Patent Publication Number: US-2022230767-A1

Title: Digital systems and methods for high precision control in nuclear reactors

Description:
RELATED APPLICATIONS 
     This application is a continuation, and claims the benefit under 35 U.S.C. § 120, of U.S. application Ser. No. 17/131,200, filed Dec. 22, 2020, which is a divisional, and claims the benefit under 35 U.S.C. § § 120 &amp; 121, of U.S. application Ser. No. 15/453,195 filed Mar. 8, 2017, now U.S. Pat. No. 10,910,115. All these applications are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
       FIG. 1  is a cross-sectional illustration of a related art control rod drive  10  useable in a nuclear reactor. For example, related art control rod drive  10  may be a Fine Motion Control Rod Drive (FMCRD) as used in next generation BWRs like ESBWRs. As shown in  FIG. 1 , control rod drive is housed outside, such as below, reactor pressure vessel  1 , where drive  10  inserts or withdraws a control element, such as a control blade (not shown), attached thereto via bayonet coupling  15 . Hollow piston  16  connects to bayonet coupling  15  and is vertically moveable inside of an outer tube in drive  10 . Drive  10  includes ball screw  11  coupled with ball nut  12  that drives screw  11  vertically when rotated, such that hollow piston  16 , bayonet coupling  15 , and the control element attached thereto may be positioned with precision at desired positions in a nuclear reactor core. During scram, hollow piston  16  may be lifted off ball nut  12  by hydraulic pressure in the outer tube, permitting rapid movement and insertion of the control element. A magnetic coupling  17  pairs internal and external magnets to rotate ball screw  11  across a pressure barrier, and a motor and brake  19  mounted below drive and stop magnetic coupling  17  to desired positioning. 
     Power and control is provided to control rod drive by a Rod Control &amp; Information System (RC&amp;IS) that in varying conventional designs uses a mix of analog systems and digital transducers, including resolvers and synchros and encoders, and any required analogue-to-digital converters, coupled to motor and brake  19  to provide position detection, control, and power to the same. Several existing mixed analog and digital systems are able to detect and resolve position of associated control elements to several centimeters, with coarser position control. Related descriptions of drive  10  and FMCRD technology are found in GE-Hitachi Nuclear Energy, “The ESBWR Plant General Description,” Chapter 3—Nuclear Steam Supply Systems, Control Rod Drive System, Jun. 1, 2011, incorporated herein by reference in its entirety. 
     SUMMARY 
     Example embodiments include all-digital control rod drives and associated systems for monitoring, powering, and controlling the drives. Control and information systems may be divided into distinct channels with switches and controls of each channel performing independent and redundant control rod drive monitoring and controlling. Control and information systems may separately be divided among main control logic associated with plant operators and top-level input from other plant systems, remote cabinet equipment including multiplexed data handling for transmission to the main control logic, fine motion controllers associated with each control rod drive, and the control rod drive themselves. Each of these subsystems may pass control rod drive position information from multiple position sensors to the plant operators and other plant systems. Each piece of position information from an individual sensor, such as a digital position transducer, may be handled by one of the distinct channels of the control and information systems. Because the entire system, including control rod drives and control and information systems, may work with digital information on computer hardware processors and associated memories and busses, no digital-to-analog or analog-to-digital converter is necessary. By connecting and multiplexing each channel throughout the system, controllers associated with each channel may verify accuracy of position information with controllers of other channels, and redundant commands and data may be transmitted and received even if one channel or sensor fails. 
     Control rod drives useable in example embodiments include fine motion control rod drives capable of positioning and detecting position of control elements in very fine increments, such as 3-millimeter increments, such as with rotating servo motors. Example control rod drives may further include several position sensors that digitally report control rod drive status and insertion position in these fine increments. A single control and information system may receive the multiple position sensor readings from multiple control drive systems and control the same using appropriate powering and control signals to achieve desired control rod positioning. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       Example embodiments will 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. 
         FIG. 1  is an illustration of a related art nuclear control rod drive. 
         FIG. 2  is a schematic of a fine motion control rod drive motor and its motor control cabinet. 
         FIG. 3  is a schematic of an example embodiment digital rod control and information system. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     It will 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). 
     It will 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. 
     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 will 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. 
