Abstract: A pressurized water reactor (PWR) comprises: a nuclear core comprising a fissile material; a cylindrical pressure vessel having a vertically oriented cylinder axis and containing the nuclear core immersed in primary coolant water; and a hollow cylindrical central riser disposed concentrically with and inside the cylindrical pressure vessel. A downcomer annulus is defined between the hollow cylindrical central riser and the cylindrical pressure vessel. The hollow cylindrical central riser has a radially expanding upper orifice that merges into an annular divider plate that separates an upper plenum above the annular divider plate from a lower plenum below the annular divider plate. The upper plenum is in fluid communication with the radially expanding upper orifice and the lower plenum is in fluid communication with the downcomer annulus. A weir may extend away from a bottom wall of the lower plenum into the lower plenum.

Abstract: A nuclear reactor core is disposed in a pressure vessel along with upper internals disposed in the pressure vessel above the reactor core. The upper internals include internal control rod drive mechanisms (CRDMs) mounted on a suspended support assembly. A hollow cylindrical central riser is disposed in the pressure vessel above the nuclear reactor core. A hollow cylindrical section is disposed in the pressure vessel below the hollow cylindrical central riser and surrounding the nuclear reactor core. A riser transition element connects with the hollow cylindrical central riser and the hollow cylindrical section to form a continuous hollow cylindrical flow separator. The suspended support assembly of the upper internals is suspended from the riser transition element. The pressure vessel may comprise upper and lower vessel sections connected by a mid-flange, with the riser transition element welded to the mid-flange by gussets extending outward and upward from the riser transition element to the mid-flange.

Abstract: In a nuclear reactor, an internal control rod drive mechanism (CRDM) includes a motor and a hydraulically driven element connected by at least one hydraulic line with at least one hydraulic connector disposed on a mounting plate of the internal CRDM. A support element mounted in the nuclear reactor includes at least one hydraulic connector. The internal CRDM is supported on the support element by its mounting plate with each hydraulic connector of the internal CRDM mated with a corresponding hydraulic connector of the support element. The hydraulically driven element may be a piston controlling SCRAM, driven by coolant water, and the coolant water pressure in the at least one hydraulic line is higher than the coolant water pressure in the nuclear reactor. The mating of each hydraulic connector of the internal CRDM with a corresponding hydraulic connector of the support element may be a leaky mating that leaks coolant water into the pressure vessel.

Abstract: A nuclear reactor includes a pressure vessel, and a control rod assembly including at least one movable control rod comprising 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 first portion comprising a first material having a first density at room temperature, and a second portion comprising a second material having a second density at room temperature that is greater than the first density. In some embodiments the coupling includes a connecting rod including a hollow or partially hollow connecting rod tube comprising a first material having a first density and a filler disposed in the hollow or partially hollow connecting rod tube, the filler comprising a second material having a second density greater than the first density.

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 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 ser 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 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 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 pressure vessel, and a control rod assembly including at least one movable control rod comprising 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 first portion comprising a first material having a first density at room temperature, and a second portion comprising a second material having a second density at room temperature that is greater than the first density. In some embodiments the coupling includes a connecting rod including a hollow or partially hollow connecting rod tube comprising a first material having a first density and a filler disposed in the hollow or partially hollow connecting rod tube, the filler comprising a second material having a second density greater than the first density.

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 ser 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 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 pressure vessel, and a control rod assembly including at least one movable control rod comprising 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 first portion comprising a first material having a first density at room temperature, and a second portion comprising a second material having a second density at room temperature that is greater than the first density. In some embodiments the coupling includes a connecting rod including a hollow or partially hollow connecting rod tube comprising a first material having a first density and a filler disposed in the hollow or partially hollow connecting rod tube, the filler comprising a second material having a second density greater than the first density.

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.

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 ser 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: Control rod drive mechanisms (CRDMs) include CRDM motors, and a support assembly provides bottom support of the CRDMs and includes a lateral alignment plate with openings receiving upper portions of the CRDMs. The upper portions of the CRDMs include compliance features engaging the openings of the lateral alignment plate. The compliance features may comprise angled leaf springs that wedge into the openings of the lateral alignment plate. In some embodiments the upper portion of each CRDM includes straps securing one or more cables to the upper portion of the CRDM, and the angled leaf springs are cut into or welded onto ends of the straps. Some embodiments further include a pressure vessel and a nuclear reactor core comprising fissile material disposed the pressure vessel, and the CRDM is an internal CRDM disposed in the pressure vessel along with the support assembly.

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 nuclear reactor core is disposed in a pressure vessel along with upper internals disposed in the pressure vessel above the reactor core. The upper internals include internal control rod drive mechanisms (CRDMs) mounted on a suspended support assembly. A hollow cylindrical central riser is disposed in the pressure vessel above the nuclear reactor core. A hollow cylindrical section is disposed in the pressure vessel below the hollow cylindrical central riser and surrounding the nuclear reactor core. A riser transition element connects with the hollow cylindrical central riser and the hollow cylindrical section to form a continuous hollow cylindrical flow separator. The suspended support assembly of the upper internals is suspended from the riser transition element. The pressure vessel may comprise upper and lower vessel sections connected by a mid-flange, with the riser transition element welded to the mid-flange by gussets extending outward and upward from the riser transition element to the mid-flange.

Abstract: A pressure vessel includes upper and lower vessel sections joined by a flanged connection. A nuclear reactor core includes an array of fuel assemblies comprising fissile material. The nuclear reactor core is disposed in the lower vessel section. A side-entry vessel penetration is located at a side of the pressure vessel and passes through one of (i) a flange of the flanged connection and (ii) the lower vessel section. An incore instrument routing tube extends from the side-entry vessel penetration and enters the reactor core from above the reactor core. The incore instrument routing tube extends from the side-entry vessel penetration with a declination angle AE and includes a 90°?AE downward turn to enter the reactor core from above. The declination angle AE may be zero so that the routing tube extends horizontally from the side-entry vessel penetration and includes a 90° downward turn.