05000391/LER-2017-004

LER-2017-004, Manual Reactor Trip Due to Inoperable Rod Position Indication

Watts Bar Nuclear Plant, Unit 2
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3912017004R00 - NRC Website

LER 17-004-00 for Watts Bar Nuclear Plant, Unit 2 Regarding Manual Reactor Trip Due to Inoperable Rod Position Indication

ML17268A210
Person / Time
Site:	Watts Bar
Issue date:	09/25/2017
From:	Simmons P Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 17-004-00
Download: ML17268A210 (6)

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3. LER NUMBER

2017 - 00 004

I. PLANT OPERATING CONDITIONS BEFORE THE EVENT

Watts Bar Nuclear Plant (WBN) Unit 2 was in Mode 3.

II. DESCRIPTION OF EVENT

A. Event Summary was in Mode 3, commencing a Reactor Startup. While in the initial phase of withdrawing the first of four Control Banks, the two associated group demand position indicators deviated greater than 2 steps from each other. In accordance with Technical Requirement (TR) 3.1.7, Position Indication System, Shutdown, {EIIS:AA} with one or more group demand position indicators inoperable, the reactor trip breakers are to be opened immediately. Operations personnel opened the reactor trip breakers immediately by initiating a manual trip of the Reactor Protection System (RPS){EIIS:JC}.

The Auxiliary Feedwater (AFW) system {EIIS:BA} was in service and controlling Steam Generator water levels at the time of the event and did not receive any valid actuation signals. No other system actuations occurred as a result of this reactor trip and all systems operated as designed.

These events are being reported to the Nuclear Regulatory Commission (NRC) under 10 CFR 50.73(a)(2)(iv)(A) for initiation of a manual reactor trip.

B. Inoperable Structures, Components, or Systems that Contributed to the Event Slave cycler logic card {EIIS:CARD} in rod control system had failed.

C. Dates and Approximate Times of Occurrences Date Time Event (EDT) 7/25/17 0426 Initiated Reactor Startup in accordance with procedure 2-GO-2, Reactor Startup.

7/25/17 0427 Observed Control Bank Al group demand indicates 0 steps. Control Bank A2 group demand indicates 3 steps 7/25/17 0428 Entered TR 3.1.7 Condition A. Reactor trip breakers (RTBs) are opened.

7/25/17 0428 Entered 2-E-0, Reactor Trip of Safety Injection, due to manually opening RTBs by inserting a Manual Reactor Trip.

7/25/17 0432 Transitioned to 2-ES-0.1, Reactor Trip Response.

7/25/17 0449 Transitioned to 2-GO-5, Unit Shutdown from 30 percent Reactor Power to Hot Standby.

D. Manufacturer and Model Number of Components that Failed During the Event The card that failed was an A406 slave cycler logic card provided by Westinghouse Electric Corporation, Style 2D82868G01.

E. Other Systems or Secondary Functions Affected

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All safety systems and secondary functions operated as designed.

F. Method of discovery of each Component or System Failure or Procedural Error An investigation following the manual reactor trip identified the failed logic card.

G. Failure Mode and Effect of Each Failed Component The cause of the logic card failure is under investigation by Westinghouse.

H. Operator Actions

Upon determining a group demand indication variance of greater than two steps, the reactor trip breakers were opened by inserting a Manual Reactor Trip. Operations personnel promptly worked through the emergency procedures and reentered normal plant operating procedures for this' condition.

I. Automatically and Manually Initiated Safety System Responses The reactor trip breakers were opened by manually tripping the reactor. No automatic actuations of safety equipment were required or occurred.

III. CAUSE OF THE EVENT

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

The failed logic card was shipped to the vendor for testing and failure analysis.

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

No human performance issues are related to this trip.

IV. ANALYSIS OF THE EVENT

During a normal start up at WBN, operations personnel commenced withdrawing Control Bank A. Within 3 steps, operations personnel determined a rod position deviation occurred and opened the reactor trip breakers in accordance with requirements. During the event the reactor was not critical, and cooling was being provided by the AFW system. The reactor trip was uncomplicated. After extensive troubleshooting and analysis by the vendor, the slave cycler card failure was identified.

V. ASSESSMENT OF SAFETY CONSEQUENCES

This event is bounded by a rod cluster control assembly misalignment, which is an anticipated operational occurrence described in the Final Safety Analysis Report (FSAR).

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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 All safety systems operated as designed during this event.

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 (CR) 1320840.

A. Immediate Corrective Actions

When the rod position deviation was identified, the reactor trip breakers were opened.

Subsequent investigation determined that a logic card had failed, and the card was replaced.

B. Corrective Actions to Prevent Recurrence or to Reduce Probability of Similar Events Occurring in the Future Additional logic cards associated with the rod control system will be tested in accordance with the preventative maintenance strategy.

VII. PREVIOUS SIMILAR EVENTS AT THE SAME SITE

An automatic reactor trip due to actuation of the Over Temperature Delta temperature bistables was reported to the NRC in LER 390/2016-004 dated May 23, 2016. This event was caused by a failure of a Valve Position Limit up/down counter circuit card in the Analog Electro-Hydraulic Turbine Control System which resulted in the closure of the turbine high pressure governor valves, resulting in an automatic reactor trip and turbine trip on WBN1. The event described in this LER is different in that it involves a component failure in an unrelated plant system.

VIII. ADDITIONAL INFORMATION

None.

IX. COMMITMENTS

None.