     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, so as 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. 
     The inventors have recognized that existing locking collet piston and magnetic jack type control rod drives lack precision, being able to move in increments of 6 inches or more. Typical ESBWRs and other large, natural-circulation-dependent reactors require greater precision for reactivity control. Related FMCRD, such as in the ABWR, while having greater precision, are operated using analog sensors such as synchros and servos, which require an analog-to-digital converter for control. The use of analog sensors results in decrease of precision accuracy. Moreover, controls for FMCRD need to have very high reliability in nuclear applications, and single-channel analog controls represent an impermissible failure risk for lack of redundancy. Example embodiments described below address these and other problems recognized by the Inventors with unique solutions enabled by example embodiments. 
     The present invention is a control rod drive control and information system. In contrast to the present invention, the small number of example embodiments and example methods discussed below illustrate just a subset of the variety of different configurations that can be used as and/or in connection with the present invention. 
     Example embodiment control rod drive (CRD) control and information systems are useable with several different types of CRDs. Example embodiments are further useable with high-precision CRDs, including FMCRDs. Further, co-owned applications 62/361,628, filed Jul. 28, 2016 by Morgan et al., 62/361,625, filed Jul. 13, 2016 by Morgan et al., and 62/361,604, filed Jul. 13, 2016 by Morgan et al. are incorporated herein by reference in their entireties. These incorporated applications describe high-precision CRDs that are useable with example embodiments; for example, example embodiment control systems may be interfaced with, and control, the control rod drives disclosed in the incorporated applications. 
       FIG. 2  is a schematic of FMCRD  10  where motor  19  and output of the FMCRD interface with an example embodiment system  100 . As shown in  FIG. 2 , motor  19  may receive power and operative signals from a motor control cabinet  21  over motor interface  26 . For example, motor interface  26  may be radiation-hardened power cables that deliver electrical power, such as three-phase pulse-width modulated electrical signals, and/or information like speed controls to motor  19  in challenging environments such as operating nuclear reactor environments. Fine motion motor controller  20  may receive such power from a plant power source  25 , including main plant electrical bus, local battery, emergency generators, or any other source of power. 
     Motor controller  20  is configured to power motor interface  26  for both very fine intervals and very large power jumps. In this way, motor  19  may be powered to move a control blade attached to FMCRD  10  at very precise intervals, such as 3 millimeter vertical insertions or withdrawals, as well as rapid, large insertion strokes for shutdown. For example, motor  19  may be a servo motor that is controllable up to ¼ th  of one revolution of a ball screw in FMCRD  10  that can self-brake and provide long-term static torque. A full revolution may equate to 12 millimeters of vertical control element movement, so positioning on an order of a few millimeters is possible. Delivery of a precise amount of power through motor interface  26  may thus achieve desired precise motor actuation and control element positioning. 
     FMCRD  10  may include multiple position detectors  18   a  and  18   b,  such as precise digital transducers that can determine an exact vertical position of ball nut  12  and/or other connective structures to report an accurate position of a control element within one-thirty-sixth of a millimeter. Position detectors  18   a  and  18   b  may be redundant or measure position of related structures as a verification of control element positioning. For example, two digital transducers as position detectors  18   a  and  18   b  may be coupled directly to a power output or shaft of motor  19  that encode rotations of the same to digitally represent motor  19  position and thus control element position. Because position detectors  18   a  and  18   b  may give digital output, informational positional signal interfaces  27   a  and  27   b  may be any connection capable of carrying digital signals, including fiber optic cable, coaxial cables, wireless signals, etc., separate or combined with motor interface  26 . 
     Fine motion motor controller  20  includes two channel interfaces  28   a  and  28   b  each configured to receive digital position information from an associated one of detectors  18   a  and  18   b  via positional signal interfaces  27   a  and  27   b.  Channel interfaces  28   a  and  28   b  may separately handle individual positional signals and control inputs so as to preserve integrity of a redundant system and allow different signals to be verified against one another without intermixing or single failure affecting both signals. Fine motion motor control cabinet  21  housing motor controller  20  and various interfaces and communicative connections may be local or remote from FMCRD  10 . Because all components of cabinet  20  may be digital with no analog-to-digital converter, cabinet  20  may be relatively small and better hardened against an operating nuclear reactor environment. 
