Abstract: A method and apparatus for use in conjunction with a passive nuclear reactor containment cooling system to significantly reduce the release of radiation and resulting off-site doses is disclosed. Gases that may contain radioactive materials are drawn from a penetration room and pass through a filter prior to being fed into the passive containment airflow path. Low pressure areas are created in the passive containment airflow path by means of eductor/airfoils. Such low pressure zones draw the gases from the penetration rooms.

Abstract: The apparatus comprises a conduit connected to a containment vessel to supply air to a water bath contained in a basin. The conduit is connected to a plurality of air nozzles in the water bath, each of which forms a unit together with a perforate baffle plate disposed above the nozzle to intensively mix the emerging air with water. A set of static mixer elements enclosed by a jacket is disposed in the water bath above the baffle plate.

Abstract: A method of constructing a top slab to provide a containment roof over a nuclear-power generating building, in particular, a method for utilizing overhead spaces bounded by a wall of the containment building and a shielding wall of the pressure vessel building, wherein the sequential steps involve; erecting a plurality of paired support columns on tops of the wall and of the shielding wall; building upper structural components across said paired support columns; installing a slab liner equipped with slab anchors beneath said lower structural components by suitable joining means; constucting a reinforcing network above said lower structural components; encasing said lower structural components and said reinforcing network; and pouring concrete over the slab liner to a suitable depth.

Abstract: The present invention is directed to a nuclear reactor facility wherein a nuclear reactor pressure vessel (RPV) is housed within an annular sealed drywell, an annular sealed wetwell houses said drywell, a pressure suppression pool of liquid is disposed in said wetwell and is connected to said drywell by submerged vents, a condenser line connects said drywell to an isolation condenser, and a bleedline from said isolation condenser is connected to said pool and terminates under the surface of said pool. The improvement of the present invention comprises a liquid reservoir disposed in said drywell and a standpipe disposed in said wetwell. The reservoir and the standpipe are connected by a duct which is located below the surface of said reservoir a distance, D. The area of the reservoir is at least 25 times larger than the area of said standpipe.

Abstract: A reactor containment vessel comprises typically a reactor pressure vessel housed in a dry well of the reactor containment vessel, a vent passage through which steam in the dry well is introduced into coolant accommodated in a pressure suppression chamber of the reactor containment vessel, a closed space formed at a position lower than the level of the normal liquid surface of the coolant, a first passage having an inlet opened into the pressure suppression chamber at a level higher than that of the normal liquid surface of the coolant and an outlet opened into the closed space, and a second passage communicating between the closed space and the dry well through a counter flow preventing arrangement for checking the flow directed toward the closed space, and therefore, noncondensable gas and liquid accumulated in the pressure suppression chamber are discharged into the dry well the pressure in which is higher than that in the pressure suppression chamber by making use of a difference in water head increased d

Abstract: The wetwell space in a suppression pool of a nuclear reactor containment is continuously ventilated by exhausting gas therefrom, while at the same time, during normal system operation atmospheric air from a source of same is admitted to the wetwell but such admission being blocked during a LOCA. All exhaust flow from the wetwell is conveyed through a conduit that outlets at a remote elevated location in the atmosphere. All exhaust flow through the conduit is before outletting therefrom passed through gas treatment operation wherein any particulates in the gas mixture are removed. Further treatment of the gas with charcoal to adsorb noble gases can be carried out. In normal reactor operation the ventilation flow rate is at minimal level. However on occurrence of a loss-of-coolant-accident, highly heated gases from the containment drywell are passed into the suppression pool where condensables condense while non-condensable gases are cooled and vent to the wetwell.

Abstract: Handling pool for nuclear fuel, located above the vessel of a pressurized water-nuclear reactor, characterized in that it has, around the vessel cover and the mechanisms surmounting it, a bulkhead, which is generally cylindrical of revolution and is tightly and detachably fixed to the pool bottom. This arrangement makes it possible to keep the pool filled with water outside the bulkhead during reactor operation, so that within the safety enclosure there is a large water reserve on the core, which facilitates its reflooding if there is a fracture to the primary circuit. The still full pool can be used for storing spent fuel.

