Abstract: The filtration plate (10), arranged in the lower part of the fuel assembly and ensuring the retention of particles contained in the cooling fluid of the reactor, has at least one active zone where it is pierced with holes (12) of a size determined according to the size of the particles to be retained. The active zones of the filtration plate come into alignment with a water-passage hole through the lower core plate of the reactor when the assembly is in operation. The water-passage orifices of the filtration plate (10) can consist of cutouts of square or triangular form or of stamped parts of the plate or be delimited by parallel lamellae constituting a grating.

Abstract: An improved lower end fitting (L.E.F.) having a bell mouth type of flow jet diffuser decrease pressure drop 10-15%, more evenly distributes flow and adds strength. It includes neutron thimble flux impingement shield of instrument and/or cable. Diffusers are stainless steel of circular cross-sect. and parabolic to optimize diffusion. Shape is based on lower core plate flow hole geometry, L.E.F. design and reactor flow rate. Thinner L.E.F. legs, smaller L.E.F. gussets and thinner L.E.F. flow plates possible.

Abstract: The connector comprises an adaptor plate (6), supporting feet (7) and a flat element (10) constituting a filter for the retention of particles contained in the cooling fluid of the nuclear reactor. The flat element (10) is fastened to the lower part of the supporting feet (7) of the assembly, in order, during operation, to come to rest on the lower core plate (1) of the reactor. At least one zone of the flat element (10) constitutes a filtration grating located opposite a cooling-water passage (2) through the lower core plate (1).

Abstract: The invention relates to a nuclear reactor with improved efficiency.The nuclear reactor comprises a massive partition (18) of material reflecting high energy neutrons at the circumference of the core (7) of the reactor, two layers (19 and 20) of material absorbing low energy neutrons and containing fertile material arranged one at the lower part and one at the upper part of the core (7) and an assembly of neutron energy spectrum variation rods (27). The rods (27) are associated with mechanisms permitting them to be either fully inserted into the core (7), or fully extracted. These rods (27) consist of a material absorbing low energy neutrons and permit a shift of the neutron spectrum towards the high energies.The invention is particularly applicable to pressurized water nuclear reactors.

Abstract: A fuel assembly for a light-water nuclear reactor contains a plurality of vertical fuel rods which are arranged, mutually spaced from each other in the lateral direction, between a bottom tie plate and a top tie plate. The bottom tie plate is provided with through-holes for conducting water through the bottom tie plate and into the spaces between the fuel rods. The through-holes in the bottom tie plate have parts, the centre lines of which are displaced in relation to each other or make an angle with each other.

Abstract: A nuclear fuel assembly with a debris filter. The lower end fitting of the fuel assembly has a stamped plate attached thereto that serves as a debris filter immediately upstream of the fuel rods. The stamped plate is provided with a plurality of flow holes in a size and pattern that provides filtration of debris damaging to the fuel rods while maintaining adequate coolant flow through the fuel assembly.

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: Pressurized water reactor fuel bundles (10) have a cast lower end fitting (20) which provides reduced pressure drop because nozzles (24) are of polygonal (rectangular or square) cross-section and the flow entrance wall portion (32) is a parabolic shape which merges into a wall portion (30) parallel to the flow direction. The parabolic shape of portion (32) and fillets (24a) at the nozzle (24) corners also give an improved draft to the casting. Pressure drop reduction was substantially greater than standard calculations indicated would be obtained.

Abstract: An apparatus for controlling the flow of coolant through a nuclear fuel assembly, in which a coolant flow restrictor 26 having longitudinal ducts 30 is provided with plug members 48, 49, 50 of different lengths. The plug members 48, 49, 50 are moved longitudinally by the effect of neutron induced growth on an actuating member 60. A connecting member 53 converts the growth of the actuating member 60 into a longitudinal movement of the plug members 48, 49, 50 so that they are progressively withdrawn from the flow restrictor 26 to increase the flow of coolant through the flow restrictor 26.

Abstract: A boiling water nuclear fission reactor is disclosed with a unique steam-water separating system. The steam-water separation means comprises an assemblage of open troughs positioned above the fuel core which reduces the amount of steam recycled through the coolant circuit.

