Feed The Beast Wiki
Feed The Beast Wiki

This is a community-written guide. It was written to help players to get accustomed to NuclearCraft.


NuclearCraft is a tech mod that focuses on generating power using nuclear reactors. It is intended to be used in mod packs to provide power for your activities. Unlike Extreme Reactors, NuclearCraft takes a semi-realistic view, introducing radioactive isotopes, multi-step chemical processes for crafting and realistic nuclear fission and fusion byproducts. The consequences of mistakes are less cinematic than in other reactor mods.

About this Guide

This guide is not an exhaustive description of items, nor a tutorial on using each item, and does not touch on every aspect of the mod. It is a helping hand to get you started with NuclearCraft, particularly the mod's fission reactors. Throughout this guide you'll find links to various blocks and items. Be sure to explore these links for full details, descriptions and illustrations and also check out the Navigation Box at the bottom of the page for more info about other parts of the mod that are not covered here.

The foundation

Start by stockpiling all the NuclearCraft ores that you find. You'll need a lot. You'll also need quite a lot of
Coal and
Iron, some
Nether Quartz,
Lapis Lazuli and

Unless other power options are available to get started, your first step is to create a Decay Generator to power your early machinery. Decay Generators generate power from the heat generated by the decay of adjacent uranium and thorium blocks - they are very inefficient so you'll want to upgrade pretty quickly.

Now craft your first NuclearCraft utility machine, the Manufactory. With it, you will create Crushed Coal, Graphite Dust and Crushed Quartz, and can also be used as a simple ore doubler if you choose. The recipe is rather simple. It requires the first example of a NuclearCraft machine component: a Copper Solenoid.

At this point, consider replacing your Decay Generators with Basic Solar Panels (5 RF/t during daylight) or Uranium RTGs (4 RF/t constantly).

Now your power is a little more stable, make an Alloy Furnace. You'll be using this machine a lot, so you might want to make more than one.

If you already have a good RF power generation setup, consider adding some Speed Upgrades to your machines.

The Isotope Separator is your next step and the most important parts of initial nuclear material processing. It separates materials into their constituent Isotopes.

Once you have your Isotope Separator set up, it is time to build your first Fission Controller, the heart of a Fission Reactor.

Building a Fission Reactor

We're almost ready to make our first, very basic Fission Reactor, but we're going to need a lot of Basic Plating, Tough Alloy and Steel to make one. The main article on Fission Reactors describes how to build a Fission Reactor in general, but this section will show how you may want to go about coming up with your own reactor designs. For simplicity, we will consider only a few of the the cheaper passive coolers, and also leave out the consideration of active coolers. You'll need to decide how big a reactor to make: due to the complex nature of how Fission Reactors work, it's not really possible to recommend a best size - you're going to have to think carefully about your design from the get-go. As a demonstration, we will construct a small, 3×3×3 reactor using LEU-235, an entry-level fuel (Try taking your Uranium or Yellorium ingots and putting them in your Isotope Separator):

Reactor Components

A basic fission reactor consists of five main components: the controller, casing, cells, moderators and coolers:

The Fission Controller is the heart of the reactor - it takes in nuclear fuel and outputs their depleted counterparts and keeps note of the reactor's heat and power gen stats.

Reactor Casing is used to build the shell of the reactor structure. Every fission reactor consists of a cuboidal interior enveloped by a layer of casing - each side of the interior must be covered, but crucially, the edges must not be or the reactor structure will not be recognised!

The Reactor Cells hold the fission fuel while it is depleting and generating heat and power. Basically, the more cells, the more heat and power produced. Additionally, cells directly adjacent to one another or separated by at most four moderator blocks in a straight line will become more efficient and generate more power - this does come at a cost of generating more heat, though.

The moderator blocks (currently Graphite or Beryllium) are used to increase the efficiency of the reactor. For every cell adjacent to each moderator block, additional power and heat is produced, making the reactor more efficient, again at a cost of producing more heat.

The coolers are the blocks which remove excess heat from the reactor. This is very important, as a reactor that overheats will melt into a nasty mess of molten corium. There are fifteen coolers available, and as well as each having their own cooling rates, they also have their own placement rules - each cooler's positioning must satisfy certain conditions to function, making cooling a reactor the most complex aspect of building a safe reactor.

Again, for more in-depth information about the mechanics of these blocks, consult the dedicated article on the Fission Reactor.

Designing the Reactor

The interior of the empty 3×3×3 reactor.

The best place to start is to estimate a reasonable number of cells to put into our reactor. To do this, it is useful to refer to this list of all of the available coolers' stats, which is also available in-game on the coolers' tooltips. It will also be useful to keep the fuel's base stats in mind, taken from this page: 120 RF/t, 50 H/t.

The four cell pillars with graphite between each pair.

