Abstract:
Control rod drives include linearly-moveable control elements inside an isolation barrier. Control rod drives move the control element through secured magnetic elements subject to magnetic fields. Induction coils may generate the magnetic fields across a full stroke length of the control element in the reactor. A closed coolant loop may cool the induction coils, which may be in a vacuum outside the isolation barrier. A control rod assembly may house the magnetic elements and directly, removably 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. Methods of operation include selectively energizing or de-energizing induction coils to drive the control element to desired insertion points, including full insertion by gravity following de-energization. No direct connection may penetrate the isolation barrier.

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. One or more induction coils are 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 a magnet immovably connected to the same by energizing and de-energizing the induction coils to linearly drive the magnets. The induction coils may be secured in a vertical distance to fully move the magnets across a whole distance equivalent to complete insert and withdrawal of the control element from the reactor. 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 housing the magnet 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 energizing and/or de-energizing at least one induction coil to drive the control element via the magnetic material secured to the same. In this way, the control element may be inserted and withdrawn with no mechanical linkage permeating the isolation barrier. With multiple induction coils, individual coils may be selectively energized and de-energized to drive the magnetic material between the same, thus driving the control element. When all coils are de-energized, 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  100  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  100  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  100  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. 
         [0017]      FIG. 2  is a plan view illustration of an example embodiment control rod drive mechanism (CRDM)  100 .  FIGS. 3 and 4  are profile views of the same example embodiment CRDM  100  of  FIG. 2 , with  FIG. 3  showing CRA  110  in a seated position and  FIG. 4  showing CRA  110  in an overtravel position. 
         [0018]      FIG. 3  illustrates a coupling and decoupling functionality between CRA  110  and the remainder of CRDM  100 . As shown in  FIG. 3 , lift rod  111  and drive rod  112  are coupled to CRA  110  below and CRDM  100  is in a near seated position against buffer assembly  101  for scram force. The uncoupled lift rod  112  and drive rod  111  position is held constant by lift coils  113  in the energized scram coil control system as the lower solenoid actuated release coil  102  is energized to lift and hold a magnetic section  114  of internal actuating rod  103 . This movement of actuating rod  103  relative to drive rod  111  compresses spring(s) above the locking plug on the lower end of actuating rod  103 . Drive rod  111  is then lowered a fixed amount over the matching contours of CRA  110  coupling spud until fully seated on CRA  110 . Solenoid actuated release coil  102  is de-energized and the spring force inserts locking plug  14  ( FIG. 1 ) into CRA  110  spud, locking drive rod  111  to CRA  110 . Release coil  102  operates for only a short period of time during coupling then the mechanical spring force captures CRA  110  during normal drive rod operation. Release coil  102  may generally operate for a short interval during shutdown within an air environment. Coil  102  may be cooled. 
         [0019]    Actuating rod indication magnet  104  in the upper end of actuating rod  103  in CRDM pressure boundary  150  may provide position indication of actuating rod  103 &#39;s released or engaged position though interaction with switches in position indication probes  105 . Position indication probes  105  are shielded to avoid other magnetic influences and the distance between probes  105  and actuating rod indication magnets  115  are minimized to ensure reliability. 
         [0020]    If decoupling is desired, example embodiment CRDM  100  is driven to CRA  110  seated position in buffer assembly for scram force  101 . Solenoid actuated release coil  102  is energized to overcome the spring force of the locking plunger (e.g., Locking Plug of  FIG. 1 ) and the position change of actuating rod  103  is detected to confirm release. Drive rod  111  is then slowly raised off of CRA  110  spud and above the seated control rod position by lift coils  113 . Release coil  102  can be de-energized to relax the spring when CRA  110  is confirmed as released and the CRDM position is above CRA  110  seated elevation. Lift rod  112  and drive rod  111  can then be raised to an overtravel hold position ( FIG. 4 ) if the CRDM lift coils  113  are to be de-energized for refueling operations. 
         [0021]    If solenoid actuated release coil  102  fails to release drive rod  111  from CRA  110 , an alternative mechanical actuation is available when shutdown. The upper flange of CRDM structural housing  106  may be removed and a tool may be threaded onto actuating rod  103  allowing it to be pulled while position of lift rod  112  and drive rod  111  are held fast. This action compresses the spring(s) above the lower lock plug and frees the spud of CRA  110  from drive rod  111  for maintenance and repairs. 
