Patent Number: 047132108
Section: description

Referring to FIG. 1, a control rod R and a control rod drive D are illustrated connected by the driveline L. The control rod is provided with a handle section H which handle section is engaged by a grapple section G. Drive D is conventional and only schematically illustrated. Specifically a drive gear motor 14 revolves a screw drive 16 which is received in a female drive nut 18 on the side of the driveline L. Presuming rod R is engaged at handle H by grapple G, up and down movement of drive nut 18 correspondly moves driveline L to effect withdrawal and insertion of rod R into the reactor. Driveline L consists of two discrete segments. First, there is a tension rod T. Second there is an outer cylinder C. As will hereinafter become more apparent by relative downward movement of tension rod T relative to cylinder C, release of grapple mechanism G to drop handle H can occur. Such movement can occur by one of two expedients. First, it will be seen that tension rod T includes an upper flange 20 for abutment to an electromagnet 22. Providing magnet 22 is energized, tension rod T will remain in the upper position with flange 20 abutted to electromagnet 22. Grapple G will remain closed with handle H therein. If magnet 22 has its power interrupted, the rod is dropped. Secondly, it will be understood that tension rod T is made of a material having a high index of thermal expansion and cylinder C is made of a material having a low index of thermal expansion. Upon thermal heating of the drive line L, tension rod T will move downwardly with respect to cylinder C. As will be hereinafter be set forth, the grapple mechanism G will open. Handle H will be released. Rod R will drop interiorly of the reactor. It will be understood that the control rod mechanism is preferably used interior of a sodium cooled fast breeder reactor. Accordingly, sodium and an inert cover gas 26 are maintained at the top of the reactor. In order to maintain isolation of the inert cover gas from the atmosphere, a first exterior bellows 28 surrounds the driveline L and is connected between the reactor at 30 and the driveline at 32. A second bellows mechanism is connected between the interior of cylinder C at 34 and the tension rod at 36. The reader will understand that a fluid type seal exists within the driveline L to prevent contamination with atmospheric gas. Having set forth the overall construction of the drive mechanism, attention will now be devoted to FIGS. 3A, 3B, 4A, 4B and 4C. The handle segment H at the upper end of the rod R will first be discussed with reference to FIG. 3A. Thereafter, the grapple segments will be set forth with reference to FIGS. 3A, 3B, 4A, 4B, and 4C. Rod R is typically connected by a cylindrical rod handle 40. As shown here, handle 40 flares outwardly in an inverted frustum to expanded cylindrical portion 43. Thereafter, the handle portion again decreases in section at contracting frustum portion 44. An upward flange portion 45 terminates the upper handle surface. A cylindrical centering pin 47 protrudes upwardly from handle surface 45. It terminates in a gathering pin point 49. Handle H forms essentially a male member. This male member is received in the female concavity of the grapple G. Centering pin 47 is received in the lower portion of the tension rod T, which lower portion will now be described. Tension rod T at lower end 50 defines a flange 52. Flange 52 includes a central pin receiving aperture 54. Aperture 54 includes lowered gathering surface 56. It will therefore be understood that when tension rod T is lowered towards handle H, centering of the pin 47 within the aperture 54 will occur. Turning now to FIG. 4A, a grapple segment S is illustrated. Seeing FIG. 4B it can be seen that each grapple segment S comprises 60.degree. (degrees) of a total grapple mechanism G. Grapple segment S will first be described with respect to that section which confronts the handle H. Thereafter, the grapple segment will be described with respect to the exterior portion which confronts the interior lower portion of cylinder C. Each grapple segment is rounded. Since six grapple segments define a circular grapple, the segments each include 60.degree. (degrees) of curvature. For simplicity, the following description will include a description of the profile of a longitudinal section. The reader's understanding of the curvature of all the segments will be assumed. There are two exceptions to this curvature. These exceptions are surfaces 72 and 74. As will hereinafter become apparent, these are surfaces on which the segments rock. A straight surface is preferred. Grapple segment S includes a lower gathering surface 60. This surface typically bears against frustum 44 on handle H when handle H is received causing the segment S to pivot outwardly. (See FIG. 3A.) A constriction point 64 includes an upper beveled segment 62. When six such segments are combined, the respective combined segments provide a female cavity on which frustum 42 of handle H rests to effect engagement between the grapple G and the handle H. (See FIG. 3A again.) The interior of the segments S must contain in the entirety the handle H. Therefore when frustum 42 is contained at segment 62, cylindrical portion 43 abuts indentation 63. Upper member 68 accommodates the profile of frustum portion 44. Segment S is designed for pivot about flange 52 on the lower end of tension rod T. Accordingly, there is a flange receiving indentation 70. Indentation 70 includes upper bearing surface 72 for bearing on the top surface of flange 52 and lower bearing surface 74 for bearing on the bottom surface of flange 52. Pivotal interaction between the top surface 45 of the enlarged portion of the handle H and each segment is required. Therefore an inwardly extending segment member 76 is provided with a lower bearing surface 78. As will hereinafter be emphasized with respect to the view of FIG. 3A, the interaction between surface 78 and surface 72 of flange receiving portion 70 causes the grapple segment to move inwardly relative to the other grapple segments to cause capture of the handle H within grapple G. The outer portion of the grapple segments S is simpler of detail. Three major portions of this outer segment are of concern. First, opposite flange receiving portion 70 the outer segment S is given at section 80 a thickness so that the inner portion of the cylinder