Patent Number: 047818824
Section: summary

The present invention relates to an improved apparatus for refueling of a nuclear reactor. As described in U.S. Pat. No. 4,311,557 to Edward F. Kowalski et al., assigned to the assignee of the present invention, the contents of which are incorporated herein, some fuel assemblies are periodically removed from the reactor core while other assemblies are moved about within the core to new positions and new fuel assemblies introduced into the core to replace those that were removed. As described in U.S. Pat. No. 4,311,557, a refueling apparatus generally uses a means for positioning the fuel assembly above the reactor and concentrically aligned vertical inner and outer masts which raise or lower the fuel assembly as desired. The inner mast carries the fuel assembly and is vertically axially movable relative to the outer mast in a telescopic manner. In order to centrally position the vertically movable inner mast relative to the surrounding outer mast, guide means or rollers are provided so as to prevent displacement of the centrally positioned inner mast. As claimed in said patent, guiding means are provided which comprises at least one member on the inner mast which cooperates with a complementary shaped member on the outer mast to guide the inner mast vertically when moved from one elevation to another, the member on the inner mast illustrated as having a grooved surface and the member on the outer mast being a rotating element which rolls in the groove during mast movement. One embodiment thereof is illustrated in FIG. 10 of that patent. Generally, about two or three guide roller assemblies are provided in a common plane at about eight spaced vertical locations along the mast, with the outer members mounted on the outside of the outer mast and projecting through openings in the wall of the outer mast. The guide roller assemblies extend through the openings in the outer or stationary mast and alignment thereof made at the manufacturing site. When the masts are readied for use in the refueling machine, further alignment is usually needed. One type of adjustment is effected by the use of shims between a roller housing and the outer mast at the location of the screws that mount the roller housing on the mast. Such an alignment system is illustrated in FIGS. 1 and 2 hereof, where an inner mast 1 is centrally disposed in an outer mast 3, with guide means 5 aligning the same. The guide means, as illustrated, includes a housing 7 that carries a shaft 9 upon which roller 11 is retained, the roller extending inwardly from the outer mast 3 through openings 13 towards the inner mast 1. Screws 15 extend through flanges 17 of the housing 7 and mount the housing 7 to the outer mast 3. Shims 19 are used between the flanges 17 of the housing and the outer surface 21 of the outer housing 3. As illustrated, one of the guide rollers 11' is provided with a groove 23 that cooperates with a projecting member 25 on the inner mast 1 to prevent the rotation of the inner mast 1 relative to the outer mast 3 during vertical movement thereof. In another existing construction of such an alignment system, as illustrated in FIGS. 3 and 4 hereof, an inner mast 31 is concentrically disposed within an outer mast 33, and guide means 35 are used to align the two masts. As illustrated, the guide means 35 include a housing 37 which slidably supports a bracket 39. The bracket extends through an opening 41 in the outer mast 33 and caries a shaft 43 upon which a roller 45 is mounted. The housing has upper and lower walls 47 and a rear wall 49, with the rear wall 49 having an aperture 51 therethrough. Extending through the aperture is a threaded rod 53 that carries the bracket 39 and the threaded rod 53 has thereon a pair of lock nuts 55 and 57 which may be loosened to permit sliding of the bracket 39 and shaft 43 towards or away from the inner mast 31 and then tightened to lock the bracket and roller in a predetermined location relative to the inner mast 31. In this device also, a groove 59 is provided in a roller 45' which cooperates with a projection 61 on the inner mast 31 to prevent rotational movement of the inner mast 31 relative to the outer mast 33. With either of the above designs of guide means, the inner mast alignment with the outer mast is accomplished in a fabricator's shop with the guide means, or roller assemblies, then marked for location and removed from the outer mast for shipment. Field realignment of the inner mast is very difficult and usually necessary. Due to a combination of misadjustment and wear, the alignment spacing often is enlarged during service. In some cases, the spacing is large enough to allow an orientation feature on the inner mast to come out of engagement with a complementary grooved guide roller permitting the inner mast to freely rotate within the outer mast. SUMMARY OF THE INVENTION An apparatus for loading or unloading a fuel assembly in a nuclear reactor has a means for positioning a fuel assembly with a housing carrying a pair of concentric inner and outer masts. The inner mast has means thereon for gripping a fuel assembly and is vertically movable axially relative to the outer mast. A guide means is provided on the inner and outer masts to align the inner mast centrally within the outer mast during relative vertical movement therebetween, the guide means including a plurality of inner members on the inner mast and cooperating outer members on the outer mast, with the outer members supported on the outer mast and pivotally mounted for movement towards and away from the inner members. Alignment means are provided to enable vertical precise alignment of superimposed outer members relative to the inner members. The outer members are supported on the outer mast, such that the rollers are pivotally movable, by a framework that comprises a top wall and bottom wall and end plate, with side bars attached to a pivot pin passing through a bore in the bottom wall of the framework. A precise adjustment of the rollers is achieved by use of an alignment beam extending between the two side bars adjacent the upper ends thereof and an adjustable device coacting with a sleeve about the alignment beam which includes a threaded sleeve and lock nut with a shoulder of a hollow stud abutting the inner wall of the end plate and the lock nut abutting the outer wall of the end plate.