Propellant actuated nuclear reactor steam depressurization valve

Abstract: A nuclear fission reactor combined with a propellant actuated depressurization and/or water injection valve (38) is disclosed. The depressurization valve releases pressure from a water cooled, steam producing nuclear reactor when required to insure the safety of the reactor. Depressurization of the reactor pressure vessel (14) enables gravity feeding of supplementary coolant water through the water injection valve to the reactor pressure vessel to prevent damage to the fuel core (16).

Description: 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 boiler system of a power generating plant. Water cooled nuclear fission reactors utilized for electrical power generation require a means to rapidly reduce high steam pressures within the system, through venting, to permit auxiliary low pressure system to provide continuous makeup flow in the event high pressure systems are no longer available. Advanced nuclear reactor plants, currently being designed, contemplate the use of "depressurization valves" to rapidly reduce the pressure within the reactor vessel. 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 the valve in its open position. Typically, the nature of the steam producing unit will determine the design requirements for such depressurizing 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 and/or water injection valves 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 highest 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 water injection valves. The depressurization valves for the advanced reactor designs have greater reliability and enhanced maintenance/performance characteristics compared to existing valve designs. FR-A-2075957 discloses a vapor suppressing means for a nuclear reactor for suppressing vapor pressure buildup within a nuclear reactor containment including a storage tank having a quantity of fluid stored therein and provided with a rupture disk and associated apparatus for explosively activating a disk rupturing element to release the fluid from the tank and into the containment in response to a buildup in vapor pressure within the containment. US-A-4003395 discloses a quick-opening valve for use in opening flow through a passageway from a source of pressurized fluid, such as a fire extinguisher fluid. The valve comprises a valve body in which a flow-blocking member is mounted to form a portion of the passageway. In one embodiment an imperforate plug is mounted within tubing to form the flow-blocking member, and a pair of weakened zones are formed by circular grooves in the tubing at opposite axial ends of the plug. In another embodiment the plug is formed integral with hollow cylindrical walls to form the flow-blocking member. A deflagrating charge is mounted in the valve body for generating explosive gas pressure so that the weakened zones are sheared. A slug which includes the plug is ejected in a direction at right angles to the passageway and into a slug receiving chamber. The ejected slug is deflected by a ramp to absorb excess energy. A one-way spring detent prevents the slug from rebounding back into the passageway and obstructing fluid flow. Patent Abstracts of Japan Vol. 2, No. 142 (M-41), 24 November 1978 discloses a boric acid pouring device for a reactor whose purpose is stated to be as follows: "To be subjected the boric acid water to be poured into a reactor by gravity, by means of provided with a pressure introducing tube and a pouring tube which are connected to a reactor pressure vessel and a boric acid storage tank via explosion opening valve, and a switch for remote controlling which opens the explosion opening valve." The present invention is as claimed in the claims. SUMMARY OF THE INVENTION This invention comprises new combination of a nuclear reactor and a new steam depressurization valve and/or water injection valve for service in power generating, water cooled nuclear fission reactor plants including their pressure retaining enclosures comprising the reactor vessel and associated conduits. The valve of this invention, which will meet the requirements for nuclear reactor service, is maintained in the closed position during normal operation and can be controlled from outside the reactor containment and thus beyond any source of radiation. The valve opens to permit depressurization and water injection when a propellant material is ignited by an electrical signal. In one aspect, the invention provides a nuclear fission reactor plant comprising : a nuclear reactor pressure vessel containing a heat producing core of fissionable nuclear fuel material and coolant water for submerging the heat producing fuel core and circulating through the pressure vessel to produce steam and transfer heat energy away from the fuel core, said reactor pressure vessel having a steam/coolant loop comprising a steam outlet from the pressure vessel for supplying produced steam to perform work, and a condensed coolant water inlet for returning coolant water from expended and condensed steam to the reactor pressure vessel; and, a nuclear reactor pressure vessel depressurization system comprising a pressure releasing conduit extending from an exhaust nozzle in the reactor pressure vessel or from the steam/coolant loop to an open discharge end, and a propellant actuated, fast-acting valve means imposed in the pressure releasing conduit between the reactor pressure vessel nozzle or from the steam/coolant loop and the related discharge end, said propellant actuated valve means comprising a diaphragm seal for blocking fluid flow through the valve means and a propellant for breaking free the diaphragm seal and thereby enabling fluid flow through the pressure releasing conduit from the reactor pressure vessel. It is a further