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The United States Nuclear Regulatory Commission (NRC) has identified a potential vulnerability where existing analytical models supporting plant specific safety analyses may be non-conservative. This vulnerability exists for electrical equipment that includes components made of aluminum when subjected to high energy arc fault (HEAF) conditions.
Recent testing conducted at the KEMA Laboratories Chalfont facility indicates that the area damaged around the equipment or the “zone of influence” (ZOI) may be larger than postulated in the current methodology for HEAF analysis, NUREG/CR – 6850 EPRI 1011989 “EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities, Volume 2: Detailed Methodology”.
High Energy Arc Faults (HEAF) events are defined as energetic or explosive electrical equipment faults characterized by a rapid release of energy in the form of heat, light, vaporized metal and pressure increase due to high current arcs between energized electrical conductors or between energized electrical components and neutral or ground.
Recent international HEAF testing was performed at KEMA Laboratories Chalfont by the NRC Office of Nuclear Regulatory Research (RES) in collaboration with 7 other member countries including; Canada, France, Finland, Germany, Korea, Japan and Spain. The project was initiated after investigating international operating events which indicated HEAF events were a worldwide fire risk driver constituting roughly 10% of the international database.
The tests suggest that HEAF scenarios involving aluminum components may have a zone of influence that is not bounded by the current guidance, thereby underestimating the risk from HEAF events. Any non-conservatisms discovered as a result of this HEAF issue would mean that the current baseline risk model at plants that have aluminum components would underestimate the risk.
The results described above demonstrate the practical value of independent physical testing vs. “paper testing” or in this case, sophisticated modelling techniques, to provide engineers and decision makers critical information to safeguard, life, property and the environment. The KEMA Laboratories were selected by the US NRC because of the unique capabilities of our people and our facilities with the added benefit of being completely independent and impartial.