Abstract:
Provided is a coil assembly having improved heat resistance for use in a control rod driver, in which the heat resistance of coils is improved to increase the lifespan thereof and the deterioration of the coils and the fall of a control rod are thus securely prevented from occurring due to continuous operations of the control rod driver during an automatic load follow operation, thereby improving the safety and economic feasibility of a nuclear power plant, and a method for manufacturing the same. The coil assembly includes a covered wire ( 110 ) which includes a coil wire ( 111 ) and a polyether ether ketone (PEEK) coating layer ( 112 ) covering an outer circumferential surface of the coil wire ( 111 ) and is wound in multiple layers; a coil coating layer ( 130 ) formed by filling gaps in the covered wire ( 110 ) with varnish; an insulating tape layer ( 120 ) covering external sides of a wound layer of the covered wire ( 110 ) insulated by the coil coating layer ( 130 ); and silicon molding ( 140 ) covering external sides of the insulating tape layer ( 120 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The application is a continuation of International Application No. PCT/KR2011/000690 filed on Feb. 1, 2011, which claims priority to Korean Application No. 10-2011-0008242 filed Jan. 27, 2011, which applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a coil assembly for a control rod driver for driving a nuclear power plant and a method for manufacturing the same, and more particularly, to a coil assembly for a control rod driver having improved thermal resistance in which coil deterioration is reduced by improving the heat resistance and thermal conductivity of coils to securely prevent coil deterioration and the fall of a control rod, caused by continuous operations of the control rod driver during an automatic load follow operation, thereby improving the safety and economic feasibility of a nuclear power plant, and a method for manufacturing the same. 
       BACKGROUND ART 
       [0003]    A nuclear reactor is a device designed to gradually discharge a large amount of energy that is instantaneously emitted due to a mass defect occurring during nuclear fission of a nuclear fuel, thereby enabling nuclear energy to be applied to real life. 
         [0004]      FIG. 1  is a cross-sectional view of a conventional nuclear reactor and a control rod driver. 
         [0005]    A fuel assembly  2  is accommodated in the nuclear reactor  1 . An assembly of a control rod  3  and a control rod driver attaching nozzle  4  that are configured to adjust the number of neutrons absorbed by nuclear fuel so as to control the combustion of the nuclear fuel, and a plurality of control rod driver  5  including control rod driving motors are installed on upper part of the nuclear reactor  1 . The control rod  3  is vertically driven by the control rod driver  5 . 
         [0006]    The control rod driver is operated by a current signal flowing through four control rod driving coils, i.e., an upper lift coil (UL), an upper gripper coil (UG), a lower lift coil (LL), and a lower gripper coil (LG), and are configured to control the vertical movement of the control rod  3  by controlling motor driving using an electromagnetic force generated by power supplied to cables of the control rod driving coils. 
         [0007]    The control rod driving coils used in the control rod driver  5  are required to have heat resistance so that the control rod driving coils may be prevented from deteriorating due to continuous operations of the control rod driver  5  during an automatic load follow operation. However, since coil wires are conventionally covered with an enamel-based insulating material, the coils deteriorate at a temperature that is higher than 220° C. to stop electricity generation. Thus, power generation is stopped until the system is re-operated, electric current is conducted through the coils due to the deterioration of and damage to the coils, and insulation breakdown thus occurs, causing the fall of the control rod and thereby degrading safety and reliability. 
       SUMMARY 
       [0008]    It is an objective of the present invention to provide a coil assembly for use in a control rod driver, in which the heat resistance of control rod driving coils is improved to increase the lifespan thereof and the deterioration of the coils and the fall of a control rod are thus securely prevented due to continuous operations of the control rod driver during an automatic load follow operation, thereby improving the safety and economic feasibility of a nuclear power plant, and a method of manufacturing the same. 
         [0009]    To accomplish the objective, a coil assembly having improved heat resistance for use in a control rod driver includes a covered wire including a coil wire and a polyether ether ketone (PEEK) coating layer covering an outer circumferential surface of the coil wire, and wound in multiple layers; a coil coating layer formed by filling gaps in the covered wire with varnish; an insulating tape layer covering external sides of a wound layer of the covered wire insulated by the coil coating layer; and silicon molding covering external sides of the insulating tape layer. 
         [0010]    The coil wire may be a copper wire having no splices. 
         [0011]    Both ends of the coil wire may be bound with a lead wire of a power supply cable by brazing. 
         [0012]    To accomplish the objective, a method of manufacturing a coil assembly having improved heat resistance for use in a control rod driver includes manufacturing a covered wire by forming a polyether ether ketone (PEEK) coating layer on an outer circumferential surface of a coil wire; forming a wound layer by winding the covered wire in multiple layers, and binding both ends of the coil wire with a lead wire of a power supply cable; forming an insulating tape layer around the wound layer; forming a coil coating layer by filling gaps in the covered wire with varnish; drying the coil coating layer in a drying furnace; and applying silicon molding on an outer circumferential surface of the dried resultant. 
         [0013]    The forming of the coil coating layer may be performed by vacuum impregnation. 
         [0014]    In a coil assembly having improved heat resistance for use in a control rod driver and a method for manufacturing the same, the coil assembly is manufactured by forming a covered wire by covering an outer circumferential surface of a coil wire with a polyether ether ketone (PEEK) coating layer having chemical and mechanical characteristics such as heat resistance, forming a coil coating layer by filling gaps in the covered wire that is wound in multiple layers with varnish by vacuum impregnation, and sealing an outer circumferential surface of the coil coating layer with silicon molding. Thus, the coil assembly has higher heat resistance and lifespan than a conventional coil for use in a control rod driver, and greatly reduces coil deterioration and the fall of a control rod due to continuous operations of a control rod driver during an automatic load follow operation, thereby improving the safety and economic feasibility of a nuclear power plant. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a cross-sectional view of a conventional nuclear reactor and a control rod driver. 
           [0016]      FIG. 2  is a cross-sectional view of a fully assembled state of a control rod driver according to an embodiment of the present invention. 
           [0017]      FIG. 3(   a ) is a plan view of a coil assembly having improved heat resistance for use in a control rod driver, and  FIG. 3(   b ) is a cross-sectional view taken along line A-A of  FIG. 3(   a ). 
           [0018]      FIG. 4  is a cross-sectional view of a state in which a coil assembly having improved heat resistance for use in a control rod driver is combined with a coil housing according to an embodiment of the present invention. 
           [0019]      FIG. 5  is a flowchart illustrating a method of manufacturing a coil assembly having improved heat resistance for use in a control rod driver according to an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
       [0020]      
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 1: nuclear reactor 
                 2: nuclear fuel assembly 
               
