Category:RBMK fuel

RBMK Fuel is fuel that is used in the RBMK. It consists of a variety of types of fissile nuclear material contained in a zirconium-steel casing which can be reused after the depletion of a full fuel assembly.

Production

Fuel assemblies for the RBMK are typically crafted by filling an empty fuel assembly with the fuel material in the following fashion:

Properties

Yield

• Not listed, but all fuel assemblies have an initial total yield that reduces as the assembly emits neutron flux. Most fuels have a yield of 100,000,000 but certain more niche fuels such as breeder assemblies have lower yields (faster depletion) and certain neutron sources have higher yields (slower depletion).

Depletion

• Depletion is the total amount of yield remaining in a fuel assembly as a percentage of its total possible yield, going from 0% to 100%
• This is primarily of concern in deciding when to replace a fuel assembly as it will become less reactive as it reaches 100% depletion, but also has special behavior in regards to fuel breeding which can be further explored in Guide: RBMK Fuel Recycling.
• Certain kinds of fuels will behave differently as they deplete which will be covered below.

Decay Function

• Another unlisted component, defines how a fuel's total reactivity will change according to its depletion.
• Can be:
  • Linear
  • Raising Slope (small increase to 120% power then a steep decrease)
  • Boosted Slope (small decrease, then a steep increase to 135% power, then an even steeper decrease)
  • Gentle Slope (tiny increase to 101%, then a slow decrease)
  • Static (no change)

Xenon Poison

• Represents the total amount of xenon neutron poisoning the fuel assembly is experiencing from 0% to 100%. At 100% poisoning, no flux will reach it.
• Xenon is gained and lost according to the fuel assembly's xenon gen and xenon burn function which will be covered later.

Splits With

• What type of neutrons are most efficient at reacting with the fuel assembly.
• A fuel assembly that reacts with slow neutrons will be 100% efficient if hit with slow (moderated) flux and 50% efficient if hit with fast flux.
• Vice versa with a fuel assembly that reacts with fast neutrons but at 30% efficiency rather than 50%

Splits Into

• What type of neutrons the fuel assembly will emit when outputting flux.
• All fuels split into fast neutrons besides from LES (Low Enriched Schrabidium) and neutron sources.

Flux Function

• The amount of flux that a fuel will output given a certain amount of input flux by evaluating a mathematical function where x is the input flux amount.
• Classified in ascending order of danger as Passive, Euler, Sigmoid, Logarithmic, Square Root, Negative-Quadratic, Linear, and Quadratic. The exact behavior of each of these functions will be described below.
• As stated previously in Depletion, the depletion of a fuel assembly will affect the exact behavior of the flux function by applying a multiplicative modifier to the fuel assembly for certain amounts of depletion. The exact behavior of these depletion functions will be described below.

Xenon Gen

• The amount of xenon the fuel assembly generates for a given amount of flux, usually x*0.5 but sometimes x*0.0 for certain types of fuel.
• Fuel assemblies are constantly generating xenon but in normal operation, it is burned away instantly.

Xenon Burn

• The amount of xenon the fuel assembly burns for a given amount of flux, usually x2/25
• This in tandem with the xenon gen function means that a fuel assembly will be xenon-free if emitting more than 25 flux with it burning xenon much faster the closer it comes to 25 flux.

Heat Per Flux

• The amount of heat the fuel assembly generates in its core for each unit of output flux.
• Usually greater for highly reactive rods and lesser for less reactive rods.

Diffusion

• The rate at which heat travels from the core of the fuel assembly to its skin, represented as what percent between 0.0 and 1.0 of half of the difference in temperature between the core and the skin will be transferred from the core to the skin.
• Labelled with the symbol "½" in game.
• For example, if a fuel assembly has a 11,000C core, a 1,000C skin, and a diffusion of 0.1, then it will send (10000-1000)/2 * 0.1 (500) degrees C to the skin.

Skin Temp

• Temperature of the fuel assembly's skin which is transferred to the column it is in in the same way heat diffuses in the rod but with a diffusion coefficient of 1.
• Can factor into a meltdown, so careful attention to its value is recommended.

Core Temp

• Temperature of the fuel assembly's core which is transferred to the skin according to the diffusion coefficient and equation above.
• Can never factor into a meltdown.

