The fact that a particular nuclear weapon has (or does not have) a “dial-a-yield capability” enabling the selection of a desired explosive yield was declassified earlier this year, in a joint decision of the Department of Defense and the Department of Energy.
Last year, the Department of Energy also declassified the thickness of the “getter nickel plating” used in tritium production. (A “getter” here means the reactive material that sustains a vacuum by capturing gas atoms.)
These and several other recent DOE declassification decisions were recorded in memoranda that were released last week under the Freedom of Information Act. Copies are available, along with the records of prior DOE declassification actions, here.