I actually thought of something that might make ReactorCraft more...interesting that has nothing to do at all with adding new reactors: tracking a player's
exposure to radiation. Not just an insta-death effect if you overdose or a glorified potion effect, but an actual counter that changes depending on environmental factors with respect to time. Things like radiation shielding, both on armour and as a functional part of some blocks, would decrease how much radiation (in microsieverts, or µSv, in double-precision floating point format) a player receives from both the background and from their reactors. As time goes on the radiation levels in the player's body decreases, representing the body's absorbing said radiation, maybe with some medications that can allow radiation to be absorbed and passed more efficiently, until they reach normal background levels. As their exposure to radiation worsens, they begin to suffer ill effects such as poison (representing the vomiting), weakness, mining fatigue, and progressing to blindness, higher levels of poisoning, and eventually outright death. The effects of radiation poisoning would persist until the player's radiation levels decrease, maybe as a minute-by-minute check to keep performance impact low.
This could allow you to bring in a Geiger counter, allowing players to not only track their own radiation levels (by shift-right clicking), but also to check and see how much radiation their reactors are producing and maybe even using it to help them find uranium deposits by checking background radiation levels when they right-click air. This would encourage players to build their reactors intelligently, using radiation shielding and decentralization to make their bases safer, as well as further encouraging the creation of hazmat suits as well as automating their reactors and properly disposing of their waste, assuming they don't just void it.