Abstract: This disclosure describes various configurations and components of a molten fuel fast or thermal nuclear reactor for managing the operating temperature in the reactor core. The disclosure includes various configurations of direct reactor auxiliary cooling system (DRACS) heat exchangers and primary heat exchangers as well as descriptions of improved flow paths for nuclear fuel, primary coolant and DRACS coolant through the reactor components.

Abstract: An industrial process transmitter includes a housing, sensor circuitry, transmitter circuitry, and a radiation shield. The sensor circuitry is contained in the housing, and is configured to sense a process parameter and generate a sensor output that is indicative of the sensed process parameter. The transmitter circuitry is contained in the housing, and is configured to communicate the sensed process parameter to an external unit. The radiation shield substantially surrounds a portion of the housing containing the sensor circuitry and shields the sensor circuitry from gamma radiation.

Abstract: A suspended basket includes a plurality of plates, tie rods, and adjustable length threaded tie rod couplings connecting threaded ends of the tie rods with threaded features of the plates. Control rod drive mechanisms (CRDMs) with CRDM motors are mounted in the suspended basket, which is suspended in a pressure vessel above a nuclear reactor core to control insertion of control rods into the reactor core. In one embodiment each adjustable length threaded tie rod coupling is a turnbuckle coupling that includes a sleeve threaded onto the threaded end of the tie rod and onto the threaded feature of the plate, and the sleeve is rotatable to adjust the position of the tie rod respective to the plate. Guide frames may be mounted in the suspended basket between the CRDMs and the nuclear reactor core to guide portions of the control rods withdrawn from the nuclear reactor core.

Abstract: A pressure vessel comprises an upper vessel section and a lower vessel section. A nuclear reactor core comprises fissile material contained in a containing structure and disposed in the lower vessel section. Upper internals are disposed in the lower vessel section above the nuclear reactor core. The upper internals include at least guide frames and internal control rod drive mechanisms (CRDMs) with CRDM motors mounted on a suspended support assembly including a plurality of hanger plates connected by tie rods. The plurality of hanger plates includes a lowermost hanger plate having alignment features configured to align the upper internals with the containing structure that contains the nuclear reactor core.

Abstract: Nuclear fuel assemblies include at least one fluence control structure for use in a nuclear reactor core with other nuclear fuel assemblies. Such flux-limiting assemblies and structures may be positioned outside of or around the other nuclear fuel assemblies in the core so as to reduce neutron flux beyond the fluence controlled nuclear fuel assemblies, and fluence control structures may be positioned at an outside edge of the core. Fluence control structures limit neutron flux with non-fuel materials in structures like fuel rods and inserts, channels, shield curtains, etc. at particular positions in fuel assemblies. An engineer may select and/or install fluence-limiting fuel assemblies with flux-limiting characteristics in cores having neutronics profiles expected to benefit from such flux limitation.

Abstract: In a nuclear installation, an instrument includes a sensor module connected to a process flange. The sensor module includes a support conduit with support conduit threads. An electronic circuit is wired to a connector that includes a key that is aligned with field circuit contacts of the connector. A thermal and nuclear radiation shield encloses the electronic circuit and includes a shock protection annulus. The connector is secured inside the shock protection annulus. The thermal and nuclear radiation shield includes shield threads that rotatably engage the support conduit threads to rotate an alignment of the key relative to the process flange.

Abstract: A method for producing a wear-resistant and corrosion-resistant stainless steel part for a nuclear reactor is provided. This method comprises steps of providing a blank in stainless steel; shaping the blank; finishing the blank to form the part in stainless steel, the finishing step allowing the prevented onset or the removal of work hardness on the outer surface of the part; hardening the outer surface of the part via diffusion of one or more atomic species.

Abstract: A control rod drive mechanism (CRDM) for use in a nuclear reactor, the CRDM comprising: a connecting rod connected with at least one control rod; a lead screw; a drive mechanism configured to linearly translate the lead screw; an electromagnet coil assembly; and a latching assembly that latches the connecting rod to the lead screw responsive to energizing the electromagnet coil assembly and unlatches the connecting rod from the lead screw responsive to deenergizing the electromagnet coil assembly. The latching assembly is secured with and linearly translates with the lead screw, while the electromagnet coil assembly does not move with the lead screw. The electromagnet coil assembly is at least coextensive with a linear translation stroke over which the drive mechanism is configured to linearly translate the lead screw.

Abstract: A rod cluster control assembly having a control rod upper end plug formed in two parts and connected together with a flexible joint coupling located at or below a connecting finger on a spider vane. The upper portion of the upper control rod end plug is screwed into the connecting finger on the spider vane and lock welded between a lower portion of the finger and a shoulder on an abutting ledge of the upper portion of the end plug.

