Fission Reactor (Mekanism)

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The Fission Reactor is a multiblock added by Mekanism. It is used in conjunction with the Industrial Turbine and possibly the Thermoelectric Boiler to produce power.


The reactor is a hollow cuboid of up to 18 x 18 x 18 blocks made of Fission Reactor Casing. The sides (not edges) of the structure can be replaced by Reactor Glass or Fission Reactor Ports. The inside is filled with towers of Fission Fuel Assembies, with the top block in the towers, right under the ceiling of the reactor, being Control Rod Assembly. For the most efficient reactor, the assembly towers should be placed in a checkerboard pattern.


The reactor can accept both Water and Sodium as coolants. Water is converted into steam, which can be fed directly into a turbine. If the turbine contains Saturating Condesers, it can recycle steam back into water to be fed into the reactor. If enough condensers are present, a closed loop can be created. Sodium, however, needs to be fed into a boiler, where it heats up Water into steam for the turbine. The boiler produces regular sodium, which can be fed back into the reactor.


If not operated correctly, the reactor could meltdown, which would be devastating for your world. To prevent this, a simple redstone circuit can be created with Fission Reactor Logic Adapter. The logic adapter can be configured to output a redstone signal on the following oncditions:

  • Reactor is overheated and can start taking damage
  • Reactor has reached the maximum damage and a meltdown is imminent
  • Reactor's waste tank is full, which will cause it to leak radiation into the environment.

The adapter can also be configured to start the reactor if a redstone signal is present, and deactivate it if not.


The reactor produces an explosion of power 8 when it melts down, regardless of the size. Large reactors will destroy many precious control rods, assemblies, and casings, while small ones will likely be almost completely destroyed, and take the room along with them. The most dangerous consequence of meltdowns, however, are the radiation.

Managing radiation

Reactors will produce a large amount of radiation when they melt down. In survival, the only way to get rid of radiation is to wait. Large reactor meltdowns may cause an area to take up to several in-game weeks to be safe again. If using cheats is ok, the command /mek radiation removeAll can be used to remove all radiation sources in the world.