RBMK

*See: Category:Nuclear 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 type of nuclear fission reactor added in version 1.0.27 X3864 (1.7.10). It is a highly modular reactor with a theoretically infinite size (if your computer can handle it), with several components, each being 4 blocks tall by default, which can be changed using the dialColumnHeight gamerule (2-16, purely aesthetic). The reactor can output several types of steam, each of which requires a higher temperature to produce. These range from normal steam to ultra dense steam. This reactor requires no coolant, as it is a BWR (boiling water reactor), as opposed to a PWR (pressurized water reactor, which the other two fission reactors most closely resemble in function), since heat is both transferred directly to the boilers and is passively removed. It also has a console that allows for remote management of several elements from far distances. This reactor has the capability of running on numerous types of fuels (many unavailable to the other two reactors), along with a novel meltdown function unique to itself.

## Component Blocks

### Fuel Rods

The most important part of a reactor; it is impossible to run one without this block. Reactors take a single fuel rod, while also taking in and outputting neutrons depending on the fuel. When fuel reacts and heats up, the block follows at a slightly lower skin temperature. This is important, as you can use this with steam channels to output steam for power generation. If the fuel inside exceeds its melting temperature, then a meltdown will occur and fill a wide area with radiation (tested with a small reactor, over 10k rads at the epicenter).

In a reactor, there are 3 basic states: subcritical, critical, and supercritical. *Subcritical* means that the fuel in the reactor does not meet the required critical mass of the fuel material and is insufficient to sustain a chain reaction, so it will fizzle out and stop. *Critical* means that it can sustain a stable chain reaction and continue to react continuously. *Supercritical* means that the chain reaction is unstable and will continue to rise in reactivity until meltdown. It's important to use ideal neutron flux levels for each fuel, to make sure it is *critical*. A fuel or fuel setup that is known to be "self-sustaining" are capable of maintaining criticality without becoming sub or supercritical.

Come in moderated variants, which automatically slows down *incoming* neutrons, removing the need for a moderator columns. Requires Bismuth to make however, which means you would need to run and deplete a lot of RBMK fuel already.

#### Fuel Rod Item

The fuel rod item is the actual rod that contains the fuel and will generate heat and flux. Each fuel rod type has a plethora of information given out, here's the most important aspects of what you need to know about them, other parts will be discussed later:

* Yield
	+ Not explicitly shown, but all fuel rods when crafted are set with a predefined "yield" value. This value is essentially its lifespan, the more flux it receives the faster it decreases. It is directly related to the "Depletion" percentage, which is the measure between initial yield and current yield. 0% depletion means the fuel is completely or virtually unused and 50% means half of the fuel has been spent and depleted.
	+ Most fuels have a yield of 100,000,000. Exceptions exist, fuels with lower yield values will deplete faster.
	+ If there's an error of some kind or if the NBT data of a fuel rod is manipulated, you can get a yield value higher than the specified maximum, resulting in a negative depletion percentage.
* Depletion
	+ As stated prior, depletion is the percentage level of how much yield has been spent vs how much yield remains and the maximum yield amount.
	+ Depletion level also relates to recycling, see Guide: RBMK Fuel Recycling for more information.
	+ The gradually rising depletion level reduces the effectiveness of a fuel's flux in a way as defined by an unseen function. It is intended that loss of effectiveness should only noticeably occur at very high depletion levels, near the end of the fuel cycle.
		- This is to simulate loss of effectiveness due to decreasing fissile material and accumulating non-burnable neutron poisons.
		- Different fuel rods' functions will behave differently to depletion, some will "hold up" better than others.
		- Different reactor types and/or different fuel setups will exhibit different behavior, just because a function type loses effectiveness quickly or not doesn't mean you should change the design before or control rod level while running simply on that fact alone. Some fuels will regain their effectiveness immediately and then some if flux is increased even a little. Your response to lost effectiveness from depletion should vary depending on the aforementioned factors.

