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High Energy Arc Fault Testing for International Nuclear Power Plant Safety at KEMA Labs Chalfont

High Energy Arc Fault Testing for International Nuclear Power Plant Safety at KEMA Labs Chalfont
01 . Dec . 2021

The United States Nuclear Regulatory Commission (NRC) has been conducting High Energy Arc Fault (HEAF) testing at the KEMA Labs Chalfont facility since 2015. 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. HEAF events may also result in hot projectiles being ejected from the electrical component or cabinet of origin and result in fire. The energetic fault scenario consists of two distinct phases.

First phase: short, rapid release of electrical energy which may result in projectiles (from damaged electrical components or housing) and/or fire(s) involving the electrical device itself, as well as any external exposed combustibles, such as overhead exposed cable trays or nearby panels, that may be ignited during the energetic phase. Second phase (the ensuing fire(s)): is treated similarly to other postulated fires as specified in Appendix M of Volume 2 NUREG/CR-6850, EPRI 1011989.

International HEAF testing was performed at KEMA Labs 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. The first series of tests can be found in the oecd/nea report found inreport on the "Testing Phase(2014-2016) of the High Energy Arcing Fault Events (HEAF) Project: Experimental Results from the International Energy Arcing Fault Research Programme."

During the Great 2011 Earthquake and Tsunami, Japan experienced a significant HEAF at one of their nuclear power plants (NPPs) and has an active HEAF research project Working with the NRC the results are published  as an International Agreement Report, NUREG/IA-0470 Volume 2 “Nuclear Regulatory Authority Experimental Program to Characterize and Understand High Energy Arcing Fault (HEAF) Phenomena”,  can be found here.

The recent international tests suggest that HEAF scenarios involving certain components may have a zone of influence (ZOI) that is not bounded by the current regulatory guidance thereby underestimating the risk from HEAF events. Additionally, mitigation techniques have been used as part of the transition to NFPA 805 including “HEAF shields” which theoretically enable an NPP to mitigate damage conditions and reduce the risk of a particular scenario. “HEAF shields” currently in use are based solely on engineering judgment and have no design basis, no qualification tests, no test standards, no acceptance criteria and minimal regulatory footprint. Subsequent testing may be needed to evaluate the performance of these HEAF shields in order to provide reasonable assurance they will perform as intended during an actual HEAF event.

The results described above demonstrate the practical value of independent physical testing necessary to provide the needed data to calibrate and validate sophisticated modelling techniques, to provide engineers and decision makers critical information to safeguard, life, property and the environment. Most recently the NRC in partnership with the Electric Power and Research Institute (EPRI) and the National Institute for Standards and Technology (NIST) have been using data collected during KEMA testing to calibrate and validate NIST computational fluids dynamics (CFD) model Fire Dynamics Simulator (FDS)  The model runs are being used to explore  actual NPP electrical configurations and their relationship to those tested at KEMA. The NRC has established a public website where you can follow their progress on the HEAF research.

KEMA Labs was 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.

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