Patent Number: 043495079
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an absorber rod 10 protruding into the internal space 12 of the pressure vessel 14 of a nuclear reactor. The upper end of the absorber rod 10 is connected with a drive piston 16 guided in a cylinder 18. The drive piston 16 and the absorber rod 10 constitute the absorber unit 20. The drive piston 16 has an upwardly directed axial, cylindrical extension 22 with a diameter smaller than the piston surface itself. It penetrates the front wall of the cylinder 18 and terminates in a space 24, which is contiguous with the inner space of the pressure vessel. The terminal surface of the extension 22 arranged transversely, preferably perpendicularly to the longitudinal axis 26 or to the direction of motion of the absorber unit 20, respectively, forms the equalizing surface 28. In order to accomplish the insertion and retraction of the absorber rod 10, the drive piston 16 is designed for dual action, i.e., the top side of the drive piston may be exposed to a fluid drive medium, for example, hydraulic oil by means of a first control line 30 and the bottom side of the drive piston by means of a second control line 32, so that the vertical motion desired will take place. Auxiliary lines 34 are further provided in the cylinder 18, to drain leakages in the event the sealing gaskets, schematically indicated at 36, do not provide absolute sealing. In order to insert the absorber rod 10 into its position of maximum absorption, a drive medium is conducted under pressure to the cylinder 18 by way of the first control line 30 so that the drive piston 16, together with the absorber rod 10 connected with it is pressured downward and into this area where absorption can more easily occur. At the same time, the medium present on the opposite side of the drive piston 16 is expelled from the cylinder 18 by way of the second control line 32. The insertion of the absorber rod 10 and absorber unit 20 respectively is completely unaffected by the internal pressure prevailing in the internal space 12 because the driving force exerted by the internal pressure on the transverse surface 38 of the absorber rod and directed vertically upwards, is compensated by the force applied by the internal pressure on the equalizing surface 28. These forces are nearly equal and act in opposite directions. By correlating the equalizing surface 28 with the surface 38 at the end of the absorber rod, equalization may be rendered complete. This correlation can also take into consideration the weight of the absorber unit 20, acting in the downward direction. As a direct result of the above-described compensation of the inner pressure of the internal space 12 on the absorber unit 20, force, acting as a driving, a drop in or a failure of the pressure of the drive medium conducted by way of the first control line 30 in the cylinder 18, or a change in the internal pressure in the inner space 12, will initiate no motion of the absorber unit 20. The absorber unit of the vessel 20 will remain in its prevailing position. This arrangement, therefore, compensates the internal forces of the vessel acting to drive the absorber rod into a retracting position by permitting the same forces to act on both sides of the absorber unit. FIG. 2 represents a variation of the embodiment of FIG. 1. The difference essentially comprises the arrangement of the absorber rod 10 in cooperation with a drive piston 40 and another drive piston 42. The latter drive piston 42 is formed by an upper axial extension of the absorber unit 20. Both drive pistons 40 and 42 have their own working spaces in the cylinder 18 with the drive piston 40 effecting the upward motion, i.e. the retraction of the absorber rod and the drive piston 42 effecting the downward motion, i.e. the insertion of the absorber rod. The equalizing surface 44 is arranged on the outermost side of the drive piston 40. The opposite side of this surface is exposed to the action of a fluid drive medium by way of the control line 32. In order to apply the equalizing forces to the equalizing surface 44, the cylinder space 46 adjacent to the equalizing surface 44 is connected by way of an orifice 48 with the inner space 12 of the pressure vessel 14. To obtain complete compensation of the forces applied by the internal pressure of the pressure vessel on the absorber unit 20, the size of the surface 38 at the end of the absorber rod 10 is correlated with the size of the equalizing surface 44, which is in this case annularly cylindrical. The downward acting weight of the absorber unit 20 is also taken into account in an advantageous variation of this embodiment. FIG. 2 represents an embodiment of the invention wherein the absorber unit features both the piston 50 provided for the insertion of the absorber rod 10 and the piston 52 effecting the retraction of the absorber rod with larger diameters than the absorber rod 10. As clearly shown in FIG. 3, the pressure of the internal space 12 acting on the equalizing surface 54 compensates the upward acting drive force applied to the circular surface 38 and the cylindrical annular surface 56. FIG. 4 shows yet another prefered embodiment of the invention wherein the absorber unit 20 is arranged for internal cooling of the absorber rod. For this purpose, both the absorber rod 10 and the corresponding drive piston 58 have hollow, cylindrical configurations. The internal space 60 of the rod 10 is exposed to a fluid driving medium which exits into the internal space 12 of the pressure vessel 14 by way of radial orifices 62 arranged in the vicinity of the bottom of the absorber rod 10. The cooling medium is supplied by way of a channel 64 provided in the cylinder 18 which is connected by way of a gap 66 between the wall of the piston and the cylinder 18 with the internal space 60. During operation of this embodiment, the cooling medium flows through the channel 64, the gap 66 and the orifices 62 in the internal space 12 of the pressure vessel 14, whereby the dynamic pressure of the cooling medium acts in addition to the pressure of the internal space on the inner bottom surface of the absorber rod 10. Thus the inner bottom surface of the absorber rod 10 is used as the equalizing surface 68. In order to obtain compensation of the forces acting in the vertical direction on the absorber unit 20, the surface 38 and the equalizing surface 68 are correlated with each other and adjusted in view of the dynamic pressure acting on the equalizing surface 68 and the internal pressure in the space 12. The weight of the absorber unit itself acting in the direction of the dynamic pressure is also considered in a prefered embodiment of this arrangement.