RBMK
See the page on RBMK Fuel to find out what fuels the RBMK can use and what stats they have.
The RBMK (Russian: реактор большой мощности канальный, РБМК; reaktor bolshoy moshchnosti kanalnyy, "high-power channel-type reactor") is a modular boiling-water type nuclear fission reactor added in 1.0.27 X3864. It consists entirely of concrete columns which by default are 4 blocks tall but this value can be changed with the gamerule dialColumnHeight (2-16). Each of these columns is either blank or has a specific function that it performs such as holding fuel rods, moderating neutrons, or storing water to be boiled into steam. Each column will also exchange heat with the column next to it such that temperature differences between columns will gradually equalize within the reactor. If any column reaches 1500C, the reactor will explode incredibly violently, spraying scrap and immensely radioactive material in every direction.
Basic Terminology
If you are already aware of terminology such as moderation, neutron poison, and neutron flux, then you can proceed to the rest of this page without reading this section further. If not, this will be a quick primer on reactor terminology.
In an RBMK, heat is provided through the fission of nuclear materials emitting neutrons. These emitted neutrons can be measured in terms of neutron flux, referred to simply as flux in NTM. Generally, these neutrons are traveling incredibly quickly and are unlikely to react with other atoms and as such are often moderated which is the term used to describe any process which slows but does not stop neutrons, therefore increasing total reactivity. Any process that stops neutrons entirely is known as a neutron poison.
Mechanics
Note: Many of these mechanics are covered at a more basic illustrated level by an in-game guidebook called "My First RBMK"
Neutrons
Referred to as a collective as "flux" in NTM, neutrons are the sole driver of fission and therefore the driver of heat production in an RBMK. Fuel assemblies in fuel rod columns will create neutrons according to a mathematically defined flux function which is described in more detail in Category:RBMK Fuel. Some will spontaneously output neutrons whereas others will only emit them when they receive input neutrons with most fuels requiring some form of input to get started. Neutrons are emitted in every horizontal direction away from the fuel rod and will interact with various types of columns during their travel before eventually being absorbed by something.
Neutrons are either emitted as fast moving or slow moving and react best with fuels in either state depending on the properties of the fuel. To convert fast neutrons to slow neutrons, they must pass through a moderator such as graphite which can come in the form of moderated rods or moderator columns. There is no way to make slow neutrons become fast after being moderated.
If not properly sealed, neutrons can leak out of the RBMK and cause immense environmental radiation. To prevent this, cover every column in the RBMK that neutrons pass through with an RBMK cover panel and seal off all paths that neutrons take with either solid blocks or a column that absorbs the neutrons fully.
Heat
Fuel assemblies generate heat when undergoing fission and when generated, heat is transferred to adjacent columns so that it can be used to generate steam for power generation. Columns also gradually lose heat passively to the environment, though this is usually negligible in most reactors. If a column reaches 1500C or greater, it will cause an immediate meltdown so always avoid reaching this point.
Fuel Temperature
When fission takes place, heat is produced. This heat is first generated in the core of the fuel assembly and is then transferred to the skin of the fuel at a rate defined by the diffusion coefficient and difference in temperature. Core heat does not affect the behavior of the rod substantially, but if skin heat meets or exceeds its melting point then the core heat and skin heat will equalize, nearly immediately melting down the column that the fuel assembly is housed in, thus imposing a hard upper limit on the temperature of certain reactors.
Meltdown
The inevitable result if heat builds up excessively in an RBMK. Consists of an incredibly violent explosion that instantly destroys the entire reactor, explodes in a large radius, throws radioactive scrap and waste in every direction, flings radiation into the atmosphere, and drips corium from where the fuel rods were located. The area around the RBMK will nearly immediately become immensely irradiated and saturated with toxic gas and fallout and this radiation will continue to linger until all radioactive elements are removed and cleaned up.
