05000272/LER-2003-005
| Docket Number | |
| Event date: | 12-21-2003 |
|---|---|
| Report date: | 03-24-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| Initial Reporting | |
| ENS 40480 | 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2722003005R01 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse — Pressurized Water Reactor (PWR/4) Auxiliary Building Ventilation System {VF/DMP} (ABV)* * Energy Industry Identification System {EDS} codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF OCCURRENCE
Event Date: December 21, 2003 Discovery Date: January 25, 2004
CONDITIONS PRIOR TO OCCURRENCE
The plant was in Mode 1 (POWER OPERATION) at the time of the event.
DESCRIPTION OF OCCURRENCE
On December 21, 2003 a notification was created to address a high differential pressure (DP) across the doors within the Auxiliary Building. An engineering evaluation identified that this excessively high DP was the result of the Auxiliary Building Ventilation (ABV) system running in an abnormal mode with only one exhaust fan in service. After the system was returned to normal mode, the building DP was still abnormally high. On January 23, 2004 engineering performed a walk down of the Salem 1 Auxiliary Building Ventilation (ABV) system to troubleshoot the cause of the high differential pressure. No airflow was noted inside the Emergency Core Cooling System (ECCS) exhaust ductwork or on the 100' elevation. Engineering suspected several different fire dampers as the possible cause and notified the Unit 1 Control Room Supervisor (CRS) of their findings.
On January 25, 2004 Fire Protection personnel inspected several fire dampers suspected to be the problem. At approximately 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> information was provided to the control room from Fire Protection that the 1ABF13 {VF/DMP} damper was found closed. This damper renders the ventilation from the Residual Heat Removal (RHR) rooms as well as other areas inoperable (no flowpath to the Charcoal filters); as such Technical Specification (TS) 3.7.7.1 should have been entered at this time (1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> on January 25, 2004).
The deficient condition (1ABF13 impaired) was corrected within 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> of discovery (1950 on January 25, 2004). A late entry was made in the Control Room Narrative documenting the late Tech Spec entry and exit, which were made within the LCO time limits of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. An 8-hour report was made as an "after-the-fact" report at approximately 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br /> on January 26, 2004. (Event Number 40480) Fire Protection personnel also found fire damper 1ABF15 and High Energy Break Analysis (HEBA) excess flow damper 1ABS8 closed. NOTE: The fire damper's manual hand quadrant was found in the open position for both 1ABF13 and 1ABF15 while the dampers were closed. The dampers were subsequently reopened and the airflows were returned to normal in the Auxiliary Building.
CAUSE OF OCCURRENCE
The cause of fire dampers 1ABF13 and 1ABF15 going closed is believed to be the bi-metallic link that holds the dampers in the open position not seating properly and inadvertently actuating. The fire dampers are required to be open under normal operating conditions and should not close under these conditions. If the damper is actuated, it is required to close. The fire dampers at Salem use a link to perform its fire protection function. This link connects to the shaft and the spring-loaded louver assembly using a pin attached to a bi-metallic strip. When heated, the bimetallic pin will expand causing it to release the spring-loaded louver assembly. Upon going closed the damper makes-up to a micro switch causing an alarm in the Unit 1 control room area. The micro switch is designed to annunciate upon the damper being fully closed. The micro switch did not annunciate the positions of 1ABF13 and 1ABF15.
The dampers were found closed; yet the fire damper's manual hand quadrant indicated the damper was open.
Typically, in order for this to occur the damper bi-metallic link would have to actuate. No heat sources (e.g., fires) sufficient to activate fire dampers 1ABF13 and 1ABF15 were identified.
The closure of the 1ABS8 excess flow damper is attributed to the closure of dampers lABF13 and 1ABF15, which caused the flow set point of the 1ABS8 damper to be exceeded, thereby closing the damper as designed.
A contributing factor in this event is the lack of guidance on resetting of dampers to assure the link pin engagement has been achieved, as well as the physical damper position that impacts damper reset and verification.