* Splits with
	+ Most fuels fission with "slow" neutrons, which means it requires moderators to be used efficiently. Some require "fast" neutrons, which means it should *not* be moderated.
* Splits into
	+ All fuels split into "fast" neutrons, which works in context with the above. With an exception is Low Enriched Schrabidium, which splits into "slow" neutrons.
* Flux function
	+ Fuels fission in different ways depending on the radioisotope and mixture, the given function describes how it does based on incoming flux, x, and outgoing flux, y.
	+ This function is given a danger rating from: safe (virtually impossible to meltdown with), medium (can melt down if you're careless), and dangerous (can meltdown extremely easily if you're not vigilant).
* Heat/tick at full power
	+ This statistic is to gauge how much thermal energy is released through fission, rather than flux.
	+ Full power means 100 flux, which is not does not necessarily mean 100 flux is the ideal flux amount for a rod, rather it's just to compare all rods the same way.
	+ If two fuel rods have the same function and receive the same flux, will emit the same flux, but if one has a higher heat output, it will generate more heat based on that flux and therefore make more electricity, but also be at a potentially greater risk of meltdown too.
* Temperature and Melting Point
	+ There are two temperatures of the item rod, skin and core temperature. Due to nuclear fuel's extremely poor thermal conductivity, the difference between the two can be drastic.
	+ The core can well exceed the surface temperature of the Sun in some cases while the skin is only a few hundred degrees. Do not worry about the core temperature too much, since only the skin temperature matters in context to the melting point of the rod and flow of heat to the fuel rod block.

#### Flux Function Types

*(If the fuel is self-igniting, it is automatically self-sustaining; Fuels that are not capable of self-sustaining criticality require a fuel that is to act as a driver, fuels that are theoretically capable of being self-sustaining means that it is possible to attain criticality with them purely, but it may not be practical to attempt it.)*

* Logarithmic
	+ Logarithmic functions are considered to be medium danger. They are capable of self-sustaining criticality.
	+ They rise in flux somewhat quickly, but that rise over run ratio decreases as x increases. It is still possible to melt down, but the function type gives you the proverbial "wiggle room". They are very resistant to the decreasing effectiveness due to depletion.
* Square Root
	+ Square root functions are considered to be medium danger. They are capable of self-sustaining criticality.
	+ They're similar to logarithmic functions in a general sense, where the rise in flux is relatively slow once at peak, but the rise over run remains roughly consistent and said peak is higher, making them somewhat more dangerous than logarithmic functions, but not significantly so. They don't resist the effectiveness loss from depletion as well as logarithmic functions, but notable loss only occurs with significant depletion.
* Euler
	+ Euler functions are considered to be safe. They are *not* capable of self-sustaining criticality.
	+ Very similar to logarithmic functions, but they use a natural logarithm (logarithm to the base of 'e', Euler's number) instead of a logarithm with a base of 10. The rise over run is very low which effectively caps out the flux and heat output. This makes the function very safe to use, but also very difficult since you will require the use of a more powerful driver fuel to allow it to reach criticality. On the flipside, this means that it can be used to act as buffers and mitigate the flux of very powerful fuels. By technicality, they are extremely resistant to the effects of depletion, due to plateauing out entirely above a certain threshold.
* Sigmoid
	+ Sigmod functions are considered to be safe. They are *not* capable of self-sustaining criticality.
	+ A very peculiar function, sigmoid functions start off very low, almost at 0 and then upon reaching a threshold it will rise almost instantaneously and the plateau out. This means that pushing flux beyond that initial threshold will not increase flux output and it will not decrease in flux output until falling back down that threshold, making it virtually immune to the effects of lost effectiveness from depletion. Sigmoid fuels may also be used as buffers like Euler, but due to their different behavior they can also be a notable contributor to the flux of the reactor too, plan ahead.
* Linear
	+ Linear functions are considered to be dangerous. They are *not* capable of self-sustaining criticality.
	+ Linear functions are the simplest functions to understand, the rise over run is constant and y is directly proportional to x. This means there is no critical level for this type of fuel, only subcritical or supercritical, this is because the function has no "peak" at all unlike most fuels. Attempting to run this fuel purely will result in meltdown guaranteed (unless perhaps using automatic control rods), so a driver fuel is a requirement. Making linear function fuels purely (or at least mostly) dependent on the driver will ensure that it will not become supercritical. Cons are that it is very easy to make the fuel become supercritical, pros are that the fuel is also easily predictable in behavior if managed correctly. Since linear has no peak, meaning that it will continue to rise at the same rate in response to incoming flux, this also means it's the most vulnerable to depletion and thus lose effectiveness the quickest from having no peak to rest on.
* Negative Quadratic
	+ Negative Quadratic functions are considered to be dangerous. They are *not* capable of self-sustaining criticality.
	+ These functions work virtually identically to linear functions, which actually makes them dangerous since, again, there is no middle ground between subcriticality and supercriticality without a driver and vigilant preparation. This also means they lose effectiveness quickly due to depletion by having no peak.
* Quadratic
	+ Quadratic functions are considered to be dangerous. They are *not* capable of self-sustaining criticality.
	+ Like an exponential function, quadratics will rise sharply and the rise over run will increase *exponentially* as x increases, effectively the antithesis to a logarithmic function. It is *extremely* easy to attain supercriticality with a quadratic function. The battle will be fought to keep incoming flux to only be enough to burn off poison and no more to prevent meltdown. This also means it will lose effectiveness extremely quickly as depletion rises.
* Sine Slope
	+ Sine Slope functions are considered to be experimental. It is capable of self-sustaining criticality.
	+ S Sine functions are *extremely* dangerous, capable of outputting insane amounts of flux even only given a tiny amount. After a certain level however, the flux will decrease, down the slope, then increase once again to an even greater peak, repeating indefinitely. As the name suggests, it is experimental and is not obtainable in normal gameplay.

