05000260/LER-2009-005
| Browns Ferry Nuclear Plant Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2602009005R00 - NRC Website | |
I. PLANT CONDITION(S)
At the time the inoperability condition was identified on Unit 2, Units 1, 2 and 3 were at 100 percent power (3458 Megawatts thermal). Units 1 and 3 were unaffected by the event.
II. DESCRIPTION OF EVENT
A. Event:
On July 18, 2009, at approximately 1425 hours0.0165 days <br />0.396 hours <br />0.00236 weeks <br />5.422125e-4 months <br /> Central Daylight Time (CDT) during scheduled performance of General Operating Instruction, Monthly Emergency Control Switch Verification - Unit 2 (0-G01-300-1 Attachment - 15.13) Operators found the Manual/Auto Transfer Switch on 480 V Reactor Motor Operated Valve (RMOV) Board 2D [EB] in the incorrect, manual, position. Operators immediately declared 480 V RMOV Board 2D and Loop I of Residual Heat Removal (RHR) [BO] System inoperable and entered Technical Specifications (TS) 3.8.7 Actions, Condition C, and TS 3.5.1 Actions, Condition A.
TS 3.8.7 Actions, Condition C, Required Action C.1, requires, with Unit 2 480 V RMOV Board 2D inoperable, that the affected RHR subsystem be immediately declared inoperable. With the affected RHR subsystem inoperable (i.e., one low pressure Emergency Core Cooling (ECCS) system injection/spray subsystem inoperable), TS 3.5.1 Actions, Condition A, Required Action A.1 requires the low pressure ECCS injection/spray subsystem to be restored to operable status within 7 days. By 1509 hours0.0175 days <br />0.419 hours <br />0.0025 weeks <br />5.741745e-4 months <br /> CDT on July 18, 2009, Operators returned the switch to the auto position and exited the associated TSs Actions. BFN assumed the switch had been out of position since the restart from the Unit 2 refueling outage on June 19, 2009.
Therefore, Unit 2 was in a condition prohibited by the plant's TSs (i.e., one low pressure EECS injection/spray subsystem was inoperable for longer than the 7 day Completion Time of TS 3.5.1 Actions, Condition A, Required Action A.1). Hence, BFN is submitting this report in accordance with 10 CFR 50.73(a)(2)(i)(B), as any operation or condition prohibited by the plant's Technical Specifications.
B. Inoperable Structures. Components. or Systems that Contributed to the Event:
None.
C. Dates and Approximate Times of Maior Occurrences:
June 19, 2009� Unit 2 restarts from Cycle 15 Refueling Outage.
July 18, 2009 at 1425 hours0.0165 days <br />0.396 hours <br />0.00236 weeks <br />5.422125e-4 months <br /> CDT � BFN determines Loop I of RHR was inoperable longer than allowed by TSs.
July 18, 2009 at 1509 hours0.0175 days <br />0.419 hours <br />0.0025 weeks <br />5.741745e-4 months <br /> CDT� Operations returned the Auto/Manual Switch to the Auto Position and exited TS 3.8.7 Actions, Condition C and TS 3.5.1 Actions, Condition A.
D. Other Systems or Secondary Functions Affected
None.
E. Method of Discovery
Operators discovered the switch in the incorrect position during scheduled performance of 0-G01-300-1 Attachment - 15.13.
F. Operator Actions
Operators immediately declared 480 V RMOV Board 2D and Loop I of Residual Heat Removal (RHR) [BO] System inoperable and entered the appropriate TSs Actions. Operators placed the Manual/Auto Transfer Switch on 480 V RMOV Board 2D in the Auto position in accordance with Operating Instruction, 480V/240V AC Electrical System (0-01-57B).
Operations then declared 480 V RMOV Board 2D and Loop 1 RHR operable and exited TS 3.8.7 Actions, Condition C and TS 3.5.1 Actions, Condition A.
G. Safety System Responses
None.
III. CAUSE OF THE EVENT
A. Immediate Cause
The Auto/Manual Transfer switch was in the incorrect position thus, 480 V RMOV Board 2D and associated Loop I RHR Subsystem were inoperable.
B. Root Cause
No reason for the Auto/Manual Transfer switch being in the incorrect position could be verified.
However, the most probable cause for the switch in the incorrect position is the switch was inadvertently bumped by an individual traversing the area of the RMOV board.
C. Contributing Factors
The Auto/Manual Transfer Switch is in an accessible area and not provided with a protective cover to prevent inadvertent operation or bumping of the switch.
