Patent Number: 
Section: claims

1. A control rod/control rod drive mechanism (CRDM) coupling comprising:a connecting rod operatively connected with a CRDM unit to provide at least one of gray rod control functionality and shutdown rod control functionality; anda terminal element connected with a lower end of the connecting rod, the terminal element including a casing defining at least one cavity and a filler disposed in the at least one cavity, the filler comprising heavy material having a higher density than a material comprising the casing, the terminal element further connected with an upper end of at least one control rod. 2. The control rod/CRDM coupling as set forth in claim 1, wherein the material comprising the casing is stainless steel. 3. The control rod/CRDM coupling as set forth in claim 2, wherein the terminal element has an average density that is greater than the density of stainless steel. 4. The control rod/CRDM coupling as set forth in claim 2, wherein the heavy material has a density of at least 16.2 grams per cubic centimeter at room temperature. 5. The control rod/CRDM coupling as set forth in claim 2, wherein the heavy material is selected from a group consisting of tungsten, depleted uranium, molybdenum, and tantalum. 6. The control rod/CRDM coupling as set forth in claim 2, wherein the filler comprises heavy material in the form of a powder or granulation. 7. The control rod/CRDM coupling as set forth in claim 1, wherein the heavy material has a density that is at least twice the density of the material comprising the casing. 8. The control rod/CRDM coupling as set forth in claim 1, wherein the terminal element further includes one or more casing cover plates that seal the at least one cavity of the casing. 9. The control rod/CRDM coupling as set forth in claim 1, wherein the terminal element has elongation in a SCRAM direction that is at least as large as a largest dimension of the terminal element transverse to the SCRAM direction. 10. The control rod/CRDM coupling as set forth in claim 1, wherein a cross-section of the terminal element oriented broadside to a SCRAM direction has an area fill factor of at least 50%. 11. The control rod/CRDM coupling as set forth in claim 1, wherein the connecting rod comprises a hollow connecting rod tube and a filler disposed in the hollow connecting rod tube, the filler comprising heavy material having a higher density than a material comprising the hollow connecting rod tube. 12. The control rod/CRDM coupling as set forth in claim 1, further comprising a J-Lock coupling connecting the terminal element with the lower end of the connecting rod. 13. An apparatus comprising:a nuclear reactor pressure vessel; anda control rod assembly including at least one movable control rod comprising a neutron absorbing material, a control rod drive mechanism (CRDM) for controlling movement of the at least one control rod, and a coupling operatively connecting the at least one control rod and the CRDM, the coupling including a connecting rod engaged with the CRDM and a terminal element connected with a lower end of the connecting rod, the terminal element including a first portion comprising a first material having a first density and a second portion comprising a second material having a second density that is greater than the first density, the terminal element further connecting with the at least one control rod, wherein the connecting rod is detachably engaged with the CRDM such that detachment of the detachable engagement causes a translating assembly including at least the connecting rod, the terminal element, and the at least one control rod to fall toward a reactor core disposed in a lower region of the nuclear reactor pressure vessel, and wherein the first portion of the terminal element supports or contains the second portion of the terminal element. 14. An apparatus comprising:a nuclear reactor pressure vessel; anda control rod assembly including at least one movable control rod comprising a neutron absorbing material, a control rod drive mechanism (CRDM) for controlling movement of the at least one control rod, and a coupling operatively connecting the at least one control rod and the CRDM, the coupling including a connecting rod engaged with the CRDM and a terminal element connected with a lower end of the connecting rod, the terminal element including a first portion comprising a first material having a first density and a second portion comprising a second material having a second density that is greater than the first density, the terminal element further connecting with the at least one control rod, wherein the first portion of the terminal element comprises a steel enclosure enclosing the second portion of the terminal element. 15. The apparatus as set forth in claim 14, wherein the second density is at least 16.2 grams per cubic centimeter at room temperature.