Patent Number: 052308600
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen in FIG. 1 that the invention is generally indicated by the numeral 10. Reactor vessel cavity seal plate 10 is generally comprised of annular plate 12, inner spacer ring 14, outer spacer ring 16, annular seal 18, inner seal ring 20, outer seal ring 22, and means 24 for covering and sealing ports in annular plate 12. Annular plate 12 is preferably formed from a sturdy material such as one inch thick steel for withstanding the weight of the water when the space between reactor vessel 26 and shield structure 28 is flooded. Annular plate 12 is formed from a plurality of plates shaped such that they form annular plate 12 when positioned adjacent each other around reactor vessel 26. For ease of description, annular plate 12 will be referred to as a single item since the plurality of plates forming it all have a similar structure. Annular plate 12 is provided with a plurality of ports 30 spaced around its circumference. Ports 30 provide access to nuclear instruments positioned therebelow in annular cavity 32 between reactor vessel 26 and shield structure 28 and also allow circulation of air from beneath reactor vessel 26 during normal reactor operations. Annular plate 12 is provided with spacer rings 14, 16 that extend axially therefrom. Spacer rings 14, 16 may be separate pieces attached to annular plate 12 or they may be integral with annular plate 12. Inner spacer ring 14 may be fabricated from bar stock rolled to the proper diameter and extends from the inner diameter of annular plate 12. As seen in FIG. 1, inner spacer ring 14 rests freely upon reactor vessel flange 34. Outer spacer ring 16 may be fabricated from angle stock rolled to the proper diameter and extends from adjacent the outer diameter of annular plate 12. Outer spacer ring 16 rests upon cavity shield ring 36. Outer spacer ring 16 is provided with holes that match the position of shield ring studs 38 so that studs 38 do not have to be removed during installation of annular plate 12. Annular seal 18, like annular plate 12, is formed from a plurality of sections. This is schematically illustrated in FIG. 2. Once the sections are in position on top of annular plate 12, their adjoining edges are welded together over a backing strip to prevent annular seal 18 from being welded to annular plate 12. In the preferred embodiment, four 90 degree sections are welded together to form annular seal 18. One-eighth inch stainless steel is used to form annular seal 18 in the preferred embodiment. This provides the necessary corrosion resistance and flexibility. As seen in FIG. 1, annular seal 18 has a smaller inner diameter and larger outer diameter than annular plate 12 such that annular seal 18 extends beyond the edges of annular plate 12. Inner and outer seal rings 20, 22 extend axially from the inner and outer diameter of annular seal 18. Inner and outer seal rings 20, 22 are preferably formed from the same material as annular seal 18 and may be integral therewith or separate parts attached thereto. Annular seal 18 is provided with cutouts 40 that match ports 30 in annular plate 12. Inner seal ring 20 is seal welded to reactor vessel flange 34 as indicated at numeral 42. Outer seal ring 22 is seal welded to the stainless steel canal liner plate 44. This provides a watertight seal around the outer and inner diameter of annular seal 18. Means 24 for removably covering and sealing ports 30 and cutouts 40 is comprised of mounting blocks 46 and cover plates 48. A mounting block 46, preferably formed from stainless steel, is seal welded to annular seal 18 around each port 30 and cutout 40. Mounting blocks 46 are tapped to threadably receive bolts 50. Gasket 52 is positioned on the top of mounting blocks 46. A cover plate 48 is bolted above each port 30 against gasket 52 and mounting block 46. In operation, a plurality of plates are positioned adjacent one another around reactor vessel 26 to form annular plate 12. Inner spacer ring 14 rests freely upon reactor vessel flange 34. Annular seal 18, formed from a plurality of sections welded together at adjoining edges, rests freely upon annular plate 12. Inner and outer seal rings 20, 22 are respectively seal welded to reactor vessel flange 34 and the stainless steel canal liner plate 44 of shield structure 28. To begin refueling operations, cover plates 48 are bolted to mounting blocks 46 to cover ports 30 in annular plate 12. The area above reactor vessel cavity seal plate 10 may then be flooded with borated water to provide neutron shielding before the reactor vessel head is removed. The seal provided by the invention prevents nuclear instruments positioned at the lower exterior of the reactor from being damaged by the water. The steel used for annular plate 12 provides the necessary support for the weight of the water. After refueling operations are completed and the reactor vessel head replaced, the borated water is drained. Cover plates 48 may then be removed and stored to allow access to the nuclear instruments and air flow from beneath the reactor vessel. Although cover plates 48 are stored between refueling operations, they present much less difficulty for installation, removal, and storage as opposed to an entire seal assembly. The cover plates 48 are smaller and lighter than previously used sections of seal assemblies and thus greatly reduce clearance and special hoisting procedures previously needed. The remainder of reactor vessel cavity seal plate 10 stays in its installed position. During normal reactor operations the reactor vessel will grow axially as much as 1.59 inches and radially as much as 0.44 inch. Since inner spacer ring 14 rests freely on reactor vessel flange 34, the reactor vessel flange will simply slide beneath inner spacer ring 14 during expansion and contraction of reactor vessel 26. Annular seal 18 is flexible enough to bow over annular plate 12 during this expansion and flattens out again when reactor vessel 26 contracts. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted and not in a limiting sense.