Abstract: A power distribution plate (PDP) sits on top of a support plate. Control rod drive mechanism (CRDM) units are mounted on top of the PDP, but the PDP is incapable of supporting the weight of the CRDM units and instead transfers the load to a support plate. The PDP has receptacles which receive cable modules each including mineral insulated (MI) cables, the MI cables being connected with the CRDM units. The PDP may further include a set of hydraulic lines underlying the cable modules and connected with the CRDM units. The cable modules in their receptacles define conduits or raceways for their MI cables and for any underlying hydraulic lines.

Abstract: Refueling of a nuclear reactor (40) includes removing a fuel assembly (10). The removal method includes lowering a lifting tool (80) of a crane (44) onto a top of the fuel assembly. The lowered lifting tool including a plurality of downwardly extending elements (82) that surround and vertically overlap a portion (74) of a control rod assembly (70) extending above the top of the fuel assembly. The downwardly extending elements are locked with corresponding mating features (26) at the top of the fuel assembly to connect the lifting tool with the fuel assembly. The connected fuel assembly is moved into a spent fuel pool (42) using the crane, and the lifting tool is disconnected from the top of the fuel assembly by unlocking the downwardly extending elements from the corresponding mating features at the top of the fuel assembly.

Abstract: A pressurized water reactor (PWR) includes a vertical cylindrical pressure vessel having a lower portion containing a nuclear reactor core and a vessel head defining an integral pressurizer. A reactor coolant pump (RCP) mounted on the vessel head includes an impeller inside the pressure vessel, a pump motor outside the pressure vessel, and a vertical drive shaft connecting the motor and impeller. The drive shaft does not pass through the integral pressurizer. The drive shaft passes through a vessel penetration of the pressure vessel that is at least large enough for the impeller to pass through.

Abstract: A pellet magazine includes a plurality of pellet bores sized to receive pellets for loading into a fuel rod. A fuel rod loading system includes a plurality of pellet loading stations each designated to load a single pellet type into one or more pellet bores of the pellet magazine, a rod loading station configured to unload pellets from the pellet bores of the pellet magazine into a fuel rod, and a conveyance system configured to transport the pellet magazine to the loading stations and then to the rod loading station in a defined sequence.

Abstract: A spacer grid welding fixture comprises a frame sized to receive an assembled spacer grid comprising a first set of parallel straps and a second set of parallel straps oriented orthogonally to the first set of parallel straps, the first and second sets of parallel straps interlocked together by slots cut into the straps. A first set of grid engagement bars is placed on a first side of the spacer grid with each grid engagement bar arranged parallel with the straps of the first set of parallel straps and engaging the straps of the second set of parallel straps. A second set of grid engagement bars is placed on an opposite second side of the spacer grid with each grid engagement bar arranged parallel with the straps of the second set of parallel straps and engaging the straps of the first set of parallel straps.

Abstract: An apparatus and method for system safety analysis evaluation is provided, the apparatus including processing circuitry configured for generating a calculation matrix for a system, generating a plurality of models based on the calculation matrix, performing a benchmarking or convolution analysis of the plurality of models, identifying a design envelope based on the benchmarking or convolution analysis, deriving uncertainty models from the benchmarking or convolution analysis, deriving an assessment judgment based on the uncertainty models and acceptance criteria, defining one or more limiting scenarios based on the design envelope, and determining a safety margin in at least one figure-of-merit for the system based on the design envelope and the acceptance criteria.

Abstract: A reactor control interface includes a home screen video display unit (VDU) displaying blocks representing functional components of a nuclear power plant and connecting arrows that connect blocks that are providing the current heat sinking path for the nuclear power plant. Directions of the connecting arrows represent the direction of heat flow along the current heat sinking path. If the current heat flow path of the plant changes, the connecting arrows are updated accordingly. Additional VDUs include: a mimic VDU displaying a mimic of a plant component; a procedures VDU displaying a stored procedure executable by the plant; a multi-trend VDU trending various plant data; and an alarms VDU displaying side-by-side alarms registries sorted by time and priority respectively. If a VDU fails, the displays are shifted to free up one VDU to present the display of the failed VDU, and one display is shifted to an additional VDU.

