Thermal malfunction criteria of fire safety electrical equipment in nuclear power plants

Malfunctions of nuclear power plants' (NPP) fire safety electrical equipment may be the consequence of a fire, leading to an increase of temperature and heat fluxes in a room and its adjacent ones. Electrical equipment manufacturers issue a so-called maximum temperature of normal operation' under which a continuous function is guaranteed. However, this manufacturer temperature does not correspond to the notably higher real maximum operating temperature. Exactly knowing this temperature has two impacts: adequate selection of fire safety equipment and new fire probabilistic risk assessment (PRA) damage threshold. Those levels are today very conservative for performance-based design: 40 degrees C for electronic boards and 55 degrees C for electromechanical materials. That is why Electricite de France, Research and Development Division (EDF R&D), performed several tests in the MILONGA facility to investigate the thermal malfunction levels of cabinet equipment classified as Important for Safety' by first defining what malfunction means, according to the material type and its required function; defining a relevant and reliable methodology of tests; testing a sample of electromechanical materials and electronic boards used in NPP and suggesting new temperature criteria for Fire PRA. Although the equipment behaviour may be dependent upon the materials of construction and equipment layout, the main results are the malfunction temperatures of 130 degrees C for electromechanical materials and 95 degrees C for electronic boards. Copyright (c) 2012 John Wiley & Sons, Ltd.