Abstract: A nuclear fuel assembly with a debris filter. The lower end fitting of the fuel assembly has a stamped plate attached thereto that serves as a debris filter immediately upstream of the fuel rods. The stamped plate is provided with a plurality of flow holes in a size and pattern that provides filtration of debris damaging to the fuel rods while maintaining adequate coolant flow through the fuel assembly.

Abstract: A debris screen for a fuel assembly for a reactor to which coolant fluid is supplied comprises a substantially planar plate member having an array of coollant openings extending through the plate member dimensioned to trap at least a portion of debris particles carried by the coolant; and a skirt member enclosing the periphery of the plate member; each of the coolant flow openings having a coolant entry region at a lower surface, a coolant exit region at an upper surface and a coolant flow path extending between the entry and exit regions, the flow path including an intermediate segment laterally offset from the entry and exit regions to cause coolant to change direction of flow in the intermediate segment and thereby prevent at least a portion of the debris particles from passing through the plate members.

Abstract: A debris filter bottom nozzle of a nuclear fuel assembly is spaced below the lowermost grid, supports the guide thimbles, and is adapted to allow flow of liquid coolant into the fuel assembly. The debris filter bottom nozzle includes an enclosure defining a coolant flow chamber therethrough, and an upper transverse nozzle structure composed of a consolidated array of elongated cylindrical sections disposed across the chamber of the enclosure in side-by-side relation to one another, extending axially in the direction of coolant flow through the chamber, rigidly connected together and to the enclosure, and having tubular cross-sectional configurations defining passages for the coolant flow through the chamber.

Abstract: A fuel assembly has a spring detent spacer grid of intersecting strips for capturing and retaining deleterious debris carried by reactor coolant before it enters the active region of a fuel assembly. A plurality of fuel end caps are peripherally grooved to receive springs projecting from the strips. The end caps are thus captured by springs and debris is wedged and trapped on opposite sides of the strip and against the end caps by pairs of adjacent integral leaves projecting from the stips intermediate and substantially symmetrically arranged about their intersections.

Abstract: A bottom nozzle plate for a fuel assembly in a nuclear reactor. The bottom nozzle plate is formed from a rigid substantially square plate having legs adapted to be positioned on the lower core plate of the reactor for supporting the fuel assembly above coolant inlet openings in the core plate. The rigid square plate has two types of coolant flow holes therethrough. The first flow holes are grouped in clusters of four to define a square pattern relative to the sides of the plate such that the width of the sections of the plate between the flow holes in each cluster is less than the width of the sections of the plate between the clusters of four holes. Each of the second flow holes is formed in an irregular pattern to define a substantially clover leaf shape. The second flow holes are positioned so as to be above the coolant inlet openings in the core plate when the bottom nozzle plate is installed in the reactor.

Abstract: A wear-reduction-sleeve for in-core-instrumentation thimbles of a pressurized water nuclear reactor having bottom mounted instrumentation to curtail flow induced excitation and increase support contact area in the region of thimble length which extends through and defines an annulus with the core support plate and extends upwardly to and through the fuel assembly flow distribution plates. The wear-reduction-sleeve includes a hollow shank portion which gives a low wear coefficient when in contact with the chrome-plated thimble and is inserted into the annulus and below where it is radially expanded and secured to a thimble guide tube. An upper portion of the wear-reduction-sleeve between the core support plate and flow distribution plate has a flow collection chamber and radial flow exit slots which divert thimble flow substantially away from the hole in the fuel assembly flow distribution plate through which the thimble extends.

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: A pressurized water nuclear reactor system includes a vortex mitigator in the form of a cylindrical conduit between the hot leg conduit and a first section of residual heat removal conduit, which conduit leads to a pump and a second section of residual heat removal conduit leading back to the reactor pressure vessel. The cylindrical conduit is of such a size that where the hot leg has an inner diameter D.sub.1, the first section has an inner diameter D.sub.2, and the cylindrical conduit or step nozzle has a length L and an inner diameter of D.sub.3 ; D.sub.3 /D.sub.1 is at least 0.55, D.sub.2 is at least 1.9, and L/D.sub.3 is at least 1.44, whereby cavitation of the pump by a vortex formed in the hot leg is prevented.

