Big Reactors: A spreadsheet, mechanics summary and reactor example. (2024)

So instead if hijacking that other threat I thought I'd update mine. Lets start by stating that yes, my spreadsheet is still up to date! There is no difference between version 0.3 and 0.4. Its just an update from 1.6.4 to 1.7.10. Nothing more, nothing less.

The spreadsheet: Big Reactors v0.3 and v0.4 - Actively cooled.

From that the following information still stands. Note that these should be taken as guide lines to help you design your own reactor. Feel free to look at my spreadsheet and copy anny design you like. But where is the fun in that? Try and beat my reactors instead!


  • Ender is the best outside coolant. More layers of coolant is better. More layers Significantly reduces block efficiency. Max 4 layers on the outside.
  • Outside coolant layers bigger then 1 should consist of the outer most layer of resonant ender and the inner layers of cryotheum.
  • Cryotheum is the best coolant inbetween rods. 1 coolant between each rod is best. In some smaller/cooler designs Graphite can be better.
  • Coolants are needed inside an actively cooled reactor, the cooling effects actually stack!
  • Coolant is not needed in area's where radiation does not travel (see radiation). So the corners can be annything you want.

Theoretical best:

  • As big as you can build it. Keep the rod's as square as possible for maximum efficiency. IE: 15x15x7 has a 11x11x5 core of fuel rods, 2 layers of coolant and 2 for the casing.
  • One big block of fuel rods "dotted" with crytheum. Aka, 1 Crytheum completly surrounded in fuel rods.
  • Suggested 1 layers of coolant between Fuel Rods and casing. Resonant Ender is the strongest. Alternatively, up to 4 layers will work: 3 layers of Cryotheum and the outermost layer of Resonant Ender


  • Higher levels of radiation is better. Produced in fuel rods. Travels upto 4 blocks in north/east/south/west direction (Not diagonal or up/down).
  • The more fuel rods inside that 4 block area, to higher the radition level inside a reactor.
  • The higher the radiation the less fuel used.


  • Lower is better. Ideal as low as you can get it. Aslong as this is under a 1000 degrees then Radiation is more important.
  • After ~1000 Degrees reactor efficiency drops significantly. If you only got 1 coolant layer then adding additional coolant layers might help you out here. (bigger reactor, more heat allowed to reach the same temperature)
  • Steam stored inside the reactor increases reactor temperature, PUMP IT ALL OUT. Alternatively, adjust fuel rod insertion to lower steam production
  • Bigger reactors will eventually go well over 1000 and even 2000 degrees. This is because of the amount of heat generated from coolants absorbing it. There is nothing you can do against this yet, the next mayor version might have a an interesting block to solve this.

Rod Control:

  • Reduces reactor temperature, radiation, fuel efficiency, steam production and fuel consumption.
  • Can be used to tweak superior reactor designs to match desired steam output.
  • Can be used to increase fuel efficiency. Certain reactor setups have better efficiency when controlled down.

This part: "Rod Control: Certain reactor setups have better efficiency when controlled down. " is probably the most important part to understand when looking for efficient reactors. As all passive cooled reactors are actually significantly more efficient when controlled down. Its only active reactors that can go all out and be efficient.

Explaining coolants:
A good page to take a look at as far as cooling goes is this one. It shows the datamined properties of coolants. Including the 4 important stats to look at: Absorbtion, Heat efficiency, moderation and thermal conductivity. For a quick explanation:

Skyqula said:

  • There are 2 types of radiation, fast and slow.
  • slow radiation can be absorbed by coolants. How much is determined by its absorbtion stat.
  • Absorbing radiation generates heat wich is used to calculate RF/t or steam/t. A high heat efficiency is obviously good to have as it determens how much of the absorbed radiation is turned into heat.
  • Fast radiation can be slowed down. How well is determined by its moderation stat.
  • Coolants next to a rod cool the reactor down. All that matters is the number of rod sides that are connected to coolants. IE: Build a 2x2 rod with coolant all around has 8 exposed sides. Fluids next to a rod should have a high heat conductivity.
  • Slow radiation passing trough a fuel rod increases a reactors radiation level and in turn reduces fuel burnup.

