Abstract: A nuclear reactor plant housed in a steel pressure vessel with a small high temperature reactor, together with a steam generator arranged over said reactor and with at least two circulating blowers connected in parallel with each other and following the steam generator in line and is provided with a decay heat removal system located in the primary loop. This system is arranged above the steam generator and a shut-off device is provided between the two component. The shut-off device, which may actuated both passively--by difference pressure--and actively, by means of a drive, is designed so that in normal operation no hot gas may enter the decay heat removal system. In the decay heat removal mode the hot gas is conducted into the decay heat removal system and the steam generator is closed off the hot gas. Simultaneously, the cold gas coming from the decay heat removal system is returned through the steam generator or a gas conduit parallel to it, to the reactor core.

Abstract: A nuclear reactor plant housed in a steel pressure vessel comprises a small high temperature reactor and a He/He heat exchanger located above the reactor, preferably followed by two circulating blowers connected in parallel. The installation further comprises at least one decay heat removal system, following in line the He/He heat exchanger in the direction of flow and with the entire flow of primary helium constantly flowing through it. In a preferred embodiment, the He/He heat exchanger is made up of two concentrically arranged coil bundles connected in succession, through which both the primary and the secondary helium are flowing in opposing directions.

Abstract: A high temperature pebble bed nuclear reactor having a medium power capacity of 300 to 500 MW.sup.e is equipped with two different shut-down arrangements comprising reflector rods used exclusively for scram. The total shut-down reactivity of the reflector rods is proportioned in order to prevent the excessive cooling of the reactor core folowing scram. In this manner, the reactor core is rendered subcritical (in the event of accidents, for example, or at the beginning of any operating state) yet capable of returning to criticality at a reduced level of temperature and power output following the removal of heat. The use of all of the reflector rods for scram is effected only in the event of reactivity accidents. For all other scram incidents, only a portion of the reflector rods are used.

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: The invention does away with the necessity of moving parts such as a check valve in a nuclear reactor cooling system. Instead, a jet pump, in combination with a TEMP, is employed to assure safe cooling of a nuclear reactor after shutdown. A main flow exists for a reactor coolant. A point of withdrawal is provided for a secondary flow. A TEMP, responsive to the heat from said coolant in the secondary flow path, automatically pumps said withdrawn coolant to a higher pressure and thus higher velocity compared to the main flow. The high velocity coolant is applied as a driver flow for the jet pump which has a main flow chamber located in the main flow circulation pump. Upon nuclear shutdown and loss of power for the main reactor pumping system, the TEMP/jet pump combination continues to boost the coolant flow in the direction it is already circulating.

Abstract: The invention relates to a heat exchanger incorporating emergency cooling means, as well as to a fast neutron nuclear reactor incorporating such an exchanger.The emergency cooling means comprise an inlet pipe issuing into the secondary fluid inlet chamber and an outlet pipe issuing into the secondary fluid outlet chamber. The inlet pipe issues into a distributing ramp positioned below the lower tue plate and the outlet pipe issues into a collecting ramp positioned above the upper tube plate. The two ramps are positioned below the intake and discharge pipes for the secondary fluid.

Abstract: The nuclear reactor installation is provided with a double-wall pressure vessel which is surrounded by a heat sink. A flood tank is provided outside the vessel in order to supply air as a heat-insulating agent to the chamber defined by the pressure chamber wall during normal operation and to supply water as a heat-conductive agent in response to a disturbance in reactor core cooling.The cover on the pressure vessel is also provided with a chamber to which air or water can be delivered. A closure member which can be activated by fusible element is incorporated in the cover to permit flooding of the cover chamber in response to an excessive heat within the pressure vessel.

Abstract: A nuclear reactor plant with a small high temperature reactor, principal heat exchangers located above the small high temperature reactor and housed in a steel pressure vessel, and a plurality of decay heat exchangers also located in the steel pressure vessel and connected on the cooling water side with an external recooling heat exchanger each, in a geodetically higher location. The object of the invention is to obtain a high degree of availability of the decay heat removal installations. This object is attained by the specific layout and connection of the components of the plant, which permits the operation of the decay heat exchangers both on the primary gas and the water side by natural convection only. The decay heat exchangers and their secondary circulation loops are active during power operations, so that potential failures and leaks are detected immediately. No special actuating measures are necessary to activate the decay heat removal operation.

