Step 1: Input the core (interior) size of the reactor: × ×

Step 2: Click on the fuel you want to use in the table below. Alternatively, you can manually enter the fuel data in the textboxes below.

Step 3: If you want to limit the usage of a type of block, enter the maximum number allowed in the table below. Enter zero to completely disable that block. You can hover over the acronym to see the full name of each block. Active coolers are disabled by default. You can enable them by removing the zeros. NOTE: Irradiators are not supported.

Step 5: Adjust the options below and click “Run” to start the optimization.
Only generate heat neutral reactor.
Optimize for power.
Optimize for breeding (maximize fuel consumption rate).
Optimize for efficiency.
X symmetry Y symmetry Z symmetry
Use reinforcement learning (requires more memory, slightly slower but can produce better design)
The most efficient reactor doesn't produce the most power. To get an efficient reactor that can still generate lots of power, you should optimize for power while limiting the cell count using the “Max Allowed” box for []. To get the ideal cell count, divide the fuel's base processing time by the time you want a fuel to last. Enabling symmetry and/or limiting block counts often speeds up the algorithm. The algorithm uses fixed seed: different runs will always yield the same results unless there is an update to the algorithm (last update: 30/6/2025).
You can use Forgematica to automate the building of your reactor. To do so, download the schematic and put it in the schematics folder of your Minecraft instance. Note that Forgematica also needs MaFgLib to run.
Alternatively, you could also use Building Gadgets to automate the building of your reactor by copying the BG String and pasting it in the Template Manager to create a template.
Note: in Chrome, this tab won't run in background! If you want to switch to other tabs, drag this tab out as a dedicated window and don't minimize it.