4 juin 2015
Des analyses ont montré que suite à un incendie qui surviendrait dans 4 zones du bâtiment des deux réacteurs, les conditions de mise à l’arrêt sûr ne seraient pas assurées. Cela conduirait à la déficience de l’une des barrières de sûreté. Pour un incendie dans une zone précise (1203), ce serait l’injection d’eau de refroidissement haute pression qui serait menacée. Dans deux autres zones (1205, 2205), ce sont deux alimentations électriques d’urgence qui seraient menacées. Même si un seul indicateur de température permettrait de réussir à protéger les réacteurs, ce seraient les trois indicateurs de température différents qui seraient affectés par un incendie en zone 1205. Des solutions transitoires ont été mises en place pour parer au problème en attendant une réparation pérenne. La découverte du problème survient après... 78 ans de fonctionnement cumulés des deux réacteurs !
Type : Fukushima I (BWR Mark1) - Puissance : 2 804 MWth - Première divergence : n° 1 : 09/1974 ; n° 2 : 07/1978
Available in english only.
Event Number : 51120
Facility : HATCH - State : GA - Unit : [1] [2] - RX Type : [1] GE-4,[2] GE-4
Event Date : 06/04/2015 - Event Time : 10:03
Emergency Class : NON EMERGENCY 10 CFR Section : 50.72(b)(3)(ii)(B) - UNANALYZED CONDITION
Initial PWR : 100 % Current PWR : 100 %
Event Text
UNANALYZED CONDITION FOR A POSTULATED FIRE
"In preparation for transitioning the Plant Hatch Fire Protection Licensing Basis from 10 CFR 50.48(b) (Appendix R) to 10CFR50.48(c) (NFPA 805), an update to the Plant Hatch Appendix R Safe Shutdown Analysis has been performed for the Unit 1 and Unit 2 Reactor Buildings. This updated analysis has identified circuit configurations in four Fire Areas where an Appendix R postulated fire could impact the ability to achieve safe shutdown conditions. These are Category 1 barrier impairments.
"In the Unit 1 Safe Shutdown Analysis, RCIC (1E51C001) (Path 1) components are impacted by a fire in Fire Area 1203. The postulated failure described above impacts HPCI (1E41C001) (Path 2) operation. Therefore, in the updated analysis there is no safe shutdown method for high pressure injection that remains free of fire damage for an Appendix R postulated fire in Fire Area 1203. While this represents an unanalyzed condition for Appendix R, the described scenario is only possible given a fire has occurred in Fire Area 1203.
"In the Unit 1 Safe Shutdown Analysis, Path 2 components are impacted by a fire in Fire Area 1205. The postulated failure described above impacts the 1E 4160 Kv (1R22S005) emergency bus power to Path 1 components. Therefore, in the updated analysis there is no safe shutdown method that remains available for an Appendix R postulated fire in Fire Area 1205. While this represents an unanalyzed condition for Appendix R, the described scenario is only possible given a fire has occurred in Fire Area 1205.
"In the Unit 2 Safe Shutdown Analysis, Path 2 components are impacted by a fire in Fire Area 2205. The postulated failure described above impacts the 2E 4160 Kv (2R22S005) emergency bus power to Path 1 components. Therefore, in the updated analysis there is no safe shutdown method that remains available for an Appendix R postulated fire in Fire Area 2205. While this represents an unanalyzed condition for Appendix R, the described scenario is only possible given a fire has occurred in Fire Area 2205.
"In the updated post-fire safe shutdown model, both safe shutdown paths include the same three options for Torus Water Temperature indication (1T48R072, 1T47R611 or 1T47R612). Only one of these three components is required to succeed, however, all are impacted by the postulated fire. Thus, there is no Unit 1 Torus Water Temperature Indication available for a fire in Fire Area 1205. While this represents an unanalyzed condition for Appendix R, the described scenario is only possible given a fire has occurred in Fire Area 1205.
"Based on the updated Plant Hatch Appendix R Safe Shutdown analysis recommendations and the plant’s Fire Hazard Analysis (FHA), compensatory measures have been taken and will remain in place until the conditions are resolved.
"The presence of the compensatory measures, in addition to portable fire protection equipment and installed fire protection and detection equipment, ensures the safe shutdown paths are preserved until the conditions are resolved. CR 10079009, 10079019, 10079022, 10079025"
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/2015/20150605en.html#en51120
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