### Steam Channels

These are the second most important part of a reactor, as they allow for generating energy with steam turbines and cooling down the reactor. Steam Channels take water from the bottom, and can be configured to output one of the following steam types:

* Steam (100 ºC)
* Dense Steam (300 ºC)
* Super Dense Steam (450 ºC)
* Ultra Dense Steam (600 ºC)

Depending on your steam type, you're going to need to run the reactor at a higher temperature to produce any of said steam. Steam channels also actively cool your reactor down by taking heat from it and using it to make steam, if they are empty they won't cool it down. Higher compressed steam types also ultimately produce more power and cool more.

Steam connectors, while not necessary, can make your reactor more pretty and realistic looking by connecting both pipes below the reactor instead of one below and one above. They can only be used in the configuration specified by the image attached (in exception to the steam pipe, which can be attached to any face except the top).

### Control Rods

Control Rods are an almost essential component to your reactor, which allows you to control the percentage of neutrons that can pass through it, and by consequence, how hot it runs. Some minimalist designs don't require this due to how the fuel works, but unless you don't want a meltdown, want to turn it off at some point, or want to control the reaction more precisely, you need to include these. You can change their color group to be able to control them in the console as a group. You can also set them manually, but you shouldn't really do this in case you have an emergency. All rods displayed in a console are fully inserted when you activate AZ-5.

Control rods are graphite tipped irregardless of them being fully moderated, so there will be spikes in criticality when inserting them below 10%. The spike is dependent on the starting position of the rods, so shutting down at from 100% means there is a brief moment where all neutrons are allowed to pass through. This means that AZ-5 may not be the safest option in all cases.

Come in moderated variants that automatically moderate neutrons passing through. Requires Bismuth to make however, which means you would need to run and deplete a lot of RBMK fuel already.

### Automatic Control Rods

Like the control rods, these control the neutron flow in a reactor. However, unlike normal control rods, these are activated by temperature: not by manual control. They have different types of insertion "curves" (actually graphing functions), as well as the ability to set minimum and maximum temperatures for insertion. They are useful for automated reactors running on highly reactive fuel or to add an automatic shutdown.

### Graphite Moderators

These will turn fast neutrons into slow (or thermal) neutrons for use in your reactor. Using the wrong neutron type reduces the reactivity of fuel rods, and could result in drastic inefficiency depending on the size and runtime of any given reactor. Since most fuels require slow neutrons to split, this is also a very important element of any reactor. Some fuels (like Neptunium) require fast neutrons instead, and using a moderator actually decreases their performance.

