Abstract: The present disclosure relates to a seawater desalination system which improves energy efficiency by applying a heated cooling water discharged from a nuclear power plant and high-temperature steam generated in a nuclear reactor to seawater desalination.

Abstract: A method of storing a chimney assembly of a reactor pressure vessel during a nuclear reactor outage includes detaching a chimney barrel with upper chimney partitions therein from a top guide assembly of the reactor pressure vessel. A height of the upper chimney partitions is less than a height of the chimney barrel so as to leave a plenum region in a top section of the chimney barrel. The top guide assembly includes lower chimney partitions therein. The lower chimney partitions are removed from the top guide assembly and inserted into the plenum region of the chimney barrel so as to be on the upper chimney partitions. As a result, the chimney assembly can be stored in a relatively compact form during a reactor outage. The chimney assembly includes a combination of at least the chimney barrel, the upper chimney partitions, and the lower chimney partitions.

Abstract: A passive containment air cooling system for a nuclear power plant that enhances air flow over a metal containment that houses the reactor system to improve heat transfer out of the containment. The heat transfer is improved by employing swirl vanes to mix the air as it rises over the walls of the containment due to natural circulation and a vortex engine proximate an exit along the cooling air path to increase the quantity of air drawn along the containment.

Abstract: A power module includes a reactor vessel containing a coolant and a reactor core located near a bottom end of the reactor vessel. A riser section is located above the reactor core, wherein the coolant circulates past the reactor core and up through the riser section. In one embodiment, a coolant deflector shield includes flow-optimized surfaces, wherein the flow-optimized surfaces direct the coolant towards the bottom end of the reactor vessel. In another embodiment, the reactor housing includes an inward facing portion that varies a flow pressure of the coolant and promotes a circulation of the coolant past a baffle assembly and towards the bottom end of the reactor vessel.

Abstract: In a nuclear reactor, a core barrel (46) is disposed in a reactor vessel (41) having an inlet nozzle (44) and an outlet nozzle (45), a core (53) is disposed in the core barrel (46), a lower plenum (58) is partitioned by the reactor vessel (41) and a bottom portion of the core barrel (46), and a downcomer portion (59) is partitioned by the reactor vessel (41) and a side wall of the core barrel (46). The lower plenum (58) includes a straightening member (61) formed of an upper ring (65) and a lower ring (69) in a ring shape, and a plurality of spokes (64 and 68) radially arranged inside the rings (65 and 69), respectively. Heat exchange efficiency is enhanced by uniformly supplying coolant introduced into a pressure vessel to the core from the lower plenum in a radial direction and a circumferential direction.

Abstract: A method of fabricating a zirconium alloy flat product, the method being characterized by: preparing or casting a zirconium alloy ingot containing at least 95% by weight of zirconium, and including the usual impurities and alloying elements; shaping said ingot in order to obtain a flat product; subjecting said flat product to a ? quenching operation under conditions that are determined to obtain within the flat product an acicular structure at the end of said ? quenching; subjecting said flat product, after the ? quenching, to a rolling operation performed in a single rolling sequence without intermediate annealing, said rolling being performed at a temperature lying in the range ambient to 200° C., and having a reduction ratio lying in the range 2% to 20%; and subjecting said rolled flat product to an annealing treatment in the a range or in the ?+? range, performed in the temperature range 500° C. to 800° C. for 2 minutes to 10 hours.

Abstract: A direct vessel injection-type pressurized light water reactor (DVI-PLWR), in which an emergency core cooling water (ECC) is directly injected into a downcomer of a reactor vessel, is disclosed. In order to reduce the ratio of ECC bypass from the downcomer to a broken area of a cold leg in the case of a cold leg guillotine break (CLGB), such as a double-ended guillo4tine break (DEGB), a plurality of corrugations, having a V-shaped cross-section, are vertically arranged around each of the inner surface of a pressure vessel and the outer surface of a core barrel at regular intervals, with a vertical groove formed between two neighboring corrugations. The grooves phase-separate the ECC from a high-speed lateral flow of fluid running in the downcomer, and the separated ECC stagnates in the form of vortexes in the grooves, prior to flowing down to the lower section of the downcomer due to gravity.