Abstract: A containment cooling system utilizes a naturally induced air flow and a gravity flow of water over the containment shell which encloses a reactor core to cool reactor core decay heat in two stages. When core decay heat is greatest, the water and air flow combine to provide adequate evaporative cooling as heat from within the containment is transferred to the water flowing over the same. The water is heated by heat transfer and then evaporated and removed by the air flow. After an initial period of about three to four days when core decay heat is greatest, air flow alone is sufficient to cool the containment.

Abstract: A liquid metal cooled nuclear reactor having a passive cooling system for removing residual heat resulting from fuel decay during reactor shutdown. The passive cooling system comprises a plurality of partitions surrounding the reactor vessel in spaced apart relation forming intermediate areas for circulating heat transferring fluid which remove and carry away heat from the reactor vessel. The passive cooling system includes a closed primary fluid circuit through the partitions surrounding the reactor vessel and a partially adjoining secondary open fluid circuit for carrying transferred heat out into the atmosphere.

Abstract: A nuclear power plant that is of a walk-away type with an encapsulated reaction core in a glass matrix pool having a reactive Thorium/U.sup.233 composition in a containment structure that radiates thermal energy for use in a closed gas cycle with a split path having a common compressor with an output that divides into a first path communicating with the thermal source and a second path communicating with an intercooler, the two paths combining in a turbine with an expander that discharges to a common collector for return to the compressor.

Abstract: A container-outer-periphery pool in which water is stored is provided between a primary containment vessel and a reactor building, and outside of a pressure suppression pool. Consequently, the natural heat transfer capabilities of reactor facilities is enhanced, and the inherent safety of the reactor facilities is improved.

Abstract: A liquid metal cooled nuclear reactor having a passive cooling system for removing residual heat resulting from fuel decay during reactor shutdown. The passive cooling system comprises a plurality of partitions surrounding the reactor vessel in spaced apart relation forming intermediate areas for circulating heat transferring fluid which remove and carry away heat from the reactor vessel. The passive cooling system includes a closed primary fluid circuit through the partitions surrounding the reactor vessel and a partially adjoining secondary open fluid circuit for carrying transferred heat out into the atmosphere.

Abstract: An assembly includes a structure. A shielding apparatus is disposed inside the structure and radioactive plant components having sides and a bottom are surrounded by the shielding apparatus. The radioactive plant components include relatively highly radioactive components and relatively weakly radioactive or non-radioactive components. A water-tight vessel embedded in the structure has an interior and an outside and exclusively surrounds the radioactive plant components at the sides and at the bottom with the relatively highly radioactive components disposed in the interior and the relatively weakly radioactive or non-radioactive components disposed at the outside. The water-tight vessel is sufficiently large to hold water serving as a shielding device and to hold crushed contaminate pieces of the radioactive plant components during subsequent dismantling of the plant components.

Abstract: A passive cooling system for the contaminant structure of a nuclear reactor plant providing protection against overpressure within the containment attributable to inadvertent leakage or rupture of the system components. The cooling system utilizes natural convection for transferring heat imbalances and enables the discharge of irradiation free thermal energy to the atmosphere for heat disposal from the system.

Abstract: A method and apparatus for fabricating a nuclear reactor and a preformed containment building for a nuclear reactor. The nuclear steam supply system (NSSS) is assemblied at a manufacturing site while the containment building is constructed in parallel at the reactor site. The completed NSSS is then transported to the reactor site and installed in the specially formed containment building. The NSSS and its safeguards system preferably are formed as a low draft barge which is tugged to the reactor site along navigable waterways.

Abstract: A novel liquid nuclear reactor is described which comprises a reactor vessel that is connected through upper and lower liquid conduit means to one or more satellite tanks that contain a heat exchanger means and pump means.

Abstract: In a high-temperature gas-cooled nuclear reactor system, which is suitable for modular utilization in combination with one or more other similar nuclear reactor systems, an arrangement which comprises passive heat sink means for absorbing decay heat energy generated at a reactor core included within said reactor system; and means for removing heat energy from said heat sink means at a rate sufficient to maintain the capacity of the heat sink means for absorption of decay heat energy such that release of fission products resulting from loss of forced circulation of gas coolant, or such loss in combination with coolant depressurization, when the reactor is critical and at power is prevented, thereby to provide safety means independent of human or automatic activation; and method embodiments corresponding to same.

