Systems and methods of monitoring operation of control rod mechanisms of nuclear power plants

Abstract

Systems and methods of monitoring operation of control rod mechanisms of nuclear power plants, including obtaining signal values from existing plant test points of at least one component of a rod movement mechanism during operation of the nuclear power plant, utilizing obtained signal values to determine a present impedance of the at least one component of the rod movement mechanism during the operation of the nuclear power plant, comparing the present impedance to a reference impedance, and indicating degradation of the rod control system if the present impedance deviates from the reference impedance by a predetermined amount.

What is claimed is: 
     
         1 . A method of monitoring operation of a control rod movement mechanism of a nuclear power plant, comprising:
 obtaining signal values from existing plant test points of at least one component of the control rod movement mechanism during operation of the nuclear power plant;   utilizing obtained signal values to determine a present impedance of the at least one component during operation of the nuclear power plant;   comparing the present impedance to a reference impedance; and   indicating degradation of the at least one component if the present impedance deviates from the reference impedance by a predetermined amount.   
     
     
         2 . The method of  claim 1 , wherein the present impedance is recorded over a length of time including one or more energy states and transitions between energy states of the at least one component, the energy states including a fully energized state, a reduced state, an inactive state, or any combination thereof. 
     
     
         3 . The method of  claim 1 , wherein the obtained signal values are voltage and current values. 
     
     
         4 . The method of  claim 1 , wherein the at least one component includes a coil, connector, cable, or any combination thereof in the rod movement mechanism. 
     
     
         5 . The method of  claim 1 , wherein the reference impedance corresponds to historical impedance measurements of the control rod movement mechanism during operation of the nuclear power plant. 
     
     
         6 . The method of  claim 1 , further comprising recording one or more determined impedances corresponding to the at least one component to determine the reference impedance. 
     
     
         7 . The method of  claim 1 , further comprising measuring a resistance of the at least one component to determine a temperature of the at least one component. 
     
     
         8 . The method of  claim 1 , further comprising displaying one or more signal values associated with the at least one component on a graphical display. 
     
     
         9 . The method of  claim 8 , wherein the displaying includes plotting the one or more signal values over a time period including one or more energy states and transitions between energy states of the at least one component. 
     
     
         10 . The method of  claim 1 , wherein the present impedance is recorded over a length of time including one or more energy states and transitions between energy states of the at least one component. 
     
     
         11 . The method of  claim 10 , wherein the energy states of the at least one component includes a fully energized state, a reduced state, an inactive state, or any combination thereof. 
     
     
         12 . The method of  claim 1 , wherein the determining, comparing, and indicating operations are performed on a lift coil, moveable gripper coil, and stationary gripper coil during six stages of a rod withdrawal sequence, including:
 a first stage in which the stationary gripper coil is energized at a reduced state, and a stationary gripper is solely latched to the rod;   a second stage in which the stationary gripper coil is energized to a fully energized state, and the moveable gripper coil is energized to the fully energized state to latch a moveable gripper to the rod;   a third stage in which the stationary gripper coil is discharged to an inactive state such that the movable gripper is solely latched to the rod;   a fourth stage in which the lift coil is energized to the fully energized stage until the rod is lifted a predetermined distance;   a fifth stage in which the lift coil is discharged to the reduced state until the stationary grip coil is energized to the fully energized state to latch the stationary grip to the rod; and   a sixth stage in which the lift coil and moveable gripper coil are discharged to the inactive state, and the stationary grip coil is discharged to the reduced state.   
     
     
         13 . A method of monitoring a rod control system of a nuclear power plant, the method comprising:
 establishing reference signals corresponding to normal operation of at least one coil of a rod control system during a step operation of the rod control system, the reference signals including a plurality of reference values corresponding to various energy states and transitions of energy states occurring during operational sequences of the at least one coil;   obtaining in situ signals from the at least one coil during an operational sequence of the at least one coil during operation of the nuclear power plant, the in situ signals including a plurality of in situ values corresponding to various energy states and transitions of energy states occurring during present operational sequences of the at least one coil;   comparing the in situ values to the reference values; and   determining whether the in situ values associated with a particular energy state or transition of energy states deviates from a corresponding reference value associated with the particular energy state or transition of energy states by a predetermined amount, and, if so, associating the deviation with a particular degradation of the rod control system.   
     
     
         14 . The method of  claim 13 , wherein the at least one coil includes a lift coil, a movable coil, a stationary coil, an upper gripper coil, a pulldown coil, a load transfer coil, a lower gripper coil, or any combination thereof, wherein each coil has its own respective operational sequence including various respective energy states and transitions of energy states occurring during operation sequences of each respective coil, wherein the reference values and in situ values include a plurality of values corresponding to the various respective energy states and transitions of energy states, and wherein the determining operation includes determining whether the in situ values associated with any one or more of the respective energy states or transitions of energy states deviates from a corresponding reference value associated with the particular respective energy state or transition of energy state.