05000391/LER-2016-006
| Watts Bar Nuclear Plant, Unit 2 | |
| Event date: | 08-13-2016 |
|---|---|
| Report date: | 10-7-2016 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3912016006R00 - NRC Website | |
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
I. PLANT OPERATING CONDITIONS BEFORE THE EVENT
Watts Bar Nuclear Plant (WBN) Unit 2 was in Mode 3 at 0 percent rated thermal power (RTP).
II. DESCRIPTION OF EVENT
A. Event
On August 13, 2016 Watts Bar Nuclear Plant Unit 2 (WBN2) was being stabilized following a pre- planned reactor trip. Both motor driven auxiliary feed water (MDAFW) pumps and the turbine driven auxiliary feed water pump (TDAFW pump) {EIIS:P} were in operation maintaining steam generator (SG) water level between 6 - 50 percent in accordance with the Reactor Trip Response Procedure.
At 0333 Eastern Daylight Time (EDT) the TDAFW pump was secured by procedure and SG water level lowered to the Lo- Lo Alarm setpoint (17 percent). With the Unit at 0 percent power, a trip time delay (TTD) of 3 minutes is present for auxiliary feedwater actuation. At 0337 EDT, the TDAFW pump automatically started with SG water levels less than the Lo-Lo alarm setpoint (lowest level reached was 15 percent).
The cause of the event was a failure to brief the auto start feature of the TDAFW pump at Lo-Lo SG water level of 17 percent when briefing the control band for the SGs is between 6 to 50 percent.
This event is being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in automatic actuation of the auxiliary feedwater system {El IS: BA}.
B. Inoperable Structures, Components, or Systems that Contributed to the Event No inoperable structures, components, or systems contributed to this event.
C. Dates and Approximate Times of Occurrences Date Time (EDT) Event 8/13/16 0230 Transitioned to 2-G0-5 Section 5.4, Shutdown by Pre-planned Manual Reactor Trip 8/13/16 0255 Started 2A-A and 2B-B MDAFW pumps 8/13/16 0306 Manually tripped the Unit 2 reactor 8/13/16 0311 Transitioned to 2-ES-0.1, Reactor Trip Response following immediate actions of 2-E-0, Reactor Trip or Safety Injection 8/13/16 0329 Transitioned to 2-GO-5, Reactor Shutdown from 30 percent Reactor Power to Hot Shutdown 8/13/16 0333 Shutdown U2 TDAFW pump.
8/13/16 0337 TDAFW Pump auto started on Lo-Lo- SG levels 8/13/16 0339 TDAFW Pump secured comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
3. LER NUMBER
2016 - 00 D. Manufacturer and Model Number of Components that Failed Not applicable.
E. Other Systems or Secondary Functions Affected
None.
F. Method of discovery of each Component or System Failure or Procedural Error The error became apparent after the automatic start of the TDAFW pump.
G. Failure Mode and Effect of Each Failed Component Not applicable.
H. Operator Actions
Following automatic start of the TDAFW pump, SG levels were raised above the TTD setpoint of 17 percent. The TDAFW pump was then re-secured.
I. Automatically and Manually Initiated Safety System Responses All automatic and manual safety systems responded as expected.
III. CAUSE OF THE EVENT
A. The cause of each component or system failure or personnel error, if known.
No component failures caused this event.
B. The cause(s) and circumstances for each human performance related root cause.
This event was the result of a human performance error. The cause of the event was a failure to brief the auto start feature of the TDAFW pump at Lo-Lo SG water level of 17 percent when briefing the control band for the SGs is between 6 to 50 percent.
IV. ANALYSIS OF THE EVENT
Watts Bar Unit 2 lowered power for a pre-planned reactor trip. With the TDAFW pump already in operation, the MDAFW pumps were manually started and the unit was tripped from about 25 percent reactor power. After the plant had stabilized, the TDAFW pump was secured. Steam generator levels lowered to the Lo-Lo alarm setpoint of 17 percent. The trip time delay at 0 percent power is three minutes, so the TDAFW pump automatically started on Lo-Lo level, with the lowest level reached being 15 percent.
This event was a result of human error during the briefing for the event to insure that SG levels remained above the Lo-Lo start level.
comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
V. ASSESSMENT OF SAFETY CONSEQUENCES
WBN Unit 2 experienced an automatic start of the TDAFW pump after the plant had been shutdown.
Steam generator levels were stable, but below the auto start level provided in the design. The safety significance of this event is considered to be low.
A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event No equipment failures occurred during this event.
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 All equipment needed for this event was available.
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 Corrective Action Program and is being tracked under condition report 1202562.
A. Immediate Corrective Actions
Steam Generator levels were increased above the Lo-Lo SG level alarm setpoint and the TDAFW pump was secured.
B. Corrective Actions to Prevent Recurrence
Additional training will be performed related to this event. In addition the Auxiliary Feedwater System Operating Instruction was revised to include the trip time delay setpoints associated with operation of the TDAFW and MDAFW pumps .
VII. ADDITIONAL INFORMATION
A. Previous similar events at the same plant On December 21, 2015, TVA submitted LER 390-2015-006, "Source Range Level Trip Channels (N-31 and N-32) Inoperable During Plant Startup." This LER describes a condition prohibited by Technical Specifications where Watts Bar Unit 1 performed a reactor start-up with the source range (SR) reactor trip in the bypass position (SR trip inoperable). This bypass condition was not comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
recognized until after the reactor startup was completed. The cause of this event was that operators failed to identify a bypassed safety function during reactor start-up due to inadequate tracking of essential information. While the event described in LER 2015-006 relates to a condition prohibited by TS, and has a human performance cause, the corrective actions taken for that event do not overlap the issue presented in LER 391-2016-006.
B. Additional Information
None.
C. Safety System Functional Failure Consideration
This condition did not result in a safety system functional failure.
D. Scrams with Complications Consideration Not applicable.
VIII. COMMITMENTS
None.