Yeah, I'm wondering about that as well. Did this exact design take 12 months previously? Or did a 30ft-wide BWR vessel take 12 months? That would be a pretty significant difference.

I did a small amount of nuclear-grade welding myself and it was always one hour of welding, one or more days of testing. So if they could replace many small passes with one all-the-way-through pass, that would vastly decrease production time. But even then, testing a weld that spans the length or circumference of a vessel is still going to take a very long time. Since they don't mention any massive, profound, fundamental improvements in post-weld testing methods, I'm guessing they just left that out of their "24hr" claim, which makes it very misleading.