Abstract: An integrated passive reactor system including a pressure vessel, a containment vessel arranged outside the pressure vessel, and a reactor core arranged inside the pressure vessel. A primary loop operates in full natural circulation. The reactor system is provided with a secondary side passive residual heat removal system including a primary loop heat exchanger arranged inside the pressure vessel and a passive residual heat removal heat exchanger arranged outside the containment vessel. The primary loop heat exchanger is arranged above the reactor core. The passive residual heat removal heat exchanger is arranged inside a water tank which is fixed outside the containment vessel. The primary loop heat exchanger and the passive residual heat removal heat exchanger are connected by heat exchanger inlet pipelines and heat exchanger outlet pipelines.

Abstract: A flow tripping device according to a non-limiting embodiment of the present invention may include a peripheral band surrounding a central space. A plurality of flow tabs may extend from an upper portion of the peripheral band toward the central space. A plurality of finger structures may extend from a lower portion of the peripheral band. When installed in a fuel channel of a boiling water reactor (BWR), the critical power ratio (CPR) performance of the periphery rods may be increased, thereby also increasing overall performance. Consequently, the increased power translates to lower fuel cycle costs.

Abstract: A pressurized water reactor (PWR) includes a pressure vessel and a nuclear reactor core disposed in the pressure vessel. A baffle plate is disposed in the pressure vessel and separates the pressure vessel into an internal pressurizer volume disposed above the baffle plate and an operational PWR volume disposed below the baffle plate. The baffle plate comprises first and second spaced apart plates and includes a pressure transfer passage having a lower end in fluid communication with the operational PWR volume and an upper end in fluid communication with the internal pressurizer volume at a level below an operational pressurizer liquid level range. A vent pipe has a lower end in fluid communication with the operational PWR volume and an upper end in fluid communication with the internal pressurizer volume at a level above the operational pressurizer liquid level range.

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: A core shroud is provided, which includes a number of planar members, a number of unitary corners, and a number of subassemblies each comprising a combination of the planar members and the unitary corners. Each unitary corner comprises a unitary extrusion including a first planar portion and a second planar portion disposed perpendicularly with respect to the first planar portion. At least one of the subassemblies comprises a plurality of the unitary corners disposed side-by-side in an alternating opposing relationship. A plurality of the subassemblies can be combined to form a quarter perimeter segment of the core shroud. Four quarter perimeter segments join together to form the core shroud.

Abstract: A pressurized water reactor (PWR) comprises: a nuclear core comprising a fissile material; a cylindrical pressure vessel having a vertically oriented cylinder axis and containing the nuclear core immersed in primary coolant water; and a hollow cylindrical central riser disposed concentrically with and inside the cylindrical pressure vessel. A downcomer annulus is defined between the hollow cylindrical central riser and the cylindrical pressure vessel. The hollow cylindrical central riser has a radially expanding upper orifice that merges into an annular divider plate that separates an upper plenum above the annular divider plate from a lower plenum below the annular divider plate. The upper plenum is in fluid communication with the radially expanding upper orifice and the lower plenum is in fluid communication with the downcomer annulus. A weir may extend away from a bottom wall of the lower plenum into the lower plenum.

Abstract: A pressurized water reactor (PWR) includes a pressure vessel and a nuclear reactor core disposed in the pressure vessel. A baffle plate is disposed in the pressure vessel and separates the pressure vessel into an internal pressurizer volume disposed above the baffle plate and an operational PWR volume disposed below the baffle plate. The baffle plate comprises first and second spaced apart plates and includes a pressure transfer passage having a lower end in fluid communication with the operational PWR volume and an upper end in fluid communication with the internal pressurizer volume at a level below an operational pressurizer liquid level range. A vent pipe has a lower end in fluid communication with the operational PWR volume and an upper end in fluid communication with the internal pressurizer volume at a level above the operational pressurizer liquid level range.

Abstract: A flow tripping device according to a non-limiting embodiment of the present invention may include a peripheral band surrounding a central space. A plurality of flow tabs may extend from an upper portion of the peripheral band toward the central space. A plurality of finger structures may extend from a lower portion of the peripheral band. When installed in a fuel channel of a boiling water reactor (BWR), the critical power ratio (CPR) performance of the periphery rods may be increased, thereby also increasing overall performance. Consequently, the increased power translates to lower fuel cycle costs.

Abstract: A lower nozzle an upper end and a lower end for the lower nozzle to rest on a lower core plate of a reactor core and a lateral surface extending along a longitudinal axis from the lower end to the upper end. The lateral surface including a longitudinal segment tapering downwardly progressively and continuously along the longitudinal axis and extending on at least 50% of the height of the lateral surface.

