Optimized nuclear fuel core design for a small modular reactor

Abstract

A fuel core for a nuclear reactor in one embodiment includes an upper internals unit and a lower internals unit comprising nuclear fuel assemblies. The assembled fuel core includes an upper core plate, a lower core plate, and a plurality of channel boxes extending therebetween. Each channel box comprises a plurality of outer walls and inner walls collectively defining a longitudinally-extending interior channels or cells having a transverse cross sectional area configured for holding no more than a single nuclear fuel assembly in some embodiments. A cylindrical reflector circumferentially surrounds channel boxes and is engaged at opposing ends by the upper and lower core plates. Adjacent cells within each channel box are formed on opposite sides of inner walls such that the cells are separated from each other by the inner walls alone without any water gaps therebetween which benefits neutronics for some small modular reactor designs.

What is claimed is: 
     
         1 . A nuclear fuel core for a nuclear reactor, the fuel core comprising:
 a longitudinal axis;   an upper core plate;   a lower core plate;   a plurality of vertically elongated prismatic channel boxes extending between the upper and lower core plates, each channel box comprising a plurality of outer walls and inner walls collectively defining a plurality of longitudinally-extending interior cells each containing a single nuclear fuel assembly, each channel box separated from adjacent channel boxes by peripheral water gaps formed between the outer walls of the channel boxes;   a plurality of cruciform control rods slideably inserted through the peripheral water gaps from above the upper core plate for vertical movement between the channel boxes;   a cylindrical reflector circumferentially surrounding the channel boxes, the upper and lower core plates engaging opposing ends of the reflector;   wherein the fuel assemblies within each channel box are separated from each other by the inner walls.   
     
     
         2 . The fuel core according to  claim 1 , wherein the control rods are disposed at junctions of corner regions between adjacent channel boxes. 
     
     
         3 . The fuel core according to  claim 2 , wherein the upper core plate includes a plurality of cruciform openings each slideably receiving one of the control rods therethrough for insertion into the fuel core. 
     
     
         4 . The fuel core according to  claim 1 , wherein the upper core plate is an open grid structure engaging upper portions of the channel boxes and defining a plurality of rectilinear open cells each axially aligned with one of the cells of the channel boxes. 
     
     
         5 . The fuel core according to  claim 4 , wherein the upper core plate has a polygonal-shaped perimeter with a multiple stepped configuration which engages a complementary configured multiple stepped interior surface of the cylindrical reflector to operably key and lock the upper core plate in rotational position relative to the cylindrical reflector. 
     
     
         6 . The fuel core according to  claim 1 , wherein the channel boxes have a rectilinear transverse cross-sectional shape and the inner walls have edges that perpendicularly intersect the outer walls. 
     
     
         7 . The fuel core according to  claim 6 , wherein the channel boxes includes a combination of rectangular channel boxes having a rectangular transverse cross-sectional shape disposed around exterior portions of the fuel core and square channel boxes having square transverse cross-sectional shapes. 
     
     
         8 . The fuel core according to  claim 1 , further comprising an upper internals unit stacked vertically on top of the cylindrical reflector, the upper internals unit comprising a plurality of vertically oriented flow tubes axially aligned with and in fluid communication with the cells of the channel boxes. 
     
     
         9 . The fuel core according to  claim 1 , wherein the cylindrical reflector is formed of multiple vertically stacked metallic annular segments abutted together to form an integral structure. 
     
     
         10 . The fuel core according to  claim 9 , wherein the cylindrical reflector includes a plurality of vertically cooling conduits extending from a top to a bottom of the reflector for cooling the reflector. 
     
     
         11 . A nuclear fuel core for a nuclear reactor, the fuel core comprising:
 a vertically elongated reactor vessel defining an internal cavity and a longitudinal axis;   an upper internals unit disposed in the internal cavity, the upper internals unit comprising:
 a top support plate, an upper core plate spaced vertically apart from the top support plate, and an intermediate support plate spaced therebetween; 
 a plurality of flow tubes extending between the intermediate support plate and upper core plate; and 
 a plurality of tie rods coupling the top support plate to the upper core plate through the intermediate support plate to form a self-supporting assemblage removably insertable in the reactor vessel as a single unit; 
   a lower internals unit disposed in the internal cavity comprising a plurality of fuel assemblies defining a fuel core, the lower internals unit further comprising:
 a plurality of vertically elongated channel boxes extending between the upper core plate of the upper internals unit and a lower core plate, each channel box comprising a plurality of outer walls and a plurality of inner walls collectively defining a plurality of longitudinally-extending interior cells each containing a single nuclear fuel assembly; and 
 a cylindrical reflector circumferentially surrounding the channel boxes, the upper and lower core plates disposed on opposing ends of the reflector; 
 wherein each channel box is vertically aligned with a respective flow tube in the upper internals unit to form a flow path therebetween; 
 wherein each channel box is separated from adjacent channel boxes by peripheral water gaps formed between the outer walls of the channel boxes. 
   
     
     
         12 . The fuel core according to  claim 11 , wherein the fuel assemblies within each channel box are separated from each other by the inner walls. 
     
     
         13 . The fuel core according to  claim 12 , further comprising a plurality of cruciform control rods slideably inserted in the peripheral water gaps for vertical movement therein to control reactivity in the reactor. 
     
     
         14 . The fuel core according to  claim 11 , further comprising a cylindrical shroud disposed in the internal cavity stacked on top of the cylindrical reflector, the shroud surrounding the upper internals unit component. 
     
     
         15 . The fuel core according to  claim 14 , wherein an upper flow plenum is formed between top and intermediate support plates in the shroud and a control rod compartment is formed between the intermediate support plate and upper core plate in the shroud, the control rod compartment configured to receive a portion of the control rods withdrawn from the fuel core. 
     
     
         16 . The fuel core according to  claim 13 , wherein the control rods are disposed at junctions of corner regions between adjacent channel boxes. 
     
     
         17 . The fuel core according to  claim 16 , wherein the upper core plate includes a plurality of cruciform openings each slideably receiving one of the control rods therethrough for insertion into the fuel core. 
     
     
         18 . The fuel core according to  claim 1 , further comprising an upper internals unit stacked vertically on top of the cylindrical reflector, the upper internals unit comprising the flow tubes which are axially aligned with and in fluid communication with the cells of the channel boxes.