A worker rides a bicycle in front of the Bushehr nuclear power plant in Iran in 2010. Iran and six world powers are meeting in Vienna this week with the goal of reaching a comprehensive deal on Iran's nuclear program before a July 20 deadline. Majid Asgaripour/Mehr News Agency/AP hide caption

itoggle caption Majid Asgaripour/Mehr News Agency/AP

The second atomic bomb test at Bikini Atoll on July 25, 1946. The Marshall Islands, where Bikini is located, is suing the U.S. for what it calls a violation of the Nuclear Non-Proliferation Treaty. Anonymous/AP hide caption

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An Aug. 31 image from DigitalGlobe shows the 5-megawatt reactor at North Korea's Yongbyon facility. South Korean officials say they have confirmed that the nuclear reactor has been restarted. DigitalGlobe/ScapeWare3d/via Getty Images hide caption

itoggle caption DigitalGlobe/ScapeWare3d/via Getty Images