Patent Number: 053655567
Section: summary

FIELD OF THE INVENTION This invention generally relates to the refueling of a nuclear reactor by the installation of fuel bundle assemblies. In particular, the invention relates to apparatus for storing nuclear fuel bundle assemblies before the fuel bundle assemblies are installed in the core of a nuclear reactor. BACKGROUND OF THE INVENTION Large-capacity power-generating nuclear fission reactor plants normally have several hundred sealed tubular containers for housing fissionable fuel. To facilitate periodic refueling, which commonly is performed by replacing fractional portions of the total fuel at intervals and rearranging other fractional portions, these fuel rods or pins are conventionally assembled into bundles or groups of elements which can be manipulated as a single composite unit. The fuel rods of each bundle are held mutually parallel and spaced apart by mechanical means. A typical fuel bundle comprises, for example, an 8.times.8 or 9.times.9 array of spaced fuel rods. Each fuel rod is usually more than 10 ft. long, e.g., 14 ft., and approximately 1/2 inch in diameter. To inhibit the fuel rods from bowing and vibrating due to high heat and high velocity of the coolant flowing past, the fuel rods are maintained in their spaced-apart relation by a plurality of spacers positioned at intervals along their length. Typical spacers for fuel rods comprise a lattice having a plurality of openings arranged in the designated pattern for spacing the parallel aligned fuel rods. The assembled bundle of a group of spaced-apart, parallel aligned fuel rods additionally each have their ends supported in corresponding sockets of upper and lower tie plates. The typical fuel bundle assembly also comprises an open-ended tubular channel of suitable cross section, such as square, which surrounds the fuel rods. The fuel channel directs the flow of coolant longitudinally along the surface of the fuel rods and channels the neutron-absorbing fission control rods, which reciprocate longitudinally intermediate a 2.times.2 array of channeled fuel bundle assemblies. A bail is connected to the upper tie plate. When a hoist is coupled to the bail, the fuel bundle assembly can be lifted and transported as a unit. When supported by a hoist, the fuel bundle assembly hangs in a generally vertical position. A conventional new fuel storage pool has a rack comprising a plurality of cells for receiving and storing new fuel bundle assemblies. To store a new fuel bundle assembly in a cell of a conventional rack, the new fuel bundle assembly must be hoisted over the open top of the cell and then lowered into the cell. Each cell has a generally square cross section and is vertically disposed so that the fuel bundle stored therein will be held in a generally upright position as it bears against the walls of the cell. The foregoing conventional means for storing fuel bundle assemblies in a new fuel storage pool has several disadvantages. First, it is undesirable from a safety standpoint to transport fuel along a path overlying stored fuel. In the event that the fuel bundle being transported were to break away from the hoist, the fuel would fall on top of any fuel stored below, thereby increasing the attendant hazards and complicating the clean-up operation. Second, if fuel bundle assemblies having a height h must be transported over stored fuel bundle assemblies of height h, then the new fuel storage pool must have a depth equal to at least 2h to ensure that the fuel bundle assemblies are entirely submerged in water during transport. The greater the depth of the new fuel storage pool, the greater are the attendant construction costs. SUMMARY OF THE INVENTION The present invention is an improved system for storing fuel bundles in a new fuel storage pool which overcomes the disadvantages of the conventional system. In particular, an array of storage racks are mounted on the floor of the new fuel storage pool. Adjacent storage racks are separated by aisles. Because fuel should not pass over stored fuel, administration control requires that the fuel be transported down the center of the pool and then down an aisle between racks. With the fuel approximately one-half meter above the floor, a hoist moves the fuel into a storage position and starts to lower the fuel into a storage slot, hereinafter referred to as a "fuel storage cell". Lowering of the fuel to the bottom of the fuel storage cell activates a locking mechanism which holds the fuel bundle assembly in place. A flag on the locking mechanism is visible from the refueling bridge to indicate that the particular storage position is locked. After the refueling machine has transported the spent fuel into the fuel transfer area, the refueling machine is operated to pick up new fuel. Moving down the aisle between the racks, the refueling machine grapples a new fuel bundle assembly and starts to lift it. This lifting operation actuates the locking mechanism to open, allowing the fuel to be lifted out of the fuel storage cell and then transported to the reactor cavity. Because of a lack of depth in the new fuel storage pool, the refueling machine has insufficient mast movement to carry a fuel bundle assembly over a stored fuel bundle assembly. The invention solves this problem by providing side-loaded racks and aisles for the movement of fuel. During a seismic event, fuel would have a tendency to fall out of side-open racks. To maintain a high level of safety during loading, the fuel remains grappled until it is secured in the fuel storage cell and then the fuel is ungrappled. During removal of the fuel bundle assembly, the fuel storage cell remains locked until the fuel is grappled and lifted. A storage rack in accordance with the invention can also be designed to temporarily store fuel control rods. The control rod racks are shorter and wider than the fuel bundle racks. The individual storage position is larger, but the locking mechanism function is the same. Both fuel bundle assemblies and fuel control rods must be stored so that they are accessible with standard equipment. In accordance with the preferred embodiment of the invention, each storage rack comprises a pair of rows of inclined fuel storage cells arrayed back to back. Each fuel storage cell comprises an aluminum storage channel having an open side facing the adjoining aisle to enable the fuel bundle assembly to be side-loaded. Each fuel storage cell stores a new fuel bundle assembly in an inclined position so that a gravitational force component tends to hold the fuel bundle assembly in the storage channel. The fuel storage cell is provided at the bottom with a contact plate having an undeflected position when the fuel storage cell is unloaded and a deflected position when the fuel storage cell is loaded. The contact plate is actuated by the weight of a fuel bundle assembly. The contact plate is mechanically linked to a latching mechanism arranged at the top of the storage channel. When the contact plate is undeflected, the latching mechanism is in an open position for allowing a fuel bundle assembly to pass through during either loading or unloading. When the contact plate is deflected, the latching mechanism is closed to retain the stored fuel bundle assembly in the fuel storage cell during storage. As a result of the mechanical linkage between the contact plate and the latching mechanism, a stored fuel bundle assembly cannot be removed from its fuel storage cell until after it has been lifted.