Patent Number: 
Section: claims

1. An apparatus comprising:a connecting rod of a control rod assembly of a nuclear reactor, the connecting rod including:a hollow or partially hollow connecting rod tube defining an interior volume and comprising a first material having a first density at room temperature, anda filler disposed in the interior volume of the hollow or partially hollow connecting rod tube, the filler comprising a second material having a second density at room temperature that is greater than the first density,wherein the connecting rod further comprises a welded plug sealing off the interior volume of the hollow or partially hollow connecting rod tube. 2. 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 and pressing against the filler. 3. The apparatus as set forth in claim 1, wherein the connecting rod further comprises:a less dense filler disposed in the hollow or partially hollow connecting rod to prevent the filler from moving inside the hollow or partially hollow connecting rod tube, the less dense filler having a third density at room temperature that is less than or equal to the first density. 4. The apparatus as set forth in claim 1, wherein the second density is at least twice the first density. 5. The apparatus as set forth in claim 1, wherein the second density is at least 16.2 grams per cubic centimeter at room temperature. 6. The apparatus as set forth in claim 1, wherein the first material is stainless steel. 7. The apparatus as set forth in claim 6, wherein the second material is selected from a group consisting of tungsten, depleted uranium, molybdenum, and tantalum. 8. The apparatus as set forth in claim 1, wherein the second material is selected from a group consisting of tungsten, depleted uranium, molybdenum, and tantalum. 9. The apparatus as set forth in claim 1, wherein the filler comprises one of a plurality of rods and a plurality of slugs comprising the second material which are disposed in the hollow or partially hollow connecting rod tube.