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 concerns a safety cooling installation for the water reactor of a nuclear power station, the installation notably incorporating a reservoir for storing a cooling liquid, the said reservoir being located outside the containment which encloses the reactor circuit, the installation being provided with aspiration and discharging means arranged to aspirate the liquid from the reservoir and to discharge it into the circuit, there being provided a passive, maintenance free means to recover and conduct the liquid and containment water, the said means being arranged to recover the liquid and the water from the reactor in the lower part of the containment by non gravitational flow in the event of a break in the reactor's circuit.

Abstract: A heat-generating member (4) is arranged in a water-filled pressure vessel (1) which is provided with a pressure relief valve or the like. The water of the pressure vessel can be partly evaporated, thereby acting as a heat sink for the generated heat. The walls of an outer vessel (6) surround at least a lower part of the pressure vessel (1) in such a way that a closed, relatively small auxiliary space (7) is formed between the two vessels. The auxiliary space (7) communicates via at least one tube (8) with an open evaporation pool (9), which is arranged above the cover (2) of the pressure vessel (1). A tube coil (10), disposed in an upper part of the pressure vessel, is connected by both ends to the evaporation pool (9).

Abstract: A steam generator recirculating system for use with the secondary coolant of the steam generators of a pressurized water nuclear reactor is comprised of two separate recirculation loops. Each loop contains a common discharge line into which a secondary coolant discharge line and blowdown discharge line from at least one steam generator feeds. The common discharge line contains a recirculating pump and a heat exchanger, with bypasses provided about each. The common discharge lines discharge into branch feedlines back to the steam generators. The system may also be used as a blowdown system leading to a steam generator blowdown processing system and may include a water purification means and used to purify the secondary coolant water. Cross-connecting lines are provided to permit optional use of a particular loop with various steam generators.

Abstract: A passive depressurization system for use during cold shutdown of a pressurized water reactor receives saturated steam from the reactor's pressurizer, condenses the steam to water, and returns the water to a nozzle within the pressurizer in order to provide a cooling spray which condenses steam within the pressurizer. The depressurization system may include coiled tubing, which is connected to input and output ports of the depressurization system by redundant valves, or a condenser formed by a housing having air vents provided by vent elements through the housing.

Abstract: Disclosed is a nuclear power plant comprising a high-temperature pebble bed reactor contained in a cylindrical steel pressure vessel in which an upper part of the cylindrical steel pressure vessel, which contains a heat utilization system, is retracted and equipped with a cover upon which circulating blowers are placed. The heat utilization system comprises, in a known manner, a single steam generator. The steam generator comprises at least two sub-systems independent of one another, with their own distributors and collectors, and with their own inlet and outlet lines. A first shut-down arrangement comprises a plurality of absorber rods insertable into bores of the side reflector from above and comprises rod drives arranged outside the steel pressure vessel in the area of its retracted upper part. A second shut-down arrangement comprises small absorber spheres for introducing into the core of the reactor, and several storage containers and annular conduits for said spheres.

Abstract: Device for the emergency removal of the heat dissipated by a fast breeder nuclear reactor when shut down, comprising a liquid-liquid heat exchanger immersed in the vessel of the reactor and a liquid-air exchanger for the cooling of the secondary liquid of the latter exchanger. The liquid-liquid comprises a casing composed of a sleeve (18,19) having openings (21,22) for the natural circulation of the cooling fluid of the reactor in contact with the tubes (25) of a nest (20) disposed in the casing of the exchanger. Each of the tubes (25) includes a straight input section and a long straight return section, separated by a helically wound section forming a loop with a low number of turns, inclined to a small extent with respect to the horizontal plane. The coil diameter of the tubes (25) is constant and identical for all the tubes and very slightly less than the interior diameter of the sleeve (18,19).The invention applies in particular to liquid sodium-cooled fast breeder nuclear reactors.

Abstract: An emergency cooling device for a water-cooled nuclear reactor comprises a heat exchanger integrated into a reactor vessel and submerged in the reactor water. One of the ends of the circuit of this exchanger is connected by means of a three-way valve to the upstream valve, while its other end is connected across a downstream valve and a second untreated water-operated cooling exchanger to the cold water tank.

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: Device for the post-accident cooling of the confinement enclosure of a pressurized water nuclear reactor, wherein it comprises in series a turbine supplied by the hot, humid air contained in the enclosure, a condenser in which the air from the turbine is dried and cooled by thermal contact with an external cooling fluid, and a compressor actuated by the turbine, and which returns the dried air into the 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: A method of cooling the primary circuit of a pressurized water nuclear reactor in which, after a first stage, during which water is injected into the steam generators and the steam produced is discharged, cooling is continued during a second stage by water-water heat exchange. In this second stage, the water is made to circulate at the secondary side of at least one steam generator (2) in countercurrent to the primary water, over at least part of its path. The secondary water heated by the primary water is cooled outside the containment enclosure (1) of the nuclear reactor in at least one heat exchanger (31) using raw cooling water. The secondary water is recycled in the steam generator (2). The invention is applicable to the effecting an maintaining of cold shutdown of pressurized water nuclear reactors.

