Patent Publication Number: US-8995605-B2

Title: Lid frame for nuclear fuel assembly shipping container and shipping container for nuclear fuel assemblies

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2010-0066765, filed on Jul. 12, 2010, the disclosure of which is expressly incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lid frame for a nuclear fuel assembly shipping container and a shipping container for nuclear fuel assemblies, capable of safely transporting a nuclear fuel assembly to a nuclear power plant, etc. after the nuclear fuel assembly has been produced. 
     2. Description of the Related Art 
     In general, nuclear fuel such as enriched uranium or mixed oxide needs to be transported between various places, for instance a place where they are concentrated, a fuel rod producing place, and so on. For this transporting stage, the fuel is typically shaped like a small pellet. 
     When stored, this fuel requires a constant level of thermal insulation and structural strength to comply with international standards, and the control of their criticality is a main concern, and the mass of enriched fuel in a shipping container should be strictly restricted such that a dangerous situation does not arise. Due to this requirement, the volume of fuel that can be transported in a shipping container of a certain volume is under strict restrictions. 
     As a result, numerous shipping containers for transporting the nuclear fuel assembly have been disclosed. As shown in  FIG. 1 , such a shipping container is designed so that a plurality of clamps  10  are installed separately apart from each other by predetermined intervals so as to clamp a nuclear fuel assembly  1 . In this case, it is impossible to safely protect the nuclear fuel assembly from external shocks caused by falling, penetration, and so on. 
     To compensate for this problem, as shown in  FIG. 2 , the shipping container may be designed so that a pair of clamping frames  20  are coupled to opposite long sides of the shipping container with the nuclear fuel assembly disposed therebetween, and are formed in a completely closed shape so that the nuclear fuel assembly is clamped. The strength of the shipping container itself including the clamping frames  20  must be reliable, and thus the containers are typically formed of a metal material. In this way, when the clamping frames  20  are formed in a completely closed shape, the nuclear fuel assembly can be safely protected, but the shipping container itself becomes very heavy, and the cost of production is increased as well. 
     Furthermore, in the case of conventional nuclear fuel assembly shipping containers with clamps that have the same size, since the positions of the spacer grids are different for each type of nuclear fuel assembly, a lid frame in which the clamps are disposed so as to correspond to the positions of the spacer grids should be used to transport different types of nuclear fuel assemblies. Accordingly, a different lid frame should be provided depending on the type of nuclear fuel assembly. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and embodiments of the present invention provide a lid frame for a nuclear fuel assembly shipping container, which is designed to improve durability, stiffness, etc. so as to be able to sufficiently withstand unexpected accidents or external shocks, and to cover an entire nuclear fuel assembly, thereby making it possible to safely protect the nuclear fuel assembly and to reduce its weight, and a shipping container for nuclear fuel assemblies as well. 
     Embodiments of the present invention also provide a lid frame for a nuclear fuel assembly shipping container and a shipping container for nuclear fuel assemblies, which allow different types of nuclear fuel assemblies, between which the position of each spacer grid is different, to be transported using one type of lid frame. 
     According to an aspect of the present invention, there is provided a lid frame for a nuclear fuel assembly shipping container, in which the shipping container includes a lower container in which a cradle is installed, an upper container detachably coupled to the lower container, and a base frame coupled to the cradle with at least one nuclear fuel assembly placed thereon. The lid frame, comprises: a plurality of supports installed apart from each other so as to surround the nuclear fuel assembly placed on the base frame; and a plurality of clamps separated from each other, coupled to the plurality of supports so as to be perpendicular to the plurality of supports, rotatably hinged to the base frame, and clamping the nuclear fuel assembly. 
     According to another aspect of the present invention, there is provided a shipping container for nuclear fuel assemblies, which comprises: a lower container in which a cradle is installed; an upper container detachably coupled to the lower container; a base frame coupled to the cradle with at least one nuclear fuel assembly placed thereon; and a pair of lid frames installed on opposite long sides of the base frame in order to clamp the nuclear fuel assembly placed on the base frame. Each lid frame includes: a plurality of supports installed apart from each other so as to surround the nuclear fuel assembly placed on the base frame; and narrow and wide clamps separated from each other, coupled to the plurality of supports so as to be perpendicular to the plurality of supports, rotatably hinged to the base frame, and clamping the nuclear fuel assembly. 