Abstract: Concrete support ledges (67) and columns (94) for the upper internals (60) and lower internals (63) structures are poured into the floor (41) and walls (36) of the refueling cavity (33) at the time of initial plant construction. Such concrete supports (67, 94) provide greater stability and do not require any external bracing. A pedestal assembly (100) is associated with each of the concrete supports (67, 94) to provide an adjustable and secure support for the internals structures (60, 63).

Abstract: A building, especially a nuclear plant, includes concrete walls enclosing components such as plant components as a protection against external action. The concrete walls have exposed locations, and the concrete walls have double-layered regions at the exposed locations with double layers defining hollow spaces therebetween. A damping material may fill the hollow space.

Abstract: A method of providing a nuclear steam supply system that is constructed to include a barge or flotation base as an integrated portion thereof. The system is tested for operability and safety at the factory and then towed along navigable coastal or inland waterways, or overseas to foreign locations, to a prepared foundation site at its point of use. The overall unit is so constructed and arranged as to permit the removal of top and side portions to permit passage under low bridges and through narrow locks without requiring disassembly of safety class piping and wiring. The method further provides for a complete nuclear power plant constructed on multiple barges at a separate factory site in parallel with plant site preparation, i.e., in estuaries or caves.

Abstract: Nuclear reactor confinement enclosure foundation comprising a skirt and a dome, the foundation comprising a footing in contact with the ground and which bears members and rods arranged annularly and supported on the confinement enclosure floor. The space between the footing and the floor can be used in different ways.

Abstract: A pressurized water nuclear reactor comprises a normally vertical main vessel externally duplicated by a confinement enclosure. The main vessel contains a simplified primary circuit essentially incorporationg the reactor core and an annular steam generator arranged in such a way that the circulation of water, pressurized once and for all during the sealing of the vessel, takes place by natural convection. All the auxiliary circuits, conventionally ensuring cooling on shut down of such a reactor are eliminated, said cooling being ensured by a special arrangement of the space formed between the vessel and the enclosure and by the fact that the latter is immersed in an external cooling liquid, no matter what the slope of the reactor. The shut down of fission reaction in the core is ensured by systems of absorbing elements and by the automatic displacement of part of the reflector in the case of a slope of the reactor.

Abstract: A novel concrete core support structure for nuclear reactors is described.

Abstract: A high-temperature gas cooled nuclear reactor system comprises a containment building, a concrete reactor pressure vessel inside the containment building, and a safety relief valve connected to the concrete reactor pressure vessel. The spring of the safety valve consists of a material with a spring constant decreasing as temperature rises. A heat exchanger is provided in close proximity to cool the spring of the safety valve which is subject to the heat of the reactor coolant escaping when the safety valve is open. The heat exchanger of the safety valve is connected to a liner cooling system of the concrete reactor pressure vessel.

Abstract: A nuclear power plant (heating plant) with a helium cooled high temperature reactor with spherical fuel elements, located in a cylindrical prestressed concrete pressure vessel, suitable for supplying heat (for local or remote heating or the generation of process steam) with a capacity of approximately 50 to 300 MWth. The high temperature reactor core is located out of center in the prestressed concrete pressure vessel, with at least two heat exchangers installed adjacent and offset in the upward direction relative to it. The heat exchangers are each connected on the secondary side to an intermediate circulation loop including an intermediate heat exchanger and circulating pump, and have an auxiliary circulation loop with a recooling system connected in parallel with them for the removal of decay heat. The auxiliary loops are closed in normal operation.

Abstract: The invention relates to a nuclear power station for a gas cooled high temperature pebble bed nuclear reactor. The nuclear power station is characterized by a combination of features, whereby the system inherent properties of a high temperature reactor are utilized to make possible the economical operation of a nuclear power station of medium capacity (300-600 MW.sub.el) while maintaining a high standard of safety. The characteristics comprise a reactor protection building equipped with pressure relief means in combination with filters, several auxiliary cooling systems separate from the operating cooling systems for the removal of decay heat in the case of accidents, and the utilization of a liner cooling system for the prestressed concrete reactor pressure vessel to assure the removal of the decay heat in case of a failure of the auxiliary cooling systems.

