05000458/LER-2015-009, Regarding Automatic Reactor Scram Due to Partial Loss of Offsite Power Caused by Fault in Local 230K Switchyard
| ML16053A095 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 01/26/2016 |
| From: | Olson E Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-47643 LER 15-009-00 | |
| Download: ML16053A095 (5) | |
| 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)(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 |
| 4582015009R00 - NRC Website | |
text
- Entergy Operations, Inc.
River Bend Station 5485 U. S. Highway 61 N StYFaninileLA707
~E t r yTel 225 381 4374 Fax 225 381 4872 eolson@entergy.com Eric W. Olson Site Vice President RBG-47643 January 26, 2016 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Licensee Event Report 50-458 / 2015-009-00 River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47 RBFI 0007
Dear Sir or Madam:
In accordance with 10 CFR 50.73, enclosed is the subject Licensee Event Report.
This document contains no commitments. If you have any questions, please contact Mr. Joseph Clark at 225-381-4177.
Sincerely, EWO /dhw Enclosure cc:
U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Blvd.
Arlington, TX 76011-4511 NRC Sr. Resident Inspector P. O. Box 1050 St. Francisville, LA 70775
Licensee Event Report 50-458 / 2015-009-00 January 26, 2016 RBG-47643 Page 2 of 2 INPO (via ICES reporting)
Central Records Clerk Public Utility Commission of Texas 1701 N. Congress Ave.
Austin, TX 78711-3326 Department of Environmental Quality Office of Environmental Compliance Radiological Emergency Planning and Response Section Ji Young Wiley P.O. Box 4312 Baton Rouge, LA 70821 -4312
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION, APPROVED BY OMB: NO. 3150-0104 EXPIRES: 0113112017 (02-201 4)
- - Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />.
- ..*Reported lessons learned are incorporated into the licensing process sod fed back to industry.
" *Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (1"-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by
°... LICENSEE EVENT REPORT (LER) internet e-mail to Infocollects.Resource~nrc.gov, and to the Desk Ofticer, Ottice otInformation and (See Page 2 for required number of Regulatory Affairs, NEOB-10202, (3150-0104), Oftice of Management and Budget, Washington, DC 20503. It a means used to impose an information collection does not display a currently valid 0MB digits/characters for each block) confrol number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE River Bend Station - Unit 1 000481O
- 4. TITLE Automatic Reactor Scram Due to Partial Loss of Offsite Power Caused by Fault in Local 230kV Switchyard
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED IsEQUNTIA~L"I EV FACnLrrY NAME DOCKET NUMBER MNH DY YEAR YEAR NUBE N.
MONTH DAY YEAR 0I 0
FAILIYNAME DDOKE T NUMa ER 11 2
05 2015 009 00 01 2
0605000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)
D] 20.2201(b) r-20.2203(a)(3)(i)
D] 50.73(a)(2)(i)(c)
['-
50.73(a)(2)(vii) 1 D 20.2201(d)
[]
20.2203(a)(3)(ii)
D
[
50.73(a)(2)(ii)(A) j] 50.73(a)(2)(viii)(A)
[] 20.2203(a)(1)
D] 20.2203(a)(4) fil 50.73(a)(2)(ii)(B)
[] 50.73(a)(2)(viii)(B) 20.2203(a)(2)(i)
[]
50.36(c)(1)(i)(A)
D] 50.73(a)(2)(iii)
D] 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL
[]
20.2203(a)(2)(ii)
[]
50.36(c)(1)(ii)(A)
[]
50.73(a)(2)(iv)(A)
[]
50.73(a)(2)(x)
D] 20.2203(a)(2)(iii)
[]
50.36(c)(2)
[]
50.73(a)(2)(v)(A)
[]
73.71 (a)(4) 100 fil 20.2203(a)(2)(iv)
[] 50.46(a)(3)(ii)
[]
50.73(a)(2)(v)(B) fi] 73.71(a)(5)
[] 20.2203(a)(2)(v)
[]
50.73(a)(2)(i)(A)
[]
50.73(a)(2)(v)(C)
[]
OTHER D] 20.2203(a)(2)(vi)
[jJ 50.73(a)(2)(i)(B)
[j 50.73(a)(2)(v)(D)
Specify( in Abstract below or in
REPORTED CONDITION On November 27, 2015, at 4:31 a.m. CST, with the plant operating at 100 percent power, an automatic reactor scram occurred following the loss of power to both divisions of the reactor protection system (RPS). This condition resulted from a single-phase fault in the local 230kV switchyard. The initial response of the protective relays for the switchyard caused the breakers connected to the north 230kV bus in the switchyard to trip. The fault caused a voltage transient on the in-plant switchgear sufficient to trip the scram relays in the Division 2 RPS, resulting in a half-scram. The action of the protective relays continued, eventually causing the de-energization of reserve station service line no. 1. This lead to the loss of Division 1 RPS and a full reactor scram.
