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Radiation exposure: How big is the threat in Japan?

Radiation exposure: Adding to the monumental losses after a Japanese earthquake and tsunami, problems at four nuclear reactors have residents near and far concerned about radiation exposure.

March 15, 2011

Radiation exposure : A radiation detector marks 0.6 microsieverts, exceeding normal levels Tuesday, near Shibuya train station in Tokyo. Concern over possible radiation exposure has increased after a fourth reactor released radiation, Tuesday.

Kyodo News/AP


New York

[Editors note: This story was updated 5.p.m EST March 16]

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A new power line could restore cooling systems in Japan's tsunami-crippled nuclear power plant, said officials Thursday morning Japan time. This raises hopes of easing a crisis that has spawned dangerous radiation surges at the 40-year-old General Electric model Fukushima I Nuclear Power Station in Japan.

Increased levels of radiation in the atmosphere has prompted the US government to urge Americans living within a 50 mile radius to stay evacuate.

Gregory Jaczko, chairman of the Nuclear Regulatory Commission told the House Energy and Commerce Committee Wednesday that water used to cool spent fuel at the plant had evaporated and that radiation levels there are thought to be “extremely high.”

With increased radiation being measured as far as 175 miles away in Tokyo, and some experts calling this the "worst nuclear accident since Chernobyl," residents and officials want to know about the risk of radiation exposure.


The disaster started after a magnitude 9.0 earthquake rocked northeastern Japan, Friday. Eleven nuclear reactors responded to the earthquakes by shutting down automatically. This began a slow cool-down process and ensured the reactors' cooling rods were in place. However, of the six reactors at Fukushima, three lost power when their backup generators failed. This kept the reactors from circulating their coolant.

By Saturday, the cooling systems in Fukushima reactors 1 and 3 had failed and the coolant began to evaporate from heat in all three reactors. To reduce pressure, the steam was vented, which released the first trace amounts of radiation. That same day, reactor 1 experienced a hydrogen explosion which released more radiation, but did not crack its containment vessel. Caesium-137 and iodine-131 were detected near reactor 1.


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