Patent Number: 050230441
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen that the invention is generally referred to by the numeral 10. Control assembly 10 is comprised of disk assembly 12 and means 14 for rotating disk assembly 12. As seen in the block diagram of FIG. 1, disk assembly 12 is positioned substantially at the longitudinal center of reactor core 16 and is coaxial with reactor core 16. This divides the core 16 into two subcritical halves when disk assembly 12 is in its fully closed position. As seen in FIG. 3, disk assembly 12 is formed from at least two disks 18, 20. Disks 18, 20 are machined with an identical surface hole pattern 22, 24 such that the rotation of one disk relative to the other causes the hole pattern to open or close. Although hole patterns 22, 24 are shown as being circular, it should be understood that the holes may be in any suitable shape such as sectors or triangles. FIG. 2 illustrates the situation where the disks are rotated s that the hole pattern is closed, that is, the holes 22 provided through first disk 18 are not in alignment with the holes 24 provided through second disk 20 and indicated in phantom view. In the preferred embodiment, the disks 18, 20 are formed from neutron absorbing material such as a cadmium or boron alloy with the holes being a void area. Cadmium and boron have large neutron cross sections as neutron absorbers and are used as alloys well known in the industry. Control of the release of neutrons and core reactivity is accomplished by rotating one of the disks relative to the other to open or close the hole pattern. In FIG. 2, the hole pattern is fully closed. This prevents neutrons in one half of the core from reaching the other half and thus divides the core into two subcritical halves. Rotation of one disk relative to another to cause partial or complete alignment of the holes in the disks allows passage of neutrons therethrough and results in an increase in core reactivity. The level of core reactivity is controlled by and is directly related to the amount of overlap of holes 22 and 24 on disks 18, 20. Means 14 for rotating one disk relative to the other as best seen in FIG. 3(shown with secondary split core control) is mounted adjacent reactor 36. Drive motor 26 is in operative engagement with drive gear 28 through drive shaft 30. Drive gear 28 meshes with gear 32 on disk rotation shaft 34 that extends up through the center of reactor 36. Disk rotation shaft 34 is held in position and rotatably received by retaining nut 38. Fuel elements 40 are rigidly attached between guide plate 42 and first disk 18. Heat pipe 41 is attached to first disk 18 and extends through guide plates 42. The lower guide plate 42 is operatively engaged with disk rotation shaft 34 by means of gear 44 such that plate 42 rotates in response to rotation of disk rotation shaft 34. The rigid connection of heat pipe 41 with guide plate 42 and first disk 18 causes corresponding rotation of first disk 18. Only one fuel element 40 is shown for ease of illustration and it should be understood that a plurality of fuel elements 40 are present in each core half 16 above first disk 18 and below second disk 20. Reactor 36 is shown as the type of reactor wherein the core halves 16 may be moved longitudinally relative to each other to affect reactivity by the use of separation motor 46 and outer drive shaft 48. First control disk 18 is threadably received on the threaded portion 50 of outer drive shaft 48 by thermal fuse 52 such that rotation of outer drive shaft 48 causes first control disk and the upper half of core 16 to move up or down depending on the direction of rotation. Although control assembly 10 is shown as being used in conjunction with movable core halves, it may be used in a reactor where the core halves are stationary. Also, in a reactor with movable core halves, control assembly 10 may be configured to act independently of the core separation mechanism. In operation, first disk 18 is rotated relative to second disk 20 such that holes 22, 24 are not in alignment to maximize neutron attenuation and keep the reactor core halves 16 isolated from each other and subcritical. To allow an increase in reactivity, first disk 18 is rotated so that holes 22, 24 partially or completely overlap depending on the amount of neutron attenuation and core reactivity desired. As seen in the graph of FIG. 4, a test of a control assembly 10 having a series of holes divided into 45 degree sectors produced a minimum neutron count at zero rotation angle(no hole overlap) and a neutron count of approximately 2500 per minute at a rotation angle of 22.5 degrees(total alignment of holes and exposed area of 25.2 percent). This indicates that predictable control of reactivity can be accomplished using control assembly 10. As alternate embdiments, moderating material or fissile material may also be used as part of control assembly 10. Fissile material may be used as inserts in holes 22, 24 to amplify neutron flux through the holes when in the open position to enhance reactivity. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modificaitons may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.