Patent Number: 043303706
Section: description

Turning now to the drawings, wherein like components are designated by like reference numerals throughout the various figures, attention is specifically directed to FIG. 1 which illustrates in part a liquid metal fast breeder reactor 10 of the pool type, although the reactor could also be of the loop type or any other type compatible with the present invention. This reactor is shown including a horizontally extending deck or cover 12 directly above a vertically depending reactor vessel (not shown). The reactor includes a number of internal components, that is, components located within the vessel 24 including those discussed or generally mentioned in the above recited co-pending patent application. As stated there, these components include a reactor core, an upper instrument structure or instrument tree which is located directly over the core in its normal operating position, a hoist arrangement (extending inside and outside the reactor vessel) and a fuel assembly track arrangement for transporting fuel assemblies into and out of the reactor vessel. These internal components as well as other components (both internally and externally) which have not been recited or shown may be conventional, and in any event, do not affect the present invention and, hence, will not be described herein. As discussed in the recited co-pending application, it is periodically necessary to move the hoist arrangement for refueling the reactor core. This is accomplished by means of a conventional plug assembly 16 located at the top of the vessel in deck or cover 12. In the embodiment shown, this assembly includes three horizontally extending, circular plugs, an outermost plug 18 which is the largest of the three, an intermediate plug 20 which is eccentrically located entirely within plug 18 and an innermost plug 22 which is eccentrically located entirely within plug 20. All three plugs are mounted for rotation about their respective axes and, as a result, each includes its own surrounding annular clearance gap. More specifically, as seen in both FIGS. 1 and 2, an annular clearance gap 24 is provided around the outermost plug 18 between the latter and deck 12. An annular clearance gap 26 is provided around the intermediate plug between the latter and plug 18. Finally, an annular clearance gap 28 is provided around the innermost plug 22 between the latter and intermediate plug 20. In addition, nuclear reactor 10 includes a combination seal and bearing arrangement associated with each of the rotatable plugs, specifically an arrangement 30 associated with outermost plug 18, an arrangement 32 associated with intermediate plug 20 and an arrangement 34 associated with innermost plug 22. As will be seen hereinafter, each combination arrangement serves to seal the annular sealing gap surrounding its associated plug while, at the same time, providing a bearing system supporting the plug for rotation. Turning now to FIG. 3, attention is specifically directed to the combination seal and bearing arrangement 30 associated with outer rotating plug 18 and surrounding clearance gap 24. As seen in FIG. 3 in conjunction with FIGS. 1 and 2 arrangement 30 includes an annular outer bearing race 36 fixedly mounted to deck 12 by suitable means such as a plurality of cooperating nuts and bolts, one pair of which is illustrated and generally indicated at 38. Race 36 includes a main body 40 which is annular in shape and which extends entirely around and just outside clearance gap 24, as best seen in FIG. 3. The interface between main body 40 and deck 12 is sealed by means of an O-ring 42 which is preferably constructed of metal and which also circumscribes deck 24 just outside the latter. Outer race 36 also includes an annular extension of main body 40 and located inwardly thereof. This extension which is generally indicated at 44 includes a horizontal base 46 spanning gap 24 just above the latter and two concentric, upstanding, annular flange walls 48 and 50 spaced inwardly of main body 40 and spaced from one another. Base 46 and annular flange wall 48, together with main body 40 define an annular channel 52 which opens upwardly. The outer wall 48 and annular flange 50 along with base 46 together define a second annular channel 54 which also opens upwardly and which is located concentrically inward of channel 52. The reason for each of these channels will be discussed hereinafter. Overall seal and bearing arrangement 30 also includes an inner race 56 fixedly mounted to the outermost plug 18 for rotation therewith by suitable means such as a plurality of circumferentially spaced bolts and associated nuts, one pair of which is generally indicated at 58 in FIG. 3. This inner race includes a main body 60 which is annular in shape and which extends entirely around the outermost plug just inside its outer periphery and in close proximity to clearance gap 24, as best seen in FIG. 3. The interface between main body 60 and the outermost plug is sealed with an O-ring 62 similar to previously recited ring 42. Inner race 56 also includes a downwardly extending annular flange 64 supported by and spaced outwardly of main body 60. This downwardly depending flange includes a bottom end section 66 which is located concentrically within channel 52 in a spatial realtion to main body 40 and upstanding flange 48, as seen in FIG. 3. It should be apparent from the foregoing that outer race 36 and inner race 56 together define what functionally may be considered a leakage path circumferentially between the two races from the clearance gap 24 outwardly to the ambient surroundings. This path which is generally indicated at 68 includes a first horizontal section between the confronting face of base 44 and the outermost edge of rotating plug 18, a second vertical section between the confronting faces of outer flange wall 50 of the outer race and main body 60 of the inner race, and a third section (both vertical and horizontal) between the downwardly