Patent Number: 048715093
Section: description

Referring to FIG. 1, a fuel rod F is illustrated at the top portion only. The fuel rod has pellets P confined in the lower portion of rod F. An end plug E is welded at welds 14 to the end of the rod F. The spring has two active portions. The first portion is a conventional coil compression spring 16. Coil compression spring 16 is in the order of 2.5 inches long. The second portion of the clamp is a locking coil spring portion 18. Coil spring 16 differs from coil spring 18. Coil spring 16 has an inside diameter less than the inside diameter of the cylindrical cladding F. Hence the coil spring can conventionally act under compression on the fuel pellets F. The locking spring 18 originally had a diameter exceeding the inside diameter of of the coil F. Insertion will, for the moment, be summarized. Typically, the locking spring 18, a helical spring, is spirally wound. It is wound in a direction that tends to bend and decrease its diameter. Winding continues until spring 18 has an outside diameter which is less than the inside diameter of the rod or cladding F. Insertion of the spring occurs. The spring is inserted as wound with the compression spring 16 inserted first and the wound locking spring inserted second. It is inserted until the compression spring 16 exerts on the fuel pellets F the designed force. For example, a total loading in the order of 7 pounds may be desired. Once this total force is achieved, the locking spring 18 is unwound. When it is unwound it keys to the inside of the cladding F. In the particular embodiment shown in FIG. 1, a getter has been placed at the end of the rod. Typically, the getter is given a diameter so that it fits into the inside diameter of the locking spring. It can be seen that once the locking spring 18 is in place the pellets P are secured. End plug E may subsequently be welded at weld 14. The winding, inserting and locking process of coil spring 18 can easily be understood. (See FIG. 2) The installation tool includes a first outer cylinder 20 and inner cylinder 22. Outer cylinder 20 includes a slot 24 for receiving an end 34 of the coil spring. Lower cylinder 22 includes a slot 26. Slot 26 keys to an end 36 of the helical spring. It can be seen that cylinder 22 has contacted at slot 26 the spring at protrusion 36. Similarly, cylinder 20 at slot 24 has contacted the spring at upper end 34. Spiral winding of the helical spring has occurred. The winding has occurred in a direction which reduces the diameter of the spring 18. As wound the spring is shown inserted within a fuel rod F. Referring to FIG. 1, the cylinders 20, 22 have been released. They have been allowed to rotate relative to one another. Spring 18 has expanded. It has expanded in its outside diameter. In its expanded disposition, it has keyed to the inside walls of the fuel rod F. It is inserted so as to register on a scale S the spring force exerted on the fuel pellets. It will be understood that in the simply illustrated process of insertion, and while the spring member 18 is wound, it will be possible to measure the compressive force against the fuel pellets. Simply stated, since the action of compression on the fuel pellets will have a reaction on the wound spring, the measurement of the reaction will enable a worker to accurately preload the fuel pellets in place. Referring to FIG. 3 and FIG. 4, an additional embodiment is shown. In this embodiment the locking spring 18 and the compression spring 16 are constructed from continuous wire coils. In FIG. 3 the getter fits interior of the compression spring. In FIG. 4 the getter G.sup.2 is located between the compression spring and the top of the fuel pellet column. Referring to FIG. 5, the installation tool is shown for the embodiment in which the locking spring and the compression spring are constructed from continuous wire coils. A single piece fuel column retainer having locking coils 18 and compression coils 16 is illustrated together with the installation tool. The installation tool consists of an outer cylinder 60 and an inner cylinder 62. The upper portion of the inner cylinder 62 has one diameter and the lower portion 64 has a smaller diameter. Tangs 64 at the bottom of the inner cylinder engage the washer 50 through the slot 52. The upper end of the locking spring 34 engages a slot 24 in the outer cylinder. Prior to insertion in the fuel rod, the fuel column retainer is placed on the installation tool and is compressed to the desired axial load. Then the inner cylinder is rotated relative to the outer cylinder to wind the locking spring onto the large diameter portion of the inner cylinder 62. The tangs 64 engage the slot 52 and prevent rotation and axial movement of washer, thus maintaining the compressive load on the compression spring. The tool and retainer are inserted into the fuel rod until the washer 50 bears on the top of the fuel column, or getter. Then the inner cylinder is allowed to rotate relative to the outer cylinder. This allows the locking portion of the spring to partially unwind and bear against the fuel rod. The locking portion of the retainer now holds the compression portion in its compressed state and the tool can be withdrawn. The reader will understand that numerous embodiments of this invention are possible. It will be understood that it is the two-part coil spring and the ability of one part to key to the inside diameter of the fuel rod F which is critical to the operation of this invention. The reader will understand that although a single one-piece construction of the spring section 16, 18 is preferred, the apparatus will admit of the use of two separate springs. These two separate springs can be connected in any manner deemed expedient. For example, the getter can be use for such interconnection.