Abstract: Disclosed herein is a guide thimble of a nuclear fuel assembly, which is capable of improving the cooling performance and the stability of a nuclear fuel, preventing a flow split in dual-cooling nuclear fuel rod and guide thimble sub channels for obtaining high combustion degree and high power, and minimizing a neutron absorption section in a reaction degree region. Since the guide thimble having the dual tube type structure is adopted, a flow split in the fuel rod and guide thimble sub channels can be reduced, and the degradation in performance of nuclear fuel due to increase of a neutron absorption section can be prevented. In order for compatibility with an existing control rod, a typical guide tube is used as an inner guide thimble, and an outer guide thimble is provided outside the inner guide thimble.

Abstract: A nuclear fuel assembly having a tube-in-tube control rod guide tube design that incorporates an end plug that extends axially upward to an elevation above the lower most grid where it is sealed at its upper end to the lower end of the control rod guide tube. The guide tube lower end plug has a threaded recess in its upper surface that mates with a corresponding dashpot end plug threaded extension that is formed as an insert in the lower end of the guide tube. A hole formed through the outer wall of the guide tube end plug at the elevation of the lower portion of the recess provides a positive inspection port for assuring the proper seating of the dashpot. A method of manufacture of such a fuel assembly is also disclosed.

Abstract: A method to design a nuclear fuel assembly having the following steps including establishing the falling speed of the control rod upon entry into the lower damping portion when the control cluster falls in the event of a shutdown of the nuclear reactor, establishing, based on the falling speed established in step a), the progression of the falling speed of the control rod in the lower damping portion, establishing, based on the progression of the speed established in step b), a maximum elevated pressure produced in the liquid contained in the lower damping portion, and establishing, based on the maximum elevated pressure established in step c), a maximum circumferential stress produced in the lower damping portion.

Abstract: A core plate assembly for a nuclear reactor includes a plurality of support beams, a flat plate positioned on top of the support beams, a plurality of control rod guide tube openings arranged in staggered rows, and a plurality of fuel supports extending through the flat plate. Each guide tube opening has a cruciform shape defines four fuel bundle receiving areas. Each fuel support includes a coolant flow inlet, and a coolant flow outlet sized to receive a lower tie plate of a fuel bundle. The coolant flow inlet is offset from coolant flow outlet so that a centerline of the coolant flow inlet is parallel to a centerline of the coolant flow outlet. The coolant flow inlets are positioned adjacent a support beam, and the coolant flow outlets are positioned in a fuel bundle receiving area.

Abstract: In order to provide a boiling water type nuclear reactor use control rod with a guide use roller which improves corrosive environment at a clearance in the guide use roller and suppresses a generation of stress corrosion cracking while maintaining sliding function of the control rod by the guide use roller, at least one of a handle 5, a lower portion supporting plate 2a and a dropping speed limiter 2 is provided with the guide use roller, and a space which causes water flow in a clearance between a pin 9 and a pin hole 12 in the guide use roller is provided adjacent the clearance.

Abstract: A tubular blank (22) is rolled on a mandrel (14) in a pilgrim rolling mill. In a first rolling stage, a first part of the blank (22) is rolled on a first part (18, 19) of the mandrel (14), with a reduction of the outside diameter of the blank (22) to the outside diameter of the guide tube and a reduction of the wall thickness of the blank (22) to one of a first wall thickness (e1) and a second wall thickness (e2) exceeding the first wall thickness (e1). The mandrel (14) is advanced in the axial direction. A second part of the blank (22) is rolled on a second part (20,21) of the mandrel spaced from the first part in the axial direction with a reduction of the outside diameter of the blank to the outside diameter of the guide tube and a reduction of the wall thickness of the blank (22) to the other of the first wall thickness (e1) and second wall thickness (e2).

Abstract: The control cluster is usable for power regulation and for load following. It comprises a spider from which are suspended rods containing a column of neutron-absorbing material. The neutron-absorbing material in at least some rods is stainless steel in lower part of the rod and, in an upper part of the rod having a length equal to 20 and 40% of the height of the column of absorbing material, another material exhibiting an interference neutron absorption which is much higher than that of stainless steel, for instance Ag-In-Cd.

