Kiyoshi Oka

Development of optical components for in-vessel viewing systems used for fusion experimental reactor

Optical components including imagefiber, periscope, glass, reflecting mirror and adhesive for lens are essential elements of in-vessel viewing system use for fusion experimental reactor and extensive of gamma irradiation tests have been conducted. These components were irradiated in the range of 1 MGy - 100 MGy under the average exposure dose rate of 1 X 106 R/h. As a result, the observation limit of the imagefiber specially fabricated for radiation hard is obtained to be 12 MGy at a illuminance of 8500 lx. Deterioration of transmissivity of three kinds of glass (alkaline barium glass, lead glass and synthetic quartz glass) is small compared with standard glass for commercial periscope. A periscope which was made of these glasses is visible even after 20 MGy at 8500 lx and in case of the standard periscope, the observation limit is 1 kGy at 8500 lx. Decrease in the reflectance on chromium nitride coated reflecting mirror is extremely small than aluminum coated and platinum coated mirrors at accumulated dose of 100 MGy. Two types of adhesive made of polyester resin and epoxy resin became discolored and exfoliated after 50 MGy.

Mechanical characteristics and position control of vehicle/manipulator for ITER blanket remote maintenance

Abstract In International Thermonuclear Experimental Reactor (ITER), blanket maintenance requires the 4-tonne module handling with high positioning accuracy of ±2 mm. In order to meet this requirement, it is essential to suppress the dynamic deflection and vibration of the remote handling equipment due to sudden transfer of the module weight from/to the back-plate supports to/from the equipment itself during installation and removal. A new control scheme was proposed and tested so as to suppress the dynamic behaviors. As a result, the dynamic deflection of the rail and the acceleration of the manipulator were sucesessfully decreased to nearly zero. Based on the test results, the proposed control scheme was concluded to be effective so as to suppress this kind of dynamic effect during heavy component handling.

Clinical study using novel endoscopic system for measuring size of gastrointestinal lesion

AIM To verify the performance of a lesion size measurement system through a clinical study. METHODS Our proposed system, which consists of a conventional endoscope, an optical device, an optical probe, and a personal computer, generates a grid scale to measure the lesion size from an endoscopic image. The width of the grid scale is constantly adjusted according to the distance between the tip of the endoscope and lesion because the lesion size on an endoscopic image changes according to the distance. The shape of the grid scale was corrected to match the distortion of the endoscopic image. The distance was calculated using the amount of laser light reflected from the lesion through an optical probe inserted into the instrument channel of the endoscope. The endoscopist can thus measure the lesion size without contact by comparing the lesion with the size of the grid scale on the endoscopic image. (1) A basic test was performed to verify the relationship between the measurement error eM and the tilt angle of the endoscope; and (2) The sizes of three colon polyps were measured using our system during endoscopy. These sizes were immediately measured by scale after their removal. RESULTS There was no error at α = 0°. In addition, the values of eM (mean ± SD) were 0.24 ± 0.11 mm (α = 10°), 0.90 ± 0.58 mm (α = 20°) and 2.31 ± 1.41 mm (α = 30°). According to these results, our system has been confirmed to measure accurately when the tilt angle is less than 20°. The measurement error was approximately 1 mm in the clinical study. Therefore, it was concluded that our proposed measurement system was also effective in clinical examinations. CONCLUSION By combining simple optical equipment with a conventional endoscope, a quick and accurate system for measuring lesion size was established.

Force control of remote maintenance robot for the ITER

This paper proposes a force control scheme for a remote maintenance robot for nuclear fusion reactors. In the International Thermonuclear Experimental Reactor (ITER), a remote maintenance system which can perform the assembly of heavy objects with high positional accuracy is required. For this kind of task, force control is much more preferable than position control. We applied force control to an experimental blanket-handling system and performed several experiments on the assembly of a dummy blanket. The experimental results illustrate the validity of the force control for the task.

Remote Operation of the Radiation-Proof Robot Using the Direct Master Arm System

Abstract In Japan Atomic Energy Research Institute, we have developed a radiation-proof robot (called Ra BOT) for accomplishing a given mission under severe conditions such as gamma radiation. RaBOT can be maneuvered by remote commands from the operation desk with the master arm system. However, the system has become large and complicated because the master arms have the same number of active joints as the slave manipulators; moreover, that provide not only the required sensory feedbacks on the operator but also uncomfortable constraints. This report examines the performance of teleoperation for the master arm system and proposes a new type of master arm as the alternative.

