Compact nuclear reactor

Abstract

A pressurized water nuclear reactor (PWR) includes a once through steam generator (OTSG) disposed in a generally cylindrical pressure vessel and a divider plate spaced apart from the open end of a central riser. A sealing portion of the pressure vessel and the divider plate define an integral pressurizer volume that is separated by the divider plate from the remaining interior volume of the pressure vessel. An internal control rod drive mechanism (CRDM) has all mechanical and electromagnetomotive components including at least a motor and a lead screw disposed inside the pressure vessel. Optionally CRDM units are staggered at two or more different levels such that no two neighboring CRDM units are at the same level. Internal primary coolant pumps have all mechanical and electromagnetomotive components including at least a motor and at least one impeller disposed inside the pressure vessel. Optionally, the pumps and/or CRDM are arranged below the OTSG

We claim: 
     
         1 . An apparatus comprising:
 a generally cylindrical pressure vessel defining a cylinder axis;   a nuclear reactor core disposed in the generally cylindrical pressure vessel;   a central riser disposed coaxially inside the generally cylindrical pressure vessel, the central riser being hollow and having an end proximate to the nuclear reactor core to receive primary coolant heated by the nuclear reactor core and an open end distal from the nuclear reactor core discharging the primary coolant;   a once-through steam generator (OTSG) disposed in an annular volume defined between the central riser and the generally cylindrical pressure vessel, the primary coolant discharged from the open end of the central riser flowing through the OTSG and heating secondary coolant also flowing through the OTSG, the primary coolant and the secondary coolant being disposed in separate flow paths in the OTSG; and   internal primary coolant pumps arranged to circulate primary coolant within the pressure vessel, the internal primary coolant pumps having all mechanical and electromagnetomotive components including at least a motor and at least one impeller disposed inside the pressure vessel.   
     
     
         2 . The apparatus as set forth in  claim 1 , wherein the OTSG comprises straight tubes arranged parallel with the cylinder axis. 
     
     
         3 . The apparatus as set forth in  claim 1 , further comprising:
 a feedwater annulus between an outer shroud of the OTSG and the pressure vessel, the feedwater annulus buffering secondary coolant injected into the OTSG; and   a steam annulus between the outer shroud of the OTSG and the pressure vessel, the steam annulus buffering secondary coolant comprising steam discharged from the OTSG.   
     
     
         4 . The apparatus as set forth in  claim 3 , wherein the feedwater annulus has a larger outer diameter than the steam annulus. 
     
     
         5 . The apparatus as set forth in  claim 1 , wherein the OTSG comprises straight tubes arranged parallel with the cylinder axis, the primary coolant flows inside the straight tubes and the secondary coolant flows outside the straight tubes. 
     
     
         6 . The apparatus as set forth in  claim 1 , further comprising:
 a divider plate spaced apart from the open end of the central riser;   wherein the generally cylindrical pressure vessel includes a sealing portion cooperating with the divider plate to define an integral pressurizer volume that is separated by the divider plate from the remaining interior volume of the generally cylindrical pressure vessel; and   wherein the apparatus comprises a pressurized water reactor (PWR) and the integral pressurizer volume contains fluid at a pressure greater than a pressure of the pressure vessel.   
     
     
         7 . The apparatus as set forth in  claim 1 , further comprising:
 neutron-absorbing control rods; and   an internal control rod drive mechanism (CRDM) configured to controllably insert and withdraw the control rods into and out of the nuclear reactor core, the internal CRDM having all mechanical and electromagnetomotive components including at least a motor and a lead screw disposed inside the pressure vessel.   
     
     
         8 . The apparatus as set forth in  claim 7 , wherein the internal CRDM comprises a plurality of CRDM units that are staggered at two or more different levels such that no two neighboring CRDM units are at the same level. 
     
     
         9 . The apparatus as set forth in  claim 1 , wherein the internal primary coolant pumps are arranged to receive primary coolant discharged from the OTSG. 
     
     
         10 . The apparatus as set forth in  claim 1 , wherein the internal primary coolant pumps have inlets and outlets that are not coupled with the OTSG. 
     
     
         11 . The apparatus as set forth in  claim 1 , wherein the internal primary coolant pumps have inlets and outlets that are not coupled with any other component. 
     