### Neutron Reflectors

Like the name implies, the reflectors send neutrons back to their source, increasing reactions without using more fuel. Depending on the design, this potentially increases efficiency significantly, on the other hand, using too many reflectors could lead to a meltdown if placed recklessly. It may also depend on the setup. Generally speaking, they're useful to improve performance, but in some cases they may be unwanted or unnecessary.

### Neutron Absorbers

Also self explanatory. These act like fully inserted control rods, except you can't raise them. Useful for sectioning off parts of the reactor so they don't interact with other parts, perhaps for multi-fuel or other radical designs.

### Irradiation Channel

These are basically just a breeding reactor for your RBMK, but it only has 7 recipes:

* Lithium -> Tritium
* Gold -> Gold-198
* Mushroom stew -> Glowing mushroom stew
* Natural Thorium -> Thorium Fuel
* Chlorinated Petroleum Wax -> High Performance Solvent
* Coal Tar -> Coal Oil
* Coal -> Coal Tar, Syngas
* PVC Bar -> C4, Colloid

To use them, they have to be irradiated by neutrons from adjacent sources, and have a valid item inside. Irradiation speed depends on incoming flux amount, fast neutrons are also only 20% as effective.

### Cooler

RBMK coolers keep the column's heat below 750 as long as it is supplied with a sufficient amount of cryogel and can be very useful to cool an extremely hot running RBMK.

### Structural Column

These don't do anything other than transfer heat and passively cool a reactor. They can be used to fill empty space between components.

### Console

The console is also a very important element of a reactor. With it, you can manage your reactor remotely, while also able to control several rod groups at the same time. To use it, one needs to use the RBMK Console Linking Device, then linking their reactor to the console. It has an area of 15x15 blocks. This doesn't mean the reactor can't be infinite, it means the console can only control that area at any given time. It also has an AZ-5 button, that when pressed, will fully insert all control rods within its control area. It can also set the control rods to more precise percentages, rather than in sets of 25. It also has configurable displays. There are up to six values that can be displayed like: Column temperature, Control rod extraction, Fuel depletion, Xenon and Fuel temperature by selecting a column and checking the panel on the top left corner in the console.

### Cover Panel/Lid

Cover panels prevent radiation from leaking out of the RBMK. They are no longer spawned on columns by default, so one must craft and place them on the RBMK to prevent radiation from being spewed out. Lead/Boron glass panels are a mostly aesthetic variant; their main benefit is shattering during a meltdown, preventing the panels from acting like a projectile and therefore reducing destruction.

## Mechanics

### Neutrons

Neutrons are what make fuel split and heat up. Neutrons are generated by fuels marked as self-igniting are in a fuel rod or when fuel is impacted by the right neutron type. Fuel has a tooltip which shows which neutron type it needs to split, as well as what type it splits into. Neutrons only travel horizontally and follow a straight path until they reach another fuel rod or a reflector. Self-igniting fuels generate neutrons automatically, and can react with itself; too many self-igniting fuel rods can potentially lead to a meltdown.

Neutron source rods are a "special" type of self-igniting rod, they do not fission and do not produce a lot of heat on their own. They also deplete quickly, so you should remove it and replace it with a regular fuel rod once the reaction has started to be most efficient.

### Heat

Fuel rods, when experiencing fission, generate heat. Heat is transferred to adjacent components, and can be used to generate steam for power generation. Components also gradually cool down through passive cooling, which increases depending on how many components your reactor has. This means you should be careful with adding too many structural columns, as it could cool the reactor down beyond any usable temperatures.

### Xenon Poison

Xenon-135 is a common product resultant from fission reactions, which can build up in the fuel rods of a reactor and act as an undesirable neutron absorber. Simply put, this is something that slows down fuel reaction when you don't want it. Xenon "burns" away at higher flux, so if your reactor can output enough neutrons, you shouldn't worry much about it. It may be problematic if you wish to run your reactor at low power however, as it may drop the reaction too much or halt the reaction entirely.

