05000368/LER-1917-002, Regarding Automatic Start of an Emergency Diesel Generator Due to the Momentary Loss of Offsite Power Due to Severe Weather
| ML17177A348 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 06/26/2017 |
| From: | Richard Anderson Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2CAN061704 LER 17-002-00 | |
| Download: ML17177A348 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation 10 CFR 50.73(b)(5) |
| 3681917002R00 - NRC Website | |
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2CAN061704 June 26, 2017 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Licensee Event Report 50-368/2017-002-00 Arkansas Nuclear One, Unit 2 Docket No. 50-368 License No. NPF-6
Dear Sir or Madam:
Pursuant to the reporting requirements of 10 CFR 50.73, attached is the subject Licensee Event Report concerning the automatic start of an emergency diesel generator caused by the momentary loss of offsite power due to severe weather for Arkansas Nuclear One, Unit 2.
There are no new commitments contained in this submittal.
Should you have any questions concerning this issue, please contact Stephenie Pyle, Manager, Regulatory Assurance, at 479-858-4704.
Sincerely, ORIGINAL SIGNED BY RICHARD L. ANDERSON RLA/rwc Attachment: Licensee Event Report 50-368/2017-002-00 Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802 Tel 479-858-3110 Richard L. Anderson Vice President - Operations Arkansas Nuclear One
2CAN061704 Page 2 of 2 cc:
Mr. Kriss Kennedy Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 NRC Senior Resident Inspector Arkansas Nuclear One P.O. Box 310 London, AR 72847 Institute of Nuclear Power Operations 700 Galleria Parkway Atlanta, GA 30339-5957 LEREvents@inpo.org
NRC FORM 366 (04-2017)
NRC FORM 366 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
(See Page 2 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 Arkansas Nuclear One - Unit 2
- 2. DOCKET NUMBER 05000368
- 3. PAGE 1 OF 4
- 4. TITLE Automatic Start of an Emergency Diesel Generator Due to the Momentary Loss of Offsite Power due to Severe Weather
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR SEQUENTIAL NUMBER REV NO.
MONTH DAY YEAR FACILITY NAME Arkansas Nuclear One, Unit 1 DOCKET NUMBER 05000313 04 26 2017 2017 002 00 06 26 2017 FACILITY NAME DOCKET NUMBER N/A
- 9. OPERATING MODE 6
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply) 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2201(d) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 20.2203(a)(1) 20.2203(a)(4) 50.73(a)(2)(iii) 50.73(a)(2)(ix)(A) 20.2203(a)(2)(i) 50.36(c)(1)(i)(A) 50.73(a)(2)(iv)(A) 50.73(a)(2)(x)
- 10. POWER LEVEL 0
20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iii) 50.36(c)(2) 50.73(a)(2)(v)(B) 73.71(a)(5) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(C) 73.77(a)(1) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(D) 73.77(a)(2)(i) 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 50.73(a)(2)(vii) 73.77(a)(2)(ii) 50.73(a)(2)(i)(C)
OTHER Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT TELEPHONE NUMBER (Include Area Code)
Stephenie L. Pyle, Manager, Regulatory Assurance 479 858-4704 CAUSE SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX
CAUSE
SYSTEM COMPONENT MANU-FACTURER REPORTABLE TO EPIX N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED SUBMISSION DATE MONTH DAY YEAR YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
NO ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)
On April 26, 2017, ANO-2 was in day 28 of a refueling outage with the core completely off loaded to the spent fuel pool (SFP). Power to ANO-2 plant equipment was supplied from Start Up Transformer 2 (SU2) while SU3 was out of service for planned maintenance. 500kV and 161kV offsite power lines were in service. The area around the plant was experiencing severe weather from thunderstorms and tornado warnings had been issued from the National Weather Service for the four county area. Switchyard work was ceased.
At approximately 1002 CST switchyard breakers for 500kV lines opened on fault current. High winds had damaged the transmission towers approximately 16 miles away from ANO and caused phase to ground faults. This resulted in a loss of all offsite power lines to the 500 kV bus. The autotransformer also locked out, as designed, when the 500 kV transmission lines faulted.
