05000529/LER-2013-002, Regarding Automatic Actuation of Unit 2 Reactor Protection System Resulting from Reactor Coolant Pump Motor Trip
| ML14035A214 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 01/31/2014 |
| From: | Mims D Arizona Public Service Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 102-06816-DCM/DJH LER 13-002-00 | |
| Download: ML14035A214 (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 |
| LER closed by | |
| IR 05000528/2000529 (13 August 2014) IR 05000528/2014003 (13 August 2014) | |
| 5292013002R00 - NRC Website | |
text
10 CFR 50.73 Oaps DWIGHT C. MIMS Senior Vice President, Nuclear Regulatory & Oversight Palo Verde Nuclear Generating Station P.O. Box 52034 Phoenix, AZ 85072 Mail Station 7605 Tel 623 393 5403 102-06816-DCM/DJH January 31, 2014 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS) Unit 2 Docket No. STN 50-529 / License No. NPF 51 Licensee Event Report 2013-002-00 Enclosed please find Licensee Event Report (LER) 50-529/2013-002-00 that has been prepared and submitted pursuant to 10 CFR 50.73. This LER reports an automatic actuation of the PVNGS Unit 2 reactor protection system due to an electrical protection trip of the circuit breaker for the 1A reactor coolant pump motor.
In accordance with 10 CFR 50.4, copies of this LER are being forwarded to the Nuclear Regulatory Commission (NRC) Regional Office, NRC Region IV, and the Senior Resident Inspector.
Arizona Public Service Company makes no commitments in this letter. If you have questions regarding this submittal, please contact Mark McGhee, Department Leader, Regulatory Affairs at (623) 393-4972.
Sincerely, DCM/DJH/hsc Enclosure cc:
M. L. Dapas J. K. Rankin A. E. George M. A. Brown NRC Region IV Regional Administrator NRC NRR Project Manager PVNGS NRC NRR Project Manager NRC Senior Resident Inspector PVNGS A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
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NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (11-2010)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. PAGE Palo Verde Nuclear Generating Station (PVNGS) Unit 2 05000529 1 OF 4
- 4. TITLE Automatic Actuation of Unit 2 Reactor Protection System Resulting from Reactor Coolant Pump Motor Trip
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEUNILRVFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.
FACILITY NAME DOCKET NUMBER 12 02 2013 2013
- - 002 -
00 01 31 2014
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMI'TED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)
El 20.2201(b)
[I 20.2203(a)(3)(i)
[I 50.73(a)(2)(i)(C)
El 50.73(a)(2)(vii) 1 E] 20.2201(d)
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[I 50.73(a)(2)(ii)(A)
El 50.73(a)(2)(viii)(A)
[I 20.2203(a)(1)
[I 20.2203(a)(4)
[I 50.73(a)(2)(ii)(B)
[I 50.73(a)(2)(viii)(B)
[I 20.2203(a)(2)(i)
[I 50.36(c)(1)(i)(A)
El 50.73(a)(2)(iii)
[I 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL
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El 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)
[I 50.73(a)(2)(x)
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El 50.36(c)(2) 0l 50.73(a)(2)(v)(A)
El 73.71(a)(4) 1[ 20.2203(a)(2)(iv)
[I 50.46(a)(3)(ii)
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[I 50.73(a)(2)(i)(B)
El 50.73(a)(2)(v)(D)
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All times are Mountain Standard Time and approximate unless otherwise indicated.
1. REPORTING REQUIREMENT(S)
This Licensee Event Report is being submitted pursuant to 10 CFR 50.73 (a)(2)(iv)(A) to report an automatic actuation of the Palo Verde Nuclear Generating Station (PVNGS) Unit 2 reactor protection system (RPS) (EIIS: JC) due to an electrical protection trip of the circuit breaker for the 1A reactor coolant pump (RCP) (EllS: AB) motor.
This event was reported to the NRC pursuant to 10 CFR 50.72 (b)(2)(iv)(B) at 2126 on December 02, 2013, via the event notification system (EN 49600).
- 2. DESCRIPTION OF STRUCTURE(S), SYSTEM(S) AND COMPONENT(S):
The reactor coolant system (RCS) (EIIS: AB) is comprised of two main flow loops each of which includes two RCPs and one steam generator (EIIS: AB). The primary function of the RCPs is to provide the necessary head to maintain forced circulation of reactor coolant through the RCS during normal operations. Critical operation of the reactor requires all four RCPs to be in operation to ensure adequate RCS flow.
Each RCP is driven by a 12,000 horsepower electric motor supplied from the non-class 13.8kV electric power distribution system. Each RCP motor circuit breaker is provided with electrical protection trip features which include protection relays for under voltage, overcurrent, phase current differential, and ground. The phase current differential relay is calibrated to operate when it senses an excessive current difference between any two of the three motor phases.