Abstract: The apparatus comprises a body (13) housed in the bore (2, 5) of the assembly head (1) and a flow rate constrictor (12) housed in the sodium passage channel (4) in the assembly head (1). The body (13) comprises axial locking fingers (30) in the assembly head, which can be maneuvered by a slide block (20) actuated by an assembly manipulating device (9). The flow rate of coolant liquid circulating in the assembly may be easily adapted to the operating conditions of the assembly.

Abstract: To provide intrinsic reactor safety, the fuel sub-assemblies of a nuclear reactor core are provided with reactivity control mechanisms operable, in response to temperature rises above desired limits, to interact with adjacent fuel sub-assemblies and effect radial dilation of the core in order to reduce reactivity. Various embodiments are disclosed in which differential thermal expansion of an operating device or devices (34; 40; 42, 44, 46; 50) is translated into radially outward displacement of a lever or levers (28) for contact with neighbouring sub-assemblies.

Abstract: A fuel assembly (10) has a lower end fitting debris collector and end cap spacer grid (20) assembled in the form of a welded assembly of an "eggcrate" grid (21) and cast base (40) with hollow legs (42). Fastener seats (46) in hollow legs (42 ) permit guide tubes (14) with internally threaded ends to be joined to the upper surface of the lower end fitting debris collector (20) by means of slotted fasteners (50). End caps (22) rest on grid (21) at the intersection of slottedly interlocked bars (24 and 26). Thin strips (30) mounted in slots between bars (24) and bars (26) provide small debris catching openings in grid (21). Thick strips (30a) project upwardly between strips (30) to limit lateral movement of the end caps. Projections (70) on bars (24) prevent axial fuel rod movement by engagement of tab (70a) in circumferential groove (23) of end caps (22). Opposing capture force is provided by a wire (72) which is supported in openings in thick strips (30a) and which is received in groove (23).

Abstract: A debris filter bottom nozzle in a fuel assembly has support structure in the form of four legs adapted to rest on a lower core plate of the nuclear reactor and a nozzle plate fixed one side of the four legs facing toward a lowermost grid of the fuel assembly. The nozzle plate has defined therethrough only a plurality of flow holes individually smaller in size than the maximum dimension of unoccupied spaces through the lowermost grid which allow flow of liquid coolant through the nozzle plate. Therefore, any debris being carried by the liquid coolant flowing through the bottom nozzle from the lower core plate to the fuel assembly which is small enough in size to pass through the flow holes will also pass through the unoccupied grid spaces, whereas any debris which is large enough to not pass through the unoccupied grid spaces and collect in the grid will not pass through the aperture plate flow holes.

Abstract: In a pressurized water nuclear reactor, the neutron flux is measured by introducing a probe into a glove finger tube, whose end is normally located in the reactor core. Each glove finger tube passes into a vertical instrumentation column, which is terminated by a nozzle (124) below one of the core assemblies. A clearance is provided around the glove finger tube in order to permit the outflow of cooling water from the core. To prevent vibration of the tubes level with nozzles (124), the latter are traversed by a passage (124a) having a constant diameter over most of its length and up to an upper planar face (124b).

Abstract: A nuclear reactor includes a reactor vessel, a reactor core disposed within the vessel and including fuel rods, a primary cooling system disposed in the vessel and including a steam generator and a pump and a poison tank disposed within the vessel and containing high concentration boric acid solution. The poison tank surrounds the reactor core, and the steam generator surrounds a portion of the poison tank.

Abstract: A wear-reduction-shield (40) for use between the core plate (24) and lower end fitting (26) of a pressurized water reactor (10) to reduce excessive wear of in-core-instrumentation thimbles (30) due to flow induced vibrations and resist fuel assembly tipping has a cylindrical body portion 42with core plate engaging lower end surface (44). At the opposite and upper end, a tapered internal end wall (46) assists upward threading of the monitor and cable. On the outside of the upper end symmetrical leg portions (52) and central land (54) surround a thimble (30) receiving opening (48). Smoothly tapering outer surface (56) minimizes turbulence in and beyond opening (34) in lower end fitting (26). Internal dimensions of shield (40) avoid structure such as sleeve (50) which may be present.

