Manufacturing method and device of control rods for nuclear reactors

Abstract

A method for manufacturing a control rod of a nuclear reactor, the control rod comprising a blade including neutron absorbers and a sheath, a tie rod for fixing the blade, a handle and a lower blade fixed to the tie rod and the blade. The method comprises a first step for cutting weep holes for water to cool the neutron absorbers in the sheath and cutting a periphery of the sheath, a second step for bending the sheath cut in the first step to a C-shape, a third step for inserting the neutron absorbers in a bent portion of the sheath formed by bending in the second step, a fourth step for successively welding the blade to the tie rod, the blade to the handle and the blade to the lower blade, and a fifth step for finishing portions welded in the fourth step.

What is claimed is:  
     
         1 . A method for manufacturing a control rod of a nuclear reactor, the control rod comprising a blade including neutron absorbers and sheathes, a tie rod for fixing the blade, a handle and a lower blade fixed to the tie rod and the blade, said method comprising: 
 a first step for cutting weep holes for water to cool the neutron absorbers in the sheath and cutting a periphery of the sheath;    a second step for bending the sheath cut in the first step to a C-shape;    a third step for inserting the neutron absorbers in a bent portion of the sheath formed by bending in the second step;    a fourth step for successively welding the blade to the tie rod, the blade to the handle and the blade to the lower blade; and    a fifth step for finishing portions welded in the fourth step.    
     
     
         2 . A method for manufacturing a control rod of a nuclear reactor according to  claim 1 , wherein in the fourth step for successively welding the blade to the tie rod, the blade to the handle and the blade to the lower blade, one of a YAG laser beam and a CO 2  laser beam is irradiated through an optical system on one of a position located immediately above a bevel and a position deviated in parallel from the bevel within a range of 2 mm.  
     
     
         3 . A method for manufacturing a control rod of a nuclear reactor according to  claim 2 , wherein when one of a YAG laser beam and a CO 2  laser beam is irradiated through an optical system on one of a position located immediately above a bevel and a position deviated in parallel from the bevel within a range of 2 mm, the laser beam is irradiated several times so as to lap over one another, shifted within a range of 0.1 to 2.0 mm from one of a first pass and a first pass target position.  
     
     
         4 . A method for manufacturing a control rod of a nuclear reactor according to  claim 2 , wherein when one of a YAG laser beam and a CO 2  laser beam is irradiated through an optical system on one of a position located immediately above a bevel and a position deviated in parallel from the bevel within a range of 2 mm, the laser beam is irradiated while traveling forward with circular motion in a diameter within 2 mm.  
     
     
         5 . A method for manufacturing a control rod of a nuclear reactor according to  claim 2 , wherein when one of a YAG laser beam and a CO 2  laser beam is irradiated through an optical system on one of a position located immediately above a bevel and a position deviated in parallel from the bevel within a range of 2 mm, a prism is inserted before a condenser lens contained in the optical system, and the laser beam is irradiated on the prism while the prism is rotating about an axis of the laser beam, so that a focus position of the laser beam is rotating relative to the condenser lens.  
     
     
         6 . A method for manufacturing a control rod of a nuclear reactor according to  claim 1 , wherein in the fourth step for successively welding the blade to the tie rod, the blade to the handle and the blade to the lower blade, TIG welding is performed on one of a position located immediately above a bevel and a position deviated in parallel from the bevel within a range of 3 mm.  
     
     
         7 . A method for manufacturing a control rod of a nuclear reactor according to  claim 1 , wherein the first step for cutting weep holes and a periphery of the sheath is carried out by laser cutting with high-pressure nitrogen gas.  
     
     
         8 . A method for manufacturing a control rod of a nuclear reactor according to  claim 1 , wherein the third step, raggedness of end faces of the sheath which are connected to the tie rod is aligned by laser cutting with high-pressure nitrogen gas.  
     
     
         9 . A method for manufacturing a control rod of a nuclear reactor according to  claim 1 , wherein in the third step, raggedness of end faces of the sheath which are connected to the tie rod is aligned by shear cutting.  
     
     
         10 . A method for manufacturing a control rod of a nuclear reactor according to  claim 1 , wherein in the fourth step for welding the blade to the tie rod, the blade to the handle or the blade to the lower blade, two slits are provided in one of the tie rod, the handle and the lower blade, projections of the blade is inserted in the slits, and the laser beam is irradiated on one of a boundary between the blade and the tie rod and a boundary between the blade and the lower blade.  
     
