Patent Number: 050283839
Section: summary

FIELD OF THE INVENTION This invention relates to power generating nuclear fission reactor plants and equipment therefor. The invention is particularly concerned with an improvement in means used for depressurizing steam within the nuclear reactor pressurized system of a power generating plant. Water cooled nuclear fission reactors utilized for electrical power generation, as with any steam producing boiler, require valve means to reduce excessively high pressures within the system, through venting, to maintain and insure system integrity and safety. Safety or relief, and combination safety-relief valves commonly used in many nuclear reactor plants, typically open at a specified pressure and reclose after the pressure of the system is reduced to a prescribed safe level. Anticipated nuclear reactor plant designs contemplate the use of "depressurization valves" to reduce excessively high pressures. Once opened, such valves have the unique feature of remaining open down to zero pressure without any further operator action and without need to provide power to maintain a valve in open position. Typically, the nature of the steam producing unit will determine the type and requirements for such depressurizing safety relief valves. This is especially so in the nuclear reactor field due to the distinctive conditions encountered with nuclear fission and the stringent safety requirements imposed in this industry, among other reasons. BACKGROUND OF THE INVENTION A unique aspect of nuclear reactors and a foremost safety consideration, is the inherent presence of radiation and radioactive materials. This highly significant condition requires the most strict design and safety conditions with respect to many components and functions of a nuclear reactor plant and imposes numerous requirements in operating and maintaining nuclear plants. For example, reactor components and related equipment which become significantly radioactive in service generally must be capable of long term, trouble free and positive functions, as well as being amenable to operation and maintenance by personnel in remote locations. Steam depressurization and/or pressure relief valves or means are especially critical devices in any type of high pressure hot water and/or steam producing units, and when employed in a nuclear reactor plant the standards and demands must be applied to design and fabrication of such valves. Various valve designs and operating modes have been proposed and considered in an effort to meet the stringent demands for such steam depressurization and pressure relief valves. For example, one proposed category of depressurization valves has been explosive/propellant-activated valves. In theory this type of valve should comply with the required design properties. This type of valve is fast operating, and routine valve maintenance and replacement of consumed parts of an opened valve can be quickly performed. However, it appears that with such explosive/propellant-activated valves, there are significant concerns such as limits upon the effective life of the explosive material as a result of exposure to heat and radiation, and flow rates obtainable with the current designs. SUMMARY OF THE INVENTION This invention comprises an improved steam depressurization valve for service in power generating, water cooled nuclear fission reactor plants. The valve of this invention, which will meet the requirements for nuclear reactor service, is maintained in the normal operating closed position by fluid pressure which can be sourced and controlled from outside the reactor containment and thus beyond any source of radiation, and opens to permit depressurization venting by release of the externally applied and controlled fluid pressure. OBJECTS OF THE INVENTION It is a primary object of this invention to provide an improved steam depressurization valve suitable for service in a nuclear fission reactor plant. It is also an object of this invention to provide a mechanically uncomplicated and reliable, light-weight and leak-tight valve for steam depressurization in a nuclear fission reactor plant. It is a further object of this invention to provide a steam depressurization valve which utilizes a positive source of fluid pressure to maintain the valve in its normal operating closed position such that the valve can be opened to its pressure relieving position simply by terminating the positive fluid pressure force applied thereto. It is a still further object of this invention to provide a steam depressurization valve for which the source of the actuating medium for opening the valve and the control of the opening medium can be located outside the reactor plant safety containment.