05000446/LER-2018-001, Automatic Reactor Trip Due to Turbine Trip
| ML18296A092 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 10/10/2018 |
| From: | Thomas McCool Luminant, TXU Energy, Vistra Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CP-201800700, TXX-18069 LER 2018-001-00 | |
| Download: ML18296A092 (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)(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) |
| 4462018001R00 - NRC Website | |
text
CP-201800700 TXX-18069 U.S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, DC 20555-0001 ENERGY
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ml Luminant 10/10/2018
SUBJECT:
COMANCHE PEA{ NUCLEAR POWER PLANT-UNIT, 2 DOCKET NO. 50-446 AUTOMATIC REACTOR TRIP DUE TO TUR~INE TRIP D'ear Sir or Madam:
Thomas P. McCool Site Vice President.
Luminant P.O. Box 1002 6322 North FM 56 Glen Rose, TX 76043 o 254.897.6042 Ref 10 CFR 50.73 Enclosed is Licensee Event Report (LER) 2-18-001-00, "Unit 2 Automatic Reactor Trip Due to Turbine Trip" for Comanche Peak Nuclear Power Plant (CPNPP), Unit 2.
This letter contains no new regulatory commitments.
If you have any questions regarding this submittal, please contact Garry Struble at (254) 897-6628 or garry.struble@luminant.com.
Enclosure Sincerely, Thomas--;;Jff COMANCHE PEAK NUCLEAR POWER PLANT-UNIT 2, AUTOMATIC REACTOR TRIP DUE TO TURBINE TRIP LICENSEE EVENT REPORT (LER) 2-18-001-00 6555 SIERRA DRIVE IRVING, TEXAS 75039 0214-812-4600 VISTRAENERGY.COM
TXX-18069 Page 2 Of 2 c -
Kriss M. Kennedy, Region IV Margaret M. O'Banion, NRR Resident Inspectors, Comanche Peak
NRC FORl'll366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)
, the NRC may not conduct or sponsor, and a person Is not required to respond to, the information collection.
3.Page Comanche Peak Nuclear Power Plant, Unit 2 05000 446 1
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- 4. Title V
Automatic Reactor Trip Due to Turbine Trip
- 5. Event Date
- 6. LER Number
- 7. Report Date
- 8. Other Facilities Involved Day Year I
Sequential I Rev Facility Name Docket Number Month Year Number No.
Month Day Year 05000 Facility Name Docket Number 08 13 2018 2018 -
001 -
00 10 10 2018 05000
- 9. Operating Mode
- 11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (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)
D 20.2201(d)
D 20.2203(a)'(3)(ii)
D 50.73(a)(2)(ii)(B)
D 50.73(a)(2)(viii)(B) 1 D 20.2203(a)(1)
D 20.2203(a)(4)
D 50.73(a)(2)(iii)
D 50.73(a)(2)(ix)(A)
D 20.2203(a)(2)(i)
D 50.36(c)(1 )(i)(A)
[Z] 50.73(a)(2)(iv)(A)
D 50.73(a)(2)(x)
- 10. Power Level D 20.2203(a)(2)(ii)
D 50.36(c)(1 )(ii)(A)
D 50. 73(a)(2)(v)(A)
D 73.71 (a)(4)
D 20.2203(a)(2)(iii)
D 50.36(c)(2)
D 50.73(a)(2)(v)(B)
D 73.71 (a)(5)
D 20.2203(a)(2)(iv)
D 50.46(aH3J(iiJ D 50.73(a)(2)(v)(C)
D 73.77(a)(1) 100 D 20.2203(a)(2)(v)
D 50.73(a)(2)(i)(A)
D 50.73(a)(2)(v)(D)
D 73.77(a)(2)(i)
D 20.2203(a)(2)(vi)
D 50.73(a)(2)(i)(B)
D 50.73(a)(2)(vii)
D 73.77(a)(2)(ii)
D 50.73(a)(2)(i)(C)
D Other (Specify in Abstract below or in SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES At 2258 CDT on August 13, 2018, Comanche Peak Nuclear Power Plant, Unit 2 received First Out Annunciator "RX >
90% PWR TRB TRIP." The turbine trip was actuated from a main Generator Total Loss of Field concurrent with a Generator High Current. Generator protective relay 40-1/2G actuation initiated a turbine trip and generator lockout.
