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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 53912 | 6 March 2019 05:00:00 | 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect | Part 21 Report - Target Rock Solenoid Valve 810000-X Positioner Circuit Failure May Cause Undesired Position | The following was received via email: Target Rock Modulating Solenoid Operated valves which utilize model 810000-X positioner manufactured and supplied by Target Rock. Target Rock Modulating Solenoid Operated valves are equipped with a separate, remote mounted, positioner unit, which is a closed loop valve position control system. The valve positioner is electronically connected to the valve assembly via a wiring harness. This defect only applies to the current production 810000-X positioner model. All previous versions of the Target Rock Modulating Solenoid Operated valve positioners do not exhibit this defect. Three (3) 810000-X model positioners were returned to Target Rock by Duke Energy Carolinas, LLC, Oconee Nuclear Station for defective operation. Target Rock evaluated these units and found two defective circuits in the positioner PC board at unrelated locations: the 80 V Regulator Circuit and the Close Indication Relay Driver Circuit. Description: 1.) 80 V Regulator Circuit Failure - In the event of a failure of the positioners 80 V Regulator Circuit, the positioner, and therefore its associated modulating solenoid operated valve, will no longer receive voltage from the positioner, resulting in the return spring moving the valve disc to its fail position (fully open or fully closed depending on the design specification requirement). Based on the positioners returned by Duke Oconee, and additional testing performed by Target Rock, this 80 V Regulator Circuit Failure will only occur during initial powering of the device. Positioner units currently in operation, and constantly energized, will not have this failure occur. In the instance where the positioner is powered down and then powered back up during maintenance activity or other event, this failure has the potential to occur upon re-energization of the device. Having said that, should the positioner continue to be operational through power-up, it would be expected to perform its intended function throughout operations. 2.) Close Indication Relay Driver Circuit Failure - In the event of a failure of the positioners Close Indication Relay Driver Circuit, the positioner will be unable to send a signal to indicate the valve has reached its fully closed position. Typically, this circuit is enabled for plant monitoring purposes. This failure has no effect on the ability of the Modulating Solenoid Operated valve or positioner to control fluid flow as intended. Root Cause: 1.) 80 V Regulator Circuit Failure - The defect observed on the 80 V Regulator Circuit is a failure of a Zener reference diode. The Zener reference diode reduces the normal (90 - 140 V) supply voltage to approximately 80 V for this portion of the circuit. In the event of a failure of the Zener reference diode, full input voltage (90 -140 V) is passed to the downstream components in the circuit. The downstream components from the Zener reference diode are not rated for 90 - 140 V operation and fail, rendering the positioner inoperable. 2.) Close Indication Relay Driver Circuit Failure - The defect observed on the Close Indication Relay Driver Circuit was a trace wire in the PCB which had opened (broke) at multiple locations. Corrective Action: Two corrective actions have been put in place. All new 810000-X positioner units manufactured by Target Rock will have these revisions incorporated: 1.) The Zener reference diode for the 80 V Regulator Circuit has been replaced with a different component. The rating for the Zener reference diode has been increased from 30 mA to 73 mA. This upgrade will ensure current ratings are not exceeded during initial powering of the device. 2.) The PCB trace which failed has been upgraded. The trace width has been changed from 12 mil to 70 mil. The wider trace width will be less susceptible to variations in width during the manufacturing process, and in the event of any minor variations in width, will still be sufficient to pass the required current. Should you have any questions regarding this matter, please contact Michael Cinque, General Manager at (631) 293-3800 Very Truly Yours, Michael Cinque General Manager Target Rock, Business Unit of Curtiss-Wright Flow Control Corporation Affected sites are Oconee, Vogtle, South Texas Project, and Millstone. |