Induced nuclear reactions: processes – systems – and elements – Seal arrangements
Reexamination Certificate
1999-04-07
2001-11-13
Jordan, Charles T. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Seal arrangements
C277S637000, C277S645000
Reexamination Certificate
active
06317477
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to sealing a space between adjacent plates or ledges. In particular, the invention relates to sealing the space between an annular flange on a nuclear reactor vessel and a surrounding ledge of a refueling canal to provide a temporary water barrier between the refueling canal and the reactor vessel during refueling operations.
2. Description of the Related Art
The conditions giving rise to the problems solved by the present invention are commonly found in nuclear reactor power plants. In particular, the refueling process in pressurized water reactors must be performed under approximately 25 feet of water in a refueling canal above the reactor vessel, while the reactor vessel cavity under the canal must be maintained dry. During normal power operation the refueling canal is dry and, with the vessel cavity, forms a single large enclosure. Typically, a portion of the floor of the refueling canal forms a ledge opposite a flange attached to the upper portion of the reactor vessel. The ledge and flange provide sealing surfaces on which prior art canal sealing interfaces were effected.
Conventional refueling pool seals are of two general types: temporary and permanent. Temporary seals typically comprise a ring plate having an outside diameter of about 25 feet and a width of from 1 to 3 feet. Compression elastomer seals carried on the underside of the ring plate rested on the flange and ledge. The ring plate was bolted down to the flange and ledge to compress the seals and form a watertight fit.
Another temporary seal was developed having a rigid plate bridging the annular space to be sealed, and a pair of inflatable seals positioned between the reactor vessel flange and the rigid plate, and between the rigid plate and the ledge of the refueling canal. This arrangement is disclosed, for example, in U.S. Pat. No. 4,908,179, which issued to Robert H. Brookins on Mar. 13, 1990, and was assigned to Combustion Engineering, Inc., assignee of the present application. These temporary seal arrangements are relatively difficult and time consuming to install, thereby resulting in an undesired amount of occupational radiation exposure.
Permanent seal arrangements have been developed that remain in place during normal power operation and during refueling. An example of a permanent refueling pool seal is disclosed in U.S. Pat. No. 5,102,612, which issued to Michael S. McDonald et al. on Apr. 7, 1992, and was assigned to Combustion Engineering, Inc., assignee of the present application. This permanent seal comprises annular deck sections supported on spaced ribs around the annular space to be sealed. The inside and outside diameters of the deck sections are welded to flexible membranes to make a watertight seal between the reactor vessel flange and the ledge of the refueling pool cavity. The deck sections include openings with removable seal covers. These openings provide reactor cavity cooling air flow and an access path to the reactor vessel cavity and external core detectors when the seal covers are removed. However, removal of the seal covers to establish a ventilation path from the reactor cavity during plant operation is time consuming, thereby resulting in an undesired amount of occupational radiation exposure.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved seal assembly for establishing a temporary water barrier between a refueling canal and a reactor vessel during refueling with a minimal amount of occupational radiation exposure.
It is a further object of the present invention to provide an improved seal assembly that can be quickly installed for sealing the space between an annular flange on a nuclear reactor vessel and a surrounding ledge of a refueling canal during refueling, and can be quickly removed to establish a ventilation path from the reactor cavity during normal plant operation.
It is a further object of the present invention to provide an improved seal assembly that uses an inflatable seal to establish a primary sealing interface, and an annular support structure that supports the inflatable seal and provides a leak limiting function in the event the inflatable seal fails.
It is a further object of the present invention to provide an improved seal assembly having a permanently installed closure plate with a plurality of access ports. and a ventilation path that permits adequate ventilation of the reactor cavity without the removal of seal covers from the access ports.
To achieve these objects, the present invention provides a seal assembly for sealing a space between an annular flange on a nuclear reactor vessel and a surrounding ledge of a refueling canal to provide a temporary water barrier during refueling operations. The seal assembly includes an annular closure plate having an outer portion secured to the surrounding ledge and an inner portion supporting a first sealing surface. A second sealing surface opposing the first sealing surface is formed on or secured to the annular flange of the reactor vessel. An annular space between the first and second sealing surfaces provides a ventilation path from the reactor cavity during normal plant operation. The annular space is sealed by an inflatable seal during refueling operations to provide a water barrier between the refueling canal and the reactor cavity.
The inflatable seal is secured to and supported by an annular support structure that straddles the annular space. The annular support structure provides a structure for handling the inflatable seal during installation and removal. The annular support structure also provides a leak limiting function in the event the inflatable seal is pulled or pushed through the annular space or otherwise fails to seal the annular space. The inflatable seal is secured to the annular support structure in a manner that allows independent movement of the seal to conform to irregularities in the sealing surfaces. The closure plate has a plurality of normally closed access ports that permit access to the external core detectors and the reactor vessel cavity. The access ports need not be opened during normal plant operation since the annular space provides sufficient ventilation for the reactor vessel.
According to a broad aspect of the present invention, a seal assembly is provided for sealing an annular space between two adjacent annular surfaces. The seal assembly comprises an inflatable annular seal, and an annular support structure connected to and supporting the inflatable seal. The annular support structure has a generally rigid structure that straddles the annular space to be sealed and engages the surfaces on both sides of the annular space. The annular support structure provides a means for handling the inflatable seal during installation and removal and provides a leak limiting structure in the event the inflatable seal fails.
The inflatable seal has a plurality of threaded inserts embedded in an upper surface of the seal. The annular support structure has a plurality of slotted openings or retainers through which shoulder bolts extend to engage the threaded inserts for connecting the annular support structure to the inflatable seal. This mounting arrangement allows the inflatable seal to move vertically and transversely relative to the annular support structure to facilitate self alignment of the inflatable seal within the annular space.
The inflatable seal is an annular elastomer structure having an upper wedge portion and a lower tubular portion. The lower tubular portion is expandable when pressurized to engage lower edges of the surfaces on each side of the annular space to form a secondary seal. The upper wedge portion is drawn into engagement with upper edges of the surfaces on each side of the annular space to form a primary seal when the tubular portion is further pressurized.
According to another broad aspect of the present invention, a method is provided for sealing a space between an annular flange on a nuclear reactor vessel and a surround
Jordan Charles T.
Mun Kyongtaek K.
Westinghouse Electric Co. LLC
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