Abstract:
Control rod drives include linearly-moveable control elements inside an isolation barrier. Control rod drives move the control element through a motor and rotor powering a linear screw internal to an isolation barrier. Induction coils may generate magnetic fields and be moveable across a full stroke length of the control element in the reactor. The magnetic fields hold closed a releasable latch to disconnect the control elements from the linear drives. A control rod assembly may join to the control element. The control rod assembly may lock with magnetic overtravel latches inside the isolation barrier to maintain an overtravel position. Overtravel release coils outside the isolation barrier may release the latches to leave the overtravel position. Operation includes moving the magnetic fields and releasable latch together on opposite sides of an isolation barrier to drive the control element to desired insertion points, including full insertion by gravity following de-energization.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to co-pending U.S. Provisional Applications 62/361,604; 62/361,625; 62/361,628, all filed Jul. 13, 2016 and incorporated by reference herein in their entireties. 
     
    
     BACKGROUND 
       [0002]      FIG. 1  is an illustration of a drive rod-control rod assembly (CRA) connection  10  useable with example embodiment control drives. In most conventional PWR control rod assemblies, drive rod  11  and actuating rod  12  extend in lateral support tube  16  from above a reactor pressure vessel  1  down to a lockable spud or bayonet  13  that joins to CRA  15  via locking plug  14 . CRA  15  contains neutron absorbent materials what can be used to control a nuclear chain reaction based on an amount of vertical insertion. Control rods are driven from above by vertical movement of actuating rod  12  and drive rod  13 , under force from the control rod drive mechanism. 
         [0003]    The following documents are incorporated herein by reference in their entireties: US Pat Pub 2015/0255178 to Tsuchiya et al; U.S. Pat. No. 4,423,002 to Wiart et al.; U.S. Pat. No. 4,369,161 to Martin; U.S. Pat. No. 4,338,159 to Martin et al.; U.S. Pat. No. 4,044,622 to Matthews; U.S. Pat. No. 9,305,669 to Hyde et al.; U.S. Pat. No. 3,933,581 to McKeehan et al.; U.S. Pat. No. 4,048,010 to Eschenfelder et al.; U.S. Pat. No. 4,092,213 to Nishimura; U.S. Pat. No. 4,147,589 to Roman et al.; U.S. Pat. No. 4,288,898 to Adcock; U.S. Pat. No. 4,484,093 to Smith; U.S. Pat. No. 5,276,719 to Batheja; U.S. Pat. No. 8,915,161 to Akatsuka et al.; U.S. Pat. No. 4,518,559 to Fischer et al.; U.S. Pat. No. 5,517,536 to Goldberg et al.; U.S. Pat. No. 5,428,873 to Hitchcock et al.; U.S. Pat. No. 8,571,162 to Maruyama et al.; U.S. Pat. No. 8,757,065 to Fjerstad et al.; U.S. Pat. No. 5,778,034 to Tani; U.S. Pat. No. 9,336,910 to Shargots et al.; U.S. Pat. No. 3,941,653 to Thorp, II; U.S. Pat. No. 3,992,255 to DeWesse; U.S. Pat. No. 8,811,562 to DeSantis; and “In-vessel Type Control Rod Drive Mechanism Using Magnetic Force Latching for a Very Small Reactor” Yoritsune et al., J. Nuc. Sci. &amp; Tech., Vol. 39, No. 8, p. 913-922 (August 2002). 
       SUMMARY 
       [0004]    Example embodiments include control rod drives including linearly-moveable control elements to control neutronics in a nuclear reactor. Example control rod drives may include an isolation barrier impermeably separating pressurized reactor internals from external spaces like containment as well as providing a vacuum environment for control rod drive elements outside the reactor. One or more induction coils are linearly moveable outside of the isolation barrier, while the control element is inside the isolation barrier in the reactor. Example control rod drives may move the control element via selective coupling between the control element and a motor-driven linear drive. The selective coupling may use a latch with magnetic-selective coupling, such as magnetized plungers that hold the drive and control element together in a first position and release the two in a second position. For example, the plungers may bias against and compress springs under magnetic force, and when the magnetic force, such as from external release coils or magnets, is released, the plungers may be driven back up by the springs and allow a releasing element, such as ball bearings or blocking elements, to slide back where the plunger diameter is now smaller and release the coupling. Otherwise, the plungers and blocking elements may maintain the joining configurations. A closed coolant loop may cool the induction coils, which may otherwise be maintained in a vacuum or other environment distinct from reactor internals in a housing about an end of the reactor. Example embodiment control rod drives may include a control rod assembly that directly joins to the control element. The control rod assembly may lock with magnetic overtravel latches inside the isolation barrier to maintain an overtravel position. Overtravel release coils outside the isolation barrier can release or otherwise move the latches, which may be spring-biased, to adjust the connection between the latches and assembly. 