Abstract: A fuel bundle assembly for a boiling water nuclear reactor comprising a plurality of fuel rods having respective fuel columns therein, and arranged in an ordered array, extending between upper and lower support structures, the plurality of fuel rods enclosed within a hollow, open-ended channel member at least partially enclosed by the open-ended channel member; at least one water rod supported on the lower tie plate and extending upwardly toward the upper tie plate, the at least one water rod having an upward flow path including at least one inlet at a lower end of the upward flow path, and a downward flow path including at least one outlet at a lower end of the downward flow path, the at least one outlet located about midway along the fuel columns within the fuel rods.

Abstract: Within an upper plenum of a nuclear reactor, a portion of a heated coolant flows radially outward from a central portion of a core barrel (30) towards outlet nozzles (12) in a region of an upper core plate (21) extending outside of an outer periphery of the core along an inner wall of a core barrel (30). Portions of the coolant flows beneath the outlet nozzles (12). Thus, streams of heated coolant flowing in opposite directions may collide with each other. After collision, the flow directions of the heated coolant are changed to flow upward. Due to the collision, the coolant flow behavior becomes complicated and unstable, making it difficult to measure the temperature of the heated coolant with an outlet pipe (42) connected to the outlet nozzle (12).

Abstract: A resistance member (e.g., fuel holding portion of the lower tie plate) is provided at the lower end of the fuel assembly. Provision is made of a coolant ascending path in which said water rods have coolant inlet ports that are open in a region lower than the resistance member to upwardly guide the coolant, and a coolant descending path which has a coolant delivery port that is open in a region higher than the resistance member to downwardly guide the coolant. The coolant ascending path and the coolant descending path are communicated with each other at their upper end portions.

Abstract: An apparatus for promoting intermixing of heated fluid streams within a nuclear reactor vessel is implemented in such structural configuration and disposition as to be capable of not only promoting uniform temperature distribution of a heated fluid stream flowing into an outlet nozzle but also reducing flow resistance which the heated fluid encounters within a upper plenum of the reactor vessel. The apparatus is disposed within a upper plenum (40) defined within a nuclear reactor vessel (10) of a nuclear reactor above a core having a low temperature region (a) and a high temperature region (d) where a heated fluid flows at a low temperature and a high temperature, respectively. The upper plenum (40) is hydraulically communicated to outlet nozzles (12) installed at a side wall of the nuclear reactor vessel (10).

Abstract: In each of a number of fuel assemblies loaded in a core of a boiling water reactor, a fuel holding portion of a lower tie plate holds lower end portions a plurality of fuel rods and at least one water rod. The water rod includes a rising pipe opened to a space in the lower tie plate below the fuel holding portion and introducing upward a coolant introduced to the rising pipe, and a falling pipe communicated with the rising pipe and introducing downward the coolant introduced through the rising pipe. The falling pipe has a coolant outlet opened to a second coolant passage defined between the fuel rods above the fuel holding portion. The rising passage is filled with the coolant during a period of rated power operation of the reactor, and a surface of the coolant is formed in the rising pipe during a period of non-rated power operation in which a flow rate of the coolant supplied to the fuel assemblies is lower than that during the period of rated power operation.

Abstract: A steam/water separating device for a nuclear fuel bundle is located in a vent volume above part-length rods and includes a helical swirl vane. In one form, the swirl device lies below a vent tube and a transition element for flowing liquid laterally outwardly into the interstices of the fuel rods and steam upwardly within the vent tube. In another form, the vane depends from a cylindrical barrel open at its lower end. An annular pick-off tube extends into the open upper end of the barrel and lies in communication through a transition element with a superposed steam vent tube. An annular outlet is defined between the barrel and pick-off tube and the transition element deflects coolant water flowing through the annular outlet in a lateral outward direction for flow into the interstices of and onto the full-length fuel rods. Steam flows upwardly in the barrel through the pick-off tube into the steam vent tube.

