ML22222A110
| ML22222A110 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 07/21/2022 |
| From: | Kevin Barclay Division of Reactor Safety II |
| To: | NRC/NRR/DRO/IRAB |
| Kenneth Kolaczyk, NRR/DRO/IRAB, 58577389 | |
| Shared Package | |
| ML22222A099 | List: |
| References | |
| Download: ML22222A110 (28) | |
Text
Davis Besse EDG Failure Field Flash Selector Switch May 2021 Kevin Barclay U.S. Nuclear Regulatory Commission 2022
Disclaimer
This training session is being recorded for future use in the NRCs knowledge management program. The recorded contents of the session, including any questions posted by audience members, will be preserved in accordance with the NRCs record management program and are subject to FOIA disclosure. Please refrain from including any sensitive information (i.e., SUNSI) in any questions that you may ask.
Please leave your chat box open to view all questions and answers posed during the session.
Event Summary
- May 27, 2021 - Fast-Start Surveillance Test - EDG 1
- Test Performed with Field Flash Selector Switch (FFSS) in the 400 RPM (Emergency Start) Position
- Diesel Started and Reached 900 RPM
- EDG Failed to Reach Rated Voltage and Frequency
- Investigation Found Generator Field Had Not Flashed
- Licensee Chose to Stop Test and Shutdown EDG 3
Event Summary
- May 27, 2021 - Fast-Start Surveillance Test - EDG 1
- During EDG Shutdown, Field Flashed After Licensee Placed the FFSS in 800 RPM (Idle Start) Position.
- Licensee Continued With EDG Shutdown
- In-situ Testing Found FFSS Emergency Start Contacts Failed 2 / 5 Times
- Licensee Replaced FFSS
- EDG Retested and Declared Operable May 28, 2021 4
EDG Field Flash Selector Switch
- Panel Mounted
- Rotary Cam Operated Switch 5
EDG Field Flash Selector Switch 6
EDG Field Flash Circuit 7
EDG Field Flash Selector Switch 8
9
Licensees Preliminary Investigation
- Contacts Failed From Fouling on the Contacts
- At regular intervals, the switch contacts should be inspected for wear and burning
- If contacts are coated with sulphide, they should be cleaned
- Licensee CR: No PM is currently performed on the switch, leading to fouling that is present on the contacts.
Part of the resolution will be to create a PM to clean the contacts on these switches.
10
Independent Failure Analysis
- Multiple Vendors
- Intrusive and Non-intrusive Inspection
- Contact Resistance Checks
- Functional Testing
- Failure Modes Analysis 11
12
Post-Failure Custody / Quarantine
- May 27, 2021 - Failure / Troubleshooting
- June 3, 2021 - Contacts Photographed
- September 9, 2021 - Switch Prepared For Shipment For Inspection / Testing 13
Licensee Post-Failure Analysis Conclusions
- Switch Failure Was Not Contact Fouling From Lack of PM
- Found Nickel Contamination on Contact
- Postulated FME From Upper Terminal Screw Location
- PM Performance Deficiency Did Not Cause May 27th Event 14
Apparent PD / Violation The Team concluded that the failure to develop a preventive maintenance schedule for the inspection of the FFSS, was contrary to Technical Specification 5.4.1 and Section 9.b of Regulatory Guide (RG) 1.33, Revision 2, February 1978, and constituted a performance deficiency.
Davis-Besse TS 5.4.1(a) requires the licensee to establish, implement, and maintain applicable written procedures for the safety-related systems and activities recommended in RG 1.33, Revision 2, Appendix A, February 1978.
Section 9.b of RG 1.33, states, in part that preventive maintenance schedules should be developed to specify lubrication schedules, inspections of equipment, replacement of such items as filters and strainers, and inspection or replacement of parts that have a specific lifetime such as wear rings.
15
Preliminary GTG Finding December 16, 2021
- FFSS Fast Start Contacts
- 184-Day TS Test Frequency
- Previously Tested November 12, 2020
- Preliminary PRA Evaluations Produced Greater-Than-Green Results 16
- Licensee Discussed Conservatisms in the PRA Model
- Key Areas Evaluated:
- Exposure Time
- Operator Recovery
- Model Conservatisms
- Licensee Significance Estimate
- White 17
- Licensee reiterated that they changed their perspective from the initial investigation:
- Determined that a PM to inspect the FFSS contacts FFSS would likely have not prevented the May 27th event
- Significance of the performance deficiency associated with the FFSS should not be based on the May 27th event 18
- Licensee Actions Taken:
- Replaced FFSS on both EDGs
- Test Procedure Enhancements - Continuity Checks Following Switch Manipulation
- Procedure Enhancement - Field Flash Pushbutton use added to Emergency Use section of Operating Procedure
- Initiated Enhancement PMs to Inspect /
Replace FFSS
- EDG Reliability Assessment 19
- Licensee Modifications Being Considered:
- Install an indicating light for the switch contacts when returned to the 400 RPM position to validate circuit integrity
- Redesign field flash circuit to remove dependence on the 400 RPM contact 20
Final Closure Letter
- Agency concluded that the cause of the malfunction was not certain
- Licensee PM schedule decisions were reasonable at the time of the modification
- The switch failure was not reasonably within the licensees ability to foresee 23
Final Closure Letter
- Under the ROP, equipment failures that are not caused by a performance deficiency are considered part of the baseline risk of the facility, in which equipment failures can occasionally occur.
24
SIT Unresolved Item FFSS
- 2006 Voltage Regulator / FFSS Modification
- TS Surveillance Testing Adequacy 25
Public ADAMS Documents
- Special Inspection Report ML21321A365
- Preliminary GTG Letter ML21348A767
- Reg Conference (NRC) ML22028A397
- Reg Conference (Licensee) ML22028A392
- Reg Conference Summary ML22084A102
- Closure Letter ML22109A157 26
Internal ADAMS Documents
- First FFSS IFRB ML21298A241
- Second FFSS IFRB ML21309A119
- SERP ML22003A084 27
Questions 28