ENS 55282
ENS Event | |
|---|---|
04:00 May 28, 2021 | |
| Title | Part 21 Report - Vacuum Breakers Failure to Close |
| Event Description | The following is a summary of the report provided by Framatome Inc.:
Identification of Component: Siemens 5kV 1200A Vacuum Breakers - 5-DPU-350-1200-78 Nature of Defect: Framtome reported during dedication testing / inspection that a batch of 5-DPU-350-1200-78 MV vacuum breakers exhibited sporadic failure to close upon both electrical and mechanical closure signals. This was entered in their Corrective Action Program and troubleshooting / testing was completed at the Siemens manufacturing facility. Using a high speed camera to troubleshoot, they determined the close latch does not have sufficient torsional force to consistently maintain the breaker close latch in the closed position during the closing cycle. In some instances the breaker will receive a close signal and the close latch will not maintain the breaker in a closed position and the breaker will fail to close. It has been observed in testing that this condition is sporadic and that subsequent attempts to close the breaker will result in a closed breaker. The issue has no impact on the breakers staying closed once they have successfully closed. The issue has no impact on the ability for the breakers to open. Number and Location of Basic Components: The reportable defect is similar to design on the 22 breakers delivered and 19 installed at St. Lucie Unit 1, during refueling cycle 30. St. Lucie was notified on May 28, 2021 by Framatome Inc. via telephone and email. Corrective Actions to Date: Preliminary evaluation determined a modification of the breakers is required to increase the torsion spring force acting on the close latch. Framatome is working with Siemens to develop a long-term solution to increase the torsional spring force acting on the close latch. An interim solution utilizing a revised spring retaining bracket could be deployed near-term. Gayle Elliott Deputy Director, Licensing & Regulatory Affairs Framatome Inc. 3315 Old Forest Road Lynchburg, Va. 24501 Office (434-832-3347) Mobile (434-841-0306)
The following information was received from Framatome via email: The preliminary evaluation determined a modification of the breakers was required to increase the torsion spring force acting on the close latch. Framatome worked with Siemens to develop an interim and long-term solution. The interim solution utilized a revised spring retaining bracket that could be deployed near-term. The original long-term solution was a new torsion spring design which applied approximately 40 percent more torsional force on the trip latch. Following a reoccurrence of the failure-to-close issue, Framatome and Siemens identified the root cause of the trip latch bounce and [determined] the associated corrective actions. The solution developed will mitigate all main failure to close causes (low power to the closing mechanism, insufficient time for the trip latch to drop, and improper trip latch to jackshaft interaction) for the 5kV replacement circuit breakers. The solution consists of the following: 1) Circuit breakers comply with the following revised design performance parameters: a. Jackshaft rotational speed (C speed #2) b. Jackshaft overtravel c. Jackshaft overtravel duration 2) Circuit breakers have the new torsion spring installed 3) Circuit breakers meet the revised bump stop gap By increasing the bump stop gap, the jackshaft is now able to rotate further before it hits the bump stop. This reduces the amount of force transferred to the bump stop and in turn the operating mechanism. This reduction significantly reduces the amount of latch bounce for this breaker design. St. Lucie was first notified of this 10CFR21 reportable defect on May 28, 2021 by Framatome Inc. via telephone and email. Notified R2DO (Miller) and Part 21 group via email. |
| Where | |
|---|---|
| Framatome Inc. Lynchburg, Virginia (NRC Region 1) | |
| Organization: | Framatome Anp |
| Reporting | |
| 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect | |
| Time - Person (Reporting Time:+12.6 h0.525 days <br />0.075 weeks <br />0.0173 months <br />) | |
| Opened: | Gayle Eliott 16:36 May 28, 2021 |
| NRC Officer: | Kerby Scales |
| Last Updated: | Sep 23, 2021 |
| 55282 - NRC Website
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Framatome with 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect | |
WEEKMONTHYEARENS 552822021-05-28T04:00:00028 May 2021 04:00:00
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