The cause of the event was a failure of the primary channel in the main generator Thyristor Voltage Regulator (TVR). A failed primary channel power supply [EIIS:(TL)(EC)] caused a loss of main generator excitation current. The primary channel shifted to manual prior to changing over to the backup channel. The backup chann.el was in manual when it assumed control due to the TVR being in manual (from the primary channel) at the time of fail over. The loss of main generator excitation caused ger,erator protective relay 40-1/2G, "Total Loss of Field" to actuate initiating a turbine trip and generator lockout. Unit 2 was operating at greater than 50% reactor power causing the automatic reactor trip.
Westinghouse permissive signal P-9, "Reactor less than or equal to 50% power turbine trip permissive" blocks a reactor trip due to turbine trip-below 50% power. Since reactor power was greater than 50'% the block was disabled and the
- turbine trip initiated the reactor trip.
The failed power supply was replaced and Unit 2 returned to MODE 1 at 0303, August 16, 2018.
E.,THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE, OR PROCEDURAL PERSONNEL ERROR Initial indication of the event was provided to the Control Room Operators by plant computer alarms, "GEN 2G PHASE A, B, & C CURRENT high and "GEN MVAFf' low. These alarms were directly followed by First Out Annunciator "RX> 50%
PWRTRB TRIP." Operators (Utility, Licensed) confirmed automatic reactor and turbine trips.
II. COMPONENT OR SYSTEM FAILURES A. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE The cause of the event was failure of the TVR primary channel power supply. The failed power supply caused a loss of main generator excitation current. The loss of excitation current caused a turbine trip and a generator lockout. The system design is for the other channel (backup channel) to automatically take control of the TVR and control excitation current. The loss of excitation current was so rapid the primary channel swapped from.automatic to manual. When the primary channel swapped from automatic to manual the backup channel also swapped to manual by design. The backup channel then became the primary channel. With the TVR in manual, excitation current _could not be recovered prior to receiving the turbine. trip. The failure of the primary channel power supply is thought to be age related.
B. FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT When the TVR primary channel power supply failed, the primary channel shifted to manual. In manual the primary channel could not adjust excitation current. When the primary channel swapped to manual the backup channel also swapped to manual by design. When the backup channel became the controlling channel it was in manual and could not recover excitation current. With the loss of excitation, protective relay 40-1/2G initiated a turbine* trip and a generator lockout. With the turbine trip occurring above 50% power the reactor automatically tripped.
C. SYSTEMS OR SECONDARY FUNCTIONS THAT WERE AFFECTED BY FAILURE OF COMPONENTS WITH MULTIPLE FUNCTIONS This event did not involve systems or secondary functions which were affected by the power supply failure.
D. FAILED COMPONENT INFORMATION
The TVR primary channel power supply failure is specifically; TVR ch~nnel 1 Sitar-Set, - 24 vdc power supply, component number 2-JD01-A100-G12, provided to Siemens by MTM Power, part number PMN10 S24.
Ill. ANALYSIS OF THE EVENT A._ SAFETY SYSTEM RESPONSES THAT OCCURRED
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a The Reactor Protection System responded as designed to the automatic turbine trip by initiating an automatic reactor trip.
Automatic start of the AFW system was the expected response and t.he system responded as designed.
I NRC FORM 3§6A (04-2018)
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B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY The event reported herein did not involve the inoperability of any safety component or system.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT A turbine trip is an ANS Condition II event (Faults of Moderate Frequency). When the main turbine tripped the reactor was automatically tripped and the auxiliary feedwater system automatically started to provide feedwater to the steam generators.
Automatic turbine trip and automatic reactor trip were exercised and the Auxiliary Feedwater System started automatically as expected and all plant safety systems responded as designed during the resultant transient. This event had no impact on nuclear safety, reactor safety, radiological safety, environmental safety or the safety of the public. This event has been evaluated as not meeting the definition of a safety system functional failure per 10 CFR 50. 73(a)(2)(v).
IV. CAUSE OF THE EVENT
The cause of the event was,a loss of excitation current to the main generator as the result of a power supply failure in the TVR. The loss of excitation current caused a turbine trip and a generator lockout. Because reactor power at the time of the turbine trip was approximately 100% power, the Westinghouse P-9 signal was unblocked (power> 50%) so when the turbine tripped an automatic reactor trip was actuated.
V. CORRECTIVE ACTIONS
The failed power supply was replaced and the Unit was restarted using Channel 2 as the primary and Channel 1 as the backup channels for the TVR. Analysis is still under review to determine if there is a need for additional process or equipment modifications to prevent recurrence.
VI. PREVIOUS SIMILAR EVENTS
There have been no similar reportable events at Comanche Peak in the past three years. Page 4
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