05000325/LER-2006-001
| Brunswick Steam Electric Plant (Bsep) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 42254 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3252006001R00 - NRC Website | |
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
INTRODUCTION
At 0400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br /> on January 12, 2006, the 2A Control Building Instrument Air [LD] Compressor was taken out of service for scheduled maintenance. On the same day, at 0920 hours0.0106 days <br />0.256 hours <br />0.00152 weeks <br />3.5006e-4 months <br />, the Control Room received annunciator, CB INSTR AIR PRESS LOW, and determined that the in-service 2B Control Building Instrument Air Compressor was not maintaining pressure. Shortly after receiving the annunciator, the Control Room Emergency Ventilation (CREV) [VI] and Control Room Air Conditioning (AC) [VI] systems shutdown due to the resulting loss of control air. The two CREV subsystems and the three Control Room AC subsystems required by Technical Specifications (TS) 3.7.3 and 3.7.4, respectively, were declared inoperable. Because Brunswick has a shared Control Room, Units 1 and 2 entered TS 3.7.3 Required Action B.1 (i.e., be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />), for two CREV subsystems inoperable, and TS 3.7.4 Required Action E.1 (i.e., enter Limiting Condition for Operation (LCO) 3.0.3 immediately), for three Control Room AC subsystems inoperable.
Operability of the three Control Room AC subsystems and one CREV subsystem was restored at 1014 hours0.0117 days <br />0.282 hours <br />0.00168 weeks <br />3.85827e-4 months <br /> when maintenance activities were completed and the 2A Control Building Instrument Air Compressor was returned to service. No power reduction took place as a result of the LCO 3.0.3 entry.
At 1607 hours0.0186 days <br />0.446 hours <br />0.00266 weeks <br />6.114635e-4 months <br />, the NRC was notified of this event (i.e., Event Number 42254) in accordance with 10 CFR 50.72(b)(3)(v)(D), as an event or condition that at the time of discovery could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
This event is being reported in accordance with 10 CFR 50.73(a)(2)(v)(D), as an event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
EVENT DESCRIPTION
Initial Conditions Prior to the event, both Units 1 and 2 were in Mode 1 operating at approximately 100 percent rated thermal power. All required safety-related systems for both units were operable, with the exception of Reactor Core Isolation Cooling (RCIC) system [BN] on Unit 2, which was out of service for maintenance.
Discussion On January 12, 2006, at 0400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br />, the 2A Control Building Instrument Air Compressor (i.e., 2A Compressor) was taken out of service for scheduled maintenance to replace a relief valve. At 0522 hours0.00604 days <br />0.145 hours <br />8.630952e-4 weeks <br />1.98621e-4 months <br />, the clearance order removing the 2A Compressor from service was completed. On the same day, at 0920 hours0.0106 days <br />0.256 hours <br />0.00152 weeks <br />3.5006e-4 months <br />, the Control Room received annunciator, CB INSTR AIR PRESS LOW, and determined that the EVENT DESCRIPTION (continued) in-service 2B Control Building Instrument Air Compressor (i.e., 2B Compressor) was not maintaining header pressure and providing adequate compressed air. Either one of the Control Building air compressors are designed to provide adequate instrument air pressure. Shortly after receiving the annunciator, the CREV and Control Room AC systems shutdown due to the resulting loss of control air. The two CREV subsystems and the three Control Room AC subsystems required by TS 3.7.3 and 3.7.4, respectively, were declared inoperable. Because Brunswick has a shared Control Room, the following action statements were entered for Units 1 and 2:
- TS 3.7.3 Required Action B.1, be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, for two CREV subsystems inoperable,
- TS 3.7.4 Required Action E.1, enter LCO 3.0.3 immediately, for three Control Room AC subsystems inoperable.
At 0955 hours0.0111 days <br />0.265 hours <br />0.00158 weeks <br />3.633775e-4 months <br />, the 2A Compressor was placed into service after the maintenance work had been completed and the clearance order was lifted. By 1007 hours0.0117 days <br />0.28 hours <br />0.00167 weeks <br />3.831635e-4 months <br />, the annunciator had cleared, and the AC units and fans that had shutdown were restarted and returned to service. At 1014 hours0.0117 days <br />0.282 hours <br />0.00168 weeks <br />3.85827e-4 months <br />, the required CREV and Control Room AC subsystems were declared operable, and the TS 3.0.3 LCO was exited. One CREV subsystem remained inoperable due to the 2B Compressor being inoperable arid out of service.
The 2B Compressor was restored to operable status on January 13, 2006, at 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br />.
EVENT CAUSE
The root cause of this event is ineffective condition monitoring of the Control Building Instrument Air Compressors. Based on trouble shooting activities associated with the 2B Compressor, it was determined that the January 12, 2006, trip of the compressor was apparently due to age related failure of the hydraulic unloader. This component prevents the compressor from loading and running without adequate oil pressure.
Neither Operations nor System Engineering have been performing routine surveillance or trending of compressor oil pressure. Had this monitoring been performed, degradation of the hydraulic unloader would have been detected prior to its failure.
SAFETY ASSESSMENT
The safety significance of this condition is considered minimal. The CREV and Control Room AC systems provide radiation, smoke, and chlorine protection for the Operators, as well as cooling for the Control Room.
The condition existed for approximately 54 minutes. The plant staff took immediate and proper actions to return the equipment to service. For the brief time that the CREV and Control Room AC systems were inoperable, performance of plant personnel and equipment in the Control Room was not adversely affected.
SAFETY ASSESSMENT (continued) The maximum temperature increase in the Control Room backpanel area during this event was determined to be no more than 4°F (i.e., from an initial temperature of approximately 69°F to a maximum of 73°F).
Additionally, the chlorine tank car had previously been moved outside the exclusion area. There was no nuclear or industrial safety consequence from this event.
CORRECTIVE ACTIONS
- Operability of the Control Room AC system and one subsystem of the CREV system was restored at 1014 hours0.0117 days <br />0.282 hours <br />0.00168 weeks <br />3.85827e-4 months <br /> on January 12, 2006, when the 2A Compressor was restored to service.
- The 2A and 2B Control Building Instrument Air Compressors have both been replaced with the new model compressors. The 2A Compressor was replaced in December 2005, and the 2B Compressor was replaced in January 2006.
- Preventive Maintenance work orders for inspection and oil change have been initiated.
- Trending parameters (i.e., oil pressure and loading cycles) have been added for the control building system monitoring plan.
Outside Auxiliary Operator Daily Check Sheets." The procedure change is scheduled to be completed by May 15, 2006.
PREVIOUS SIMILAR EVENTS
A review of LERs and corrective action program condition reports for the past three years identified the following similar events:
- LER 1-2005-004, dated July 11, 2005, documents a condition where the CREV and Control Room AC systems were declared inoperable when electrical power was lost to bus El, making the 2B Compressor inoperable. The 2A Compressor should have automatically started, but did not start due to a wire lug that had broken and interrupted the control power circuit. The corrective actions associated with LER 1-2005-004 could not have reasonably been expected to prevent the condition reported in this LER.
PREVIOUS SIMILAR EVENTS (continued)
- Condition Report 179103, initiated on December 16, 2005, documents an event that resulted in the replacement of the 2A Compressor. However, the investigation of the 2A Compressor failure had not been completed at the time of the 2B Compressor failure on January 12, 2006.
COMMITMENTS
No regulatory commitments are contained in this report.