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In this July 4, 2015 photo, two persons walk in the rain near the ground zero of 1945 A-Bomb, near now known as Atomic Bomb Dome in Hiroshima, western Japan. On Aug. 6, 1945, a U.S. plane dropped an atomic bomb on Hiroshima, the first nuclear weapon has been used in war. Japan surrendered on Aug. 15, ending World War II. (Eugene Hoshiko/AP)

In this Sept. 8, 1945 file photo, an allied correspondent stands in the rubble in front of the shell of a building that once was a exhibition center and government office in Hiroshima, Japan, a month after the first atomic bomb ever used in warfare was dropped by the U.S. on Aug. 6, 1945. (Stanley Troutman/AP)

In this July 1, 2015 photo, a visitor photographs now known as Atomic Bomb Dome in Hiroshima, western Japan. On Aug. 6, 1945, a U.S. plane dropped an atomic bomb on Hiroshima, the first nuclear weapon has been used in war. Japan surrendered on Aug. 15, ending World War II. (Eugene Hoshiko/AP)

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In this July 5, 2015 photo, a man checks with a public street map at a crossroad near now known as Atomic Bomb Dome in Hiroshima, western Japan. On Aug. 6, 1945, a U.S. plane dropped an atomic bomb on Hiroshima, the first nuclear weapon has been used in war. Japan surrendered on Aug. 15, ending World War II. (AP Photo/Eugene Hoshiko) (AP)

In this July 4, 2015 photo, visitors walk in the rain next to now known as Atomic Bomb Dome in Hiroshima, western Japan. (Eugene Hoshiko/AP)

In this Aug. 6, 1945 file photo, shortly after the first atomic bomb ever used in warfare was dropped by the United States over the Japanese city of Hiroshima, survivors are seen as they receive emergency treatment by military medics in Hiroshima, Japan. The explosion instantly killed more than 60,000 people, with ten of thousands others dying later from effects of the radioactive fallout. (AP)

In this July 5, 2015 photo, a visitor stands near the symbolic "Thousand Cranes" near Hiroshima Peace Memorial Museum in Hiroshima, western Japan. (Eugene Hoshiko/AP)

In this Aug. 8, 1945 file photo, the shell of a building stands amid acres of rubble in this view of the Japanese city of Hiroshima. (Mitsugi Kishida/AP)

In this July 5, 2015 photo, a man waits at a crossroad about 1.2 miles northeast of now known as Atomic Bomb Dome in Hiroshima, western Japan. (Eugene Hoshiko/AP)

In this Sept. 8, 1945 file photo, only a handful of buildings remain standing amid the wasteland of Hiroshima, the Japanese city reduced to rubble following the first atomic bomb to be dropped in warfare. (AP)