Patent Number: 
Section: claims

1. A pressurized water nuclear reactor comprising:a pressure vessel having a core region for supporting fuel assemblies;a core barrel removably disposed within the pressure vessel;a core shroud disposed within the core barrel, the core shroud having an alignment slot;an upper core support plate removably disposed above the core shroud, the upper core support plate having an alignment slot; andan alignment plate attached to the core barrel and disposed within the alignment slot of the core shroud and within the alignment slot of the upper core support plate. 2. The pressurized water nuclear reactor of claim 1, wherein the core barrel has an inner surface and an outer surface and the alignment plate is attached to the inner surface of the core barrel and further comprising a reinforcement pad disposed on the outer surface of the core barrel and attached to the alignment plate. 3. The pressurized water nuclear reactor of claim 2 wherein the reinforcement pad is attached to the alignment plate with at least two dowel pins that engage the reinforcement pad and alignment plate through the core barrel. 4. The pressurized water nuclear reactor of claim 3 wherein the dowel pins are shrink fit into the reinforcement pad, core barrel and alignment plate or reinforcement pad and core barrel. 5. The pressurized water nuclear reactor of claim 3 wherein the alignment plate and reinforcement pad are affixed in a vertical direction, including a bottom hole and a top hole in the alignment plate with corresponding aligned holes in the core barrel and reinforcement pad, wherein the holes respectively on the alignment plate, the core barrel and the reinforcement pad are positioned spaced one above the other and are sized to receive the dowel pins. 6. The pressurized water nuclear reactor of claim 5 wherein one of the bottom or top dowel pin-alignment plate holes is designed to accommodate differential axial thermal growth between the core barrel and alignment plate, whereby a gap exists between a top, bottom and side surfaces of the one of the top or bottom dowel pin alignment plate holes and the corresponding dowel pins with machined flats on the vertical surfaces of the one of the bottom or top dowel pin-alignment plate holes allowing differential thermal growth in the vertical direction. 7. The pressurized water nuclear reactor of claim 2 wherein the alignment plate is attached to the core barrel with threaded fasteners. 8. The pressurized water nuclear reactor of claim 7 wherein the reinforcement pad is welded to the core barrel. 9. The pressurized water nuclear reactor of claim 8 wherein the reinforcement pad is welded to the core barrel with a fillet weld. 10. The pressurized water nuclear reactor of claim 1 wherein a back of the alignment plate fits in a recess in the core barrel. 11. The pressurized water nuclear reactor of claim 1 wherein a back of the alignment plate that interfaces with the core barrel is machined to have the same curvature as the core barrel. 12. The pressurized water nuclear reactor of claim 1 wherein the pressure vessel has an inlet nozzle and the alignment plate is positioned on the inner circumference of the core barrel radially in-line with the inlet nozzle. 13. The pressurized water nuclear reactor of claim 1 wherein the pressure vessel has a plurality of inlet nozzles and a plurality of alignment plates, with each alignment plate positioned on the inner circumference of the core barrel radially in-line with a corresponding one of the plurality of inlet nozzles. 14. The pressurized water nuclear reactor of claim 1 including an insert in the core shroud alignment slot and an insert in the upper core support plate alignment slot so that a predetermined clearance can be obtained between the sides of the slots and the alignment plate.