Patent Number: 050341847
Section: claims

1. In a control assembly for a nuclear reactor having a piston within a cylinder controlling the longitudinal movement of a control element during insertion into a reactor core, the improvement comprising: an accelerating fluid of predetermined volume and pressure propelling said piston, causing rapid insertion of said control element,  a decelerating fluid of decreasing volume and pressure decelerating the movement of said piston, and  absorbing means arresting the longitudinal movement of said control element at the point of full insertion of said control element into said reactor core,  wherein said decelerating fluid is exhausted through an orifice which is adjustable to control the rate of exhaust, and wherein said orifice is adjusted by means of an end cap of varying diameter which is operatively connected with said absorbing means and is movable longitudinally in said cylinder. 2. The control assembly improvement defined in claim 1, wherein the longitudinal movement of said absorbing means and end cap causes said orifice to open or close, increasing or decreasing, respectively, the rate of exhaust of said decelerating fluid. 3. The control assembly improvement defined in claim 2, wherein said decelerating fluid is contained within said cylinder tube surrounding said piston and within a compression tube in fluid communication with the interior of said cylinder tube. 4. The control assembly improvement defined in claim 3, where said accelerating fluid is air. 5. The control assembly improvement defined in claim 3, wherein said decelerating fluid is air. 6. The control assembly improvement defined in claim 3, wherein said accelerating fluid is a compressible gas. 7. The control assembly improvement defined in claim 3, wherein said decelerating fluid is a compressible gas.