     
         12 . The apparatus as set forth in  claim 1 , wherein the generally cylindrical pressure vessel is vertical with its cylinder axis oriented vertically, and the internal primary coolant pumps are located below the OTSG. 
     
     
         13 . The apparatus as set forth in  claim 12 , wherein the generally cylindrical pressure vessel has a lower region with a relatively larger diameter containing the nuclear reactor core and an upper region with a relatively smaller diameter not containing the nuclear reactor core. 
     
     
         14 . An apparatus comprising:
 a pressurized water nuclear reactor (PWR) including a generally cylindrical pressure vessel defining a cylinder axis, a nuclear reactor core disposed in the generally cylindrical pressure vessel, and a hollow central riser disposed coaxially inside the generally cylindrical pressure vessel with an end proximate to the nuclear reactor core to receive primary coolant heated by the nuclear reactor care and an open end distal from the nuclear reactor core discharging the primary coolant;   a once-through steam generator (OTSG) disposed in the pressure vessel and including a primary coolant flow path and a secondary coolant flow path, primary coolant flowing in the primary coolant flow path heating secondary coolant flowing in the secondary coolant flow path to generate secondary coolant comprising steam; and a divider plate spaced apart from the open end of the central riser;   wherein the generally cylindrical pressure vessel includes a sealing portion cooperating with the divider plate to define an integral pressurizer volume that is separated by the divider plate from the remaining interior volume of the generally cylindrical pressure vessel; and   wherein the integral pressurizer volume contains primary coolant at a temperature greater than a temperature of primary coolant disposed in the remaining interior volume of the generally cylindrical pressure vessel.   
     
     
         15 . The apparatus as set forth in  claim 14 , wherein the OTSG is disposed in an annular volume defined between the central riser and the generally cylindrical pressure vessel, the primary coolant discharged from the open end of the central riser flowing through the primary coolant flow path of the OTSG. 
     
     
         16 . The apparatus as set forth in  claim 15 , further comprising:
 a feedwater annulus between an outer shroud of the OTSG and the pressure vessel, the feedwater annulus buffering secondary coolant injected into the OTSG; and   a steam annulus between the outer shroud of the OTSG and the pressure vessel, the steam annulus buffering secondary coolant comprising steam discharged from the OTSG.   
     
     
         17 . The apparatus as set forth in  claim 16 , wherein the feedwater annulus has a larger outer diameter than the steam annulus. 
     
     
         18 . The apparatus as set forth in  claim 14 , wherein the OTSG comprises straight tubes arranged parallel with the cylinder axis. 
     
     
         19 . The apparatus as set forth in  claim 18 , wherein the primary coolant flow path is disposed inside the straight tubes and the secondary coolant flow path is disposed outside the straight tubes. 
     
     
         20 . The apparatus as set forth in  claim 14 , wherein the divider plate comprises:
 a flow diverter having a flow-diverting surface facing the open end of the central riser to redirect primary coolant discharged from the open end of the central riser toward primary coolant inlets of the OTSG.   
     
     
         21 . The apparatus as set forth in  claim 14 , further comprising:
 neutron-absorbing control rods; and   an internal control rod drive mechanism (CRDM) configured to controllably insert and withdraw the contra I rods into and out of the nuclear reactor core, the internal CRDM having all mechanical and electromagnetomotive components including at least a motor and a lead screw disposed inside the pressure vessel.   
     
     
         22 . The apparatus as set forth in  claim 21 , wherein the internal CRDM comprises a plurality of CRDM units that are staggered at two or more different levels such that no two neighboring CRDM units are at the same level. 
     
     
         23 . The apparatus as set forth in  claim 14 , further comprising:
 primary coolant pumps arranged to receive primary coolant discharged from the OTSG.   
     
     
         24 . The apparatus as set forth in  claim 14 , wherein the generally cylindrical pressure vessel is vertical with its cylinder axis oriented vertically, and the sealing portion cooperating with the divider plate to define the integral pressurizer volume is a sealing top portion of the vertical pressure vessel that cooperates with the divider plate to define the integral pressurizer volume at the top of the vertical pressure vessel. 
     
     
         25 . The apparatus as set forth in  claim 24 , wherein the generally cylindrical vertical pressure vessel has a lower region with a relatively larger diameter containing the nuclear reactor core and an upper region with a relatively smaller diameter containing the integral pressurizer volume.