Initially I assumed this was going to be about how nuclear tests were 'self-declassifying' since all the bomb components, test fixtures and equipment, the tower it was mounted on etc. would be completely vaporized in the explosion, so there was nothing left to classify as secret. Except for that one embarassing time when the UCRL device in test Upshot-Knothole Ruth[0] fizzled and failed to destroy the steel tower it was detonated on...

0. https://en.wikipedia.org/wiki/Operation_Upshot%E2%80%93Knoth...