Abstract: The invention pertains to a containment system for a nuclear power plant which provides protection in the event of a loss of coolant accident or other malfunctions wherein the stored energy within the components of the system is contained and absorbed by the use of a plurality of coolant reservoirs capable of absorbing steam and supplying coolant to the reactor coolant system and feedwater to the secondary systems. The system includes a plurality of steam generators which may selectively be employed as an energy source during cooldown, and the design of the reservoirs provides high initial energy absorption as well as extended energy dissipation during cooldown.

Abstract: A nuclear reactor installation comprising a housing including therein a reactor core and provided with means for dissipating the heat generated in the reactor core during operation, which means comprise a primary cooling fluid circuit passing at least one partly through the reactor core in which is included a pump, a secondary cooling fluid circuit arranged outside the housing of the nuclear reactor and consisting of at least one closed loop in which is included a pump, a loop of the primary circuit being coupled by means of a heat exchanger, to a loop of the secondary circuit, said installation is also provided with means for dissipating the decay heat produced in the core of the nuclear reactor after the reactor has been switched off, which dissipation means are at least partly formed by the primary cooling fluid circuit.

Abstract: The nuclear boiler comprises at least one heat exchanger located externally of the reactor vessel in order to effect heat exchange between the liquid metal coolant in the form of liquid and water to be vaporized and superheated together with a main storage tank connected to the reactor vessel for receiving liquid metal and inert gas. A main storage tank pipe system fitted with valves consists of a first overflow pipe for connecting the top of the reactor vessel to the bottom of the storage tank, and at least one second pressure-equalizing pipe between the top of the reactor vessel and the top of the storage tank. Controlled-atmosphere compartments forming the reactor containment structure and containing the unclear steam supply systems provide biological protection for operating personnel and guard against impacts of external origin.

Abstract: An after-heat removal system for a nuclear reactor, especially a gas-cooled uclear reactor in which the core is formed by a pile of spherical nuclear fuel elements, comprises an outlet in the side reflector of the reactor core which is connected to an after-heat removal system and draws the hot gases from a location within the pile, the return line from the after-heat removal system opening into the main cooling gas inlet.

Abstract: A cooling system for a gas-cooled nuclear reactor is disclosed which includes at least one primary cooling loop adapted to pass coolant gas from the reactor core and an associated steam generator through a duct system having a main circulator therein, and at least one auxiliary cooling loop having communication with the reactor core and adapted to selectively pass coolant gas through an auxiliary heat exchanger and circulator. The main and auxiliary circulators are installed in a common vertical cavity in the reactor vessel, and a common return duct communicates with the reactor core and intersects the common cavity at a junction at which is located a flow diverter valve operative to effect coolant flow through either the primary or auxiliary cooling loops.

Abstract: In a control apparatus for residual heat removal system for a nuclear reactor in which the steam generated in the reactor vessel is cooled and condensed into water through a heat exchanger and the condensed water is fed back by a feedwater pump driven by the reactor steam so as to cool the reactor core, the pressure of the condensed water at the exit of the heat exchanger is increased with the rise of the reactor water level so as to decrease the flow of the condensed water, that is, coolant water and the flow-in of the make-up water from the make-up water reservoir communicating with the outlet port of the condenser while the quantity of the reactor steam supplied to the turbine is decreased with the increase in the reactor temperature fall rate so as to decrease the flow of the coolant water fed back into the reactor vessel.

Abstract: A nuclear reactor installation comprising a housing including therein a reactor core and provided with means for dissipating the heat generated in the reactor core during operation, which means comprise a primary cooling fluid circuit passing at least one partly through the reactor core in which is included a pump, a secondary cooling fluid circuit arranged outside the housing of the nuclear reactor and consisting of at least one closed loop in which is included a pump, a loop of the primary circuit being coupled by means of a heat exchanger to a loop of the secondary circuit, said installation is also provided with means for dissipating the decay heat produced in the core of the nuclear reactor after the reactor has been switched off, which dissipation means are at least partly formed by the primary cooling fluid circuit.

Abstract: A passive decay heat removal system in which gas pressurization of a gap between the double walls of heat exchanger tubes initiates heat removal by triggering an increase in tube heat conductivity.