Abstract: A method for the manufacture of a three-dimensional object using a refractory matrix material is provided. The method includes the additive manufacture of a green body from a powder-based refractory matrix material followed by densification via chemical vapor infiltration (CVI). The refractory matrix material can be a refractory ceramic (e.g., silicon carbide, zirconium carbide, or graphite) or a refractory metal (e.g., molybdenum or tungsten). In one embodiment, the matrix material is deposited according to a binder-jet printing process to produce a green body having a complex geometry. The CVI process increases its density, provides a hermetic seal, and yields an object with mechanical integrity. The residual binder content dissociates and is removed from the green body prior to the start of the CVI process as temperatures increase in the CVI reactor. The CVI process selective deposits a fully dense coating on all internal and external surfaces of the finished object.

Abstract: A method for manufacturing a nuclear fuel compact is provided. The method includes forming an additive structure, consolidating a fuel matrix around the additive structure, and thermally processing the fuel matrix to form a fuel compact in which the additive structure is encapsulated therein. The additive structure optionally includes a vertical segment and a plurality of arm segments that extend generally radially from the vertical segment for conducting heat outwardly toward an exterior of the fuel compact. In addition to improving heat transfer, the additive structure may function as burnable absorbers, and may provide fission product trapping.

Abstract: A fuel assembly for use in a core of a nuclear power reactor. The assembly includes a plurality of helically twisted fuel elements supported by a frame in a fuel rod bundle. Each of the fuel elements includes fissile material. When viewed in a cross-section that is perpendicular to an axial direction of the fuel assembly, the outermost fuel elements of the fuel rod bundle define a substantially circular perimeter. The fuel elements are arranged in a mixed grid pattern that includes a first, rectangular grid pattern and a second, triangular grid pattern.

Abstract: A fuel assembly for use in a core of a nuclear power reactor. The assembly includes a plurality of helically twisted fuel elements supported by a frame in a fuel rod bundle. Each of the fuel elements includes fissile material. When viewed in a cross-section that is perpendicular to an axial direction of the fuel assembly, the outermost fuel elements of the fuel rod bundle define a substantially circular perimeter. The fuel elements are arranged in a mixed grid pattern that includes a first, rectangular grid pattern and a second, triangular grid pattern.

Abstract: A nuclear fission reactor comprising a core, a pool of coolant liquid, and a heat exchanger. The core comprises an array of hollow tubes which contain molten salts of fissile isotopes. The tube array is at least partly immersed in the pool of coolant liquid. The tube array comprises a critical region, where the density of the fissile isotopes during operation of the reactor is sufficient to cause a self-sustaining fission reaction. Heat transfer from the molten salts of fissile isotopes to the tubes is achieved by any one or more of natural convection of the molten salts, mechanical stirring of the molten salts, and oscillating fuel salt flow within the tubes. The molten salts of fissile isotopes are contained entirely within the tubes during operation of the reactor.

Abstract: The invention pertains to a nuclear fuel rod for a nuclear reactor. The fuel rod has a cladding. The cladding's external surface has a surface texture that includes a rib. The rib coils around the circumference of the cladding. The rib length forms a sequence of continuous rib loops uniformly spaced along an axial length of the cladding. The ratio of rib height to cladding diameter is greater than or equal to 0.0134 and less than or equal to 0.0268. The ratio of rib height to rib width is greater than or equal to 0.8 and less than or equal to 1.2. A pitch measured between adjacent rib loops is greater than or equal to 9× rib height and less than or equal to 12× rib height. The rib enhances fuel rod heat transfer in a region downstream of grid mixing vanes, where turbulence is dissipated.

Abstract: A flow limiter may include a head and a fin extending from a bottom of the head. The head may include a side surface having at least one first hole and the side surface may be symmetric about a first axis. The fin may include at least one second hole and the at least one second hole may have an axis substantially perpendicular to the first axis. The flow limiter may be inserted into a support casting that may interface with a nuclear fuel bundle to reduce the flow of water to the nuclear fuel bundle thereby reducing a moisture carry over (MCO) level at an exit of a fuel bundle of a nuclear reactor.