     
         11 . An apparatus for manufacturing a control rod of a nuclear reactor, the control rod comprising a blade including neutron absorbers inserted in a recess portion of a sheath formed by bending, a tie rod for fixing the blade, a handle fixed to the tie rod and an upper end of the blade, and a lower blade fixed to the tie rod and a lower end of the blade, 
 said apparatus comprising a welding apparatus for welding the blade to the tie rod, the blade to the handle and the blade to the lower blade,    said welding apparatus comprising: 
 a work head on which an image pickup apparatus is mounted;  
 a moving apparatus for moving the work head to a bevel position as designed in each of welding portions;  
 an image processing apparatus for processing an image signal picked up by the image pickup means;  
 a detecting apparatus for detecting an actual bevel position based on image data processed by the image processing apparatus;  
 arithmetic processing apparatuses for comparing the actual bevel position detected by the detecting apparatus with a bevel position as designed, and calculating deviation of the work head from the bevel position;  
 a control apparatus for providing the moving apparatus with a control command to move the work head by a distance corresponding to an amount of the deviation of the work head calculated by the arithmetic processing apparatus plus an amount of an offset of the work head and the image pickup apparatus; and  
 an apparatus for starting welding after completion of movement of the work head.  
   
     
     
         12 . An apparatus for manufacturing a control rod of a nuclear reactor, the control rod comprising a blade including neutron absorbers inserted in a recess portion of a sheath formed by bending, a tie rod for fixing the blade, a handle fixed to the tie rod and an upper end of the blade, and a lower blade fixed to the tie rod and a lower end of the blade, 
 said apparatus comprising a welding apparatus for welding the blade to the tie rod, the blade to the handle and the blade to the lower blade,    said welding apparatus comprising a fixing jig for fixing the blade by chillers worked so as to be externally accessible at a welding bevel, said fixing jig including bulk or two metal plates containing a cooling mechanism therein, and a space between the metal plates in which the blade including the neutron absorbers and the sheath is inserted.    
     
     
         13 . An apparatus for manufacturing a control rod of a nuclear reactor, the control rod comprising a blade including neutron absorbers and a sheath, a tie rod for fixing the blade, a handle and a lower blade fixed to the tie rod and the blade, said apparatus comprising: 
 a work table on which objects to be welded constituting the control rod are set and welding is carried out;    a laser oscillator for outputting one of a YAG laser beam and a CO 2  laser beam;    a work head comprising an optical system for transmitting the laser beam oscillated by the laser oscillator and converging it to the objects to be welded by a condenser lens;    an image pickup apparatus, mounted on the work head, for picking up images of a portion near a bevel of the objects to be welded;    an image processing apparatus for detecting a bevel position from the image picked up by the image pickup apparatus;    an arithmetic processing apparatus for comparing the bevel position obtained by the image processing apparatus with a bevel position as designed, and calculating deviation therebetween;    a servo motor for moving one of the work head and the work table by a distance corresponding to an amount of the deviation of the bevel position calculated by the arithmetic processing apparatus plus an amount of an offset of the work head and the image pickup apparatus; and    a control apparatus for driving and controlling the servo motor, said apparatus comprising at least two work heads and two work tables and a movable mirror between the laser oscillator and the work heads.    
     
     
         14 . An apparatus for manufacturing a control rod of a nuclear reactor, the control rod comprising a blade including neutron absorbers and a sheath, a tie rod for fixing the blade, a handle and a lower blade fixed to the tie rod and the blade, said apparatus comprising: 
 a work table on which objects to be welded constituting the control rod are set and welding is carried out;    a TIG welding torch;    an image pickup apparatus, mounted on the work head, for picking up images of a portion near a bevel of the objects to be welded;    an image processing apparatus for detecting a bevel position from the image picked up by the image pickup apparatus;    an arithmetic processing apparatus for comparing the bevel position obtained by the image processing apparatus with a bevel position as designed, and calculating deviation therebetween;    a servo motor for moving one of the TIG welding torch and the work table by a distance corresponding to an amount of the deviation of the bevel position calculated by the arithmetic processing apparatus plus an amount of an offset of the welding torch and the image pickup apparatus; and    a control apparatus for driving and controlling the servo motor,    said apparatus comprising at least two TIG welding torches and two work tables, which simultaneously or alternately perform welding.