         [0005]    Example methods include applying a magnetic field to hold the latch in the joined configuration inside the isolation barrier. The latch and holding magnetic field on opposite sides of the isolation barrier may be moved by a common motor driving an interior and exterior rotor two which the two are respectively mounted. For example, a linear screws may be independently driven by the rotors to move the latch and magnetic elements at a same vertical position. When the magnetic element is de-energized or removed, the latch may release and the control element may be driven by gravity into a reactor, achieving a scram. Example methods may drive the control rod to an overtravel position, where overtravel latches hold the same, for removal, attachment, and/or other maintenance of the control element from/to/on the control rod assembly. Following desired overtravel actions, the overtravel coils may be energized to release the latches through magnetic materials in the latch biasing them to an open position. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0006]    Example embodiments may become more apparent by describing, in detail, the attached drawings, wherein like elements are represented by like reference numerals, which are given by way of illustration only and thus do not limit the terms which they depict. 
           [0007]      FIG. 1  is an illustration of a drive rod connection to a control rod assembly useable in example embodiments. 
           [0008]      FIG. 2  is a plan illustration of an example embodiment control rod drive mechanism using extended lift coils. 
           [0009]      FIG. 3  is a profile illustration of the example embodiment control rod drive mechanism using extended lift coils. 
           [0010]      FIG. 4  is another profile illustration of the example embodiment control rod drive mechanism using extended lift coils. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Because this is a patent document, general broad rules of construction should be applied when reading it. Everything described and shown in this document is an example of subject matter falling within the scope of the claims, appended below. Any specific structural and functional details disclosed herein are merely for purposes of describing how to make and use examples. Several different embodiments and methods not specifically disclosed herein may fall within the claim scope; as such, the claims may be embodied in many alternate forms and should not be construed as limited to only examples set forth herein. 
         [0012]    It may be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited to any order by these terms. These terms are used only to distinguish one element from another; where there are “second” or higher ordinals, there merely must be that many number of elements, without necessarily any difference or other relationship. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments or methods. As used herein, the term “and/or” includes all combinations of one or more of the associated listed items. The use of “etc.” is defined as “et cetera” and indicates the inclusion of all other elements belonging to the same group of the preceding items, in any “and/or” combination(s). 
         [0013]    It may be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” “fixed,” etc. to another element, it can be directly connected to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” “directly coupled,” etc. to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). Similarly, a term such as “communicatively connected” includes all variations of information exchange and routing between two electronic devices, including intermediary devices, networks, etc., connected wirelessly or not. 
         [0014]    As used herein, the singular forms “a,” “an,” and “the” are intended to include both the singular and plural forms, unless the language explicitly indicates otherwise. It may be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, characteristics, steps, operations, elements, and/or components, but do not themselves preclude the presence or addition of one or more other features, characteristics, steps, operations, elements, components, and/or groups thereof. 
         [0015]    The structures and operations discussed below may occur out of the order described and/or noted in the figures. For example, two operations and/or figures shown in succession may in fact be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Similarly, individual operations within example methods described below may be executed repetitively, individually or sequentially, to provide looping or other series of operations aside from single operations described below. It should be presumed that any embodiment or method having features and functionality described below, in any workable combination, falls within the scope of example embodiments. 
         [0016]    The Inventors have newly recognized that control rod drives in nuclear reactors are typically mechanical drives using direct contact points that must pass through or be inside a reactor CRDM pressure boundary  150 . Such direct contact and positioning creates a challenging environment for the mechanical drives that typically must operate to move control rods over a period of several months or years without maintenance. For example, reactor temperatures, leaked coolant, and noncondensible gasses found inside example embodiment CRDM  200  pressure boundary  150  can cause corrosion and associated stress corrosion cracking, hydriding, and hydrogen deflagration problems with mechanical drive parts. The cooling mechanisms and heat from direct contact with the drives interact with example embodiment CRDM  200  pressure boundary  150  to also cause thermal cycling problems during actuation of mechanical drives over the course of operation. Penetrations in a control rod drive required for mechanical connection also represent an avenue for leakage of reactor coolant. The Inventors have newly recognized a need for a control rod drive that has less engagement with example embodiment CRDM  200  pressure boundary  150  as well as mechanical contacts that represent high-failure points. Example embodiments described below uniquely enable solutions to these and other problems discovered by the Inventors. 
