Abstract: A system for refueling a nuclear reactor is provided. The system includes a lower reactor vessel with a plurality of fuel rods and a plurality of control rods disposed therein, the lower reactor vessel further comprising an upper flange. An upper reactor vessel is provided which encloses a steam generator and a pressurizer, the upper reactor vessel further comprising a lower flange that matingly engages the upper flange of the lower reactor vessel. A transporter surrounds an outer surface of the upper reactor vessel, wherein the transporter is configured to translate the upper reactor vessel vertically toward and away from the lower reactor vessel and also to translate the upper reactor vessel horizontally toward or away from alignment with the lower reactor vessel.

Abstract: A nuclear reactor includes a nuclear reactor core comprising fissile material disposed in a reactor pressure vessel having vessel penetrations that exclusively carry flow into the nuclear reactor and at least one vessel penetration that carries flow out of the nuclear reactor. An integral isolation valve (IIV) system includes passive IIVs each comprising a check valve built into a forged flange and not including an actuator, and one or more active IIVs each comprising an active valve built into a forged flange and including an actuator. Each vessel penetration exclusively carrying flow into the nuclear reactor is protected by a passive IIV whose forged flange is directly connected to the vessel penetration. Each vessel penetration carrying flow out of the nuclear reactor is protected by an active IIV whose forged flange is directly connected to the vessel penetration. Each active valve may be a normally closed valve.

Abstract: A nuclear reactor includes a nuclear reactor core disposed in a pressure vessel and immersed in primary coolant water at an operating pressure higher than atmospheric pressure. A containment structure contains the nuclear reactor. A reactor coolant inventory and purification system (RCI) is connected with the pressure vessel by make-up and letdown lines. The RCI includes a high pressure heat exchanger configured to operate responsive to a safety event at the operating pressure to remove heat from the primary coolant water in the pressure vessel. An auxiliary condenser located outside containment also removes heat. The RCI also includes a pump configured to inject make up water into the pressure vessel via the make-up line against the operating pressure. An emergency core cooling system (ECC) operates to depressurize the nuclear reactor only if the RCI and auxiliary condenser are unable to manage the safety event.

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 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 control rod drive mechanism (CRDM) includes a lifting rod supporting a control rod and a holding mechanism comprising an electromagnetic circuit with magnetic poles drawn together when the electromagnetic circuit is energized to hold the lifting rod. The hold is released upon de-energizing the electromagnetic circuit. A translation mechanism linearly translates the lifting rod held by the holding mechanism. The holding mechanism may include a non-magnetic spacer between the magnetic poles that defines a gap between the drawn together magnetic poles. The translation mechanism may include latches configured to engage an upper end of the lifting rod, and the holding mechanism draws the magnetic poles together to hold the latches engaged with the upper end of the lifting rod. A four-bar cam assembly may be used to cam the latches closed in response to a vertical actuation force applied to the cam bars.

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: A spacer grid includes interlocked straps comprising metal sheets or plates welded together to define a spacer grid having a top and bottom. The interlocked straps define a plurality of cells comprising vertical passages connecting the top and bottom of the spacer grid. The cells include: upper dimples proximate to the top of the spacer grid and distal from the mid-plane of the spacer grid; lower dimples proximate to the bottom of the spacer grid and distal from the mid-plane of the spacer grid; cantilevered upper springs having fuel rod engagement surfaces proximate to the top of the spacer grid and distal from the mid-plane of the spacer grid; and cantilevered lower springs having fuel rod engagement surfaces proximate to the bottom of the spacer grid and distal from the mid-plane of the spacer grid.

Abstract: A control rod guide frame comprises a self supporting stack of two or more columnar elements defining a central passage. The columnar elements may include mating features that mate at abutments between adjacent columnar elements of the stack. The control rod guide frame is suitably used in conjunction with a control rod drive mechanism (CRDM) operatively connected with at least one control rod, and a nuclear reactor core, in which the CRDM moves the at least one control rod into and out of the nuclear reactor core under guidance of the control rod guide frame. In another embodiment, a control rod guide frame comprises a stack of two or more columnar elements defining a central passage having a constant cross-section as a function of position along the central passage. In another embodiment, a control rod guide frame comprises an extruded columnar element providing continuous control rod guidance.

