand, aged reactors are increasing and they are not necessarily designed and constructed using the latest technology. Stress Corrosion Cracking (SCC) on reactor internal components has become a major concern regarding aged reactors in recent years. Usually maintenance work such as inspection, repair, and preventive maintenance for core components is done by using underwater remote handling and robotic technology. It becomes very important to develop not only new efficient technology for inspection, repair, and preventive maintenance for all suspect components and but also the associated application technology for execution in a reactor. We have been developing several kind of remote handling equipment for underwater maintenance work. This paper describes some results obtained in the area of underwater remote handling that can contribute to the progress of plant reliability.© 2002 ASME

Phased Array UT Application for Boiling Water Reactor In-Vessel Inspection

This paper describes development and application of Phased Array Ultrasonic Testing (UT) and Remotely Operated Vehicles (ROV) for In-Vessel Internals Inspection. Stress Corrosion Crack (SCC) on reactor internals is one of the most important issues since 1990s, and demand to inspect the reactor internals is increasing. Instrument manufactures and inspection venders have developed and applied 1) Phased Array UT technologies and technique as one of our Non-Destructive Examination (NDE) technologies, 2) several kinds of ROVs and special tools for probe delivery and positioning. They are available and effective in In-Vessel Inspection (IVI) and maintenance, which shall be conducted in the narrow room under water. Furthermore, the UT technique for Alloy 182 weld that used to be difficult to detect and size flaws was developed and deployed in the BWR IVI. UT experiences in reactor vessels are increasing in recent years. An immersion technique by Phased Array UT is a key to perform the In-vessel UT on a complex geometric surface to be inspected, and to achieve very wide accessible range by ROVs or simple special tools efficiently. Advantages of the water immersion method and a ROV development result are shown in this paper. Particularly, TOSHIBA developed a flat type ROV for Shroud (Shroud ROV), which can be held against the surface of the shroud by thrusting propellers and scan mechanically through narrow gap within 2 inches {50mm}. The ROV’s positioning accuracy and applications for Shroud UT are shown. As the field experience, this introduces the UT results for CRD Stub tube Alloy 182 weld that is located on the vessel bottom head in Hamaoka UNIT 1 of Chubu Electric Power Company in Japan. An axial SCC flaw was detected by underwater visual testing, after the CRD stub tube leakage was detected. Then UT examination for the flaw was accomplished on the Alloy 182 weld in the vessel. We evaluated that the flaw penetrated into the weld metal of the CRD stub tube-pat weld and didn’t propagate into the low alloy of Reactor Pressure Vessel base metal. After UT sizing, the CRD stub tube was removed and replaced. The examination result was proven to have a good agreement with the actual crack depth. As a result, the efficiency of our Phased Array Technique was confirmed. As the other immersion method application, UT coverage example and accessible range for Shroud inspection are shown.Copyright

Development of Remotely Operated Inspection Devices for BWR Internals

Two ultrasonic testing (UT) devices to inspect the internals of nuclear reactor have been developed. The one is a jet pump UT device to inspect the inner weld line of the jet pump, and the other is a shroud UT device to inspect the outer weld line of the shroud. The jet pump UT device is mainly composed of an inspection probe scanner and a wheeled platform with a telescopic guide. Since the inspection probe scanner has been designed slim enough to pass through the narrow opening of the jet pump nozzle, it can be remotely positioned inside the jet pump transported by the wheeled platform. The shroud UT device is mainly composed of a flat-type remotely operated vehicle (ROV) and a positioning mast of ROV. The ROV is installed remotely on the outer surface of the shroud using the positioning mast. And the ROV has been designed thin enough to pass through the narrow gap between the jet pump and the shroud, so that it can move horizontally on the surface of the shroud with automatic cable feeding. Consequently, the proposed remote and automatic inspection devices can perform the inspection work in short time without using fuel handling machine (FHM). Therefore, the inspections can be performed simultaneously with the refueling work, which contributes to the shortening of regular inspection periods of nuclear power plants.Copyright

Remotely Operated Equipments for In-Vessel Inspection in BWRs

This paper describes development and application of remotely operated equipments for reactor internals ultrasonic testing (UT) and visual testing (VT) in boiling water reactors (BWRs) to enhance the availability of operating nuclear power plants. Stress Corrosion Cracking (SCC) in reactor internal components causes relatively low operating rate of BWR as one of the most important issues since the 1990s, and demand to inspect the reactor internals become greater. The remotely operated equipments have been developed for in-vessel inspection of core shrouds, shroud supports, jet pumps and so on. The equipments are evaluated in the point of the positioning precision as an application of a phased array UT technique and visual length measurement system. And as results of application to the actual plants and improvement, a Shroud vehicle, a Crawler vehicle and a Visual position measurement system are enhanced in an aspect of the accessible range and/or positioning precision. Their configurations and functional testing results are shown in this paper. As the other application, micro replication devices are developed for CRD Stub tube and shroud in BWR. This paper indicates the functional testing result using the prototype for the CRD stub tube with observing material microstructure.Copyright