Events such as fires at a nuclear power plant (NPP) albeit infrequent, can pose a significant risk to safe plant operations when consequences of fires are not mitigated. NPP operators in the United States combat this risk by having robust Defence-in-Depth fire protection programs designed to minimize the likelihood and consequences of fire events.
In this respect, high energy arcing faults (HEAFs) are one of the fire hazards that need to be assessed. HEAFs can occur when electrical equipment fails producing an electrical arc leads to the rapid release of energy in the form of heat, vaporized metal, and mechanical force. The current methodology for quantifying HEAFs, known as fire probabilistic risk assessment (PRA), was published in 2005. PRA requires a systematic and iterative approach to quantity facility risk. Review of Operating Experience and additional testing and research can improve realism and accuracy of this method.
One of the key steps to better understand and update the HEAF PRA methodology is to provide evidence (test data) by conducting physical testing including small‑, medium-, and full-scale tests.
In this respect, KEMA Labs Chalfont (USA) performed twenty-six full-scale experiments, which were led by the U.S. Nuclear Regulatory Commission (NRC) Office of Nuclear Regulatory Research (RES) and conducted in partnership with other International Regulators and Researchers as an OECD Nuclear Energy Agency (NEA) project, issued in 2017. The NRC conducted an additional thirteen full-scale and thirteen medium-scale experiments issued in 2021, to support the NRC evaluation of the impact of aluminum in HEAF events.
The experiments performed at our North American facility were carried out on equipment rated from 480 volts up to 10,000 volts at various fault current levels and durations. The NEA project experiments were instrumented and measured by the Fire Research Group of the National Institute of Standards and Technology (NIST) and the Sandia National Laboratories. This instrumentation included Inconel plate thermometers, tungsten slug calorimeters, and ASTM copper slugs measured the heat flux or incident energy. High speed video and infrared (IR) imaging was also used to characterize and document the experimental progression.
For this effort, the data was shared with the NRC NIST and the Electric Power Research Institute (EPRI) working group (WG). The WG used this information to advance existing models to allow for numerical simulation of the HEAF event to predict the extent of the hazard. The data included photographs of cable samples after the experiment and thermal data near the cable samples.
The NRC is currently planning a second phase of OECD/NEA HEAF testing scheduled for later this summer at KEMA Labs Chalfont. The NRC expects this testing to help validate their modeling approach and fill in any knowledge gaps in the data.
With these tests, KEMA Labs proved again to be a trusted, independent partner for the NRC, having carried out testing at the Chalfont facility since 2015.
To follow the NRC OECD/NEA HEAF Research including upcoming testing at KEMA please click on the NRC HEAF web page.