feature of the plant to comprise a water injection conduit extending from a water supply to the reactor vessel and a propellant actuated valve imposed in the conduit, for introduction of coolant water into the nuclear reactor pressure vessel through a propellant actuated valve following depressurization. It is a feature of this invention to provide a new combination of steam depressurization valve and/or water injection valve with a nuclear fission reactor plant. It is also a feature of this invention to provide a mechanically simple, reliable and leaktight valve for steam depressurization and/or water injection valve combined with a nuclear fission reactor plant. It is a further feature of this invention to provide a steam depressurization valve and/or water injection valve in a nuclear reactor plant which is maintained in its normally closed position such that the valve can be opened to its pressure relieving or water injection position simply by igniting a propellant material. It is a still further feature of this invention to provide a nuclear reactor plant incorporating a steam depressurization valve and/or water injection valve wherein control of the actuating means for opening the valve can be located outside the reactor plant safety containment. BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a schematic illustration of a nuclear fission reactor plant. Figu 2 is an elevation view, partly in cross-section, illustrating the construction and mode of operation of a nuclear reactor propellant actuated depressurization valve of this invention in the normally closed position. DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, in particular Figure 1, a typical water cooled, steam producing nuclear fission reactor plant 10 comprises a containment structure 12 for enclosing and sealing in radiation and radioactive materials from the outer environment. Enclosed within the safety containment 12 is the reactor pressure vessel 14 containing the core of heat producing fissionable fuel 16 and water coolant 18 which comprises the source of steam for turbine operation. A steam/condensate coolant water loop 20 is comprised of a steam outlet pipe 22 for conducting the generated steam to its location of use, such as a turbine, and condensate water return inlet pipe 24 recycles the condensed steam back to the reactor pressure vessel 14 as coolant water for reuse. The reactor pressure vessel and associated tanks and conduits including the steam/condensate coolant water loop comprise a pressure retaining enclosure. For the advanced nuclear fission reactor plants currently being designed, an auxiliary coolant water system is provided such as the gravity feed arrangement shown in Figure 1. For instance, an auxiliary coolant water tank 26 is positioned at an elevated level within the containment structure 12 of the nuclear reactor plant 10 to provide for gravity flow or supply of auxiliary coolant water through a gravity feed conduit 28 and through a propellant actuated valve 38' into the reactor pressure vessel 14. Such an auxiliary coolant water system is designed to provide a supply of supplementary coolant water for replacing any significant losses of coolant water from the reactor pressure vessel 14 and its contained fuel core 16 caused by a major breach of coolant water carrying conduits such as the steam/coolant loop 20. However, reactor operating temperatures and pressures preclude gravity feed of coolant water into the reactor pressure vessel 14. Due to the inherent high operating pressures within nuclear reactor pressure vessels, including all pressure retaining enclosures associated therewith, reactor pressure vessel depressurizing measures are required to assure the safety of the advanced plants. In accordance with this invention, a unique combination of a water cooled and moderated, boiling water nuclear reactor plant and a propellant actuated depressurization valve provides for the venting of high pressure steam from the pressure vessel and/or rapid injection of cooling water into the reactor vessel of such plants. The depressurization system 30 of the combination of this invention includes a pressure releasing conduit 32 extending from a nozzle 34 in the pressure vessel 14, or from a significant conduit such as the steam/coolant loop 20 in fluid communication with the pressure vessel. Flow through the pressure releasing conduit 32 for venting pressure from the reactor pressure vessel 14 is controlled by a propellant actuated depressurization valve 38. Depressurization or water injection valve 38, such as illustrated in Figure 2, is comprised of a housing 40 which can comprise a pair of joined conduit sections providing a valve controlled potential fluid flow path therethrough, namely an upstream section 42 and a downstream section 44 which incorporate a valve means therein. A diaphragm valve member 46, or fluid seal, is located within the fluid flow path provided by adjoined sections 42 and 44 of housing 40, blocking off all fluid flow therethrough. Diaphragm valve member 46 is formed integral with a conduit section such as 42, or a sleeve section inserted and secured within the flow path provided by section 42 or 44. The fluid flow blocking diaphragm valve member 46 can be machined from a single body of metal forming both a portion of the conduit section such as 42, or a sleeve affixed therein, or united by integrally adjoining a composite of a diaphragm valve member 46 to such a component by welding. In any case, a portion of reduced thickness or cross-section extending around the periphery defining the diaphragm valve member 46 is provided to form a shear section 48 which when subjected to a sudden impact such as that resulting from a propellant driven piston, will fracture and separate the diaphragm valve