Patent Number: 047073233
Section: description

DETAILED DESCRIPTION OF THE INVENTION For convenience, the present invention will be described with respect to a particularly preferred application, namely, the closure of a fuel transfer duct leading into a liquid-metal cooled, breeder reactor. Referring to FIGS. 1 and 2 therein is depicted a typical fuel transfer cell 10 which includes a drive means 12, a piston actuator 14 and guide 16 for positioning a fuel transfer assembly 18. Piston actuator 14 and guide 16 provide for the positioning of transfer assembly 18 above and in axial alignment with ducts 20 and 22. Typically, duct 20 as shown would lead to a vessel for storage of fuel elements and duct 22 would lead to an internal portion of a nuclear reactor core containment vessel. Located vertically above duct 22 is a closure assembly 24 in accordance with the present invention. Broadly, closure assembly 24 comprises a hoist mechanism 26, a cap assembly 28, a vertical assembly of plug members 30 and a guide rail 32. Referring to FIG. 3 it is seen that assembly 30 comprises a vertical array of cylinders 34. Each of cylinders 34 is provided with a longitudinally extending axle 36. Axles of adjacent cylinders are interconnected by a plurality of endplates 38 to provide for movement of the assembly in one plane but substantially inhibit movement at right angles to that plane, somewhat analogous to a bicycle chain. The uppermost cylinder is connected to cap assembly 28 by a plate member 39. Referring now to FIGS. 4-6, the details of cap assembly 28 will be more apparent. Specifically, it is seen that cap assembly 28 comprises a base plate 40. Affixed to an upper surface of base plate 40 is a guide arm 42 terminating in a rotatable guide wheel 44 which extends into a U-shaped channel formed by vertical guide member 32. Cap assembly 28 is provided with a lifting rod 46 which is connected at its upper end to a flexible cable or chain 48 which is in turn connected to hoist assembly 26. Lifting rod 46 has a lower end axially moveable in a vertical direction within a cavity 50. Axial movement is limited by upper and lower plates 52 and 54 respectively. A biasing means, typically a spring 56, is provided for maintaining lifting rod 46 in a lower position when no lifting forces are provided by cable 48 (as shown in FIG. 5). A bottom surface of plate 40 of cap assembly 28 advantageously includes a positioning member 55 which has substantially the same shape as the passageway in duct 22. The cross sectional area adjacent the bottom surface of plate 40 is close to the same as that of the passageway in duct 22 and tapers downwardly to a lesser cross sectional area to facilitate last minute positioning of cap assembly 28. Cap assembly 28 further includes a latching mechanism comprising a plurality of latch control arms 58, each control arm has one end attached to lifting rod 46 and an opposite end connected to a pivotally mounted latching member 60. The operation of the closure assembly of the present invention is initiated prior to or upon completion of a fuel transfer operation. Specifically, referring to FIGS. 1 and 2. The fuel transfer mechanism 18 is returned to a substantially neutral position. As depicted in FIG. 1, closure assembly 24 is in a raised position. The vertical array of plug members 30 is suspending directly above duct 22 by hoist mechanism 26. When it is time to close duct 22, hoist member 26 is actuated lowering assembly 30 in a vertical direction. As it decends, guide roller 44 moves vertically downward through the channel defined by vertical guide member 32. Vertical guide member 32 has a sufficient length such that guide roller 44 remains in vertical guiding alignment until the lowermost of cylinders 34 has entered the passageway defined by duct 22. Referring to FIG. 3, it is seen that axles 36 and end plates 38 freely permit movement of plug members 30 in the plane in which duct 22 is inclined. In addition, since cylinders 34 are freely rotatable, they move readily into the passageway defined by duct 22. After guide roller 44 has left the bottom end of vertical guide member 32, at least two or more of cylinders 34 have entered the passageway in duct 22 and now act as guides for the remaining assembly of plug members. As closure assembly 24 reaches its lowermost position, cap assembly 28 contacts the open end of duct 22 and is guided into position by positioning member 55. Referring to FIG. 6 as hoist assembly 26 continues to lower cap assembly 28 spring 56 retracts lifting rod 46 into cavity 50. This in turn extends latch control arms 58 causing pivotally mounted latching members 60 to close and lockingly engage the upper end of duct 22. In a similar manner when lifting forces are applied to the upper end of lifting rod 46, the sequence of operation is reversed. The temperatures and nature of radiation to which the closure assembly 24 is exposed are such that typically cylinders 34 will be hollow and may be made from carbon steel since the principal radiation will be gamma ray. In some instances it may be advantageous to fill at least the lower portion, and in some instances, all of cylinders 34 with a material such as steel wool to enhance their thermal insulation capabilities. Thus it is seen that the present invention provides a substantially less complex method of achieving a satisfactory closure of a duct leading to an area exposed to both radiation and high temperatures. In addition, the present invention provides a closure system for an inclined fuel transfer duct which will automatically latch and secure a cap to a duct as well as automatically retracting the latch when it is desired to remove the cap. The precise number of cylinders 34 utilized and the decision whether to fill them with any additional material or not will be a function of the temperatures to which they will be exposed and the intensity and type of radiation eminating through the duct. However, these matters are all well within the skill of those versed in the art. Various modifications may be made to this closure system without departing from the true spirit and scope of the invention. For example for a duct with a round passageway spherical plugs could be utilized as well as other types of lifting and latching mechanisms. In addition other materials of construction could be utilized. Therefore, the foregoing description and drawings should be considered illustrative rather than limiting.