Abstract: A control rod drive mechanism (CRDM) configured to latch onto the lifting rod of a control rod assembly and including separate latch engagement and latch holding mechanisms. A CRDM configured to latch onto the lifting rod of a control rod assembly and including a four-bar linkage closing the latch, wherein the four-bar linkage biases the latch closed under force of gravity.

Abstract: A nuclear reactor includes a pressure vessel and a nuclear reactor core comprising fissile material disposed inside the pressure vessel at the bottom of the pressure vessel. A secondary core containment structure includes a containment basket comprising insulation with a maximum stable temperature of at least 2200K cladded by steel. The bottom of the pressure vessel and the nuclear reactor core are disposed inside the containment basket with the containment basket spaced apart from the bottom of the pressure vessel by a clearance gap. The containment basket may comprise zirconia insulation cladded by steel. In some embodiments the clearance gap between the containment basket and the bottom of the pressure vessel is no larger than one meter. The secondary core containment structure may further comprise conduits arranged to inject water into the clearance gap between the containment basket and the bottom of the pressure vessel.

Abstract: A fuel assembly includes a plurality of fuel rods comprising fissile material, a plurality of guide tubes interspersed amongst the fuel rods, an upper end fitting connected with upper ends of guide tubes, and a lower end fitting. End plugs are connected with the lower ends of the guide tubes. The end plugs have threaded male shafts extending from the lower ends of the guide tubes which pass through openings of the lower end fitting. Female lock nuts are threaded onto the threaded male shafts of the end plugs and lock with the lower end fitting to secure the lower end fitting to the lower ends of the guide tubes. The female lock nuts suitably have locking portions that are outwardly deformed into recesses of the lower end fitting to lock the lock nuts in place after tightening.

Abstract: A control rod assembly including at least one movable control rod including a neutron absorbing material, a control rod drive mechanism (CRDM) for controlling movement of the at least one control rod, and a coupling operatively connecting the at least one control rod and the CRDM. The coupling includes a terminal element engaged with a connecting rod of the CRDM and the at least one moveable control rod, and a kinetic energy absorbing element supported by the terminal element for absorbing kinetic energy during a SCRAM event, the kinetic energy absorbing element configured to act between the terminal element and an upper plate of an associated fuel assembly.

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: A control rod guide frame has a central passage of constant cross-section as a function of position along a central axis that passes through the central passage. The central passage is sized and shaped to guide a traveling assembly including at least one control rod as it moves along the central axis. The control rod guide frame comprises at least two radial guide frame sections secured around and defining the central passage. Each radial guide frame section may comprise an extruded radial guide frame section, which may be made of extruded steel. The central passage may include control rod guidance channels parallel the central axis and machined into the extruded radial guide frame sections. The at least two radial guide frame sections may be interchangeable. In some embodiments the at least two radial guide frame sections consist of between four and eight radial guide frame sections.

Abstract: A control rod drive mechanism (CRDM) configured to latch onto the lifting rod of a control rod assembly and including separate latch engagement and latch holding mechanisms. A CRDM configured to latch onto the lifting rod of a control rod assembly and including a four-bar linkage closing the latch, wherein the four-bar linkage biases the latch closed under force of gravity.

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 internal 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 internal pressurizer. A central riser may be disposed concentrically inside the pressure vessel, and the RCP impels primary coolant downward into a downcomer annulus between the central riser and the pressure vessel. A steam generator may be disposed in the downcomer annulus and spaced apart from with the impeller by an outlet plenum. A manway may access the outlet plenum so tube plugging can be performed on the steam generator via access through the manway without removing the RCP.

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) 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 nuclear reactor includes a nuclear reactor core comprising fissile material and a pressure vessel containing the nuclear reactor immersed in primary coolant water at an operating pressure. The pressure vessel has a vessel penetration passing through a wall of the pressure vessel. An electrical feedthrough seals the vessel penetration and has an outside electrical connector mounted at the pressure vessel. The outside electrical connector is at atmospheric pressure. The electrical feedthrough may include a flange disposed inside the pressure vessel and sealing against an inside surface of the wall of the pressure vessel. The outside electrical connector of the electrical feedthrough may be inset into the wall of the pressure vessel.