Patent Number: 043449158
Section: description

DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. In FIG. 1, part of a fuel assembly 10 is shown. A typical nuclear reactor contains many fuel assemblies. Each fuel assembly typically contains over a hundred nuclear reactor fuel rods, which are also called fuel pins. Only three nuclear reactor fuel rods 12 are shown in the fuel assembly 10 in FIG. 1. Preferably the bottom of a fuel rod 12 is attached to a support member 14 of the fuel assembly 10. Only the lower end of the fuel rod 12 is shown in FIG. 1. As FIG. 1 is a sectional view, the fuel assembly duct tube 16 is so indicated. The shield/inlet nozzle assembly walls 18 form a channel for the coolant to flow upwards through the space between the fuel rods and out the top of the fuel assembly. The bottom of the fuel rod 12 is fastened to the top part 22a of a locking cap. The middle part 22b of the locking cap joins the top part 22a to a transition section 22c. The lower part 22d forms a socket, and the lower part is connected to the middle part by the transition section 22c. For particular applications, two or more adjoining locking cap parts may be configured of different materials to allow for their relative rotation and attachment requirements. The locking cap socket forming lower part 22d is rigidly attached to a locking strip 24. FIG. 1 depicts a sectional view of the locking strip which preferably is widened to allow for attachment of additional fuel rods in front of, and behind, the fuel rods shown in FIG. 1. A pin bar 26 secures the locking strip 24 to the support member 14. The locking cap 22 is shown in more detail in FIG. 2. The lower part 22d of the locking cap terminates in opposing fingers 24a and 24b defining a socket 25. Preferably, there are two fingers defining the socket 25. These cantilever fingers can be deflected apart. They are resilient so that they will spring back toward their original configuration when the deflecting force is reduced. The socket 25 has a body portion 26, a throat portion 28, and a mouth portion 30. The socket's body portion 26 narrows to the throat portion 28 along a decoupling-aiding tapered or chamfered section 32. Likewise, the mouth portion 30 narrows to the throat portion 28 along a coupling-aiding tapered or chamfered section 34. The locking cap is reusable allowing for repeated attachment and removal of the nuclear reactor fuel rod to the support member. Preferably, the locking cap is fastened or secured to the nuclear reactor fuel rod and the locking strip is connected to the support member. However, the locking cap could be secured to the support member and the locking strip fastened to the nuclear reactor fuel rod. Preferably, the socket's body portion 26 has generally flat or planar surfaces which are generally parallel to the longitudinal axis of the socket. This will prevent rotation with a likewise configured locking strip extension. Preferably a plurality of nuclear reactor fuel rods, each having a locking cap, are secured to one widened locking strip, with standard spacer grids or wire wrap used to control positioning. Generally a nuclear reactor has two parallel, spaced-apart support members 14, with each of the reactor's many widened locking strips supported towards each end by one support member 14. The coupling-aiding tapered section 34 is made generally planar to aid in the attachment process. It is preferable that the coupling-aiding tapered section 34 be made to have a more gradual taper than the taper of the decoupling-aiding tapered section 32 such that the decoupling force required for removal would be much greater than the coupling force required for attachment. The locking strip is depicted in FIG. 3. The locking strip 24 has an extension 36. The extension 36 consists of a top section 36a, which preferably has a convex shape to allow for easier attachment, a middle section 36b, having generally planar surfaces which are generally parallel to the longitudinal axis of the socket to help prevent rotation when the extension is attached to the socket, and a bottom section 36c. The extension is configured to always make a rigid connection within the socket's body portion 26. Due to irradiation relaxing effects on prestressted members, it is preferable that a rigid connection be made when the fingers are relaxed (not deflected at all). Preferably the extension is shaped to generally fill the area of the socket's body portion when the extension is attached to the socket. The locking strip extension's planar middle section 36b abuts the socket's generally planar body portion 26 to prevent rotation. To attach the nuclear reactor fuel rod to the support member, the fuel rod is lowered to a point just above the support member. The fuel rod is then lowered until the locking cap's coupling-aiding tapered section 34 makes contact with the top section 36a of the locking strip extension. The fuel rod is then pushed onto the locking strip by application of a coupling force sufficient to pry apart or deflect open the locking cap fingers 24a and 24b to widen the socket's throat portion 28 to allow passage of the locking strip's extension 36 into the body portion 26 of the socket. Upon complete insertion, the locking cap fingers spring back towards, and preferably to, their original position so that there is rigid attachment of the fuel rod to the support member. While the fuel rod is attached to the support member, in the preferred embodiment, relative rotation of the locking cap and the locking strip is prevented by engagement of the planar surfaces of the extension's middle section 36b and the socket's body portion 26. However, it may not be desirable to prevent fuel rod rotation for all applications of the system, such as in certain testing situations, by rotatably mounting the fuel rod to the locking cap or rotatably mounting the locking cap to the locking strip. The attached nuclear reactor fuel rod is removed from the support member by applying a decoupling force to pull apart the locking cap and locking strip. Upon application of the decoupling force, the bottom portion 36c of the locking strip's extension engages the socket's decoupling-aiding tapered section 32 to push apart or deflect open the locking cap fingers to widen the socket's throat portion and allow removal of the extension from the socket. The locking cap fingers thereupon spring back towards their original configuration. The locking cap and locking strip are designed for repeated use. Preferably appropriate tapers are chosen as previously discussed to require a much greater force for removal than for attachment. An alternate system for removably attaching a nuclear reactor fuel rod to a support member would include an optional locking strip made of materials allowing the locking strip's extension to be compressed in a transverse direction with a resilient return towards the original shape upon reduction of the compressive force. One shape for the optional locking strip, which allows transverse compression, is shown in the optional locking strip 40 of FIG. 4, which includes decoupling-aiding tapered sections 42. Such a system would also have an optional locking cap 50, which matches the optional locking strip 40 to allow for a rigid connection, as shown in FIG. 5. The optional locking cap 50 is made of materials providing for generally rigid fingers instead of resiliently deflectable fingers. Now, during the attachment procedure, instead of the fingers moving apart, the optional locking strip 40 would be transversely compressed to allow insertion of the optional locking strip's extension 44 into the locking cap's socket. Preferably the rigid connection is made when the compressive force is removed and the extension returns to its original shape. Removal of an attached fuel rod from a support member would be accomplished in a similar manner when they are pulled apart. In this option, it is understood that the optional locking cap could be fastened to the nuclear reactor fuel rod and the optional locking strip to the support member, or the optional locking cap could be secured to the support member while the optional locking strip is fastened to the nuclear reactor fuel rod. In summary, by using a resiliently deflectable socket and/or a transversely compressible extension, both suitably shaped to aid coupling and decoupling and to allow for rigid attachment of the extension to the socket, a nuclear reactor fuel rod can be removably attached to a support member in a reusable system by securing a locking cap having the socket to the nuclear reactor fuel rod (or support member) and securing a locking strip having the extension to the support member (or fuel rod). This provides a reusable, economical and rapid push-pull type attachment and removal system for nuclear reactor fuel rods. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention in the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.