05000327/LER-2008-002
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. Sequoyah Nuclear Plant Unit 2 05000328 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3272008002R01 - NRC Website | |
I. PLANT CONDITION(S)
Unit 1 and Unit 2 were operating at 100 percent power.
II. DESCRIPTION OF EVENT
A. Event:
On September 24, 2008, at 1705 Eastern daylight time (EDT), Technical Specification (TS) Limiting Condition for Operation (LCO) 3.8.1.1, "A/C Sources," was entered for scheduled maintenance of the 1A-A emergency diesel generator (EDG) [EIIS Code EK] 125-volt battery bank. The scheduled battery bank maintenance was expected to take approximately 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br />. On September 25, 2008, at 2255, LCO 3.7.15, "Control Room Air-Conditioning System," was entered because of a motor failure on the associated "B" train main control room air handling unit [EIIS Code VI]. Under this condition TS .LCO 3.0.5 was entered, which required action to be initiated within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> to place both units in Hot Standby in the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
Enforcement discretion was requested and granted on September 26, 2008, to extend the expiration time of LCO 3.0.5 an additional 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. Compensatory measures were initiated to administratively control and protect vital plant equipment during this period of time for completing maintenance to replace the batteries for the 1A-A EDG and the unplanned maintenance to replace the motor in the "B" train main control room air handling unit. Subsequently, SQN returned the EDG battery bank to service and exited LCO 3.8.1.1 and LCO 3.0.5 on September 26, 2008 at 1400 EDT.
B. Inoperable Structures, Components, or Systems that Contributed to the Event:
None.
C. Dates and Approximate Times of Major Occurrences:
September 24, � EDG 1A-A was declared inoperable in preparation for EDG 2008� 125-volt battery bank maintenance.
at 1705 EDT September 25,� A swap of main control room air conditioning system, from 2008� train "A" to "B" was attempted, at which time the "B" train at 2250 EDT� main control room air handling unit tripped when attempting to start. Train "A" continued to operate.
September 25,d Main control room air conditioning system "B" train was 2008d declared inoperable when an investigation revealed smoke at 2255 EDTd and a burnt smell from the B-B main control room air handling unit motor. TS LCO 3.0.5 was entered which required both units to be in Hot Standby at 0655 on September 9, 2008.
September 26,d NRC granted TVA's verbal request for enforcement 2008 at -0400d discretion to extend the expiration time of LCO 3.0.5 an EDTd additional 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
September 26,d The EDG 1A-A battery bank was aligned to the 125-volt dc 2008d distribution board and charger. The 1A-A EDG was at 0507 EDTd considered functionally available but inoperable per TS.
September 26,d EDG 1A-A was declared operable after its battery passed its 2008d TS required surveillance test. TS LCO 3.0.5 was exited.
at 1400 EDT
D. Other Systems or Secondary Functions Affected:
No other systems or secondary functions were affected by this event.
E. Method of Discovery:
"B" train main control room air handling unit tripped while attempting to start. Control room air conditioning system "B" train was declared inoperable when an investigation revealed smoke and a burnt smell from the B-B main control room air handling unit motor.
F. Operator Actions:
Main control room air conditioning system "B" train was declared inoperable because of the "B" train main control room air handling unit motor failure. TS LCO 3.0.5 was entered on both units. Compensatory measures were initiated to administratively control and protect vital plant equipment during this period of time to complete maintenance to replace the batteries for the 1A-A EDG and the unplanned maintenance to replace the motor in the "B" train main control room air handling unit. Subsequently, SQN returned the EDG 1A-A battery bank and the "B" train main control room air handling unit to service.
G. Safety System Responses:
No safety system response was required.
CAUSE OF THE EVENT
A. Immediate Cause:
"B" train main control room air handling unit motor failed during the time 1A-A EDG was inoperable for battery bank replacement.
B. Root Cause:
The risk associated with swapping the main control room air handling units while the 1A-A EDG was inoperable was not adequately assessed.
C. Contributing Factor:
None.
IV.� ANALYSIS OF THE EVENT Main control room air conditioning system train "A" was inoperable solely because of its emergency power source being unavailable (EDG 1A-A). The redundant main control room air conditioning system train "B" became inoperable which required both units to enter LCO 3.0.5 which required 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> to return the EDG to service or place both units in Hot Standby in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. Train "A" main control room air conditioning system continued to perform its intended function of maintaining control room temperature.
If a loss of off-site power occurs, the EDG battery provides control power during the blackout period and field flash current for excitation during a EDG start. Prior to expiration of the time limit of LCO 3.0.5, the EDG battery was made available and was sufficiently charged to assure that the battery would perform its function in support of EDG 1A-A.
In the unlikely event the "A" train main control room air handling unit was lost, TVA calculations demonstrate that more than 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> exist before the main control room would become an uninhabitable environment. In addition, shutdown of both units can be accomplished from the backup control room. The backup control room is located outside the main control room and is supplied by a different air-conditioning system that was available during the 36-hour extension time.
There was no net increase in radiological risk to the public by avoiding the unnecessary transient imposed by compliance with LCO 3.0.5 and safety continued to be assured by the "A" train main control room air conditioning system, which was performing its intended function of maintaining control room temperature.
V.�ASSESSMENT OF SAFETY CONSEQUENCES Based on the above "Analysis of The Event," this event did not adversely affect the health and safety of plant personnel or the general public.
VI.�CORRECTIVE ACTIONS A. Immediate Corrective Actions:
Compensatory measures were put in place to ensure no activities would take place that could affect the supporting systems and equipment for the "A" train main control room air conditioning system. Actions were expedited to repair the "B" train main control room air handling unit motor and return to operable the 1A-A EDG.
B. Corrective Actions to Prevent Recurrence:
Operations clarified guidance for operating out of train equipment and developed required approval for manipulating 'protected' equipment.
Establish a process for review and control of site work activities for potential nuclear safety or generation risk that provides a mechanism to reassess nuclear safety or generation risk upon change to the original scope or planning of the activity.
Establish visual aids for work packages and procedures that identify the type and level of risk associated with the work.
VII.�ADDITIONAL INFORMATION
A. Failed Components:
Main Control Room Air Handling Unit motor.
B. Previous LERs on Similar Events:
A review of previous reportable events did not identify any previous similar events.
C. Additional Information:
None.
D. Safety System Functional Failure:
This event did constitute in a safety system functional failure in accordance with 10 CFR 50.73(a)(2)(v).
E. Unplanned Scram with Complications:
This condition did not result in an unplanned scram with complications.
VIII. COMMITMENTS
None.