05000289/LER-2003-001
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| 2892003001R00 - NRC Website | |
IV. Component Failure Data:
This event was not the result of a component failure.
V. Cause of Event
The apparent cause of this event is the spiral cam-type latching mechanisms were not properly closed. The application of this design relies on friction to hold the latching mechanism in the closed position. The further the cam is rotated, the tighter the clamping force.
A review of ventilation flow trends indicated that the duct in the vicinity of the "found open" access panel experienced a negative pressure shortly before the access panel was found open. The negative pressure was due to a planned, non-routine ventilation configuration, i.e. auxiliary building supply fan out of service with two auxiliary building ventilation exhaust fans operating. As a result of this pressure change, it is postulated that the access panel door deflected inward removing some of the force on the latching mechanisms, allowing the latches to become disengaged and the access panel to open.
This event produced no adverse safety consequences, since the Control Building Ventilation system was not required to be placed in the emergency recirculation configuration during the time the access panel was open.
The access panel is located in an area that is toured shiftly by a Control Room Operator (CRO) and is readily visible. Therefore, it is reasonable to expect that this open access panel would have been identified by a CRO during the normal operator tours.
The Control Room Habitability design basis assumes that all of the filtered air supply used to pressurize the Control Building emergency envelope comes from the Air Intake Tunnel source, which is approximately 300 feet from the Reactor Building. If, during the period in which this access panel was open, an emergency required that the Control Building Ventilation System be placed in its emergency mode, the system would have been operating outside of its design basis. The open access panel would have allowed additional air flow beyond the design configuration to be removed from the 322' Control Building (within the CBE) and exhausted into the 305' elevation of the Control Building and into the Auxiliary Building (outside the CBE). Because less airflow and pressure would be provided to the rest of the CBE, the CBE ventilation would then have been unbalanced. Some areas of the CBE could not have been assured of having sufficient air pressure to maintain a positive pressure with respect to adjacent areas outside the CBE to prevent unfiltered in-leakage. In the event of a design basis accident (DBA) requiring the control tower ventilation system to be put in the emergency recirculation configuration, the condition could have resulted in increased airborne activity in the control tower ventilation system.
VIII. Previous Events of a Similar Nature:
There have been no similar events reported at TMI.
IX. Corrective Actions
Actions Taken:
The open access panel was promptly closed, and the latching mechanisms were verified to be properly dosed. The System Engineer walked down 45 accessible access panels within the control building. Two additional panels were found with each panel having one of its two spiral cam type latches loose. Each panel's remaining latch was tight and the panel doors were being held in the closed position. The loose latches were properly closed.
Surveillance and Maintenance procedures for safety related ventilation systems will be reviewed to identify any access panels in safety related ventilation systems that are periodically opened. The associated, readily accessible latching mechanisms will be inspected and verified properly closed.
This activity will be completed by 09/30/03.
Surveillance and Maintenance procedures for safety related ventilation systems that require access panels in safety related ventilation systems to be periodically opened will be revised. The revision will add steps to verify the latching mechanisms are properly closed. This action will be completed by 03/15/04.
- Energy Industry Identification System (EllS), System Identification (SI) and Component Function Identification (CFI) Codes are included in brackets, {SI/CFI] where applicable, as required by 10 CFR 50.73 (b)(2)(ii)(F).