Abstract: The strip is of the type comprising a wall portion for delimiting a cell with interlaced strips, a spring formed in the strip and provided on the wall portion for biasing a fuel rod extending through the cell away from the wall portion, the spring comprising a cantilevered tab formed in the strip and a contact portion formed at least partially in the tab and protruding from the tab for contacting a fuel rod received in the cell.

Abstract: Fuel elements are supported by fuel assemblies configured for use in land-based nuclear reactors such as the VVER-1000. The fuel elements include a kernel having a multi-lobed profile that forms spiral ribs that include fissionable material (e.g., uranium or plutonium), a central metal displacer extending along a longitudinal axis of the kernel, and a metal cladding (e.g., zirconium and/or other refractory metals) enclosing the kernel. The fuel element may be fabricated by joint extrusion of the displacer, kernel, and cladding through a die to metallurgically bond the kernel and cladding.

Abstract: Example embodiments are directed to tiered tie plates and fuel bundles that use tiered tie plates. Example embodiment tie plates may include upper and lower tiered tie plates. Example embodiment tiered tie plates may have a plurality of bosses divided into groups, or tiers, having differing vertical (axial) displacement. Example embodiment fuel bundles may use tiered tie plates such that fuel rods in example bundles may originate and terminate at different vertical displacements, based upon the vertical displacement of the bosses receiving the fuel rods into the tiered tie plates. Optionally, shanks may be used to further vary fuel rod axial displacement and diameter.

Abstract: A fuel support for a nuclear reactor may include: a plurality of fuel support apertures, each fuel support aperture dimensioned for receiving a lower tie plate of a fuel assembly; and a plurality of lumens, each lumen being coupled to a different fuel support aperture. At least one lumen may be configured for attenuating a fluid flow differently than the fluid flow in at least one other of the lumen.

Abstract: Fuel supports for a nuclear reactor and methods of modifying fluid flow in a reactor using a fuel support. The fuel supports include a plurality of lumens and a plurality of fuel support apertures with each fuel support aperture being dimensioned for receiving a lower tie plate of a fuel assembly. Each lumen is fluidly coupled to a different fuel support aperture. At least one lumen is configured for attenuating a fluid flow differently than the fluid flow in at least one other of the lumen.

Abstract: An fuel assembly with a connection between a fuel channel and a lower tie plate to allow the fuel channel to be removed from an internal fuel rod assembly without the necessity of moving interior fuel rods during removal of the fuel channel.

Abstract: A fuel element for a nuclear reactor has fuel rods with nuclear fuel guided through spacers. The spacers are equipped with devices that exert a swirling impulse upon a coolant flowing along the fuel rods. In order to present as little flow resistance as possible for the coolant, these swirl-introducing devices have the form of a vane with a spoonlike or bladelike shape and they extend into the coolant flow. Owing to the shape—here the vane is curved in the longitudinal and in the transverse directions—practically all cross sections of the vane have such a high geometrical moment of inertia that even a vane made of a thin sheet metal is sufficiently rigid. Fuel elements configured according to the invention are particularly suitable for use in boiling water nuclear reactors.

Abstract: One object of the present invention is to provide a production method for a nuclear fuel assembly support grid that improves the corrosion resistance of welded parts without impairing the characteristics of the support grid so as to be able adequately withstand highly efficient operation. In order to achieve the object, the present invention provide a production method for a nuclear fuel assembly support grid comprising the steps of: assembling a plurality of straps in a grid form; welding intersections of each strap; and carrying out annealing thereafter to precipitate an intermetallic compound on the welded parts.

Abstract: A spacer grid with hybrid flow-mixing devices for nuclear fuel bundle is made up of an intersection of a plurality of thin straps at right angles to form a plurality of cells for receiving and supporting fuel rods. Each strap is composed of two types of strap units, called a primary strap unit and a secondary strap unit, which are alternately arranged along the strap. The primary strap unit is a strap section having a primary vane set, and a secondary strap unit is a strap section having a secondary vane set. The straps intersect such that, by primary and secondary strap units, each intersection forms a hybrid flow-mixing device around the top of each junction. The primary vane set, consisting of a trapezoidal primary vane stand and two bent primary mixing vanes on both sides, protrudes upwardly from the strap and is primarily for generating cross flow between channels.