The radioactive scrap hurled by the meltdown can be picked up and disposed of relatively easily, but certain components like hot graphite chunks and RBMK fuel chunks have multiple deadly properties that make handling and disposal of them very difficult. The corium is more difficult to dispose of as it melts through the ground and penetrates any barrier put in its way in addition to being very resistant to mining and explosions, making it incredibly difficult to remove entirely.
As a whole, the RBMK meltdown is the worst of all of the fission based reactor meltdowns that are present in NTM with the meltdown of even a small reactor requiring extensive cleanup with heavy radiation protection gear.
Xenon Poison
A decrease in reactive potential of a fuel assembly from the buildup of Xenon-135 which is a product of fission reactions. This decrease in reactive potential can be great enough to render a fuel rod nearly completely unreactive if let get bad enough but can be readily burned away by stimulating the rod with a strong enough flux input. This process of burning must be taken very carefully though as an increased level of neutron flux intended only to burn away xenon can cause the fuel to reach a point of normal reactivity where it will cause the reactor to melt down.
Certain types of fuels are immune to xenon poisoning but these are either neutron sources or later game fuels, so xenon poisoning will be a consistent problem in most situations. As well as this, xenon poisoning can slightly lower the yields from spent RBMK fuel processing so it is best to burn away any xenon should it appear.
Component Blocks
Fuel Rods 
Comes in multiple forms but the base unmodified form "RBMK Fuel Rod" is the one whose function will be focused on.
One of the only strictly essential components of an RBMK. Not to be confused with fuel rods (the item) which for convenience will be referred to as fuel assemblies in this page. The fuel rod holds a single fuel assembly and pulls heat from the fuel in order to heat itself up and provide heat energy to components like boilers to convert it to a useful product. In generating this heat, it also produces neutron flux which will fire out from the fuel rod in all 4 cardinal directions. Fuel assemblies can be removed and placed into columns with a valid RBMK crane setup.
Fuel Assembly
The fuel assembly is the item that contains the fuel and generates heat and flux. Each fuel assembly type lists a huge amount of information, but the majority of it is information that is shared by either all or all but a few types.
Steam Channels 
Allow for the conversion of water contained within them into steam which can then be sent to turbines to convert the thermal energy of fission into electricity. Steam Channels take water from the bottom and output steam from the top with the additional option of being able to send steam to a steam connector contained one block below them. Steam channels can be configured to produce one of the following types of steam.
- Steam (100 °C)
- Dense Steam (300 °C)
- Super Dense Steam (450 °C)
- Ultra Dense Steam (600 °C)
Higher levels of steam density will require higher reactor temperatures in order to be produced which can mean a more dangerous reactor in addition to requiring multiple turbines for every stage, but they require less cooling compared to lower settings of steam.
Steam connectors are recommended for operating most RBMKs as they allow for the laying of pipes entirely below the reactor so that the player does not have to navigate through a web of fluid ducts in order to interact with parts of the reactor, though they do marginally increase the cost as each steam channel will require one steam connector.
Control Rods 
Non-essential but useful RBMK component that can smoothly vary the amount of flux that is allowed to pass through it between 0% and 100%. Their level of extension can be controlled in increments of 25% through directly accessing their GUI and their color group can be set which is an important component of operating a reactor remotely with an RBMK console. The RBMK console is capable of setting control rods to any whole number value, so it is recommended for finer manipulation of their position.
Automatic Control Rods 
Function exactly as a standard control rod does in preventing the flow of neutrons but has automatic operation that is determined by its current heat value. The exact parameters of this operation can be set in its GUI
Graphite Moderators 
Turns fast neutrons that pass through it into slow neutrons. Does not impede slow neutrons. Often replaced by the moderated forms of essential components like fuel rods and control rods later on.
Neutron Reflectors 
Reflects flux that impacts it backwards, usually back to its original source. Should be used with extreme caution with fuels that have a "dangerous" flux function.
Neutron Absorbers 
Absorbs all neutron flux that impacts it.
Irradiation Channels 
Stores items to be exposed to neutron radiation in order to convert them into a new form. Useful for a variety of things but particularly useful for the manufacture of thorium fuel which can make a thorium fuel RBMK self sustaining if consistently supplied with unenriched thorium billets.