       Positioning and Scramming the CRDM 
       [0022]    Following coupling of lift rod  112  and drive rod  111  to CRA  110 , CRA  110  is positioned by lift coils  113  in the scram coil positioning and control system. Groups of lift coils  113  within the extended coil feature are sequenced on and off to magnetically couple and move lift rod  112  via lift magnets  117  ( FIGS. 2 &amp; 4 ) or other magnetic materials within example embodiment CRDM  100  pressure boundary  150 . There may be no moving parts within CRDM structural housing  106 , only vertically traveling magnetic fields produced by the arrangement of the extended scram lift coils  113 . The levitated lift rod  112 , drive rod  111 , and CRA  110  follow the magnetic field. Feedback from position indication probes  105  continues to adjust the magnetic field generated by lift coils  113  and move CRA  110  to its desired position for reactor control. The spacing, number, and strength of the extended lift coil  113  arrangement provides the fine motion step control of the internal lift rod  112 , drive rod  111 , and CRA  110 . 
         [0023]    There may be a vacuum between example embodiment CRDM  100  pressure boundary  150  and extended lift coil  113  arrangement within CRDM structural housing  106  to limit heat transfer between the scram lift coils  113  and CRDM pressure boundary  150 . This may provide a more uniform temperature gradient on example embodiment CRDM  100  pressure boundary  150  that minimizes thermal cycling. 
         [0024]    Simplification of example embodiment CRDM  100  pressure boundary  150  and lift rod  112  internals may allow the size of the CRDM pressure boundary  150  to be reduced such that example embodiment CRDM  100  pressure boundary  150  wall thickness can be enhanced to minimize effects of corrosion, hydriding, and/or hydrogen deflagration problems. 
         [0025]    Reactor safety features requiring a scram provide inputs to the control system for the extended scram lift coils  113  in their energized state. If reactor conditions warrant a scram, the control system de-energizes all of the extended lift coils  113 . This drops the magnetic field levitating the internal lift rod  112 , drive rod  111 , and CRA  110 , and gravity quickly acts on the unsupported weight to scram the reactor. Any CRDM failures causing a loss of extended scram lift coil  113  currents may also lead to a conservative control rod scram. 
         [0026]    Guide rollers or key features  118  ( FIG. 2 ) on the lift rod interface with example embodiment CRDM  100  pressure boundary  150  and prevent rotation of lift rod  112 , drive rod  111 , and CRA  110  during operational shims. CRDM buffer assembly for scram force  102  ( FIG. 3 ) provides a means to dampen the impact of lift rod  112 , drive rod  111 , and CRA  110  during scram in addition to the spring in CRA  110  coupling. 
         [0027]    Position indication magnets  115  on lift rod  112  head actuate switches in two position indication probes  105  to provide position indication and scram response timing for CRDM performance analysis. Portions of the extended scram lift coils  113  are continuously energized during CRDM operation and may be cooled with cooling flow through their travel range. Coolant inlet/outlets  107  ( FIG. 4 ) are connected to a fixed position at the top of CRDM  100  and run throughout the coil arrangement. 
       CRDM Preparation for Refueling Process 
       [0028]    Drive rod  111  is decoupled from CRA  110  as described above. The extended scram lift coils  113  and their control system are then used to maneuver lift rod  112  and drive rod  111  to an overtravel position as shown in  FIG. 4 . In the overtravel position, two spring actuated overtravel latches  116  engage a shoulder or window in example embodiment CRDM  100  pressure boundary  150  to lock CRDM  100  at the overtravel height. Power can then be secured or shut down to the extended scram lift coils  113  and their control system. The lower drive rod end is carried to an elevation that is clear of the upper to lower vessel disassembly process. 
         [0029]    When refueling is completed, the extended scram lift coils  113  and their control system are energized to carry the weight of lift rod  112  and drive rod  111  in the overtravel position. Overtravel release coils  108  are then energized to compress the spring actuated structural support  117  resting on example embodiment CRDM  100  pressure boundary  150  structural support. A magnet or magnetic material  119  is drawn outward in overtravel latches  116  by the overtravel release coil  108 , causing spring actuated support  117  to clear example embodiment CRDM  100  pressure boundary  150  structural support and lift rod  112  and drive rod  111  can be positioned with the extended lift coil control system to recouple CRA  110  for operation. Overtravel release coils  108  may be only briefly energized at shutdown in an air atmosphere to overcome spring forces and drive out of the overtravel position. Therefore, cooling of these coils  108  is considered optional. 
       CRDM Support Structure 
       [0030]    As shown in  FIG. 2 , CRDM pressure boundary  150  is supported vertically off of the CRDM pressure boundary flange  120  in CRDM structural housing  106  of the RPV flange. Lateral support to upper portions of the CRDM pressure boundary  150  is not provided other than the close proximity of the scram spring coil arrangement across a vacuum gap  121 . 
         [0031]    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 the CRDM  100 . The extended scram lift coil arrangement is supported from CRDM structural housing  106  and not pressure boundary  150  to avoid heat conduction. PIP probes  122  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 . An additional horizontal CRDM support interface can be applied between the upper vessel CRDM supports and the individual CRDM support structures. 
         [0032]    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.