The fission reactor is a type of nuclear reactor where one can place Fissile Fuel Rods within to start nuclear fission. The reaction will heat up nearby water blocks and start turning them into steam. The steam is used by a Turbine (above the water) to generate Electricity, which is conducted out through your Copper Wires. To place a uranium rod in the reactor, right click the reactor core with a uranium rod in your hand.
The fission reactor has to be properly controlled to make sure it is constantly cooled down. If the reactor reaches above 2000°C, it will explode out fire and lava and generating Radioactive Material.
Fission Reactor Recipe