05000390/LER-2016-001

From kanterella
Jump to: navigation, search
LER-2016-001, Channel Mode Switch in Incorrect Position Renders Lower Containment Atmosphere Particulate Radiation Monitor Inoperable
Watts Bar Nuclear Plant, Unit 1
Event date: 01-12-2016
Report date: 03-09-2016
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3902016001R00 - NRC Website
LER 16-001-00 for Watts Bar, Unit 1, Regarding Channel Mode Switch in Incorrect Position Renders Lower Containment Atmosphere Particulate Radiation Monitor Inoperable
ML16069A205
Person / Time
Site: Watts Bar Tennessee Valley Authority icon.png
Issue date: 03/09/2016
From: Walsh K T
Tennessee Valley Authority
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML16069A205 (7)


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 1 was in Mode 1 at 100 percent rated thermal power (RTP).

II. DESCRIPTION OF EVENT

A. Event

On January 12, 2016, at 1645 Eastern Standard Time (EST), Watts Bar Nuclear Plant (WBN) Instrumentation and Control (I&C) maintenance personnel were performing a 92 day Channel Operational Test for radiation monitor 1-RM-90-106A, Lower Containment Atmosphere Particulate Radiation Monitor {EIIS:MON}, and found the mode switch {EIIS:AS} in the "DIFF" position, which was not expected. Maintenance personnel stopped the surveillance and an investigation was conducted. It was determined that the design requires the mode switch to be in the "INT" position for the monitor to be considered operable. The monitor was declared OPERABLE at 1743 on January 12, 2016 when the surveillance was completed with the mode selector switch placed in the "INT" position .

Placing the mode selector switch in the "DIFF" position resulted in low and high discrimination of the radiation monitor circuit, and effectively prevented any alarms from being received by plant operations. The containment particulate atmosphere radiation monitor is required to be operable by Technical Specification 3.4.15. Because the switch position resulted in a loss of the alarm function for the containment particulate radiation monitor, and loss of operability of the monitor was for a period of time greater than permitted by Technical Specification (TS) 3.4.15, this condition is reportable as an operation or condition prohibited by TS per 10 CFR 50.73(a)(2)(i)(B).

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 Event 10/25/15 N/A 1-SI-90-13, 92 day Channel Operability Test performed on 1-RM-90- 106A. Procedure leaves mode switch in the "INT" position.

11/02/15 N/A Setpoint change conducted to 1-RM-90-106A. No evidence that switch position changed from the "INT" position.

11/25/15 N/A Performed 1-SI-902A and B. No evidence that switch position changed from "INT.

12/08/15 1654 EST Mode selector switch for 1-RM-90-106A placed in the "DIFF" position.

No log note or information identifies the reason for the switch reposition. (Monitor INOPERABLE) 1/12/16 1645 EST l&C personnel discover 1-RM-90-106A with mode selector switch in the "DIFF" position while performing 1-SI-90-13.

1/12/16 1743 EST Surveillance completed with Mode selector switch for 1-RM-90-106A placed in the "INT" position (Monitor OPERABLE).

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.

05000-390

3. LER NUMBER

2016 - 00 D. Manufacturer and Model Number of Components that Failed There were no failed components associated with this event.

E. Other Systems or Secondary Functions Affected

There were no systems or secondary functions affected by this event.

F. Method of discovery of each Component or System Failure or Procedural Error The switch reposition was found during the performance of routine maintenance.

G. Failure Mode and Effect of Each Failed Component There were no component failures associated with this event.

H. Operator Actions

Upon identifying the incorrect position of the switch, its position was corrected.

I. Automatically and Manually Initiated Safety System Responses There were no automatic or manual system responses associated with this event.

III. CAUSE OF THE EVENT

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

There were no component or system failures as a result of this event notification. The most likely cause of the switch reposition was inadvertent manual operation.

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

A cause analysis was performed to determine when the switch was repositioned. Based on a review of plant computer history, it was determined the switch was repositioned on December 8, 2015 at 1654 EST. Work was being performed during this time on the same control room panel that the affected switch was located. However, no maintenance or operator instructions specified that the switch was to be repositioned. Interviews with personnel working in the control room at this time did not identify an individual who repositioned the switch.

IV. ANALYSIS OF THE EVENT

Reactor Coolant System (RCS) leakage detection instrumentation is required by TS 3.4.15. The purpose of this instrumentation is to monitor for reactor coolant pressure boundary (RCPB) leakage as soon after occurrence as practical to minimize the potential for propagation of a leak to a gross failure of the RCPB.

The instruments credited in TS 3.4.15 with monitoring RCPB leakage are the containment pocket sump level monitor and one lower containment atmosphere particulate radioactivity monitor (1-RM-90-106A). TS 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.

05000-390

3. LER NUMBER

2016 - 00 Action 3.4.15.B requires when a containment atmosphere particulate radioactivity monitor is inoperable that containment atmosphere grab samples are to be taken and analyzed every

24 hours
2.777778e-4 days
0.00667 hours
3.968254e-5 weeks
9.132e-6 months

or to perform an RCS inventory balance every

24 hours
2.777778e-4 days
0.00667 hours
3.968254e-5 weeks
9.132e-6 months

and to restore the containment atmosphere particulate radioactivity monitor to operable status in 30 days.

With the mode switch for 1-RM-90-106A in the "DIFF" position, high and low radiation signals were discriminated by the monitor, and the alarm from the containment atmosphere particulate radioactivity monitor was effectively blocked. With the monitor alarm blocked, this monitor is considered to be INOPERABLE.

When the mode switch was placed in the "DIFF" position (monitor INOPERABLE), actions were required by TS 3.4.15.B to take containment atmosphere samples every

24 hours
2.777778e-4 days
0.00667 hours
3.968254e-5 weeks
9.132e-6 months

or to perform an RCS inventory balance every

24 hours
2.777778e-4 days
0.00667 hours
3.968254e-5 weeks
9.132e-6 months

. While entry into TS 3.4.15.6 was not recognized, the plant does perform an RCS inventory balance at least every

24 hours
2.777778e-4 days
0.00667 hours
3.968254e-5 weeks
9.132e-6 months

. The monitor was not, however, returned to operable status in the 30 days required by TS Action 3.4.15.B.2. Accordingly, a condition prohibited by Technical Specifications occurred.

V. ASSESSMENT OF SAFETY CONSEQUENCES

A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event During the time period that the alarm function was lost for 1-RM-90-106A, other means of detecting RCPB leakage remained operable. The containment pocket sump level monitor remained operable, along with the non-credited containment atmosphere radioactivity monitor. In addition, during this time period, RCS inventory balances were performed every shift, with no indication of increasing RCS leakage. Accordingly, the safety consequences of this event are minimal.

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 (CAP) and is being tracked under condition report (CR) 1124181.

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 05000-390

3. LER NUMBER

2016 - 00

A. Immediate Corrective Actions

Upon identifying the incorrect position of the channel mode switch, the switch was placed in the correct position.

B. Corrective Actions to Prevent Recurrence

Plant procedures will be revised to check the position of the mode selector switch for the containment radiation monitors 1/2-RM-90-106A and 1/2-RM-90-112A every shift.

VII. ADDITIONAL INFORMATION

A. Previous similar events at the same plant

On December 21, 2015, NA 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 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 is somewhat different than this LER, and had other contributing causes, it involves a bypassed safety function not being recognized. Because the issue described in this LER involved an undocumented switch reposition, the corrective actions in LER 2015-006 would not be expected to have prevented this event.

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 There was no scram associated with this report.

VIII. COMMITMENTS

None.