C is loosely abutted. This thickness makes sure that the assembled grapple G is maintained firmly about the lower flange 52 on the tension rod T. Secondly, each segment is provided with a lower protruding flange portion 82. Lower protruding flange portion 82 restricts opening of each segment S of the grapple to close the grapple G itself. Specifically, when segment 82 is within the cylinder C, the grapple is closed and the handle H may not enter or leave. Finally, and between shoulder 80 and annulus 82, there is a tapered portion 84 of the segment. Tapered portion 84 gradually constricts the overall dimension of the grapple G in a downward flaring frustum shape. This shape ends at annulus 82. This portion 84 ensures that when annulus 82 clears the bottom of cylinder C, the grapple segment may pivot outwardly so as to release and/or receive handle H. Having completely described the handle H, the single grapple segment S, the assembled female configuration of the grapple G by confrontation of six of the segments S may be understood. First, the assembled segments S form a flange receiving portion 170. Secondly, the assembled segments form a gathering portion 160. Finally, the assembled segments form a handle capturing portion 163. Bearing in mind these respective portions, attention will now be directed to the cartoon series of FIG. 2A together with the sections of FIGS. 3A and 4A to describe operation. First, assembly to the configuration of FIG. 2A can easily be understood. Six segments S are assembled around a tension rod T at flange 52. The tension rod T and flange 52 are moved interior of the cylinder C. Cylinder C captures the segments between flange portion 70 and shoulder 80. Grapple segments S are constricted as a unitary body about the lower part of the tension rod T. To initially engage a rod R at handle H with respect to FIG. 2A, tension rod T is released at flange 20 by electromagnet 22. Flange 82 of the grapple segments S extends beyond the lower portion of cylinder C. The grapple segments S can all open. The cavity interior of the grapple G is open to receive the rod R at handle H. This occurs because gathering surfaces 60 tend to pivot the grapple segments S outwardly. In the view of FIG. 2B, drive D (not shown in the view of FIG. 2) has been lowered. Grapple G has come into contact with handle H. Even though the flange 82 is not within the cylinder C, closure of the grapple segments S about the handle H occurs. The action by which this occurs can best be explained with references to FIGS. 3A and 4A. Upon downward movement of the tension rod T, shoulders 74 (see FIG. 4A) and 78 bear respectively against the lower portion of the tension rod T and the flat handle surface 45. Since the respective shoulders 72 and 78 are separated by a lever arm, the particular grapple segment in FIG. 4A attempts to pivot counterclockwise as shown in the view of FIG. 4A. In such counterclockwise pivot, the grapple segments 64 all move to and towards one another. Consequently, handle H is captured at frustum 42 by the constriction 64. Just as a single segment S moves singularly, all segments S move inwardly collectively. This being the case, grapple G is configured so that when cylinder C moves downwardly relative to the grapple G, all the segments S are confined within it (see FIG. 2C). When the driveline L begins to move upwardly, handle H falls away interior of the female segment defined by the grapple G (see FIG. 2D). However, release cannot occur if electromagnetic 20 engages flange 22. With this engagement, rod R is fully coupled to driveline L. Referring to FIG. 2E, it is easy to understand how full withdrawal of rod R can occur. Assuming full withdrawal of rod R occurs, all that remains to be explained is the thermal release of FIG. 2F and the electromagnetic release of FIG. 2D. It will be understood that any relative movement sufficient to clear flange 82 of the lower portion of cylinder C will cause release of the handle H. Referring to FIG. 2F, it will be remembered that tension rod T is constructed of a material having a relatively high coefficient of expansion. Cylinder C is constructed of a material having a relatively low coefficient of expansion. Further, it is well known to design such bimetallic parts to have precise movement responsive to overall temperature conditions. Specifically, when tension rod T expands, a large amount and cylinder C expands only a small amount, flange 82 clears the lower portion of cylinder C. Grapple segments S open and handle H is released. Rod R falls and causes SCRAM responsive to its penetration within the reactor core (not shown). Finally, and with respect to FIG. 2G, control circuits can cause a release of the current to the electromagnetic portion 22. Flange 20 at the upper end of tension rod T is released. When the tension rod is released again, flange 82 clears the lower portion of cylinder C. Handle H is released with the result that rod R effects full core penetration and responsive SCRAM. The reader will understand that we have illustrated only a single reactor rod. In actual fact many will be used for control of a reactor. It will be further understood that the particular grapple mechanism here illustrated is exemplary only. For example, the grapple segments shown could be virtually any shape which would co-act with the lower and cylindrical portion of the cylinder to restrict a handle captured in the interior of the device. It will be apparent also that the handle H does not have to have the particular preferred shape here illustrated. The handle could be spherical in shape. Likewise it could be given any imparted shape which could be received and restricted in the lower end of the driveline L. It will be also understood that the disclosed driveline and grapple can be used with many alternate drives. Examples of some drives include rack and pinion, hydraulic, pneumatic and other equivalent mechanical and electromechanical expedients. Likewise, magnet 20 and flange 22 may have equivalent devices substituted, such as pneumatic, hydraulic and other mechanical and electromechanical expedients. Likewise, the manner in which the grapple segments attach to the rod can vary. For example, a pivotal attachment between the lower end of the tension rod and the grapple segments may be used. Additionally, the number of grapple segments may vary, although the illustrated six segments are preferred.