Abstract: Example embodiments provide a Basemat-Internal Melt Arrest and Coolability device (BiMAC) that offers improved spatial and mechanical characteristics for use in damage prevention and risk mitigation in accident scenarios. Example embodiments may include a BiMAC having an inclination of less than 10-degrees from the basemat floor and/or coolant channels of less than 4 inches in diameter, while maintaining minimum safety margins required by the Nuclear Regulatory Commission.

Abstract: A nuclear reactor includes a reflector and a flow path. The reflector reflects neutrons, contains graphite and a moderator having a smaller moderating power than the graphite, and is sectioned into plural parts along a direction of flow of fuel pebbles. The flow path is surrounded by the reflector, and the fuel pebbles flow through the flow path and undergo nuclear reaction to generate power. Volume ratio of the graphite to the moderator having a smaller moderating power than the graphite in each part of the reflector is determined based on a power distribution in the reactor core in the direction of flow of the fuel pebbles.

Abstract: A fuel assembly is charged in a reactor core of a nuclear reactor using a liquid metal as a coolant and includes a wrapper tube storing a plurality of fuel pins and including an entrance nozzle at a lower end thereof for introducing the coolant and an operation handling head at an upper end thereof, grids for supporting the plurality of fuel pins in the wrapper tube in the radial direction of the wrapper tube, liner tubes inserted in the wrapper tube for fixedly holding the grids in the axial direction of the wrapper tube, and peripheral flow suppressing members disposed in a peripheral flow passage extending between peripherally disposed ones of the fuel pins and the wrapper tube over a length corresponding to a heat generation length, which is a length range in the axial direction of the fuel pins storing a radioactive fuel material.

Abstract: A natural circulation boiling water reactor provides to a chimney with a plurality of tubes. That is to say, each of the plurality of tubes partitions the coolant flow path above a core. Thus, unlike the conventional natural circulation boiling water reactor providing the flow path partition wall grid in which the plate members are made integral by welding and coolant flow paths are partitioned, the chimney of the natural circulation boiling water reactor can reduce the number of welded portions because the edges of the four corners of each flow path do not need to be welded. The natural circulation boiling water reactor can avoid removal as a single unit, as in the case of the flow path partition wall grid in the conventional natural circulation boiling water reactor, by detaching each tube. The chimney can be easily detached from the reactor pressure vessel.

Abstract: A nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

Abstract: In a nuclear reactor internal structure, generation and promotion of object-downstream separating vortices are suppressed so that coolant uniformly flows in a reactor core and pressure loss of flow of the coolant is reduced so that the flow of the coolant is stabilized. A lower connecting plate 30 arranged in a lower plenum 8 comprises a ring portion 31 in which an arcuate portion 32 and a cut-off portion are alternately formed. An outer peripheral portion of the ring portion 31 is asymmetric relative to a flow direction of main flow and also asymmetric relative to a separating flow generation direction.

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: 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: An in-vessel structure for a top-entry type fast reactor wherein a core is positioned in the interior of a reactor vessel, an upper core structure being provided above the core, a coolant passing through a cold leg piping inserted from an upper portion of the reactor vessel thereinto and reaching the core, in which the coolant is heated, the coolant then flowing out to an upper plenum, the resultant coolant passing through a hot leg piping, which is inserted from an upper portion of the reaction vessel thereinto, and reaching the outside of the reactor vessel. A plurality of annular fins are fixed horizontally in an axially spaced manner to both the portions of an outer circumferential surface of the upper core structure and the opposite portions of an inner circumferential surface of the reactor vessel, these portions being under the free liquid surface during a rated operation of the reactor.

Abstract: A drain system for a shutdown cooling system of a pressurized water reactor type of a nuclear power plant (10) has an increased flow rate in the drain pipe (28) and drain pump (33). The hot leg (18) connected drain pipe has a vaned vortex breaker (30) mounted therein between its connection with the hot leg (18) lower region and the drain pump (33). This minimizes vortex-created cavitation in the drain pump thereby permitting the increased flow rate.

Abstract: A plug assembly for plugging the flow hole of a core support barrel employs an offset arm for securing the plug to the core support barrel above the flow hole and the adjacent thermal shield. The disclosed embodiments do not require the cutting of an access opening through the thermal shield.

