05000416/LER-2005-003
| Grand Gulf Nuclear Station | |
| Event date: | 10-7-2005 |
|---|---|
| Report date: | 12-19-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4162005003R00 - NRC Website | |
Engineered Safety Features (ESF) Degraded Voltage set points were found to be higher than the Technical Specification Allowable Values. This condition was immediately corrected; however, since the cause of the setpoints being outside the allowed values occurred during the power supply replacement on October 7, the setpoints had been out of the allowable values from October 7 until October 25. Technical Specifications require that the setpoints be brought to within allowable values within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or declare the associated emergency diesel generator (EDG) [DG] inoperable (which prohibits changing plant operational modes). Since the impact of the power supply replacement on the Bus Under Voltage (BUV) bistable setpoints was not recognized and the appropriate Technical Specification action statement was not entered, the station violated Technical Specifications 3.0.4 when the plant was brought into Mode 2 on October 16 and again on October 18 when the plant was brought into Mode 1.
This condition was determined to be reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) since the plant was in an Operation or Condition prohibited by Technical Specification Limiting Condition for Operation (LCO) 3.0.4. There was no loss of safety function since it was limited to a single division and was a deviation in a setpoint. The system would have actuated somewhat earlier on a low voltage transient but would have functioned properly otherwise.
B. INITIAL CONDITIONS
At the time of the event, the reactor was in OPERATIONAL MODE 2 (STARTUP), at zero percent power.
C. DESCRIPTION OF OCCURRENCE
The Division I Load Shed and Sequencer power supply was replaced on October 7, 2005 as part of routine preventative maintenance in a Refueling Outage. This power supply provides the reference voltage for the Division 1 ESF Degraded Voltage bistable setpoints. A functional test of the power supply output was performed per the retest matrix contained in Administrative Procedure, 01-S-07-2 (Test Control), Revision 104.
During a Technical Specification Surveillance performed on October 25, the as found voltages for the Division I ESF Degraded Voltage set points were found to be higher than the Technical Specification Allowable Values. (The Load Shed and Sequencer uses a series of BUV bistables with a setpoint of 90 percent BUV and a series of BUV bistables with a setpoint of 70 percent BUV.
Attachment I Only the 90 percent bistables were found out of Technical Specification Allowable Values. The 70 percent bistables were within Technical Specification Allowable.) This condition was immediately corrected; however, since the cause of the setpoints being outside the allowed values occurred during the power supply replacement on October 7, the setpoints had been out of the allowable values from October 7 until October 25.
Technical Specifications require that the setpoints be brought to within allowable values within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> or declare the associated EDG inoperable (which prohibits changing plant operational modes). Since the impact of the power supply replacement on the BUV bistable setpoints was not recognized and the appropriate Technical Specification action statement was not entered, the station violated Technical Specification LCO 3.0.4 when the plant was brought into Mode 2 on October 16 and again on October 18 when the plant was brought into Mode 1.
D. APPARENT CAUSE
The cause has been determined to be a failure to recognize that a BUV bistable setpoint check was needed following the replacement of the power supplies within the LSS panel. Although the power supplies were within the manufacturer's specified voltage range, a difference in output voltage from the previously installed power supply altered the reference voltage utilized by the LSS logic, thus altering the setpoints to some degree.
E. CORRECTIVE ACTIONS
Immediate Corrective Actions:
- Bistable setpoints were adjusted within Technical Specification limits per Surveillance Work Order.
Long Term Corrective Actions:
- Condition Report (CR)-GGN-2005-04665 was initiated.
F. SAFETY ASSESSMENT
There was no loss of safety function since it was limited to a single division and was only a deviation in a setpoint. The system would have actuated somewhat earlier on a low voltage transient but would have functioned properly otherwise.
Therefore, there were no adverse safety consequences or implications as a result of the condition and the condition did not adversely affect the safe operation of the plant or health and safety of the public.
Attachment 1 The condition would not have prevented the fulfillment of the safety function and did not result in a safety system functional failure as defined by 10 CFR 50.73(a)(2)(v).
G. ADDITIONAL INFORMATION
There have been no LERs written on a similar GGNS event in the past two years. Additionally reviewed CR's in the past 2 years and found no similar setpoint issues.
Attachment 1