Abstract: A chimney which can be reconfigured or removed during refueling to allow vertical removal of the fuel assemblies. The chimney is designed to be collapsed or dismantled. Collapse or dismantlement of the chimney reduces the volume required for chimney storage during the refueling operation. Alternatively, the chimney has movable parts which allow reconfiguration of its structure. In a first configuration suitable for normal reactor operation, the chimney is radially constricted such that the chimney obstructs vertical removal of the fuel assemblies. In a second configuration suitable for refueling or maintenance of the fuel core, the parts of the chimney which obstruct access to the fuel assemblies are moved radially outward to positions whereat access to the fuel assemblies is not obstructed.

Abstract: A natural circulation reactor, especially a boiling water reactor, includes a reactor pressure vessel, a reactor core and a core jacket disposed within the reactor pressure vessel, surrounding the reactor core and having at least one inlet port and one outlet port for core coolant. A flow path for the core coolant, which is formed between the core jacket and the reactor pressure vessel, leads through the inlet port into the core jacket and has a flow cross section. At least one throttle element is disposed in the flow path for varying the flow cross section in order to regulate the core coolant flow rate. The flow cross section can be both increased and reduced in size by varying the cross sectional area of the throttle element, so that a regulation of the power of the natural circulation reactor is carried out in a simple way and, in an incident, a reduction in power to approximately 40% of the instantaneous reactor power is ensured.

Abstract: In a fuel bundle for use in the core of a boiling water nuclear reactor, part length rods having a tendency to reduce pressure drop are used in combination with spacers and spacer attached devices tending to utilize pressure drop to improve critical power. The addition of the part length rods has the advantage of lowering the pressure drop. Attached devices substantially increase the pressure drop. Exemplary spacer attached mechanisms for the utilization of pressure drop are set forth including vanes--preferably swirl vanes on the spacers, decreasing the spacer pitch to increase the total number of spacers in the upper two phase region of the fuel bundle, increasing the vertical height of the spacers, and increasing the thickness of the metal from which the spacers are constructed. Two classes of separation devices are disclosed for placement in the volume overlying the end of the partial length fuel rods.

Abstract: Control rod guide tube adapted to reduce vibration of a plurality of control rods disposed therein. The guide tube comprises an elongate housing surrounding the control rods, the housing having an opening at an end thereof for receiving a flowing fluid therethrough. The fluid has a velocity component acting transversely to the control rods sufficient to induce vibration of the control rods. However, the housing of the present invention has an intermediate portion pierced by a plurality of apertures for exit of the fluid from the housing to reduce the velocity of the fluid acting transversely to the control rods in order to reduce vibration of the control rods. As control rod vibration is reduced, control rod wear is mitigated.

Abstract: The present invention is directed to a modular steam separator with integrated dryer especially adapted for separating and drying steam exiting the core of a nuclear boiling water reactor. The instant modular separator with integrated dryer has a standpipe with a proximal end that is connectable to the upper plenum of the core of the nuclear reactor and a distal end that is connected to a proximal end of a steam separator. A distal end of the steam separator is connected to a steam distribution channel that extends in fluid communication to a steam dryer. The steam dryer has a steam vent for passage of dry steam to the steam dome of the reactor and a water drain connected to the reactor's downcomer region.

Abstract: A natural circulation boiling water reactor system comprises a reactor vessel enclosing a reactor core, for generating steam to drive a turbine which can drive a generator to generate electricity. The vessel includes a chimney for guiding the recirculating water and steam vertically above the core and a dryer for helping to remove water from steam exiting the vessel toward the turbine. In contrast to prior reactor systems, the chimney is height-staggered so that its central sections are taller than its peripheral sections. Likewise, a dryer is elevation-staggered. This staggering minimizes carryover, water in the steam flow to the turbine, and carryunder, steam in the water recirculating through the core. In addition, the staggered chimney causes the fastest recirculation flow through the hottest portions of the core. The overall effect is a more efficient reactor system.

Abstract: A nuclear reactor core assembly includes a support plate having a plurality of inlets for channeling water to a core lattice fixedly joined thereto. The lattice includes a plurality of flow channels, each including a respective separately removable fuel bundle. In a preferred embodiment, the core lattice includes a plurality of flow dividers joined together for allowing unrestrained expansion and contraction thereof, and which prevent crossflow of water therebetween.