     Here, the shipping container can further include buffers interposed between the lower container and the cradle in order to absorb shocks applied to the nuclear fuel assembly. 
     Further, the shipping container can further include: hinge couplers formed at one end of the cradle; hinge pieces formed on the base frame so as to correspond to the hinge couplers; and hinge bolts, each of which couples each of the hinge couplers and the hinge pieces. 
     Also, the shipping container can further include a support rod, which supports the nuclear fuel assembly when the nuclear fuel assembly stands erect at one end of the lower container. 
     In addition, the lid frame can further include press members installed on inner surfaces of the narrow and wide clamps in order to press spacer grids of the nuclear fuel assembly. 
     Each press member can include: a press plate that is interposed between each of the narrow and wide clamps and each spacer grid and pressing the spacer grid; and an adjustment screw that passes through each of the narrow and wide clamps to be coupled to the press plate. 
     The lid frame can further include: a first press plate holding recess formed inside the narrow clamp so as to hold the press plate; and second press plate holding recesses formed inside the wide clamp so as to hold the press plates. The second press plate holding recesses can hold the press plates so as to be able to press each spacer grid in different types of nuclear fuel assemblies between which the position of each spacer grid is different. 
     According to the present invention configured in this way, the lid frame installed in the shipping container to stably clamp the nuclear fuel assembly has a lattice shape, so that it is possible to improve stability of the nuclear fuel assembly compared to an existing method of clamping the nuclear fuel assembly only with clamps. Further, it is possible to remarkably reduce the weight compared to an existing clamping frame having a completely closed shape, so that the lid frame can be used at a nuclear power plant equipped with a nuclear fuel assembly handling crane having a relatively small capacity, and can also reduce the cost of production, which is advantageous from the economical point of view. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view showing a conventional nuclear fuel assembly shipping container; 
         FIG. 2  is a perspective view showing another conventional nuclear fuel assembly shipping container based on technology of AREVA® company of France and NFI® company of Japan; 
         FIG. 3  shows an appearance of a nuclear fuel assembly shipping container according to an exemplary embodiment of the present invention; 
         FIG. 4  is an exploded perspective view showing the nuclear fuel assembly shipping container of  FIG. 3  according to the exemplary embodiment of the present invention; 
         FIG. 5  is a perspective view showing a nuclear fuel assembly shipping container according to an exemplary embodiment of the present invention, wherein an upper container is removed from the nuclear fuel assembly shipping container; and 
         FIG. 6  is a perspective view showing a nuclear fuel assembly shipping container according to an exemplary embodiment of the present invention, wherein a lid frame clamping a nuclear fuel assembly stands erect. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in greater detail to exemplary embodiments of the invention with reference to the accompanying drawings. 
       FIG. 3  shows an appearance of a nuclear fuel assembly shipping container according to an exemplary embodiment of the present invention. The shipping container of this embodiment is configured so that a cross section of a lower container  100  and an upper container  200  is semi-circular such that at least one nuclear fuel assembly can be held, and are coupled so as to be opposite to each other. Here, each of the lower and upper containers  100  and  200  can be formed of a metal material strong enough to safely transport the nuclear fuel assembly. 
     In detail, the shipping container of this embodiment is configured so that the upper container  200  is detachably coupled to the lower container  100 , the lower and upper containers  100  and  200  are provided with flanges  110  and  210  on outer circumferences thereof, the flange of the lower container  100  has a plurality of assembly protrusions  111  protruding therefrom at regular intervals, and the flange of the upper container  200  is provided with a plurality of assembly holes  211  (see  FIG. 4 ) so as to correspond to and be engaged with the protrusions. 
     Further, the lower container  100  has a plurality of support legs  120  installed on an outer surface thereof at predetermined intervals so as to support the shipping container. The upper container  200  is provided with loading parts  220  on opposite sides thereof in a lengthwise direction. Each loading part  220  is provided with lift holes  221  such that the upper container  200  can be lifted by, for instance, a crane. 
