Will the Second Cable Tray Be Ignited In a Nuclear Power Plant?

To ensure the systems related to nuclear safety maintain their functions during a fire, designers often use redundant trains of cables to support those systems and assure that a fire involving one train does not damage or ignite the other. This may be accomplished by meeting separation requirements between redundant cables or installing automatic fire suppression systems as specified by applicable codes. Some spaces, such as the cable spreading room, involve large concentrations of redundant safe shutdown cables, often making it difficult to meet the cable separation requirements. This article demonstrates the use of the Fire Dynamics Simulator (FDS) to determine the exposure conditions from a cable tray fire to a redundant cable tray. The results show that the 20 ft of separation between cable trays, as required by 10CFR50, could be reduced by a performance-based approach in some configurations.