Diagram: US NRC High Energy Arc FaultTwo relatively recent accidents at operating US atomic power plants have once again spotlighted how a lack of understanding of fire hazards contribute to growing risk, uncertainty and potentially the next nuclear meltdown. The incidents also focus on how reactor “safety” is a tug-of-war between reactor safety regulators trying to manage the public safety risk and associated costs to prevent the recurring accidents and industry effort to cap costs to protect corporate finances. At issue now between the U.S. Nuclear Regulatory Commission (NRC) and the nuclear industry is how much laboratory testing and the range of destructive testing is sufficient to “reasonably” capture and manage the accident risks and the consequences of fires and explosions caused by high energy arc flashing (HEAF). By NRC’s own account, fire is the leading contributor to a potential nuclear meltdown.
Both incidents demonstrated how a full range low, medium and high voltage electricity flowing through cables or metal bars called “buses” can jump from the intended energy pathways in a high energy arc, like lightning, to a nearby metal cabinet or tray.
On March18, 2017, a high energy arc caused an explosion and fire in switchgear room that houses safety-related circuitry for reactor cooling pumps at the Florida Power & Light Turkey Point nuclear generating station just twenty miles from Miami. The accident caused the nuclear power station to automatically SCRAM or shut down. A contract worker was installing a fire barrier blanket material (Thermo-Lag 700) as an overlay to safety-related electrical circuits covered by another fire barrier material (Thermo-Lag 330-1) that had been deemed by the NRC “inoperable” for decades. The worker was cutting and fitting the fire barrier blanket in the switchgear room without de-energizing the electrical circuitry because the adjacent back-up switchgear room was down for repair. Unbeknownst to the contractor, meshing the fire blanket cutting process created a fine cloud of carbon particles which conducted electricity causing the arc and explosion that burned and injured the worker. The pressure wave from the explosion blew open a fire proof door and potentially a fire path into the adjacent room housing the back-up Switchgear Room for the redundant safety-related circuitry to the reactor cooling pumps. Ironically, in February 2017, Turkey Point contractors were installing the same fire barrier material overlay to similarly inoperable fire barriers using the same faulty and risky installation technique that caused electrical breakers to trip. The Thermo-Lag installation instructions did not warn of the electrical hazard.
Just over a year later, on March 19, 2018, another electrical arc flash in a non-safety area of the Tennessee Valley Authority’s Sequoyah nuclear power station in Tennessee, burned and injured two more plant workers that were working in the vicinity.
Numerous accidents like these and others going back years are the current impetus for NRC to step up studies and laboratory testing. The causes of these high energy arc flashes and damage consequences are still not well understood. In a January 2019 public meeting between NRC and industry representatives at the Nuclear Energy Institute (NEI), NRC staff revealed that in recent tests measurement devices needed to determine the HEAF “zone-of-influence” from the extreme heat, blast effects and pressure waves were destroyed along with the valuable and costly data. The NRC staff efforts to expand the testing program to include simulated high energy arc faults of longer duration (up to 8 seconds) is being resisted by industry as unreasonable and unwarranted. The Union of Concerned Scientists posted a video of the NRC HEAF testing program that was used for data collection.
According to analysis by the Union of Concerned Scientists on fires and explosions generated by high energy arc flashes, the NRC and the industry are repeatedly unlearning the critical lessons gleaned from an actual and near miss fire in March 1975, where a single fire destroyed both the primary safety systems and their backups. The 1975 Browns Ferry fire lead to the promulgation of fire codes in 1980 intended to prevent a single fire from destroying all reactor safety systems that was amended in 2004 to provide still non-compliant operators with “an alternative means for managing the fire hazard risk.” In March 2017, Turkey Point workers were finally installing those alternative fire protection material to bring the reactor into compliance with the regulations as amended in 2004. The resulting accident could have been much worse, in fact, causing the very fire it intended to prevent, throwing the nuclear power station into “station blackout” and setting it on the path to a reactor meltdown.
Despite these setbacks and mounting costs, the nuclear industry is desperately fighting to limit fire protection testing and backfit to control cost for an increasingly economically marginal industry. The present state of play between NRC and industry is inadequate and dangerous for the public safety.
The National Academy of Sciences Nuclear Radiation and Studies Board is hosting a workshop to discuss establishing a registry for long-term health monitoring following radiological emergencies in the U.S. The public can register to attend either in person or by webcast. The workshop, "Challenges in Initiating and Conducting Long-Term Health Monitoring of Populations following Nuclear and Radiological Emergencies in the United States", will be March 12-13, 2019. Staff from Beyond Nuclear will be attending in person. Agenda topics include biodosimetry (examining damage to biological markers in the human body to assess how much radiation a person was exposed to), population monitoring and health screening, environmental impacts, and examination of existing health registries following the Chernobyl and Fukushima nuclear power meltdowns and explosions. 
February 25, 2019