Patent Number: 047175311
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates generally to nuclear reactors, and more particularly to a system for transferring nuclear fuel assemblies between a fuel handling building having a spent fuel storage pool or pit disposed therein, and a reactor handling pool defined within the nuclear reactor containment area. 2. Description of the Prior Art: The fuel for large nuclear reactors, of the type, for example, employed for generating electrical power, is contained within long, small diameter fuel rods or elements which may vary in length from approximately 12-20 feet. Typically, approximately 225-400 fuel elements are arranged in a predetermined pattern within a fuel assembly, spaces being provided or defined between the fuel elements for the reception of vertically adjustable control rods. Although the number of fuel assemblies disposed within reactors will vary depending upon the size of the reactor and the desired power requirements thereof, a perspective of reactor size may be appreciated from the fact that an 1100 megawatt reactor will in fact contain approximately two hundred fuel assemblies. When the fuel assemblies are properly disposed within the reactor, and the reactor is rendered operative, the nuclear fission process consumes the fuel within an appreciable period of time thereby necessitating the removal of the old fuel assemblies and the replacement of the same with new fuel assemblies containing fresh fuel. Since the metallic rods and other supporting structures comprising each fuel assembly become radioactive, the operation which effects the replacement of the old fuel assemblies with the new fuel assemblies must be accomplished in an entirely underwater mode so as to avoid any hazards due to the radiation. In addition, since the old fuel elements have been heated to a considerable elevated temperature by means of the nuclear fission process, and will continue to produce substantial amounts of heat from the decay process for a period of at least several months, the old fuel assemblies cannot simply be immediately removed from the plant, but to the contrary, must be stored in an underwater environment which therefore provides radiation protection from, and the necessary cooling of, the fuel assemblies. Conventionally, therefore, each old or spent fuel assembly is removed from the reactor core and transported to a spent fuel storage pool or pit. Subsequently, when the old or spent fuel assemblies have decayed sufficiently, they may be removed from the storage pool or pit and shipped out from the plant for suitable disposal, reprocessing, or other viable disposition processing. Since it will obviously be imperative that the reactor be operative with its freshly replaced fuel assemblies while the spent fuel assemblies are disposed within the storage pool or pit, the spent fuel storage pit must be located externally of the reactor core and container vessel. Since the reactor container vessel is designed to withstand relatively high pressures, and to provide radiation shielding, it is impractical and uneconomical to provide large transfer-transport openings within the container vessel. Conventionally, therefore, the spent fuel storage pool or pit has been located externally of the reactor containment wall which peripherally surrounds the reactor and defines therewithin the reactor handling pool. Transfer tubes or conduits are disposed within the reactor containment wall and/or the fuel-handling building wall so as to fluidically connect the two pools which are located upon substantially the same elevational level. The elongated fuel assemblies are longitudinally transported in a horizontal mode through the transfer tubes or conduits between the pools as required. In accomplishing the actual replacement of the old or spent fuel assemblies with fresh fuel assemblies, the fuel assemblies are disposed within fuel carriers or containers, and the latter are transported upon railroad-type cars movable within the transfer tubes or conduits between the two pools. Elevators and/or crane mechanisms are provided for depositing, or withdrawing, the fuel assemblies within, or from, respectively, the fuel carriers or containers in a vertical mode, and in accordance with conventional fuel-handling-transfer systems and techniques, additional means are provided for angularly moving the fuel carriers or containers to or from a horizontal disposition such that the carriers or containers may either be transported upon the railroad cars through the transfer tubes or conduits, or re-oriented in conjunction with the hoisting cranes or elevators. In particular, one conventional fuel-handling-transfer system comprises a first hydraulic mechanism for pivotably moving, for example, the spent fuel assembly-fuel container assemblage from its vertical mode to a horizontal mode so as to be ready for translational transportation through the transfer tube or conduit upon the railroad-type car transportation system. A second mechanism, which may, for example, take the form of a reversible, electrically driven sprocket-chain drive system, translates the railroad-car vehicle, with the fuel assembly-fuel container assemblage disposed thereon, through the transfer tube and into the spent fuel storage pit or pool, and a third mechanism, which may be substantially the same as the first hydraulic mechanism, pivotably elevates the fuel assembly-fuel container assemblage to its vertical orientation. Transference of fresh fuel assembly-fuel container assemblages is understood to entail substantially the same, but reverse, processing, and this type of conventional system is exemplified by means of U.S. Pat. No. 4,053,067 issued to Leonard R. Katz et al. on Oct. 11, 1977, and assigned to the assignee of the present application, Westinghouse Electric Corporation. It may thus be appreciated that while such conventional prior art systems obviously operate quite satisfactorily, such systems nevertheless encompass, and require, the provision of three separate, distinct, and diverse drive mechanisms. This exemplary system therefore requires separate control means which is costly to implement, and additionally renders the entire system relatively complex. Still further, processing time is necessarily extensive during the various transfer modes or steps as a result of the discontinuous pivotable and translational movements of the fuel assembly-fuel container assemblages during a transfer mode cycle as accomplished by means of the aforenoted three separate, distinct, and diverse drive mechanisms. Another conventional fuel-handling-transfer system is disclosed within U.S. Pat. No. 3,637,096 issued to John J. Crate on Dec. 25, 1972 and assigned to Combustion Engineering, Inc. While this patented system admittedly encompasses a system wherein only a single transfer drive mechanism is employed, this conventional system is nevertheless appreciated to be costly to implement in view of the necessity of providing the extensive guide rail system for cooperating with the fuel carrier guide rollers. Accordingly, it is an object of the present invention to provide a new and improved nuclear reactor fuel transfer system. Another object of the present invention is to provide a new and improved nuclear reactor fuel transfer system for transferring nuclear reactor fuel assemblies between a fuel handling building and its spent fuel storage pool or pit, and the nuclear reactor containment