Patent Number: 
Section: claims

1. An apparatus comprising:at least one control rod comprising a neutron absorbing material;a control rod drive mechanism (CRDM) unit; anda control rod/CRDM coupling connecting the control rod and the CRDM unit such that the CRDM unit provides at least one of gray rod control and shutdown rod control for the at least one control rod;wherein the control rod/CRDM coupling includes a connecting rod having an average density greater than the density of stainless steel at room temperature, wherein the connecting rod comprises:a hollow or partially hollow connecting rod tube;a filler disposed in the interior volume of the hollow or partially hollow connecting rod tube, the filler comprising a material having a density greater than the density of stainless steel at room temperature, anda welded plug sealing off the interior volume of the hollow or partially hollow connecting rod tube with the filler disposed in the interior volume. 2. The apparatus as set forth in claim 1, wherein the hollow or partially hollow connecting rod tube is made of stainless steel. 3. The apparatus as set forth in claim 1, wherein the filler has a density of at least 16.2 grams per cubic centimeter at room temperature. 4. The apparatus as set forth in claim 1, wherein the hollow or partially hollow connecting rod tube comprises a material having a first density and the material comprising the filler has a density that is at least twice the first density. 5. The apparatus as set forth in claim 1, wherein the connecting rod further comprises:an additional element disposed in the hollow or partially hollow connecting rod tube, the additional element not being the filler comprising a material having a density greater than the density of stainless steel at room temperature, the additional element preventing the filler from moving inside the hollow or partially hollow connecting rod tube. 6. The apparatus as set forth in claim 1, wherein the connecting rod further comprises:a compressed spring disposed in the hollow or partially hollow connecting rod tube and pressing against the filler. 7. The apparatus as set forth in claim 6, wherein the spring is disposed below the filler in the hollow or partially hollow connecting rod tube such that the spring at least contributes to dissipating kinetic energy accrued by the filler during a SCRAM. 8. The apparatus as set forth in claim 3, wherein the hollow or partially hollow connecting rod tube is made of stainless steel. 9. The apparatus as set forth in claim 2, wherein the filler comprises a material selected from the group consisting of tungsten, depleted uranium, molybdenum, and tantalum. 10. The apparatus as set forth in claim 1, wherein the filler comprises a material selected from the group consisting of tungsten, depleted uranium, molybdenum, and tantalum. 11. An apparatus comprising:at least one control rod comprising a neutron absorbing material;a control rod drive mechanism (CRDM) unit; anda connecting rod having its lower end connected with the control rod and its upper end connected with the CRDM unit such that the CRDM unit provides at least one of gray rod control and shutdown rod control for the at least one control rod;wherein the connecting rod comprises (i) a hollow or partially hollow stainless steel rod tube having a length of 250 centimeters or greater and (ii) a filler material disposed inside the hollow or partially hollow stainless steel rod tube, the filler material having a density greater than the density of stainless steel at room temperature. 12. The apparatus of claim 11 wherein the at least one control rod comprises a plurality of control rods and the apparatus further comprises:a spider via which the lower end of the connecting rod is connected with the plurality of control rods. 13. An apparatus comprising:at least one control rod comprising a neutron absorbing material;a control rod drive mechanism (CRDM) unit;a connecting rod having its lower end connected with the control rod and its upper end connected with the CRDM unit such that the CRDM unit provides at least one of gray rod control and shutdown rod control for the at least one control rod; anda detachable attachment assembly via which the lower end of the connecting rod connects with the at least one control rod, the detachable attachment assembly including mating male and female attachment components;wherein the connecting rod comprises (i) a hollow or partially hollow rod tube made of a rod tube material and (ii) a heavy material disposed inside the hollow or partially hollow rod tube, the heavy material having a density greater than the density of the rod tube material, the heavy material disposed inside the hollow or partially hollow rod tube being different from the male and female attachment components of the detachable attachment assembly. 14. The apparatus of claim 13 wherein the rod tube material is stainless steel. 15. The apparatus of claim 14 wherein the heavy material comprises tungsten. 16. The apparatus of claim 14 wherein the heavy material comprises depleted uranium. 17. The apparatus of claim 14 wherein the heavy material comprises molybdenum. 18. The apparatus of claim 14 wherein the heavy material comprises tantalum. 19. The apparatus of claim 13 wherein the heavy material comprises tungsten. 20. The apparatus of claim 13 wherein the heavy material comprises depleted uranium. 21. The apparatus of claim 13 wherein the heavy material comprises molybdenum. 22. The apparatus of claim 13 wherein the heavy material comprises tantalum. 23. The apparatus of claim 13 wherein the heavy material has a density that is at least twice the density of the rod tube material. 24. The apparatus of claim 23 wherein the rod tube material is stainless steel. 25. The apparatus of claim 13 wherein the at least one control rod comprises a plurality of control rods and the apparatus further comprises:a spider via which the lower end of the connecting rod is connected with the plurality of control rods, the spider including the female attachment component of the detachable attachment assembly and the lower end of the connecting rod including the male attachment component of the detachable attachment assembly. 26. The apparatus as set forth in claim 1, wherein the hollow or partially hollow connecting rod tube has a length of 250 centimeters or greater. 27. The apparatus as set forth in claim 13, wherein the hollow or partially hollow connecting rod tube has a length of 250 centimeters or greater. 28. The apparatus as set forth in claim 11, wherein the connecting rod further comprises:a welded plug sealing off the interior volume of the hollow or partially hollow connecting rod tube. 29. The apparatus as set forth in claim 13, wherein the connecting rod further comprises:a welded plug sealing off the interior volume of the hollow or partially hollow connecting rod tube. 30. The apparatus as set forth in claim 1, further comprising:a detachable attachment assembly via which a lower end of the connecting rod connects with the at least one control rod, the detachable attachment assembly including mating male and female attachment components;wherein the filler disposed in the hollow or partially hollow rod tube is different from the male and female attachment components of the detachable attachment assembly. 31. The apparatus as set forth in claim 11, further comprising:a detachable attachment assembly via which the lower end of the connecting rod connects with the at least one control rod, the detachable attachment assembly including mating male and female attachment components;wherein the filler disposed inside the hollow or partially hollow stainless steel rod tube is different from the male and female attachment components of the detachable attachment assembly. 32. An apparatus comprising:at least one control rod comprising a neutron absorbing material;a control rod drive mechanism (CRDM) unit; anda connecting rod having its lower end connected with the control rod and its upper end connected with the CRDM unit such that the CRDM unit provides at least one of gray rod control and shutdown rod control for the at least one control rod;wherein the connecting rod comprises (i) a hollow or partially hollow rod tube made of a rod tube material and (ii) a heavy material comprising depleted uranium disposed inside the hollow or partially hollow rod tube, the heavy material having a density greater than the density of the rod tube material. 33. The apparatus of claim 32 wherein the rod tube material is stainless steel.