               
                 3: control rod 
                 4: control rod driver 
               
               
                   
                 attaching nozzle 
               
               
                 5: control rod driver 
                 100, 100-1, 100-2, 100-3, and 
               
               
                   
                 100-4: coil assembly 
               
               
                 110: covered wire 
                 111: coil wire 
               
               
                 112: PEEK coating layer 
                 120: insulating tape layer 
               
               
                 130: coil coating layer 
                 140: silicon molding 
               
               
                 210, 220, 230, 240: coil housing 
                 211, 221, 231, 241: lead wire 
               
               
                   
                 connector 
               
               
                 310: the first control rod driving coil unit 
                 320: the second control rod 
               
               
                   
                 driving coil unit 
               
               
                 330: the third control rod driving coil unit 
                 340: the fourth control rod 
               
               
                   
                 driving coil unit 
               
               
                 410: upper plate 
                 420: lower plate 
               
               
                 430, 440, 460, 470: connection plate 
                 450: housing connection 
               
               
                   
                 member 
               
               
                 431, 441, 461, 471: retainer coupling 
                 500: motor housing 
               
               
                 610: cable box 
                 620: cable assembly 
               
               
                 621: power supply cable 
                 622: connector 
               
               
                 710: cooling shroud 
                 720: upper shroud 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION 
       [0021]    Hereinafter, structures and operations of exemplary embodiments of the present invention will be described in greater detail with reference to the accompanying drawings. 
         [0022]      FIG. 2  is a cross-sectional view of a fully assembled state of a control rod driver according to an embodiment of the present invention.  FIG. 3(   a ) is a plan view of a coil assembly having improved heat resistance for use in a control rod driver, and  FIG. 3(   b ) is a cross-sectional view taken along line A-A of  FIG. 3(   a ).  FIG. 4  is a cross-sectional view of a state in which a coil assembly having improved heat resistance for use in a control rod driver is combined with a coil housing according to an embodiment of the present invention. 
         [0023]    Referring to  FIG. 2 , the control rod driver according to the present invention includes coil assemblies  100 ,  100 - 1 ,  100 - 2 ,  100 - 3 , and  100 - 4 , and first to fourth control rod driving coil units  310 ,  320 ,  330 , and  340  in which the coil assembly  100  is mounted on inner circumferential surfaces thereof and that include coil housings  210 ,  220 ,  230 , and  240  acting as a passage of an electromagnetic field induced when electric current is conducted through the coil assembly  100 , respectively. An upper portion of the first control rod driving coil unit  310  and a lower portion of the fourth control rod driving coil unit  340  are combined with an upper plate  410  and a lower plate  420  each having a hole through which a motor housing  500  passes on a center portion thereof, respectively. 
         [0024]    The upper plate  410  functions not only as a passage of an electromagnetic field when electric current is conducted through the coil assembly  100  but also as a cover of an upper face of the first coil housing  210 . Screw taps are formed on the upper plate  410  to recover an assembly of the coil housings  210 ,  220 ,  230 , and  240 . 
         [0025]    The lower plate  420  functions not only as a passage of an electromagnetic field when electric current is conducted through the coil assembly  100  but also as a cover of a lower face of the fourth coil housing  240 , and supports all the control rod driving coil units  310 ,  320 ,  330 , and  340  when the motor housing  500  is assembled. 
