05000389/LER-2015-002, Regarding 2A Emergency Diesel Generator Actuation Logic
| ML15329A373 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 11/16/2015 |
| From: | Costanzo C Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2015-281 LER 15-002-00 | |
| Download: ML15329A373 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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) 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)(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)(iv), System Actuation |
| 3892015002R00 - NRC Website | |
text
0IFPLo November 16, 2015 L-2015-28 1 10 CFR 50.73 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Re:
St. Lucie Unit 2 Docket No. 50-3 89 Reportable Event: 2015-002-00 Date of Event: September 17, 2015 2A Emergency Diesel Generator Actuation Logic The attached Licensee Event Report 20 15-002-00 is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.
Sincerely, Christopher R. Costanzo Site Vice President St. Lucie Plant CRC/rcs Attachment Florida Power & Light Company
/,*
6501 S. Ocean Drive, Jensen Beach, FL 34957
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 1/3112017 (02-2014)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 13. PAGE St. Lucie Unit 2 05000389l 1 OF 3
- 4. TITLE 2A Emergency Diesel Generator Actuation Logic
- 5. EVENTH DT
- 6. LER NUMBER J7. REPORT DATE___
- 8. OTHER FACILITIES INVOLVEDDOKTNME MOT DY YER YERSEQUENTIAL REV MOT DA ER FACILITY NAMEDOKTNME
- - 09 17 2015 2015 -
002 00 I11 1
36 I2015 /FCLT AENADOKTNME
- 9. OPERATING MODE 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
El 20.2201(b)
El 20.2203(a)(3)(i)
El 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii)
El 20.2201(d)
El 20.2203(a)(3)(ii)
El 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
El 20.2203(a)(1)
El 20.2203(a)(4)
El 50.73(a)(2)(ii)(B)
El 50.73(a)(2)(viii)(B)
____________E 20.2203(a)(2)(i)
El 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
El 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL
[] 20.2203(a)(2)(ii)
El 50.36(c)(1)(ii)(A) 0] 50.73(a)(2)(iv)(A)
El 50.73(a)(2)(x)
El 20.2203(a)(2)(iii)
[J 50.36(c)(2)
El 50.73(a)(2)(v)(A)
El 73.71(a)(4)
El 20.2203(a)(2)(iv)
El 50.46(a)(3)(ii)
El 50:73(a)(2)(v)(B)
El 73.71(a)(5) 0%
El 20.2203(a)(2)(v)
El 50.73(a)(2)(i)(A)
El 50.73(a)(2)(v)(C)
El OTHER El 20.2203(a)(2)(vi)
El 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
Specifyin Abstract below or fn NR aFrm 366A
- 12. LICENSEE CONTACT FOR THIS LER NAME TELEPHONE NUMBER (Include Area Code)772-467-7156 Richard Sciscente -
Principal Engineer, Licensing
- 13. COMPLETE ONE LINE FOR EACH CO d
MANU-CAUS SYSTEM COMPONENT FACTURER.
REPORTABLE TO EPIX B
EA T NSBU C770 YES
- 14. SUPPLEMENTAL REPORT EXPECTED Ii YES (f yes, complee15. EXPECTED SUBMISSION DATE)
[
NO A.BSTRACT (Limit to 1400 spacesi.e., approximatey15single-spaced tpewriten lies)
On September 17,
- 2015, at 1222 hours0.0141 days <br />0.339 hours <br />0.00202 weeks <br />4.64971e-4 months <br />, with Unit 2 in Mode 5 at the beginning of a refueling outage, an electrical fault on the 2A 6.9 kV bus resulted in the loss of the 2A startup transformer (SUT) and its associated non-safety related 2A2 and safety-related 2A3 buses.
The loss of the 2A SOT actuated the under-voltage relays that would have started the 2A EDG, which had been properly removed from service for preplanned maintenance.
The root cause was that the protective boots for a bus bar bolted connection on a vertical riser were not installed (left between bus conductors) during initial plant construction.
Immediate corrective actions included extensive inspections and repair of the remaining vertical portions of this bus.
Follow-up corrective actions include performing internal visual inspections of remaining vertical sections of non-segregated buses to ensure that bolted connections have properly installed protective boots.
This event is reportable pursuant to 10 CFR 50.73 (a) (2) (iv)
(A) as an event or condition that resulted in automatic actuation of an EOG.
All safety related systems functioned as designed.
This event had no effect on the health and safety of the public.
NCR FORM 366 (02-2014)
Description of the Event On September 17,
- 2015, at 1222 hours0.0141 days <br />0.339 hours <br />0.00202 weeks <br />4.64971e-4 months <br />, with Unit 2 in Mode 5 at the beginning of a refueling outage, an electrical fault on the 2A 6.9 kV bus resulted in the loss of the 2A startup transformer (SUT) and its associated non-safety related 2A2 and safety-related 2A3 buses.
At the time of the event, only the 2B emergency diesel generator (EDG) was required to be in service.
The 2A EDG had been removed from service for scheduled maintenance, and did not start.
The loss of the 2A SUT actuated the under-voltage relays that would have started the 2A EDG.
Additionally, the 2A train of shutdown cooling (SDC) was de-energized; the 2B (protected) train of SDC was not affected by the event and remained in service to remove decay heat.
The 2A shutdown cooling train was restored and made available on September 19, 2015 at 0030.
The 2B EDG and 2B SUT were not affected by the event.
During this event, Unit 1 experienced a loss of the lA startup transformer.
There was no other effect on Unit 1 operation, as its associated non-safety and safety-related buses remained powered by the auxiliary transformer.
