05000219/LER-2002-003
| Oyster Creek | |
| Event date: | 10-10-2002 |
|---|---|
| Report date: | 04-02-2004 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii) |
| 2192002003R02 - NRC Website | |
DATE OF DISCOVERY
This event was discovered on October 10, 2002, at 5:59 PM.
IDENTIFICATION OF OCCURRENCE
While performing a cable pulling evolution, it was noticed that a void existed beneath a portion of the two 480 VAC switchgear rooms. This void created an open area between two 4160 VAC feeder conduits to Unit Sub Stations (USS) 1A2 and 182. This discovery was considered reportable under 10 CFR 50.73(a)(2)(ii).
CONDITIONS PRIOR TO DISCOVERY
At the time of discovery, the plant was in cold shutdown for refueling. However, it is not known when the void formed and it has been concluded that it existed during all modes of plant operation.
DESCRIPTION OF OCCURRENCE
During replacement of the 4160 VAC feeder cable to transformers in the 480 VAC A switchgear room, it was discovered that an opening existed around the conduit that penetrated the floor. This opening had previously been sealed with M-board and Kaowool and had been broken during the cable replacement project. Upon examination to determine a repair for the floor seal, an open underground void was discovered (approximately four feet deep, three feet wide, and 50 feet long) in the area between the Reactor and Turbine Building walls. This void affected the Appendix R fire separation of the 4160 VAC feeder cables. With this area open, the 4160 VAC feeder cables to USS 1A2 and 1B2 were not sufficiently separated from each other under the floor area. These cables were routed in separate conduits. And the conduits were separated horizontally by approximately ten feet.
Without the sand in place, the separation of these redundant cables failed to meet Appendix R Section III.G.2 requirements (provide a three hour fire barrier; or provide a one hour barrier with automatic suppression and detection; or provide 20 ft separation with no intervening combustibles with automatic suppression and detection).
As the cables are both enclosed in rigid steel conduit, they do meet class 1 E electrical separation criteria as required by Installation Specification SP-9000-41-005.
APPARENT CAUSE
The apparent cause of this discovery is that sand may not have completely filled the area and/or had settled over time, thus opening this void beneath the A and B 480 VAC switchgear room floors.
ANALYSIS OF OCCURRENCE AND SAFETY ASSESSMENT
This discovery has minimal safety significance for Appendix R scenarios. The only combustible material within the void is in the cables in the conduits. A fire in either conduit would not propagate to the other conduit. Additionally, the rooms where the conduits terminate have detection systems, which would alert operators to any fire. The most likely source of fire exposure to these cables is from the 480 v room(s) directly above the void. These rooms are provided with automatic fire suppression and detection, making it unlikely that a fire of sufficient magnitude would develop capable of affecting the cables. Any combustible attempting to enter the void would have to originate from an area, which also has detection capability, again alerting operators to the fire.
This discovery has no impact on the safety significance for non-Appendix R scenarios. This discovery does not affect the Class 1 E operability of the 4160 VAC feeder cables to USS 1A2 & 1B2 as the Class 1 E separation criteria is maintained and would be fully operable during a non-Appendix R scenario.
CORRECTIVE ACTIONS
Immediate Corrective Actions
1. A continuous fire watch was stationed.
2. A rated fire seat was installed at the floor penetration of both A and B transformers where feeder cables enter, to prevent a fire in either 480 VAC room from propagating into the void area.
3. Holes were drilled in hallway floor plate above the void to allow any potential smoke to communicate with hallway area smoke detectors and the fire watch was changed to hourly.
4. Potential seismic issues were reviewed and found not to be an issue.
5. Extent review was performed for possible other cases where below grade conduits are required to be covered for Appendix R separation criteria, no other concerns were discovered.
Short term corrective actions 1. A supporting Operability Documentation review was completed prior to plant start-up from the 1R19 refueling outage.
2. The Fire Brigade received additional instructions on this discovery. The Fire Brigade Pre-Fire Information Plan was updated for a fire in this area.
3. Tools, additional fire extinguishers, and a cellar nozzle were stationed for use in the unlikely event of a fire in the void area.
Long term corrective actions Adequate separation will be provided by re-filling the void between the two 4160 VAC feeder conduits to USS 1A2 and 1B2 to meet Appendix R, Section III.G.2 requirements. This installation is expected to be completed by April 30, 2004. The void area will be periodically monitored as necessary to ensure the sand fill maintains adequate cable separation. When adequate separation is restored, the immediate and short term corrective actions listed above will be discontinued.
SIMILAR EVENTS
None.