As you can see there are a few things you can play around with. But generally this is what it comes down to:

  • Cryotheum is good at cooling with a high heat conductivity
  • Cryotheum is the best moderater
  • Cryotheum has the highest heat efficiency
  • Resonant Ender has the highest absorbtion
  • Resonant Ender has the highest absorbtion * heat efficiency
  • Graphite blocks have nearly no absorbtion (realy good for letting radiation trough to fertilize fuel rods)

Taking the above aswell as knowing that radiation travels a maximum of 4 blocks we get:

  • Cryotheum between fuel rods. Graphite is a close second (better in some low temperature reactors, it is defenitly worth to try it).
  • 3 layers of cryotheum between rods and casing. Absorbs most radiation with the highest efficiency. (optional)
  • 1 layer of Resonant Ender between casing and Cryotheum. Last block radiation can be absorbed. Highest value for absorbtion * heat efficiency, meaning the most heat generated. If you use only 1 layer of coolant, use Resonant Ender.

All that theory is to complicated, whats a good reactor?

My favorite design looks as follows:

Skyqula said:

  • Grey = Casing
  • Green = Resonant Ender
  • cyan = Gelid Cryotheum
  • Orange = Fuel Rod
  • White = Annything, I preffer Glass, but can also be air.

The resonant ender can also be Gelid Cryotheum, it doesnt matter to much. But for pure max efficiency its the best.

For passive cooling:

it goes from 13.4k RF/t with a fuel efficiency of 97M RF per fuel ingot for 1 layer to 55k* RF/t for 5 layers with a fuel efficiency of 96M RF per fuel ingot.

*note: This value is lower then expected. This is because the reactor is starting to overheat and more and more radiation is being turned into fast radiation, lowering energy production. If you need this much power, I highly suggest moving to turbines.

For active cooling

: it goes from ~6850 mB/t with a fuel efficiency of 828M* RF per fuel ingot for 1 layer (3 high) to 40B/t with a fuel efficiency of 1099M* RF per fuel ingot for 5 layers (7 high).

*note: Assuming a ludicrite turbine mentioned below wich produces 27800 RF/t at 2000mB/t.

Some Reactor building tips:

  • Use a Extra Utilities builders wand. Saves you alot of block placing!
  • Use a Buildcraft Floodgate. Easy to fill anny Reactor with a single coolant type!
  • Prebuild your reactor in creative and save it to a BC blueprint. Note that it doesnt save anny big reactor blocks. But it does save the coolants! Making it easy to build a reactor with both resonant ender and cryotheum. Simply use the builder to fill it for you!
  • You can pre-design your reactor using this online simulator!

So what about turbines?

I didnt do anny research on turbines. The only one I did was make one using ludicrite. Namely a 7x7x16 turbine with 4, 8 block coils of ludicrum and 80 blades. it produces ~27800 RF/t and consumes 2B/t. If you want more information, I suggest you take a look at this spreadsheet made by @Saice.

A screenshot of the turbine aswell as the reactor used wich produces just under 2000mB/t good for a fuel efficiency of 617M RF per fuel ingot:

Skyqula said:

Big Reactors: A spreadsheet, mechanics summary and reactor example. (3)

Big Reactors: A spreadsheet, mechanics summary and reactor example. (4)

Yes, thats only 3 Resonant Ender source blocks!

I can give you a usefull tip: A turbine will convert all steam back to water without anny loss. Meaning you only need to fill the reactr with water once and you will never have to do it again. Just make sure you extract the steam/water fast enough or set the turbine to never fent fluids.

Reactor fuels?
There are 2 types of fuel for Big Reactors. Yellorium and Blutonium. Both ingots and blocks work. Additionally, if the oredictionary with Uranium is set to true then Uranium and Plutonium are valid aswell.