PREVIOUS OCCURRENCES
A review of LERs at Salem and Hope Creek Generating Stations dating back to 2001 identified a similar event reported in January 2001. LER's 272/01-001 and 272/01-002 described a similar event where a failed fire damper (damper found closed) limited the ability of the auxiliary building ventilation system to perform its safety function.
The cause of the failure was attributed to the locking wing nut on the damper operator being loose due to the improper restoration of the damper after functional testing. The corrective actions associated with this event would not have prevented the current event as the wing nut was found secured.
SAFETY CONSEQUENCES AND IMPLICATIONS
The Salem ABV system is a once through ventilation and exhaust filtration system that maintains a slight negative pressure within the building, delivering outside air in sufficient volume to maintain auxiliary building temperatures within design limits. The supply system consists of two fans, each of 100% capacity, powered from vital buses that deliver outside air via ductwork distribution throughout the building.
The exhaust system consists of three fans, each of 50% capacity, taking exhaust from a common plenum, three High Efficiency Particulate Air (HEPA) filters, and one High Efficiency Carbon Adsorber. The HEPA filters receive air from the exhaust system ductwork, and discharge it to a common plenum. The carbon adsorber can be aligned interchangeably between either of two of the three HEPA filters and the common plenum.
SAFETY CONSEQUENCES AND IMPLICATIONS (contd.) The carbon adsorber is placed in the exhaust stream only during post OCA conditions to remove radioactive iodine, which may be introduced to the auxiliary building through ECC equipment leakage. The exhaust fans are powered from vital buses and are designed for continuous operation. uring normal conditions the charcoal adsorber is not in service and filtration of the effluent is provided by the HEPA filter. Monitoring of the effluent is done by the installed radiation instrumentation in the plant vent.
The following areas were affected by the closure of the Excess Flow HEIBA Damper 1ABS8, fire damper 1ABF13, and fire damper 1ABF15: Salem Unit 1 piping penetration area, pipe chase area, RHR Heat exchanger area, and the RHR and Safety Injection pump area's. With Excess Flow HEBA Ddmper 1ABS8 fully closed, and fire dampers 1ABF13 and 1ABF15 closed, the negative pressure of the Auxiliary Buil ing to outside atmosphere was always maintained. Any potential release would have been through the plant ve t, and radiation detectors would have monitored the release.
The RHR and Safety Injection pump room coolers were unaffected by this event. If an accident condition had occurred during the time the dampers were failed (December 21, 2003 through January 25, 2004), the area room coolers, along with low outside ambient temperatures would have contribuited cooling of the ECCS equipment environment to limit the area temperatures to below their maximum limits.
A review of this condition determined that a Safety System Functional Failure (SSFF) had occurred as defined in Nuclear Energy Institute (NEI) 99-02, Regulatory Assessment Performance Indicator Guideline. Closure of the dampers could have resulted in flows from the ECCS areas being below the minimum required by Technical Specifications and prevented the ability to mitigate the consequences of accident. The shortfall in filtered flowrate did not present a risk to the health and safety of the public or plant personnel. There were no actual safety consequences associated with this event.
CORRECTIVE ACTIONS:
1. Immediate corrective action was to open and reset fire dampers (1ABS8, 1ABF13 and 1ABF15). Flow through the HEPA Charcoal train was verified to meet Technical Specification acceptance criteria.
2. Fire Protection personnel performed a field validation of fire damper positions on both Salem Unit 1 and Unit 2.
This will continue, on a monthly basis, until evaluation and appropriate corrective actions are complete.
3. An evaluation (e.g., internal inspection of bi-metallic link assembly, micro switch and dampers) to determine the cause of the dampers failing and lack of annunciation, and the corrective actions to prevent recurrence is not yet complete. If new information is identified that changes the understanding of the event, this LER will be supplemented.
COMMITMENTS
The corrective actions cited in this LER are voluntary enhancements and do not constitute commitments.