Xenon can also be a problem with certain types of fuels that require an initial neutron flux burst to initiate criticality and become self-sustaining or requires a significant driver to keep it critical. Xenon prevents this initial neutron burst from being as effective and thus requires increased power (ie raised control rods) to burn it off and attain criticality. This means that once the Xenon is burned off, the flux level will be at a level far higher than what would've been necessary, potentially causing a meltdown if the reaction doesn't stabilize itself or by means of lowering control rods.

### Fuel Temperature

When fuel reacts, it generates heat, which is shown as core and skin temperature. As stated before, core temperature doesn't matter too much, as it can be way higher than the skin temperature which is what transfers to the fuel rod block. Skin temperature is almost always higher than the reactor temperature even if you have good cooling due to heat transfer. As long as the skin temperature is nowhere near the melting point of the rod and flux is stable, you should be fine.

### Meltdown

Probably the most interesting part, a meltdown is when things get out of control and the reactor literally melts. It happens when the skin temperature gets past the melting point of a given fuel, or when a reactor component's temperature reaches more than 1500 ºC. It explodes violently, releasing debris and high amounts of radiation into the environment. Debris can be collected by hand and will give you the respective debris item. They can't be processed yet, and are just waste for now. After a meltdown, Corium replaces the fuel rods and is highly radioactive, while regular RBMK debris variants replace the rest of the components. Corium can melt into the ground if left too long without effective preventation. Corium solidifies over time, turning into corium blocks which are fatally radioactive in seconds; cleanup is extremely difficult until they have decayed as a result. Reactor Corium and Sellafite-Corium are not to be confused.

### ReaSim (Realistic Simulation)

ReaSim is both a gamemode 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 (they can also be made moderated with a cheaper recipe). Steam boiling can be done within any component column, this can be activated by gamerule dialReasimBoilers, water can be inserted and steam extracted with special inlets and outlets, however the only steam compression type usable is super dense.

## Tips and Trivia

* Based off the IRL RBMKP-2400 design.
* The IRL 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.
* A planned machine called a "deaerator", which is a machine that purifies water by removing dissolved oxygen and other gases, is to work in tandem with the RBMK.
	+ Either the boilers will switch to using this purified water or this water just runs better than regular water.

* 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.

* Control rod groups can be very useful if used right.
* In the 1.12.2 port, water pipes don't connect to the connectors but still function *(intentional/not a bug)*
* If things are getting out of control, AZ-5 could potentially make the difference between a saved reactor and a meltdown.
* The AZ-5/АЗ-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 АЗ-5.
* If you right click the "HOW 2 RBMK" book on the console, it will actually give you a guide book which is basically an abridged version of this wiki page.
	+ It can be burned in a furnace for 4 operations.
	+ Since the book is a part of the model, it will remain there even if you "take" it. There is a cooldown of several seconds until you can pick up another to mitigate this slightly.
* Highly prone to Chernobyl jokes.
	+ Which is not great, nor terrible
	+ Go Big or Go Boom
	+ Why is there graphite on the roof
* Some fuels are not finished.
	+ Some are not craftable, balanced, or even added yet.
* Spent fuel can contain Xenon-135 poison, which can be extracted in tiny amounts if it is high enough.
	+ If you do not wish to have the Xenon byproduct, you can just expose the highly depleted rod to a neutron source rod (maybe near some neutron reflectors so you don't have to use too many source rods) and when the Xenon burns away, remove it manually.
* 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.

## 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.
	+ Takes *lots* of Asbestos and rare earths like Zirconium and Boron.
* 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.

## Design Philosophy

*See also: Guide: Designing A 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.)

Minimalist RBMK design, takes self-igniting fuel.Neptunium RBMK reactor, uses neptunium fuel for the outermost layers.Common RBMK design.Idiot-proof™️ design. Uses a self-igniting plutonium rod in the middle, U235 in the outer rods and neptunium in corner rods.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.RBMK with irradiators.Funny ReaSim RBMK for breeding dangerous fuel.A large pure NU ReaSim RBMK, utilize normal fuel rods and moderated control rods