Patent Number: 053234278
Section: description

DETAILED DESCRIPTION OF THE INVENTION The feature of this invention that allows the laterally translating permanent cavity seal ring to laterally translate is a specially designed custom bellows used on the outer portion of the seal ring. Most existing welded seal rings used in the nuclear industry utilize either an L-shaped section or a U-shaped section to allow thermal expansion of the reactor. These designs generally have the serious drawback in that they are axisymetric, i.e., the cross section of the seal does not vary at all with the circumference. For these arrangements, significant lateral translation of the reactor tends to cause a shear failure of the flexure at locations 90 degrees off the movement axis. Although traditional bellows with several annular U-shaped folds can accommodate some movement by flexing the bellows (elongating/compressing the opposite sides to rotate the bellow sections), the very large diameter and relatively short height of the seal ring makes this type of mechanical action impractical or impossible. The bellows used in this invention differs in that the radial corrugations extend transverse, rather than parallel, to the end surfaces. The features of this invention are better understood in reference to the drawings. Referring now to FIG. 1 and 2, a pressurized water reactor 1 is positioned within a space 2 defined by a containment wall 4. The reactor is of the pressurized water type, and the figure depicts a fuel rod assembly 6 contained within the reactor vessel 8. The reactor vessel s is supported by means not shown. A coolant flow inlet 10 and a coolant flow outlet 12 penetrate the cylindrical peripheral wall 14 of the reactor vessel 8. The control rods (not shown) that moderate the nuclear reaction are moved vertically by control means 22 extending through the removable reactor vessel head 16. The reactor cavity 2 is divided into an upper portion which defines a refueling canal 18 and a lower portion defining a well 20 that surrounds the lower portion of the reactor vessel 8. A ledge 24 in the containment wall divides the refueling canal 18 from the well 20. The peripheral wall 14 of the reactor vessel has a horizontally extending annular flange 26 at about the elevation of the containment wall ledge 24. The reactor vessel head 16 is removably sealed to the lower portion of the reactor vessel by an annular flange 28 at an elevation above the horizontally extending reactor vessel flange 26. A permanent cavity seal ring 30 of the present invention extends between the containment wall ledge 24 and the horizontally extending flange 26 of the peripheral wall of the reactor vessel. During a refueling operation the refueling canal 18 is first flooded with water and then the reactor head 16 is lifted, thereby exposing the reactor core. The water flooding the refueling canal provides a radiation shield for the exposed core and refueling assemblies. The detailed construction of the annular seal ring 30 of this invention can be better understood by reference to FIG. 3. According to a preferred embodiment of this invention, a cylindrical support 32 is attached to the upper surface 34 of the horizontally extending annular flange 26 and extends vertically upward therefrom. An annular main seal plate 36 extends across most of the gap 2 defined by the containment wall 4 and the peripheral wall 14 of the reactor vessel 8. The main seal plate 36 rests, near its inner edge 38, upon the cylindrical support 32. The upper side 40 of the main seal plate 36 preferably has an annular protrusion 42 extending upwards from a location proximate the main seal plate outer edge 44. A first annular Belleville plate 46 is welded to the annular protrusion near the Belleville plate's inner edge 48. The upper edge 50 of a radially corrugated vertical cylinder 52 is welded to the bottom side 54 of the Belleville plate near the plate's outer edge. The lower edge 56 of the radially corrugated vertical cylinder 52 is welded to the upper side 58 of a second annular Belleville plate 60 near the Belleville plate's inner edge. The outer edge 64 of the second Belleville plate is then sealingly affixed to the containment wall 4. The inner flexible seal 66 is preferably provided by a flexible sealing member 68 having an L-shaped radial cross section. An annular, horizontally extending portion 70 is welded to the upper surface 34 of the annular flange 26. A cylindrical portion 72 is welded at its upper edge to the inner edge 38 of the main seal plate 36. The flexible sealing member 68 is located radially inside the cylindrical support 32 as depicted in FIG. 3. Various arrangements can be used to provide a seal attachment of the second annular Belleville plate 60 to the containment wall 4. A preferred embodiment is