Abstract: A reactor cavity flooding system, which is used to immerse the hemispherical lower head of a nuclear reactor vessel by flooding the reactor cavity, is connected to both coolant injection nozzles located at the annulus gap between the lower head and the thermal insulator of a reactor and the discharge loops which are used to drain the hot water of the annulus gap into either the cavity floor or a liquid eductor. The subcooled water at a fire protection system can be directly injected into the annulus gap through twenty-five (25) nozzles at the lowest, middle, and top injection headers by a pump. The hot water heated at the lower head will be drained into either the cavity floor and/or the liquid eductor via two discharge loops that consist of both a suction header in the annulus gap at the equator level of the lower head and four (4) leakage collectors at the outside of four (4) shear keys of a reactor vessel. Drainage and recirculation of the hot water can be achieved in two ways.

Abstract: A device for collecting reactor-meltdown products from a reactor pressure vessel includes an antechamber disposed below the reactor pressure vessel, an expansion chamber having a floor forming an expansion surface for reactor-meltdown products, and a bulkhead being disposed between the antechamber and the expansion chamber and being destructible by the reactor-meltdown products. The bulkhead has a plurality of parts including at least one part being thermally destructible by the reactor-meltdown products. The at least one part is joined to the other parts for clearing a flow path for the reactor-meltdown products from the antechamber into the expansion chamber upon a destruction of the at least one part.

Abstract: The detection device includes at least one thermocouple (10) arranged aligned with the bottom head of the vessel of the nuclear reactor, having a first branch (9) made of a first metallic material and at least one second branch (11) made of a second metallic material, different from the first material, welded to a point on the first branch constituting a hot junction of the thermocouple (10). The first branch (9) of the thermocouple has the form of an elongate hollow section. The device furthermore includes means for analyzing the measurements taken by the thermocouples (10).

Abstract: A nuclear reactor facility has a collecting chamber for a core melt, a coolant tank and a coolant connecting line having an inlet end connected to the coolant tank and an outlet end protruding into the collecting chamber and having an outlet cross section. A closing device at the connecting line which opens as a function of temperature for initiating cooling of the core melt includes a closing member disposed at the outlet end of the connecting line for normally tightly closing the outlet end. The closing member has a temperature-dependent opening element for tripping clearance of at least a portion of the outlet cross section of the connecting line upon thermal action by the core melt to direct the coolant from the coolant tank, through the connecting line and into the collecting chamber. The opening element being a plastic block which thermally insulates the coolant, and is corrosion-resistant.

Abstract: The reactor vessel of a nuclear reactor installation which is suspended from the cold leg nozzles in a reactor cavity is provided with a lower thermal insulating barrier spaced from the reactor vessel to form a chamber which can be flooded with cooling water through passive valving to directly cool the reactor vessel in the event of a severe accident. The passive valving also includes bistable vents at the upper end of the thermal insulating barrier for releasing steam. A removable, modular neutron shield extending around the upper end of the reactor cavity below the nozzles forms with the upwardly and outwardly tapered transition on the outer surface of the reactor vessel, a labyrinthine channel which reduces neutron streaming while providing a passage for the escape of steam during a severe accident, and for the cooling air which is circulated along the reactor cavity walls outside the thermal insulating barrier during normal operation of the reactor.

Abstract: The device includes a corium collector arranged below the vessel of the reactor, with circulation channels for cooling the collector and the corium. These channels are connected to a water feed and cooling-fluid removal circuit including a water storage tank, a tank for collecting fluid removed from the channels and a steam ejector which receives steam from the cooling fluid originating from the collection tank and sucks water from the storage tank and injects the water into the channels.

Abstract: A device for collecting reactor-meltdown products from a reactor pressure vessel includes an expansion chamber for receiving the reactor-meltdown products and for receiving a coolant, such as cooling water, for cooling the reactor-meltdown products spreading in the expansion chamber. The expansion chamber is disposed laterally of the reactor pressure vessel and has a floor and a cooling system in the floor.

