Patent Number: 041683943
Section: summary

FIELD OF THE INVENTION This invention relates to an apparatus for making an electrical connection through a vessel wall wherein the connection should withstand high temperature and high pressure with a life span of over 40 years. The apparatus, more particularly, should be capable of being used with nuclear reactor vessels and is known in the art as an electrical penetration assembly. BACKGROUND OF THE INVENTION Electrical penetration assemblies are utilized to pass electrical conductors through containment vessels of nuclear power generating stations. The wall of the containment vessel, which is a relatively thick concrete combined with a steel dome, has a steel penetration nozzle which penetrates the wall. The nozzle, on its outer end, has a flange suitably welded thereto and may have a similar flange on the interior end. The electrical penetration assemblies are basically of two types, the canister type and the unitized header type. In the canister type, two header plates, each containing several feed-through modules, are mounted and sealed on the opposing flanges of a nozzle to form a canister wherein the inside may be pressurized with dry nitrogen to monitor any gas leakage out of the nozzle. In the unitized header electrical penetration assembly, a header plate is provided with one or more conductors or modules (i.e., a conductor surrounded with insulation which is sealed thereto). The modules are suitably affixed to the header plate which is bolted or fixed onto the exterior flange of the nozzle. Porting holes or narrow passageways interconnect all of the modules in the header plate thereby providing means to monitor any gas leakage. Typical unitized header electrical penetration assemblies are taught by U.S. Pat. Nos. 3,781,453 and 3,828,118. The system described in 3,781,453 consists of a canister containing two epoxy resin bushings having the conductors fixed at each end and the conductors are spliced internally of the canister. The system described in U.S. Pat. No. 3,828,118 consists of modules made of glass-reinforced, anhydride-cured epichlorohydrin bisphenol A-type epoxy resin with conductors bonded therebetween. Anhydride-cured epoxy resin undergoes reversion due to hydrolysis when subjected to super heated steam as would be encountered during an accident to a reactor system. Furthermore, such resins show considerable degradation under thermal aging simulating 40 years of design life and show a decrease in strength and flexibility when subjected to gamma radiations of over 100 million rads. A typical canister type is taught by U.S. Pat. No. 3,856,983 wherein each conductor passes through a seal means on each end of the penetration nozzle. As is obvious by studying this patent, canister types are inherently complicated and costly. Although the prior art teaches the bolting of a header plate onto the flange of a penetration nozzle for unitized header types, the prior art does not teach how the seal therebetween is to be monitored for leaks. OBJECTS OF THE INVENTION An object of this invention is to provide an improved means and method for providing hermetically sealed electrical feed-through or penetration structures or assemblies. Another object of this invention is to provide an improved method of making and constructing an electric feed-through assembly which can withstand the abnormal conditions during a loss of coolant accident in a nuclear reactor. Another object of this invention is to provide a medium voltage power feed-through structure suitable for electrical power supply for the purpose described and in the environment mentioned hereinabove, allowing for both longitudinal and lateral movement of the conductors during a three phase short circuit while maintaining sealed integrity against gas leaks. Another object of this invention is to provide an improved means and method of maintaining pressure and monitoring gas leakage between the header plate and the welded flange for an unitized header type electrical penetration assembly so that plates and flanges with flat surfaces may be utilized. Another object of this invention is to provide a suitable flat gasket between the flange and header plate, wherein the gasket has opposing circumferential indentations or grooves interconnected together and a passageway in the header plate communicates with these grooves and with the gas monitoring system in the header. These and other objects and features of advantage will become more apparent after studying the following embodiments of my invention, together with the appended drawing.