Japan’s nuclear emergency

Damage at a nuclear power plant has made leaking radiation the primary threat facing a country grappling with devastation from a 9.0-magnitude earthquake and tsunami.
For a narrated animation of what happened, click here.

State of the reactors

A look at where things stand at the Fukushima Daiichi plant as of 2:30 p.m. Saturday, local time.


March 18 image by GeoEye

Water from units 1-4 has contaminated adjacent seawater with iodine-131 and cesium-137. Engineers are processing about 60,000 tons of contaminated water found in the turbine buildings of units 1, 2 and 3, diverting it to reactor condensors and temporary storage tanks, with plans to send it to a radiation waste treatment facility before discharging the water into the sea.


State of the Daiichi reactors Boiling water reactor

How dangerous is the radiation?

The highest reported level of radiation released from the Daiichi plant was 1,000 millisieverts per hour on March 27. The spreading contamination represents a critical safety concern for workers at the plant. On March 24, three workers were hospitalized for radiation burns to their legs and feet.

Radiation chart

Effects of radiation

A blast of radiation often causes immediate, obvious symptoms, but damage from low levels of exposure -- generally 100 mSv or less -- may not appear for decades, if ever. Japanese officials have set a dose limit of 250 mSv for nuclear workers during emergencies.


Radioactive contamination

Officials at the Fukushima Daiichi power plant said that highly contaminated water was found in tunnels outside the nuclear reactors, and they were concerned that it would spread to the soil or the surrounding seawater, where high radiation levels have been detected for days.

Of the hundreds of types of radioactive atoms that may have escaped the reactors, scientists are generally concerned about iodine, plutonium, cesium and stronium. Samples of vegetables and drinking water on March 26 and 27 detected iodine and cesium, but the majority of measurements remained below regulation values. Small amounts of plutonium were also found in the soil outside the plant, though not enough to pose a significant health risk.


Japanese officials expanded the evacuation zone from 12.5 miles to 19 miles on March 25.

GRAPHIC: Wilson Andrews, Alberto Cuadra, Bonnie Berkowitz, Patterson Clark, Laris Karklis, Nathaniel Vaughn Kelso, Todd Lindeman, Alicia Parlapiano, Jason Samenow, Laura Stanton, Gene Thorp, Bill Webster, Karen Yourish - The Washington Post. Updated March 25, 2011.

Video: Inside Japan’s nuclear emergency

Watch how the crisis at the Fukushima Daiichi power plant unfolded in this narrated animation.

Map: A wave of destruction

See how the powerful tsunami barreled across the Pacific.

Recent quakes in Japan

Japan is one of the most active seismic areas in the world. More than a thousand earthquakes of 4.0 magnitude or greater have struck in and around the country since 2009.

SOURCES FOR "JAPAN'S NUCLEAR EMERGENCY": Tokyo Electric Power Company; Mitch Singer, Biff Bradley, Rod McCullum and Alex Marion, Nuclear Energy Institute; IAEA; The National Academies Press; "Power Plant Engineering;" "Nuclear Reactor Engineering: Reactor Systems Engineering;" Bulletin of the Atomic Scientists; Japan Ministry of Land, Infrastructure and Transport; Nuclear and Industrial Safety Agency of Japan; Nuclear Regulatory Commission; U.S. Food and Drug Administration; Kenneth D. Bergeron, Training Centre for Nuclear Technology; International Nuclear Safety Center; Argonne National Laboratory; U.S. Dept of Energy; Global Seismic Hazard Assessment Program; United Nations Population Division; World Health Organization, World Nuclear Association; NOAA Hysplit Model; U.S. Nuclear Regulatory Commission; Environmental Protection Agency; Japan Nuclear Energy Safety Organization; CDC; Health Physics Society; Physicians for Social Responsibility; Thomas McKone, senior staff scientist at the Lawrence Berkeley National Laboratory; General Electric.