depending flange 66 and those surfaces defining channel 52. Unless this path is sealed, it is capable of allowing the liquid metal coolant and cover gases within the reactor vessel to escape to the ambient surroundings while at the same time allowing oxygen and other ambient elements to enter the reactor. As will be seen hereinafter, this passage is sealed in accordance with the present invention. In addition to the various components thus far described, arrangement 30 also includes a bearing system comprised of a plurality of ball bearings 70 located in cooperating pockets 72a and 72b which are located within the confronting faces of main body 40 of the outer race and downwardly depending flange 66 of the inner race and which are circumferentially spaced from one another in an outermost end section leakage path 68. The ball bearings, only one of which is illustrated, are provided for suspending the inner race and plug to which it is mounted for rotation about the axis of the latter. In accordance with the present invention, previously described leakage passage 68 is sealed by means of a sealing and lubricating fluid 74, specifically, a liquid, provided within annular channel 52 and surrounding end section 66 of flange 64, thereby filling an entire circumferential section of the leakage path between clearance gap 24 and the ball bearings 70. In this way, the leakage path is sealed. However, at the same, the lubricant extends around and is provided for lubricating the ball bearings 70, as seen in FIG. 3. To this end, while fluid 74 may be of any suitable type which (1) functions in the manner intended, that is, as a sealant and a lubricant, and which (2) is compatible with its surrounding environment (but not necessarily the inner components within the reactor vessel), in a preferred embodiment this fluid is a silicone lubricating fluid such as Dow-Corning 710 silicone. In the unlikely event that a seismic occurrence might cause fluid 74 within channel 52 to splash, the adjacent channel 54 is provided for capturing it rather than any fluid to pass down through the leakage path and into the clearance gap 24. In this regard, it should be noted that the inner flange wall 50 extends upward beyond the top edge of flange wall 48 and serves to deflect the splashed liquid into channel 54. In order to fill channel 52 with sealing and lubricating fluid 74 and in order to replace this fluid periodically, outer race 36 includes at least one fill passage 80 extending through body 40 between bearing pocket 72a and the ambient surroundings and a drain passage 82 extending through the lower end of the body 40 between channel 52 (at its bottom) and the ambient surroundings. One or more drain passages 84 are also provided through the bottom of body 40 and base 46 between splash channel 54 and the ambient surroundings. While not shown, all of these passages include end caps for closing them when not in use. From the foregoing, it should be apparent that overall arrangement 30 does not have to be disassembled in order to provide sealing and lubricating fluid 74 or for periodically replacing this fluid with new fluid. It should also be apparent that the fluid itself does not have to be compatible with the reactor coolant, and, in fact, in a preferred embodiment, it is not. Rather, as stated, in a preferred embodiment the fluid is a non-metallic one which serves not only as a seal but as a lubricant for the ball bearings 70, thereby eliminating the need for a separate lubricant or for a separate inflatable seal between the fluid sealant and the bearing system which was necessary in the past. While, as just stated, it is not necessary to provide a seal between the combination sealing and lubricating fluid and the bearing system making up arrangement 30, it is nevertheless desirable to include a secondary seal outboard of the bearing system. This seal is only required during the periods of reactor operation (when the rotating plugs are stationary) to protect against reactor cover gas pressure surges. When the rotating plugs are moved, the seals are not necessary at all. Accordingly, an inflatable-deflatable seal constructed of any suitable material, e.g., elastomeric material as in the past, may be used. One such seal is shown in FIG. 3 and generally indicated by the reference numeral 86. This seal is annular in shape and extends entirely around adjacent inner race 56 just above outer race 36 and is supported in this position by an annular support ring 88 which also extends around the inner race and sits on top of the outer race. Support ring 88 is fixedly mounted to the outer race by suitable means such as a plurality of circumferentially spaced nuts and bolts, a pair of which is shown in FIG. 3 and generally indicated at 90. The interface between this support ring and the top surface of outer race 36 is sealed by means of an O-ring 92 similar to previously recited O-rings 42 and 62. As seen best in FIG. 3, ring 88 supports annular seal 86 such that the latter is maintained in sealed engagement entirely around and against inner race 36 when the seal is inflated, thereby sealing the outboard end of leakage path 68 for preventing any of the fluid 74 from passing into the ambient surroundings during cover gas pressure surges. However, this seal is not necessary for protecting the bearing system when the rotating plugs are moved during refueling of the reactor because cover gas pressure surges will not be present. Therefore, the seal may be entirely deflated so as to disengage itself from inner race 56 and, thus, the seal is not subjected to the rotational movement of the inner race, thereby increasing its useful life. From the foregoing description of combination seal and bearing arrangement 30, it should be apparent that the outer or fixed race could carry the downwardly depending flange part of the overall arrangement instead of the two channels and that the inner or rotating race could carry the two channels rather than the downwardly depending flange.