Patent Number: 
Section: claims

1. A pressurized water nuclear reactor pressure vessel comprising:an upper support plate;a removable upper head;a plurality of rod cluster control assembly upper guide tubes, each guide tube extending from the upper support plate toward the removable upper head; anda plurality of in-core instrumentation assembly column extensions, each column extension continuously extending from and being supported by a horizontal section of the support plate and extending toward the removable upper head to an elevation substantially at or above the rod cluster control assembly upper guide tubing, and each column extension connected by a bracket to one of the upper guide tubes and each column extension provides support for in-core instrumentation over substantially the entire length of the column extension. 2. The pressurized water reactor pressure vessel of claim 1 wherein coolant is conveyed to the reactor pressure vessel by a reactor coolant pump having a rotation frequency and wherein an assembly of the upper guide tube attached by the bracket to the upper mounted instrumentation columns have natural resonant vibration frequencies substantially different from the excitation frequency of the reactor coolant pump. 3. The pressurized water reactor pressure vessel of claim 1 wherein each column extension is connected by bracket to a different one of the upper guide tubes. 4. The pressurized water reactor pressure vessel of claim 1 wherein the column extensions are respectively connected to or adjacent the top of the upper guide tubes. 5. The pressurized water reactor pressure vessel of claim 1 wherein the bracket is welded to the upper guide tube at one end and the column extension is screwed into the bracket at another end. 6. The pressurized water reactor pressure vessel of claim 1 wherein each of the column extensions is fastened at one end to the upper support plate. 7. The pressurized water reactor pressure vessel of claim 1 wherein one end of each of the column extensions is aligned with its own penetration in the upper head. 8. The pressurized water reactor pressure vessel of claim 1 wherein at least some of the in-core instrument assembly column extensions provide moveable in-core detectors access to a nuclear fuel assembly within a core within the pressure vessel. 9. The pressurized water reactor pressure vessel of claim 1 wherein a lower end of the column extensions are respectively fastened to a support column that extends between the upper support plate and an upper core plate. 10. The pressurized water reactor pressure vessel of claim 1 wherein the lower end of the column extensions are respectively screwed into the support columns. 11. The pressurized water reactor pressure vessel of claim 1 wherein at least some of the column extensions extend above the upper guide tubes. 12. The pressurized water reactor pressure vessel of claim 1 wherein the instrumentation assembly column extensions end in funnels between the upper support plate and the removable upper head. 13. The pressurized water reactor pressure vessel of claim 1 further comprising:a core including a plurality of fuel assemblies;an upper core plate situated over the fuel assemblies; anda plurality of support columns extending vertically between the upper core plate at a lower end of the support columns and the upper support plate at an upper end of the support columns, the support columns respectively in line and communicating with a corresponding one of the in-core instrumentation column extensions. 14. The pressurized water reactor pressure vessel of claim 1 wherein the instrumentation assembly column extensions are substantially straight and substantially rigid and guide an instrumentation assembly substantially through the instrumentation assembly column extension's entire length. 15. A pressurized water reactor power generating facility having a pressure vessel comprising:an upper support plate;a removable upper head;a plurality of rod cluster control assembly upper guide tubes, each upper guide tube extending from the support plate toward the removable upper head; anda plurality of in-core instrumentation assembly column extensions, each column extension continuously extending from the upper support plate toward the removable upper head to an elevation substantially at or above the rod cluster control assembly upper guide tubing, and each column extension connected by a bracket to one of the upper guide tubes and each column extension provides support for in-core instrumentation over substantially the entire length of the column extension.