area and its reactor handling pool. Still another object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which overcomes the various disadvantages of the known prior art conventional systems. Yet another object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which eliminates the requirement for multiple drive means in order to achieve the various transfer orientation modes of the fuel assembly-fuel container assemblages during a transfer process between the spent fuel storage and reactor handling pools. Still yet another object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which is substantially more simplified than conventional nuclear reactor fuel assembly transfer systems. Yet still another object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which accomplishes a substantial reduction in the number of drive systems required within the overall fuel assembly transfer system so as to effectively reduce the maintenance costs of the transfer system. A further object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which effectively reduces the requisite space requirements of the overall fuel assembly transfer system by eliminating the multiple drive system characteristic of conventional fuel assembly transfer systems and replacing the same with a single drive mechanism fuel assembly transfer system. A yet further object of the present invention is to provide a new and improved nuclear reactor fuel assembly transfer system which is substantially more cost-effective to implement than conventional systems in that the initial construction costs and investment required is substantially less than that of comparable conventional systems in light of the elimination of the multiple drive systems characteristic of the prior art. DISCLOSURE OF THE INVENTION The foregoing and the other objectives of the present invention are achieved through the provision of a nuclear reactor fuel assembly transfer system which comprises a single power source drive mechanism or system for achieving both the pivotable rotation of the fuel assembly-fuel container assemblage between its vertical and horizontal modes, as required at the extreme ends of the assemblage's translational transportation movement, as well as the aforenoted longitudinal translational movement of the fuel assembly-fuel container assemblage through the nuclear reactor plant transfer tube or conduit interposed between the reactor containment handling and spent fuel storage pools. In accordance with a first embodiment of the present invention, the fuel container, within which a fuel assembly is disposed, is pivotably mounted upon the railroad-type transport car by means of suitable trunnion devices, and the upper and lower surfaces of the fuel container are provided with upender brackets. The brackets are disposed upstream of the trunnions as viewed in the direction of translational travel of the transport car and the fuel assembly-fuel container assemblage, and slots are defined within the brackets. Upender arm mechanisms, having pick-up bars for engaging the slots of the fuel container brackets, are pivotably disposed within the reactor containment handling and spent fuel storage pools at sufficient distances from the ends of the transfer tube or conduit so as to permit pivotable movement of the fuel assembly-fuel container assemblage without any interference between the trailing end of the fuel container and the transfer tube or conduit. The drive system for the railroad-type transport car and the fuel assembly-fuel container assemblage is conventionally an electrically powered, cable or chain-driven sprocket system, however, this single drive system performs both the aforenoted pivotable rotation of the fuel assembly-fuel container assemblage between its vertical and horizontal modes, and the translational transportation of the fuel assembly-fuel container-railroad car assemblage through the plant transfer tube or conduit. In particular, for example, when a fuel assembly-fuel container assemblage is being translationally transported by means of the railroad car through the plant transfer tube or conduit between the reactor containment handling pool and the spent fuel storage pool, that is, the assemblage is proceeding toward the spent fuel storage pool, as the fuel assemblage emerges from the transfer tube or conduit, the upper upender brackets will engage the upender pick-up bars whereby, under the influence of the translational movement of the railroad car-fuel assemblage, the upender arm mechanism will be caused to pivot upwardly thereby automatically causing pivotable re-orientation of the fuel assembly-fuel container assemblage from its horizontal mode to its vertical mode. The fuel assemblage is of course nevertheless still supported upon the railroad transport car through means of the trunnion devices. At this stage, the fuel assembly is ready to be removed from the fuel container by means of suitable elevator or hoist-crane apparatus. In a similar manner, when the fuel assemblage is being translationally transported by means of the railroad-type car through the plant transfer tube or conduit from the spent fuel storage pool within the fuel handling building to the reactor containment handling pool, new or fresh fuel is initially deposited within the vertically oriented fuel container, and subsequently, the railroad car transport system is activated. Translational movement of the railroad car in the opposite direction toward the reactor containment handling pool initially causes automatic re-orientation of the fuel assemblage from its vertical mode to its horizontal mode by means of the reverse pivotal movement of the upender arm mechanism, followed by disengagement of the upper fuel container brackets from the upender arm pick-up bars. Continued translational movement of the railroad car and fuel assemblage toward the reactor containment handling pool, and through the transfer tube or conduit, causes engagement of the lower fuel container brackets with the pick-up bars of the upender mechanism disposed within the reactor containment handling pool after the brackets have emerged from the plant transfer tube. The translational movement of the transport car-fuel assemblage causes the downward pivotable movement of the reactor pool upender mechanism whereby the fuel assemblage is automatically re-oriented from its horizontal mode to its vertical mode. The new or fresh fuel assembly is then ready to be removed from the fuel container by means of suitable elevator or hoist-crane apparatus for deposition within the reactor. In accordance with a second embodiment of the present invention, in lieu of the upender brackets being disposed atop and beneath the fuel container, the brackets may be fixedly secured to the sides of the fuel container, and the upender arm mechanisms are accordingly provided with inwardly projecting pick-up bars for engaging the slotted brackets mounted upon the sides of the fuel container. Thus, it may be appreciated that the nuclear reactor fuel assembly transfer system of the present invention provides a simple means for automatically transferring fuel assemblies between the reactor handling containment and spent fuel storage pools, through means of the requisite pivotable and translational transport modes including both vertical and horizontal dispositions of the fuel assembly-fuel container assemblages, under the influence of a single translational transport drive means or system.