The RBMK is NTM’s graphite-moderated, channel-type nuclear reactor — inspired directly by the real-world Soviet RBMK design that powered Chernobyl. Unlike a traditional block-style reactor, the RBMK is a flat, modular grid of independent columns: fuel channels, moderators, control rods, and cooling channels arranged side by side in any configuration you choose. This open-ended architecture means there is no fixed multiblock shape; instead you design the reactor layout yourself, balancing reactivity, heat output, and safety margins. Neutron flux travels up to five blocks in the four cardinal directions from each fuel channel, so column placement directly determines how much flux each fuel rod receives and how efficiently the reactor burns. Master the RBMK and you have NTM’s most powerful and most dangerous source of sustained nuclear power.Documentation Index
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Components
RBMK Structural Column (Blank)
RBMK Structural Column (Blank)
RBMK structural columns, often called “blanks”, are components of the RBMK that allow neutrons to pass and which conduct heat, but otherwise do not serve any added function. They are commonly used as filler in setups that are not very dense, and for making reactors more aesthetically pleasing.
RBMK Fuel Channel
RBMK Fuel Channel
The RBMK fuel channel is the most important part of the RBMK since it holds the fuel rod, allowing the reaction to happen. Neutron flux created by the fuel will be emitted in four cardinal directions, with a maximum range of five blocks.A Moderated Fuel Channel variant converts incoming fast neutron flux into slow flux, similar to how a graphite moderator works, though outgoing flux is not affected. A ReaSim Fuel Channel uses alternate neutron-spread mechanics.
RBMK Graphite Moderator
RBMK Graphite Moderator
The graphite moderator converts all passing neutrons into slow neutrons. Most RBMK fuels split more effectively with slow neutrons, meaning that most RBMK designs either require dedicated graphite moderators between the fuel channels, or moderated fuel channels directly.
RBMK Tungsten Carbide Neutron Reflector
RBMK Tungsten Carbide Neutron Reflector
The reflector can be used to utilize neutrons that would otherwise leave the RBMK. Neutrons that hit the reflector are not path-simulated — they teleport directly back to their source fuel channel. This is the most efficient way to border your reactor and recapture escaping flux.
RBMK Boron Neutron Absorber
RBMK Boron Neutron Absorber
The absorber simply blocks neutrons from passing. Unlike a solid wall, the absorber has the advantage of being able to transfer heat through it and generate heat from the neutron flux it absorbs. While a reflector is usually more useful, absorbers can separate incompatible fuel rods in high-heat reactor designs that use linear or exponential fuels.
RBMK Control Rods
RBMK Control Rods
RBMK Control Rods throttle or shut down the RBMK. Neutrons passing through the rod are reduced proportionally to the rod’s insertion level — a 100% inserted rod blocks all incoming neutrons, 50% blocks half, and so on. Control rods can be managed remotely via the RBMK Console. Moderated control rods function the same way but also convert fast neutrons into slow neutrons.
RBMK Automatic Control Rods
RBMK Automatic Control Rods
RBMK Automatic Control Rods cannot be controlled manually. They are configured with a minimum and maximum temperature, corresponding minimum and maximum extraction levels, and a response curve. They are useful for smoothing reaction spikes and controlling neutron sources on subcritical reactors, but running a reactor exclusively on auto rods is not recommended.
RBMK Steam Channel
RBMK Steam Channel
The RBMK steam channel is the primary way to cool the RBMK and extract energy from it. The channel uses as much water as it can at once to cool itself down to the target temperature. Since fuel channels are the only parts that actively heat up, place steam channels as close as possible to them.The compression level (configurable via the Console) determines what steam tier is output. Higher-density steam generates more power but requires the reactor to run at a higher temperature, leaving less safety margin. In practice, most reactors work fine with regular uncompressed steam.Water enters from the bottom; steam exits at the top. An RBMK Steam Connector placed below the steam channel allows both connections to come from the bottom.
RBMK Fluid Heater
RBMK Fluid Heater
An alternative to the steam channel, the fluid heater heats a coolant fluid rather than boiling water. Hot coolant can then drive a heat exchanging heater or a secondary boiler loop. Note: PWR-exclusive coolants such as liquid sodium are not compatible with the RBMK fluid heater.
RBMK Cooler
RBMK Cooler
The RBMK cooler is an optional component for cooling without extracting energy. It consumes cold perfluoromethyl (PFM) at 50 mB/t and rapidly cools all RBMK components in a 5×5 area by 200 °C/t.
RBMK Console
RBMK Console
The RBMK console monitors and controls an RBMK over a 15×15 block area. To link it, shift-click the central position of the RBMK with an RBMK linker, then shift-click the console.The console provides:
- A visual display showing fuel status and component heat across the reactor
- Six configurable info displays for monitoring specific columns
- A total neutron flux graph to detect fuel depletion or dangerous reaction spikes
- Color-coded control rod group selection and extraction-level input
- Steam channel compression settings for selected channels
RBMK Crane Console
RBMK Crane Console
The RBMK crane console allows fuel rods to be extracted, transported, and inserted safely from a distance. Once linked to an RBMK with the linker tool, it spawns a crane over the reactor. The crane is controlled using arrow keys (default) to move and the Enter key to load or unload a fuel rod. Compatible with all fuel channel variants and the Storage Column.
