Patent Number: 
Section: claims

1. A method for installing an extension tube in a nuclear reactor comprising a control rod drive mechanism (CRDM) housing with a non-threaded head penetration nozzle and a thermal sleeve disposed therein, the method comprising:removing the thermal sleeve from the CRDM housing;machining an end of the non-threaded head penetration nozzle;installing and aligning a threaded adapter to the machined end of the non-threaded head penetration nozzle;joining the threaded adapter to the machined end of the non-threaded head penetration nozzle;machining a bore defined by the non-threaded head penetration nozzle;machining a bore defined by the threaded adapter;machining an outside diameter of a joint defined between the machined end of the non-threaded head penetration nozzle and the threaded adapter;installing the extension tube to the threaded adapter, wherein the threaded adapter and the extension tube replace the thermal sleeve removed from the CRDM housing; andinstalling retention fillets welds between the extension tube and the threaded adapter. 2. The method of claim 1, wherein machining the end of the non-threaded head penetration nozzle comprises:machining a face of the non-threaded head penetration nozzle to reduce an outer elongated length thereof; andmachining an inside diameter of the non-threaded head penetration nozzle to increase a diameter of a portion of the bore defined by the non-threaded head penetration nozzle. 3. The method of claim 1, wherein joining the threaded adapter to the machined end of the non-threaded head penetration nozzle comprises performing a penetration welding technique to form the joint. 4. The method of claim 3, wherein joining the threaded adapter to the machined end of the non-threaded head penetration nozzle comprises performing a full penetration welding technique to form the joint. 5. The method of claim 1, wherein installing the extension tube to the threaded adapter comprises:threading the extension tube on the threaded adapter; andtorqueing the extension tube on the threaded adapter. 6. The method of claim 1, comprising gauging an alignment of the extension tube relative to the non-threaded head penetration nozzle. 7. The method of claim 1, comprising installing a guide funnel to a non-threaded end of the extension tube. 8. The method of claim 7, comprising installing a compressible guide sleeve to the non-threaded head penetration nozzle. 9. The method of claim 8, wherein installing the compressible guide sleeve to the non-threaded head penetration nozzle comprises:compressing the compressible guide sleeve;inserting the compressed guide sleeve through the extension tube and the non-threaded head penetration nozzle; andreleasing the compression of the compressible guide sleeve to retainably couple the compressible guide sleeve to the non-threaded head penetration nozzle. 10. The method of claim 9, wherein the compressible guide sleeve comprises multiple leaf compressible flex sections, wherein each of the multiple leaf compressible flex sections comprises a flange, the method comprising:compressing the multiple leaf compressible flex sections to contract the flanges prior to inserting the compressed guide sleeve into the extension tube; andreleasing the compression of the compressible guide sleeve after insertion into the non-threaded head penetration nozzle to release the flanges to engage a counterbore ledge defined by the non-threaded head penetration nozzle. 11. The method of claim 10, comprising performing a gauging of an alignment of the extension tube. 12. The method of claim 11, wherein the compressible guide sleeve is inserted into the guide funnel from a position below a reactor vessel head of the nuclear reactor. 13. The method of claim 1, wherein the extension tube is installed from a position below a reactor vessel head of the nuclear reactor. 14. A method for installing an extension tube in a nuclear reactor comprising a control rod drive mechanism (CRDM) housing with a non-threaded head penetration nozzle and a thermal sleeve disposed therein, the method comprising:removing the thermal sleeve from the CRDM housing;coupling a threaded adapter to an end of the non-threaded head penetration nozzle; andcoupling the extension tube to the threaded adapter, wherein the threaded adapter and the extension tube replace the thermal sleeve removed from the CRDM housing. 15. The method of claim 14, further comprising machining the end of the non-threaded head penetration nozzle, wherein coupling the threaded adapter to the end of the non-threaded head penetration nozzle comprises coupling the threaded adapter to the machined end of the non-threaded head penetration nozzle. 16. The method of claim 15, wherein machining the end of the non-threaded head penetration nozzle comprises:machining a face of the non-threaded head penetration nozzle to reduce an outer elongated length thereof; andmachining an inside diameter of the non-threaded head penetration nozzle to increase a diameter of a portion of a bore defined by the non-threaded head penetration nozzle. 17. The method of claim 15, wherein coupling the threaded adapter to the machined end of the non-threaded head penetration nozzle comprises performing a welding technique to form a joint. 18. The method of claim 17, further comprising machining an outside diameter of the joint defined between the machined end of the non-threaded head penetration nozzle and the threaded adapter. 19. The method of claim 14, further comprising:machining a bore defined by the non-threaded head penetration nozzle; andmachining a bore defined by the threaded adapter. 20. The method of claim 14, further comprising installing retention fillets welds between the extension tube and the threaded adapter.