Abstract:
A fuel channel fastener having a body with a hole, a bolt inserted into the hole, at least two anti-rotation supports attached to the body, a spring configured to attach to the body and to extend away from the body down the sides of a fuel assembly fuel channel, and at least two spring anti-rotation pads connected to the body.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention is related to nuclear fuel assembly channel fasteners. More specifically, the invention relates to a boiling water reactor fuel channel fastener which restricts rotation during torquing and detorquing. 
       BACKGROUND INFORMATION 
       [0002]    Fuel channel fasteners have been used for many years in boiling water reactor fuel assemblies. The purpose of the fastener is to mechanically attach the external fuel channel to the fuel assembly, so that under operating conditions, the reactor coolant is restrained around each fuel assembly. The fastener utilizes a spring to separate the fuel channel from other fuel assemblies in the proximity of the fuel channel. The current designs of fuel channel fasteners, therefore, provide a solid stop between adjacent channels. 
         [0003]    Previous fuel channel fastener designs have several significant shortcomings. The bolt in these designs was moved toward a more inward position, as compared to the exterior edge of the fuel channel. The placement of the bolt in this arrangement provided a tendency for the entire fastener to rotate during tightening of the bolt. As manufacturers have modified the bolt position of fuel channel fasteners from a position close to the edge of the fuel channel further toward an inside part of the fuel assembly, the additional distance from the bolt to the external parts of the fastener decreases the rotational resistance due to the additional moment arm. 
         [0004]    The rotation of the bolt caused the body of the fastener to rotate on the fuel assembly channel, thus allowing the bottom edge of the fastener body to protrude from the exterior of the channel wall. This rotation thereby allows an additional contact edge which may lead to premature failure of the fuel channel fastener as there is an additional contact surface for impact. The rotation also allows the end of the fuel channel spring to extend beyond the protective configuration of the body of the fastener. When the fastener body or spring extends outward, they are more likely to be damaged by interacting with in-reactor blade guides, fuel storage racks, other fasteners, or reactor components during, for example, fuel assembly movement. Industry experience has shown that fuel channel fasteners can prematurely fail using these designs. 
         [0005]    There is a need to provide a fuel channel fastener that will allow for adequate seating of the fuel channel fastener to the fuel assembly. 
         [0006]    There is also a need to provide a fuel channel fastener that will be rugged for anticipated operating and accident conditions for a nuclear reactor. 
         [0007]    There is a still further need to provide a fuel channel fastener that will be less susceptible to damage compared to current fuel channel fastener designs. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an objective of the current invention to provide a fuel channel fastener that will allow for adequate seating against the fuel channel fastener to the fuel channel. 
         [0009]    It is also an objective of the current invention to provide a fuel channel fastener that will be rugged for anticipated operating and accident conditions for a nuclear reactor, while maintaining adequate seating between the fuel channel fastener and the fuel channel. 
         [0010]    It is a further objective of the current invention to provide a fuel channel fastener that will be less susceptible to damage compared to current fuel channel fastener designs. 
         [0011]    The objectives of the current invention are achieved as described and illustrated. The invention provides a fuel channel fastener. The fuel channel fastener comprises a washer, a body with a first hole, a spring with a second hole and with two perpendicular spring members configured to extend away from the body down sides of a fuel assembly fuel channel, wherein the spring is configured adjacent to the body such that the first hole and the second hole are concentric, a bolt inserted through the washer, the second hole and the first hole, at least two anti-rotation supports attached to the body, and at least two anti-rotation pads connected to the body, wherein the anti-rotation supports are configured to provide resistance to fastener rotation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a side perspective view of a fuel assembly channel fastener in conformance with an example embodiment of the current invention. 
           [0013]      FIG. 2  is a top view of a fuel assembly channel fastener of  FIG. 1  wherein bolt  26  and washer  14  have been removed for clarity. 
           [0014]      FIG. 3  is a side view of the fuel assembly channel fastener of  FIG. 1  in an installed arrangement. 
           [0015]      FIG. 4  is a top view of the fuel assembly channel fastener of  FIG. 1  for discussion purposes with previous fastener plate design configurations. 
           [0016]      FIG. 5  is a side perspective view of the components of the fuel assembly channel fastener with the individual components separated. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to  FIG. 1 , a fuel channel fastener  10  for a boiling water reactor fuel assembly is illustrated. The overall length of the fuel channel fastener  10  for the boiling water reactor fuel assembly may be, for example, approximately 5 inches (12.7 cm). The fuel channel fastener  10  is comprised of a bolt  26  that extends through lock washer  14 , a body  38  and a spring  22 . The fuel channel fastener  10  establishes a connection between a fuel channel of a nuclear fuel assembly and the internal structures of the fuel assembly. This connection allows the fuel channel of the fuel assembly to provide a rigid structure around the fuel assemblies. The fuel channel also allows for the channeling of moderator, such as reactor water, through the internal components of the fuel assembly including the nuclear fuel rods. 
         [0018]    The body  38  has a body first end  34  and a body second end  32 , wherein the body  38  is configured to fit over an edge of a fuel channel of a nuclear fuel assembly. The body  38  may be inserted near a corner end of a fuel assembly fuel channel such that a surface of the body  38  contacts the exterior surface of the fuel channel. The body  38  is made of a metallic material, such as stainless steel, to account for adequate corrosion resistance. As illustrated, the bolt  26  of the current invention is torqued to about 6 pound feet. The body first end  34  may be configured at a top with a chamfered edge to provide an alignment feature for the spring form. The body second end  32  may be configured with a chamfered end as illustrated to provide a leading edge for interaction. The body  38  is configured with varying uniform thickness to provide adequate strength and form for interfacing with spring  22  and other channel fasteners. 
