Patent Number: 052176819
Section: summary

BACKGROUND OF THE INVENTION This invention relates generally to pressure vessel enclosures and in particular to pressure vessel enclosures in which the compression in the enclosure walls can be continuously controlled and adjusted. This invention also relates to pressure safety enclosures that can be disassembled and assembled for inspection of the primary pressure vessel and its welds with a minimum of time and effort. Increasingly, in the operation of nuclear reactors, environmental degradation due to corrosion, mechanical or radiation effects on reactor vessel steels and weld materials have become a major concern. In order to extend its useful life, operating pressure or volume, a concept of a prestressed safety enclosure has been developed a nuclear reactor system. For safety reasons, pressure vessels, particularly nuclear reactor pressure vessels, must be designed so that all pressure or load carrying welds can be inspected periodically. This inspection can be performed on the pressure vessel either prior to service or later while the system is temporarily out of service, such as, during a reactor refueling outage. Most of the primary pressure vessels of the prior art comprised a single large vessel with one or more openings to gain access to the interior of the vessel. A flanged dome cover, usually fastened by studs to one end of the pressure vessel, provided the primary access to the interior of the vessel. To inspect the interior of the pressure vessel the studs in the peripheral flange surrounding the dome cover had to be removed in order for the dome to be removed. The main purpose of the pressure safety enclosure (PSE) of the present invention is to contain the fragments of the primary pressure vessel (PPV), the hot radioactive coolant fluid, the fragments of the nuclear core and any fission products in the unlikely event of an explosion, leak or other failure of the primary pressure vessel (PPV). SUMMARY OF THE INVENTION Since the primary safety enclosure (PSE) is designed to function during an accident, the PSE must always be prepared for an accident. Therefore, it must be permanently stressed so that it is in a state of three-dimensional (3-D) compression. This is necessary so that the "gapping," that is, opening or separation of the cast-iron blocks, will never occur even during the worst accident scenario, when the PSE becomes pressurized and hot due to a (postulated) primary pressure vessel explosion. The pressure vessel safety enclosure of the present invention is also adapted to enclose a primary pressure vessel, such as, a nuclear reactor pressure vessel, and contain it during operation. The pressure vessel safety enclosure of the present invention comprises a first pressure vessel containment assembly enclosing the primary pressure vessel. This first pressure vessel enclosure comprises a set of cast-iron blocks defining a vault or enclosure under pressure. The cast-iron block core vault must be so thick that it will not buckle when subjected to the external pressure load provided by the surrounding filler, jackets and tendons. The pressure vessel safety enclosure of the present invention further comprises a pair of first upper and first lower pressure vessel jackets that are adapted to enclose and be spaced apart from, respectively, the upper and lower halves of the pressure vessel safety enclosure (PSE). The space between the upper and lower pressure vessel jackets is filled with a low melting point, high boiling point metal. The rims of the upper and lower pressure vessel jackets are adapted to slidably engage, in a sealed relationship, the outer surface of the pressure vessel safety enclosure (PSE). The upper and lower jackets are supported, respectively, by upper and lower bearing plates or seats attached to respective upper and lower frusto-conical skirts. The upper and lower skirts are, respectively, attached to upper and lower ring girders. The upper and lower ring girders are connected to each other by a number of equally spaced, high-strength, post-tensioned tendon cables contained in insulated sleeves for corrosion protection. The ends of each of the tendon cables are connected to the respective upper and lower ring girders by a base anchor at the lower end and a permanent hydraulic or screw jack at the upper end. The hydraulic or screw jacks provide the force necessary to move the upper and lower jackets toward or away from each other to increase or decrease the compression in the pressure vessel safety enclosure. It is, therefore, an object of the present invention to provide a pressure vessel safety enclosure. It is another object of the present invention to provide a pressure vessel safety enclosure in which the compression in the enclosure can be continuously monitored, controlled and adjusted. It is a further object of the present invention to provide a pressure vessel safety enclosure in which moving jackets are used to control the compression in the vessel enclosure walls. It is still another object of the present invention to provide a pressure vessel safety enclosure that is easily dismantled without the use of stud and flange connections. It is another object of the present invention to provide a pressure vessel safety enclosure in which the compression in the walls of the enclosure is controlled and adjusted by the tension members holding the upper and lower pressure vessel jackets together. These and other objects of the present invention will become manifest upon study of the following specification taken together with the drawings.