Abstract: A natural-circulation boiling-water reactor has skirts extending downward from control rod guide tubes to about 10 centimeters from the reactor vessel bottom. The skirts define annular channels about control rod drive housings that extend through the reactor vessel bottom. Recirculating water is forced in through the low-level entrances to these channels, sweeping bottom water into the channels in the process. The sweeping action prevents cooler water from accumulating at the bottom. This in turn minimizes thermal shock to bottom-dwelling components as would occur when accumulated cool water is swept away and suddenly replaced by warmer water.

Abstract: A natural circulation boiling water reactor system using free-surface steam separation incorporates a series of tubes near the inner wall of its reaction vessel extending from a downcomer to well-above the downcomer. These tubes allow steam bubbles which would otherwise be trapped within the downcomer to escape from the recirculating water toward the steam exit of the vessel. This lowers the volume of steam in the downcomer, lowering the water velocity required to maintain a given volume of water recirculation. The reduced water velocity results in less carryunder which results in smaller voids in the reactor core. The smaller voids provide longer fuel burnups and enhance reactor stability.

Abstract: A natural circulation boiling water reactor system comprises a reactor vessel enclosing a reactor core, for generating steam to drive a turbine which can drive a generator to generate electricity. The vessel includes a chimney for guiding the recirculating water and steam vertically above the core and a dryer for helping to remove water from steam exiting the vessel toward the turbine. In contrast to prior reactor systems, the chimney is height-staggered so that its central sections are taller than its peripheral sections. Likewise, a dryer is elevation-staggered. This staggering minimizes carryover, water in the steam flow to the turbine, and carryunder, steam in the water recirculating through the core. In addition, the staggered chimney causes the fastest recirculation flow through the hottest portions of the core. The overall effect is a more efficient reactor system.

Abstract: A boiling water nuclear reactor plant is provided with a standby supply of auxiliary coolant water for use in the event of a loss of coolant mishap to provide supplementary coolant water for cooling the fuel core. The supply of standby auxiliary coolant water is maintained within the reactor pressure vessel and is administered by inherently passive means.

Abstract: The present invention is directed to gas-liquid separators especially adapted for the separation of steam exiting the core of a nuclear boiling water reactor that utilizes natural circulation. Such separator has a barrel having a longitudinal axis and width, has an inlet and an outlet, and has a plurality of spaced-apart pickoff rings in fluid communication with annular flow discharge passages. The improved separator of the present invention comprises the pickoff rings having curvilinear shape to direct flow into the flow discharge passages. A twisted strip swirler is positioned along the axis of the barrel after the initial pickoff ring and does not extend the full width of the barrel. The width of the barrel increases at each succeeding pick-off ring from the barrel inlet to the barrel outlet. Advantageously, a low expansion angle exists between the rings and the top of the separator barrel.

Abstract: A forced-circulation boiling-water reactor includes bypass check valves between a downcomer and a core inlet plenum. When the recirculation pumps are operating at full capacity, there is a maximum pressure differential from the downcomer to the core inlet plenum. This pressure differential keeps the valves closed so that recirculating fluid is constrained to flow through the pumps. When the pumps are not operating, a driving water head in the downcomer forces the valves open, augmenting the flow cross section between the downcomer and the core inlet plenum, enhancing natural circulation. The enhanced natural circulation provides greater core stability during pump shutdown. The valves are selected or adjusted so that they open when the pressure differential falls through a predetermined range to augment diminished pumping capacity with a higher natural circulation flow rate.

Abstract: The present invention discloses an improved methodology for achieving the desirable feature of recirculation flow control in a sparger-type natural-circulation BWR, enabling reactors utilzing the method to perform in load-following and/or spectral shift modes of power operations. In its broadest aspects, the invention is based on locating the feedwater sparger at an elevational level which is about water level established during normal operation of the BWR. One or more of load following or spectral shift can be performed by controlling the feedwater fed to said BWR through the feedwater inlet and into the sparger to vary the water level to be above, at or below the elevational level of such sparger.

