Abstract: A BWR fuel assembly has a bundle 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 with a lower flow inlet end, an opposite upper flow outlet end and an open inner cruciform flow channel for subcooled moderator fluid flow through the fuel assembly. The water cross extends through the outer flow channel and is interconnected with the outer channel so as to divide it into separate compartments and the bundle of fuel rods into a plurality of mini-bundles thereof. Also, a pair of upper and lower tie plates are connected to the opposite ends of the fuel rods in each mini-bundle thereof so as to provide a separate fuel rod subassembly in each of the compartments. The tie plates have flow openings defined therethrough for allowing the flow of the coolant/moderator fluid into and from the separate fuel rod subassembly.

Abstract: A quick release guide sleeve assembly comprises an outer sleeve, an inner sleeve axially slidably received in the outer sleeve and having first and second axial positions with respect to the outer sleeve; and a locking mechanism movably mounted on the outer sleeve for frictionally engaging wall surfaces defining an opening for receiving the outer sleeve. The locking mechanism has a locking position in which at least part of the locking mechanism projects radially outwardly beyond the external circumferential surface of the outer sleeve. The locking mechanism further has a releasing position in which the locking mechanism is in a radially inwardly withdrawn state relative to the circumferential surface of the outer sleeve.

Abstract: A device which controls coolant flow through a nuclear reactor assembly comprises a baffle means at the exit end of said assembly having a plurality of orifices, and a bimetallic member in operative relation to the baffle means such that at increased temperatures said bimetallic member deforms to unblock some of said orifices and allow increased coolant flow therethrough.

Abstract: A single guide tube and tube sheet tube, as an upper extension, carries a nuclear control rod in storage, poised for downward insertion into the guide tube. An inner tube, termed a bypass tube, is mounted within the cylindrical tube sheet tube and fitted closely about the control rod. Mounting connections between the upper and lower ends of the bypass tube and the tube sheet tube are provided to route the coolant in control of the rod vibration.

Abstract: A fuel assembly is disclosed which comprises a fuel channel (1) with square cross-section supported by an inlet sleeve (22) having at its lower part an inlet opening for a flow of coolant flowing through the fuel assembly. The inlet sleeve (22) is made of stainless steel and is mechanically connected to a transition sleeve (21) made of thick zirconium alloy sheet, which is welded to the more thin-walled fuel channel (1).

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 spray device adapted to spray cooling water vertically to a reactor core in the event of a coolant accident and located in a space between the reactor core surrounded by a shroud and a shroud head mounted on the shroud. The spray device comprises a duct assembly disposed along an inner periphery of the shroud, a plurality of pipes pivotably connected to the duct assembly so as to be movable between horizontal and vertical positions, and nozzles provided for the respective pipes for downwardly ejecting the cooling water to the reactor core.

Abstract: A flow exchange element is presented which lowers temperature gradients in fuel elements and reduces maximum local temperature within high temperature gas-cooled reactors. The flow exchange element is inserted within a column of fuel elements where it serves to redirect coolant flow. Coolant which has been flowing in a hotter region of the column is redirected to a cooler region, and coolant which has been flowing in the cooler region of the column is redirected to the hotter region. The safety, efficiency, and longevity of the high temperature gas-cooled reactor is thereby enhanced.

Abstract: A fuel assembly for a boiling water reactor is provided with at least one vertical water channel (4, 5) for a by-pass flow through the fuel assembly. At its lower end the channel is connected to a radial tube (10) which opens out at the outer side surface of the fuel assembly. Below the radial tube, the wall of the assembly base (2) is provided with a through-hole (12).

Abstract: A device for regulating the flow of a fluid comprising a series of gratings positioned perpendicularly to the fluid flow, wherein it is formed by a stack of identical, contiguous gratings, whereof each is constituted by identical meshes forming a flat system, said meshes being staggered from one grating to the following contiguous grating, and wherein the mesh is formed by two adjacent equilateral triangles, one corresponding to an orifice and the other containing a crosspiece with three branches.The invention also relates to a nuclear reactor fuel assembly incorporating such a device.

Abstract: A nuclear radiation actuated valve for a nuclear reactor. The valve has a valve first part (such as a valve rod with piston) and a valve second part (such as a valve tube surrounding the valve rod, with the valve tube having side slots surrounding the piston). Both valve parts have known nuclear radiation swelling characteristics. The valve's first part is positioned to receive nuclear radiation from the nuclear reactor's fuel region. The valve's second part is positioned so that its nuclear radiation induced swelling is different from that of the valve's first part. The valve's second part also is positioned so that the valve's first and second parts create a valve orifice which changes in size due to the different nuclear radiation caused swelling of the valve's first part compared to the valve's second part. The valve may be used in a nuclear reactor's core coolant system.

Abstract: A liquid metal cooled nuclear reactor of the kind wherein a fuel assembly is supported on a diagrid and submerged in a pool of coolant. The diagrid comprises a plenum supported on a load bearing undershell and has an array of resilient spikes upstanding from the upper face of the plenum each for locating a fuel sub-assembly. The load of the fuel assembly is distributed over the upper face plate of the plenum and transmitted to the undershell by an array of strut members.

Abstract: A self-actuated device, of particular use as a valve or an orifice for nuclear reactor fuel and blanket assemblies, in which a gas produced by a neutron induced nuclear reaction gradually accumulates as a function of neutron fluence. The gas pressure increase occasioned by such accumulation of gas is used to actuate the device.

