Photos reveal the structure's rise and fall
In 1946 the US detonated an atomic bomb at Bikini Atoll in the Marshall Islands, Micronesia; it was the first underwater test of the device
While radiation has subsided in some areas others maintain contamination levels that are dangerously high
The fire erupted in the transformer of the third reactor unit at Rivne
International cooperation still needed to address consequences, says UN
"For many years, this has been a secret"