Patent Number: 050193279
Section: description

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawing, FIG. 1 in particular, a typical liquid metal cooled, pool type nuclear reactor plant 10, comprises a reactor vessel 12 having an open top and side and bottom walls without any penetrations passing therethrough. A fuel core 14 containing heat producing fissionable fuel comprising oxides of uranium, plutonium and/or thorium, is located in the lower portion of vessel 12, supported on a fuel core support structure 16. The fissionable fuel material of the core is enclosed within sealed tubes which are grouped and assembled into units or fuel assemblies 18. A liquid metal coolant 20, such as sodium metal, substantially fills the reactor vessel 12, forming the coolant pool with the fuel core 14 submerged therein. The liquid metal coolant is circulated by means of a pump (not shown) through a circuit including the heat generating fuel core 14 and a heat exchanger (not shown) to transfer the heat from the core to a means for its consumption such as steam turbine generators (not shown). The reactor vessel 12 is provided with a cover member 22 to close the vessel and to contain and isolate its contents including the fissionable fuel material and radioactive fission products along with the liquid metal coolant 20 from the outside atmosphere. The cover member 22 includes both at least one access opening for the introduction or removal of fuel units and maintenance tools, and at least one revolving section 24 to enable greater versatility and maneuverability for implements passing therethrough for operations within the reactor vessel. A gaseous blanket of an inert gas such as nitrogen or argon is provided over the pool of liquid metal coolant forming a gaseous barrier precluding contact of the coolant with the external atmosphere and foreign matter and in turn its contamination or any deleterious reactions. As illustrated in FIG. 2 of the drawing, a conventional type of fuel assembly 18 for liquid metal cooled, pool nuclear reactors, comprises a multiplicity of sealed tubes containing fuel which are grouped into an assembly having an angular cross-section 26 such as hexagonal. The lower end of the fuel assembly 18 is provided with a generally conical portion and projection 28 to facilitate mounting into openings of a support structure. The upper end of the fuel assembly comprises a cylindrical intermediate portion 30 of relatively reduced diameter and an uppermost end portion comprising a transverse annular flange 32 of an angular cross-section such as hexagonal. The upper end structure of the fuel assemble facilitates both securing and aligning the unit in either the fuel core or storage racks. A typical in-vessel transfer device 34 for moving fuel assemblies 18 within the vessel of a liquid metal cooled, pool nuclear reactor comprises a vertical support structure 36 or shaft which penetrates down through the vessel cover member 22 into vessel 12, and is provided with a gripping mechanism 38 at its lower portion within the vessel for securely grasping and holding a fuel assembly 18 for transfer. The vertical support structure 36 normally extends through a rotatable section of cover number 22 whereby an operator from above the reactor vessel 12 can manipulate the gripping mechanism 38 within the vessel 12 over a broad area including the fuel core. In a preferred arrangement the gripping mechanism 38 is mounted on a pantographic type system which is mounted on the vertical support structure 36 whereby it provides greater flexibility in its capacity to reach or extend over the area above the fuel core. In accordance with this invention, a fuel assembly transfer device 40, suspended on a support member 42 passing through a port in the reactor vessel cover 22, comprises a basket unit 44 having an intermediate body section 46 provided by a hollow cylinder or other encircling housing. Cylindrical housing 46 is provided with an elongated side access port 48 of an apt configuration and area for passing therethrough of a fuel assembly 18. The transfer basket 44 comprises a lower end annular base member 50 having a conical shaped central opening 52 for receiving and securely seating the conical portion 28 and projection of a conventional fuel assembly 18. An upper end of the transfer basket 44 also comprises a semicircular cap member 54 having a central opening 56 extending vertically therethrough and with the gap 58 of the semicircular cap member 54 aligned with and corresponding to the side access port 48 of the intermediate body section 46. The central opening 56 extending vertically through upper end semicircular cap member 54 is provided with an upper semi-annular downward sloping surface 60 directed towards the central opening 56, and an adjoining intermediate portion 62 having an angular peripheral edge 64 or vertical wall portion surrounding the central opening 56. Adjoining the lower side of the intermediate portion 62 is a semicircular portion 66 of relatively reduced diameter. In a preferred embodiment of this invention the basket unit 4 of the transfer device 40 is suspended and vertically moved by a support member 42 comprising an extendable tape such as a bi-stem drive tape which extends down through a port in the reactor cover member 24. With this arrangement of the transfer basket 44, a fuel assembly unit 18 can be securely mounted and carried within the side loading basket 44 for transfer. This is effected by means of laterally introducing the conical portion 28 and projection of the fuel assembly into the conical shaped central opening 52 of the annular base member 50, and the upper annular flange 32 of the fuel assembly into the sloping downward central opening 56 and dropping down into and seating into the adjoining intermediate portion 62. New fuel assemblies 18 for refueling the reactor fuel core 14 are introduced into the reactor vessel 12 passing through a port in the vessel cover member 22 while retained and carried within the transfer basket 44. Then the in-vessel transfer device 34 takes the fuel assembly 18 from the transfer basket 44 within the vessel and either places it within the fuel core 14, or positions it in a storage rack 68 such as shown mounted on the fuel core support structure 16 for temporary keeping. The reverse procedure is employed for removing spent fuel assemblies 18 from the fuel core 14, and their disposal from the reactor vessel 12. As is apparent, the transfer of a fuel assembly to the novel side loading transfer basket 44 of this invention significantly reduces the distance of vertical travel for the in-vessel transfer device 34 in handling and manipulating a fuel assembly. This decreases the travel distance of the in-vessel transfer device and reduces the costly path time required for a refueling outage a significant amount. Moreover, the side loading transfer basket reduces the in-vessel transfer device duty cycles which provides a substantial improvement in the device's reliability and service life. Also, the consequences of mishandling and dropping a fuel assembly due to a malfunction of the in-vessel transfer device are minimized with the side loading transfer basket of the invention because of the substantially shorter falling distance of any dropped fuel assemblies. And in the event of an in-vessel transfer device drive failure while transferring a fuel assembly, the side loading transfer basket of this invention can assist in recovering a fuel assembly by being raised or lowered to any elevation corresponding to an immobilized fuel assembly whereby the fuel assembly can be transferred from the in-vessel transfer device to the side loading transfer basket utilizing normal procedures.