The IA startup transformer was returned to service on September 18, 2015 at 2103.
Cause
The actuation of the 2A EDG was a direct result of the electrical fault on the 2A 6.9 kV bus.
The root cause of the electrical fault was that the protective boots for a bus bar bolted connection, at a vertical riser section, were not installed properly from initial plant construction (legacy human performance error).
Over time, contaminates built up on a boot between the "B" and "C"
- phases, creating a fault path.
Analysis of the Event
On 9/17/15, a differential relay trip of the lA/2A SUTs occurred separating the "A" train from off-site power.
A phase-to-phase fault occurred on the 2A SUT 6.9kv non-segregated bus, between the "B" and "C" phases, that ionized the air in the vicinity of the fault and allowed a phase-to-phase-to-phase event.
The initiator of the event was a legacy human performance issue where the protective boots were left off of the bolted connections and placed in between the phases. This allowed the collection of corrosion products over the years to create a path across one of the boots between the "B" and "C" phases.
Safety Significance
This event is reportable pursuant to 10 CFR 50.73 (a) (2) (iv)
(A) as an event or condition that resulted in automatic actuation of an EDG.
The EDG had been previously removed from service and prohibited from starting; however, the actuation logic was satisfied when the undervoltage relays changed state.
The safety significance is minimal because of the preplanned defense-in-depth, the limited cause of the event (improper location of boot) and the prompt actions by station staff, which included restoration of the 2A train of SDC.
With no complications and all systems responding as designed, the associated risk impact is considered very small.
Given the response of the plant and the insignificant risk, the health and safety of the public were not affected by this event.
Corrective Actions
Immediate corrective actions were extensive inspections and repair of the remaining vertical portions of this bus.
These inspections included visual inspection, checking bus joint bolt torque, replacing insulating boots and megge-r testing.
The follow-up corrective actions listed below have been entered into the site corrective action program.
Any changes to the action will be managed under the corrective action program.
- 1. Perform internal visual inspections of remaining vertical sections of non-segregated buses to ensure that bolted connections on risers have properly installed protective boots.
- 2.
Perform internal inspections on the external buses as part of planned preventative maintenance.
Failed Component(s)
Rectangular Nonsegregated Bus Manufacturer Cutler-Hammer
Description of the Event On September 17,
- 2015, at 1222 hours0.0141 days <br />0.339 hours <br />0.00202 weeks <br />4.64971e-4 months <br />, with Unit 2 in Mode 5 at the beginning of a refueling outage, an electrical fault on the 2A 6.9 kV bus resulted in the loss of the 2A startup transformer (SUT) and its associated non-safety related 2A2 and safety-related 2A3 buses.
At the time of the event, only the 2B emergency diesel generator (EDG) was required to be in service.
The 2A EDG had been removed from service for scheduled maintenance, and did not start.
The loss of the 2A SUT actuated the under-voltage relays that would have started the 2A EDG.
Additionally, the 2A train of shutdown cooling (SDC) was de-energized; the 2B (protected) train of SDC was not affected by the event and remained in service to remove decay heat.
The 2A shutdown cooling train was restored and made available on September 19, 2015 at 0030.
The 2B EDG and 2B SUT were not affected by the event.
During this event, Unit 1 experienced a loss of the lA startup transformer.
There was no other effect on Unit 1 operation, as its associated non-safety and safety-related buses remained powered by the auxiliary transformer.
The IA startup transformer was returned to service on September 18, 2015 at 2103.
Cause
The actuation of the 2A EDG was a direct result of the electrical fault on the 2A 6.9 kV bus.
The root cause of the electrical fault was that the protective boots for a bus bar bolted connection, at a vertical riser section, were not installed properly from initial plant construction (legacy human performance error).
Over time, contaminates built up on a boot between the "B" and "C"
- phases, creating a fault path.
Analysis of the Event
On 9/17/15, a differential relay trip of the lA/2A SUTs occurred separating the "A" train from off-site power.
A phase-to-phase fault occurred on the 2A SUT 6.9kv non-segregated bus, between the "B" and "C" phases, that ionized the air in the vicinity of the fault and allowed a phase-to-phase-to-phase event.
The initiator of the event was a legacy human performance issue where the protective boots were left off of the bolted connections and placed in between the phases. This allowed the collection of corrosion products over the years to create a path across one of the boots between the "B" and "C" phases.
Safety Significance
This event is reportable pursuant to 10 CFR 50.73 (a) (2) (iv)
(A) as an event or condition that resulted in automatic actuation of an EDG.
The EDG had been previously removed from service and prohibited from starting; however, the actuation logic was satisfied when the undervoltage relays changed state.
The safety significance is minimal because of the preplanned defense-in-depth, the limited cause of the event (improper location of boot) and the prompt actions by station staff, which included restoration of the 2A train of SDC.
With no complications and all systems responding as designed, the associated risk impact is considered very small.
Given the response of the plant and the insignificant risk, the health and safety of the public were not affected by this event.
Corrective Actions
Immediate corrective actions were extensive inspections and repair of the remaining vertical portions of this bus.
These inspections included visual inspection, checking bus joint bolt torque, replacing insulating boots and megge-r testing.
The follow-up corrective actions listed below have been entered into the site corrective action program.
Any changes to the action will be managed under the corrective action program.
- 1. Perform internal visual inspections of remaining vertical sections of non-segregated buses to ensure that bolted connections on risers have properly installed protective boots.
- 2.
Perform internal inspections on the external buses as part of planned preventative maintenance.
Failed Component(s)
Rectangular Nonsegregated Bus Manufacturer Cutler-Hammer