       FIG. 3  is a schematic diagram of an example embodiment digital rod control and information system (RC&amp;IS)  100 . As shown in  FIG. 3 , example embodiment RC&amp;IS  100  interfaces with a FMCRD  10  and fine motion motor controller  20  ( FIG. 2 ) through remote links  37   a  and  37   b.  RC&amp;IS  100  may be located closer to an operator or control room, outside of containment and remote from FMCRD  10  and its motor control cabinet  21  ( FIG. 2 ), in which case remote links  37   a  and  37   b  may be any kind of digital data connection, including higher-reliability fiber optic cables or wireless connections. Remote links  37   a  and  37   b  together communicate dual-channel positional data from an FMCRD, such as digital positional data generated by position detectors  18   a  and  18   b  for redundant position determination of individual control elements. 
     RC&amp;IS  100  includes remote communication cabinet equipment  110  networked with an RC&amp;IS main control logic  111  that is configured to receive input  200  from operators and other plant systems for control element operation and positioning. RC&amp;IS  100  is completely digital, using microprocessors, field-programmable gate arrays, and digital communications for higher reliability and less space requirement. Cabinet equipment  110  may be all stored in a discreet and smaller cabinet remote or local to a control rod drive. For example, cabinet equipment  110 , lacking any analog-to-digital converter, may fit in a relatively small space and handle control element operations for a quarter of a nuclear core. Moreover, all-digital RC&amp;IS  100  is less susceptible to noise and vibration found in an operating nuclear operating environment and thus can be located anywhere in a nuclear plant and can perform self-testing and alerting functions to maintain desired operations with lower failure rates than analog equipment. 
     Example embodiment RC&amp;IS  100  is configured to handle and control an FMCRD with dual, redundant inputs to maintain operations in the case of single-channel failure, such as if a single position detector becomes unusable or signals are lost from one channel in example embodiments. As shown in  FIG. 3 , RC&amp;IS  100  includes two independent channels  120  and  130  in its cabinet equipment  110 , each in communication with an individual position data source such as remote links  37   a  and  37   b.  Although shown in communication with a single set of remote links  37   a  and  37   b,  it is understood that multiple FMCRDs and related motor controls may be input into and controlled by cabinet equipment  110 , including an entire core quadrant&#39;s worth of control drives. 
     Each channel  120  and  130  independently handles distinct digital position and operation signals; however, channels  120  and  130  are also connected in order to verify and potentially replace one another. Bus communications  115  between all elements of channels  120  and  130  may be typical digital communications lines, including internal computer buses, motherboard connections, wired connections, or wireless connections. Each channel  120  and  130  includes multiplexed and redundant switches  121 ,  122 ,  124 ,  131 ,  132 , and  134 . Switches  122 ,  124 ,  132 , and  134  may receive positional data and issue motor command signals, as well as other data, for each control rod drive associated with RC&amp;IS  100 . As shown by bus communications  115 , switches  121  and  122  associated with channel  120  may include connection to switches  131  and  132  of the other channel  130 . Thus, if a switch fails in either channel, or if other channel components become inoperative, the operative channel and switches therein may still receive, transmit, and otherwise handle all control information. 
     Each channel  120  and  130  includes a controller  123  and controller  133 , respectively. The controllers  123  and  133  may receive, buffer, issue, and interpret control rod drive operational data. For example, controllers  123  and  133  may receive rod movement commands from RC&amp;IS control channel controllers  165  and  155 , and such commands may be interpreted and sent to one or more motor controllers  20  ( FIG. 2 ) through remote links  37   a  and  37   b.  Motor controller  20  ( FIG. 2 ) may then provide power transmission to a motor  19  through motor interface  21  ( FIG. 2 ) to achieve desired driving, braking, and position from detectors  18   a  and  18   b  ( FIG. 2 ), interpreted for operator readout. 
     As shown in  FIG. 3 , controllers  123  and  133  may also perform comparison of rod movement commands from the RC&amp;IS control logic controllers  155  and  165  to ensure that inconsistent rod movement commands do not result in rod movement. Switches  124  and  134  may provide redundant data links between each RC&amp;IS logic channel controller  165  and  155 , and each remote cabinet controller  123  and  133 . Switches  122 ,  132 ,  121 , and  131  may provide redundant data links between each controller  123  and  133  and multiple motor controllers  20  ( FIG. 2 ). 