Will not operate if not directly in the path of flowing neutrons. Significantly more effective with slow neutrons and will absorb all neutrons that impact it no matter their type.
Fluid Heaters 
Behaves nearly exactly the same as a steam channel but can accept a variety of kinds of heatable liquids and has no density settings. Will not connect to steam connectors, making piping out the fluid from the top a necessity.
Fluid Cooler
Rapidly cools itself by evaporating cryogel if it exceeds 750C. Rarely ever useful as any heat lost or cryogel used is permanently gone.
Storage Column
Stores items in a 12 item buffer that always shifts items towards the first red slot. Can be pulled from by an RBMK crane and can have extraction and insertion of items automated with conveyor parts.
Structural Columns 
Empty column that does not perform any function besides from the universal RBMK column function of transferring heat.
Console
Allows for remote control and monitoring of any RBMK reactor. Must be linked to a specific RBMK reactor by with an RBMK console linking device with the column that is clicked on representing what will be considered the center point for the reactor. The console will display as much of a linked reactor on its 17x17 screen as is possible with a special icon representing each type of column along with some other visual information. As well as this, the 6 panels on the sides of the monitor can be set to display a variety of information about the RBMK, such as average column temp, average depletion, average xenon poisoning, and more.
The other primary function of the console is the remote operation of control rods using the panel below the monitor setup buttons. Control rods can be selected on the main monitor and manually set to a certain level of extension or put into color groups and then selected in order for more convenient access to large amounts of control rods at once. The large button labelled "AЗ-5" at the bottom of the screen is the RBMK's equivalent of a SCRAM button, instantly setting every control rod to begin to move as far down as possible.
As well as all of this, the console also displays the total flux output of the reactor and can change the compression settings of selected steam channels.
Crane Console
Requires the same linking procedure as the regular console. Spawns a large crane over the RBMK which can be used to remove fuel from and place fuel into fuel rods using the space bar. Particularly useful when paired with storage columns as they can have items extracted from and inserted into them by way of conveyor belt automation.
Cover Panel
Block radiation from leaving the bounds of the RBMK. A cover panel must be placed over every column in the RBMK which has neutron flux moving through it even if it does not interact with the neutrons like neutron moderators or fuel rods.
It should also be noted that neutron flux can escape from an RBMK horizontally if there is not something blocking its path when it encounters air.
Miscellaneous
ReaSim (Realistic Simulation)
ReaSim is both a gamerule and set of alternate components that are meant to give a more "realistic" style to the reactor on top of its mechanics. ReaSim fuel columns emit neutrons in a random set of 6 directions around the fuel rod, instead of the 4 cardinal directions and steam boiling can be done within any component column, activated by /gamerule dialReasimBoilers true. Water must be input with a reasim water inlet attached anywhere on the reactor and output with a reasim steam outlet attached anywhere on the reactor. As well as this, reasim only produces super dense steam which requires a multi stage turbine setup to fully process.
Pros and Cons
Pros
- BWR, no coolant required.
- Can make huge amounts of power with the right setup and fuel.
- 100% modular, allows creativity.
- Can run on a multitude of fuels for your needs, capabilities, and desires.
- Will maintain use even in Fusion or Watz stages.
- Very aesthetic compared to the regular reactors.
- Extremely violent meltdown.
Neutral
- Designing can be complicated or take a lot of space.
- Fuel depletion percentage very slowly decreases effectiveness of the rods.
- Can take a long time to "fully" deplete (rather deplete to an appreciable percentage), which means breeding can take a very long time but the power produced is incredible even from little fuel.
Cons
- Egregiously expensive.
- Self-igniting fuels cannot be fully stopped from reacting unless manually removed.
- Steam production can be very high, requiring use of numerous Industrial or Leviathan Steam Turbines, which are also expensive.
- Extremely violent meltdown.
- It's so violent it ignores blast resistance.
Tips and Trivia
- Based off the real RBMK-1000 design.