Abstract: The reactor vessel is placed inside a reactor pit having a vertical axis and including a bottom (5) arranged below and aligned with the vessel bottom head. In the event of meltdown of the reactor core as a result of accidental operation of the nuclear reactor, which may lead to perforation of the vessel bottom head, the temperature at a plurality of points (14) distributed over the surface (8) of the reactor pit bottom (5) in line with the vessel bottom head is measured continuously. Optical measurement of the temperatures on the bottom (5) of the reactor pit is preferably carried out by using a plurality of optical fibers (10) arranged on the reactor pit bottom (5), along the length of which Bragg gratings (14), each capable of reflecting a light signal having a particular wavelength, are distributed.

Abstract: Pressure vessel apparatus includes upper and lower pressure vessel housings maintained together under pressure by tendons. Bellows are connected to the pressure vessel housings in order to provide leaktight barriers, and to permit motion of the pressure vessel housings. The tendons are divided into two sets, with the tendons of each set of tendons being stressed differently than the tendons of the other set of tendons. The apparatus when utilized as a nuclear reactor pressure vessel includes a core catcher with flotation pool connected to and disposed below the pressure vessel housings and defining a core catcher interior in communication with the pressure vessel interior for receiving core material from the pressure vessel interior resulting from reactor melt-down.

Abstract: A core-melt source reduction system for ending the progression of a molten core during a core-melt accident and resulting in a stable solid cool matrix. The system includes alternating layers of a core debris absorbing material and a barrier material. The core debris absorbing material serves to react with and absorb the molten core such that containment overpressurization and/or failure does not occur. The barrier material slows the progression of the molten core debris through the system such that the molten core has sufficient time to react with the core absorbing material. The system includes a provision for cooling the glass/molten core mass after the reaction such that a stable solid cool matrix results.

Abstract: A nuclear reactor system having a water-cooled reactor includes a reactor containment. A shielding pit inside the reactor containment has a lower region with an outlet opening formed therein. A reactor pressure vessel is disposed in the shielding pit. A moderating cell is disposed downstream of the outlet opening and has a device for slowing down and diverting a melt flowing through the outlet opening. A catch basin is disposed downstream of the moderating cell for receiving a melt and a supply of water. A method for operating a nuclear reactor system includes covering the bottom of the catch basin with water during normal operation of the reactor, and maintaining the water in the catch basin at a surface level being lower than the lowermost region of the bottom of the shielding pit.

Abstract: The device (4) for the retention of core melt-through in light-water reactors by means of a crucible (40) disposed beneath the reactor pressure vessel (2) comprising of a vat (41) and a plurality of sack-like protuberances (42) on its underside and also of a metal lid (43). The lid forms a water-tight upper seal for the crucible and has a reinforcement (43b) to absorb the kinetic energy of the impact of the core melt-through. The crucible consists of a metal wall (40a), which is lined with a ceramic material (40b)--preferably made from high-temperature isostatic pressed boron nitride. The device (4) is disposed in a water-filled cooling basin (32), which forms the lowest part of the containment sump and which can be constructed as a cavity in the containment foundation. The water vaporized during cooling if the requirements are met condenses on the walls of the containment and flows back into the containment sump.

Abstract: A shield for restricting molten corium from flowing into a water sump disposed in a floor of a containment vessel includes upper and lower walls which extend vertically upwardly and downwardly from the floor for laterally bounding the sump. The upper wall includes a plurality of laterally spaced apart flow channels extending horizontally therethrough, with each channel having a bottom disposed coextensively with the floor for channeling water therefrom into the sump. Each channel has a height and a length predeterminedly selected for allowing heat from the molten corium to dissipate through the upper and lower walls as it flows therethrough for solidifying the molten corium therein to prevent accumulation thereof in the sump.

Abstract: A nuclear reactor installation includes a reactor pressure vessel and a reactor core in the reactor pressure vessel. A supporting and protective structure supporting the reactor pressure vessel and surrounding the reactor pressure vessel on the bottom and laterally, has a bottom region and a circumferential wall. A core catcher device for the reactor core has a collecting basin for a core melt being installed below the reactor pressure vessel. The collecting basin has a bottom wall and a jacket wall being respectively separated from the bottom region and the circumferential wall of the supporting and protective structure by a spacing gap. Cooling channels are disposed in the spacing gap at the bottom wall and the jacket wall for exterior cooling of the collecting basin with a cooling liquid. Turbulence bodies are disposed in a surface region of the bottom wall for generating a turbulent flow of the cooling liquid flowing from the inside to the outside over the bottom wall toward the jacket wall.

