05000391/LER-2016-004, Regarding Reactor Trip and Safety Injection Actuation Caused by Turbine Governor Valve Failure
| ML16217A398 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 08/04/2016 |
| From: | Simmons P Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 16-004-00 | |
| Download: ML16217A398 (7) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(iii) |
| 3912016004R00 - NRC Website | |
text
Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381 August 4, 2016 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C 20555-0001
Subject:
10 cFR 50 73 Watts Bar Nuclear Plant, Unit 2 Facility Operating License No. NPF-96 NRC Docket No.50-391 Licensee Event Report 391/2016-004-00, Reactor Trip and Safety lnjection Actuation Caused by Turbine Governor Valve Failure This submittal provides Licensee Event Report (LER) 39112016-004-00. This LER provides details concerning a recent reactor trip with safety injection as a result of a turbine governor valve failure. This report is being submitted in accordance with 1 0 cFR 50.73(a)(2)(ivXA).
Please direct any questions concerning this matter to Gordon Arent, WBN Licensing Director, at (423) 365-2004.
Paul Simmons Site Vice President Watts Bar Nuclear Plant Enclosure cc: See Pag e 2 Respectfully,
U.S. Nuclear Regulatory Commission Page 2 August 4, 2016 cc (Enclosure):
NRC Regional Administrator - Region ll NRC Senior Resident lnspector - Watts Bar Nuclear Plant
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION
{11-2015)
$tto*"t'o" iw; e-:Y.c LTcENSEE EVENT REPoRT (LER)
- - r a*rl APPROVED BY OMB: NO. 3150-0104 EXPIRES: t0/31/2018
, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection,
- 1. FACILITY NAME Watts Bar Nuclear Plant, Unit 2 2, DOCKET NUMBER 0500039 1
- 3. PAGE 10F5
- 4. TITLE Reactor Trip and Safety lnjection Actuation Caused by Turbine Governor Valve Failure
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED MONTHI DAY I YEAR YEAR I 'i,Hrut$
REV NO, MONTH I DAY YEAR FACTLTTY NAME I
DOCKET NUMBER N/A lN/A 06 05 I 2016 2016 -004
- - 00 08 a4 2016 FACILITY NAME I
DOCKET NUMBER N/A IN/A
- 9. OPERATING MODE IT.THISREPORTISSUBMITTEDPURSUANTTOTHEREQUlREMENTSOFl0CFR$:
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OTHER Specify in Abstract betow or in D. Manufacturer and Model Number of Components that Failed A bracket that mounted the LVDT to the No. 1 governor valve failed due to vibration related fatigue.
E. Other Systems or Secondary Functions Affected
During the event, anomalies were noted with the 2B Motor Driven Auxiliary Feedwater Pump (MDAFWP) and the Turbine Driven Auxiliary Feedwater Pump (TDAFWP). The 28 MDAFWP was shutdown due to smoke coming from the pump packing. After discussion with the vendor, this was determined to be an expected condition for this type of new packing with minimal break-in time and the pump was restarted. During operation of the TDAFWP, no oil was noted in one of the bearing sight glasses and the pump was manually secured. This was determined to be an issue with the sight glass providing inaccurate indication and not a lack of oil. The pump was subsequently returned to service.
F. Method of discovery of each Component or System Failure or Procedural Error
The failure became apparent after the plant trip.
G. Failure Mode and Effect of Each Failed Component The No. 1 governor valve mounting bracket failed from vibration related fatigue.
H. Operator Actions
This reactor trip was complicated by a concurrent Sl. Operations personnel were able to promptly terminate Sl in accordance with plant procedures and restore the plant to a normal shutdown alignment.
L Automatically and Manually lnitiated Safety System Responses All automatic and manualsafety systems responded as expected.
III. CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known.
The Unit 2 No. 1 governor valve LVDT bracket experienced failure due to short term cyclic fatigue during extended start-up conditions.
B. The cause(s) and circumstances for each human performance related root cause.
There were no apparent human performance related root cause.
NRC FORM 3664 (11-2015)
Paqe 3 of 5
IV. ANALYSIS OF THE EVENT
The turbine governor valves experience high vibration when operated at low steam flow. This flow induced vibration is inherent to the turbine governor valve design when its position is less than 20 percent open.
Vibration is highest with the valve less than 12 percent open. While operating WBN Unit 2 at low power for an extended period, a bracket supporting a position transducer failed, causing an associated failure on the LVDT position rod. During operation, the broken LVDT core rod "walked off'the actuator arm, giving a false low position of the governor valve. The control system, based on the false indication, provided an open demand signal to the No.1 governor valve, which lead to a steam header pressure rate of decrease safety injection actuation signal and an automatic reactor trip.
V. ASSESSMENT OF SAFETY CONSEQUENCES
WBN Unit 2 experienced a safety injection with an automatic reactor trip. All safety equipment responded as expected and operations personnel promptly terminated safe$ injection. The plant was stabilized in Mode 3 without any additional complications. The risk associated this event was determined to be less than 1E-6.
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event The failure that occurred was on a non-safety related turbine component. No safety systems were impacted as a result of this failure.
B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat control the release of radioactive material, or mitigate the consequences of an accident Not applicable.
C. For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from the discovery of the failure until the train was returned to service Not applicable.
VI. CORRECTIVE ACTIONS
This event was entered into the Tennessee Valley Authority (TVA) Corrective Action Program and is being tracked under condition report 1178855.
A. lmmediate Corrective Actions The plant was placed in a safe condition. The failed turbine governor components were replaced.
B. Corrective Actions to Prevent Recurrence Plant operating procedures will be revised to minimize governor valve operation when the valve position is less than 12 percent open. TVA will work with the turbine vendor to determine if work can be performed within the existing valve design requirements to reduce flow induced vibration.
VII. ADDITIONAL INFORMATION
A. Previous similar events at the same plant No similar events have been identified at the Watts Bar plant.
B. Additional lnformation None.
C. Safety System Functional Failure Consideration This condition did not result in a safety system functionalfailure.
D. Scrams with Complications Consideration There was an Sl associated with this plant trip. Operations personnel were able to promptly terminate Sl in accordance with plant procedures and restore the plant to a normal shutdown alignment.
VIII. COMMITMENTS
None.