Melting Point

• Temperature at which point the fuel in the fuel assembly will begin to melt which will nearly always result in a meltdown.
• The exact function of fuel reaching its melting point is that upon reaching or exceeding it, the rod's core temperature and skin temperature are added up and divided by 3. This value is then added to the skin heat, core heat, and the temperature of the fuel rod the fuel assembly is residing in which is nearly universally fatal except for specific rods like the Ra226Be neutron source with a melting point of only 700C

Decay Function Cont: Decay Function Types

Each function is plotted from 0% depletion to 100% depletion with a maximum possible value of 1.50x reactivity.

• 

  Function "Linear"

• 

  Function "Gentle Slope"

• 

  Function "Raising Slope"

• 

  Function "Boosted Slope"

Flux Function Cont: Flux Function Types

Note: Any self igniting fuel is necessarily self-sustaining.

Passive

• Outputs a constant amount of flux whose magnitude does not change in response to a greater amount of input flux.
• The safest function, especially paired with the fact that it is present only in neutron sources which as a whole have a low thermal output.
• Self-sustaining (technically).

Euler

• Outputs an amount of flux according to a constant minus an inverse natural exponential function, producing a curve that rapidly grows to within microscopic fractions of a maximum value but never passes it.
• A very safe function as it has an absolute maximum possible flux output which a reactor can be designed around.
• Self-sustaining.

Sigmoid

• Outputs an amount of flux according to the reciprocal of a positive inverse natural exponential function, producing a curve that grows slowly at first before rapidly rising and then reaching a euler-like peak, resembling the shape of an S.
• Similar in safety to euler but its tendency towards falling into low reactivity states make encourage reckless control rod use.
• Not self-sustaining

Logarithmic

• Outputs an amount of flux according to a base 10 logarithm, producing a curve resembling exponential growth but rotated, producing an output that grow exponentially smaller for the same increase in input as it becomes larger.
• Also a very safe function. Has no absolute maximum limit but will very strongly resist large increases in reactivity.
• Self-sustaining.

Square Root

• Outputs an amount of flux according to a square root, producing a curve resembling quadratic growth but rotated in the same way a logarithmic function is.
• Reasonably dangerous, responds to increases in reactivity pretty readily and has a much softer cap than logarithmic but can still be safely run as the sole fuel in a setup.
• Self-sustaining.

Negative Quadratic

• Outputs an amount of flux according to a highly stretched negative quadratic function, producing an output that behaves very similar to linear but very gradually lowers in reactivity as it reaches immense flux values.
• Very dangerous, the level where it begins to reach a stable flux equilibrium is so high and the heat output of rods with this function are all so high that it will inevitably melt a reactor down.
• Practically not self-sustaining.

Linear

• Outputs an amount of flux according to a linear function, producing a straight line that guarantees that an exact fraction of input flux will be returned as output.
• The most typical dangerous function, primarily on account of the fact that if allowed to react with itself past a certain margin then it will inevitably melt down as it enters into an exponential feedback loop of it continually outputting more flux than it takes in forever.
• Not self-sustaining.

Quadratic

• Outputs an amount of flux according to a quadratic function, producing a rapidly growing curve that resembles gravitational acceleration but reversed.
• Immensely dangerous, entering into a state of unfathomably high flux if ever exposed to its own neutrons reflected back at it which nearly instantly will result in a meltdown.
• Self-sustaining.

Sine Slope

• Outputs an amount of flux according to a sinusoidal function, producing a curve that rapidly alternates between high and low flux output.
• Currently just implemented in test functions, but has more of weird and unpredictable behavior than most other fuels.
• Sometimes self sustaining, sometimes not self sustaining