When the 500kV bus tripped, the 4.16kV bus that feeds a vital 480 volt bus was subjected to a voltage transient; subsequently; the #1 emergency diesel generator (EDG) auto started. The EDG output breaker never closed due to the fact that voltage was restored to normal almost immediately. This EDG was secured due to running unloaded.
Both SFP cooling pumps were out of service after the transient. A SFP cooling pump was restarted at 1020 CST.
The temperature of the SFP did not change during this event.
A. PLANT STATUS Arkansas Nuclear One, Unit 2 (ANO-2) was operating at 0% rated thermal power with the core completely offloaded to the Spent Fuel Pool (SFP) when the condition was discovered. Startup Transformer No. 3 (SU3)
(one normal off-site power source) and the 4160-volt bus 2A2 were out of service for planned maintenance. The 500kV transmission line to the substation at Pleasant Hill was out of service for planned maintenance. The area around the plant was experiencing severe weather from thunderstorms and tornado warnings had been issued from the National Weather Service for the four county area. There were no other structures, systems, or components (SSCs) that were inoperable at the time that contributed in the event.
B. BACKGROUND The switchyard 500kV bus is a ring bus design, which allows transmission of 500kV power through three transmission lines to substations in Mabelvale, Ft. Smith, and Pleasant Hill, Arkansas. A fourth line supplies power to the bus tie auto-transformer. The autotransformer interconnects the 500kV and 161kV busses. It has two tertiary windings to provide 22kV power from the 500kV or 161kV buses to SU1, which supplies power to ANO-1, and to SU3, which supplies power to ANO-2. The 161kV bus is also a ring bus design, and includes two transmission lines to substations at Russellville East and Pleasant Hill, Arkansas, and a distribution line to the London, Arkansas, substation. It also supplies power to the SU2 which can supply power to both ANO-1 and ANO-2.
During normal operation of ANO-2, station equipment is supplied from the main generator through the Unit Auxiliary Transformer (UAT). During startup and shutdown conditions, the switchyard is used as a means of supplying station equipment from the utility grid through one of the startup transformers.
There are four 4160-volt buses. The main buses, 2A1 and 2A2 [EA], provide power to non-Engineering Safeguard Features (ESF) motors and supply transformers that feed 480-volt non-ESF load centers. The 4160-volt ESF buses, 2A3 and 2A4 [EB], are powered through 2A1 and 2A2, and supply equipment essential for the safe shutdown of the plant. Two 6.9kV buses, 2H1 and 2H2 [EA], supply the reactor coolant pumps. During shutdown, all of these buses are supplied from either SU3 or SU2.
SU3, which only supplies ANO-2, can support buses 2A1, 2A2, 2H1, and 2H2 simultaneously. Since SU2 has limited capacity and is shared by both units, it must be protected from overload. Procedures administratively limit automatic transfer of loads to SU2 only to ANO-1 buses A1 and A3, and ANO-2 buses 2A1 and 2A3. This is assured by normally maintaining the supply breakers from SU2 to ANO-1 buses A2, H1, and H2, and ANO-2 buses 2A2, 2H1, and 2H2 in pull-to-lock. In this condition, the associated supply breakers from SU2 to these buses will not close automatically after a loss of power from another power source.
Another source of power to ESF bus 2A3 / 2A4 cross-tie is the alternate AC diesel generator (AACDG). The AACDG is an independent, non-safety related power source intended to be used in the event of a station blackout (SBO). The AACDG is started using a touch screen in the ANO-2 Control Room or the AACDG building.
Page 3 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (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/)
- 3. LER NUMBER Arkansas Nuclear One, Unit 2 05000-368 YEAR SEQUENTIAL NUMBER REV NO.
2017 002 00
C. DESCRIPTION OF EVENT
On April 26, 2017, ANO-2 was in day 28 of a refueling outage with a complete core off load that had moved all fuel to the SFP. Power to ANO-2 plant equipment was supplied from SU2 while SU3 was out of service for planned maintenance. 500kV lines to Fort Smith and Mabelvale, Arkansas, were in service. 161kV transmission lines to Russellville and Pleasant Hill, Arkansas, were also in service.
