Fission Power

The Fission Reactor is certainly an uncommon sight in GregTech - both in theme, and how it works. But fear not, we are here to guide you with this multi-purpose big-brain multiblock!

The most important thing you should know is that the reactor is like a big thermal battery-generator. You input proper fuel, and get heat (just like EU/t) that gets stored in the reactor as rising temperature (stored EU).

You can then transfer this heat to coolant fluids for running turbines, or performing EBF-style crafting recipes.

Fission's gameplay loop is mostly about delicately balancing the heat generated by a fuel rod against how fast your reactor can cool itself down. Manage this correctly, and you'll have more power than you know what to do with!

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Note the central column of Fuel Holders and empty space for Components and Material Holders.

Fission Mechanics

The more fuel rods you have installed in the reactor, the hotter it gets. And the hotter it is, the more heat it is able to transfer out to the coolant fluid and processable items.

But physics has its limits, and the reactor can only ever get so hot, so don't install too many fuel rods.

But fear not! Should the heat level of the reactor border dangerous territory, the reactor enters an automatic cooldown sequence, and won't start again until all heat has been safely dissipated.

It's quite slow, though, and that's valuable time you could be using to produce more power instead. This cooldown also damages the fuel rod, making it produce less byproducts when it's depleted.

Components
Components

In addition to the 5 Fuel Holders, you can install up to 20 Components.

The stats of all installed components will simply be summed up, and that's it! No other fancy positioning required.

Components can influence the reactor in four different ways:

  • Max Temperature (insulator)
  • Object Holder (allows additional item inputs)
  • Efficiency (fuel lasts longer)
  • Throttle (slows down the reactions)

    At the moment, you only have access to insulators and the Object Holder.

While a hotter reactor makes steam and byproducts faster, it is also more demanding for the fuel rods. Each fuel rod has limited durability, and this scales linearly with the temperature.

As you need more fuel rods for the higher heat, this in effect makes the damage scale quadratically.

If you want to heat coolants the most efficiently, you'll use low temperature. But if you want faster fissile conversion, use as high a heat as the insulation allows.

To start off, you'll want to fill your fission reactor with Blue Ice or Framed AES Insulation, as those are the only two insulators you'll have access to after landing on Mars, but you'll want to upgrade to Framed Glacian Wool ASAP.

Processing Recipes

Fuel rods aren't the only item you can put in the reactor! Putting a Material Holder inside your reactor will allow it to do Processing Recipes - Press U on a Material Holder to view the recipes in EMI. You can do more recipes at once with more Material Holders. These recipes can affect the level of heat in the reactor or provide other outputs.

Example

The simplified math is as follows: with sufficient coolant fluid and a 100% heat fuel rod, the reactor will reach a temperature of about 200 HU. This can also be referred to as heat level, or just heat. Having two 100% fuel rods is equal to one 200% rod, and both lead to about 400 HU.

This is because the fuel rod generates 200 HU/t. Coolant fluids are able to extract 1 HU/t per 1 degree of heat.

If the reactor's max heat is 190, a 100% fuel rod will overheat it. You can increase this with the components, or alternatively active coolants via the processing system. Each recipe has a heat impact.

For example, if the recipe's temperature is 100, and impact -10 HU/t, it is able to cool down the reactor by 19 HU/t at 190 degrees.

That makes it possible to run the reactor with lower max heat, and not overheat! If the temperature is below 100, it won't run at all - just like how EBF recipes have limits.

Thorium Fuel Rod

To start off, get your hands on some Thorium. Remember to wear all the relevant PPE, as Thorium is radioactive. Your space suit will protect you for a little while, but will also take damage while it's in your inventory.

Next, craft some empty Fuel Rods and fill them with the Nuclear Fuel Factory. The rods are reusable, so you don't have to make too many. In fact, you might want to make just a single one for now.

You'll of course need a completed reactor, too.

Why just a single rod? Let's delve deep into the reactor mechanics in the next page.

Depleted Fuel Rods

After your first Thorium Fuel Rod has finished processing, the reactor will output a Depleted fuel rod. The lifetime average heat number on your rod's tooltip will indicate how much "damage" the rod took from overheating - the lower the number this is, the better.

Output all Depleted Rods back into your Nuclear Fuel Factory, where it will refund the empty fuel rod as well as some Waste. The waste product is what you're after, as the amount you receive will depend on its lifetime average heat.

In Thorium's case, the only thing you can use it for at the moment is crafting the next tier of fuel rod - Uranium.

Uranium Fuel Rod

While Thorium rods don't produce much power, their real appeal is the Thorium Waste needed to produce Uranium Fuel Rods. Make sure you understand how the fission reactor works before moving on to these, as a reactor without any components won't be able to handle their heat of 435.

At this point, you have three options for safely running Uranium rods:

  • 20x Framed Glacian Wool will raise your maximum heat to 440. This solution is easiest but requires shearing a lot of Glacian Sheep first.
  • Use Material Holders and insert large amounts of Dry Ice to drop the reactor's temperature. You will want access to a Liquid CO₂ Fluid Vein if you go this route.
Refrigerant Pellet

  • Use Refrigerant Pellets in combination with Material Holders. They behave like Dry Ice but are far more potent. Note that Refrigerant Pellets consume a decent amount of Fluorine to craft, and you do not have infinite Fluorine at this point.

Obviously, you can also make your own sauce and mix all of these options together. We recommend having separate rectors for both Thorium and Uranium, though in the future once you get better cooling capabilities you may be able to mix them together.

Make sure your steam turbines are ready too! Uranium rods last 4x as long but produce 5x more steam than Thorium.

Heat Exchanger

Speaking of steam, the steam that Uranium rods output is a bit too spicy for your steam turbines to handle - you'll need to send it through a Heat Exchanger first.

Plutonium Fuel Rod

Just like before, the main goal of Uranium rods is producing byproducts to make the next tier of fuel rods, in this case Plutonium. These are your final test - you'll need a reactor full of your best Passive and Active cooling (such as TerraFirmaGuard PA6) in order to maximize your yields of the precious Tritiated Water.

Fission on Earth

Hungry for more Fission? Starting with the Thorium-Uranium Breeder Rod, you can produce other exciting kinds of fuel rods that also work on Earth. You will want a robust Railgun network to produce the rods on Mars and send them over to your main base, and in exchange you will have a difficult but rewarding power source for a long long time.

Tips

If you're struggling to send your steam around fast enough, try Tungsten-Bismuth Oxide or Tungsten Steel Fluid Pipes, or AE2's Fluid P2P.

Don't try to send it around through interfaces or buffer it in your ME Drives, it won't be fast enough!

Item Input Buses will always pull items from their indicated face.

Remember you can also input items through their other faces, where you will have more control over how items are input.

Export Buses with Threshold Switches or even Create components can be useful here, along with other redstone devices.

Need to produce more Heavy Water?

Remember the Large Centrifuges can be overclocked to IV, and can also accept multi-amp hatches to go even faster.

Fission outputs a lot of energy, take advantage of it!

Finally, be sure to read the EV quests for fission as well! They go into much more depth about all the other steps in between each fuel rod, and overall progression.