05000327/LER-2019-001, Reactor Trip on Low-Low Steam Generator Level Due to the Loss of a Main Feedwater Pump
| ML19163A049 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 06/11/2019 |
| From: | Rasmussen M Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LER 2019-001-00 | |
| Download: ML19163A049 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3272019001R00 - NRC Website | |
text
Tennessee Valley Authority, Sequoyah Nuclear Plant, P.O. Box 2000, Soddy Daisy, Tennessee 37384 June 11, 2019 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Unit 1 Renewed Facility Operating License No. DPR-77 NRC Docket No. 50-327
Subject:
Licensee Event Report 50-327/2019-001-00, Reactor Trip on Low-Low Steam Generator Level Due to the Loss of a Main Feedwater Pump The enclosed licensee event report provides details concerning an automatic reactor trip on low-low steam generator level as a result of the loss of a main feedwater pump. This event is being reported, in accordance with 10 CFR 50.73(a)(2)(iv), as an event that resulted in an automatic actuation of the reactor protection system and the auxiliary feedwater system.
There are no regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact Mr. Jonathan Johnson, Site Licensing Manager, at (423)843-8129.
Respectfully, flatthew Rasmussen Site Vice President Sequoyah Nuclear Plant Enclosure: Licensee Event Report 50-327/2019-001-00 cc:
NRC Regional Administrator - Region II NRC Senior Resident Inspector-Sequoyah Nuclear Plant printed on recycled paper
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)
, the NRC may not conduct or sponsor, and a person is not reauired to respond to. the information collection.
Sequoyah Nuclear Plant Unit 1 05000327
- 3. Page 1 OF5
- 4. Title Reactor Trip on Low-Low Steam Generator Level Due to the Loss of a Main Feedwater Pump
- 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 NA Docket Number 05000 04 14 2019 2019
- - 001
- - 00 06 11 2019 Facility Name Docket Number NA 05000 9.OperatingMode 1
) ^
No N/A N/A N/A Abstract (Limit to 1400 spaces, i.e., approximately 14 single-spaced typewritten lines)
On April 14, 2019, at 0320 eastern daylight time (EDT), Sequoyah Nuclear Plant, Unit 1, experienced an automatic reactor trip. The reactor trip was preceded by a turbine runback, because main feedwater pump (MFP) 1A tripped on low lube oil pressure. In response to the 1A MFP trip, the Auxiliary Feedwater (AFW)
System actuated, as designed; however, AFW and the remaining main feedwater pump (1B) were not able to provide sufficient feedwater flow to maintain steam generator level. This resulted in an automatic reactor trip due to low-low level in the Loop 3 steam generator (SG). The causes of the reactor trip were previous MFP turbine hydraulic control system modifications coupled with an unvalidated turbine runback setpoint resulting in the inability to supply adequate feedwater flow to the SGs during the loss of a MFP transient. The corrective actions to prevent recurrence are: (1) implement digital feed pump control upgrade via an engineering change package, and (2) implement a revised turbine runback setpoint, as determined, as part of an engineering change package.
NRC FORM 366 (04-2018)
I.
Plant Operating Conditions Before the Event
At the time of the event, Sequoyah Nuclear Plant (SQN) Unit 1 was in Mode 1 at 100 percent rated thermal power.
II.
Description of Event
A.
Event Summary
On April 14, 2019, at 0320 eastern daylight time (EDT), SQN Unit 1 experienced an automatic reactor trip. The reactor trip was preceded by a turbine runback, because main feedwater pump (MFP) [EMS: SJ] 1A tripped on low lube oil pressure. In response to the 1A MFP trip, the Auxiliary Feedwater (AFW) System [EMS: BA] actuated, as designed; however, AFW and the remaining main feedwater pump (1B) were not able to provide sufficient feedwater flow to maintain steam generator [EMS: AB, SG] level. This resulted in an automatic reactor trip due to low-low level in the Loop 3 steam generator (SG).
All plant safety systems responded as designed. During this operating cycle, one rod [EMS: ROD]
position indicator (RPI) has been inoperable. Due to the inoperable RPI, the associated shutdown rod was assumed to be full out and untrippable. Consequently, boration was required to ensure adequate shutdown margin. All control rods and shutdown rods indicated fully inserted.
This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A), as an event that resulted in an automatic actuation of the Reactor Protection System and the AFW System.
B.
Status of structures, components, or systems that were inoperable at the start of the event and contributed to the event:
No inoperable structures, components, or systems contributed to this event.
C.
Dates and approximate times of occurrences
(04-2018)
YEAR 2019
- 3. LER NUMBER SEQUENTIAL NUMBER
- - 001 REV NO.
- - 00 Page 2 of 5(04-2018)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020
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V
, the NRC may not conduct or sponsor,anda personis notrequired to respondto,the informationcollection.
