Ambient office  = 122 nanosieverts per hour

Ambient outside = 103 nanosieverts per hour

Soil exposed to rain water = 106 nanosieverts per hour

Crimini mushroom from Central Market = 159 nanosieverts per hour

Tap water = 143 nanosieverts per hour

Filter water = 136 nanosieverts per hour

Part 2 of 2 Parts (Please read Part 1 first)
      Experience with actual HEAFs at nuclear power plants has demonstrated that the current preventative and mitigative factors are not sufficient to deal with the threat posed by some HEAFs. In some cases, arcs have lasted much longer than predicted durations and caused more damage than expected. In other cases, HEAF have caused damage to equipment that is outside of the defined ZOI.
       During the Fukushima nuclear disaster in Japan in March of 2011, there was a HEAF at the Onagawa nuclear power plant. The motion of the ground caused by the earthquake prevented the automatic shut off of a circuit breaker. The fire burned for seven hours because firemen were not able to enter the room to extinguish the blaze due to the smoke and heat.
       The U.S., Japan and other countries subsequently studied HEAFs. The NRC was involved with a series of tests to pin down critical variables that contribute to the intensity of a HEAF and the damage caused. This resulted in the NRC taking two actions.
       First, the NRC put HEAF events into its generic issues program in August of 2017. Second, the NRC issued an information notice to the operators of all nuclear power plants in the U.S. with details on the tests that had been carried out and the information gained from the tests.
       The test results suggest that a tiered approach be used to deal with HEAFs. After the key factors such as voltage levels, materials, and arc durations were identified, they were used to separate out configurations in a nuclear power plant that might threaten safety margins. As an example, an electrical cabinet configuration that could be problematic is not a concern if it is far enough away from any safety equipment that it could not possibly cause a problem even it was vaporized by a HEAF. There will also be no concern if configurations satisfy safety standards.
       For configurations that might cause a problem, there are different possible remedies. Some situations might call for a more reliable and robust fault detector that quickly shuts off a circuit breaker in order to shorten the duration of the arc. In other situations, it might be wise to switch materials for buses like using copper buses in place of aluminum buses. In still other cases, the remedy might be to just build a wall between an electrical cabinet and safety equipment.
       Although the problems with HEAFs and applicable rules and regulations have been known for some time, the NRC and others have only recently been able to obtain the necessary knowledge needed to move forward with improvements in the handling of HEAFs. While the improvement in understanding of HEAFs and developing possible solutions is important, the next step is to finish testing and studying and move forward with implementing the proposed solutions.

Ambient office  = 115 nanosieverts per hour

Ambient outside = 89 nanosieverts per hour

Soil exposed to rain water = 87 nanosieverts per hour

Beefsteak tomato from Central Market = 67 nanosieverts per hour

Tap water = 115 nanosieverts per hour

Filter water = 108 nanosieverts per hour

Ambient office  = 100 nanosieverts per hour

Ambient outside = 108 nanosieverts per hour

Soil exposed to rain water = 105 nanosieverts per hour

Blueberry from Central Market = 96 nanosieverts per hour

Tap water = 143 nanosieverts per hour

Filter water = 136 nanosieverts per hour

Ambient office  = 126 nanosieverts per hour

Ambient outside = 119 nanosieverts per hour

Soil exposed to rain water = 119 nanosieverts per hour

Orange bell pepper from Central Market = 92 nanosieverts per hour

Tap water = 108 nanosieverts per hour

Filter water = 100 nanosieverts per hour

Ling Cod – Caught in USA = 112 nanosieverts per hour

       The U.S. Nuclear Regulatory Commission defines a high energy arc fault (HEAF) as “… a very intense abnormal discharge of electrons between two electrodes that are carrying an electrical current. Since arcing is not usually a desirable occurrence, it is described as an arcing fault.” Nuclear power plants generate electricity and use some of the generated electricity to power equipment in the plant. The electricity is carried through cables or metals bars which are called “buses”. When electricity jumps from the cables or buses to some nearby metal object, that is an arc.
       Electricity is available in different voltages for different types of devices. Consumer and office electronics use 120-volts. Nuclear power plants usually employ electric power at higher voltages including 480-volts, 4,160-volts and 6,900-volts. The main generators of a nuclear power plant produce 22,000-volt electricity which is then stepped up to 345,000-volts in order to make the electricity flow efficiently in the transmission lines of the power grid being fed by the nuclear reactor.
       Last year, there was an explosion and fire at the Turkey Point nuclear plant in Florida. A HEAF at the plant was the cause of the accident. The NRC has been aware of the danger of HEAFs at nuclear power plants but a final resolution for the problem has been elusive.
       Nuclear power plants employ what is called a “defense-in-depth” to support nuclear safety. Preventative measures are in place to stop HEAF events and there are additional measures to minimize the consequences of any HEAFs that do occur.
       One of the preventative measures consists of rules and restrictions on the handling of electrical cables when they are installed. There are defined limits on exactly how much a worker is allowed to bend or twist a cable. There are also limits on how much force can be applied when pulling cables through walls to ensure that their insulation which protects against arcs is not damaged. Another preventative measure consists of detecting an arc as it occurs and automatically shutting off a circuit breaker to reduce subsequent damage.
       Measures that are dedicated to reducing the consequences of an arc include creating what are called zones of influence (ZOI) around pieces of equipment that are powered by electricity. For example, an electrical cabinet is a metal box that contains circuit breakers, relays and other control devices. Current regulations for fire protection mandate a three-foot ZOI around the sides of an electrical cabinet and eighteen inches above an electrical cabinet. It is assumed that if there is a HEAF in an electrical cabinet, then all the components in the cabinet might be damaged. This means that there must be redundant equipment outside of the cabinet and its ZOI that can take over and cool the nuclear reactor if necessary.
        The Nuclear Energy Association issued a report in May of 2017 that said “The electrical disturbance initiating the HEAF often causes loss of essential electrical power and the physical damage and products of combustion provide significant challenges to the operators and fire brigade members handling the emergency. It is clear that HEAFs present one of the most risk significant and challenging fire scenarios that a [nuclear power plant] will face.”
Please read Part 2