Patent Number: 047972475
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus shown in the drawings is a reactor 11 including a pressure vessel having a body 13 and a head 15. The body 13 is generally circularly cylindrical terminating at the bottom in a spherical bowl. The head 15 is dome-shaped and is provided at its base with an annular flange 17. The head 15 is secured to the body 13 by studs 19 which compress sealing O-rings (not shown) between the closure-head flange 17 and the top of the body 13. The control rods, instrument parts and the like (not shown in detail) extend from the top of the head 15. The body 13 and head 15 are enclosed in thermal insulating shields 21, 23 and 24. The shields 21, 23 and 24 could be composed of a material such as Ricardo Neutron Shielding sold by Richardson, Battery Parts Division, Melrose Park, Ill. 60160. In this case, the shields would reflect neutrons as well as serving as a thermal shield. The shielding can also be purely neutron reflecting. The shield 24 covers the top 26 of the head and need not be removed to afford access to remove the head. The shield 23 embodies a unique feature of this invention. The thermal shield 23 includes a frame 25 of thermal insulating material. Near or at the top of the frame 25, a plurality of panels 27 of thermal insulating material are mounted pivotal each on a hinge 29. The frame 25 is of polygonal transverse cross-section with a panel 27a pivotally mounted on hinges 29 near or at the top of each side 25a of the frame. Typically, the frame 25 may be of octagonal transverse cross-section. Each unit including a side 25a and a panel 27a may be separate from the other units 25a-27a or several or all sides 25a of the frame 25 may be joined. The frame 25 and the panels 27 may be composed of insulating board as shown. In this case, the frame 25 must have sufficient strength and rigidity to support the panels 27 notwithstanding the high temperature of the head 15 during normal operation. The frame 25 and/or the panels 27 may also be formed of opposite metallic plates defining between them a pocket within which thermal insulating material is disposed. The frame 25 and/or the panels 27 may be laminated structures formed of a plurality of overlaid insulating board. Instead of being of polygonal section, the frame 25 may be of circular transverse section with the panels 27 suitably shaped, i.e., curved, at their outer ends so that they are adapted to be pivotally mounted on the frame. At its lower end, the frame 25 is supported on a flange 31 extending from the body near its top. The panels 27 are pivotal from a generally horizontal position (FIGS. 1, 3, 4, 6) to a retracted position (FIGS. 3, 5, 7) in which they are generally vertical or at a relatively small angle to the vertical. Each panel 27a is of generally trapezoidal shape so that when the panels are in a horizontal position, they mate to form a substantially closed thermal shield over the portion of the head over which they extend (FIGS. 2, 6). In the horizontal position, the inner ends of the panels 27 are supported on a bracket 33 mounted on the head. For raising or lowering the thermal shield 23, a plurality of mechanisms or linkages 41 (FIGS. 3, 4, 5) are provided. The mechanisms 41 are disposed so that a single mechanism operates on adjacent sides 27a of the shield 23. Each mechanism 41 (FIGS. 3, 4) includes a rod 43 having a hook 45 at its upper end. A finger 47 projects from the rod 43 at its lower end. Below the hook 45, a circular plate 49 is mounted on the rod 43 and below the plate 49 a sleeve 51 is secured to the bar. The sleeve 51 and bar 43 are penetrated by cross rod 53. The rod 43 is passed between the adjacent panels 27a with the plate 49 above the panels and the sleeve 51 and cross rod 53 below the panels. The rod 43 is moveable in U-shaped guides 55 and 57 suspended from a bar 59 connected to the adjacent sides 25a at their joint. Guide 55 is shorter than guide 57 to accommodate the bar 43 which, when panels 27a are in a horizontal position, is at an angle to the vertical. In moving the panels 27a from the horizontal to the retracted position, the rod 43 slides along the walls of the guides 55 and 57 which function as cam surfaces. The cross bar 53 is positioned to engage a pair of parallel U-shaped members 61 suspended side-by-side each from one of the adjacent panels 27a (FIG. 4). The members 61 function as a cam with the cross rod 53 as a cam follower. The apparatus 63 (FIGS. 6 and 7) for raising or lowering the thermal shield 23 includes a plurality of cable 65 which extend from a rig (not shown) on the seismic support platform 67. The rig is driven by a motor (not shown) in turn pulling the cables 65 upwardly or downwardly. The motor is energized when receiver 80 on the platform 67 is enabled. The platform 67 is supported on columns 69, each provided with a sleeve 71 slideable along the column. Each sleeve 71 has a pulley 73 through which a corresponding cable 65 passes. A cantilever rod 75 extends from each sleeve 71. Each cantilever rod 75 has a hole 77 (FIG. 7) near its outer end through which the cable 65 passes. Each cable 65 has a loop 79 (FIG. 4) at its lower end which engages the hook 45 extending from a bar 43. In normal operation, the thermal shield 23 is in the shielding position (FIG. 6). The sleeve 71 is in the lowermost position with the cantilever rod 75 above the hook 45. When the head 15 is to be removed the motor (not shown) is energized by a remotely-actuable switch (not shown). The actuation is carried out by personnel 82, remote from the reactor who enables a transmitter 84 which communicates with receiver 80 on the platform 67. The cable 65, sleeve 71, cantilever bar 75, linkage bar 43, and cross bar 53 (FIG. 4) of each pair of sides 25a and panels 27a which are to be raised are pulled upwardly. Each cross bar 53 engages the lower surfaces of its associated panels 27a and pivots these panels to the retracted position as shown in dash-dot lines in FIG. 4. As each bar 43 is raised, its finger 47 engages the bottom of guide 55. As each bar continues to rise, it carries the associated frame sides 25a with it. Ultimately, the portion of the shield 23 which was raised is in the position shown in FIG. 7. The thermal shield 23 may be raised in separate sections and the tension studs 19 removed as indicated in FIG. 7. Alternatively, the thermal shield as a whole may be raised and then the studs may be removed. In either event, the head 15 is ultimately removed and the reactor 11 processed as required. When the shield 23 is to be replaced after the head 15 has been secured to the body 13, the motor (not shown) is energized in the reverse direction. Each linkage 41 is then lowered. Initially, each cross bar 53 is in the position shown in dash-dot lines in FIG. 4 As cables 65 are lowered, the shields 23 are lowered until the lower edges of sides 25 engages flange 31. Once this downward movement is completed, each cross bar 53 engages the webs 83 of the members 61 pivoting the panels 27a to the shielding position. While preferred embodiments of this invention have been disclosed herein, many modifications thereof are feasible. This invention is not to be restricted except insofar as is necessitated by the spirit of the prior art.