         [0026]    An inner side of the coil assembly  100  mounted on the inner circumferential surfaces of the coil housings  210 ,  220 ,  230 , and  240  is combined with the motor housing  500 . In the motor housing  500 , a motor assembly (not shown) which is a control rod driver is installed. Thus, the motor housing  500  is designed to endure pressure of a nuclear reactor, and transmit an electromagnetic force applied from the coil assembly  100  combined with external surfaces of the motor housing  500 . 
         [0027]    Lead wire connectors  211 ,  221 ,  231 , and  241  in which both ends of coils of the respective coil assemblies  100 - 1 ,  100 - 2 ,  100 - 3 , and  100 - 4  and a lead wire of a power supply cable  621  are united are formed at one side of the coil housings  210 ,  220 ,  230 , and  240 . The lead wire of the power supply cable  621  and both ends of the coils of the respective coil assemblies  100 - 1 ,  100 - 2 ,  100 - 3 , and  100 - 4  are electrically connected to a connection terminal inside a cable box  610 . 
         [0028]    It is desired that both of the ends of the coils of the respective coil assemblies  100 - 1 ,  100 - 2 ,  100 - 3 , and  100 - 4  and the lead wire of the power supply cable  621  may be united using brazing to minimize resistance therebetween. 
         [0029]    The power supply cable  621  and a connector  622  coupled to one end of the power supply cable  621  form a cable assembly  620  configured to supply power to coils. 
         [0030]    A cooling shroud  710  that guides cooled air to uniformly flow along the inside thereof is formed around the coil housings  210 ,  220 ,  230 , and  240  to absorb heat generated by the coil assembly  100 . An upper shroud  720  is formed on the coil housing  210 , and a control rod location indicator (not shown) is installed in the upper shroud  720 . The upper shroud  720  is combined with the coil housing  210  to recover the control rod driver. 
         [0031]    Here, although the motor housing  500 , the cooling shroud  710 , and the upper shroud  720  are not elements of the control rod driver, these elements have also been illustrated and described above to assist in understanding of the present invention. 
         [0032]    Referring to  FIG. 3 , the coil assembly  100  for use in the control rod driver includes a coil wire  111 , a polyether ether ketone (PEEK) coating layer  112  covering an outer circumferential surface of the coil wire  111 , a covered wire  110  that includes the coil wire  111  and the PEEK coating layer  112  and is wound in multiple layers, a coil coating layer  130  formed by filling gaps in the covered wire  110  that is wound in multiple layers with varnish, an insulating tape layer  120  covering external sides of a wound layer of the covered wire  110  insulated by the coil coating layer  130 , and a silicon molding  140  that seals the insulating tape layer  120  while encompassing external side surfaces of the insulating tape layer  120 . 
         [0033]    The coil wire  111  may be formed of a copper wire that has no splices when it is wound to improve heat resistance more than that of a conventional coil for use in a control rod driver. 
         [0034]    A temperature at which the PEEK coating layer  112  covering the outer circumferential surface of the coil wires  111  can be continuously used is about 260° C. which is higher than a temperature at which the conventional enamel-based insulating material can be continuously used is about 220° C. Thus, the PEEK coating layer  112  greatly increases the heat resistance of coils. 
         [0035]    PEEK is a crystalline resin that can be dissolved and shaped in a desired form, has good chemical properties including high thermal resistance, fatigue resistance, chemical resistance, radiation resistance, a hard burning property by which it generates no corrosive gas and less smoke, and good mechanical properties including high strength, high coefficient of expansion, and high shock resistance. Also, PEEK is very strong at high temperature and tensile stress applied to PEEK is maintained constant even when it is used for a long time. 
         [0036]    According to the present invention, the covered wire  110  is formed by covering the external surfaces of the coil wire  111  formed of copper wire having no splices with the PEEK coating layer  112 . Thus, the coil assembly  100  configured to operate in a special high-temperature environment of a nuclear reactor may be prevented from deteriorating and being damaged beforehand. 
         [0037]    The insulating tape layer  120  is a heat-resistant glass fiber fabric, that fixes the shape of the wound layer of the covered wire  110  when external sides of the wound layer are covered with the insulating tape layer  120  and increases the adhesive properties of the silicon molding  140  applied onto the external sides of insulating tape layer  120 . 
