Patent Number: 043127088
Section: summary

FIELD OF THE INVENTION This invention relates to closure members for nuclear reactors and, more particularly, to stud hole plug units or other plug units for reactors requiring temporary or semi-permanent seals. DESCRIPTION OF THE PRIOR ART During the refueling operation in a nuclear reactor, the closure head assembly or reactor head, which is connected to the reactor vessel, is removed and the reactor vessel is flooded with a liquid such as a boric acid solution to prevent radiation from escaping while the fuel cells are being replaced. The closure head assembly is secured to the reactor vessel by a large number of studs extending around and through the closure head assembly for threaded engagement into the wall of the reactor vessel. When these studs are removed, it is necessary to plug the stud holes in the reactor wall during refueling so that corrosion does not occur within the stud holes. Presently, plugs are used which are generally complex in construction and include O-ring seals. However, these O-ring seals are not always reliable and leakage into the stud holes has occurred. Other standard closure members cannot be employed if they include metal expansion grips since the metal grips can damage the side of the opening into which the studs are reinstalled after the fueling operation has been completed. The down time on a nuclear reactor is extremely expensive and it often takes as long as two weeks to complete refueling. Therefore, since the stud hole plugs must perform for periods of time up to two weeks or longer, and unnecessary delays merely add to the already expensive down time, it is necessary that a dependable and reproducible seal be formed. Other applications for nuclear reactors in which the stud hole plug or the like can be used may involve a pressurized cavity such as with an inert gas to protect threads or the like and, therefore, reproducible and predictable sealing results are mandatory. SUMMARY OF THE INVENTION My stud hole plug provides a positive seal and a predictable and reproducible seal from unit to unit. In addition, my stud hole plug resists etching and corrosion and can be used to close off a pressurized cavity. My invention is a reactor stud hole plug unit comprising a compression plate, a mandrel, an elastomeric ring and a tightening means such as a nut. The compression plate includes an inner and outer surface, a peripheral edge, a central opening therethrough and an annular rim extending outward from the inner surface and spaced inward of the peripheral edge. The compression plate is dimensioned so that the peripheral edge rests on the reactor surface and the rim extends into the opening to be plugged. The mandrel has a centrally threaded stud extending outward through the compression plate. The mandrel has a cylindrical upper section and cylindrical lower section joined by a frustoconical connecting section. An elastomeric seal ring having a rectangular cross section snugly fits about the cylindrical upper section of the mandrel plate and engages the compression plate rim in aligned relationship. As the nut is tightened, the mandrel moves linearly toward the compression plate causing the seal ring to be forced along the conical section. When the compression plate bottoms on the mandrel, the seal ring has been forced to a position substantially planar with the bottom surface of the lower cylindrical section.