Abstract: A composite nozzle for a fuel assembly adapted for installation on the upper or lower end thereof and which is constructed from two components. The first component includes a casting weldment or forging designed to carry handling loads, support fuel assembly weight and flow loads, and interface with structural members of both the fuel assembly and reactor internal structures. The second component of the nozzle consists of a thin stamped bore machine flow plate adapted for attachment to the casting body. The plate is designed to prevent fuel rods from being ejected from the core and provide orifices for coolant flow to a predetermined value and pressure drop which is consistent with the flow at other locations in the core.

Abstract: A device which mitigates against the effects of a failed coolant loop in a nuclear reactor by restricting the outflow of coolant from the reactor through the failed loop and by retaining any particulated debris from a molten core which may result from coolant loss or other cause. The device reduces the reverse pressure drop through the failed loop by limiting the access of coolant in the reactor to the inlet of the failed loop. The device also spreads any particulated core debris over a large area to promote cooling.

Abstract: The fuel assembly is supported by means of a cylindrical supporting member which is introduced into a shore of the cross-member. The foot of the fuel assembly is introduced into the upper part of the cross-member. Orifices, coinciding with those made with the shore permit the introduction of the liquid metal into the supporting member and from there into the actual assembly. The supporting member is closed at its lower end.Application to the construction of the core of a fast neutron nuclear cooled with liquid sodium.

Abstract: A reusable system for removably attaching the lower end 21 of a nuclear reactor fuel assembly duct tube to an upper end 11 of a nuclear reactor fuel assembly inlet nozzle. The duct tube's lower end 21 has sides terminating in locking tabs 22 which end in inwardly-extending flanges 23. The flanges 23 engage recesses 13 in the top section 12 of the inlet nozzle's upper end 11. A retaining collar 30 slides over the inlet nozzle's upper end 11 to restrain the flanges 23 in the recesses 13. A locking nut 40 has an inside threaded portion 41 which engages an outside threaded portion 15 of the inlet nozzle's upper end 11 to secure the retaining collar 30 against protrusions 24 on the duct tube's sides.

Abstract: A nuclear reactor including an inner core containing both fuel and blanket assemblies and means for cooling the assemblies by passing liquid coolant, specifically sodium, across and in contact with the latter is disclosed herein. The nuclear reactor also includes a particular technique for distributing the liquid coolant into first and second separate plenums, each of which includes an inlet adapted to receive the coolant. These first and second plenums are maintained in fluid communication with the fuel and blanket assemblies, respectively, whereby to pass received coolant across and in contact with all of the assemblies. In addition, the distribution of the coolant is automatically changed, at least to a limited extent, between these first and second plenum in response to predetermined thermal changes in said assemblies.

Abstract: A perforated depressor plate extending across the bottom of the instrument ree of a fast breeder reactor cooperates with a circular cylindrical metal bellows forming a part of the upper adapter of each core assembly and bearing on the bottom of the depressor plate to restrict flow of coolant between core assemblies, thereby reducing significantly the pressure differential between the coolant inside the core assemblies and the coolant outside of the core assemblies. Openings in the depressor plate are slightly smaller than the top of the upper adapter so the depressor plate will serve as a backup mechanical holddown for the core. In addition coolant mixing devices and locating devices are provided attached to the depressor plate.

Abstract: A self-actuating, self-locking flow cutoff valve particularly suited for use in a nuclear reactor of the type which utilizes a plurality of fluid support neutron absorber elements to provide for the safe shutdown of the reactor. The valve comprises a substantially vertical elongated housing and an aperture plate located in the housing for the flow of fluid therethrough, a substantially vertical elongated nozzle member located in the housing and affixed to the housing with an opening in the bottom for receiving fluid and apertures adjacent a top end for discharging fluid. The nozzle further includes two sealing means, one located above and the other below the apertures.

Abstract: A nuclear reactor core assembly is described in which a plurality of fuel elements and a plurality of blanket elements are arranged in a core assembly. Conduit means direct fluid coolant through the fuel elements and through the blanket elements. The conduit means which direct the coolant through the blanket elements have flow restrictor means therein comprising a plurality of surface roughened elements for limiting the flow of coolant through the blanket elements. The flow restrictor means have a static configuration such that at shutdown, the percentage of coolant flow through the blanket elements compared with the total coolant flow is substantially greater than the percentage of coolant flow through the blanket elements during full power operation.

Abstract: Device for holding jacketed fuel assemblies of a gas-cooled nuclear reactor in a grid plate disposed beneath a reactor core and formed with cylindrical bores for receiving therein a respective fuel-assembly foot which serves simultaneously as a coolant inlet, including a tubular grid-plate insert member connected respectively to each of the bores for hydraulically holding down the respective fuel assemblies against flow pressure of the coolant, the insert member being closed at the bottom thereof and having at least one lateral opening for passage of coolant to the respective fuel-assembly foot, piston rings peripherally disposed on the fuel-assembly foot above and below the lateral opening for sealing the foot with respect to the inner surface of the insert member, a plurality of wedge-like structural members uniformly distributed about the periphery of the fuel-assembly foot above the lower of the piston rings, and a piston central to the foot and actuatable by a pressure difference of the coolant between a

Abstract: A liquid metal-cooled nuclear reactor has a reactor vessel with a cover at the top thereof and is partly filled with liquid metal up to a given surface level, the liquid metal surface and the reactor-vessel cover defining therebetween a gas-filled space, at least one quasi-tight convection barrier being disposed in the space and subdividing it in elevation.