Abstract: Method and apparatus for improving coolant flow in a nuclear reactor during accident as well as nominal conditions. The reactor has a plurality of fuel elements in sleeves and a plenum above the fuel and through which the sleeves penetrate. Holes are provided in the sleeve so that coolant from the plenum can enter the sleeve and cool the fuel. The number and size of the holes are varied from sleeve to sleeve with the number and size of holes being greater for sleeves toward the center of the core and less for sleeves toward the periphery of the core. Preferably the holes are all the same diameter and arranged in rows and columns, the rows starting from the bottom of every sleeve and fewer rows in peripheral sleeves and more rows in the central sleeves.

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: Upper internals for a pressurized nuclear reactor include an assembly for collecting the coolant leaving the core and a separating device. The device has guides for the control clusters and their drive shafts, a lower plate formed with passages for the coolant leaving the core and an upper plate formed with holes for passage of the same coolant into the collection assembly or plenum. A peripheral shroud may connect the plates together. Each cluster guide of the flow separation device has an internal casing devoid of openings, having a practically coolant-tight connection with the plates, whereby the control clusters and their drive shafts are protected against the high speed coolant flow from the core to the outlet nozzle.

Abstract: A nuclear reactor includes a spaced sidewall and a core shroud defining a flow passage for channeling a coolant. A foreign object separator includes an arcuate endwall extending from the sidewall, with the core shroud including an intermediate portion spaced from the endwall to define an annular inlet for receiving coolant from the flow passage. The core shroud also includes a distal end spaced from the endwall to define a throat. A separator member has a proximal end joined to the endwall, and a distal end spaced from the core shroud to define an outlet. The distal end of the separator is spaced from its proximal end for allowing the coolant from the throat to impinge against the separator member for turning the coolant prior to discharge from the outlet and using centrifugal force to separate any foreign objects of predetermined size from the coolant. The separated foreign objects are retained adjacent to the separator member proximal end.

Abstract: In a liquid metal cooled fast neutron nuclear reactor plant, surfaces (12) which are immersed in the flowing liquid metal and are vulnerable to liquid metal temperature fluctuations are provided with fins (20) defining cavities (22) for at least temporarily trapping the liquid metal to produce a thin layer of the liquid metal on the surface and thereby attenuate the effect of temperatures fluctuations occurring in the liquid metal flow.

Abstract: Lower internals for a reactor--typically a PWR--having a pressure vessel containing a core cooled by an upward flow of coolant and a core support include a shell defining a coolant volume between the support plate and the lower part of the vessel. The shell has a wall and ducts opening into passages of the support plate. Guide tubes passing through the volume receive glove fingers for in-core instrumentation probes. The internals further include a separation plate fixed to the wall means, situated below the core support plate. The separation plate is formed with holes connected to the coolant conveying ducts and is fixed to the lower support plate of the core by mechanical connection means spaced apart at the periphery of the separation plate and defining passages for radial access of the coolant to the distribution chamber.

Abstract: In a liquid metal cooled fast breeder nuclear reactor of the pool type, the hot and cold pools (13, 19) are separated by an intermediate plenum (24) which, under steady state conditions, encloses a volume of substantially stagnant liquid metal to form a thermal barrier between the hot and cold pools (13, 19). To avoid undesirably large temperature differentials developing for example in the event of large temperature excursions within the hot pool (13) as a result of a reactor trip, the intermediate plenum (24) is designed to permit, in such circumstances, rapid interchange of liquid metal coolant between the hot pool and the intermediate plenum, for example by way of a thermal siphon arrangement (30).

Abstract: Modular neutron reflector assemblies removably insertable into the irregular space in a nuclear reactor between a generally cylindrical array of square fuel assemblies comprising the core and the cylindrical core barrel surrounding the core, include an elongated enclosure having a strongback adjacent the core barrel and flat plates adjacent the fuel assemblies. The strongback is thicker than the steel plates by an amount which results in the strongback and plates reaching approximately the same temperature to minimize thermal stresses despite the 8 to 20 times greater nuclear heating at the core side of the enclosure as opposed to that at the core barrel side. The enclosure is suspended by a single point mounting on the core barrel which permits vertical, radial, and circumferential expansion but a pin depending from the lower end of the enclosure slides in a vertical bore in the reactor lower core support plate to limit lateral movement while allowing unrestrained vertical expansion and contraction.