Abstract: Device for the recovery of a molten core of a nuclear reactor essentially constituted by partitions (4) for subdividing a volume located below the core into narrow empty volumes (5), into which the molten material will slowly flow, and cooling channels (6) for solidifying said material. The vaporization of the coolant advantageously brings about its automatic replenishment under the effect of the hydrostatic pressure of a raised source.

Abstract: This invention relates to a method for protecting the integrity of the reactor container base in nuclear power plants, and a device for implementing the method.The proposed method and device are applicable to all reactor types (PWR or pressurized water reactor, BWR or boiling water reactor, HWR or heavy water reactor, etc.) and to all types of containing system (large dry type, steam suppression type, condensation on ice type, subatmospheric type etc.), although for simplicity the present text will describe only their application to a PWR with a steam suppression and large dry containing system.

Abstract: A corium protection assembly includes a perforated base grid disposed below a pressure vessel containing a nuclear reactor core and spaced vertically above a containment vessel floor to define a sump therebetween. A plurality of layers of protective blocks are disposed on the grid for protecting the containment vessel floor from the corium.

Abstract: The reactor comprises a vessel (3) containing the core of the reactor (4) and arranged with its axis vertical in a vessel well (2). The cooling and protection device (11) rests on the bottom of the vessel well. It consists of a metal floor (11) which covers the bottom of the vessel well (5) and in which are made channels (20) for cooling by circulation of a cooling fluid. The cooling fluid supply is connected to the cooling channels (20).

Abstract: In order to ensure the recovery and confinement of the core of a nuclear reactor, such as a pressurized water reactor, in the case of a serious accident leading to its melting or meltdown, it is proposed that below the reactor vessel (16) be placed a receptacle (20) able to evacuate the water accumulated below the vessel (16) in the initial phase of the accident and then collect the molten core debris. The water automatically flows through overflow and siphon devices (46, 50) into a cooling space (40) located below the receptacle. If the meltdown of the core (18) has been detected, the water contained in tanks (56) flows by gravity into the space (40), so as to entirely immerse the containers (26) placed in said space. The molten core traversing the bottom of the vessel (16) flows into the receptacle (20) and then into containers (26) via meltable plugs (32) and a natural convection flow is established between the tanks (56) and the space (40) in order to ensure cooling.

Abstract: A penetration (51) through the bottom of a pool in the reactor containment below a reactor vessel is protected against the effects of a core meltdown, by the penetration (51) being surrounded by a pipe (60) having an inlet (61) located below the surface (31) of the water and above the highest level (41) which the bed (4) of granulate formed by the descending molten core material could be expected to reach. The pipe (60) has an outlet (62) at its lower end, located in the bed (4). The gap (64) between the penetration (51) and the pipe (60) is covered by a screen (7) which prevents granulate from entering. Granulate is also prevented from entering the outlet (62). The pool water flows in through the inlet (61), down through the gap (64), out through the outlet (62) and into the particle bed (4) where the water is vaporized and rises through the bed without obstructing the flow of water through the gap for cooling the penetration.

Abstract: The device is constituted by a metal structure (10) resting on the bottom of the reactor pit (3) and submerged in a mass of water filling the lower portion of the reactor pit (3). The metal structure (10) comprises a central chimney (11), a recovery wall (12) constituted by juxtaposed dihedra (22) made from metal sheet, and a peripheral wall (13) fixed to the external edges of the dihedra (22) and providing water passages at the periphery of the reactor pit. When the molten core of the reactor spreads into the reactor pit, following an accident, the structure (10) ensures its recovery and prevents contact between the molten core and the bottom of the reactor pit. The molten core flows onto the wall (12) in such a manner as to constitute a layer of small thickness which is cooled over its upper surface and over its lower surface and which solidifies rapidly.