Abstract: A crud-resistant nuclear fuel element cladding in which the axial locations that experience nucleate boiling during reactor full power operation are highly polished so that the maximum size of any surface defect on the highly polished surface is approximately 0.1 microns. The remainder of the cladding surface remains unpolished so that crud is more evenly redistributed over the entire fuel cladding surface to limit the thickness of the crud that is formed to less than 35 microns.

Abstract: A double strip mixing grid for nuclear reactor fuel assemblies is disclosed. This grid is fabricated by intersecting at right angles a plurality of double strips, each fabricated by welding two thin sheets together into a single structure with coolant channels. The mixing grid, having the channels, effectively mixes low temperature coolant with high temperature coolant within a fuel assembly, thus improving the thermal efficiency of the fuel assemblies. This mixing grid also effectively prevents the coolant from being partially overheated, thus improving the soundness of nuclear reactors. This mixing grid also has swirling flow blades and/or lateral flow blades to further improve the thermal efficiency of the fuel assembly. This mixing grid elastically supports the fuel rods by the sheets of the double strips, collaterally acting as positioning springs.

Abstract: A spacer grid for PWR assemblies is characterized by curved flow channels between adjacent fuel rods and straight, essentially flat strips connecting opposite side plates of the spacer. The latter strips prevent bowing-out of the side plates during fuel assembly fabrication and during operation in the reactor. Additionally, the spacer grid allows accurate positioning of the fuel rods on a square lattice with a precisely defined pitch, and support of the rods in their spacer cells is such that rod bow will be minimized. The direction of the nozzles on the flow channels has been chosen to promote cross-flow of the coolant through the assembly.

Abstract: Flow of mercury from a liquid-heavy-metal inflow port toward an inner forward end of a container body is rectified by a plurality of incoming-passage guide vanes in a liquid-heavy-metal incoming passage. Flow of the mercury from the forward end of the container body toward a liquid-heavy-metal outflow port is rectified by a plurality of return-passage guide vanes in a liquid-heavy-metal return passage. As a result, occurrence of stagnation and/or recirculation flows of the mercury in the container body is suppressed and a steady and highly uniform stream of the mercury is formed throughout in the container body. The container body is covered with a container outer shell to prevent any leakage of the mercury to outside due to a damage of the container body.

Abstract: A Critical Channel Power (CCP) enhancement system is provided for a pressurized fuel-channel-type water-cooled nuclear reactor of the type adapted to be refuelled on-line by the insertion and removal of fuel bundles onto and from of a plurality of said fuel channel assemblies, each of said fuel channel assemblies. A means is provided for interlocking fuel bundles into pairs having their fuel elements aligned, thereby lowering the hydraulic resistance in the fuel channel and enhancing CCP. The means for interlocking prevents misalignment of the paired bundles during their residence time inside the reactor due to continuous rocking and vibration of the fuel bundles exposed to very high coolant mass flow rate and misalignment due to axial separation of bundles impacting upon one another during fuelling operations.

Abstract: The invention concerns a spacer (14) for a nuclear boiling water reactor. The spacer (14) comprises a plurality of cells (16) for holding or allowing elongated elements (12) to pass through the cells. Between the cells (16) there are a plurality of flow channels (18). The spacer comprises at least a plurality of deflecting members (22). The deflecting member comprises a vane (24) which extends in a direction from a cell (16) into the neighbouring flow channel (18). The vane is inclined relative to a vertical plane (26) and is wider in its upper part than in its lower part. The invention also concerns a fuel assembly for a nuclear boiling water reactor, comprising a deflecting member with vane of similar construction.

Abstract: The present invention relates to a fuel assembly for a light-water reactor with a substantially square cross section wherein the fuel assembly comprises a plurality of fuel rods (4). The fuel rods (4) extend between a bottom tie plate (5) and a top tie plate (6) and a coolant is adapted to flow upwards through the fuel assembly. At least one of the top tie plates (6) or the bottom tie plates (5) comprises flow openings (22, 22a, 22b) for the passage of the coolant and side supports (17) for supporting the fuel rods (4) in the lateral direction. The side supports (17) are designed in one and the same sheet-metal piece as the flow openings (22, 22a, 22b) and the side supports (17) are folded substantially 90° in relation to the other structure of the top tie plate (6) or the bottom tie plate (5).