Abstract: Nuclear reactor having upper internal equipments and lower internal equipments with probe guiding means including probe guide ducts for slidably guiding flexible elongated probes into the core. The upper internal equipments include a plenum chamber for collecting the coolant coming out of the core and separating means disposed between the core and the plenum chamber, said separating means including two plates, one upper and one lower, connected at their periphery by an envelope and comprising spacer tubes through which pass the coolant so as to avoid passing through cluster guides for guiding the clusters of control elements into and out of the core. Lower internal equipments placed between the core and the bottom of the vessel include an enclosure and ducts for the passage of the coolant entering the core, said enclosure thus defining a tranquilized volume in which the probe guide ducts are distributed.

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: 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 nuclear reactor has a pressure resistant vertical vessel with inlet and outlet pipes situated at the same horizontal level. It also includes internals having a barrel supporting the core and defining with the vessel a down flow path for the coolant from the inlet pipes towards a space under the core and upper internals defining a flow path for the coolant leaving the core, above this latter, and flowing towards the outlet pipes. The upper internals include dividing walls defining circumferentially distributed volumes located at the common level of the pipes and each over a different angular sector. Some volumes belong to the initial part of the downgoing coolant path and the others force part at least of the coolant leaving the core to follow a path which is successively directed upwardly then curving towards the outlet pipes. The invention is particularly suitable for use in pressurized water reactors.

Abstract: The cover plug (4) comprises a cylindrical barrel (8), a support plate (10), a group of vertical tubes (12) for the control rods and for the instrumentation of the core, an apertured transverse plate (28) fixed to the lower end of the barrel (8) and a transverse deflection plate (32) located above the apertured plate (28). The transverse deflection plate (32) is suspended from the barrel (8) by substantially vertical elastically yieldable strips (34) evenly spaced apart on the periphery of the barrel (8). The strips (34) are welded to the barrel (8) by their upper end and to the edge of the deflection plate (32) by their lower end. They are located in the region of openings (35) in the barrel (8) which permit radial movement of the deflection plate. The deflection plate (32) is also integral with tubes (14b) receiving the control rods disposed in a single row coaxial with the barrel (8).

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: Disclosed is a reactor internals hold down spring and upper head region cooling passage. The hold down spring utilizes a plurality of stacks of Belleville spring washers to provide spring load and deflection capability to hold down the reactor vessel internals. Each spring assembly includes a generally leak tight means for passing an adjustable coolant flow to the upper reactor vessel head region in order to maintain that region at inlet coolant temperature. The spring assemblies are angularly spaced about a core barrel support flange to cooperate with coolant flow passage formed therein.

Abstract: The fuel rods located in areas of a nuclear reactor core where water jetting damage to the rods can occur are secured together by a clip, in order to change the mass subject to fretting damage. The change of mass changes the amplitude of the induced fuel rod vibration, thus reducing possible fuel rod fretting an/or damage. To repair such damage, the combination of clip(s) and an inert rod are used to replace a damaged fuel rod.

Abstract: For operating a PWR with spectral shift during all combustion cycles and with undermoderation during some cycles only, the reactor structure is designed for receiving either one of two types of fuel assemblies, having the same geometry. All fuel assemblies have guide tubes for receiving spectral shift clusters containing fissile material but with different elements bundles so as to be able to choose the type of operation.

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: An array of plural rod guides each housing therewithin corresponding pluralities of rods, as disposed in parallel axial relationship within the cylindrical sidewall of the inner barrel assembly of a pressurized water reactor, defines a plurality of peripheral regions between the inner circumferential surface of the cylindrical sidewall and the peripheral edges of the array. A plurality of modular formers is installed within the respective plurality of peripheral regions, at each of one or more banks of predetermined, respective elevations within the inner barrel assembly. Each modular former comprises a pair of parallel former plates having arcuate outer edges corresponding to the interior circumference of the cylindrical sidewall and chordlike inner edges contoured to correspond to the juxtaposed peripheral edge of the array, and a vertical column extending between and rigidly interconnecting the associated plates of a pair.

Abstract: A pipe loop arrangement for the closed primary system of a nuclear reactor. The heated reactor coolant flows through a horizontally positioned hot leg pipe while the return flow cooled reactor coolant flows through a cold leg pipe concentrically mounted within the hot leg pipe. A bell-mounted suction port and the high pressure discharge port of the reactor coolant pump are located within an outlet chamber with the steam generator. A transition piece slip fitted to an opening within the reactor vessel outlet flange connects the cold leg pipe to the inlet to the nuclear core. A flow shroud surrounding the pump discharge connects the pump discharge to the cold leg pipe, forms a volute for the pump discharge and separates the outlet chamber from the inlet chamber of the steam generator.

