05000324/LER-2009-001
| Brunswick Steam Electric Plant (Bsep), Unit 2 | |
| Event date: | 01-27-2009 |
|---|---|
| Report date: | 03-29-2009 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 44810 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 3242009001R00 - NRC Website | |
Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
Introduction Initial Conditions At the time of the event, Unit 2 was in Mode 1, operating at approximately 100 percent of Rated Thermal Power (RTP). The Reactor Core Isolation Cooling (RCIC) system [BN], the Automatic Depressurization system (ADS), the Core Spray (CS) system [BM] and the Low Pressure Coolant Injection (LPCI) system [BO] were all operable.
Reportability Criteria On January 27, 2009, at 2007 hours0.0232 days <br />0.558 hours <br />0.00332 weeks <br />7.636635e-4 months <br /> Eastern Standard Time (EST), the Unit 2 High Pressure Coolant Injection (HPCI) system [BJ] was declared inoperable due to a sustained high water level in the HPCI exhaust line drain pot. 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. :The NRC was initially notified of this event on January 27, 2009 (i.e., Event Number 44810).
Event Description
The HPCI Turbine Gland Exhauster system provides a means of minimizing steam leakage to the HPCI room atmosphere. The system consists of a barometric condenser, vacuum tank, condensate pump, and vacuum pump. The steam, condensate, and noncondensable gases from the HPCI turbine seals, and the governor and stop valve stem leakoff, plus drainage from the turbine exhaust line drain pot, are routed to the barometric condenser. The barometric condenser condensate pump automatically starts on a high level in the vacuum tank, and discharges the condensate to the suction of the HPCI booster pump when HPCI is operating or to the Reactor Building equipment drain tank when HPCI is in standby. Additionally, high level in the HPCI exhaust line drain pot will cause the exhaust drain pot drain bypass valve (i.e., 1(2)-E41-F053) to automatically open. This drains condensate to the barometric condenser. Once operating, a failure of either the condensate or vacuum pump will not prevent the HPCI system from performing its design function. However, if HPCI is shutdown, a failure of the condensate pump could lead to water backing up into the exhaust line drain pot, and eventually enter the turbine casing and exhaust line.
If HPCI is started with water in the casing, water hammer damage could result.
On January 27, 2009, HPCI Turbine Exhaust Line Drain Pot Level High alarms were being experienced and, per design, the exhaust drain pot was automatically draining the condensate to the HPCI barometric condenser. At 1745 hours0.0202 days <br />0.485 hours <br />0.00289 weeks <br />6.639725e-4 months <br /> EST and again at 1839 hours0.0213 days <br />0.511 hours <br />0.00304 weeks <br />6.997395e-4 months <br />, the HPCI Vacuum Tank Level High alarm was received. After the alarm at 1839 hours0.0213 days <br />0.511 hours <br />0.00304 weeks <br />6.997395e-4 months <br />, an auxiliary operator (AO) was sent to investigate the condensate pump because its operation time had exceeded the expected one to two minutes. The AO reported that the condensate pump was not running, contrary to the control room indication. Upon recognition that the Event Description (continued) condensate pump had failed, Operations personnel pursued establishment of the preferred alternate drain path from the barometric condenser (i.e., via a test connection downstream of the condensate pump) in accordance with section 5-3, "HPCI Vacuum Lvl Hi," of procedure 2APP-A-01, "Annunciator Procedure for Panel A-01." This alternate path was established at 1901 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.233305e-4 months <br />; however, the HPCI Vacuum Tank Level Hi alarm did not clear. At 2007 hours0.0232 days <br />0.558 hours <br />0.00332 weeks <br />7.636635e-4 months <br />, the HPCI Turbine Exhaust Line Drain Pot Level High alarm returned. At this point, the HPCI system was declared inoperable due to the high exhaust line drain pot level and the threat of system damage due to a potential turbine start with water inside the turbine casing.
The high drain pot level alarm cleared within one to two minutes, but returned at 2018 hours0.0234 days <br />0.561 hours <br />0.00334 weeks <br />7.67849e-4 months <br /> and would not clear.
Subsequently, at approximately 2140 hours0.0248 days <br />0.594 hours <br />0.00354 weeks <br />8.1427e-4 months <br />, a second alternate drain path from the barometric condenser vacuum tank was established through the barometric condenser drain collecting valve (i.e., 2-E41-V5003).
This path was successful in reducing condenser level and, at 2204 hours0.0255 days <br />0.612 hours <br />0.00364 weeks <br />8.38622e-4 months <br />, the HPCI Turbine Exhaust Line Drain Pot Level High annunciator cleared.
