05000458/LER-1917-007, Unit 1 Regarding Automatic Reactor Scram Due to Failure of Main Generator Voltage Regulator Mode Transfer Relay
| ML17234A339 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 08/21/2017 |
| From: | Maguire W Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBF1-17-0095, RBG-47781 LER 17-007-00 | |
| Download: ML17234A339 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 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)(ix)(A) 10 CFR 50.73(a)(2)(x) 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)(i) |
| 4581917007R00 - NRC Website | |
text
u:::;-Entergx RBG-47781 August 21 1 2017 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
RBF1-17-0095 Licensee Event Report 50-458 / 2017-007-00 River Bend Station - Unit 1 Docket No. 50-458 License No. NPF-47
Dear Sir or Madam:
Entergy Operations, Inc.
>1lver Selld Stall >n 5485 U S rtgr,way 61 ~,
- 51. FrancIsville, LA 70775
~o;ll 225381 4 ;7 William F. Maguire lIe Vice P eSlde~t 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. Tim Schenk at 225-381-4177.
Sincerely, WFM / 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 INPO (via ICES reporting)
Licensee Event Report 50-458 / 2017-007-00 August 21, 2017 RBG-47781 Page 2 of 2 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: 03131/2020 (04*2017) h!!J;!:lIv.ww.n!lO.gov/regding*rmldoc::l<ollegtiQnslnuregslstafflsr1022J@
the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
. PAGE River Bend Station - Unit 1 05000-458 10F3
- 4. TITLE Automatic Reactor Scram due to Failure of Main Generator Voltaae Reaulator Mode Transfer Relav
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR MONTH DAY YEAR NUMBER NO.
~5000 06 23 2017 2017 007 00 08 21 2017 FACILITY NAME DOCKET NUMBER
~5000
- 9. OPERATING MODE
- 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: Check all that apply) 1 o 20.2201 (b) o 20.2203(a)(3)(i) o 5O.73(a)(2)(ii)(A) o 50.73(a)(2)(viii)(A) o 20.2201 (d) o 20.2203(a)(3)(ii) o 50.73(a)(2)(ii)(B) o 50.73(a)(2)(viii)(B) o 20.2203(a)(1) o 20.2203(a)(4) o 5O.73(a)(2)(iii) o 50.73(a)(2)(ix)(A) o 20.2203(a)(2)(i) o 50.36(c)(1 )(i)(A) 181 5O.73(a)(2)(iv)(A) o 50.73(a)(2)(x)
- 10. POWER LEVEL o 20.2203(a)(2)(ii) o 50.36(c)(1 )(ii)(A) o 5O.73(a)(2)(v)(A) o 73.71 (a)(4) o 20.2203(a)(2)(iii) o 50.36(c)(2) o 5O.73(a)(2)(v)(B) o 73.71 (a)(5) 100 o 20.2203(a)(2)(iv) o 50.46(a)(3)(ii) o 50.73(a)(2)(v)(C) o 73.77(a)(1) o 20.2203(a)(2)(v) o 50.73(a)(2)(i)(A) o 50.73(a)(2)(v)(D) o 73.77(a)(2)(i) o 20.2203(a)(2)(vi) o 50.73(a)(2)(i)(B) o 5O.73(a)(2)(vii) o 73.77(a)(2)(ii) o 50.73(a)(2)(i)(C) o OTHER Specify in Abstract below or in NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER ICENSEE CONTACT r~LEPHONE NUMBER (Include Area Code)
Irim Schenk, Manager - Regulatory Assurance
~25*381.4177
- 13. COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT
CAUSE
SYSTEM COMPONENT MANU*
REPORTABLE
CAUSE
SYSTEM COMPONENT MANU*
REPORTABLE FACTURER TO EPIX FACTURER TO EPIX X
EL RLY GE yes
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY YEAR D YES (If yes, complete 15. EXPECTED SUBMISSION DATE) t8J NO SUBMISSION DATE f.'\\BSTRACT (Limit to 1400 spaces, i.e., approximately 15 single*spaced typewritten lines)
On June 23, 2017, at 10:18 PM COT, an unanticipated reactor scram occurred during scheduled testing ofthe main turbine
~enerator. The plant was operating at 100 percent power at the time, and no safety-related equipment was out of f5ervice. A reactor recirculation system flow control valve runback occurred as designed, and the recirculation pumps properly downshifted to slow speed. The main feedwater system responded properly to control reactor water level. The
~cram signal was initiated by the closure of the main turbine control valves, which was an automatic response to a trip of he main generator. The associated steam pressure increase following turbine valve closure resulted in the actuation of 12 main steam safety-relief valves. A reactor water level 3 signal was received, as expected, following the turbine trip and reactor scram and was promptly restored to the normal reactor water level band. The non-safety related turbine building chillers tripped as a result of the electrical transient caused by the generator trip. One area served by that cooling system is the reactor water cleanup (RWCU) system heat exchanger room. Approximately 20 minutes after the scram, the emperature in that room exceeded the trip setpoint of the area temperature monitors, resulting in the automatic closure of the primary containment isolation valves for the RWCU system.