Abstract: The lower connector (10) comprises a transverse element (12) having a box-shaped structure. The transverse element (12) comprises a reticular structure (13) resistant to bending and limited externally by a frame (14), the cross-section of which corresponds substantially to the cross-section of the assembly. The structure (13) has large-size cells. The transverse element comprises, furthermore, a retaining plate (20) pierced with small-size orifices and superposed on and fastened to the recticular structure (13) parallel to the latter and with a spacing (b), to form the upper part of the connector (10) and delimit a free space for steadying the cooling water of the reactor and for recovering debris carried along by the water, forming the hollow central part of the box-shaped structure.

Abstract: A nuclear reactor complex includes fusible plugs to prevent water from a wetwell from flowing into a drywell including the reactor vessel. In case the core overheats and molten corium falls to the drywell floor, the heat from the corium melts the fusible plugs and water floods the drywell. The water inhibits a corium-concrete reaction, minimizing pressure increase within the drywell and thus the chances of radioactive materials being released into the environment.

Abstract: A protection system for the basemat of reactor containment buildings in nuclear power stations. The system comprises a structure located in a cavity below the reactor vessel and submerged in water. The structure comprises staggered layers of stainless steel beams for intercepting molten material escaping from the reactor vessel during meltdown of the reactor core. The system is designed so that the molten material is distributed in thin layers over wings of the beams and transfers its heat to the surrounding water thus affording a rapid quenching of the molten core and safeguarding the integrity of the basemat.

Abstract: A light water nuclear reactor melt-retention structure to mitigate the extent of direct containment heating of the reactor containment building. The structure includes a retention chamber for retaining molten core material away from the upper regions of the reactor containment building when a severe accident causes the bottom of the pressure vessel of the reactor to fail and discharge such molten material under high pressure through the reactor cavity into the retention chamber. In combination with the melt-retention chamber there is provided a passageway that includes molten core droplet deflector vanes and has gas vent means in its upper surface, which means are operable to deflect molten core droplets into the retention chamber while allowing high pressure steam and gases to be vented into the upper regions of the containment building.

Abstract: An arrangement is disclosed for preventing the molten corium of a nuclear reactor from penetrating into the ground. The reactor is supported by a concrete raft bearing on the ground, and inserted in the raft is a retaining basin having an upper portion of refractory material which is chemically inert towards the constituents of the corium oriented toward the corium, and a lower portion made of a refractory material with a heat conductivity much greater than that of the upper portion. Generally the upper layer of the retaining basin will be made of zirconia and the lower layer will be made of graphite. Disposed between the reactor and the retaining basin is a means for deflecting the vertical attack of corium on the basin and spreading out the corium, comprising a plurality of concentric cavities, each successive cavity having a greater outer diameter than that of the preceding cavity and having a center located at a greater vertical distance from the reactor than the preceding cavity.

Abstract: Disclosed is a nuclear reactor containment including a reactor vessel disposed within a cavity with capability for complete inherent decay heat removal in the earth and surrounded by a cast steel containment member which surrounds the vessel. The member has a thick basemat in contact with metal pilings. The basemat rests on a bed of porous particulate material, into which water is fed to produce steam which is vented to the atmosphere. There is a gap between the reactor vessel and the steel containment member. The containment member holds any sodium or core debris escaping from the reactor vessel if the core melts and breaches the vessel.

Abstract: Disclosed is a nuclear reactor containment adapted to retain and cool core debris in the unlikely event of a core meltdown and subsequent breach in the reactor vessel. The reactor vessel is seated in a cavity which has a thick metal sidewall that is integral with a thick metal basemat at the bottom of the cavity. The basemat extends beyond the perimeter of the cavity sidewall. Underneath the basemat is a porous bed with water pipes and steam pipes running into it. Water is introduced into the bed and converted into steam which is vented to the atmosphere. A plurality of metal pilings in the form of H-beams extends from the metal base plate downwardly and outwardly into the earth.

