05000391/LER-2017-002

LER-2017-002, Manual Reactor Trip as a Result of a Secondary Plant Transient

Watts Bar Nuclear Plant, Unit 2
Event date:	03-20-2017
Report date:	05-12-2017
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3912017002R00 - NRC Website

LER 17-002-00 for Watts Bar, Unit 2, Regarding Manual Reactor Trip as a Result of a Secondary Plant Transient

ML17132A267
Person / Time
Site:	Watts Bar
Issue date:	05/12/2017
From:	Simmons P Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 17-002-00
Download: ML17132A267 (7)

I. PLANT OPERATING CONDITIONS BEFORE THE EVENT

Watts Bar Nuclear Plant (WBN) Unit 2 was at 100 percent rated thermal power (RTP) prior to the secondary system transient.

II. DESCRIPTION OF EVENT

A. Event Summary operations personnel manually tripped the plant from approximately 91 percent power based on lowering steam generator (SG){EIIS:SG} levels. Prior to the plant trip, the 2A Hotwell pump {EllS:P}, a component of the condensate system {EIIS:SD}, tripped at 0759 EDT and the 2C Condensate Booster Pump subsequently tripped at 0803 EDT. Operations personnel commenced to lower plant power after the 2A Hotwell pump trip in an attempt to maintain steam generator levels, but were unable to recover level and manually tripped the unit.

All control rods fully inserted and all automatically actuated safety related equipment operated as designed. At 0905 EDT, operations personnel exited the emergency operating instructions after the plant was stabilized.

This event is being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(a)(2)(iv)(A) as a safety system actuation of the reactor protection system {EIIS:JC} and the auxiliary feedwater (AFW) system {EIIS:BA}.

B. Inoperable Structures, Components, or Systems that Contributed to the Event No inoperable systems or components contributed to this report.

C. Dates and Approximate Times of Occurrences Date Time Event (EDT) 3/20/2017 0759 Craft personnel inadvertently depressed local trip pushbutton for 2A Hotwell Pump 3/20/2017 0803 2C Condensate Booster pump tripped automatically 3/20/2017 0806 Operations enter 2-AOI-39, Rapid Load Reduction 3/20/2017 0811 2B Condensate Booster pump tripped on loss of Net Positive Suction Head (NPSH).

3/20/2017 0813 Operations personnel manually trip WBN Unit 2 at 91 percent RTP based on lowering SG levels. Main feedwater automatically isolated.

3/20/2017 0905 Operations personnel exit emergency operating instructions.

D. Manufacturer and Model Number of Components that Failed During the Event None APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 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.

E. Other Systems or Secondary Functions Affected

The inadvertent trip of the 2A Hotwell pump led to multiple secondary system pump trips on loss of NPSH.

F. Method of discovery of each Component or System Failure or Procedural Error The inadvertent trip of the 2A Hotwell pump was discovered after the trip based on interviews with plant personnel.

G. Failure Mode and Effect of Each Failed Component No components failed during this event.

H. Operator Actions

With SG levels lowering as a result of lost secondary pumps, operations personnel commenced a rapid load reduction and established a manual trip criteria based on SG level. SG levels were recovering when the 2B Condensate Booster pump was lost. With lowering SG levels the reactor was manually tripped above the SG low level alarm.

I. Automatically and Manually Initiated Safety System Responses The reactor was manually tripped and the AFW system automatically actuated. All safety systems operated as expected.

III. CAUSE OF THE EVENT

A. The cause of each component or system failure or personnel error, if known.

The plant trip was a result of scaffold workers inadvertently depressing the local trip pushbutton for the 2A Hotwell pump.

B. The cause(s) and circumstances for each human performance related root cause.

The plant trip was a result of scaffold workers inadvertently depressing the local trip pushbutton for the 2A Hotwell pump. These workers did not display appropriate situational awareness around trip sensitive equipment. Operations personnel did not establish proper controls for work being performed on WBN Unit 2 while WBN Unit 1 was in an outage.

IV. ANALYSIS OF THE EVENT

The inadvertent trip of the 2A Hotwell pump resulted in reduced suction head to downstream pumps, resulting in additional pump trips on low suction pressure. This resulted in reduced feedwater flow and lowering SG levels. Operations commenced a rapid downpower to address lowering SG levels, but APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 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.

multiple pump trips led to the decision to manually trip the plant rather than wait for an automatic plant trip.

All safety systems operated as expected. While main feedwater isolated by design, it was recoverable using normal plant procedures. This trip is considered to be uncomplicated.

V. ASSESSMENT OF SAFETY CONSEQUENCES

The event resulted from an inadvertent trip of the 2A Hotwell pump, which led to other secondary pumps tripping due to a loss of NPSH. The resultant secondary plant transient required a manual plant trip. The event that occurred is bounded by the Loss of Normal Feedwater event described in the Final Safety Analysis Report (FSAR), which is considered an anticipated operational occurrence.

A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event All safety systems operated as designed 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 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 All safety systems operated as designed during this event.

VI. CORRECTIVE ACTIONS

This event was entered into the Tennessee Valley Authority (TVA) Corrective Action Program and is being tracked under Condition Reports (CRs) 1274558, 1274800, and 1275064.

A. Immediate Corrective Actions

Upon determining the nature of the human performance error, coaching was provided to site construction personnel related to situational awareness around trip sensitive equipment.

Additional controls were specified for field personnel working on an operating unit while the adjacent unit was in an outage.

B. Corrective Actions to Prevent Recurrence or to Reduce Probability of Similar Events Occurring in the Future Operations personnel were coached on the need to control work activities near operating equipment. Bump guard covers were installed on local pushbuttons for a number of secondary pumps in the turbine building to prevent inadvertent actuation.

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 Infocollects.Resource@nrc gov, and to the Desk Officer, Office of Information and Regulatory Affairs, 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

2017 - 00 002

VII. PREVIOUS SIMILAR EVENTS AT THE SAME SITE

A plant trip due to loss of main feedwater was reported to the NRC in LER 391/2016-005 dated August 19, 2016. This event was attributed to operations personnel failing to precisely control the plant, resulting in a loss of vacuum to the main feedwater pump condenser. The event described in this LER is different in that it involved an inadvertent equipment contact by non-operations personnel.

VIII. ADDITIONAL INFORMATION

None.

IX. COMMITMENTS

None.