The Nuclear Reactor processes Uraninite Crystal-based Reactor Rods into Energy for use by a Seabase. The Nuclear Reactor is constructed with the Habitat Builder, and can only be placed in the center of a Multipurpose Room.
The Nuclear Reactor generates energy at a rate of 250 power units per minute (4.166667 per second) regardless of how many Reactor Rods are installed. Each Nuclear Reactor can store a maximum of 2500 energy units.
The Nuclear Reactor can hold a maximum of four Reactor Rods, which will become depleted Reactor Rods once fully consumed.
Despite the Data Bank Entry saying do not replace the Reactor Rods without a Radiation Suit, one is not needed to replace them.
Data Bank Entry
Renewable energy sources will usually be sufficient for maintaining a small outpost. For everything else there's nuclear power.