Abstract: A passive safety system for a nuclear reactor is comprised of a first subsystem for circulating water solely by natural convection from a first branch to a second branch of a reactor coolant circuit with the circumvention of a steam generator for removing decay heat from the reactor coolant circuit at any pressure. The first branch guides heated water from the reactor vessel into the steam generator and the second branch guides cooled water from the steam generator into the reactor vessel. The first subsystem includes a heat exchanger for cooling water flowing from the first branch and prior to being introduced into the second branch and a first valve for allowing flow of water from the first branch into the second branch solely in response to a parameter value pertaining to operational safety. There is also provided a second subsystem for introducing stored cold water solely by gravity into the reactor vessel for making up for lost water in the reactor coolant circuit at any pressure.

Abstract: A gas cooled high temperature nuclear reactor utilizes an independent cooling system for the safety enclosure surrounding the reactor vessel. The cooling system comprises means for circulating cooling medium at least on the reactor side of a concrete safety enclosure shell and a separate closed cooling loop for circulation of separate cooling medium through a reservoir of the first cooling medium and to the outside of the entire nuclear reactor installation.

Abstract: A nuclear component horizontal seismic restraint. Small gaps limit horizontal displacement of components during a seismic occurrence and therefore reduce dynamic loadings on the free lower end. The reactor vessel and reactor guard vessel use thicker section roll-forged rings welded between the vessel straight shell sections and the bottom hemispherical head sections. The inside of the reactor guard vessel ring forging contains local vertical dovetail slots and upper ledge pockets to mount and retain field fitted and installed blocks. As an option, the horizontal displacement of the reactor vessel core support cone can be limited by including shop fitted/installed local blocks in opposing alignment with the reactor vessel forged ring.

Abstract: Antiseismic support structure for the pile block of a fast neutron nuclear reactor.It comprises a concrete covering slab resting on the reactor building structure. The vessel and components of the pile block are suspended on said slab in a well of said structure. The building rests on the ground by means of two superimposed floors, namely an upper floor and a lower floor. The two floors are separated from one another by elastic supports, permitting a horizontal oscillatory displacement with respect to one another with a view of filtering the horizontal components of the earthquake with respect to the vessel. These elastic supports are in particular fretted elastomer supports.

Abstract: The invention relates to floating roof tanks for liquids, of the type comprising a cylindrical wall (2), a floating roof (3), and a flexible membrane (4) connecting the periphery of the floating roof to the wall. In accordance with the invention, the tank further includes an overflow duct for providing protection against over-filling when the roof (3) is in its top position. The overflow duct (26) is mounted on the outside of the tank and has an upsidedown U-shaped portion disposed at a height corresponding to a maximum predetermined level for liquid inside the tank when the roof is in its top position. The invention is applicable to the nuclear power industry for storage tanks for topping up the primary circuit of a nuclear reactor with de-gassed water.

Abstract: A fast neutron nuclear reactor having a vessel filled with liquid metal and sealed in its upper part by a box slab having a central opening in which is placed a plug-cover-core overhanging the core of the reactor. The central opening is surmounted by a cell containing the handling and storage mechanism for the plug-cover-core and a mechanism for handling the assemblies. The latter can be moved on annular rails and can be collapsed against the wall of the cell, in order to permit the manipulation of the plug-cover-core. A radial passage connects the cell to a transfer station.

Abstract: The invention relates to floating roof tanks for liquids, of the type comprising a cylindrical wall (2), a floating roof (3), and a flexible membrane (4) connecting the periphery of the floating roof to the wall. In accordance with the invention, means are provided for emptying the counter-pressure liquid which is located in the space (6) delimited by the membrane (4) and the wall (2) and which is open to the atmosphere. These emptying means are disposed near the top of the tank so that the membrane, under the effect of pressure exerted by the liquid contained in the tank, serves to expel the counter-pressure liquid when the roof is in abutment against a top stop. Such tanks are of particular use in the nuclear power industry for storing de-gased water to top up the primary circuit of a nuclear reactor.