- 3. LER NUMBER Sequoyah Nuclear Plant Unit 1 05000-327 YEAR 2019 SEQUENTIAL NUMBER
- 001 REV NO.
- - 00 Date/Time (EDT)
Description
04/14/19,03:19:02 The 1A MFP tripped. AFW actuated in response to the loss of a MFP.
The Unit 1 turbine runback balance of plant alarm annunciated.
04/14/19,03:20:24 Main control room (MCR) operators took manual control of the 1B MFP and ensured output was maximized.
04/14/19, 03:20:40 The Unit 1 reactor tripped due to low-low level in the Loop 3 SG. The reactor trip was followed by a turbine trip.
04/14/19,03:21 MCR operators took appropriate actions, in accordance with procedures, and transitioned the reactor to Mode 3.
D.
Manufacturer and model number of each component that failed during the event
Prior to the event, the drive end radial bearing of a Homewood Products Corporation motor model no. TBFC, motor style 71D2176, serial no. 2S-1H12088, failed. This motor is associated with the 1A1 Main Oil Pump on the 1A MFP.
E.
Other systems or secondary functions affected
There were no other systems or secondary functions affected by this event.
F.
Method of discovery of each component or system failure or procedural error
MCR alarms and annunciators provided indication to the operators.
G.
Failure mode, mechanism, and effect of each failed component:
The drive end radial bearing experienced a bearing cage failure that caused a loss of even bearing ball retention within the bearing races. The cause of the bearing failure was from bearing degradation that occurred during a winding failure of this motor during a no-load test run at the Tennessee Valley Authority's (TVA's) Power Service Shop after the motor was refurbished in 2017.
The failure of the 1A1 Main Oil Pump resulted in a trip of the 1A MFP.
H.
Operator actions
MCR operators responded to the MFP trip, reactor trip, and turbine trip as required. They promptly identified the condition and took appropriate actions.Page 3 of 5(04-2018)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020
, the NRC may not conduct or sponsor, anda personis notrequired to respondto,the informationcollection.
- 1. FACILITY NAME 2
DOCKET NUMBER
& LER NUMBER Sequoyah Nuclear Plant Unit 1 05000-327 YEAR 2019 SEQUENTIAL NUMBER
- - 001 REV NO.
- - 00 I.
Automatically and manually initiated safety system responses
The reactor protection system, including feedwater isolation and AFW start, responded to the trip, as designed.
III.
Cause of the Event
A.
Cause of each component or system failure or personnel error
The causes of the reactor trip were previous MFP turbine hydraulic control system modifications coupled with an unvalidated turbine runback setpoint resulting in the inability to supply adequate feedwater flow to the SGs during the loss of a MFP transient.
B.
There was no identified human performance related root cause.
IV.
Analysis of the Event
The plant safety system responses during and after the reactor trip were bounded by the responses described in the Final Safety Analysis Report. Therefore, this event did not adversely affect the health and safety of plant personnel or the general public.
V.
Assessment of Safety Consequences
There were no actual safety consequences as a result of this event.
A.
Availability of systems or components that could have performed the same function as the components and systems that failed during the event:
Prior to the event, the failure of the operating 1A1 main oil pump resulted in the standby 1A2 main oil pump auto-starting. The 1A2 main oil pump was not able to prevent the bearing oil pressure from reaching the 1A MFP low bearing oil pressure switch set point. This resulted in a trip of the 1AMFP.
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:
The event did not occur when the reactor was shut down.Page 4 of 5(04-2018)
U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020
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Estimated burden perresponse to comply with this mandatory collection request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated intothe licensing process and fed backto industry. Send comments regarding burden estimate to the Information Services Branch (T-2 F43), U. S. Nuclear Regulatory Commission, Washington, DC 20555-0001,or bye-mail to lnfbcollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office oi Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, anda person is notrequired to respond to,the informationcollection.
Sequoyah Nuclear Plant Unit 1 05000-327 YEAR 2019 1 LB*NUMBER SEQUENTIAL NUMBER
- - 001 C.
For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from discovery of the failure until the train was returned to service:
There was no failure that rendered a train of a safety system inoperable.
VI.
Corrective Actions
This event was entered into the Tennessee Valley Authority Corrective Action Program under Condition Reports 1507644 and 1508834.
A.
Immediate Corrective Actions
The 1A1 main oil pump motor was replaced.
B.
Corrective Actions to Prevent Recurrence or to reduce probability of similar events occurring in the future:
The corrective actions to prevent recurrence are: (1) implement digital feed pump control upgrade via an engineering change package, and (2) implement a revised turbine runback setpoint, as determined, as part of an engineering change package.
VII.
Previous Similar Events at the Same Site
There were no previous similar events at SQN occurring within the last three years.
VIM.
Additional Information
There is no additional information.
IX.
Commitments
There are no commitments.
REV NO.
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