Fuel Stats List

Note: The xenon burn function is the same for all fuel types, that being x2 / 25

Name	Yield	Decay Function	Splits With	Splits Into	Flux Function	Xenon Gen	°C/Flux	Diffusion	Melting Point (°C)	Self Igniting
NU	100,000,000	Raising Slope	Slow	Fast	Logarithmic	x * 0.5	0.65	0.02	2865.0	No
MEU	100,000,000	Raising Slope	Slow	Fast	Logarithmic	x * 0.5	0.65	0.02	2865.0	No
HEU235	100,000,000	Gentle Slope	Slow	Fast	Logarithmic	x * 0.5	1.0	0.02	2865.0	No
HEU233	100,000,000	Gentle Slope	Slow	Fast	Linear	x * 0.5	1.25	0.02	2865.0	No
ThMEU	100,000,000	Boosted Slope	Slow	Fast	Euler	x * 0.5	0.65	0.02	3350.0	No
LEP239	100,000,000	Raising Slope	Slow	Fast	Logarithmic	x * 0.5	0.75	0.02	2744.0	No
MEP239	100,000,000	Gentle Slope	Slow	Fast	Square Root	x * 0.5	1.0	0.02	2744.0	No
HEP239	100,000,000	Gentle Slope	Slow	Fast	Linear	x * 0.5	1.25	0.02	2744.0	No
HEP241	100,000,000	Gentle Slope	Slow	Fast	Linear	x * 0.5	1.75	0.02	2744.0	No
LEA	100,000,000	Raising Slope	Slow	Fast	Square Root	x * 0.5	1.5	0.02	2386.0	Yes
MEA	100,000,000	Gentle Slope	Slow	Fast	Negative Square Root	x * 0.5	1.75	0.02	2386.0	Yes
HEA241	100,000,000	Gentle Slope	Slow	Fast	Square Root	x * 0.5	1.85	0.02	2386.0	Yes
HEA242	100,000,000	Gentle Slope	Slow	Fast	Linear	x * 0.5	2.0	0.02	2386.0	No
MEN	100,000,000	Raising Slope	Any	Fast	Square Root	x * 0.5	0.75	0.02	2800.0	No
HEN	100,000,000	Gentle Slope	Fast	Fast	Square Root	x * 0.5	1.0	0.02	2800.0	No
MOX	100,000,000	Raising Slope	Slow	Fast	Logarithmic	x * 0.5	1.0	0.02	2815.0	No
LES	100,000,000	Gentle Slope	Slow	Slow	Square Root	x * 0.5	1.25	0.02	2500.0	No
MES	100,000,000	Gentle Slope	Slow	Fast	Negative Square Root	x * 0.5	1.5	0.02	2750.0	No
HES	100,000,000	Linear	Slow	Fast	Linear	x * 0.5	1.75	0.02	3000.0	No
LEAus	100,000,000	Linear	Slow	Fast	Sigmoid	x * 0.5	1.5	0.02	7029.0	Yes
HEAus	100,000,000	Gentle Slope	Slow	Fast	Square Root	x * 0.5	2.0	0.02	5211.0	No
Ra226Be	100,000,000	Linear	Slow	Slow	Passive	x * 0.0	0.035	0.5	700.0	Yes
Po210Be	25,000,000	Linear	Slow	Slow	Passive	x * 0.0	0.1	0.05	1287.0	Yes
Pu238Be	50,000,000	Gentle Slope	Slow	Slow	Square Root	x * 0.5	0.1	0.05	1287.0	Yes
Bismuth ZFB	50,000,000	Gentle Slope	Slow	Fast	Square Root	x * 0.5	1.75	0.02	2744.0	No
Pu241 ZFB	50,000,000	Gentle Slope	Slow	Fast	Square Root	x * 0.5	1.0	0.02	2865.0	No
RGA ZFB	50,000,000	Gentle Slope	Slow	Fast	Linear	x * 0.5	1.75	0.02	2744.0	No
Flashgold	100,000,000	LInear	Slow	Fast	Negative Square Root	x * 0.0	1.0	0.02	2000.0	Yes
Flashlead	250,000,000	Linear	Slow	Fast	Negative Square Root	x * 0.0	1.0	0.02	2050.0	Yes
Balefire	100,000,000	Gentle Slope	Slow	Fast	Linear	x * 0.0	3.0	0.02	3652.0	Yes
Digamma	1,000,000	Gentle Slope	Slow	Fast	Quadratic	x * 0.5	0.1	0.02	100000.0	Yes

Usage

For more information, see: Guide: Recycling Depleted Fuel and Guide: RBMK Fuel Recycling.

The RBMK has a more unique processing of reprocessing spent fuel than the other reactors. Every 20% interval (with an exception for the required 1% minimum to be able to disassemble a fuel rod to begin with) of depletion denotes a different level. The proportion of recycling products correlate to the depletion level. Fuel pages will go into specifics about the outputs for each byproduct at each depletion level.

Also note that fuel must have a hull and core temperature of 50 or cooler before they can be disassembled. Non-self-igniting fuel can be cooled off quickly in a powered down RBMK. Alternatively, if that is not possible or if the fuel is self-igniting, they can be cooled off in a spent fuel cooling pool.