The main generator remained online until it was tripped, as designed, by the reverse-power relays when reactor steam pressure was insufficient to drive the main turbine. The Division 1 and 3 emergency diesel generators started as designed to restore power to their respective safety-related onsite electrical distribution subsystems. Both trains of the standby gas treatment system started, and the primary containment isolation system logic responded as designed. No safety-related systems Were out of service at the time of the scram, and reactor pressure and water level were promptly stabilized. All reactor control rods inserted properly. The "B" reactor recirculation pump should have automatically downshifled to slow speed, but instead tripped off.
Multiple actuations of the main steam safety-relief valves (SRVs) occurred during the event. The nuclear steam supply system vendor rePorted this action was likely due to a localized pressure transient in the SRV instrumentation lines. SRV tailpipe temperature recorders indicated that all valves.re-seated correctly following the initial transient.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an automatic actuation of the reactor protection system, the primary containment isolation logic, and the Division 1 and 3 emergency diesel generators.
INVESTIGATION and IMMEDIATE CORRECTIVE ACTION" When power was restored to both divisions of RPS, the primary containment isolation signal was reset, and the affected systems were restored to service. The isolation had caused a partial loss of the normal service water system, resulting in the automatic actuation of the standby service water system. The isolation had also caused the spent fuel pool cooling pump to trip, and operators aligned the alternate pump for service. The plant was taken to cold shutdown in a controlled manner, CAUSAL ANALYSIS The root cause of this event remains under investigation. The results of that evaluation will be provided in a supplement to this report.
CORRECTIVE ACTIONS TO PREVENT RECURRENCE Long-term corrective actions will be specified by the completed root cause evaluation.
SAFETY SIGNFICANCE Other than the response of the reactor safety-relief valves and the "B" reactor recirculation pump, the plant responded as designed to the reactor scram. The emergency diesel generators responded as designed, and no conditions requiring the actuation of the emergency core cooling systems occurred. The operators were able to quickly stabilize RPV parameters without complication. This event was of minimal significance with regard to the safety of the public.
REPORTED CONDITION On November 27, 2015, at 4:31 a.m. CST, with the plant operating at 100 percent power, an automatic reactor scram occurred following the loss of power to both divisions of the reactor protection system (RPS). This condition resulted from a single-phase fault in the local 230kV switchyard. The initial response of the protective relays for the switchyard caused the breakers connected to the north 230kV bus in the switchyard to trip. The fault caused a voltage transient on the in-plant switchgear sufficient to trip the scram relays in the Division 2 RPS, resulting in a half-scram. The action of the protective relays continued, eventually causing the de-energization of reserve station service line no. 1. This lead to the loss of Division 1 RPS and a full reactor scram.
The main generator remained online until it was tripped, as designed, by the reverse-power relays when reactor steam pressure was insufficient to drive the main turbine. The Division 1 and 3 emergency diesel generators started as designed to restore power to their respective safety-related onsite electrical distribution subsystems. Both trains of the standby gas treatment system started, and the primary containment isolation system logic responded as designed. No safety-related systems Were out of service at the time of the scram, and reactor pressure and water level were promptly stabilized. All reactor control rods inserted properly. The "B" reactor recirculation pump should have automatically downshifled to slow speed, but instead tripped off.
Multiple actuations of the main steam safety-relief valves (SRVs) occurred during the event. The nuclear steam supply system vendor rePorted this action was likely due to a localized pressure transient in the SRV instrumentation lines. SRV tailpipe temperature recorders indicated that all valves.re-seated correctly following the initial transient.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an automatic actuation of the reactor protection system, the primary containment isolation logic, and the Division 1 and 3 emergency diesel generators.
INVESTIGATION and IMMEDIATE CORRECTIVE ACTION" When power was restored to both divisions of RPS, the primary containment isolation signal was reset, and the affected systems were restored to service. The isolation had caused a partial loss of the normal service water system, resulting in the automatic actuation of the standby service water system. The isolation had also caused the spent fuel pool cooling pump to trip, and operators aligned the alternate pump for service. The plant was taken to cold shutdown in a controlled manner, CAUSAL ANALYSIS The root cause of this event remains under investigation. The results of that evaluation will be provided in a supplement to this report.
CORRECTIVE ACTIONS TO PREVENT RECURRENCE Long-term corrective actions will be specified by the completed root cause evaluation.
SAFETY SIGNFICANCE Other than the response of the reactor safety-relief valves and the "B" reactor recirculation pump, the plant responded as designed to the reactor scram. The emergency diesel generators responded as designed, and no conditions requiring the actuation of the emergency core cooling systems occurred. The operators were able to quickly stabilize RPV parameters without complication. This event was of minimal significance with regard to the safety of the public.