The RPS is an assemblage of sensors, calculators (including the core protection calculators (CPCs)), logic circuits, and supporting equipment that monitor nuclear steam supply system (EIIS: AB) parameters and ensure the reactor is rapidly and reliably shut down to protect the fuel and RCS pressure boundary and assist the engineered safety features systems in accident mitigation. A pump speed signal from each RCP is provided to each of the four CPCs to support calculation of RCS flow. If any RCP slows to less than 95 percent of rated speed, the CPC software will introduce significant mathematical penalty factors into the departure from nucleate boiling ratio (DNBR) and local power density (LPD) calculations that result in DNBR and LPD trip signals on each RPS channel. The RPS actuation then causes simultaneous trips of the reactor trip switchgear breakers (EIIS: AA) which de-energize the control element drive mechanisms so that all control element assemblies are released to insert and shutdown the reactor.
3. INITIAL PLANT CONDITIONS
On December 02, 2013, PVNGS Unit 2 was operating in Mode 1 (Power Operation) at 100 percent power and normal operating temperature and pressure. There were no structures, systems, or components out of service that contributed to the event.
4. EVENT DESCRIPTION
At approximately 1758 on December 2, 2013, the PVNGS Unit 2 control room received alarms indicating an automatic RPS actuation due to low DNBR and high LPD trip signals from each of the four core protection calculators. No other RPS actuation signals or actuations of plant engineered safety features occurred and all control element assemblies fully inserted. Control room personnel entered the emergency operating procedures and performed the standard post trip actions. The reactor trip was determined to be uncomplicated and the reactor trip procedure was implemented to stabilize the plant in Mode 3. RCS forced circulation was maintained throughout the event as RCPs 1 B, 2A, and 2B remained in operation.
PVNGS Unit 1 and Unit 3 were operating at 100 percent power at the time of the event and were not impacted by the Unit 2 reactor trip.
Inspection of the 1A RCP motor circuit breaker found the related electrical protection differential relay and "86 lockout" relay both tripped. Troubleshooting of the 1A RCP circuit breaker, cabling, and motor determined an electrical fault had occurred within the motor windings. A plant cooldown was initiated and Unit 2 was placed in Mode 5 to allow for replacement of the faulted RCP motor.
5. ASSESSMENT OF SAFETY CONSEQUENCES
This event did not result in a challenge to the fission product barriers or result in the release of radioactive materials to the environment. There were no actual safety consequences as a result of this event and the event did not adversely affect the health and safety of the public.
The reactor protection system functioned as designed and initiated an automatic reactor trip that expeditiously placed the plant in a safe condition. Throughout the event all vital and non-vital electrical power sources remained energized and RCS forced circulation was maintained with RCPs 1 B, 2A and 2B remaining in operation.
This event did not result in conditions more severe than the limiting loss of flow event contained in Chapter 15 of the PVNGS Updated Safety Analysis Report which is based on a sheared RCP shaft accompanied by a loss of off-site power that results in the loss of all RCS forced circulation. This was determined to be an uncomplicated reactor trip which rn-iMlli :uUlVI-MMý..Tv*.Lm:Ur ER-"t'
NRC FORM'366A U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
(10-2010)
CONTINUATION SHEET
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE YER SEQUENTAL REVISION YEAR Palo Verde Nuclear Generating Station NUMBER NUMBER 05000529 4OF 4 Unit2 2013 002 00 NARRATIVE results in a very small increase in calculated core damage frequency according to the guidance in Regulatory Guide 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis."
The condition did not result in a safety system functional failure as described in 10 CFR 50.73 (a)(2)(v).
6. CAUSE OF THE EVENT
The direct cause of the event was an electrical protection trip of the RCP 1A motor circuit breaker that initiated CPC trip signals for low DNBR and high LPD when the RCP speed dropped below 95 percent of rated speed. The RCP 1 A motor circuit breaker tripped as a result of excessive differential current between electrical phases of the motor.
The investigation determined the probable cause of the circuit breaker trip to be a high impedance fault within the C phase of the motor stator coil.
The faulted motor has been shipped to an offsite facility for dissassembly and further root cause analysis.
If information is subsequently developed that significantly affects a reader's understanding or perception of this event, a supplement to this LER will be submitted.
7. CORRECTIVE ACTIONS
To repair the 1A RCP, Unit 2 was cooled down to Mode 5 and the faulted 1A RCP motor was replaced with an on-site spare RCP motor. Following completion of appropriate retests Unit 2 was returned to full power operations.
8. PREVIOUS SIMILAR EVENTS
No previous similar events involving an automatic RPS actuation due to a RCP motor failure have occurred at PVNGS.
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