Abstract: A restraint to enable temporary bracing and operation of a thermally cracked sparger nozzle mounted from a sparger manifold at the end of a pipe elbow is disclosed. The restraint includes a second and surrounding restraint elbow which is fitted over and captures the sparger elbow. The restraint elbow has a saddle surface baseplate communicated to the lower end which rest on the sparger manifold to form a substantially water tight base for the restraint. The nozzle end of the restraint elbow is fitted with a nozzle aperture plate for surrounding the outside of the sparger nozzle again in substantially water tight relation. The plate is mounted for movement on the end of the restraint elbow for conforming threading of the restraint at the plate over the sparger nozzle. The restraint can be rapidly mounted (in less than a minute), tack welded at the aperture and seat tensioning bold (in less than 4 minutes) and left in the reactor for a complete fuel cycle.

Abstract: The core is constituted by detachable assemblies (21) disposed vertically and maintained in position by a support or bolster (22) receiving the lower part or foot (21a) of the assemblies (21) inside sleeves having a vertical axis (25). Each of the sleeves (25) includes at least one orientation configuration (31) for the assembly (21) and each of the assemblies (21) includes on its foot (21a) at least one orientation configuration (30) adapted to cooperate with the orientation configuration (31) of the sleeve (25). The charging of the first core of the reactor may be carried out in a simple operation without a prior charging of false assemblies in an air atmosphere.

Abstract: A fuel assembly (10) has a lower end fitting debris collector (40) assembled in the form of a welded assembly of an "eggcrate" grid (21) and cast base (40) with hollow legs (42). Fastener seats (46) in hollow legs (42) permit guide tubes (14) with internally threaded ends to be joined to the upper surface of the lower end fitting debris collector (40) by means of slotted fasteners (50). Bevels (62) and notches (64) in the grid bars (26 and 24a, respectively), provide an embodiment with contoured seats for fuel rod end caps (22). Otherwise, end caps (22) rest on grid (21) at the intersection of slottedly interlocked bars (24 and 26). Thin strips (30) mounted in slots between bars (24) and bars (26) provide small debris catching openings in grid (21).

Abstract: A debris resistant bottom nozzle in a fuel assembly has a support structure in the form of four legs adapted to rest on a lower core plate of a nuclear reactor and a top flat plate fixed on one side of the four legs facing upwardly toward a lowermost grid of the fuel assembly. The flat plate is of a substantially solid configuration with a plurality of spaced cut-out regions defined therethrough in alignment with and directly above a plurality of inlet liquid coolant flow holes in the lower core plate. A plurality of open separate criss-cross structures are provided, each being fixed to the plate and extending across one of the cut-out regions therein within the plane of the plate.

Abstract: A fuel assembly for a boiling water reactor is provided with at least one vertical channel for a by-pass flow through the fuel assembly. The channel is supplied with water through a vertical supply tube surrounded by the base of the assembly, the supply tube being arranged with its lower end in the vicinity of the lower end of the base.

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 debris catching strainer grid for capturing and retaining deleterious debris carried by reactor coolant before it enters the active region of a fuel assembly and creates fuel rod cladding damage has a plurality of fuel end cap compartments defined by pairs of first and second intersecting and slottedly interlocked grid-forming strips attached to a perimeter member and to each other. The end cap compartments defined by strips including vertical rows of integral leaves on opposite sides of the strip or by pairs of adjacent integral leaves intermediate their intersections. In the latter case, each leaf of the pair of leaves is the mirror image of the other leaf of the pair with an asymmetric shape with the greatest distance of projection out of the plane of the strip remote from the midpoint of the strips between their intersections.

Abstract: In a boiling water reactor (BWR) of the D-lattice type an improved apparatus and method for the mounting of a nuclear fuel assembly is disclosed. Specifically, a D-lattice nuclear fuel assembly is diagonally displaced at the top and diagonally displaced at the bottom to and toward the cruciform shaped control rod interstices. Displacement at the bottom end of the nuclear fuel assembly occurs by an eccentrically centered lower tie plate and fluid inlet for fitting to the core plate at the bottom end of the assembly. Displacement at the top end of the nuclear fuel assembly occurs by shims in the vicinity of the upper end of the channel at the top guides. The disclosed channel assembly is capable of installation during refueling cycles, with a displaced channel being substituted for prior art conventional D-lattice channels. Substitution of one displaced channel occurs with each refueling cycle in a group of four channels.