       Example Method—Coupling/Decoupling Ball Latch 
       [0017]      FIG. 2  is a plan view illustration of an example embodiment control rod drive mechanism (CRDM)  300 .  FIGS. 3 and 4  are profile views of the same example embodiment control rod drive mechanism  300  of  FIG. 2 , with  FIG. 3  showing assembly  310  in a seated position and  FIG. 4  showing assembly  310  in an overtravel position. Co-owned application Ser. No. 15/640,428 filed Jun. 30, 2017 to Morgan et al. for “STATIONARY ISOLATED ROD COUPLINGS FOR USE IN A NUCLEAR REACTOR CONTROL ROD DRIVE” and Ser. No. 15/644,908 filed Jul. 10, 2017 to Morgan et al. for “MOVEABLE ISOLATED ROD COUPLINGS FOR USE IN A NUCLEAR REACTOR CONTROL ROD DRIVE” are incorporated herein by reference in their entireties. It is understood that any control rod drive elements from the incorporated applications and provisional applications may be used in any combination with embodiments described herein. Descriptions of position indication magnet  115  and lift rod actuating magnet  104  are given in the incorporated &#39;428 application. 
         [0018]    As shown in  FIG. 2 , a position of nut and ball latch  127  is established by zeroing position sensors  105  at a known position of lift rod  111  and latch  127  such as the overtravel position or the seated position at buffer assembly for scram force  101 . 
         [0019]    With lift rod  111  sitting in the overtravel position and nut and ball latch  127  nested in its opening, nut and ball latch  127  and coils  128  on exterior linear screw  130  ( FIG. 3 ) are energized. Coils  128  pull down magnetic material in spring-opposed plungers  141 , forcing out ball latches  137  so as to engage lift rod  111  shoulders. Lift rod  111  is then coupled to a nut of ball latch  127 , and linear hollow screw  131  and outer linear screw  130  ( FIG. 9 ) will drive in concert to maintain a configuration where energized ball latch coils  128  hold ball latch  127  engaged to lift rod  111 . 
         [0020]    Following a scram, nut and ball latch  127  will follow the scrammed lift rod  111  down to buffer assembly for scram force  101  ( FIG. 3 ) and will drive itself down into the seated lift rod  111 . This action resets CRDM  300  for further operation. Ball latch coils  128  may be re-energized before lift rod  111 , drive rod  112 , and CRA  310  are lifted out of buffer assembly for scram force  101 . Lift rod  111  and drive rod  112  may be coupled to nut and ball latch  127  in CRDM  300  prior to coupling with CRA  310  as shown in  FIG. 1 . 
         [0021]    If solenoid actuated release coil  102  fails to release drive rod  112  from CRA  310 , an alternative mechanical actuation is available when shutdown. Motor  126 , with associated brake and position sensors, and outer rotor  132  may be removed from above CRDM housing  106 . The upper flange of CRDM housing  106  may be removed, and a tool may be run down through hollow inner rotor  133  and screw  131 . The tool is threaded onto actuating rod  103 , allowing it to be pulled while lift rod  111  and drive rod  112  position are held fast. This action compresses the spring(s) above the lower lock plug and frees the spud of CRA  310  from drive rod  112  for maintenance and repairs. 
       Example Method—Positioning and Scramming the CRDM 
       [0022]    As seen in  FIG. 3 , after lift rod  111  is coupled to ball latch  127  and drive rod  112  is coupled to CRA  310 , CRA  310  is positioned by the motor-driven inner linear screw  131 . Ball latch coils  128  mounted on outer linear screw  130  remain energized to keep the ball latch nut coupled to lift rod  111  within pressure boundary  150 . CRDM motor  126  ( FIG. 4 ) rotates inner rotor  133  ( FIG. 4 ) and screw  131  within CRDM housing  106 . The rotation of screw  131  causes vertical movement of ball latch  127  having a nut that is keyed to prevent rotation. Lift rod  111  travels with nut and ball latch  127  as long as balls  137  remain engaged. That is, inner linear screw  131 , when rotated by inner rotor  133  inside pressure boundary  150  moves and holds drive rod  112 , lift rod  111 , and CRA  310  therebelow by rotation and resultant linear movement of those features on threads inside pressure boundary  150 . 
         [0023]    As seen in  FIG. 4 , nut and ball latch  127  and outer energized ball latch coils  128  move vertically together on screw(s)  130  traversing the drive range or stroke distance. Feedback from position sensors of motor  126  and position indication probes  105  ( FIG. 3 ) control rotation of motor  126  and move CRA  310  to its desired position for reactor control. Internal linear screw  131  and external linear screw  130  provide fine motion control of internal lift rod  111 , drive rod  112 , and CRA  310 . 
         [0024]    Vacuum gap  121  ( FIG. 2 ) between pressure boundary  150  and the ball latch coils  128  limits heat transfer between coils  128  and pressure boundary  150 . This provides a more uniform temperature gradient on pressure boundary  150  that minimizes thermal cycling. Pressure boundary  150  wall thickness can be enhanced to minimize effects of corrosion, hydriding, and hydrogen deflagration problems. 