Abstract: A pressurized nuclear water reactor has a substantially cylindrical flow liner with a cylindrical wall section and bottom and an open top. A barrel forms a riser chamber that contains the core in the flow liner. A pressure vessel contains the cylindrical flow liner to form a second annular chamber therebetween that contains a supplementary liquid coolant, with insulation means to provide a major portion of the supplementary liquid coolant at a first temperature and a minor portion thereof at a second higher temperature. Upon depressurization in the vessel, fluid communication means enable injection of supplementary liquid coolant from the second annular chamber into the core upon flashing of a minor portion to vapor. A further pool of water outside the pressure vessel, and insulation on the wall, maintain the desired temperature in the supplementary liquid coolant supply. Injection or removal of borated solution, as a chemistry control solution, into or from the supplementary liquid coolant is provided.

Abstract: Piping of a nuclear reactor containment vessel comprises pipes passing through the containment vessel and, extending to the outside of the containment vessel, outer shut-off valves each provided at a portion of the pipe which is located at the outside of the containment vessel for closing the pipe and isolating vessels for covering at least outer surfaces of welded portions of the pipes each being located between an outer wall surface of the containment vessel and a portion including the outer shut-off valve and for isolating the covered portions of the pipes from atmosphere.

Abstract: A fast breeder reactor has a nuclear reactor container filled with a liquid metal, a reactor core disposed within the nuclear reactor container, and a first supporting structural member which is mounted to the nuclear reactor container such as to support the reactor core. The fast breeder reactor is provided with a cylindrical structural member which surrounds the periphery of the reactor core such as to define an annular gap between the cylindrical structural member and the reactor core for allowing the liquid metal to exist therein, the cylindrical structural member being mounted to the nuclear reactor container by means of a second supporting structural member. The inertial resisting force produced when the liquid metal existing in the annular gap will flow out from the annular gap in response to the vibration of the reactor core acts such as to suppress the vibration of the reactor core, thereby allowing an improvement in the anti-vibration properties of the fast breeder reactor.

Abstract: In a modular liquid-metal pool breeder reactor, a radiant vessel auxiliary cooling system is disclosed for removing the residual heat resulting from the shutdown of a reactor by a completely passive heat transfer system. A shell surrounds the reactor and containment vessel, separated from the containment vessel by an air passage. Natural circulation of air is provided by air vents at the lower and upper ends of the shell. Longitudinal, radial and inwardly extending fins extend from the shell into the air passage. The fins are heated by radiation from the containment vessel and convect the heat to the circulating air. Residual heat from the primary reactor vessel is transmitted from the reactor vessel through an inert gas plenum to a guard or containment vessel designed to contain any leaking coolant. The containment vessel is conventional and is surrounded by the shell.

Abstract: The invention relates to a nuclear reactor cooled by a liquid metal comprising a vessel (12) containing the reactor core (24), a vessel shaft (18) and a sealing slab (14).The bottom (12a) of the vessel rests on the bottom (52) of the vessel shaft via supports (54) defining between the said two bottoms a space (56) in which circulates a cooling fluid such as air. A skirt (74) surrounds vessel (12) and rests on the vessel shaft bottom (52) for supporting slab (14).Application to the construction of simpler and less expensive fast neutron reactors than those hitherto known.

Abstract: The present system uses measurement inputs which reveal fission product barrier functional characteristics for emergency event classification in nuclear generating stations. The process determines the functional status of barriers to fission product release under transient or emergency conditions. The first part of the present process specifies which key indicators within a nuclear plant provide data indicative of fission product barrier status, and develops a logic table or diagram relating specific key symptoms to barrier status such that a computer identifies the functional status of each fission product barrier. In the second part of the present process nuclear power plant operators utilize the computer to determine emergency event classification.

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: Nuclear power plant with a reactor building, a fuel building, buildings for the ancillary nuclear, electrical and safety equipment, and a building for turbo-electric machines.The group of buildings is in the general shape of a T, with the fuel and ancillary equipment buildings (2) and (3) in line at both sides of the reactor building, and the engine building (6) facing the reactor building (1) and perpendicular to the latter. The vault of the protective enclosure is connected to the foundation of the reactor building and is in the shape of a cylinder with horizontal generatrices.The invention is applicable to light water nuclear power stations.