Abstract: In a fuel bundle for a boiling water reactor having one or more part length rods in the two phase region, a steam vent tube is introduced overlying the part length rods. The fuel bundle includes a lower tie plate for admitting water moderator and supporting a plurality of fuel rods in upstanding side-by-side relation, an upper tie plate for permitting water and steam to be discharged from the top of the fuel bundle and maintaining the fuel rods in upstanding side-by-side relation, a surrounding fuel channel for confining moderator flow along a path over the fuel rods and between the tie plates, and dispersed vertically intermittent spacers for maintaining the fuel rods in their designed side by side relation. One or more fuel rods extends from the lower tie plate vertically less than the full length to the upper tie plate ending interior of the fuel bundle at a disposition where the upper end of the part length rods is braced in the vertical position by a spacer.

Abstract: The present invention is directed to a separator for dividing a steam/water mixture into its liquid and steam components. The inventive separator comprises a pipe having an annular spiral strip which is attached to its inside wall, said pipe being in fluid communication with ports for removal of liquid water divided from said mixture. The width of the annular spiral strip preferably is about 1/10th to 1/20th of the diameter of the pipe to which it is attached. A method for dividing steam/water mixtures into their liquid and steam components by passing such mixture through the inventive separator forms yet another aspect of the present invention.

Abstract: A natural circulation boiling-water reactor system using free-surface steam separation incorporates a steam separator near the inner wall of its reaction vessel and extending into a downcomer. Steam so collected supplements the main steam flow from the reactor vessel to drive a turbine, which in turn drives a generator. A flow controller opens and closes a valve to adjust the flow of steam from the steam collector to the turbine. The flow controller can be programmed to implement a predetermined power output level or to adjust power output as a function of load or time. When this level is exceeded, as indicated by feedback from the generator, the flow controller valve is constricted. The auxiliary steam flow to the turbine is directly decreased, reducing power output. Concomitantly, less steam is removed from the steam collector, and thus from the downcomer. As a result there is more carryunder steam, which reduces the power generated at the reactor core.

Abstract: In a boiling water reactor having discrete bundles of fuel rods confined within channel enclosed fuel assemblies, an improved fuel design of bundles of fuel rods interior of the channels is disclosed. Specifically, partial length rods are utilized which extend from the bottom of the channel only part way to the top of the channel. These partial length rods are shortened with respect to the remaining rods and are symmetrically distributed throughout the fuel bundle with the preferred disposition being in the second row of the bundle of fuel rods from the channel wall. The symmetrical distribution of the partial length rods is at spaced apart locations one from another. The partial length rods extend from the bottom of the fuel bundle and terminate within the boiling region. during shutdown of the reactor, an improved cold shutdown margin is produced at the top of the fuel assembly due to the improved moderator-to-fuel ratio and reduction in plutonium formation at the upper portion of the bundle.

Abstract: A nuclear reactor internal pump has a pump shaft connected to a motor and rotatably passing through the bottom of a nuclear reactor pressure vessel, an impeller fitted to a front end portion of the pump shaft, a diffuser disposed on the downstream side of the impeller and having an inner cylinder fixed to the bottom of the reactor pressure vessel to surround the pump shaft, a purge water passage defined between the pump shaft and the inner cylinder to communicate with the inside of the reactor pressure vessel and a purge water supply device for supplying purge water to reactor pressure vessel through the passage. Further, the nuclear reactor internal pump comprises a clad dropping preventive device for trapping clad coming from the reactor pressure vessel in the passage to prevent the clad from dropping.

Abstract: A steam separating system for boiling water nuclear reactors comprising a combination of mechanical steam separators with steam collecting and transferring units.

Abstract: A baffle (12) is provided for the gaps between a pair of surfaces (10, 14). The baffle has a lantern configuration and comprises a number of spring steel foils (15) arranged in side-by-side relation with overlap between adjacent foils. Each foil (15) is of shallow V-configuration. The ends of the V are attached by stud and slot connections (22, 24, 26, 28) to one of the surfaces separated by the gap at axially spaced locations and the midpoint of the V bears against the opposing surface. The stud and slot connections afford limited axial movement of the ends of the V to compensate for irregularities in the gap width.

