Patent Number: 051732483
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a remote control apparatus for maintaining in-vessel components in a structure having an inner torus space, and in more particular to a remotely controlling maintenance apparatus adapted for a tokamak type nuclear fusion reactor. 2. Description of the Related Art With a nuclear fusion reactor in which a D-T reaction occurs, the maintenance of the in-vessel components must always be remotely controlled in order to protect the operator from radiation produced in the reactor after it begins to be run. As shown in FIG. 34 the tokamak type nuclear fusion reactor has a hollow donut shape vessel 1, the torus space 2 of which has an outer diameter of substantially 10 meters and which is covered with a shield member 3 having a thickness of several meters. The peripheral components such as a toroidal coil 4 and a poloidal coil 5 surround the inner torus space 2 in a complicated manner. Accordingly, it is necessary to insert a maintenance device housed in a cask 8 disposed outside of the reactor into the torus space 2 through maintenance ports 9 each extending radially of the torus space 2 and further to move the maintenance device in the circumferential directions in the space 2 so that the maintenance device is accessible to the in-vessel components such as diverter plates 6 and first wall armor tiles 7 without interference with the peripheral components. Since the in-vessel components include very heavy components such as the diverter plate weighing more than 1 ton, these heavy components impose many technical problems on a maintenance device. The conventional maintenance devices are classed into two types. One of them has, as shown in FIG. 35, a cantilever type multi-joint arm (articulated arm) 10 which has its base joint disposed at the outside of the reactor. The arm 10 is inserted in the torus space 2 through the maintenance port 9 to have access to the in-vessel components. The maintenance devices of this type have been used in the United States and Europe. However, as the vessel becomes larger and larger, the articulated arm becomes longer and longer. In addition, the in-vessel components to be handled become heavier. These make it difficult to accurately set the distal end of the articulated arm 10 at a required position. Further, the maintenance device of this type has the problem that its operational efficiency and reliability are lowered because the long overall articulated arm 10 must be moved in the narrow torus space 2 at each time when the in-vessel components are handled. An example of the maintenance devices of this type is disclosed in the thesis titled "THE TFTR MAINTENANCE MANIPULATOR" by M. Selig et. al. (Proceedings of a Technical Committee Meeting on Robotics and Remote Maintenance Concepts for Fusion Machines--Karlsruhe, Feb. 22-24, 1988--issued by The International Atomic Energy Agency). The maintenance device of the other type has a vehicle which runs on a rail laid in the torus space so that the vehicle is accessible to the in-vessel components to handle them. The maintenance device of this type has the features that the positioning of the vehicle at the time of access to the in-vessel components is accurately carried out due to one degree of freedom defined by the running of the vehicle on the rail and that the in-vessel components are efficiently transported. An example of the rail-mounted devices is disclosed in the thesis titled "VEHICLE CONCEPT FOR NET IN-VESSEL INSPECTION AND MAINTENANCE" by D. Maisonnier (Proceedings of a Technical Committee Meeting on Robotics and Remote Maintenance Concepts for Fusion Machines--Karlsruhe, Feb. 22-24, 1988--issued by The International Atomic Energy Agency). Maisonnier's system comprises two boom rails extended through 90.degree. in the torus space. The boom rails are inserted therein through the opposed maintenance ports and connected at their front ends to form a vehicle-guiding rail extending through 180.degree. in the torus space. Each boom rail comprises three curved box-like link elements serially articulated at their ends to one after another. Maisonnier's thesis only briefly describes that the joint of each link member is driven by a lever mechanism and depicts that each link element contains a drive rod for driving the corresponding joint. The vehicle moves radially outwardly along the rail. In the rail system, the semi-circularly extended rail is supported on its both ends so that the rigidity can be made larger than the articulated arm as shown in FIG. 35. However, the semi-circularly arcuated rail is supported only on both ends and it cannot be supported at its central portion because the vehicle is moved along the radially outer side of the rail. When a heavy invessel component is handled by the vehicle at the central portion of the rail, a large bending moment and a large torsional moment are exerted on and at the vicinity of the end portion of the rail at which the rail is supported so that the rail is likely to be bent. Therefore, the arcuated links forming a boom rail must be rendered large in size as well. For example, when the radius curvature of the rail is 5,200 mm, the height, the width and the length of the links should be 1,000 mm, 150 mm and 2,250 mm, respectively. A large space for storing the rail is required. Further, the rail requires complicated mechanisms such as lever mechanisms for extending and shrinking the rail and drive rods. This requires complicated control when the rail is extended in the vessel. A circular arc telescope type rail system can be used to extend a rail in the torus space. However, it has the drawback that its reliability is lowered when it remains exposed under radiation of a high level during a long maintenance time, because an actuator or a complicated driving mechanism must be provided in the rail. Further, the thickness of the telescope rail is not constant throughout the whole length. This makes it difficult to guide and move the vehicle in a stable state and makes the structure and the control of the rail complicated. SUMMARY OF THE INVENTION The object of the invention is to provide a remote control maintenance apparatus which has a high operational efficiency and reliability and is particularly useful for a tokamak nuclear fusion reactor. In order to attain the object, this invention provides a remote control apparatus for maintaining a structure which comprises a vessel having a torus space formed therein and a plurality of maintenance ports extending radially for causing the torus space to communicate with the outside of the vessel and components arranged in the vessel, comprising: a rail having generally similarly arcuated links pivoted to one after another and extensible in the circumferential directions in the torus space, the links forming, in the torus space, a continuous semi-circular arc having a center substantially coincident with the center of the torus space when the links are extended; a vehicle carrying at least one manipulator for handling the components and guided along the rail extended in the torus space; rail housing means arranged outside of the vessel, for housing the rail when the remote control device is not used; rail mounting means carrying the last link of the rail and delivering, into the torus space, the links housed in the rail housing means from the first link to the last link in succession through one of the maintenance ports and causing the links to form the continuous semi-circular arc; and a rail supporting device inserted in the torus space through another maintenance port adjacent to the first mentioned maintenance port, for supporting the central portion of the rail. In this remote control maintenance apparatus, the rail comprises a plurality of links and joints for articulating the adjacent links and each provided with a locking mechanism for locking the respective link at the position in which the arcuated links form the semi-circular arc and the rail is transmitted into the torus space by means of a transmitting mechanism. In this respect, the arcuated links can be housed in the rail housing means having a limited space. Further, when the rail is transmitted into the torus space, the links are delivered from the first one to the last one in succession by means of the rail mounting device, whereby the links pass through a narrow maintenance port easily. The rail formed in a continuous circular arc shape is supported by means of the rail supporting device inserted from another maintenance port adjacent to the first mentioned maintenance port. This not only renders the rigidity of the rail high and the movement of the vehicle stable but also minimizes the overall apparatus. Further, the stable operation of the vehicle makes the operation of the manipulator mounted on the vehicle stabilized, enabling the components to be handled at a high operational efficiency. Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.