Abstract: The present invention relates to a fuel assembly for a light-water reactor with a substantially square cross section wherein the fuel assembly comprises a plurality of fuel rods (4). The fuel rods (4) extend between a bottom tie plate (5) and a top tie plate (6) and a coolant is adapted to flow upwards through the fuel assembly. At least one of the top tie plates (6) or the bottom tie plates (5) comprises flow openings (22, 22a, 22b) for the passage of the coolant and side supports (17) for supporting the fuel rods (4) in the lateral direction. The side supports (17) are designed in one and the same sheet-metal piece as the flow openings (22, 22a, 22b) and the side supports (17) are folded substantially 90° in relation to the other structure of the top tie plate (6) or the bottom tie plate (5).

Abstract: A fuel assembly for a boiling water reactor comprising at least one rotary cell (13a-13d) which has fuel rods (4) arranged in a number of concentric rings with a substantially circular shape, and a steam conducting channel (17a-17d) arranged in the centre of the concentric rings through which steam flows upwards through the fuel assembly. At least certain of the fuel rods in the rings are arranged such that their upper ends are displaced in relation to their lower ends in the tangential direction such that water and steam are brought to rotate around the steam conducting channel.

Abstract: A fuel assembly for a boiling water reactor comprises a plurality of first full-length fuel rods arranged in an orthogonal lattice, wherein each fuel rod is included in two rows of fuel rods perpendicular to each other, and a number of second fuel rods arranged in parallel with the first fuel rods and having the length considerably smaller than the length of the first fuel rods. The second fuel rods are arranged in the lower part of the fuel assembly in the space which is formed between a number of first fuel rods located adjacent to each other, that is, in a position which does not belong to the orthogonal lattice.

Abstract: A fuel assembly and a spacer for a boiling reactor comprises an elongated fuel channel which is connected to a coolant intended to flow therethrough. In the fuel channel there is arranged a bundle of also elongated fuel rods retained by a plurality of spacers. The spacers have an external spacer frame which is provided all around with a plurality of openings. There is arranged, at the inside of the spacer frame, an edge which is obliquely positioned in relation to the longitudinal direction of the fuel assembly and which extends in an inclined manner in a direction downstream of the spacer and toward the corner of the spacer to deflect coolant to the fuel rods arranged at these corners.

Abstract: A spacer for use with a fuel bundle in a nuclear reactor includes a matrix of ferrules for surrounding individual fuel rods within a bundle; a band surrounding the matrix and defining a peripheral wall of the spacer, the band having an upper edge; and a plurality of laterally spaced flow tabs extending upwardly from the upper edge, each flow tab having a lower substantially vertical portion and an upper inclined portion extending away from the vertical portion. The vertical portion and the inclined portion are formed with centrally located creases which define reverse bends in the upper and lower portions of the tab.

Abstract: A critical power enhancement system is provided for a pressurized fuel channel type nuclear reactor comprising a plurality of fuel bundles contained in a fuel channel and containing a plurality of fuel elements horizontally oriented within the fuel channel. The system comprises at least one appendage strategically located on each of certain fuel elements along its length and projecting outwardly from the surface of the fuel element. The appendages generate turbulence in the coolant flowing at locations along the length of the fuel bundle, where the critical heat flux is most likely to occur. The presence of the appendages suppress the occurrence of the critical heat flux in the fuel bundle thereby increasing the safety limit on the maximum power that can be produced by the reactor.

Abstract: An improved fuel rod is provided having a part-length fuel rod portion that improves performance with respect to typical part-length fuel rods without significant degradation of the benefits that are achieved by using such a system, e.g., improved fuel utilization, stability, and shut down margin. The present invention provides a fuel rod for a light water nuclear reactors that comprises a part-length fuel rod and an extension tube having at least one wall member defining an enclosed flow path therethrough, the extension tube being coupled to a portion of the part-length fuel rod so as to be disposed axially above the part-length fuel rod, and including at least one inlet opening, for allowing fluid that surrounds the rod and initially comprises a two phase mixture of steam and liquid, to enter the enclosed fluid path and at least one outlet opening located above the inlet opening, the extension tube includes means for separating at least some of the steam located in the fluid from the liquid located therein.

