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Fukushima: EPA's Radiological Monitoring

On March 11, 2011, a 9.0-magnitude earthquake struck off the coast of northern Japan. The epicenter of the powerful earthquake was under the Pacific Ocean, approximately 80 miles east of Sendai, where the Fukushima Daiichi nuclear power plant is located. The plant’s automatic earthquake detectors successfully inserted all the control rods into the three reactors that were operating at the time. However, less than an hour later, a massive tsunami inundated the Fukushima power plant, causing widespread destruction and knocking out the reactors' emergency cooling systems. The reactors overheated, damaging the nuclear fuel and producing hydrogen explosions that breached the reactor buildings and allowed radioactive elements to escape into the environment.

EPA's Response

EPA’s RadNet system detected nothing unusual in the first week after the Fukushima accident. During this time, EPA deployed additional portable air monitors in Alaska, Hawaii, Idaho and two U.S. Pacific Territories. The RadNet system went on an emergency schedule, with accelerated sampling and analysis of precipitation, drinking water and milk. After a thorough data review showing declining radiation levels in these samples, EPA returned to the routine RadNet sampling and analysis schedule for precipitation, drinking water and milk on May 3, 2011. The last time that EPA detected radioactive elements associated with Fukushima was July 28, 2011 in Hawaii.

On March 18, 2011, the RadNet air monitor in Hawaii detected very low levels of iodine-131 in real-time. Iodine-131 is a radionuclide that would be expected from the Fukushima nuclear incident. During the rest of March and April, laboratory analyses of RadNet samples collected throughout the U.S. detected very low amounts of iodine-131 and other radionuclides expected following a nuclear incident. All of the radionuclides detected in the U.S. from Japan were far below levels of public health concern. No protective actions were needed in the U.S. or its Pacific Territories. After a thorough review of all the sampling and monitoring results showed declining levels of radiation from Japan, RadNet returned to a routine sampling schedule on May 3, 2011.

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Sharing Data with the Public

To keep the public informed, EPA launched a Japan 2011 website which displayed near real-time air monitoring results and associated laboratory analysis data from RadNet. Search the EPA Archives for the EPA Japan 2011 website or search Envirofacts for sampling results.

You can view EPA news releases related to the Japanese Nuclear Incident by visiting, 2011 Japanese Nuclear Incident: EPA News Release by Date.

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