member 46 section from the other portion. When so separated the disconnected diaphragm valve member 46 will be further dislodged by the high pressure steam from the reactor pressure vessel 14 through the upstream section 42 of the pressure releasing conduit 32, and/or simply the effects of gravity upon the then unsupported valve member 46. Pivoting means 50, such as a hinge-like member, can be provided to enable the pivoted opening of the separated diaphragm valve member 46 without it being carried away by the impact of released fluid pressure through the pressure releasing conduit 32 from the reactor pressure vessel 14 upon its opening by fracturing the shear section 48. Opening of the depressurization or water injection valve 38, which under normal operating conditions is closed to all flow or any leakage due to the integral diaphragm valve member 46 sealing off the pressure releasing conduit 32, is achieved by means of applying a sudden high velocity impact, such as the impact force produced by a propellant driven piston. As shown in Figure 2 of the drawing, a ballistics chamber 52 can be provided adjoined to a component of the valve, such as upstream section 42 with the open discharge aptly directed at the diaphragm valve member 46. The ballistics chamber 52 is loaded with a suitable propellant material 54 and sealed therein with a retaining device 56 such as a piston. Detonation of the propellant 54 abruptly and forcefully accelerates the piston which impacts upon the integral diaphragm valve member 46, fracturing the encircling thin area of the shear section 48 thereby breaking free the diaphragm valve member 46 from its adjoining component, thereby opening the propellant actuated depressurization valve 38. Thus, fluid flow comprising high pressure steam is permitted to rapidly escape from the reactor pressure vessel 14 through the pressure releasing conduit 32. A suitable electrical ignition means 58, such as a spark plug or other electrical discharge device, with a detonator, can be used to actuate the propellant material directing a forceful high velocity impact device against the diaphragm valve member 46 for dislodging same to open the valve 38. Upon actuating the normally closed propellant actuated depressurization or water injection valve 38 and as a result thereof, the depressurizing of the reactor pressure vessel 14, supplementary coolant water can be fed by gravity flow from the overhead auxiliary coolant water supply 26 through gravity feed conduit 28 and a water injection valve 38' into the reactor pressure vessel 14 to make up for any coolant water loss due to a breach of the system, or otherwise. The system of this invention comprising the combination of a power generating nuclear reactor plant with a propellant actuated depressurization and/or water injection valve, provides a high degree of reliability and rapid depressurization of the reactor pressure vessel whereupon a gravity driven coolant water feed arrangement is possible, effective and practical, as well as precluding any pressure or fluid leakage from the pressure vessel until the valve is actuated, whereupon the valve thereafter remains open to prevent a possible subsequent pressure buildup. Moreover this arrangement does not require a continuous power source, only a momentary electrical signal to initiate the depressurization of the reactor system.

Claims: A nuclear fission reactor plant (10) comprising: a nuclear reactor pressure vessel (14) containing a heat producing core (16) of fissionable nuclear fuel material and coolant water (18) for submerging the heat producing fuel core (16) and circulating through the pressure vessel (14) to produce steam and transfer heat energy away from the fuel core (16), said reactor pressure vessel (14) having a steam/coolant loop (20) comprising a steam outlet (22) from the pressure vessel (14) for supplying produced steam to perform work, and a condensed coolant water inlet (24) for returning coolant water from expended and condensed steam to the reactor pressure vessel (14); and a nuclear reactor pressure vessel depressurization system (30) comprising a pressure releasing conduit (32) extending from an exhaust nozzle (34) in the reactor pressure vessel (14) or from the steam/coolant loop (20) to an open discharge end, and a propellant actuated, fast-acting valve means (46) imposed in he pressure releasing conduit (32) between the reactor pressure vessel nozzle (34) and the related discharge end, or from the steam/coolant loop (20) said propellant actuated valve means (46) comprising a diaphragm seal (46) for blocking fluid flow through the valve means, and a propellant (54) for breaking free the diaphragm seal (46) and thereby enabling fluid flow through the pressure releasing conduit (32) from the reactor pressure vessel (14). The plant of claim 1, comprising a water injection conduit (28) extending from a gravity-feed (26) water supply to the reactor vessel (14), and a propellant actuated valve (38') imposed in the conduit (28), for introduction of coolant water into the nuclear reactor pressure vessel (14) through a propellant actuated valve (38') following depressurization. The plant of claim 1 or 2, wherein the propellant (54) is electrically detonated. The plant of any one of claims 1 to 3, wherein the diaphragm seal (46) is provided with a reduced area shear section (48) for facilitating its breaking free and removal by the propellant (54). The plant of any preceding claim, wherein the diaphragm seal (46) is secured to a pivoting means (50).

Inventors: EHRKE ALAN CARL, KNEPP JOHN BURALL, SKODA GEORGE IVO, EHRKE, ALAN CARL, KNEPP, JOHN BURALL, SKODA, GEORGE IVO
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1992
Main classification: G21C9
IPC codes: G21C13, G21D3, G21D1, G21C15, G21C9, F16K17