Abstract: A nuclear reactor comprises a pressure vessel containing a nuclear reactor core. A reactor core cooling system comprises a standpipe including a plurality of orifices in fluid communication with a refueling water storage tank (RWST) to drain water from the RWST into the standpipe, and an injection line configured to drain water from the standpipe to the pressure vessel. In some embodiments the standpipe is disposed in the RWST, while in other embodiments the standpipe is disposed outside of the RWST and cross-connection pipes connect the plurality of orifices with the RWST. The reactor core cooling system may further comprise a valve configured to control flow through one orifice of the plurality of orifices in fluid communication with the RWST based on water level in the standpipe. The valve may comprise a float valve having its float disposed in the standpipe.

Abstract: In a pressurized water reactor (PWR), emergency core cooling (ECC) responds to depressurization due to a vessel penetration break at the top of the pressure vessel by draining water from a body of water through an injection line into the pressure vessel. A barrier operates concurrently with the ECC to suppress flow of liquid water from the pressure vessel out the vessel penetration break. The barrier may comprise one or more of: (1) an injection line extension passing through the central riser to drain water into the central riser; (2) openings in a lower portion of a central riser to shunt some upward flow from the central riser into a lower portion of the downcomer annulus; and (3) a surge line providing fluid communication between a pressurizer volume at the top of the pressure vessel and the remainder of the pressure vessel which directs water outboard toward the downcomer annulus.

Abstract: A standoff supporting a control rod drive mechanism (CRDM) in a nuclear reactor is connected to a distribution plate which provides electrical power and hydraulics. The standoff has connectors that require no action to effectuate the electrical connection to the distribution plate other than placement of the standoff onto the distribution plate. This facilitates replacement of the CRDM. In addition to the connectors, the standoff has alignment features to ensure the CRDM is connected in the correct orientation. After placement, the standoff may be secured to the distribution plate by bolts or other fasteners. The distribution plate may be a single plate that contains the electrical and hydraulic lines and also is strong enough to provide support to the CRDMs or may comprise a stack of two or more plates.

Abstract: A spacer grid welding fixture comprises a frame sized to receive an assembled spacer grid comprising a first set of parallel straps and a second set of parallel straps oriented orthogonally to the first set of parallel straps, the first and second sets of parallel straps interlocked together by slots cut into the straps. A first set of grid engagement bars is placed on a first side of the spacer grid with each grid engagement bar arranged parallel with the straps of the first set of parallel straps and engaging the straps of the second set of parallel straps. A second set of grid engagement bars is placed on an opposite second side of the spacer grid with each grid engagement bar arranged parallel with the straps of the second set of parallel straps and engaging the straps of the first set of parallel straps.

Abstract: An apparatus including a lower end fitting having a top planar surface, a bottom planar surface, a counterbore defined therebetween, an opening extending from the counterbore to the top planar surface, and a lock recess that extends both radially outwardly from the counterbore and extends inwardly into the lower end fitting from the bottom planar surface. The apparatus includes a guide tube having a lower end and an end plug configured to connect with the lower end of the guide tube. The end plug has a threaded shaft sized to pass through the opening of the lower end fitting, and a female lock nut has a deformable side wall configured to be swaged into the recess of the lower end fitting. The lock recess remains visible as viewed from the bottom planar surface of the lower end fitting when the female lock nut is fully disposed in the counterbore.

Abstract: A nuclear reactor has a core installed on a lower core plate and formed from multiple fuel assemblies, each fuel assembly including a structural cage assembly. The structural cage assembly has an upper end fitting, mid grids, and a lower end fitting (LEF). The LEF positions the fuel assembly using four locating pins located at each corner of the LEF. The pins position the fuel assembly laterally by mating with receiving holes in the lower core plate. The locating pins have a chamfered tip with a flat end. The chamfered tip allows for a greater positioning margin when installing the fuel assembly in the core by guiding the pins into holes in the lower core plate, and the flat tip provides strength and stability in case the assembly is inadvertently rested on the tip of the pin instead of the LEF pads.