       FIG. 4  is an exploded perspective view showing the nuclear fuel assembly shipping container of  FIG. 3  according to the exemplary embodiment of the present invention, wherein lower and upper containers  100  and  200  are separated from each other.  FIG. 5  is a perspective view showing a nuclear fuel assembly shipping container according to an exemplary embodiment of the present invention, wherein an upper container is removed from the nuclear fuel assembly shipping container.  FIG. 6  is a perspective view showing a nuclear fuel assembly shipping container according to an exemplary embodiment of the present invention, wherein a lid frame clamping a nuclear fuel assembly stands erect. 
     As shown in  FIG. 4 , a lower container  100  is provided therein with a base frame  300  and a pair of lid frames  400  and  400 ′ so as to be able to stably support at least one nuclear fuel assembly  10 . A cradle  130  is installed in the lower container  100  such that the base frame  300  can be placed on the cradle  130 . The base frame  300  is placed on the cradle  130  with the nuclear fuel assembly  10  placed on an upper surface of the base frame. The cradle  130  has a plurality of supports  131  installed in a lengthwise direction at predetermined intervals. The cradle  130  is fixed to the lower container  100  by fasteners  134  such as screws. Here, buffers  140  formed of a rubber material are interposed between the lower container  100  and the cradle  130  in order to relieve external shocks that can be applied to the nuclear fuel assembly  10 . Each buffer  140  is provided with a fastener hole (not shown) in the center thereof in a lengthwise direction. The fasteners  134  are fastened into the fastener holes through the cradle  130 . Thereby, the cradle  130  is fixedly coupled to the lower container  100  so as to be able to absorb shocks. 
     The lid frame  400  or  400 ′ includes supports  410  or  410 ′ stably surrounding the nuclear fuel assembly  10 , narrow clamps  420  or  420 ′ and wide clamps  420   a  or  420   a ′ disposed on the supports  410  or  410 ′ at predetermined intervals, and end support plates  444  supporting opposite ends of the nuclear fuel assembly  10 . The supports  410  or  410 ′ are separated from each other, and are installed in a lengthwise direction of the nuclear fuel assembly  10 . 
     Here, the supports  410  or  410 ′ are disposed apart from each other at predetermined intervals, rather than integrally formed in one flat plate shape. Thus, a guide slot is naturally formed between the two adjacent supports. 
     Each of the narrow clamps  420  or  420 ′ and the wide clamps  420   a  or  420   a ′ is rotatably hinged to the base frame  300  at one end thereof. Here, the narrow clamps  420  or  420 ′ and the wide clamps  420   a  or  420   a ′ are welded to the supports  410  or  410 ′, which are separated from each other, so as to be perpendicular to the supports  410  or  410 ′, and thus are integrally formed with the supports  410  or  410 ′ so as to be able to be rotated. 
     Meanwhile, in this embodiment, the shipping container for transporting two nuclear fuel assemblies  10  at the same time has been described by way of example. As shown in  FIG. 5 , the lid frames  400  and  400 ′ are rotatably installed on the base frame  300  on opposite long sides of the base frame  300  so as to be opposite to each other. Further, each pair of narrow clamps  420  and  420 ′ or each pair of wide clamps  420   a  and  420   a ′ are configured to be fastened to each other, and are provided with male and female fasteners  421  and  421 ′ on free ends thereof so as to be engaged with each other, respectively. Further, the male and female fasteners  421  and  421 ′ are provided with bolting holes  422  and  422 ′ respectively, so that they can be firmly fixed to each other by a fixing bolt (not shown). Here, the narrow clamps  420  or  420 ′ are arranged so as to correspond to the spacer grids of the nuclear fuel assembly  10 , so that they can stably clamp the nuclear fuel assembly. 
     In this manner, the lid frame  400  or  400 ′ of this embodiment is configured so that the supports  410  or  410 ′, which are separated from each other, and the narrow clamps  420  or  420 ′ and the wide clamps  420   a  or  420   a ′, which are coupled to the supports  410  or  410 ′ at predetermined intervals respectively, have a lattice shape. Thus, the lid frames  400  and  400 ′ can be remarkably reduced in weight compared to a conventional lid frame where a pair of clamping frames  20  are formed in a completely closed shape as shown in  FIG. 2 , and thus make transportation easier. Furthermore, the lid frames  400  and  400 ′ can also reduce the cost of production, which is advantageous from the economical point of view. 
