Patent Number: 053234278
Section: summary

BACKGROUND OF THE INVENTION This invention relates to nuclear reactor containment arrangements, and more particularly to permanent seal rings extending across an annular thermal expansion gap between a peripheral wall of a nuclear reactor vessel and a containment wall wherein the seal ring provides a water tight seal across the expansion gap allowing for lateral translation of the reactor vessel relative to the containment wall. Nuclear reactor vessels are typically positioned within a cavity defined by a concrete containment wall that may also contain shielding material. The containment wall is generally cylindrical in shape, having an upper portion defining a refueling canal above the reactor vessel and a lower portion spaced apart from and surrounding the reactor vessel. The annular expansion gap between the peripheral wall of the reactor vessel and the containment wall allows for thermal expansion and lateral movement of the reactor vessel in relation to the containment wall. Generally, the refueling canal is maintained dry during normal reactor operations. However, during refueling the upper portion of the reactor vessel is raised to expose the reactor core for the exchange of fuel assemblies. During the refueling operation, it is advantageous to fill the refueling canal with water to provide additional shielding. It is generally not desirable to fill the entire space defined by the containment wall with water, but rather to only flood the upper portion defining the refueling canal. A water tight seal ring is therefore provided across the annular gap between the peripheral wall of the reactor vessel and the containment wall at the boundary between the refueling canal and the lower annular portion, or well, in which the vessel is positioned. Typically, the reactor vessel has a horizontally extending flange and the containment wall has a horizontally extending ledge at about the same elevation at which the seal ring attaches. Although removable gasket type seal rings are known, the elastomeric gaskets used must be carefully installed during each refueling operation and are susceptible to thermal degradation and leakage. Furthermore, the gasket must be replaced during each refueling operation. It is advantageous to provide a permanent seal ring to reduce the time required for the refueling operation. However, permanent seal rings need to allow for thermal expansion of the reactor vessel that reduces the gap between the peripheral wall of the reactor vessel and the containment wall, and also ideally provide for some vertical and lateral movement of the reactor vessel relative to the containment wall. In addition, the seal ring should be able to withstand heavy blows from objects, such as fuel assemblies, accidentally dropped during refueling. Thus, the seal ring must have (1) strength to retain the large volume of water used in the refueling operation; (2) flexibility to accommodate movement of the reactor vessel within the containment wall; and (3) structural integrity to resist damage from falling objects. Prior art seal rings are discussed in U.S. Pat. No. 4,747,993 to Hankinson et al. and in U.S. Pat. No. 4,904,442 to Swidwa et al., the disclosures of which are herein incorporated by reference. Although those designs provide accommodation for radial and axial thermal expansion/contraction of the reactor vessel relative to the containment wall experienced during reactor operation, they fail to provide for lateral movement of the reactor vessel relative to the containment wall. Such movement of the reactor vessel, that may be encountered during operation of the reactor, can cause a loss of integrity of the seal ring. SUMMARY OF THE INVENTION It is an object of the present invention to provide a permanent seal ring for a nuclear reactor containment arrangement that accommodates radial thermal expansion/contraction of the reactor vessel relative to the containment wall. Another object of this invention to provide a permanent seal ring for a nuclear reactor containment arrangement that accommodates axial thermal expansion/contraction of the reactor vessel relative to a neutral position. Another object of this invention is to provide a permanent seal ring for a nuclear reactor containment arrangement that accommodates lateral movement of the reactor vessel relative to the containment wall. Another object of this invention to provide a permanent seal ring for a nuclear reactor containment arrangement that can provide a water seal between the refueling canal and the well that is resistant to damage from falling objects. According to this invention, a nuclear reactor containment arrangement has an annular seal ring provided for the gap defined by the peripheral wall of a reactor vessel and a containment wall spaced apart from and surrounding the reactor vessel. The annular seal ring is sealingly affixed, proximate its inner radius, to an annular flange horizontally extending from the peripheral wall of the reactor vessel and sealingly affixed, proximate its outer radius, to the containment wall. The annular seal ring incorporates a unique outer attachment arrangement that allows the seal ring to accommodate axial and lateral movements of the reactor vessel. The key feature of the outer attachment arrangement is a radially corrugated cylinder that is connected to and works in conjunction with a pair of annular cantilever plates, or Belleville plates. The Belleville plates, which have some radial curvature between their inner and outer edges, provide flexible accommodation for axial movements. The corrugated cylinder, having its radial corrugations extending longitudinally between its edges, accommodates lateral movements. An inner attachment arrangement accommodates radial expansion and contraction of the reactor vessel. A heavy gauge, annular, main seal plate extends horizontally across most of the gap. The lower surface of the main seal plate, proximate its inner edge, is supported by a cylindrical support affixed to and extending vertically upwards from the reactor vessel annular flange. An inner flexible seal connects the upper surface of the annular flange to the main seal plate at a radius inside the cylindrical support. An inner, first annular Belleville plate is sealingly affixed to the main seal plate near the first Belleville plate's inner edge, and extends radially outward therefrom. The main seal plate can have an annular protrusion extending upward from its upper surface proximate its outer edge to provide an attachment point for the first Belleville plate. The first Belleville plate, near its outer edge, is sealingly affixed to an edge of the radially corrugated cylinder. The other edge of the radially corrugated cylinder is sealingly affixed to an outer, second annular Belleville plate near the second Belleville plate's inner edge. The second Belleville plate is sealingly attached to the containment wall with an outer seal. According to another aspect of the invention, the inner flexible seal can be provided by a flexible sealing member having a cylindrical portion sealingly affixed at its upper end to the main seal plate, and an annular, horizontally extending portion sealingly affixed to the annular flange of the reactor vessel. During radial expansion or contraction of the reactor vessel, the main seal plate and the outer flexural arrangement typically do not move. The cylindrical support slides underneath the main seal plate and the inner flexible seal deforms to accommodate the movement. According to another aspect of the invention, the outer seal can comprise an annular member having an L-shaped radial cross section, wherein a horizontally extending portion of the annular member is sealingly affixed to the ledge of the containment wall, and the radially inner surface of a vertically extending cylindrical portion is sealingly attached to the outer edge of the second Belleville plate.