Abstract: The present invention is directed to a rod connector assembly for removably securing a control rod to a spider structure. The rod connector assembly includes a tubular boss fixedly secured to the spider structure and a mounting assembly which includes a receiving structure and a biasing structure. The assembly also includes a cap having a cavity formed therein, the biasing structure including a driver and disposed in the cavity such that the driver extends outwardly from the cavity and into the boss, and wherein the cap is secured to the boss. When the control rod is in a prescribed position with respect to the boss, the mounting assembly is operative to resist rotation of the control rod upon application to the control rod of an amount of torque less than a predetermined amount of torque.

Abstract: A nuclear reactor, such as advanced pressurized water reactor, with controlled power output includes a reactor core having a cross section in a given plane with a center of area and axes of symmetry passing through the center of area. A multiplicity of control elements are disposed in groups, each having at least one of the control elements. The control elements of each of the groups with more than one control element are joined together. The groups are symmetrical to at least two of the axes of symmetry. Drive mechanisms each move a respective one of the groups of control elements. Each of the control elements has a plurality of control rods. A support structure joins the control rods to one another. Fuel assemblies are disposed in groups. Each of the groups of control elements has a given number of control elements being associated with one of the groups of fuel assemblies having the given number of fuel assemblies.

Abstract: An end fitting for a fuel assembly. A lower plate having a pin extending perpendicular thereto at each corner slidably receives a main body portion on the pins. Stop washers or nuts on the pins prevent the main body portion from sliding off the pins. A hairpin shaped spring along each side of the main body portion is positioned between the plate and main body portion to resiliently bias them apart. The end of the spring against the lower plate is offset from the end of the plate to preload the spring tension.

Abstract: A method and apparatus is disclosed for reducing the exposure of pressure vessel welds to fast neutron fluxes. Localized peripheral core areas are provided with rod assemblies which may be made up of nuclear absorbing materials, nuclear reflecting materials, or any combination thereof, and of any desired length so as to reduce the exposure of the welds to such fast neutron fluxes. The rod assemblies are precisely tailored consistent with nuclear calculations to provide the desired effect without substantially reducing core ratings or adversely affecting reactor shutdown margins.

Abstract: A method and apparatus for removably attaching a top nozzle to a nuclear fuel assembly to permit easy access to the fuel rods. The quick disconnect top nozzle structure includes guide thimbles which are clearance fitted into an adapter plate of the top nozzle. Load collars are attached to the guide thimbles to support compressive loads such as those imposed by holddown springs. Tensive forces, such as lift forces, are transferred through the top nozzle into peripheral straps of a top spacer grid. The peripheral straps include extensions which resiliently latch onto the top nozzle for ease of assembly and disassembly.

Abstract: The invention relates to a fuel assembly with cooled guide tubes for a nuclear reactor.It consists of a bundle of parallel fuel tubes (1) held in a structure comprising spacer grids, guide tubes (6) and end plates. At least a part of the guide tubes (10) comprises a set of guiding surfaces (16) projecting towards the interior of the tubes (10) over the whole of their length. The projections (16) are formed by embossing of the wall of the tube (10) and permit the guidance of the rod of absorbing material which is moved in the tube and the provision of circulating spaces for the cooling fluid between the tube and the rod of absorbing material.The invention applies in particular to pressurized water reactors and to reactors with neutron spectrum variation.

Abstract: A control rod assembly arrangement is disclosed for a light water nuclear reactor. Absorber rods are combined with stainless steel rods to achieve a more homogeneous poison distribution effect which reduces power depression within associated fuel assemblies and thereby flattens the overall power distribution within the core. In addition to improved load follow performance, safety analysis margins are improved due to the reduction in control rod reactivity worth.

Abstract: Control cluster guide devices, for light water cooled nuclear reactors, including housings. The reactor includes means outside the core for guiding control clusters (7) during their movements.The housings (12) are associated respectively with the several control clusters (7) and comprise plates which ensure discontinuous guidance at intermediate levels for the individual pencils and an associated spider, each housing including for continuous of the individual pencils, tubes which connect two tube plates for the pencils to pass through, which are proper to the housing, the one terminating it and the other forming a positioning flange on the core plate.

Abstract: An improved control rod guide tube for use in a fuel assembly in a nuclear reactor. The guide tube extends the complete length of the fuel assembly and has its upper end fastened in a cylindrical housing by swaging the guide tube material into grooves formed in the housing walls. To eliminate wear on the guide tube inner walls caused by hydraulic induced vibratory forces on a control rod adapted to move therein, a thin-walled chrome plated sleeve is threaded into the top end of the guide thimble and extends downwardly a distance sufficient to be engaged by the control rod during reactor operation. The sleeve serves as a highly resistant wear surface between the control rod and walls on the guide tube in the fuel assembly.