IV. ANALYSIS OF THE EVENT
BFN was unable to establish the exact time and action that lead to the Auto/Manual Transfer Switch in the incorrect position. However, for this report, BFN assumed the event occurred prior to when Unit 2 entered the mode of applicability for the affected RMOV board and associated RHR Subsystem (i.e., restart from the Unit 2 refueling outage on June 19, 2009).
The monthly performance of 0-G01-300-1 Attachment - 15.13 was previously performed on April 15, 2009. At that time, the subject switch was confirmed in the correct, Auto, position.
Performance of this procedure is not required when Unit 2 is in Modes 4 or 5. The monthly check list was not performed during the Cycle 15 Refueling Outage (i.e., during Modes 4 and 5) which commenced on April 25, 2009. BFN's investigation found that the Auto/Manual Transfer Switch should have been manipulated on May 15, 2009, when the 2DA Low-Pressure Coolant Injection (LPCI) [BO] Motor Generator (MG) was placed in service following maintenance activities on the alternate feed, 480 V RMOV Board 2B. Operating Instruction 0-01-57B requires the Auto/manual Transfer Switch be left in the Auto position when placing the 2DA LPCI MG in service. Indications are that the switch was in the correct position following the performance of 0-01-57B on May 15, 2009.
V. ASSESSMENT OF SAFETY CONSEQUENCES
The safety consequences of this event were not significant. BFN TS LCO 3.8.7 requires that the RMOV board remain operable with the reactor in Modes 1, 2 and 3. TS LCO 3.0.4 prohibits ascending reactor mode changes unless the TS Systems required for the mode are operable. The objective of this TS provision is to ensure that TS Systems required for plant startup and operation are in service to support safe plant operation. The Auto/Manual Transfer switch must be maintained in the Auto position in order to maintain the RMOV board fully operable. With the Auto/Manual Transfer Switch in the manual position loss of the feed from 480 V Shutdown Board 2A results in a failure to automatically transfer to the alternate feed, 480 V Shutdown Board 2B.
The 480 V RMOV Board 2D has only three (3) loads, all Division 1. These are the normally open Reactor Recirculation System Pump 2B [AD] discharge valve, the normally closed Loop 1, RHR inboard low pressure core injection (LPCI) valve , and the normally open Loop 1 RHR pumps A and C minimum flow bypass valve. The failure of 480 V RMOV Board 2D to transfer on loss of the upstream feed, 480 V Shutdown Board 2A which is provided power from 4.16 kV Shutdown Board B, during a postulated Design Basis Accident - Loss of Coolant Accident (DBA-LOCA) would result in a failure of the valves to actuate including, failure of the LPCI injection to open. The postulated board failure results in a Loss of Loop 1 RHR injection path which is bounded the BFN single failure analysis described in Updated Safety Analysis Report Section 6.5 and Table 6.5-3.
The analysis concludes that peak clad temperature during a DBA-LOCA is maintained below 2200 degrees F. Therefore, BFN concludes that the health and safety of the public was not affected by this event.
VI. CORRECTIVE ACTIONS
A. Immediate Corrective Actions The Units 2 and 3 Reactor Building Auxiliary Unit Operator Rounds Instruction has been revised to verify the Auto/Manual Transfer switches on both the 480 V RMOV Board 2D and 2E on both Units 2 and 3 are in the Auto position. These two 480 V RMOV boards do not have a protective cover on the Auto/Manual Transfer switch. The verification is performed once per shift.
B. Corrective Actions to Prevent Recurrence - The corrective actions are being managed by BFN's corrective action program.
For Units 1 and 2, the BFN operating instructions governing plant startup are being revised to require that the Emergency Control Switch Verification be performed prior to entry into Mode 3 or 2.
For Unit 3 which is restarting from a short forced outage the BFN operating instruction governing plant startup has been revised to require that the Emergency Control Switch Verification be performed prior to entry into Mode 3 or 2.
VII. ADDITIONAL INFORMATION
A. Failed Components
None.
B. PREVIOUS LERS ON SIMILAR EVENTS
None.
C. Additional Information
Corrective action document for this report is Problem Evaluation Report 176648.
D. Safety System Functional Failure Consideration:
This event is not a safety system functional failure according to NEI 99-02.
E. Scram With Complications Consideration:
This event was not a complicated scram according to NEI 99-02.
VIII. COMMITMENTS
None.