Patent Number: 
Section: claims

1. A gray rod for a rod control assembly of a pressurized water nuclear reactor, said gray rod comprising:an elongated tubular member having a first end, a second end, an outer diameter, and a length; anda neutron-absorber having an outer diameter and a length extending from a first end to a second end, disposed within said elongated tubular member over at least a portion of said length of said elongated tubular member, generally toward the first end thereof, said neutron-absorber comprising only one absorber material, said only one absorber material having a 2200 m/s neutron absorption microscopic capture cross-section of from 10 to 30 barns,wherein neutron absorption is substantially uniform over said length of said neutron-absorber. 2. The gray rod of claim 1 wherein said absorber material is selected from the group consisting of substantially-pure tungsten at near or full theoretical density; reduced density or porous tungsten metal; tungsten-based alloys such as tungsten-rhenium and tungsten-nickel-iron; tungsten-based compounds such as tungsten carbide and tungsten oxides; substantially pure scandium, ytterbium and manganese; scandium-, ytterbium- and manganese-based alloys, and scandium-, ytterbium- and manganese-based compounds. 3. The gray rod of claim 1 wherein said absorber material is arranged in a cylindrical geometry. 4. The gray rod of claim 1 wherein the neutron-absorber has a material density of from 16.5 to 19.4 g/cm3. 5. The gray rod of claim 1 wherein the neutron-absorber is substantially pure tungsten. 6. The gray rod of claim 1 wherein the outer diameter of the neutron-absorber is from 0.15 to 0.40 inch and the outer diameter of the elongated tubular member is from 0.37 to 0.45 inch. 7. The gray rod of claim 1 further comprising a support tube structured to surround said neutron-absorber within said elongated tubular member. 8. The gray rod of claim 7 wherein the support tube comprises a material selected from the group consisting of zirconium and zirconium-based alloys, aluminum metal, nickel-based alloys and stainless steel. 9. The gray rod of claim 7 wherein the support tube material is selected to enhance neutron absorption of the gray rod. 10. The gray rod of claim 7 wherein the support tube material has a lower 2200 m/s neutron absorption microscopic capture cross section than the neutron-absorber. 11. The gray rod of claim 9 wherein the support tube material has a 2200 m/s neutron absorption microscopic capture cross section of from 2 to 6 barns. 12. The gray rod of claim 9 wherein the support tube material has a density of from 7 to 9 gm/cm3. 13. The gray rod of claim 9 wherein the support tube material is selected from the group consisting of nickel-based metal alloys and stainless steel. 14. The gray rod of claim 7 wherein the outer diameter of the neutron-absorber is from 0.10 to 0.38 inch, the outer diameter of the elongated tubular member is from 0.37 to 0.45 inch and the support tube has a wall thickness of from 0.01 to 0.10 inch. 15. The gray rod of claim 7 wherein said neutron-absorber is substantially concentrically disposed within said elongated tubular member; and wherein said support tube has a wall thickness which is substantially defined by the space between the second outer diameter and the inner diameter of said elongated tubular member. 16. An advanced gray rod control assembly for a pressurized water nuclear reactor, said advanced gray rod control assembly comprising:a plurality of gray rods wherein each of said gray rods comprises:an elongated tubular member having a first end, a second end, and an outer diameter; anda neutron-absorber having a length extending from a first end to a second end, disposed within said elongated tubular member toward the first end thereof, said neutron-absorber comprising only one absorber material, said only one absorber material having a 2200 m/s neutron absorption microscopic capture cross-section of from 10 to 30 barns,wherein neutron absorption is substantially uniform over said length of said neutron-absorber. 17. The advanced gray rod control assembly of claim 16 wherein said neutron-absorber is distributed among all of said gray rods of said plurality of gray rods. 18. The advanced gray rod control assembly of claim 17 wherein said plurality of gray rods comprises 24 gray rods; and wherein said neutron-absorber is distributed generally equally among all 24 gray rods. 19. The advanced gray rod control assembly of claim 16 wherein said absorber material is selected from the group consisting of substantially-pure tungsten at near or full theoretical density; reduced density or porous tungsten metal; tungsten-based alloys such as tungsten-rhenium and tungsten-nickel-iron; tungsten-based compounds such as tungsten carbide and tungsten oxides; substantially pure scandium, ytterbium and manganese; scandium-, ytterbium- and manganese-based alloys, and scandium-, ytterbium- and manganese-based compounds. 20. The advanced gray rod control assembly of claim 16 wherein the neutron-absorber is substantially pure tungsten. 21. The advanced gray rod control assembly of claim 16 wherein the neutron-absorber has a material density of from 16.5 to 19.4 g/cm3. 22. The advanced gray rod assembly of claim 16 further comprising a support tube structured to surround said neutron-absorber within said elongated tubular member. 23. The advanced gray rod control assembly of claim 22 wherein the support tube comprises a material selected from the group consisting of zirconium and zirconium-based alloys, aluminum metal, nickel-based alloys and stainless steel. 24. The advanced gray rod control assembly of claim 22 wherein the support tube material has a 2200 m/s neutron absorption microscopic capture cross section of from 2 to 6 barns. 25. The advanced gray rod control assembly of claim 22 wherein the support tube material has a density of from 7 to 9 gm/cm3. 26. The advanced gray rod control assembly of claim 23 wherein the support tube material is selected from the group consisting of nickel-based metal alloys and stainless steel. 27. A pressurized water nuclear reactor having a gray rod control assembly, said gray rod control assembly comprising:a plurality of gray rod assemblies;a plurality of gray rods, wherein each of said gray rods comprises:an elongated tubular member having a first end, a second end, and an outer diameter; anda neutron-absorber having a length extending from a first end to a second end, disposed within said elongated tubular member generally toward the first end thereof, said neutron-absorber comprising only one absorber material, said only one absorber material having a 2200 m/s neutron absorption microscopic capture cross section of from 10 to 30 barns,wherein neutron absorption is substantially uniform over said length of said neutron-absorber. 28. The nuclear reactor of claim 27 wherein said neutron-absorber is distributed among all of said gray rod assemblies of said gray rod control assembly. 29. The nuclear reactor of claim 28 wherein said plurality of gray rod assemblies comprises 24 gray rod assemblies; and wherein said neutron-absorber is distributed generally equally among all 24 gray rod assemblies of said gray rod control assembly. 30. The nuclear reactor of claim 27 further comprising a support tube structured to surround said neutron-absorber within said elongated tubular member. 31. A gray rod for a rod control assembly of a pressurized water nuclear reactor, said gray rod comprising:an elongated tubular member having a first end, a second end, and a length; andonly one neutron-absorber material disposed within said elongated tubular member over at least a portion of said length of said elongated tubular member, generally toward the first end thereof, said only one neutron-absorber material selected from the group consisting of a substantially pure material, reduced density or porous material metal, material-based alloy and material-based compound, said only one neutron-absorber material having a 2200 m/s neutron absorption microscopic capture cross-section of from 10 to 30 barns.