I don't buy that claim. The amount of nuclear contamination in steel is really small. It matters when you're building sensitive instruments, but I don't think nuclear weapons care very much. After all, they contain at least several pounds of radioactive material by necessity. A tiny amount of extra background radiation from the steel casing won't affect things.

Adding to my doubt is the article's mention of "pre-1942 vessels." Why would that be the date? The first nuclear weapon was detonated in summer 1945, and I'd wager that contamination remained sufficiently low until sometime in the 50s. According to this page, there were only 7 nuclear test explosions in the 40s, for a total of 9 nuclear explosions all together:

https://www.armscontrol.org/factsheets/nucleartesttally

But even if a single bomb is too much, the date should be 1945.

I believe that 1942 refers to https://en.m.wikipedia.org/wiki/Chicago_Pile-1, the world's first artificial nuclear reactor.

Back at the time, there was not very much requirement for nuclear safety/contamination prevention... so if you want steel definitely free from non-natural radiation you'll need 1942 or earlier steel.

That seems likely, although I strongly doubt the requirements are that stringent. The issue with bombs isn't just that they release (and create!) a lot of radioactive material, but that they pulverize that material and push it high into the atmosphere where a lot of it spreads around the world. Whatever radioactive material might have escaped from something like Chicago Pile 1 would have stayed local.

Supporting this idea, here's another article on salvaging Japanese wrecks which mentions low-background steel in the context of ships built in 1943 and 1944: https://www.theguardian.com/world/2017/feb/09/images-reveal-...

People will steal anything, even kill a rhino in zoo. https://www.washingtonpost.com/news/animalia/wp/2017/03/09/a...