Interesting fact: 1 yellorium = 2 fuel cycles.

1 yellorium ==> 1 cyanite ==> 1/2 blutonium
1/2 blutonium ==> 1/2 cyanite ==> 1/4 blutonium
1/4 blutonium ==> 1/4 cyanite ==> 1/8 blutonium
1/8 blutonium ==> 1/8 cyanite ==> 1/16 blutonium
1/16 blutonium ==> 1/16 cyanite ==> 1/32 blutonium

In other words: 1 + 0.5 + 0.25 + 0.125 + 0.0625 + 0.03125 + etc

Taking just the above values we get 1.96875. Wich is already enough to see that we are aproaching 2.

A better explanation here.

BR vs IC2

lets look at the mechanics, they arent all that different.

  • IC2 has you move around parts inside an UI. Big Reactors has you rebuild your entire reactor.
  • IC2 has a readiation mechanic with cooling and reflecting, Big Reactors has a radiation mechanic with cooling, moderation and absorbtion.
  • IC2 Uses a single uranium ingot for 3 cycles, Big Reactors for 2.
  • An IC2 reactor costs no uranium to build, Big Reactors does (Startup cost).
  • IC2 starts at an efficiency of 1-5 (3-15 adjusted for fuel cycles) or assuming the IC2 "standard" of 4RF = 1EU 4-20 (12-60)MRF. Big Reactors has a wide range but starts around 9-250(18-500 adjusted for fuel cycles)MRF. Buildup and total cost of the reactor, aswell as resources drain speed are significantly higher for BR then IC2 at max range. Additionally, IC2 builds up Plutonium.
  • IC2 has MOX reactors at an efficiency of 25 or 100 MRF. Big Reactors has turbine at an efficiency ranging from 20M to 1568M. Buildup and total cost of the reactor, aswell as resources drain speed are ludicrously higher for BR then IC2 at max range. Ontop of needing to configure 2 layouts instead of 1.
  • IC2 has left over Plutonium wich can be used to generate EU free using Radioisotope Thermoelectric Generators. Big reactors has no such mechanic.
  • Interesting side effect: Converting yellorium into cyanite into blutonium into RTG pellets is the quickest way to get Radioisotope Thermoelectric Generators going. (the x10 fuel use is actually helping here!)


  • At small scale, BR and IC2 are realy close in terms of just about everything (Default settings!!!).
  • Big Reactors can be made significantly bigger for better efficiency and way higher cost.
  • In the end IC2 wins because of infinite power trough RTG's.

BR is OP, how would you nerf it?

  • Reduce maximum reactor size. Greatly reduces maximum efficiency potential. Something like: 15x15x15 or 9x9x13, exterior ofcourse.
  • Dont increase fuel consumption, actually beneficial with packs that contain IC2 and is completly pointless with a proper reactor design. You can go as high as x40 and still be able to run a possitive loop. This "nerf" is the definition of a bad change!
  • Reduce turbine power output. Turbine power output is realy high and far outperforms anny other mod. It has a price, ofcourse. Try something like a turbine power multiplier of 0.5 or reduce turbine power to 0.8 and total power output to 0.8.
  • Disable uranium unification. Prevents yellorium ==> plutonium for free unfinite power trough IC2 RTG's.
  • Disable cyanite crafting recipy, its cheap and makes getting turbines realy quick and helps out with the IC2 RTG situation. It also combos realy well with the next point...
  • Disable the power port. This effectvely disables passive reactors, in combination with a disabled cyanite crafting recipy this means people would first need to make a breeder reactor to get cyanite before they can start producing power.

I plan in redoing the spreadsheet when version 0.5 of Big Reactors comes out. This version, according to the roadmap, will change the coolant values around to provide more variaty. Meaning ill get to redo everything Big Reactors: A spreadsheet, mechanics summary and reactor example. (5)

As previously, found a mistake? Found something new? See a way to improve? Do comment!

Big Reactors: A  spreadsheet, mechanics summary and reactor example. (2024)


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