A worker is given a radiation screening as he enters the emergency operation center at Tokyo Electric Power Co.'s tsunami-crippled Fukushima Dai-ichi nuclear power plant on Feb. 20. AFP/Getty Images hide caption

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After the earthquake, workers were sent inside Reactor 1 at the Fukushima plant to release some of the pressure building up inside the reactors. Frontline hide caption

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A Tokyo tuna wholesaler adds slices of fish to his stall on March 23. Fish prices have plummeted in Japan amid fears that radioactive material leaking from the damaged Fukushima Dai-ichi nuclear power plant may have contaminated the animals. But experts say there's no risk right now and that fish is safe to eat. Lee Jin-man/AP hide caption

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Japan Self-Defense Force officers in radiation protection suits hold a blue sheet over patients who were exposed to high levels of radiation at the Fukushima Dai-ichi nuclear power plant on March 25. A team of experts at Japan's National Institute of Radiological Sciences have helped treat injured workers. Jiji Press/AFP/Getty Images hide caption

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Cows that consume feed, grass or water contaminated with radioactive iodine-131 can concentrate the element in their milk. Peter Elvidge/iStockphoto.com hide caption

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Japanese Buddhist monk Tanaka Tokuun, who was evacuated from Fukushima prefecture, looks over an instrument measuring radiation levels at a hotel on March 17. Buddhika Weerasinghe/Getty Images hide caption

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Chiyoko Kaizuka, 83-year-old farmer, weeds a spinach field March 20, in Moriya, Ibaraki prefecture. Eugene Hoshiko/AP hide caption

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Police officers wear gas masks while on patrol in a vehicle at the Fukushima nuclear power plant on March 12. Experts are concerned about the safety of the nuclear workers, but they say that so far, there's no risk for others in Japan or in the U.S. Kaname Yoneyama/AP hide caption

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The No. 2 reactor at the Fukushima Daiichi nuclear power plant, as seen in screen grab. What will happen to the workers left behind to battle radiation leakage? AFP/Getty Images hide caption

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Children in Kawamata, Japan, take potassium iodide on Monday to protect against thyroid cancer after being evacuated from the vicinity of the Fukushima Daiichi Nuclear Power Plant. Asahi Shimbun via Getty Images hide caption

itoggle caption Asahi Shimbun via Getty Images