NuclearCaft is a significantly more in-depth nuclear power mod that offers a wider selection of components to build with than BigReactors or Physica, while completely filling their respective roles at each level of progression (offers fusion, fission, and molten salt reactors).

Physica specifically is very outdated and only recently actually got working again, and it only barely works. The reactors and machines are very ugly and don't have the same responsiveness that NuclearCraft does. It would be fine to keep Physica in for forcefields if need be, since those are integral to the Voltz experience, but the reactors and various other items should be removed in lieu of NuclearCraft.

BigReactors is an extremely unbalanced mod for what it requires; it vastly outpaces any form of power generation in early and mid game, and requires significantly less effort than other forms of power generation. It's also braindead easy to set up, requiring no amount of thought when throwing together the parts, which just further exacerbates the previous issue. NuclearCraft is more in line with the balanced progression of energy generation, and rewards people for learning the mechanics, while still offering a useful source of energy for players who may not want to get into it all that much.

NuclearCraft also introduces a realistic radiation mechanic which, while also adding a layer of difficulty and complexity, would allow players to irradiate their opponents, adding another way to raid.

NuclearCraft is significantly more rewarding, fun to use in general, and has more mechanically interesting parts to work with, while also introducing a third type of reactor (molten salt reactors), and many more types of fissile fuel. It can easily replace the existing nuclear mods, since it offers the same mechanics (fusion and fission).