05000389/LER-2021-001, Automatic Reactor Trip Due to a Breaker Failure on the 2B2 480V Motor Control Center
| ML21069A341 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 03/10/2021 |
| From: | Deboer D Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2021-001-00 | |
| Download: ML21069A341 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) |
| 3892021001R00 - NRC Website | |
text
March 10, 2021 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Re:
St. Lucie Unit 2 Docket No. 50-389 Reportable Event: 2021-001-00 Date of Event: January 20, 2021 L-2021-061 10CFR50.73 Automatic Reactor Trip Due to a Breaker Failure on the 2B2 480V Motor Control Center The attached Licensee Event Report 2021-001 is being submitted pursuant to the requirements of 10 CFR 50. 73 to provide notification of the subject event.
Respectfully, Daniel DeBoer Site Vice President St. Lucie Plant DD/res Attachment cc:
St. Lucie NRG Senior Resident Inspector St. Lucie NRG Program Manager Florida Power & Light Company 6501 S. Ocean Drive, Jensen Beach, FL 34957
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION (08-2020)
APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
(See Page 3 for required number of digits/characters for each block)
(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 1. Facility Name St. Lucie Unit 2
- 2. Docket Number 05000389
- 3. Page 1 of 3
- 4. Title Automatic Reactor Trip Due to a Breaker Failure on the 2B2 480V Motor Control Center
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Month Day Year Year Sequential Number Revision Number Month Day Year Facility Name n/a Docket Number 05000 01 20 2021 2021 -
001 - 00 03 10 2021 Facility Name n/a Docket Number 05000
- 9. Operating Mode 1
- 10. Power Level 100
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 10 CFR Part 20 20.2203(a)(2)(vi) 50.36(c)(2) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2201(b) 20.2203(a)(3)(i) 50.46(a)(3)(ii) 50.73(a)(2)(v)(A) 10 CFR Part 73 20.2201(d) 20.2203(a)(3)(ii) 50.69(g) 50.73(a)(2)(v)(B) 73.71(a)(4) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C) 73.71(a)(5) 20.2203(a)(2)(i) 10 CFR Part 21 50.73(a)(2)(i)(B) 50.73(a)(2)(v)(D) 73.77(a)(1) 20.2203(a)(2)(ii) 21.2(c) 50.73(a)(2)(i)(C) 50.73(a)(2)(vii) 73.77(a)(2)(i) 20.2203(a)(2)(iii) 10 CFR Part 50 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 73.77(a)(2)(ii) 20.2203(a)(2)(iv) 50.36(c)(1)(i)(A) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(2)(v) 50.36(c)(1)(ii)(A) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A)
OTHER (Specify here, in abstract or in NRC 366A)
- 12. Licensee Contact for this LER Licensee Contact Richard Sciscente, Licensing Engineer Telephone Number (Include area code)
(772) 467-7156 Cause System Component Manufacturer Reportable To IRIS
Cause
System Component Manufacturer Reportable To IRIS B
EC BKR S345 Y
- 14. Supplemental Report Expected YES (If yes, complete 15. Expected Submission Date)
NO
- 15. Expected Submission Date Month Day Year Abstract (Limit to 1560 spaces, i.e., approximately 15 single-spaced typewritten lines)
On January 20, 2021 at 1822 EST with Unit 2 in Mode 1 at 100% power, the reactor automatically tripped on Reactor Protection System Loss of Load Actuation concurrent with an unexpected deenergization of the 480V Motor Control Center 2B2. The trip was uncomplicated with all systems responding normally post trip. Operations stabilized the plant in Mode 3. Auxiliary feedwater automatically actuated on the 2A steam generator post trip. Decay heat removal transitioned from auxiliary feedwater to main feedwater through the 2B main feedwater pump to both steam generators and the steam bypass control system to the main condenser.
A breaker failure caused two of the four undervoltage relays in the Diverse Turbine Trip system to deenergize to their failed condition creating an unexpected trip path for actuation. The cause of this event was a legacy drawing issue from 1983 that resulted in inadvertently mis-assigning power to two of the four undervoltage (UV) relays to the incorrect train of power when the system was later modified in 2019.
The failed breaker has been removed from service, and field configuration of Diverse Turbine Trip relay power supplies was immediately corrected such that the loss of a single power supply will not result in turbine trip.
Automatic reactor trips are analyzed events in the Updated Final Safety Analysis Report. The trip was uncomplicated.
Therefore, this event had no impact on the health and safety of the public.
Page 3 of 3 There were no complications, and all safety related systems functioned as designed. There were no safety system actuations other than RPS and AFAS actuations as a result of the event. Given the response of the plant and the plant design that can accommodate this anticipated operational occurrence, the health and safety of the public were not affected by this event.
Corrective Actions
The corrective actions listed below have been entered into the site corrective action program. Any changes to the actions will be managed under the corrective action program.
- 1. The failed breaker was replaced.
- 2. The field configuration of Diverse Turbine Trip relay power supplies was corrected such that the loss of a single power supply will not result in turbine trip.
- 3. Additional corrective actions track improvements to CEDMCS drawings to clearly define the UV Relay Assembly assignment to each power supply.
Failed Components Identified
- 1) 2-40404, Feeder Breaker to the 480V MCC 2B2
Description
Masterpact NT breaker with micrologic 5.0A trip unit Part Number: NT08N1 with Micrologic 5.0A trip unit (originally supplied in 2009).
Manufacturer: Schneider Electric (Square D / NLI)
Breaker S/N: 064091040005 Trip Unit S/N: 0429027 Sensor Plug Rating: 400A Rating Plug Type: Type A
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