Abstract: Metallic reflector units supported solely by the core barrel substantially fill the annular spaces between the vertically spaced former plates which traverse the irregular space between the fuel assembly array and the core barrel in a pressurized water reactor. The support for each reflector unit comprises a pin extending radially outward along an extended line passing through the center of the metallic mass to support the vertical loads, and four elongated bolts in a rectangular pattern centered on the pin to resist overturning moments induced by seismic loads. The elongated bolts engage the core barrel and the bottoms of bores in the reflector units so that the bolts are free to bend to accommodate for thermal expansion of the reflector unit in all directions from the pin.

Abstract: A fuel assembly for a pressurized water nuclear reactor incorporating fluid moderator spectral shift control means. During the first part of the fuel cycle when there is excess reactivity, neutron moderation may be decreased by replacing a portion of the water within the core with a less effective moderator such as heavy water. During the life of the fuel, the heavy water is gradually replaced with regular water. The fuel assembly incorporates the necessary means and apparatus to effectuate such control.

Abstract: An upwardly convex resilient annular strainer, fixed to the secondary core support base plate in a PWR, bends to remain in contact with the lower hemispherical head section of the pressure vessel as the gap between the internals and the lower hemispherical head section varies in size with reactor temperature to prevent debris from lodging in the gap where it could lead to reactor damage.

Abstract: Failure of the control-rod assemblies, particularly the control-rod guides and the WDRC's, by transverse flow of coolant through these members is prevented by directing the flow through a calandria above the guides. To avoid a high pressure drop in the coolant between the calandria and the outlet nozzles, the outlet nozzles are at the same level as the calandria. The calandria has hollow tubes between upper and lower supports. The length of the portion of the tubes between the supports is greater than the diameter of the outlet nozzles.

Abstract: An improved nuclear reactor wherein the bolted connections between the baffle plates and baffle former and the baffle former and the core barrel are provided with a noval locking device that prevents loosening of the bolted connections. The locking device to prevent loosening of bolted connections where a threaded bolt is used to secure two components together uses a threaded lock nut over the bolt head, cooperative with a threaded wall in a recess in a component. The lock nut and wall of the recess have threads opposite the threads of the bolt. Deformable sections are formed in the base of the lock nut to engage an unsymmetrical cavity in the head of the bolt. Turning of the bolt in a direction that would tend to loosen the connection causes tightening of the lock nut. The wall of the lock nut may be threadedly engaged with the wall of the recess or the lock nut wall may have slits formed thereon which enable deformation of wall portions to engage the threaded wall of the recess.

Abstract: A top end support for rod guides disposed in closely spaced, parallel axial relationship within an inner barrel assembly of a pressurized water reactor vessel includes, in telescoping relationship, a generally cylindrical support having an end closure with a central aperture therein for receiving a downwardly depending extension from a lower calandria plate and a sleeve having an outer periphery corresponding in cross-section to that of said rod guide and affixed thereto at its lower end, the sleeve having an interior, generally cylindrical surface for receiving the cylindrical support in close engagement therein. The telescopingly engaged, generally cylindrical surfaces of the cylindrical support and the sleeve provide substantial area to function as a long-life wear couple.

Abstract: An apparatus and method for under water remote replacement of the screws which secure together first and second structures in the internal region of a nuclear reactor core, wherein the screws are received and counterbored screw bores in the first structure. First, one or more lateral recesses are machined in the side wall of the counterbore portion. Then an external hex head screw with a shoulder flange is inserted in the screw bore and is threadedly engaged with the second structure with the flange seated in the counterbore portion. A locking cup with a central hex opening is fitted over the hex head of the bolt in the counterbore portion. Then a bifurcated die is seated against the first structure with die fingers extending into the cup, and a drive member is driven through the die coaxially with the screw to move the die fingers against the side wall to deform it into the recesses, thereby locking the assembly in place.

Abstract: A nuclear reactor including, in the upper internals, a guide structure capable of effectively accommodating and guiding without binding the large number of neutron-absorber rods included in modern reactors of improved efficiency. The neutron-absorber rods include control rods, gray rods, and water-displacement rods. All rods are suspended in clusters from spiders or vanes. The upper internals of the reactor includes cruciform guides for the control-rod and gray-rod clusters. Each of these guides is composed of a plurality of vertical guide sections of transverse cruciform cross section. Plates extending throughout the cross-section of the reactor are supported between each pair of successive guide sections. The plates are perforated, the perforations in each plate being patterned to pass the water-displacement rod clusters. The plates are oriented so that the patterned perforations are aligned to serve as guides for the water-displacement rod clusters.