Abstract: In a boiling water reactor of the type having a reactor core for heating feedwater to generate a two-phase steam/water mixture and a core shroud head overlying the reactor core and defining a core upper plenum region, a plurality of conduits disposed in the upper plenum region to provide supplemental water coolant. Each conduit has at least one open end located in the primary water coolant and a conduit body that extends laterally from the open end through the core shroud head and into the plenum region. Each conduit is closed with respect to the plenum region and is filled with primary water coolant during normal operation of the reactor to provide supplemental water coolant. The supplemental water coolant drains into the reactor pressure vessel when the primary coolant level falls below the open end to cool the reactor core during a loss-of-coolant accident.

Abstract: A nuclear fuel assembly for a boiling reactor comprises a plurality of fuel rods arranged in four sub-bundles surrounded by a fuel channel of substantially square cross-section. A vertical channel-formed support member for the passage of water, separates the sub-bundles of fuel rods. By arranging each sub-bundle with a reduced corner portion by not locating a fuel rod in that corner of the sub-bundle towards the center of the fuel assembly, the sub-bundles can be located in a separating channel-formed support member with an enlarged central channel. The enlarged central channel makes it possible to contain a larger quantity of non-boiling water in the central part of the fuel assembly, which results in better neutron moderation in the central part of the fuel assembly.

Abstract: A nuclear reactor in which rupture by fatigue of the components of the control-rod assemblies is precluded. The fatigue is caused by the vibration of the components or cavitation under the action of the coolant flowing at a high velocity transversely to the control-rod assemblies. A perforated shroud is provided between the control rod assemblies and the outlet nozzles. The shroud distributes the transversely-flowing coolant over a large volume so that its velocity is substantially lower than the resonant velocity at which vibrations of substantial amplitude of the components or cavitation is produced.

Abstract: A calandria for use in conducting the hot coolant of a nuclear reactor transversely. The calandria includes an upper plate and a lower plate which support tubes. The plates and tubes are enclosed in a shell which extends above the upper plate and has a supporting flange. The lower plate has holes for transmitting coolant into the region between the plates. The shell has openings whose boundaries mate with the outlet nozzles of the reactor. The tubes are of stainless steel and are dimensioned so that they have mass, stiffness and strength such that they are not subject to failure by the transverse flow of the coolant even at a high velocity.

Abstract: A method for converting a vertically downward flow of bypass coolant through coolant flow holes in a core barrel and former plates in a nuclear reactor to a vertically upward flow. Coolant flow holes are provided in the normally solid top former plate by suitable means such as drilling. These new coolant flow holes are located so as to be substantially in coaxial alignment with the existing coolant flow holes in the intermediate and lower former plates. Existing coolant flow holes in the core barrel adajcent the top former plate are plugged. Existing coolant flow holes in the lower former plate are plugged in an alternating pattern with each fifth hole being plugged having only forty-four percent of its flow area plugged.

Abstract: In a liquid metal-cooled fast neutron nuclear reactor which has a vessel sealed by a horizontal slab on which is suspended a core cover plug, the lower part of said plug comprises a deflecting grid, optionally duplicated by a thermal protection grid. Each of the grids is formed from a peripheral plate and modular plates defining between them passages for the liquid metal. The peripheral plates can be fixed to a perforated part of an external ferrule or can be suspended on a core cover plate by tie bolts and/or by certain of the control rod guidance sleeves. The modular plates are fixed to the other sleeves and traversed by sodium sampling tubes and tubes for housing thermocouples.

Abstract: A calandria assembly is received within the pressure vessel of a nuclear reactor system, at an elevation corresponding to the level of the outlet nozzles of the vessel, and receives pressurized coolant traveling in an axial flow direction within the vessel and turns same to a radial direction for exit through the outlet nozzles. Hollow tubes mounted in parallel relationship at opposite ends to first and second plates of the calandria in conjunction with a cylindrical skirt of cylindrical configuration joining the first and second plates of the calandria, present a redundant structure introducing the potential of thermal stresses, which are limited by selection of the pattern of flow holes in the lower plate and the provision of flexible annular weld joints of J-shaped configuration between the lower ends of the calandria tubes and the lower, second calandria plate.