Abstract: A spacer sleeve is installed within an instrumentation tube of a nuclear fuel assembly comprising two end nozzles connected by tie rods and a plurality of fuel rod supporting grids distributed at axial intervals along the tie rods. The instrumentation tube has a first end received in an initially blind bore formed in one of the end nozzles and communicating with the outside by a coolant restriction.

Abstract: A nuclear reactor has a pressure vessel containing a core supported by the bed-plate. The bed-plate is arranged for admitting an upward flow of coolant into the core. The coolant, generally pressurized water, collects in an outlet plenum. The core comprises fuel assemblies each having a lower end piece. The bed-plate defines an inner volume containing coolant at a pressure lower than the coolant pressure under said bed-plate; the lower end piece of each of said fuel assemblies has a lower extension having a cross-sectional area smaller than the cross-sectional area of the fuel assembly above the bed-plate, cooperating with said bed-plate to define a passage for said flow of coolant into said core; and said extension is surrounded by an annular chamber communicating with said volume and defined by a downwardly facing external surface of said lower end piece.

Abstract: A BWR fuel assembly having an array of spaced fuel rods, an outer tubular flow channel surrounding the fuel rods so as to direct flow of coolant/moderator fluid along the fuel rods, and a hollow central water cross extending through the channel and composed of radially extending members dividing the fuel rods into separate fuel rod mini-bundle subassemblies, includes features which eliminate or at least minimize degradation of CHF performance and the penalties and uncertainties associated therewith. Each subassembly has spacers which surround its fuel rods and maintain them in side-by-side spaced relationship. The spacers are axially displaced apart between the bottom and top of the subassembly.

Abstract: In the fast breeder reactor according to this invention, a medium-pressure plenum and a high-pressure plenum are disposed, in the mentioned order from above in a reactor core. Sodium is filled in the medium- and high-pressure plenums. The pressure in the medium-pressure plenum is lower than that in the high-pressure plenum. The lower ends of the entrance nozzles of a multiplicity of fuel assemblies loaded in the reactor core are supported by a supporting plate which forms a boundary between the medium- and high-pressure plenums. The entrance nozzles of control rod guide pipes disposed among the multiplicity of fuel assemblies are also supported by said supporting plate. The sodium in the medium-pressure plenum is supplied into each control rod guide pipe through a first opening provided in the lateral surface of the entrance nozzle of each control rod guide pipe.

Abstract: A BWR fuel assembly includes a bundle of elongated fuel rods disposed in side-by-side relationship so as to form an array of spaced fuel rods, an outer tubular flow channel surrounding the fuel rods so as to direct flow of coolant-moderator fluid along the fuel rods, and bottom and top nozzles mounted at opposite ends of the flow channel and having an inlet and outlet respectively for allowing entry and exit of coolant fluid into and from the flow channel and along the fuel rods contained therein. The BWR fuel assembly includes an improvement in the form of a coolant flow direction control device mounted in the bottom nozzle of the fuel assembly and being operable to open the inlet thereof to flow of coolant fluid in an inflow direction into the flow channel through the bottom nozzle inlet but close the inlet to flow of coolant fluid from the channel through the bottom nozzle inlet upon reversal of coolant liquid flow from the inflow direction.

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: A self-actuated shutdown system incorporated into a reactivity control assembly in a nuclear reactor includes pumping means for creating an auxiliary downward flow of a portion of the heated coolant exiting from the fuel assemblies disposed adjacent to the control assembly. The shutdown system includes a hollow tubular member which extends through the outlet of the control assembly top nozzle so as to define an outer annular flow channel through the top nozzle outlet separate from an inner flow channel for primary coolant flow through the control assembly. Also, a latching mechanism is disposed in an inner duct of the control assembly and is operable for holding absorber bundles in a raised position in the control assembly and for releasing them to drop them into the core of the reactor for shutdown purposes.

