Classification in the nuclear world (DOE/NNSA in the USA) is unfortunately often done to hide things like massive cost overruns (Hanford cleanup costs for examp

Classification in the nuclear world (DOE/NNSA in the USA) is unfortunately often done to hide things like massive cost overruns (Hanford cleanup costs for example), the scale of environmental problems (like how much nuclear waste the US Navy has dumped at sea and where that dumping took place, or just how much radioactive fallout spread across the western USA due to atmospheric testing in Nevada), and other things that really shouldn't be classified. The Federation of American Scientists regularly brings this up, most recently: https://fas.org/blogs/secrecy/2021/05/nuclear-secrecy-reform/ https://fas.org/blogs/secrecy/2021/05/nuclear-secrecy-reform... There are of course many things that should be kept secret - although I assume the secrecy surrounding the current distribution of nuclear weapons on submarines, planes, missile bases, etc. falls under the military secrets sector. Blueprints for nuclear reactors are not really supposed to be available, due the risk of being utilized by terrorists etc. to inflict massive damage, but as I recall right after Fukushima it was easy to find quite detailed drawings of that reactor model online, which were useful for understanding how the accident took place. There's a whole cyber division of the U.S. government devoted to nuclear reactor security issues, a cousin of US-CERT. However, manufacturing fisson-type nuclear weapons, even the D-T boosted ones that are small enough for ballistic missiles, is really not that secret of a technology anymore - all it takes is access to the required materials (plutonium and/or enriched uranium), some working nuclear reactors, and graduate-level metallurgical / chemical / electronics knowledge, plus access to the historical non-classified research literature and state-level support (This is how AQ Khan developed the Pakistani nuclear weapons program, and even the relatively poor state of North Korea managed it).