Reactor
A reactor is a hollow shell built from Reactor Casing and Reactor Glass (transparent faces). Inside you place fuel Reactor Rods, optional heat sinks, optional coolant fluid, ports on the casing, and exactly one Reactor Controller that drives operation and on-screen readouts.
New here? Read Getting started first — Complete example, then Setup 1 (RF-only) or Setup 2 (coolant → turbine).