A 3×3×3 reactor has 27 spaces to put cells, moderators and coolers. Let's consider the cooling required for four sets of pairs of cells connected by a graphite block:

The heat generated by these cells, according to the mathematics of heat generation (explained in the main Fission Reactor article), is 8×[50×(2×3/2) + 50×2/3] = 1467 H/t. These cells and moderators would take up 12 blocks, so we would have 15 left. This means we require an average of at least 1467/15 = 97.8 H/t of cooling per block space. Looking at the available coolers' cooling rates, this is definitely a viable option, so we will go for it.

Lapis cooler positioning. The front-most cooler has been removed for visibility.

Given the compact nature of our design, we have a lot of options to consider - we want to find the cheapest cooling configuration that will give us a heat-negative reactor:

The simplest coolers to consider are the water, redstone and lapis varieties. Because all of the spaces redstone coolers are valid for (adjacent to at least one cell) are also adjacent to casing, the lapis can go anywhere that the redstone can, and so immediately seems to be the better option. We therefore place eight lapis coolers down in all positions available to them, for a combined cooling power of 8×120 = 960 H/t. In more open designs, where cells are not necessarily near any casing, it is better to go with water and redstone coolers to then set up valid spaces for gold and iron coolers.

Glowstone cooler positioning. The front-most lapis cooler has been removed for visibility.

The next places to consider are the four spots between the graphite blocks. As there are two adjacent moderator blocks for each of these positions, the best option to go with is four glowstone coolers, adding 4×130 = 520 H/t to the total cooling power for a total of 960+520 = 1480 H/t.

The fully-cooled reactor, finished off with two faces of transparent casing.

As the heat generated by the fuel is 1467 H/t, we have already got all the cooling we need for our cell structure! This means we could try to replace one of the lapis coolers with an extra graphite block between two of the cells. However, unless we are able or prepared to use more expensive coolers, dealing with the additional heat in the last three available block spaces would be impossible, as the new heat level would be 6×[50×(2×3/2) + 50×2/3] + 2×[50×(3×4/2) + 2×50×3/3] = 1900 H/t, so we would need an extra 1900-1480+120 = 540 H/t of cooling, or an average of 540/3 = 180 H/t per remaining block space.

The additional moderator block, the extra heat of which we will attempt to deal with.

If you do not yet have access to cryotheum and liquid helium, then the four pillars of cells is as far as is possible to go for a heat-negative reactor, generating 8×[120×2 + 120×2/6] = 2240 RF/t.

However, if you can build these coolers, then it is possible to deal with the additional heat generated by the addition of the graphite block. Cryotheum coolers must be adjacent to at least two reactor cells, and so any of the lapis coolers could be switched out for cryotheum, resulting in an extra cooling rate of 40 H/t per exchange. Keeping this in mind, we now look at the centre column of the reactor, which has still not been filled.

New cryotheum coolers and additional tin, copper and magnesium coolers for some additional cooling.

On the bottom layer of the reactor, the only adjacent coolers are lapis coolers, and so immediately a tin cooler, which must sit between two lapis coolers, seems like the best option, for an extra 100 H/t of cooling power. We then look at the centre position which is surrounded by glowstone coolers. Here, the obvious choice is a copper cooler - which requires at least one adjacent glowstone cooler - for another 80 H/t. Finally, we have the top-centre position, adjacent to three lapis and one graphite. Again, the tin cooler is an option, but the adjacent graphite makes a magnesium cooler the best option, at 110 H/t. After these three coolers are added, we bring the required extra cooling down to 540-100-80-110 = 250 H/t. We can also replace two lapis coolers on the bottom layer and all three on the top layer for an additional 5×40 = 200 H/t of cooling... but this is not enough - we still have 50 H/t left over!

The bottom layer of our design as it stands.

We now have to go back to check if we can improve on the cooling configuration anywhere - the first place to check is the lapis coolers and tin cooler on the bottom layer. Originally, we discarded the idea of using redstone coolers, but we should use one in place of one of the lapis coolers here to set up a liquid helium cooler instead of the tin cooler at the centre.

This new set of coolers has an additional 50 H/t of cooling power.

This replacement of lapis and tin with redstone and liquid helium only gives us an extra 140+90-120-100 = 10 H/t of cooling, but we can now also replace the final lapis cooler with a cryotheum cooler for another 40 H/t of cooling! So with these two changes, we have now dealt with the extra 50 H/t that we needed to get rid of!

The new heat-neutral reactor, finished off with two faces of transparent casing.

This more efficient (albeit more expensive) reactor is heat neutral, and so can run indefinitely, and generates 6×[120×2 + 120×2/6] + 2×[120×3 + 2×120×3/6] = 2640 RF/t, an 18% improvement on the original design.


Hopefully this guide has been useful in getting you up and running with your first reactor. Your next step is to explore the various links in this wiki, learn about the other parts and see what amazing reactors you can make! Separate articles on Fission Reactors and Fusion Reactors will go into more detail on advanced reactor design.