- The real RBMK technically isn't a BWR, it's design is unique to itself, but it's referred to as a BWR for sake of simplicity and since that's the reactor classification it most closely resembles
- Neptunium fuel (and other fast fissioning fuels) only requires fast neutrons to split, and splits into more fast neutrons. Use this to your advantage.
- LES splits with slow neutron and splits into slow neutron which also don't require moderator between them unless there is another fuel outputting neutron into it.
- If things are getting out of control, AZ-5 could potentially make the difference between a saved reactor and a meltdown.
- The AZ-5/A3-5 button on the model of the console is actually called "SPAM" instead, which is a play on the word "SCRAM", which is basically the western equivalent to the A3-5.
- While fuel rods cool much faster when inside the reactor, this may not be feasible if you are actively replacing depleting fuel rods or if the fuel is self-igniting, use a Spent Fuel Pool Drum to cool them down in these cases.
- Fuel rods increase in radioactivity as they deplete to simulate the effect of accumulating fission and neutron absorption products.
- This includes DRX as well.
- Xenon-135 also massively increases radiation.
- The exceptions are Highly Enriched Australium Fuel and Low Enriched Australium Fuel, which are fully stable even after depleting and accumulating Xenon.
Design Philosophy
See also: Guide: Designing an RBMK Reactor
The most important goals of any RBMK reactor is to generate energy whilst preventing a meltdown. Heat is necessary to produce steam in steam channels and heat is generated by fuel rods receiving and outputting neutrons. This means that the most optimal placement for steam channels is somewhere near the fuel rods of a reactor; ideally diagonally from them. However, since neutrons travel horizontally, and most fuel types require slow neutrons to react whilst splitting into fast neutrons, some thought must be placed into where the neutrons in your reactor are going and what type they are. Fuel rods should be placed horizontally from each other. Neutrons that reach the edge of a reactor are wasted, but reflectors can be placed there to reflect neutrons back into the fuel rods, increasing the efficiency of your reactor. If a fuel rod requires slow neutrons, moderators should be placed between it and any other source of neutrons, such as reflectors and other fuel rods.
Preventing a meltdown is important as well, since a destroyed reactor is not very useful. Making the fuel rods of a reactor too reactive or not having enough sources of cooling, will lead to the reactor overheating and causing a meltdown. The primary way to reduce reactivity is control rods; which will reduce the amount of neutrons passing through depending on how much of the rod is inserted. Control rods should be placed between fuel rods and other sources of neutrons, whether it be another fuel rod or a reflector. An alternate way is neutron absorbers. As seen in the example to the right, neutron absorbers can be used instead of reflectors to prevent these three fuel rods from becoming too reactive, since they are receiving plenty of neutrons from other sources.
Steam channels are important for cooling down a reactor. Boiling water into steam takes heat away from the reactor, and as such steam channels should be placed regularly and have enough water to be boiled, lest the reactor overheats. Similarly, since increasing the amount of components in a reactor increases passive cooling, there should also be enough additional columns in a reactor to provide a passive cooling effect.
With ReaSim, every component is a boiler itself, this can effectively reduce space and allowing a more power density or minimalist reactor design.
Designs
There are more designs in the #rbmk-designs channel in the discord server.
(Note that some of these designs were made before critical RBMK fuel changes, and as such, might cause an immediate meltdown or not work at all. Please test the optimal fuel rods and power settings for them before use! This area will be updated soon with better reactor designs.)
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Minimalist RBMK design, takes self-igniting fuel.
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Neptunium RBMK reactor, uses neptunium fuel for the outermost layers.
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Common RBMK design.
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Idiot-proof™️ design. Uses a self-igniting plutonium rod in the middle, U235 in the outer rods and neptunium in corner rods.
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Modification of the minimalist RBMK design. Uses a self-igniting fuel for startup and runs on Low Enriched Schrabidium. Perfectly (or almost perfectly) self-regulating.
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RBMK with irradiators.
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Funny ReaSim RBMK for breeding dangerous fuel.
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A large pure NU ReaSim RBMK, utilize normal fuel rods and moderated control rods