Abstract: A debris trap is mounted within a bottom nozzle of a fuel assembly so as to capture and retain debris carried by coolant flowing from the lower core plate openings of the nuclear reactor to the fuel assembly. The trap includes a structure disposed below the adapter plate of the bottom nozzle and between the corner legs of the nozzle. The structure is composed of a plurality of straps aligned with one another in a crisscross arrangement and defining a plurality of interconnected wall portions which form a multiplicity of small cells each having open opposite ends and a central channel for coolant flow through the trap. A plurality of spring-like fingers are punched out of the wall portions and bent to extend into the cell channels toward the downstream end of the trap structure to provide means to capture and retain pieces of debris carried through the channels by flowing coolant.

Abstract: An improved bottom nozzle of a fuel assembly includes a housing and a modified adapter plate formed by a network of ligaments which extend across the housing and are connected to the side walls of the housing a short distance below its upper peripheral edge so as to define an open region therein. The improved bottom nozzle also includes a debris trap having a structure disposed within the open region of the housing upon the adapter plate and adapted to capture and retain debris carried by collant flowing from openings in the lower core plate of the nuclear reactor to the fuel assembly. The trap structure is composed of a plurality of straps aligned with one another in a crisscross arrangement and defining a plurality of interconnected wall portions which form a multiplicity of small cells each having open opposite ends and a central channel for collant flow through the trap.

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.

Abstract: A BWR fuel assembly having an array of spaced fuel rods, an outer tubular flow channel surrounding the fuel rods so as to direct flow of coolant/moderator fluid along the fuel rods, and a hollow central water cross extending through the outer flow channel and composed of respective pairs of spaced apart sheet members interconnected together at their outer and inner ends so as to define an open inner cruciform flow channel for subcooled moderator fluid flow through the fuel assembly and to the outer channel so as to divide the array of fuel rods into a plurality of fuel rod subassemblies, includes features which improve structural and hydraulic characteristics as well as CHF characteristics. The features which improve structural and hydraulic characteristics relates to closures in the form of perforated plates connected across the bottom and top ends of the sheet members of the water cross.

Abstract: A guide tube flow restrictor for use on an upper guide tube housing support plate of a nuclear reactor, for guiding of a control rod drive shaft through an aperture in the support plate and restriction of flow of coolant therethrough, has an outer ring seatable on the support plate, the outer ring having a flange member from which there depends a plurality of flexible members, the flexible members having inwardly disposed deflectors thereon, and extending through the bore of the outer ring and the aperture of the support plate. An axially insertable sleeve, upon insertion into the outer ring, between the flexible members, contacts the deflectors thereon to radially force the flexible members outwardly to secure the same with the walls of the aperture of the support plate. Baffles are provided on the flexible segments and additional locking members provided between the outer ring and inner sleeve.

Abstract: A debris trap is mounted within a bottom nozzle of a fuel assembly so as to capture and retain debris carried by coolant flowing from the lower core plate openings of the nuclear reactor to the fuel assembly. The trap includes a hollow enclosure disposed below the adapter plate of the bottom nozzle and between the corner legs of the nozzle. The enclosure is composed of upper and lower walls and a continuous side wall which spaces apart the upper and lower walls and interconnects their peripheries so as to form a debris capturing and retaining chamber within the hollow enclosure. The walls are composed of a material, such as wire mesh screen, which is permeable to liquid coolant but impermeable to debris. A plurality of wall sections severed from the lower wall and bent into the chamber of the enclosure define a plurality of openings into the chamber.

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: An improved nuclear fuel assembly includes a plurality of elongated water tubes arranged in a cross-like pattern spaced among a plurality of fuel rods for providing individual, spaced-apart coolant-moderator water flow paths lengthwise through the assembly. Some of the water tubes also function as tie rods interconnecting upper and lower tie plates of the fuel assembly.

Abstract: A trap for catching debris carried by coolant flowing from the bottom nozzle of a fuel assembly to the bottom or lowermost one of the grids of the assembly which support the fuel rods in an organized array therein includes a structure disposed between the bottom nozzle and the bottom grid and generally aligned with the lower end plugs of the fuel rods. The structure forms a multiplicity of hollow cells each being open at opposite ends and defining a central cavity which receives one of the fuel rod lower end plugs while providing for passage of coolant flow therethrough from the bottom nozzle to the bottom grid. Also, the trap includes means in the form of dimples defined in each of the cells for catching debris carried into the cells by the coolant flowing therethrough. The dimples are formed from the wall portions defining the cells and extend into the cavities of the cells.