Patent Application
20140369455
The present application relates generally to nuclear reactor rod control systems, and more particularly relates to systems and methods of confirming rod movement, determining step movements, and providing step indication of control rods in nuclear power plants.
In a nuclear Pressurized Water Reactor (PWR), the power level of the reactor is controlled by inserting and retracting control rods, which may include shutdown rods, in a reactor core.
Current designs of many nuclear power plants are equipped with control and shutdown rods which are inserted and withdrawn from the reactor core to control the reactivity by absorbing neutrons. Specifically, in Pressurized Water Reactors (PWRs), the movement of each rod is facilitated by its own electromechanical magnetic jack mechanism located atop the reactor vessel. Two examples of rod control systems that use this mechanism are the Control Rod Drive Mechanism (CRDM) and Control Element Drive Mechanism (CEDM). Both of these mechanisms consist of a set of coils that provide precise vertical movement to the rod by sequentially inducing a magnetic field in the coils to operate the mechanical parts of the system. The magnetic flux provides the energy needed to hold, insert, or withdraw the rod from the reactor core.
Existing methods make count steps based on demands from the control room. The method proposed herein makes an assessment of rod movement from the output of the rod movement mechanism. This allows steps to only be counted when movement actually occurs based on verification of a proper rod movement sequence. This method will help mitigate step count errors which can cause reactor trips.
Example embodiments of the present general inventive concept provide systems and methods of verifying proper step movements of control rods in nuclear power plants.
Additional features and embodiments of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present general inventive concept.
Example embodiments of the present general inventive concept can be achieved by providing a method of monitoring step movements of control rods of a nuclear power plant, including measuring output signals of a plurality of rod movement coils during a step movement sequence of one or more control rods, analyzing the output signals to determine a direction of the step movement sequence, and comparing one or more output signals to the reference rod movement sequence to verify that a step of the control rod has occurred.
Verification of the step movement includes verification of sequencing, timing, and mechanical operation of the rod control mechanism as related to the reference rod movement sequence.
The method may include decrementing or incrementing a step counter based on the analyzing and comparing operations.
The method may include generating a warning signal if a determined direction of step movement does not correspond to a commanded direction of step movement and/or if a difference between the one or more output signals deviates from the reference rod movement sequence by a predetermined amount.
The method may include displaying step information.
Example embodiments of the present general inventive concept can also be achieved by providing a step counter system for a rod control system of a nuclear power plant, including a measuring unit to measure output signals of a plurality of rod movement coils during a step movement sequence of one or more control rods, and a controller to analyze the output signals to determine a direction of the step movement sequence, and to compare one or more output signals to the reference rod movement sequence to verify that a step of the control rod has occurred.
The controller can be configured to decrement or increment a step counter based on a determined direction of the step movement sequence and a comparison of the one or more output signals to the reference rod movement sequence.
The controller can be configured to generate a warning signal if a determined direction of step movement does not correspond to a commanded direction of step movement and/or if a difference between the one or more output signals deviates from the reference signal by a predetermined amount.
The step counter may include a display unit to display step counter information based a determined direction of the step movement sequence and a comparison of the one or more output signals to the reference rod movement sequence.
The following example embodiments are representative of example techniques and structures designed to carry out the objects of the present general inventive concept, but the present general inventive concept is not limited to these example embodiments. In the accompanying drawings and illustrations, the sizes and relative sizes, shapes, and qualities of lines, entities, and regions may be exaggerated for clarity. A wide variety of additional embodiments will be more readily understood and appreciated through the following detailed description of the example embodiments, with reference to the accompanying drawings in which:
Reference will now be made to example embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings and illustrations. The example embodiments are described herein in order to explain the present general inventive concept by referring to the figures.
In the embodiment of
Referring to
Presently, step counters that are used to display the current step of the drive mechanism are based on up or down rod movement commands coming from either the reactor operator or reactor control system. Since the step counter is based on demanded movement, and not actual movement, the information may become inaccurate if a problem occurs in the drive mechanism or rod control system. An example solution is with a data driven solution that uses the outputs of the drive mechanism coils to confirm rod movement and determine the step of the rod.
Referring to
In some embodiments, verifying the sequencing of the coil states alone may not be enough to verify that a step of the drive rod has occurred. For example, the latching of the magnetic jacks may be confirmed as well as the times at which the latches occur. Moreover, the coil(s) associated with a given gripper may go to a high state but that does not guarantee that the latch was properly engaged. To verify the latch engagement, embodiments of the present general inventive concept examine the phenomena which causes the latch ‘dip’ in the coil output data. That is, when a gripper coil has enough energy it causes the gripper assembly to be slightly lifted causing the gripper to engage the grooved rod. The upward movement of the gripper causes a back EMF to be induced in the coil which causes the latch ‘dip’ seen on the coil current data. For example, if the lift coil cannot perform the lift movement over the distance required to complete one step the rod will most likely remain on the current step. Additionally, if the rod becomes stuck, LC only partially lifts the gripper assembly, or some other obstacle hinders the grippers to fully engage or disengage it will be detected in the gripper movement analysis. Further analysis of this change in current can verify that the grippers have been fully engaged or disengaged, and that the lift coils have properly lifted the gripper assembly for which they are responsible. The time at which the latch has been engaged should also be compared to other critical events in the coil sequence. For instance, if the MG disengages prior to the SG engaging in the step of the CRDM, then the rod may slip or completely be dropped into the reactor core.
An example method of monitoring step movements of control rods of a nuclear power plant, comprises: measuring output signals of a plurality of rod movement coils during a step movement sequence of one or more control rods; analyzing the output signals to verify the rod movement; and analyzing the output signals to determine a direction of the step movement sequence. An example method further comprises verifying step movement sequence. An example method further comprises verification of mechanical movement of the mechanism as it relates to the rod step movement sequence. An example method further comprises decrementing or incrementing a step counter based on the analyzing and comparing operations. An example method further comprises generating a warning signal if a determined direction of step movement does not correspond to a commanded direction of step movement and/or if a difference between the one or more output signals deviates from the reference signal by a predetermined amount. An example method further comprises displaying step information.
An example step counter system for a rod control system of a nuclear power plant, comprises: a measuring unit to measure output signals of a plurality of rod movement coils during a step movement sequence of one or more control rods; and a controller to analyze the output signals to determine a direction of the step movement sequence, analyzing the output signals to verify the rod movement. An example controller is configured to decrement or increment a step counter based on a determined direction of the step movement sequence and a comparison to one or more output signals of the reference output signal. An example controller is configured to generate a warning signal if a determined direction of step movement does not correspond to a commanded direction of step movement and/or if a difference between the one or more output signals deviates from the reference sequence by a predetermined amount. An example system further comprises a display unit to display step counter information based a determined direction of the step movement sequence and verification through a comparison of the one or more output signals to the reference rod movement sequence.
The examples described herein provide a metric which may be utilized to diagnose rod movement problems because the calculation results may be predictable from step to step wherein a significant variation from normal may be noticed because a problem, such improper rod movement, exists.
While embodiments of the present general inventive concept are described herein, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional modifications will readily appear to those skilled in the art. The present general inventive concept in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.
