Section F of Clinton Power Stations operating license
NPF-62, states that the licensee shall implement and maintain in effect all provisions of the approved
fire protection program as described in the
USAR. The
USAR required that the
fire protection program follow the requirements of Branch Technical Position APCSB 9.5-1, Appendix A, Plants Under Construction and Operating Plants. Branch Technical Position APCSB 9.5-1, Appendix A, requires that floors, walls and ceilings enclosing separate fire areas be sealed or closed to provide a fire resistance rating at least equal to the
fire barrier itself. On November 2, 2006, the licensee identified two open, unsealed, 12\" x 12\" penetrations in the floor of the Division 3 switchgear room. The penetrations were under the main feed and reserve feed breakers to the
4kV switchgear for Division 3 . The inspectors determined that the failure to seal two penetrations between separate fire zones was a performance deficiency warranting a significance determination. The inspectors performed a Phase 2 evaluation using
IMC 0609, Appendix F, Fire Protection
Significance Determination Process. The inspectors determined that a credible fire scenario existed in that an energetic fault in the
4 kV Division 3 switchgear located directly above the open penetrations could ignite a non-safety related cable tray located directly below the open penetrations. A fire could then propagate horizontally along the non-safety related cable tray and then involve a Division 1 cable tray. The inspectors conservatively assumed that only Division 2 equipment would be available in such a scenario. Based on four vertical cabinet sections as being potential ignition sources, a 30 minute fire propagation time to reach the Division 1 cable tray, and remaining mitigating Division 2 equipment available, the inspectors determined that the issue was of very low safety significance.