     As shown in  FIG. 3 , each controller  123  and  133  in channel  120  and  130  interfaces with an input/output switch  124  and  134  for sending and receiving operational data to operator controllers in RC&amp;IS main control logic  111 . Because main control logic  111  interfaces with several other plant safety systems and operator controls, control logic  111  is typically located in or near a control room or other plant operator station. Input/output switches  124  and  134  multiplex control commands and information from both channels over main logic interfaces  140  to main control logic  111 . For example, main control logic may include two or more main RC&amp;IS channel controllers  165  and  155 , each with two switches  161 ,  162 ,  151 , and  152 . Main logic interfaces  140  may be multiplexed to provide digital information and control data from both channels  120  and  130  to each switch  151 ,  152 ,  161 , and  162 . In this way, main RC&amp;IS channel controllers  155  and  165  may have redundant switches that each have access to both channels associated with each control rod drive. 
     Main RC&amp;IS channel controllers  155  and  165  receive and implement operator feedback and input, including control element positioning commands, as well as input  200  from other plant systems, such as plant steady-state information or trip alerts. Because each main controller  155  and  165  receives redundant control and command data, and can issue redundant commands to independent channels  120  and  130 , either controller  155  and  165  may be used to report on and operate all aspects of a control drive, regardless of failure of the other controller and/or of channel equipment or position reporting equipment. 
     Similarly, because main RC&amp;IS channel controllers  155  and  165  may themselves be connected and communicate through an internal bus or other plant communicative connections, controllers  155  and  165  may verify positional and operational data received as well as operator inputs between themselves. Controllers  155  and  165  may be configured to detect discrepancies between information received from either channel  120  and  130 , as well as inputs  200  or operator controls received by them both. Upon detection of a discrepancy, an operator may be notified and/or a channel may be identified as out-of-service. For example, an operator or plant control system may input a very fine control element repositioning, such as 3 mm, for a single control blade, and system  100  may receive and process the move, resulting in rod movement commands to the motor controller  20  and appropriate power and signaling transmitted to motor  19  from the motor controller  20  through motor interface  26  ( FIG. 2 ). Position detectors  18   a  and  18   b  ( FIG. 2 ) may then report digital, accurate rod repositioning information, which may be processed by the motor controller  20  and transmitted to the remote controllers  123  and  133 , which may interpret and transmit the rod repositioning information to the main controllers  165  and  155 . Main controllers  165  and  155  may verify this position data from both channels and thus detectors, and ensure it reflects the input command. Because channel controllers  155  and  165  are themselves digital, such analysis and notification or disregarding of bad channel data may be implemented as simple programming or hardware structuring in microprocessors of controllers  155  and  165 . Each channel of RC&amp;IS controller logic,  155  and  165 , may contain one or more microprocessors, such as three redundant microprocessors R, S, and T each performing the same RC&amp;IS logic computations independently and asynchronously of each other. Redundant microprocessors in each RC&amp;IS control logic channel,  165  and  155  may ensure detectability and continuity of rod control logic functions in the presence of a single microprocessor failure. 
     Example embodiment RC&amp;IS  100  is end-to-end digital, handling data and commands received directly from digital inputs and outputs. Such digitization allows for a smaller footprint, faster analysis and action, less susceptibility to noise, vibration, heat, and radiation damage, finer motor control and monitoring, and easier handling of multiple-channel data for redundancy and verification in control rod drive operation. Further, connections among various components, such as by internal connections  115  or connections  140  between potentially remotely-situated cabinet  110  and main logic  111 , may be reliable communicative connections between systems, including internal busses on motherboards, fiber optic cables, etc. 
     Example embodiments and methods thus being described, it will 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, although only one FMCRD  10  is shown schematically connected to example embodiment system  100 , use of multiple different FMCRDs, as well as other types of control rod drives for a variety of different reactor sizes and configurations are compatible with example embodiments and methods simply through proper dimensioning of example embodiments - and fall within the scope of the claims. 
     Such variations are not to be regarded as departure from the scope of these claims.