Reactor Builder

The Reactor Builder places the reactor interior and shell from materials in its buffer and tank. It does not place the Reactor Controller, power ports, or resource ports — see Getting started.

What Build places (in order)

1. Casing shell (optionally open top for later edits)
2. Rod controllers on the top layer above each rod column
3. Reactor rods in the interior pattern
4. Fluid heat sinks (1000 mB per cell) when configured
5. Solid heat sink blocks in remaining interior cells

Typical workflow

1. Place the builder against the intended footprint (orientation matters).
2. Open the GUI: set size, rod pattern, pattern mode, heat sink type, and open top if needed.
   • Website pattern: paste a design seed / URL; heat-sink / rod cells follow the seed (including mixed heat sinks per column). On Website, the heat-sink cycle button is inactive.
3. Preview (under Center) — purple border, yellow rod positions, red = invalid/extra blocks. Status warnings appear beside Center.
4. Mark Input (just above the builder buffer):
   • Assign buffer slots to specific items (see button tooltips).
   • Drag items from JEI onto buffer slots for ghost mark filters; double-click a slot to clear.
5. Build when the buffer/tank hold enough materials; Stop if red zones appear or you need to edit.
6. Remove or ignore the builder block — it is not part of the multiblock.
7. Manually add controller, power port, and resource port(s) after the build — controller outside one wall; ports on that same face, replacing glass cells.

Simulation estimates stats and material counts (Website seeds included when valid); it does not start the real reactor.

Example finished layout (builder + hand-placed ports on the casing frame). See Getting started for labels.