View source for 05000458/LER-2015-009-01, Regarding Automatic Reactor Scram Due to Partial Loss of Offsite Power Caused by Fault in Local 230kV Switchyard

{{Adams
| number = ML16155A053
| issue date = 05/18/2016
| title = Regarding Automatic Reactor Scram Due to Partial Loss of Offsite Power Caused by Fault in Local 230kV Switchyard
| author name = Maguire W
| author affiliation = Entergy Operations, Inc
| addressee name = 
| addressee affiliation = NRC/Document Control Desk, NRC/NRR
| docket = 05000458
| license number = NPF-047
| contact person = 
| case reference number = RBG-47685
| document report number = LER 15-009-01
| document type = Letter, Licensee Event Report (LER)
| page count = 5
}}
{{LER
| Title = Regarding Automatic Reactor Scram Due to Partial Loss of Offsite Power Caused by Fault in Local 230kV Switchyard
| Plant = 
| Reporting criterion = 10 CFR 50.73(a)(2)(ii)(A), 10 CFR 50.73(a)(2)(viii)(A), 10 CFR 50.73(a)(2)(ii)(B), 10 CFR 50.73(a)(2)(viii)(B), 10 CFR 50.73(a)(2)(ix)(A), 10 CFR 50.73(a)(2)(iv)(A), 10 CFR 50.73(a)(2)(x), 10 CFR 50.73(a)(2)(v)(B), 10 CFR 50.73(a)(2)(v), 10 CFR 50.73(a)(2)(i)(A), 10 CFR 50.73(a)(2)(i)(B), 10 CFR 50.73(a)(2)(vii)
| Power level = 
| Mode = 
| Docket = 05000458
| LER year = 2015
| LER number = 9
| LER revision = 1
| Event date = 
| Report date = 
| ENS = 
| abstract = 
}}

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RBG-47685 May 18, 2016.
U. S. Nuclear Regulatory Commission ATTN: Document Centro) Desk Washington, DC 20555, 

==Subject:==
Licensee Event Report 50-45812015..fl00.. 01 River Bend Statiqn - Unit 1 Docket No. SQ-458 Ucense No. NPF-47 ABF1-1&0057 

==Dear Sir or Madam:==
&iF.:5 u.s. rHgrrcay Gm S!. Frc:r.G::;11i::i', LA 70775 
~""!i!J~1il P. r::::::;1.~~v S::c; Vlc3 Prc:;;:.::ant In accordance with 10 CFR 50.73, enctosed is the subject UCensee Event Report. This document contains no commitments. This is a supplement to tile report originally submitted on January 26, 2016. New information is highlighted by change bars in the right margin. ff you have any questions, please contact Mr. Marvin Chase at 225-381*3612.
Sincerely, WFM/dhw Enclosure cc:
U. s. Nuclear Regulatory Commission ReglontV 1600 East Lamar Blvd.
Arlington, TX 76011"4511 NAO Sr. Resident Inspector P. 0. Box 1050 St. FrancisvlHet LA 70775 INPO (via ICES reporting) 

RBG-47685 May18,2016 Page2of2 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 Wiiey P.O. Box4312 Baton Rouge, LA 70821-4312 

I I
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015) 
, the NRC may not conduct or sponsor, and a person is not required to respond to, the infonmation collection.
: 3. PAGE River Bend Station - Unit 1 05000 458 1 OF 3
: 4. TITLE Automatic Reactor Scram* Due to Partial Loss ofOffsite Power Caused by Fault in Local 230kV Switchyard
: 5. EVENT DATE
: 6. LER NUMBER
: 7. REPORT DATE
: 8. OTHER FACILITIES INVOLVED I
SEQUENTIAL I REV FACILllY NAME DOCKET NUMBER MONTH DAY YEAR YEAR MONTH DAY YEAR NUMBER NO.
05000 FACJLllY NAME DOCKET NUMBER 11 27 2015 2015 -
009 - 01 05 18 2016 05000
: 9. OPERATING MODE
: 11. THIS REPORT IS SUBMITTE_D PURSUANT TO THE REQUIREMENTS OF 10 CFR &sect;: (Check all that apply)
D 20.2201 <b>
D 20.2203(a)(3)(i)
D 50.73(a)(2)(ii)(A)
D 50.73(a)(2)(viii)(A) 1 D
20.2201 <ct>
D 20.2203<a><3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B)
D 20.2203<a><1>
D 20.2203(a><4>
D so.13<a><2><iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1)(i)(A)
[{] 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
: 10. POWER LEVEL D
20.2203<a><2>cn>
D 50.36(c)(1)(ii)(A)
D
: 50. 73(a)(2)(v)(A)
D
: 73. 11 <a><4>
D 20.2203(a)(2)(m>
D so.36(c><2>
D 50.73(a)(2)(v)(B)
D 13.11ca><s>
D 20.2203(a)(2)(iv)
D so.46(a)(3)(ii)
D 50.73(a)(2)(v)(C)
D 13.77(a><1>
100 D
20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 13.11ca><2><i>
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 13.77(a><2>cn> 
~:.ii'.
D so.13<a><2><i><Cl D
OTHER 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)[JC]. rhis condition resulted from a single-phase fault in the local 230kV switchyard. The initial response of the protective relays for the switchyard 
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caused the breakers connected to the north 230kV bl.is 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 [BH] st6rted, 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 downshifted to slow speed, but instead tripped off. 
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Multiple actuations of the main steam safety-relief valves (SRVs)(**RV**) 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 ofthe 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 cause of the event was an animal-induced fault in the 230kV switchyard that resulted in the automatic trip of the north bus feeder breaker to the RSS No. 1. The fault also caused the south bus feeder breaker to trip, de-energizing RSS No. 1. The associated voltage transient on the in-plant switchgear also caused the trip of relays on both RPS buses for the scram and containment isolation logic circuits.
Contributing to this event was the insufficient recognition of risk in power operations with both RPS buses on the alt~rnate power sources. 'f (11-2015)
: 1. FACILITY NAME River Bend Station - Unit 1 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET
: 2. DOCKET NUMBER 05000-I 458 CORRECTIVE ACTIONS TO PREVENT RECURRENCE The following actions are being taken to prevent a recurrence of the event.
I /
Page 2 of 2 U.S. NUCLEA~1REGULATORY COMMISSION
: 3. LER NUMBER r::-:1 NUMBER NO.
I YEAR SEQUENTIAL REV 
~-I 009 1-0 
*The transmission department is evaluating the appropriate means of minimizing animal intrusion to the 230kV switchyard. 
*An engineering study was performed to evaluate the transient limitations of the RPS motor-generator sets and alternate power sources, and the associated risk of the impact to the RPS scram logic. The study also provided recommendation for operational restrictions on aligning the RPS buses to the alternate power sources. The RPS system design criteria document was updated to identify the risk associated with aligning both RPS buses to the alternate power source during power operations. 
*A design change was implemented to correct a legacy error in the wiring configuration of the Division 2 RPS bus discovered during this investigation. This modification will significantly reduce the risk of tripping bo'th RPS buses for a given fault if both buses are aligned to the alternate power sources. 

==SAFETY SIGNIFICANCE==
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.
(NOTE: Energy Industry Identification System component function identifier and system name of each component or system referred to in the LER are annotated as (**XX**) and [XX], respectively.) 
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