05000263/LER-2014-008
| Monticello Nuclear Generating Plant | |
| Event date: | 05-15-2014 |
|---|---|
| Report date: | 07-14-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 2632014008R00 - NRC Website | |
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EVENT DESCRIPTION
At the time of discovery, the plant was operating in Mode 1 at approximately 88% rated thermal power.
There were no other structures, systems, or components inoperable that contributed to the condition.
On February 25, 2014, during a plant walk down with a NRC inspector during the Triennial Fire Protection Inspection, nylon cable pull ropes were found passing through a conduit. The conduit traversed between two fire zones, Division I and Division II of safe shutdown equipment in the Emergency Filtration Train (EFT) building. At the time there were no additional observed issues with the penetration.
On May 15, 2014, while performing further investigation of the nylon cable pull rope, the Fire Protection Engineer identified that there was no seal (approximately 0.5 inch gap) between the conduit and the wall.
The unsealed penetration is not easily accessible and required a camera to perform an adequate visual inspection. The fire barrier was declared non-functional and an hourly fire watch was established with verification of functional fire detectors on at least one side of the non-functional barrier.
EVENT ANALYSIS
This condition is being submitted in accordance with 10 CFR 50.73(a)(2)(ii)(B) as an "Unanalyzed Condition That Significantly Degrades Plant Safety." The conduit penetrates a wall which is required to be a two hour fire barrier to support the Fire Hazards Analysis and is also a 10 CFR 50, Appendix R fire barrier that separates two divisions of safe shutdown equipment. As a result of the non-functional fire barrier, a fire in one area could have affected both divisions of safe shutdown equipment.
SAFETY SIGNIFICANCE
Due to the opening found in the Appendix R fire barrier/boundary, both safe shutdown divisions have the potential to be challenged in the event of a fire. Fire protection features in the two fire zones consists of ionization smoke detection with alarms to the Control Room. Upon alarm receipt, the fire brigade is promptly dispatched and will address adverse conditions using manual suppression capabilities that consist of hose stations and portable extinguishers. In addition, the combustible loading is considered to be low for both of these fire zones, as the equivalent fire severity is approximately 10 minutes or less.
CAUSE
The cause of the unsealed penetration is unknown and is considered a legacy issue, as this conduit was routed prior to 1991.
The conduit penetration was not included on the drawing of EFT building fire penetrations and was not assigned a fire penetration unique identification number. Without a unique identification number, this penetration was never included in the Fire Barrier Penetration Seal Visual Inspection surveillance.
Additionally, the Fire Barrier Wall, Damper and Floor Inspection procedure did not require or suggest use of additional tools (e.g., cameras or boroscope) to perform inspections on portions of fire barriers that cannot be easily inspected.
CORRECTIVE ACTION
- The EFT building fire protection barrier will be restored to functional status.
- The penetration will be assigned a unique identification number to ensure periodic inspection.
- The Fire Barrier Wall, Damper and Floor Inspection surveillance procedure will be revised to add use of additional tools (e.g., cameras or boroscope) to perform inspections on portions of fire barriers that are not easily accessed.
PREVIOUS SIMILAR EVENTS
There were no previous similar Licensee Event Reports in the past three years.