05000315/LER-2008-002
| Donald C. Cook Nuclear Plant | |
| Event date: | 02-06-2008 |
|---|---|
| Report date: | 04-01-2008 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3152008002R00 - NRC Website | |
Conditions Prior to Event Both Unit 1 and Unit 2 were at 100% power.
Description of Event
On February 6, 2008, during verification performed as part of'preparation for fire protection analysis compliance transition to NFPA 805, Donald C. Cook Nuclear Plant (CNP) personnel identified an error in the original, and subsequent, Appendix R analyses for the Train B 4 kV switchgear room fire analysis area in both units.
The error involved a failure to identify a short section of Train A 250 VDC conduit enclosed cable passing through the Train B 4kV switchgear room. This cable run connects the Train A battery charger transfer switch cabinet to the shunt cabinet.
The routing of this unprotected Train A 250 VDC cabling in the Train B 4 kV switchgear room presented the possibility of a fire in the Train B 4kV switchgear room disabling the Train B switchgear as well as remote control to the Train A 4 kV switchgear. The loss of remote control could occur from disabling Train A 250 VDC [EJ] as a result of fire damage to the conduit enclosed cable.
Inspection of the associated conduit on both units identified no supplementary fire barrier, such as fire retardant wrapping, on the affected conduit. The Train B 4 kV switchgear area contains fire detection and CO2 fire suppression capability.
As an interim corrective action, the conduit and associated Train B 4 kV rooms were monitored by compensatory fire watch tours until permanent corrective action was completed. Fire detection and CO2 fire suppression capability remained available.
This event was reported in accordance with 10 CFR 50.72(b)(3)(ii)(B) as an unanalyzed condition. Further, this condition has been determined to be reportable in accordance with 10 CFR 50.73(a)(2)(ii)(B) as an unanalyzed condition that had the potential to significantly degrade plant safety.
Cause of Event
The cause of.CNP's failure to identify and correct the error has been determined to be human error. Specifically, the errors were not identified in 1994 during CNP's Appendix R revalidation project or in 2003 during CNP's Appendix R optimization project. The exact nature of the human performance error could not be determined because the personnel involved in these projects are no longer employed at CNP.
Analysis of Event
In the unlikely event of a postulated fire in the Train B 4 kV switchgear room, this condition could have resulted in the loss of the Train B 4 kV switchgear, with the added complexity of the loss of control power to the Train A 4 kV switchgear.
The existing Appendix R and normal operating procedures provide capability for restoration and operation of important plant equipment. Additionally, a number of the safety systems for both units have been designed with cross-unit cross-ties.
Therefore, an impacted unit could respond to and mitigate an event such as this and prevent core damage and an off-site release. CNP has determined that system and equipment coping capability existed to mitigate the consequence of such a postulated event.
Corrective Actions
CNP has completed an extent of condition evaluation and no additional non-compliances were identified.
Compensatory fire watch tours of the affected fire zones were established until permanent corrective action was implemented.
The affected conduits have been wrapped with a fire retardant material, And the CO2 Suppression System has been converted from manual to automatic, in accordance with the requirements of Appendix R III.G.2(c), thus, restoring conformance with original design and Appendix R program assumptions.
The applicable design documents have been updated to reflect the added fire protective material, and the Appendix R analysis has been updated to reflect the omitted cable routing and the changed compliance strategy.
Since the time of the events, CNP has made significant improvements'in its human performance, design, and configuration control processes. These improvements address the underlying causes of this event.
Previous Similar Events
None.