Patent Number: 
Section: claims

1. An apparatus comprising:a control rod guide frame having a central passage of constant cross-section as a function of position along a central axis that passes through the central passage, the central passage sized and shaped to guide a traveling assembly including at least one control rod as the traveling assembly moves along the central axis,wherein the control rod guide frame comprises at least two radial guide frame sections that are secured to each other in alternating up and down orientations and configured to surround and define the central passage. 2. The apparatus as set forth in claim 1, wherein each radial guide frame section comprises an extruded radial guide frame section. 3. The apparatus as set forth in claim 2, wherein the central passage includes control rod guidance channels parallel to the central axis and machined into the extruded radial guide frame sections. 4. The apparatus as set forth in claim 2, wherein the extruded radial guide frame sections are made of extruded steel. 5. The apparatus as set forth in claim 1, wherein the at least two radial guide frame sections consist of between four and eight radial guide frame sections. 6. The apparatus as set forth in claim 1, wherein the central passage includes control rod guidance channels parallel to the central axis. 7. The apparatus as set forth in claim 1, wherein the control rod guide frame further comprises:bands wrapped around the outside of the at least two radial guide frame sections to secure the at least two radial guide frame sections together to define a control rod guide frame body of the control rod guide frame. 8. The apparatus as set forth in claim 1, wherein the control rod guide frame further comprises:welds at interfaces between the at least two radial guide frame sections that secure the at least two guide frame sections together to define a control rod guide frame body of the control rod guide frame. 9. The apparatus as set forth in claim 1, wherein the at least two radial guide frame sections secured around and defining the central passage define a guide frame body, and the control rod guide frame further comprises:a lower plate connected to a lower end of the guide frame body; andan upper plate connected to an upper end of the guide frame body. 10. The apparatus as set forth in claim 9, wherein each radial guide frame section is a single element that extends the entire length along the central axis between the lower and upper plates. 11. The apparatus as set forth in claim 1, wherein the at least two radial guide frame sections secured around and defining the central passage define a guide frame body having a constant outer perimeter as a function of position along a center axis. 12. The apparatus as set forth in claim 1, wherein the at least two radial guide frame sections secured around and defining the central passage define a guide frame body, and the radial guide frame sections include flow slot passages providing fluid communication between the central passage and the exterior of the guide frame body. 13. The apparatus as set forth in claim 1, wherein the control rod guide frame further comprises:keys disposed in alignment features of the at least two radial guide frame sections. 14. The apparatus as set forth in claim 1, further comprising:a nuclear reactor core comprising a fissile material; anda control rod drive mechanism (CRDM) arranged to control movement of the traveling assembly as the traveling assembly moves along the central axis. 15. The apparatus as set forth in claim 14, further comprising a reactor pressure vessel that contains the nuclear reactor core, the CRDM, and the control rod guide frame.