Abstract: Coolant recirculation arrangement for a nuclear reactor including a plurality of vertically oriented tubular conduits arranged in spaced relation between an unshrouded nuclear core and the inner pressure vessel wall for conducting coolant from an upper plenum above the core to a lower plenum below the core.

Abstract: A nuclear reactor is equipped with a cooling water circulation system which includes a water-feed conduit and a drain conduit to circulate the cooling water to and from a pressure vessel which surrounds a reactor core, the cooling water having a free liquid level maintained above the reactor core. The drain conduit is inserted in the pressure vessel from the upper side toward the lower side relative to the free liquid level. A double tube consisting of an inner tube and an outer tube maintaining a gap therebetween is formed in the end portion of the drain conduit. The inner tube and outer tube being continuous with the drain conduit, the opening at the lower end of the inner tube is located below said free liquid level but above the reactor core. The opening at the upper end of the outer tube is located above the free liquid level. The opening at the lower end of said outer tube is located below the reactor core.

Abstract: To preclude failure of components of control-rod assemblies or of unprotected control rods (WDRC's) a calandria is provided above the upper internals. The calandria includes hollow tubes through which the drive rods for the various control rods pass and which protect the drive rods. The guides for the control rods are closed except at the top so that the coolant flows vertically through the guides into the calandria. In the calandria, the coolant flows transversely to the hollow tubes and out through the outlet nozzle. The tubes have a mass and stiffness and strength such that they resist failure by reason of the transverse flow of the coolant to which they are subjected.

Abstract: A nuclear reactor having a reactor vessel adapted to be supplied with a coolant, a reactor core disposed in the reactor vessel and including a plurality of fuel assemblies, a plurality of control rods adapted to be inserted into the reactor core and a plurality of control rod driving devices for driving the control rods into and out of the reactor core. A plurality of tubular coolant passage members are disposed above the fuel assemblies so as to receive the heated coolant discharged from the fuel assemblies, so that the heated coolant flows upwardly through the tubular coolant passage members. The tubular coolant passage members provide a chimney effect which enhances the upward flow of the coolant and, hence, increases the flow rate of coolant flowing through the reactor core. In consequence, a greater cooling effect is obtained and the range of power controllable by the control rods is widened.

Abstract: A system and a method of confirming the operation of a steam relieving safety valve for a water-cooled nuclear reactor are provided. Acoustic vibration generated by steam relieved from the safety valve when the latter is opened is detected by an acoustic emission sensor. The acoustic emission sensor is mounted on the safety valve or a steam relief pipe connected to the safety valve.

Abstract: A fuel asembly with a fuel channel (2) which surrounds a plurality of fuel rods (1) and which is divided, by means of a stiffening device (3) of cruciform cross-section and four wings (5), into four sub-channels (4) each of which comprises a bundle of fuel rods.Each fuel channel side has a plurality of stamped, inwardly-directed projections (6) arranged vertically one after the other, said projections being welded to one and the same stiffening wing. Each one of the wall portions located between the projections (6) defines, together with two adjacently positioned projections and a portion of the stiffening wing, a communication opening between two bundles located on one side each of the stiffening wing.

Abstract: In a boiling water reactor having a reactor pressure vessel, a reactor core disposed in the reactor pressure vessel, a plurality of reactor water circulators arranged on the circumference at equal intervals along the reactor pressure vessel and below the reactor core in the reactor pressure vessel and water spargers circumferentially arranged in the reactor pressure vessel, each of the water spargers comprises a plurality of vertical water supplying headers which surround the reactor core above and between adjacent ones of the reactor water supplying circulators and which have vertically arranged water spraying apertures directed to the reactor core.

Abstract: A boiling water reactor fuel assembly is provided with an elongated, vertical stiffening device having four stiffening wings which are each attached to a wall of the fuel box. Each stiffening wing has at least one vertically directed passageway for water.