Shell, faces & rods

Building the shell

• Use Reactor Casing for opaque walls and Reactor Glass for transparent faces where you want to see inside or emit light.

• The interior must form a closed box with valid faces only on the outside. Leave room for rods, fluids, interior components, and any casing ports before you seal the last blocks.

Rod controller

The Rod Controller sits on the top shell layer of the box where you want a fuel rod column. Every interior cell below it in that column must be Reactor Rod blocks—otherwise validation fails. Use it to declare rod placement and geometry for the multiblock (distinct from the Reactor Controller block on an outer face, which runs the GUI).

Fuel rods

• Reactor Rods hold fuel items. Place them where your design allows; adjacency and layout change RF output and fuel consumption in the controller readouts.

• Insert and extract fuel through the Reactor Controller or automation that targets fuel slots (see the controller page).

Heat sinks (passive)

Heat sinks are passive thermal components inside the reactor air volume. They can be solid blocks or stationary liquid volumes you place within the shell (counted as interior fill for layout rules—not the same as the active coolant loop).

They change RF output and fuel consumption based on how you fill interior cells next to rods. Thermal / instability readouts that depend on them appear only when the pack enables reactor instability; otherwise there is no separate “temperature” mechanic tied to heat sinks.

They are not consumed like the active coolant circuit.

Coolant (active)

Coolant (active) is the working fluid in the circuit: it is consumed while the reactor runs. Some coolants (e.g. water in steam mode) divert would-be RF into exhaust fluid—with enough conversion, RF can go to zero while fuel still burns. Datapack RF and consumption multipliers apply on top; other coolants may only scale RF and fluid use without that diversion. If the circuit is starved, RF can also fall until supply returns.

Thermal / instability behaviour from the fluid circuit applies only when reactor instability is enabled; otherwise you see normal power and fluid levels without that layer.

Fill or drain through the Reactor Controller or compatible fluid-capable ports, depending on your build.