Abstract: An improved fuel rod is provided having a part-length fuel rod portion that improves performance with respect to typical part-length fuel rods without significant degradation of the benefits that are achieved by using such a system, e.g., improved fuel utilization, stability, and shut down margin. The present invention provides a fuel rod for a light water nuclear reactors that comprises a part-length fuel rod and an extension tube having at least one wall member defining an enclosed flow path therethrough, the extension tube being coupled to a portion of the part-length fuel rod so as to be disposed axially above the part-length fuel rod, and including at least one inlet opening, for allowing fluid that surrounds the rod and initially comprises a two phase mixture of steam and liquid, to enter the enclosed fluid path and at least one outlet opening located above the inlet opening, the extension tube includes means for separating at least some of the steam located in the fluid from the liquid located therein.

Abstract: A mixing grid for use in a pressurized reactor comprises at least two sets of crossed fixed together at their cross-points, delimiting cells, some for receiving fuel rods and the others for receiving guide tubes, the plates being provided with coolant stirring fins extending the plates downstream and disposed to deflect the coolant transversely to its general flow direction, each plate being provided with abutment means projecting inwardly from each of the faces of the cells for receiving fuel rods, thereby delimiting a passage that is larger than the size of the rods but small enough to prevent a rod contained in the cell coming into contact with the fins. In each wall the abutment means comprise two portions of plate that are cut out and deformed into a scoop-shape, and that are offset relative to each other in the coolant flow direction, with the scoops projecting in opposite directions and tending to cause coolant to pass from one cell to another.

Abstract: A nuclear reactor using gas as a primary coolant and a liquid as a moderator and/or reflector. Gas coolant flows through inlet passages around the outlet plenum to a distributor plate. The gas is directed between fuel element housing thimbles and fuel elements therein, through the fuel elements, and into the reactor outlet plenum. Fins on the thimble housings conduct heat to the gas from a liquid moderator circulating in the core. The use of a liquid moderator enhances safety, allows the fissile material and reactor mass to be reduced and eliminates problems associated with cooling of a solid moderator.

Abstract: A spacing grid is provided for a nuclear fuel assembly comprising two sets of intersecting metal plates having fins and defining fuel element receiving pockets. The plates comprise solely half-fins each associated with a single pocket of the grid, disposed in opposed pairs at the angles of the pockets, the half-fins of one pocket being placed at 90.degree. from the half-fins of adjacent pockets.

Abstract: A soluble burnable absorber rod for a nuclear reactor fuel assembly has a tubular body with a pair of end plugs sealing the opposite ends thereof and defining a chamber within the body. A neutron absorber material in liquid form, preferably boric acid with an enhanced concentration of boron isotope B-10, is contained within the chamber. The tubular body has reinforcing convolutions formed therein for strengthening the body to withstand external pressure acting thereon. Also, one of the end plugs acts as a hydride sink and a hydrogen getter material is disposed adjacent the other end plug.

Abstract: An integral nuclear fuel element assembly utilizes longitudinally finned fuel pins. The continuous or interrupted fins of the fuel pins are brazed to fins of juxtaposed fuel pins or directly to the juxtaposed fuel pins or both. The integrally brazed fuel assembly is designed to satisfy the thermal and hydraulic requirements of a fuel assembly lattice having moderator to fuel atom ratios required to achieve high conversion and breeding ratios.

Abstract: A nuclear fuel assembly of the type having a plurality of nuclear fuel elements disposed in parallel, and forming a plurality of longitudinal flow channels, in a closely packed array is disclosed. Axially spaced longitudinal fins formed integrally on at least some of the fuel elements, at an angle with the fuel element axis, serve to divert coolant flowing longitudinally past the fuel elements between adjacent flow channels to promote mixing and even heating of the coolant. Each fin traverses the clearance between adjacent fuel elements, tangentially contacts the body of an adjacent fuel element, and is fixedly connected thereto. Sets of the axially spaced fins are fixedly connected to adjacent fuel elements, as described, in substantially the same transverse plane relative to the longitudinal axis of the fuel assembly.

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.