Abstract: A fluid cooled heat exchanger molten core retention and solidification apparatus (10) is a vertically oriented array of tube assemblies located beneath a reactor vessel. Water under forced circulation flows through inlet tube (18) into an inlet plenum (20) beneath the heat exchanger (10) up through the inner vertical tube (22), down through the annular space between the outside of the inner tube (22) and the inside of the outer tube (24) into an outlet plenum (28), then through tube (30) to a heat exchanger outside containment building (16) where heat is released. The array of vertical tube assemblies provides heat transfer surface within a few centimeters of all molten material and sufficient volume between the exterior surface of outer vertical tubes (24) to accommodate all expected molten material in the event of a meltdown of the core of the nuclear reactor.

Abstract: A passive "core catcher" is provided for preventing the escape of radiation in the unlikely event of a major failure of a nuclear reactor by melt-down of the core. The "core-catcher" structure includes a narrow vertically downwardly extending isolation tube, and aligned narrow heat-exchange structure forming a chilled wall crucible in which the molten uranium oxide forms a container for itself including a "frozen" or solid layer of uranium oxide adjacent the heat exchanger wall. A passive cooling system may include a water tower adjacent the above-ground reactor structure, which dissipates heat from the core-catcher heat exchanger, and from within the above-ground reactor structure by a second local heat exchanger.

Abstract: A device which mitigates against the effects of a failed coolant loop in a nuclear reactor by restricting the outflow of coolant from the reactor through the failed loop and by retaining any particulated debris from a molten core which may result from coolant loss or other cause. The device reduces the reverse pressure drop through the failed loop by limiting the access of coolant in the reactor to the inlet of the failed loop. The device also spreads any particulated core debris over a large area to promote cooling.

Abstract: A plurality of radially arranged and neutron absorbing baffles are stacked in vertical sets under the fuel core assemblies, and the whole enclosed in a bottle shaped containment vessel. The radially arranged baffles of each set extend vertically, and each set has double the number of baffles as the set above it in the stack. A melt-down of a fuel core assembly drops the fissioning nuclear fuel into the stacked sets of baffles, there, as it passes through, to be progressively divided, redivided and dispersed in smaller and smaller masses between the doubling number of baffles in safe fuel pellet size. Neutron absorbing containment prevents contamination of the environment and together with cooling means stops fissioning of fuel.

Abstract: A nuclear power plant constructed with a nuclear reactor core centrally mounted within an elongated, split chamber pressure vessel having contained solid state heat transfer conductors for transfer of heat from a liquid core coolant to a gas power medium in an upper heat exchange chamber of the pressure vessel, and having a discharge mechanism for dumping the reactor core when spent into a lower radioactive material storage chamber of the pressure vessel, the power plant including a power generating system having a steam turbine, an electrical generator and a gas compressor.

Abstract: An emergency melt down core catcher apparatus for a nuclear reactor having a retrofitable eutectic solute holding vessel connected to a core containment vessel with particle transferring fluid and particles or granules of solid eutectic solute materials contained therein and transferable by automatically operated valve means to transport and position the solid eutectic solute material in a position below the core to catch and react with any partial or complete melt down of the fuel core.

Abstract: A method and arrangement for containing the core melt flowing from a nuclear reactor into a core catcher below the core wherein the core melt is permitted to gradually penetrate layers of a core catcher materials of inorganic reactor soluble oxides or salts disposed in the core catcher which core catcher materials are dissolved by the oxidic part of the core melt, and the molten solution, after solidification and after being cooled down to a temperature at which hydrogen generating reactions do not take place, is leached with water and rinsed out of the core catcher without the need for humans to be present in the reactor containment and to be exposed to radiation.

Abstract: The invention teaches safety apparatus that can be included in a nuclear reactor, either when newly fabricated or as a retrofit add-on, that will minimize proliferation of structural damage to the reactor in the event the reactor is experiencing an overheating malfunction whereby radioactive nuclear debris might break away from and be discharged from the reactor core. The invention provides a porous bed or sublayer on the lower surface of the reactor containment vessel so that the debris falls on and piles up on the bed. Vapor release elements upstand from the bed in some laterally spaced array. Thus should the high heat flux of the debris interior vaporize the coolant at that location, the vaporized coolant can be vented downwardly to and laterally through the bed to the vapor release elements and in turn via the release elements upwardly through the debris. This minimizes the pressure buildup in the debris and allows for continuing infiltration of the liquid coolant into the debris interior.