PART 21 NOTIFICATION - INTROL POSITIONERS POTENTIAL LATENT DEFECT
The following is an excerpt of the Part 21 information received via email:
"Introl Positioners used by stations in G32 Terry Turbine control applicators have the potential to contain a latent defect. The defect is the result of internal corrosion which has been identified in Tl Operational Amplifiers Part No.TL084CN on the SL3EX Controller Boards of the turbine throttle valve positioner. It is believed the likely cause is associated with the ingress of solder flux into the IC Chip package on the controller board due to delamination caused by the soldering process during fabrication. The corrosion over time can result in intermittent open circuiting and high resistance in the aluminum metallization. Chlorine ionic contamination can also result in high leakage currents within the component circuitry. Failures may be manifested by a reduced valve position signal disproportional to the expected demand condition, no actuation signal (i.e. throttle valve remaining full open), or other anomalous unexpected behavior. There are three TL084CN chips on each SL3EX Controller Board within the positioner assembly. There have been two documented failures to date occurring in 2015 and 2019 in installed systems.
"Date determination was made: May 29, 2019
"Affected sites: Farley, SONGS, Cooper, Almaraz Trillo Nuclear Power Plant (Spain), Clinton, Harris, Wolf Creek, Point Beach, Hatch, Watts Bar, Sequoyah.
"Stations are advised to work directly with Curtiss-Wright SAS via the technical contacts below.
"Randy F. Iantorno Project Manager, T: 585.596.3831, M: 585.596.9248, email riantorno@curtisswright.com or Justin Pierce 585.596.3866."
* * * UPDATE FROM RANDY IANTORNO (CURTISS-WRIGHT) TO DONALD NORWOOD AT 1537 EDT ON 6/7/2019 * * *
The following is a synopsis of information received via E-mail:
Shearon Harris Nuclear Plant experienced an overspeed trip of the Turbine Driven Auxiliary Feedwater Pump (TDAFW) on January 18, 2019 during routine system testing. Upon receipt of the initial start signal, the valve remained in the fully open position causing the TDAFW to trip on overspeed. Investigation into the overspeed trip revealed the positioner was not controlling the actuator properly in response to the governor command signal. This situation and subsequent troubleshooting led to replacement with the site spare positioner. Once installed, the system responded as expected and the suspect positioner was sent to Curtiss-Wright SAS (CW SAS) for evaluation.
In a joint effort between CW SAS and Paragon Energy Solutions (PES), the positioner was tested and evaluated to determine the cause of the failure.
Corrective action which has been, is being, or will be taken:
- The three TI chips on the affected board have been successfully replaced at PES. The repaired positioner will be configured and returned to Shearon Harris.
- The evaluation of suspect chips has been limited to those removed from the failed positioner, along with some supplied to PES by CW SAS. Work is ongoing in this area.
- A complete list of potentially affected installations is listed in the PES Part 21 Report dated May 31, 2019.
- Although this defect has the potential of preventing the Electronic Governor Speed Control System (EGSCS) from performing its intended safety function, it does not prevent the Terry Steam Turbine from operating. If the EGSCS fails, the turbine can be operated manually using the Trip and Throttle Valve (TTV) to control speed by regulating steam flow to the turbine.
- Steps are being taken to develop a plan to replace chips on affected positioner boards. This is still in the preliminary stages and specific recommendations will follow.
Notified R1DO (Carfang), R2DO (Rose), R3DO (Kozak), R4DO (Kellar), Part 21 Reactors E-mail group, and Part 21 Materials E-mail group.
* * * 1058 EDT ON 7/11/2019, UPDATE FROM RANDY IANTORNO (CURTIS-WRIGHT) TO MICHAEL BLOODGOOD * * *
The following was received via e-mail.
"This is a follow up letter related to Curtiss-Wright SAS (CW SAS) Report no. 48 submitted on June 6, 2019 regarding the Introl positioner failure discovered at the Shearon Harris Nuclear Plant on January 18, 2019.
"As reported in the initial report, the failure has been isolated to internal corrosion discovered inside TL084N Operational Amplifier chips on the SL3EX Controller Board. The cause of the failure has yet to be determined; however CW SAS and Paragon Energy Solutions (PES) continue to investigate potential causes.
"CW SAS will continue working with affected sites to provide guidance on additional testing, along with developing solutions that include replacement of suspect chips on the Introl positioner control boards. To allow CW SAS to coordinate efforts on a site by site basis, this will be the final correspondence sent directly to the NRC on this matter."
Notified R2DO (Ehrhardt), R3DO (McCraw), R4DO (Azua), Part 21 Reactors E-mail group, and Part 21 Materials E-mail group. |