NRC FORM 366 (04*2017)
REPORTED CONDITION SEQUENTIAL NUMBER 007 REV NO.
00 IOn June 23, 2017, at 10:18 PM COT, an unanticipated reactor scram occurred during scheduled testing of the main urbine generator. The plant was operating at 100 percent power at the time, and no safety-related equipment was out of service. A reactor recirculation system flow control valve runback occurred as designed, and the recirculation pumps properly downshifted to slow speed. The main feedwater system responded properly to control reactor water level.
rrhe scram signal was initiated by the closure of the main turbine control valves, which was an automatic response to a rip of the main generator. The associated steam pressure increase following turbine valve closure resulted in the actuation of 12 main steam safety-relief valves. A reactor water level 3 signal was received, as expected, following the urbine trip and reactor scram and was promptly restored to the normal reactor water level band.
~he non-safety related turbine building chillers tripped as a result of the electrical transient caused by the generator trip.
One area served by that cooling system is the reactor water cleanup (RWCU) system heat exchanger room.
IApproximately 20 minutes after the scram, the temperature in that room exceeded the trip setpoint of the area em perature monitors, resulting in the automatic closure of the primary containment isolation valves for the RWCU system.
This event is being reported in accordance with 10 CFR SO.73(a)(2)(iv)(A) as an unplanned actuation ofthe reactor protection system.
INVESTIGATION IAt the time of the event, the operators were performing scheduled quarterly testing of the voltage regulator for the main jgenerator [ELl. It has both a manual and automatic mode of operation.
Generator excitation is controlled by varying field current to the exciter, and field excitation is controlled by a static Ivoltage regulator. The regulator includes both automatic and manual functions to regulate generator terminal voltage or jgenerator field voltage, respectively.
rvvhen operating in manual control, the DC regulator holds the main generator field voltage constant. When operating in automatic control, the AC regulator holds the main generator output voltage constant. A transfer voltmeter is used for matching signals to provide a smooth transfer between the two regulators. A tracking circuit is provided to automatically match the two regulators. The regulator mode transfer relay (**RLY**) is energized by the automatic mode pushbutton o place the excitation system in automatic control. It is de-energized by the auto mode pushbutton, over excitation limit
!circuit, or high exciter field current.
~he voltage regulator test is performed on a quarterly basis. At a specific point in the test, the "Voltage Regulator Mode
~elect MAN" pushbutton is depressed. The expected response would be a swap of the voltage regulator control to the manual mode from the automatic mode. This test had been successfully performed in March 2017, following the Page 2 of 3 (04*2017)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 3/31/2020
/""',
~.
~/
LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1 022, R.3 for instruction and guidance for completing this form httpJIwww.nrc.gov/reading-rm/doc-collections/nuregslstaff/sr10221r3/)
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
- 3. LEA N-lABER YEAR River Bend Station - Unit 1 05000-458 2017 SEQUENTIAL NUMBER 007 REV NO.
00 replacement of the mode transfer relay. During the test performed on June 23rd, the main generator tripped when that procedure step was performed.
CAUSAL ANALYSIS The main generator trip and subsequent turbine trip and reactor scram was caused by a failed relay in the transfer circuit between the automatic and manual voltage regulation modes. The regulator mode transfer relay was changed in the March 2017 refueling outage as a scheduled 10-year preventive maintenance task. The failed relay has been shipped to a vendor for failure analysis. Possible signs of arcing were seen on several contact pins, but no definitive failure cause was found. The postulated failure mode could not be replicated. Since the relay had been in service for only 4 months, his is considered an "infant mortality" type of failure.
Based on the failure analysis, it was determined that the generator voltage regulator mode transfer relay failed to perform its function when the operator attempted to switch from the automatic mode to the manual mode. High electrical resistance measured across some of the contact pins exceeded the troubleshooting acceptance criteria. It is postulated that the relay contacts did not effectively change state during the test, and thus failed to provide continuous excitation to the voltage regulator, which led to the automatic generator trip.
CORRECTIVE ACTION TO PREVENT RECURRENCE
~he voltage regulator mode transfer relay was replaced with an updated model that has demonstrated no vulnerability o the failure mode postulated to have caused this event.
PREVIOUS OCCURRENCE EVALUATION No similar occurrence has been reported by River Bend Station in the last three years.
~AFETY SIGNIFICANCE trhe plant response to this event was bounded by the Updated Safety Analysis Report analysis of a main generator load reject with steam bypass / pressure regulation in service. Thus, this event was of minimal significance to the health and
~afety of the public.
(NOTE: Energy Industry Identification System component function identifier and system name of each component or
~ystem referred to in the LER are annotated as (**XX**) and [XX], respectively.) Page 3 of 3