FILE - This April 27, 1956, file photo shows the area in which the United States hydrogen bomb tests will take place in the Pacific Ocean. North Korea said it successfully detonated a hydrogen bomb in its latest nuclear test Sunday, Sept. 3, 2017. Outside experts haven't been able to verify that claim, but say it's plausible. If true, it would represent a major step forward in North Korea's effort to develop a nuclear weapon capable of reaching the United States. (AP Photo/Ed Gunder, File)