ANO-1 was operating normally at full power. The area around the plant was experiencing severe weather from thunderstorms, and tornado warnings had been issued from the National Weather Service for the four county area. Switchyard work was ceased.
At approximately 1002 CST switchyard breakers for 500kV lines to Fort Smith and Mabelvale, Arkansas, opened on fault current. These two transmission lines run offsite in the same right-of-way. High winds had damaged the transmission towers approximately 16 miles away from ANO and caused phase to ground faults. This resulted in a loss of all offsite power lines to the 500 kV bus. The autotransformer also locked out, as designed, when the 500kV transmission lines faulted. This also resulted in an ANO-1 unplanned scram because the ANO-1 main generator was connected to the 500 kV bus with no transmission lines available (addressed in LER 50-313/2017-001-00).
When the 500kV bus tripped, 4160-volt bus 2A1, which feeds 2A3 vital 480 volt bus, was subjected to a voltage transient and the #1 EDG [EK] auto started. The EDG output breaker never closed due to the fact that 2A3 bus voltage was restored to normal almost immediately from SU2. This EDG was secured due to running unloaded.
Bus 2A2 was out of service for maintenance. Both SFP cooling pumps were out of service after the transient (pumps required manual re-start following loss of power). A SFP cooling pump was restarted at 1020 CST. The temperature of the SFP did not change during the time no forced cooling was available. SFP temperature remained at approximately 91 °F.
D. EVENT CAUSES The identified condition occurred due to a very short voltage transient on SU2. The voltage lowered to ~149.8kV and immediately restored to ~ 160kV. The transformer remained operable and capable of performing its required function. The #1 EDG performed as designed and remained capable of performing its 30-day mission time.
E. CORRECTIVE ACTIONS
The following corrective actions were completed upon identification Entered the Spent Fuel Pool Emergencies procedure and restarted both SFP cooling pumps.
Secured the #1 EDG due to running unloaded.
Page 4 of 4 (04-2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (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/)
- 3. LER NUMBER Arkansas Nuclear One, Unit 2 05000-368 YEAR SEQUENTIAL NUMBER REV NO.
2017 002 00
F. SAFETY CONSEQUENCES
This event had no actual safety consequences impacting plant or public safety. In general, when the unit is shut down, the Technical Specifications requirements ensure that the unit has the capability to mitigate the consequences of postulated accidents that are assumed to potentially occur during shutdown conditions.
However, assuming a single failure and concurrent loss of all offsite or all onsite power is not required. The rationale for this is based on the fact that many Design Basis Accidents (DBAs) that are analyzed in Modes 1, 2, 3, and 4 have no specific analyses in Modes 5 and 6 or when the fuel is completely offloaded from the reactor vessel and placed in the SFP. Worst case bounding events are deemed not credible in Modes 5 and 6 or when the vessel is defueled because the energy contained with the reactor pressure boundary, reactor coolant temperature and pressure, and the corresponding stresses result in the probabilities of occurrence being significantly reduced or eliminated, and have minimal consequences.
The #1 EDG automatically started properly when a loss of AC power was detected, as designed. All other systems functioned normally.
G. BASIS FOR REPORTIBILITY This event is reportable pursuant to the following criteria:
Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section.
Paragraph (B)(8) of 10 CFR 50.73 lists Emergency ac electrical power systems, including: emergency diesel generators (EDGs).
The guidance provided in NUREG 1022 states under 10 CFR 50.73(a)(1):
The holder of an operating license for a nuclear power plant (licensee) shall submit a Licensee Event Report (LER) for any event of the type described in this paragraph within 60 days after the discovery of the event.
H. ADDITIONAL INFORMATION
10 CFR 50.73(b)(5) states that this report shall contain reference to any previous similar events at the same plant that are known to the licensee. NUREG 1022 reporting guidance states that term previous occurrences should include previous events or conditions that involved the same underlying concern or reason as this event, such as the same root cause, failure, or sequence of events.
A review of the ANO corrective action program and LERs for the previous three years was performed. There were no similar events identified at ANO during this time period.
Energy Industry Identification System (EIIS) codes and component codes are identified in the text of this report as [XX].