         [0019]    The bolt  26  is inserted through a washer  14 . The washer  14  provides an arrangement to accept the bolt head  12  compressive forces and transfer those compressive forces to the spring  22  and the body  38 . The washer  14  may be made of materials, such as stainless steel, for example, to limit corrosion or galvanic reaction. The washer  14  can be configured as a locking washer to prevent unintended removal or loosening of the bolt. The washer  14  can have a low profile such that vertical protrusion of the bolt  26  above the top of the fuel assembly is minimized. 
         [0020]    The spring  22  is also compressed by the combination of the bolt head  12  connection to the fuel assembly. The spring  22  is configured with a spring first end  16  which extends around the fuel channel to a spring second end  20 . The spring  22  has an inflection point  24  such that the spring  22  extends away from the body  38  up to the inflection point  24 . The spring  22  is configured with a bend  18  to allow the spring  22  to extend from a horizontal section to a vertical section. The spring  22  may be made of a metallic material which provides a sufficient spring constant so that adjacent fuel is separated during normal reactor operation. The spring  22  may be made of nickel Alloy 718, for example. 
         [0021]    The bolt  26  is arranged in a configuration such that the bolt  26  cannot be removed from the body  38  and the spring  22  in a detorqued condition. The body  38  may be staked during manufacturing such that the removal of the bolt  26  from the body  38  and the spring  22  is prevented due to bolt material exceeding bolt hole  52  dimensions. The staking procedure eliminates concerns for loose parts, thereby encouraging foreign material exclusion from sensitive areas of the nuclear reactor. 
         [0022]    Referring to  FIG. 2 , a top view of the fuel channel fastener  10  of  FIG. 1  is illustrated. Bolt  26  and washer  14  are not illustrated for clarity. The fuel channel fastener  10  has a first anti-rotation support  40  positioned, as illustrated in  FIG. 2 , on an exterior portion of the fastener  10 . The first anti-rotation support  40  is configured to engage the exterior of the fuel channel of the fuel assembly, such that when the bolt  26  is rotated in a clockwise direction, the resulting overall torque placed on the fuel channel fastener  10  will cause the first anti-rotation support  40  to contact the external surface of the fuel channel. The resulting contact between the first anti-rotation support  40  and the external surface of the fuel channel restricts movement of the fastener during torquing thereby allowing tightening of the fastener without fastener rotation. A second anti-rotation support  42  is located on an opposite corner of the fastener  10 . The second anti-rotation support  42 , similar to the first anti-rotation support  40 , contacts the external surface of the fuel channel of the fuel assembly, such that when the bolt  26  is detorqued, the second anti-rotation support  42  contacts the fuel channel, thereby preventing rotation of the fuel channel fastener  10 . As an illustrative example, the supports  40 ,  42  may be approximately 0.38 millimeters in thickness. 
         [0023]    The bolt hole  52  is positioned such that it is located away from the edge of the fastener and such that the hole  52  is positioned along an axis drawn from the joints formed from the intersection of anti-rotation support  42  and back adjacent edge  50  with anti-rotation support  40  and back adjacent edge  54 . Other configurations of hole position may be chosen, wherein the bolt hole  52  is moved respectively toward the front edge  48  or the back edge  46 . The configuration presented, therefore, is merely illustrative of the possible configurations, including bolt hole  52  positions near the edge of the back edge  46 , for example. 
         [0024]    The first anti-rotation pad  60  is in between spring  22  and the first anti-rotation support  40 . The second anti-rotation pad  44  is likewise in between spring  22  and the second anti-rotation support  42 . The first anti-rotation pad  60  and second anti-rotation pad  44  contact the spring  22  during torquing and detorquing of the bolt  26  to prevent the spring from rotating. 
         [0025]      FIG. 3  presents a side view of a fuel channel fastener  10  installed on a fuel channel fuel channel  64  in contact with another fuel channel  68 . The fuel channel fastener  10  positioned on each fuel channel  64  has a spring  22  which provides a bearing surface between the individual fuel channels  64 ,  68 . The springs  22  of the individual fuel channel fasteners  10  contact other adjacent springs  22 . The springs  22  are configured to deflect a sufficient amount such that a space  66  is always maintained between the respective fuel channels  64 ,  68 . 
         [0026]    Referring to  FIG. 4 , a top view of the fuel channel fastener  10  of the present invention is illustrated. A center point  72  of the hole  52  is located along a neutral axis  70  defined by a first body connection end point  74  and a second body connection end point  76 . Other configurations are possible wherein the center point  72  of the hole  52  may be closer or further from the front edge  48 . 
         [0027]    Referring to  FIG. 5 , a side perspective view of the fuel channel fastener  10  with the individual components separated is illustrated. The bolt  26  is inserted through the washer  14  and the spring  22  into the bolt hole  52 . The spring  22  is placed over the body  38  and into depressions  78  located on the body  38 . 
         [0028]    The present invention provides a fuel channel fastener  10  which provides for a connection between the fuel channel and a fuel assembly. The fuel channel fastener  10  provided in the current invention prevents rotation of the fuel channel fastener  10  during tightening and loosening. The fuel assembly channel fastener  10  of the current invention provides a more resistant structure for bending as compared to other designs. The anti-rotation capabilities of the fuel assembly channel fastener  10  are established without modifying fuel channels of fuel assemblies and without detrimental impact to overall core flow characteristics. 
         [0029]    In the foregoing specification, the invention has been described with reference to specific exemplary embodiments, thereof. It will be evident that modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.