RBMK Autoloader
RBMK Autoloader
The autoloader is an advanced component placed on top of fuel channels. It holds fresh fuel in one inventory grid and spent fuel in another, and includes a selector for the minimum fuel enrichment percentage (adjustable in 5% increments). When a fuel channel’s enrichment drops below the configured threshold, the autoloader descends, swaps out the spent rod, and inserts a fresh one. Item access ports are on the very top, compatible with hoppers and conveyors.
RBMK Storage Column
RBMK Storage Column
The storage column is mainly used in conjunction with the RBMK crane as a queue-based fuel store. The crane picks up the first rod in the queue; rods dropped by the crane are added to the back of the queue.
Fuel Types
The RBMK accepts a wide variety of fuel rods. Each rod is characterized by its reactivity function (how flux output scales with incoming neutron flux), neutron type (slow or fast), and heat per outgoing flux. Rods range from basic natural uranium to exotic Schrabidium compounds.| Fuel Rod | Isotope | Notes |
|---|---|---|
rbmk_fuel_ueu | Natural Uranium (UEU) | Very low enrichment, starter fuel |
rbmk_fuel_meu | Medium-Enriched Uranium (MEU) | Balanced general-purpose fuel |
rbmk_fuel_heu233 | HEU-233 | High reactivity, U-233 based |
rbmk_fuel_heu235 | HEU-235 | High-enriched, strong output |
rbmk_fuel_uzh | Uranium–Zirconium Hydride | Specialized fuel type |
rbmk_fuel_thmeu | Thorium/MEU Mix | Thorium-cycle hybrid |
rbmk_fuel_mox | Mixed Oxide (MOX) | Pu-239 + U-238 blend |
rbmk_fuel_lep / mep / hep239 / hep241 | Plutonium Grades | LEP through HEP-241, increasing power |
rbmk_fuel_lea / mea / hea241 / hea242 | Americium Grades | High heat, exotic late-game |
rbmk_fuel_men / hen | Neptunium Grades | Np-237 based |
rbmk_fuel_les / mes / hes | Schrabidium Grades | NTM exotic fuel, extreme reactivity |
rbmk_fuel_balefire | Balefire | Special extreme fuel |
rbmk_fuel_po210be / ra226be / pu238be | Neutron Source Rods | Emit flux passively for subcritical setups |
Fuel rods have a melting point (default 1000 °C for the hull). The rod’s core temperature can exceed this, but if the hull overheats, a meltdown is triggered. Always keep your cooling adequate.
Reactor Physics
Xenon-135 Poisoning
Positive Void Coefficient
Key Reactor Parameters (RBMKDials)
These parameters can be tuned via Minecraft game rules (managed by theRBMKDials system):
| Parameter | Default | Description |
|---|---|---|
dialPassiveCooling | 2.5 | Passive heat loss rate |
dialColumnHeatFlow | 0.2 | Heat transfer between columns |
dialFluxRange | 5 | Maximum neutron flux range (blocks) |
dialReactivityMod | 1.0 | Global reactivity multiplier |
dialControlSpeed | 1.0 | Control rod insertion/extraction speed |
dialBoilerHeatConsumption | 0.1 | Heat consumed per boiler operation |
dialDisableXenon | false | Toggle xenon poisoning |
dialDisableMeltdowns | false | Toggle meltdowns (for testing) |
dialDisableDepletion | false | Toggle fuel depletion |
Building Your First RBMK
Gather Materials
Craft the basic RBMK column components: RBMK Structural Columns (blanks), at least one RBMK Fuel Channel, RBMK Graphite Moderators, RBMK Reflectors (for borders), and RBMK Steam Channels. You will also need at least one RBMK fuel rod, a water supply, and a way to connect power output (steam turbines).
Lay Down the Reactor Floor
Place your RBMK columns in a flat grid. A minimal working reactor might be a 3×3 arrangement:
- Center: Fuel Channel with a fuel rod inserted
- Cardinals (N/S/E/W): Graphite Moderators or additional fuel channels
- Corners and outer border: Reflectors to return escaping neutrons
Place Steam Channels
Add RBMK Steam Channels adjacent (cardinally) to your fuel channels. They do not block neutrons, so they can share a column slot with the reaction grid. Connect a water pipe to the bottom and route the top steam output to a turbine or steam consumer.
Add Control Rods
Place at least one Control Rod in your layout. For a small reactor, one centrally-placed control rod is sufficient for routine throttling. Configure its initial extraction level to ~50% before starting.
Install the RBMK Console
Place the RBMK Console within 15 blocks of the reactor center. With an RBMK Linker in hand, shift-click the reactor’s center column, then shift-click the console. The console is now linked and will display fuel status and component heat.
Load Fuel and Start
Insert fuel rods into fuel channels by right-clicking the channel with the rod. Once fuel is loaded, the reaction starts automatically as long as criticality conditions are met (sufficient flux from neighboring columns or self-igniting fuel). Monitor the neutron flux graph on the console — a stable, non-spiking flux line indicates a healthy reaction.
Monitor Temperature and Steam Output
Watch component temperatures via the console display. Keep all columns below their melting thresholds (default 1000 °C for fuel channel hulls) by ensuring continuous water supply to steam channels. Adjust control rod insertion levels to throttle power if temperatures rise.
Automation
- Autoloaders placed on top of fuel channels handle refueling automatically. Set the enrichment threshold (e.g., 20%) and pipe fresh rods in via hoppers or conveyors.
- RBMK Crane allows manual remote fuel handling from a crane console without standing over live fuel channels.
- Storage Columns act as fuel queues next to the crane’s reach, holding spare rods for pickup.
- The RBMK Console can remotely set extraction levels for all control rods in a color group, making centralized power control straightforward.