Development of in-pipe access welding and cutting tool using YAG laser

In the International Thermonuclear Experimental Reactor (ITER), the blanket is categorized into the schedule maintenance component and has to be replaced by remote handling technology due to activation by the 14-MeV neutrons during DT operations. The blanket is segmented into a number of modules to facilitate remote operation and requires the welding and cutting of cooling pipes connected to each module from the inside of the pipe due to space constraints. A prototype tool fabricated for branch pipe welding/cutting demonstrates the required mobility for traveling the cooling pipe with a diameter of 102.3 mm and a bent radius of 400 mm, and for accessing to the branch pipe with a diameter of 54.5 mm. The welding and cutting performance has been also tested, including the dependency of laser power, processing speed, and gaps on weldability. In addition, a composite optical fiber composed of a number of thin fibers arranged around a core fiber is also tested for direct viewing of the edge preparation before welding and for monitoring during welding/cutting. This paper describes the test results of the prototype tool performance and of in-pipe access welding and cutting operations.

Development of bore tools for blanket cooling pipe connection in ITER

According to the ITER R&D program, the bore tools for welding, cutting and weld inspection of blanket cooling pipes by the in-pipe access have been developed. In order to meet the ITER requirements, the YAG laser transmitted through a flexible optical fiber and the electro-magnetic acoustic transducer (EMAT) were adopted for welding/cutting and weld inspection, respectively. Their performance have been verified, including the movement and positioning in the cooling pipes. In addition, the radiation hard ultrasonic transducer (UT) and the leak detectors have been also tested. This paper describes the design outline and test results of bore tools developed for welding, cutting and weld inspection of the ITER blanket cooling pipes.

Laser technology for maintenance of nuclear pipe

A remote maintenance technology to process cooling pipes internally for the ITER (International Thermonuclear Experimental Reactor) has been developed. The fundamental welding properties of austenite stainless steel obtained by using high power YAG laser indicates the tendency of porosity increase as the welding depth increases. It is also found out that the occurrence of porosity was prevented when N2 gas was used as a shielding gas and that the material strength of weld joint is kept unchanged. Furthermore, a processing equipment that can access the cooling pipes internally has been developed. The main body of this processing equipment can be inserted into a cooling pipe and consists of an focusing optics, clamping and driving mechanism, and an optical fiber. Operational experiments of this processing equipment is carried out and the basic verification experiments such as welding and cutting tests were conducted. As a result, a good quality of pipe welding joint was obtained without any defects.

Development of a remote handling system for replacement of armor tiles in the Fusion Experimental Reactor

Abstract The armor tiles of the Fusion Experimental Reactor (FER) planned by JAERI are categorized as scheduled maintenance components, since they are damaged by severe heat and particle loads from the plasma during operation. A remote handling system is thus required to replace a large number of tiles rapidly in the highly activated reactor. However, the simple teaching—playback method cannot be adapted to this system because of deflection of the tiles caused by thermal deformation and so on. We have developed a control system using visual feedback control to adapt to this deflection and an end-effector for a single arm. We confirm their performance in tests.

FEASIBILITY STUDY OF BLANKET HANDLING SYSTEM FOR FUSION EXPERIMENTAL REACTOR

Remote maintenance technology is essential for the realization of fusion experimental reactors, such as International Thermonuclear Experimental Reactor(ITER) and Fusion Experimental Reactor(FER), because the reactor components are activated by 14-MeV neutrons. Japan Atomic Energy Research Institute(JAERI) has been conducting the research and development to demonstrate the feasibility of remote maintenance equipments mainly for key components, such as divertor plates and blanket modules. Especially, the blanket modules are asymmetric structure, and are the heaviest(80 tons max. in weight) and the slenderest(20 m max. in length) of the in-vessel components to be handled remotely. The blanket modules are not frequently maintained but require high-grade maintenance technology, because the replacement of such structures must be carried out through the limited space of the upper port within the positioning accuracy of a few mm. In FER, JAERI has developed a new maintenance concept for the blanket modules. Key features of this concept are (1) the reliable toroidal movement of the blanket side modules inside the vacuum vessel in the cooperation of main and sub manipulators, (2) adjustment of the eccentric posture of the asymmetric blanket modules by a counter weight and (3) accurate installation of the blanket modules along the guide structures on the vacuum vessel. The feasibility study of the concept of the blanket handling system has been demonstrated by a 1/5 scale model in computer control.