         [0038]    The coil coating layer  130  filled with the varnish is formed by vacuum impregnation. Here, vacuum impregnation means a process of dipping the wound layer of the covered wire  110  whose shape is fixed by the insulating tape layer  120  into a tub containing an impregnation varnish solution, placing the tub in a vacuum chamber, and causing the tub to have a vacuum state so as to emit air and moisture present in gaps in the covered wire  110  to the outside due to the vacuum, thereby causing the varnish solution to impregnate into the gaps. 
         [0039]    By forming the coil coating layer  130 , impurities or air may be removed from the gaps in the covered wire  110  to increase a heat discharging effect and to maintain the shape of the coil assembly  100  after the coil coating layer  130  is dried to be hardened. 
         [0040]    The silicon molding  140  is a heat-resistant rubber wrapping material configured to completely encompass the external sides of the coil coating layer  130  after the coil coating layer  130  is dried to be hardened, and protects the coil coating layer  130  from foreign substances such as external moisture, dust, air, etc. 
         [0041]    Referring to  FIG. 4 , the coil assembly  100  configured as described above is manufactured using the first to fourth coil assembles  100 - 1 ,  100 - 2 ,  100 - 3 , and  100 - 4  having the same structure. The first to fourth coil assembles  100 - 1 ,  100 - 2 ,  100 - 3 , and  100 - 4  are respectively installed in the first to fourth coil housings  210 ,  220 ,  230 , and  240  to form the first to fourth control rod driving coil units  310 ,  320 ,  330 , and  340 . The control rod drive mechanism (motor assembly) is operated by an electromagnetic field formed by sequentially supplying current to the first to fourth control rod driving coil units  310 ,  320 ,  330 , and  340 , according to programming of a controller (not shown). 
         [0042]    The four coil housings  210 ,  220 ,  230 , and  240  are connected by the connection plates  430 ,  440 ,  460 , and  470  installed therebetween, and a housing connection member  450  is bound between the second coil housing  220  and the third coil housing  230  to maintain the distance between the second coil housing  220  and the third coil housing  230 . 
         [0043]    The first coil housing  210 , the second coil housing  220 , the housing connection member  450 , the third coil housing  230 , and the fourth coil housing  240  are fixed to be engaged with one another by retainer couplings  431 ,  441 ,  461 , and  471  disposed on external surfaces of the respective connection plate  430 ,  440 ,  460 , and  470 . 
         [0044]      FIG. 5  is a flowchart illustrating a method of manufacturing a coil assembly having improved heat resistance for use in a control rod driver according to an embodiment of the present invention. 
         [0045]    The method of manufacturing a coil assembly having improved heat resistance for use in a control rod driver according to an embodiment of the present invention includes manufacturing the covered wire  110  by forming the PEEK coating layer  112  on an outer circumferential surface of the coil wire  111 , forming a wound layer by winding the covered wire  110  in multiple layers, binding both ends of the covered wire  110  with two pieces of a lead wire connected to the power supply cable  621 , forming the insulating tape layer  120  around the wound layer of the covered wire  110 , forming the coil coating layer  130  by filling the gaps in the covered wire  110  with varnish, drying the coil coating layer  130  in a drying furnace, and applying the silicon molding  140  onto an outer circumferential surface of the dried resultant. 
         [0046]    It is desired that the binding of both of the ends of the covered wire  110  with the two pieces of the lead wire connected to the power supply cable  621  is performed using brazing to minimize resistance at the interfaces between both of the ends of the covered wire  110  and the two pieces of the lead wire connected to the power supply cable  621 . The forming of the coil coating layer  130  may be performed by vacuum impregnation. 
         [0047]    As described above, in a coil assembly having improved heat resistance for use in a control rod driver and a method for manufacturing the same according to the present invention, the heat resistance of the coil assembly may be improved and insulating properties between covered wires may be improved by vacuum impregnation. Thus, coils may be prevented beforehand from deteriorating or being damaged due to heat generation and insulation breakdown caused when electric charge is conducted through coils during driving of the control rod driver, thereby preventing the fall of a control rod.