Troubleshooting activities determined that the failure of the HPCI barometric condenser condensate pump was due to worn motor brushes. The brushes were replaced and, following post-maintenance testing, the HPCI system was returned to service at 2050 hours0.0237 days <br />0.569 hours <br />0.00339 weeks <br />7.80025e-4 months <br /> on January 28, 2009.
Event Cause There are two root causes associated with this event. The HPCI barometric condenser condensate pump failed because no Preventive Maintenance (PM) activities had been established for the pump and motor.
The difficulties in establishing an alternate drain path from the barometric condenser were a result of an incorrect annunciator response procedure.
The HPCI system was declared inoperable when the ability to control water level at or below the exhaust line drain pot level alarm was lost. Level control was originally challenged due to failure of the HPCI barometric condenser condensate pump, which resulted in the condenser and the vacuum tank filling with water. The pump failure was caused by wear of the motor brushes, which resulted in a loss of contact between the brushes and the collector ring. There were no PM activities to inspect or refurbish the condensate pump and motor.
Initial attempts to establish the primary alternate drain path from the barometric condenser were unsuccessful because procedure 2APP-A-01 was technically incorrect. The primary alternate drain path was through a test connection downstream of the HPCI barometric condenser condensate pump. The test connection consists of two globe-type isolation valves in series (i.e., 2-E41-V13 and 2-E41-V14).
However, between the condensate pump and the test connection is valve 2-E41-F058, which is a stop check valve with a spring-loaded disc requiring a differential pressure of approximately 5 psig to lift. System pressure was inadequate to actuate the disc in the spring-loaded stop check valve.
Safety Assessment The safety significance of this event is considered minimal The RCIC system, the ADS, the CS system, and the LPCI system were all operable during the time that HPCI was inoperable. Adequate core cooling was ensured by the operability of the redundant and diverse low pressure injection systems in conjunction with ADS. Additionally, the RCIC system would have automatically provided makeup at high reactor operating pressures.
Corrective Actions
The following corrective actions to prevent recurrence have been identified.
- PM activities will be established for the Unit 1 and 2 HPCI system barometric condenser condensate pumps and motors and the Unit 1 and 2 RCIC system barometric condenser condensate pumps and motors. These PMs are currently scheduled to be established by May 15, 2009.
- Procedures 1(2)APP-A-01 were revised to ensure proper alternate drain paths can be established in the event of failure of the HPCI system barometric condenser condensate pumps. These procedure revisions were completed on February 2, 2009.
- Procedures 1(2)APP-A-01 were revised to minimize sources of condensate to the HPCI system barometric condenser when the HPCI system is not running and a HPCI vacuum tank high level condition exists. These procedure revisions were completed on March 9, 2009, for Unit 1 and March 12, 2009, for Unit 2.
Additional corrective actions include the following.
- The HPCI system was declared operable, following repair of the HPCI barometric condenser condensate pump, on January 28, 2009, at 2050 hours0.0237 days <br />0.569 hours <br />0.00339 weeks <br />7.80025e-4 months <br /> EST.
- The Unit 1 HPCI system barometric condenser condensate pump motor brushes will be inspected and any necessary repairs completed. This action is currently scheduled to be completed by June 30, 2009.
- The Unit 1 and Unit 2 RCIC system barometric condenser condensate pump motor brushes will be inspected and any necessary repairs completed. This action is currently scheduled to be completed by July 30, 2009.
- The PM requirements for other components needed to ensure HPCI condensate removal will be reviewed and any necessary changes implemented. This action is currently scheduled to be completed by June 15, 2009.
Previous Similar Events
A review of LERs and corrective action program condition reports for the past three years identified the following similar event.
- Nuclear Condition Report (NCR) 223820, "HPCI Overspeed Test Halted Due to Unexpected Annunciation," generated on February 27, 2007, documented a high vacuum tank alarm that occurred while performing procedure OPT-09.8, "HPCI System Coupled Overspeed Trip Test," on Unit 2. One of the apparent causes of this event was identified as minor degradation of the HPCI system barometric condenser condensate pump. The pump had been in service for many years and the potential for age-related degradation was identified. However, a subsequent review found that performance of the pump had been acceptable. As such, the PM activities for the pump were not questioned.
Additionally, during investigation of this event, it was discovered that valve 2-E41-F058 was a stop check valve versus a globe valve as shown on the Piping and Instrument Drawing and described in the Equipment Database. Activities to correct the condition were informal and failed to evaluate how the finding could impact operability of the system or to update applicable plant drawings.
These errors were individual human performance errors.
Based on the factors discussed above, the actions taken in response to NCR 223820 did not prevent the HPCI system inoperability discussed in LER 2-2009-001.
Commitments No regulatory commitments are contained in this report.