Abstract: A nuclear reactor comprises a nuclear reactor core disposed in a pressure vessel. An isolation valve protects a penetration through the pressure vessel. The isolation valve comprises: a mounting flange connecting with a mating flange of the pressure vessel; a valve seat formed into the mounting flange; and a valve member movable between an open position and a closed position sealing against the valve seat. The valve member is disposed inside the mounting flange or inside the mating flange of the pressure vessel. A biasing member operatively connects to the valve member to bias the valve member towards the open position. The bias keeps the valve member in the open position except when a differential fluid pressure across the isolation valve and directed outward from the pressure vessel exceeds a threshold pressure.

Abstract: A pressurized water reactor (PWR) comprises a pressure vessel containing primary coolant water. A nuclear reactor core is disposed in the pressure vessel and includes a plurality of fuel assemblies. Each fuel assembly includes a plurality of fuel rods containing a fissile material. A control system includes a plurality of control rod assemblies (CRA's). Each CRA is guided by a corresponding CRA guide structure. A support element is disposed above the CRA guide structures and supports the CRA guide structures. The pressure vessel may be cylindrical, and the support element may comprise a support plate having a circular periphery supported by the cylindrical pressure vessel. The CRA guide structures suitably hang downward from the support plate. The lower end of each CRA guide structure may include alignment features that engage corresponding alignment features of the upper end of the corresponding fuel assembly.

Abstract: An apparatus having a nuclear reactor comprising a pressure vessel containing primary coolant water and further containing a nuclear reactor core comprising fissile material, a mounting/electrical distribution plate secured entirely within the pressure vessel and configured to be submerged in the primary coolant, a set of control rod drive mechanism (CRDM) units mounted directly on the mounting/electrical distribution plate, and a plurality of cable modules mounted in receptacles of the mounting/electrical distribution plate wherein each cable module includes mineral insulated (MI) cables connected with one or more of the CRDM units, the cable module including its MI cables being removable as a unit from the receptacle of the mounting/electrical distribution plate.

Abstract: A fuel rod for a nuclear reactor, including a cladding tube having a first end with an annular end face, a second end with an annular end face, and a cylindrical body portion extending therebetween, and a first tube end plug including a front portion, an annular lip with an annular end face, and a substantially straight cylindrical body portion extending therebetween, wherein the surface area of the annular end face of the first end of the cladding tube and the annular end face of the annular lip of the first tube end plug are substantially equal, and the annular end face of the first end of the cladding tube and the annular end face of the annular lip of the first tube end plug are connected by a resistance pressure weld.

Abstract: Apparatuses for reducing or eliminating Type 1 LOCAs in a nuclear reactor vessel. A nuclear reactor including a nuclear reactor core comprising a fissile material, a pressure vessel containing the nuclear reactor core immersed in primary coolant disposed in the pressure vessel, and an isolation valve assembly including, an isolation valve vessel having a single open end with a flange, a spool piece having a first flange secured to a wall of the pressure vessel and a second flange secured to the flange of the isolation valve vessel, a fluid flow line passing through the spool piece to conduct fluid flow into or out of the first flange wherein a portion of the fluid flow line is disposed in the isolation valve vessel, and at least one valve disposed in the isolation valve vessel and operatively connected with the fluid flow line.

Abstract: An apparatus and method for system safety analysis evaluation is provided, the apparatus including processing circuitry configured for generating a calculation matrix for a system, generating a plurality of models based on the calculation matrix, performing a benchmarking or convolution analysis of the plurality of models, identifying a design envelope based on the benchmarking or convolution analysis, deriving uncertainty models from the benchmarking or convolution analysis, deriving an assessment judgment based on the uncertainty models and acceptance criteria, defining one or more limiting scenarios based on the design envelope, and determining a safety margin in at least one figure-of-merit for the system based on the design envelope and the acceptance criteria.

Abstract: A nuclear reactor core comprising fissile material is surrounded by a core former. The core former comprises one or more single-piece annular rings wherein each single-piece annular ring comprises neutron-reflecting material. In some embodiments the core former comprises a stack of two or more such single-piece annular rings. In some embodiments the stack of single-piece annular rings is self-supporting. In some embodiments the stack of single-piece annular rings does not include welds or fasteners securing adjacent single-piece annular rings together. A core basket may contain the nuclear reactor core and the core former, and in some embodiments an annular gap is defined between the core former and the core basket. In some embodiments the core former does not include welds and does not include fasteners.