     Further, each of the narrow clamps  420  or  420 ′ and the wide clamps  420   a  or  420   a ′ can be provided with press members  600  for pressing the spacer grids of the nuclear fuel assembly  10  to more stably clamp the nuclear fuel assembly  10   
     Each press member  600  includes a flat-plate-shaped press plate  610 , which is interposed between each of the clamps  420 ,  420 ′,  420   a  and  420   a ′ and each spacer grid, and an adjustment screw  620 , which passes through each of the clamps  420 ,  420 ′,  420   a  and  420   a ′ to be coupled to the press plate  610 . Thus, pressure is applied to or released from the press plate  610  using the adjustment screw  620 , so that the nuclear fuel assembly  10  can be firmly clamped to the lid frame  400  or  400 ′. 
     A first press plate holding recess  423  or  423 ′, which holds the flat-plate-shaped press plate  610 , is formed inside the narrow clamp  420  or  420 ′, and second press plate holding recesses  423   a  or  423   a ′, which hold the flat-plate-shaped press plates  610 , are formed inside the wide clamp  420   a  or  420   a′.    
     Here, the second press plate holding recesses  423   a  or  423   a ′ are provided inside the wide clamp  420   a  or  420   a ′ so as to correspond to dimensions (width and length) of the wide clamp  420   a  or  420   a ′ and to have a width of the first press plate holding recess  423  or  423 ′. 
     These wide clamps  420   a  or  420   a ′ are formed so as to have a width that covers a change in position of each spacer grid of the nuclear fuel assembly to be transported. Thereby, in different types of nuclear fuel assemblies between which the position of each spacer grid is different, the spacer grid located at a different position can be fixedly pressed using the press plate  610 . Accordingly, the lid frame  400  or  400 ′ can clamp and transport the different types of nuclear fuel assemblies without requiring a separate change in structure. 
     In the shipping container of the present invention constructed as described above, after the nuclear fuel assembly has been transported to a nuclear power plant, the nuclear fuel assembly must be erected from the shipping container. Thereby, it is easy to store the nuclear fuel assembly in a temporary storehouse. 
     Thus, as shown in  FIG. 6 , the nuclear fuel assembly is erected from the shipping container by lifting one end of the nuclear fuel assembly in an upward direction using, for instance, a nuclear fuel assembly handling crane. 
     Here, as shown in  FIG. 5 , the cradle  130  is provided with hinge couplers  132  at one end thereof, and the base frame  300  is provided with hinge pieces  310  that correspond to the hinge couplers  132 . The hinge couplers  132  and the hinge pieces  310  are provided with hinge holes  311  so as to be aligned with each other. A hinge bolt  133  ( FIGS. 4 and 5 ) is fitted into the hinge holes  311 . When one end of the nuclear fuel assembly is lifted, the nuclear fuel assembly can be more stably pivoted because the other end of the nuclear fuel assembly is coupled to the cradle  130  by the hinge bolt  133  that functions as a rotational shaft. As shown in  FIG. 4 , the hinge bolt  133  is provided with a fixing hole  133   a  in one end thereof. After the hinge bolt  133  is inserted into the hinge holes  311  formed in the hinge coupler  132  and the hinge piece  310 , it is rotatably fixed by a fixing rod  133   b  and a fixing pin  133   c  fixing the fixing rod  133   b . To fix the hinge bolt  133 , all fixing means for rotatably coupling the hinge bolt  133  to the hinge coupler  132  and the hinge piece  310  can be used in addition to the fixing rod  133   b  and the fixing pin  133   c.    
     In this manner, when the nuclear fuel assembly is erected by pivoting one end of the nuclear fuel assembly, the nuclear fuel assembly can be erected by a nuclear fuel assembly handling crane having a relatively small capacity, because the lid frame  400  or  400 ′ of this embodiment is formed in a lattice shape and thus its weight is sufficiently reduced compared to an existing closed-type clamping frame. 
     Meanwhile, the lower container  100  of this embodiment is provided with a bedplate  150  at one end thereof which can support a load of the nuclear fuel assembly when the nuclear fuel assembly stands erect. A support rod  160  can be hinged to the lower container  100  and the base frame  300  at opposite ends thereof, respectively, so as to be able to sufficiently support the nuclear fuel assembly. 
     Although exemplary embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.