Abstract: A reactor cavity surrounding a reactor coolant inlet or outlet pipe is designed to reduce pressurization of the cavity in the event of a LOCA pipe break therein.

Abstract: A safety coolant injection system for nuclear reactors wherein a core reflood tank is provided to afford more reliable reflooding of the reactor core in the event of a break in one of the reactor coolant supply loops. The reactor vessel, reactor coolant supply loops, emergency water storage tank and pump modules are arranged in separate compartments in the containment structure to control the flow of spilled coolant. An integrated containment spray system and normal cooldown system are also described.

Abstract: Hydraulic jacks are arranged radially both inside and outside the confinement chamber (EC), substantially on a level with the center of gravity of the boiler (BV, EA) disposed inside. The inside jacks transmit thrust to the boiler via an annular floor (20). The outside jacks transmit thrust to the walls (M) of the hall. The outside jacks are arranged as energy-absorbing dampers. The inside and outside jacks resist fast compression by means of calibrated fluid flow orifices, while they expand readily by means of one way valves and pressure accumulators. The boiler and the confinement chamber stand on a base that is resiliently movable in a horizontal direction relative to the raft (R) of the building. This ensures that the reactor is returned to its normal position once an earthquake is over.

Abstract: A pressurized water reactor system having circulation means outside the containment vessel for the circulation of loss of coolant emergency water is provided which prevents exposure of such water to the atmosphere. The system includes an enclosure, separate from the containment vessel, the interior of the enclosure being sealed to the atmosphere and containing a pumping means, and encased inlet and outlet conduits communicating between the interior of the containment vessel and the pump means within the enclosure. The enclosure may also contain a heat exchange means, while the emergency water storage tank can be positioned in the containment vessel, in the enclosure, or separate from both. Provision is also made for use of the pump in the enclosure for circulation of residual heat removal coolant water.

Abstract: Reactor building structure comprising a ring building roof embedded in the cylindrical skirt of the confinement enclosure.The structure is constituted by a confinement enclosure comprising a cylindrical skirt and a dome, as well as by a ring building surrounding the confinement enclosure. The ring building comprises a cylindrical skirt and a roof, the confinement enclosure and the ring building being erected on a common general foundation raft or floor. The internal structures are positioned with the confinement enclosure. The roof of the ring building is toroidal or frustum-shaped, being embedded in the cylindrical skirt of the confinement enclosure. The internal structures are disengaged from the confinement enclosure.

Abstract: A self-contained modular nuclear reactor which can be prefabricated at a factory location, nuclear-certified at the factory, transported to a field location for final assembly and connection to a large-scale electric-power generating facility. The modular reactor includes a prefabricated nuclear heat supply module and a plurality of shell segments which can be assembled about the heat supply module and which provide a form for the pouring and curing of a cementatious biological shield about the heat supply module. The modular reactor includes passive shutdown heat removal systems sufficient to render the reactor safe in an emergency. A large-scale power plant arrangement is disclosed which incorporates a plurality of the modular reactors.

Abstract: The invention relates to a fast neutron nuclear reactor in which the primary pumps and exchangers are suspended on the rigid slab sealing the vessel containing the reactor core.The slab has in its thickness housings of reduced dimensions in which are confined the heads of the exchangers and the primary pumps. The flywheels of the pumps and part of the pipes of the secondary circuits are also contained in the housings. Other housings can be provided in the slab, particularly for the handling of fuels.Application to the improvement of the safety and reliability of fast neutron reactors is taught.

Abstract: A standpipe runs up from a liquid storage vessel located between the safety vessel of a nuclear reactor and the safety enclosure around it and connected by a pressure equalization line to the interior space of the safety vessel. Undesired pressure increases in the interior of the safety vessel are absorbed by pushing water out of the storage vessel up the standpipe to a discharge above the safety vessel which is still within the safety enclosure. With sufficient pressure, the liquid, which may be conveniently water, flows from the standpipe to an overflow collar at the top of the safety vessel from which it runs down over the surface of that vessel to cool it. Water that evaporates is collected on the interior wall of the safety enclosure and also percolates down to the base of the safety enclosure, from which it is pumped back to the overflow collar, from which it can flow back into the pressure vessel when the pressure inside the safety vessel of the reactor goes back to normal.