Nuclear reactors should change some of the blocks within a certain radius (probably based on how efficient the reactor was or how much uranium was in it) in to radioactive versions of that tile when they explode in addition to their explosion damage, of course. Probably would be fine to only do this on natural blocks such as sand, smoothstone, dirt, and grass. Perhaps this block would glow. These blocks would need a special tool to mine up (something for cleaning up radioactiveness i don't know what it would be called) and cause slow damage if a player is within a certain number of tiles. Perhaps if they wear certain armor it would protect them.
Mainly I think it would be cool for the repurcussions of a nuclear blast to include some of the natural blocks (maybe even some of the unnatural ones) to be changed to radioactive ones.
LMK what you think.