Patent Number: 
Section: claims

1. A nuclear reactor including a pressure vessel housing a core of fissile material and an upper core plate substantially covering the core, a control rod guide tube having an extended axial length, for guiding a control rod assembly comprising a plurality of individual control rods, into and out of the core, the control rod guide tube extending between the upper core plate and an upper support plate supported above the upper core plate, the control rod guide tube comprising:a lower guide tube section connected at a first end to the upper core plate and terminating at a second end at a rigid intermediate coupling;an upper guide tube section connected at a first end portion to the upper support plate and terminating at a second end at the rigid intermediate coupling; andan extended control rod guide assembly supported substantially at the rigid intermediate coupling and extending axially, a finite distance into at least one of an interior of the lower guide tube section or the upper guide tube section, the extended control rod guide assembly being configured to provide support for the plurality of individual control rods, wherein the finite distance is substantially less than the extended axial length of the control rod guide tube, and wherein the extended control rod guide assembly comprises at least one flange installed in a recess in the intermediate coupling. 2. The nuclear reactor of claim 1 wherein at least some of the plurality of control rods are continuously guided over substantially an entire axial length of the extended control rod guide assembly. 3. A nuclear reactor including a pressure vessel housing a core of fissile material and an upper core plate substantially covering the core, a control rod guide tube having an extended axial length, for guiding a control rod assembly comprising a plurality of individual control rods, into and out of the core, the control rod guide tube extending between the upper core plate and an upper support plate supported above the upper core plate, the control rod guide tube comprising:a lower guide tube section connected at a first end to the upper core plate and terminating at a second end at a rigid intermediate coupling;an upper guide tube section connected at a first end portion to the upper support plate and terminating at a second end at the rigid intermediate coupling; andan extended control rod guide assembly supported substantially at the rigid intermediate coupling and extending axially, a finite distance into at least one of an interior of the lower guide tube section or the upper guide tube section, the extended control rod guide assembly being configured to provide support for the plurality of individual control rods, wherein the finite distance is substantially less than the extended axial length of the control rod guide tube, wherein at least some of the plurality of control rods are continuously guided over substantially an entire axial length of the extended control rod guide assembly, and wherein some of the control rods are guided over discrete axial sections of the extended control rod guide assembly. 4. The nuclear reactor of claim 3 wherein the control rods guided over continuous sections are provided with support by support channels extending through cardinal axes of the extended control rod guide assembly. 5. The nuclear reactor of claim 2 wherein all of the control rods are continuously guided over substantially the entire axial length of the extended control rod guide assembly. 6. The nuclear reactor of claim 5 wherein the extended control rod guide assembly extends axially approximately between 1.6 and 23 inches (4.1 and 58.4 cm). 7. The nuclear reactor of claim 6 wherein the extended control rod guide assembly extends axially approximately between 1.6 and 7 inches (4.1 and 17.8 cm). 8. The nuclear reactor of claim 1 wherein the extended control rod guide assembly has a first axially extending segment and a second axially extending segment with the first segment extending into the lower guide tube section and the second segment extending into the upper guide tube section, with the first axially extending segment and the second axially extending segment being supported at the rigid intermediate coupling. 9. The nuclear reactor of claim 1 wherein the extended control rod guide assembly extends axially approximately between 0.9 and 23 inches (2.3 and 58.4 cm). 10. The nuclear reactor of claim 9 wherein the extended control rod guide assembly more preferably extends axially approximately between 0.9 and 7 inches (2.3 and 17.8 cm). 11. The nuclear reactor of claim 1 wherein at least some of the plurality of control rods are continuously guided over substantially an entire axial length of the extended control rod guide assembly, and are provided with support by support channels extending through cardinal axes of the extended control rod guide assembly. 12. The nuclear reactor of claim 3 wherein the extended control rod guide assembly extends axially approximately between 1.6 and 23 inches (4.1 and 58.4 cm). 13. The nuclear reactor of claim 12 wherein the extended control rod guide assembly extends axially approximately between 1.6 and 7 inches (4.1 and 17.8 cm). 14. The nuclear reactor of claim 3 wherein the extended control rod guide assembly has a first axially extending segment and a second axially extending segment with the first segment extending into the lower guide tube section and the second segment extending into the upper guide tube section, with the first axially extending segment and the second axially extending segment being supported at the rigid intermediate coupling. 15. The nuclear reactor of claim 3 wherein the extended control rod guide assembly extends axially approximately between 0.9 and 23 inches (2.3 and 58.4 cm). 16. The nuclear reactor of claim 15 wherein the extended control rod guide assembly more preferably extends axially approximately between 0.9 and 7 inches (2.3 and 17.8 cm).