         [0025]    Reactor safety features requiring a scram provide inputs to the control system for the ball latch coils, normally energized to magnetically pair with magnetic elements. If reactor conditions warrant a scram, the control system de-energizes ball latch coils  128 . This drops the ball latch magnetic field allowing spring-opposed plungers  141  to raise and retract the balls  137  supporting lift rod  111  shoulders. Gravitational force acts on lift rod  111 , drive rod  112 , and CRA  310 , collapsing nut and ball latches  127  and dropping the unsupported components into a seated position on buffer assembly for scram force  101  ( FIG. 3 ). Any failure causing a loss of current to ball latch coil  128  may also lead to a conservative control rod scram. 
         [0026]    As shown in  FIG. 2 , guide rollers or key features  118  on a head interface of ball latch  127  and lift rod  111  with pressure boundary  150  prevent rotation of ball latch  127 , lift rod  111 , drive rod  112 , and CRA  310  during operation. Ball latch coils  128  may be continuously energized during operation and may be cooled by coolant inlet/outlet  107  through their travel range. Flexible lines of coolant inlet/outlet  107  may be oriented from the top of CRDM  300  and reach ball latch coils  128  through slotted openings of CRDM structural housing  106 . These lines along with latch coil control circuits can have counter weights or spring reel feeds to keep them under slight tension during drive operation. 
       Example Method—CRDM Preparation for Refueling Process 
       [0027]    As shown in  FIG. 4 , drive rod  112  may be decoupled from CRA  310  as described above using solenoid actuated release coil  102  ( FIG. 3 ). For refueling, motor  126 , linear screw(s)  131 , and ball latch  127  are used to maneuver the coupled lift rod  111  and drive rod  112  to the overtravel position. In the overtravel position, two spring actuated overtravel latches  116  engage a shoulder or window in CRDM housing  106  to lock CRDM  300  at the overtravel height. Power and cooling can then be disconnected from or secured to motor  126  and ball latch coils  128  for a duration of the refueling process. The lower end of drive rod  112  may be carried to an elevation that is clear of the upper to lower vessel disassembly process. 
         [0028]    When refueling is completed, motor  126  and ball latch coils  128  may be energized to carry the weight of lift rod  111  and drive rod  112  in the overtravel position. Overtravel release coils  108  are then energized to compress spring actuated structural support  117  resting on pressure boundary  150  structural support as discussed above. 
       CRDM Support Structure 
       [0029]    As shown in  FIG. 2 , CRDM Pressure Boundary  150  is supported vertically off of CRDM nozzle pressure boundary flange  120  in CRDM structural housing  106  of the RPV flange. Lateral support to upper portions of CRDM pressure boundary  150  may be provided by the close proximity of outer rotor  132  across vacuum gap  121 . Inner rotor  133  ( FIG. 4 ), inner linear screw  131 , ball lath  127 , and lift rod  111  may be laterally supported off walls of CRDM pressure boundary  150 . 
         [0030]    CRDM structural housing  106  is also fixed to the CRDM nozzle pressure boundary flange  120 . Insulating washers and other items can be utilized to reduce the thermal heat transfer from the RPV head to components in CRDM  300 . The internal bearings/bushings of outer linear screw(s)  130  ( FIG. 3 ) are supported off CRDM structural housing  106  and not pressure boundary  150  to avoid heat conduction. PIP probes  105  are inserted vertically through the upper flange of CRDM structural housing  106  and are laterally supported at a minimum of the upper and lower ends of CRDM structural housing  106 . Motor  126  ( FIG. 4 ) and associated brake and position sensors are mounted on the top end of CRDM structural housing  106  and engage outer rotor  132  and linear screw(s)  131  ( FIG. 4 ) for ball latch coils  128  through drive gear train  134  (FIG.  4 ). Coolant inlet/outlet lines  107  are run to the fixed motor  126  which is located as remote as possible from the reactor&#39;s thermal and radiation output. Motor  126  is also isolated from CRDM pressure boundary  150  by vacuum gap  121  to prevent conduction. 
         [0031]    Example embodiments and methods thus being described, it may be appreciated by one skilled in the art that example embodiments may be varied and substituted through routine experimentation while still falling within the scope of the following claims. For example, a generally vertical orientation with control rod drives above a pressure vessel is shown in connection with some examples; however, other configurations and locations of control rods and control rod drives, are compatible with example embodiments and methods simply through proper dimensioning and placement—and fall within the scope of the claims. Such variations are not to be regarded as departure from the scope of these claims.