I mean with just a few semesters of physics education you can bring people who don't know anything about physics at all to a Bachelor's degree. So in principle you can explain basically anything to an intelligent person of any time period if you put sufficient effort into it.

But to me that feels different than saying that inventions where sufficiently small steps away from a general engineer's education that you could "simply" explain them and not be met with wonder.

Knowing radioactivity is just the first step toward discovering the internal structure of the atom. You need a measuring instrument that is much smaller than a whole atom to make any progress.

The atom nucleus was discovered by counting how many alpha particles bounced off the nucleus of a piece of gold foil and how many simply passed through it. The bounce rate was incredibly low and therefore the nucleus must have been orders of magnitude smaller than the gap between the next nucleus.

Those experiments were conducted between 1908 and 1913.

Personally I think you could tell a GE engineer in 1912 that their company would be building a radiation-powered electrical plant and they'd be keen to find out how, not baffled at the very concept. No way of knowing for sure, of course. Just that, this was an era when radioactivity and (what became) nuclear research was very much something the educated were reading about in their monthly magazines.