depicted in FIG. 3. An annular member 74 having an L-shaped cross section attached to the ledge of the containment wall provides a fixture to weld to the second annular Belleville plate. The annular member 74 is affixed to and sealed to the concrete containment wall 4 by means well known in the construction arts. All materials for the laterally translating permanent cavity seal 30 are preferably stainless steel although other materials with similar qualities of strength, flexibility and corrosion resistance can be equally useful. The main seal plate 36 is preferably 1-1/2 inches (2.5-3.8 cm) thick, providing a strong barrier to falling objects. While the dimensions of the inner and outer diameters of the main seal plate depend upon the sizes of the containment wall 4 and the reactor vessel 8, the inner diameter will generally be between 15 and 20 feet (460 and 730 cm) and the outer diameter between 25 and 30 feet (760 and 910 cm). The cylindrical support 32 that the main seal plate 36 rests upon will also be heavy gauge stainless steel and will be about 6-12 inches (15.2-30.5 cm) in height. The Belleville plates 46, 60, the radially corrugated cylinder, the flexible sealing member 68 and the L-shaped annular member 74 attached to the containment wall 4 are made of much lighter gauge stainless steel, generally 0.04-0.08 inches (0.10-0.20 cm) wall thickness, allowing for the necessary flexibility. A segment of the radially corrugated vertical cylinder 52 is depicted in horizontal cross section in FIG. 4. Its vertical height will range between 6-12 inches (15.2-30.5 cm). The difference between the nominal inner and nominal outer radii of the radially corrugated vertical cylinder is typically 0.2-0.8 inches (0.51-2.03 cm). In other words, the amplitude of each of the corrugations is typically 0.2-0.8 inches (0.51-2.03 cm). The density of corrugations is approximately one per inch (0.4 per cm). During operation of the nuclear reactor 1, radial thermal expansion and contraction of the reactor vessel 8 is accommodated by the inner connection arrangement. Radial expansion of the reactor vessel 8 moves the horizontally extending annular flange 26 radially outward relative to the main seal plate 36. The cylindrical support 32 slips radially outward beneath the main seal plate 36. The lower, annular portion 70 of the inner flexure member 66 that is attached to the annular flange 26 moves radially outward relative to the main seal plate 36 as depicted in FIG. 5. Radial contraction of the reactor vessel 8 relative to the containment wall 4 involves movements in opposite directions from that described above. A lateral translation of the reactor vessel 8 relative to the containment wall 4 is mainly accommodated by the outer attachment arrangement comprising the Belleville plates 46, 60 and the radially corrugated vertical cylinder 52. FIG. 6a is a radial view of a section of the outer attachment arrangement in a neutral position. FIG. 6b shows the effect of lateral movement of the reactor vessel 8 (in a direction indicated by the arrow) on the outer attachment arrangement. Lateral movement of the main seal plate 36 in the horizontal plane will deform the upper end of the radially corrugated vertical cylinder 52 in the direction of the lateral movement. The upper end of the radially corrugated vertical cylinder, being attached to the first Belleville plate 46, will move rigidly with movement of the main seal plate 36 and the reactor vessel 8. The lower end of the radially corrugated vertical cylinder, being welded to the second Belleville plate 60 that is affixed to the containment wall 4, will typically remain in place. The flexible sealing member 68 does not significantly deform during a purely lateral movement of the reactor vessel 8. Axial thermal expansion/contraction of the reactor vessel 8 relative to the containment wall 4 is accommodated by flexure of the first 46 and second 58 Belleville plates as depicted in FIG. 7. Another embodiment of the outer attachment arrangement that provides for an equivalent degree of movement is arranged such that the radially corrugated vertical cylinder 52 is welded at its bottom edge to the upper side of the inner, first annular Belleville plate, and extends upwards therefrom. The outer, larger diameter, second annular Belleville plate is welded at its lower side proximate its inner edge to the upper edge of the radially corrugated cylinder. The second Belleville plate's outer edge is then sealingly affixed to the containment wall 4. This arrangement provides equivalent freedom of movement to those embodiments described above. It will be understood that the above description of the present invention is capable of various additional modifications, changes and adaptations and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.