Fusion Reactor

The Fusion Reactor is a Mekanism multiblock that burns Deuterium and Tritium to make power, and it’s the strongest generator in the mod at up to 19.6 million FE/t. It’s always the same 5x5x5 shape, built from 66 blocks, with a Fusion Reactor Controller in the middle of the top face.

To set one up, you’ll need to pipe both fuels in, put a full Hohlraum in the controller and then hit a Laser Focus Matrix with a single Laser pulse of at least 400 million FE (1 billion J). That pulse is the hard part, as it has to arrive all at once, which is what a Laser Amplifier is used for.

How to Build It

Most of the reactor is made from Fusion Reactor Frames, which are crafted 4 at a time from 4 Atomic Alloy, 4 Polonium Pellets and a Steel Casing. The pellets are what hold you back here, as they come from the waste of a Fission Reactor, so you’ll want one of those running first, and the Nuclear Waste page covers how they’re made.

Fusion Reactor Frame

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4

Fusion Reactor Controller

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Fusion Reactor Port

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2

Fusion Reactor Logic Adapter

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The Fusion Reactor Controller takes 5 frames, 2 Ultimate Control Circuits, a Glass Pane and a Basic Chemical Tank. Fusion Reactor Ports come 2 at a time from 4 frames around an Ultimate Control Circuit, and the Fusion Reactor Logic Adapter is a frame with 4 Redstone Dust around it.

You’ll also need a Laser Focus Matrix, which is crafted 2 at a time from 4 Reactor Glass around a Block of Redstone, and at least one Hohlraum. That one is made in a Metallurgic Infuser from 4 Gold Dust and 10 mB of Carbon, and one is used up every time the reactor is lit.

Laser Focus Matrix

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2

Hohlraum

4

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There are 36 spots in the shape that only a frame will fill. Counting the 5 that go into the controller and the 4 that make a pair of ports, the cheapest working reactor needs 45 frames, which is 12 crafts and 48 Polonium Pellets. That’s as long as you fill the rest of the face spots with Reactor Glass, which is far cheaper to make.

The Shape

The reactor is a 5x5x5 cube with its corners cut off, and the 3x3x3 space inside has to be left as air. The bottom and top layers are a plus shape of 13 blocks, the second and fourth layers are a 5×5 ring without its 4 corners, and the middle layer is a full 5×5 ring.

Each of the 6 faces has 5 blocks in its middle that form a small plus, and those are the only spots where a port, Reactor Glass, a Laser Focus Matrix or a Logic Adapter is able to go. Everything else has to be a Fusion Reactor Frame, which works out at 36 frames that can’t be swapped, and the center of the top face has to be the controller.

Why It Won’t Form

If the reactor says there’s no controller found, it means the controller isn’t in the center of the top face, as that’s the only place it counts. A second controller anywhere else will stop it from forming as well, and so will anything placed inside the 3x3x3 space, like a Torch or a cable that was left behind.

The other common mistake is putting a port or a piece of Reactor Glass on an edge, as those are only allowed in the plus in the middle of each face. Once everything is in the right place the reactor will form by itself, and right-clicking the controller will open its screen.

How It Works

Once it’s lit, the reactor will burn D-T Fuel to heat its plasma, which then heats the casing, and the heat leaving the casing is what gets turned into power. It mixes Deuterium and Tritium into D-T Fuel by itself, taking half of each, so you only have to keep both tanks topped up, which hold 1,000 mB each.

Everything goes in and out through Fusion Reactor Ports, which carry the fuels and Water in, and power and Steam out. A port starts as an input, and you’ll need to sneak and right-click it with a Configurator to switch it to output, as only output ports will push power and Steam into your cables and tubes.

Deuterium and Tritium

Both fuels are chemicals that take a few machines to make. Deuterium starts as Heavy Water, which an Electric Pump will pull from any Water source once it has a Filter Upgrade inside, whereas Tritium starts as Lithium from a Thermal Evaporation Plant.

Deuterium Line

Water

Any source

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Electric Pump

Filter Upgrade

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Heavy Water

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Electrolytic Separator

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Deuterium

Tritium Line

Brine

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Thermal Evaporation Plant

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Liquid Lithium

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Rotary Condensentrator

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Lithium

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Solar Neutron Activator

Daylight

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Tritium

The Electrolytic Separator uses twice its normal power on Heavy Water, and the Solar Neutron Activator only runs in daylight, so Tritium tends to be the fuel you’ll want to store. The Chemical Infuser isn’t needed to feed the reactor, as it’s only there to make the D-T Fuel that goes into a Hohlraum.

Filling a Hohlraum

A Hohlraum holds 10 mB of D-T Fuel, and it only counts when it’s completely full, which its tooltip shows as “Ready for Reaction!”. You’re able to fill one by placing it in the output slot of the Chemical Infuser that’s making the fuel, or in the slot of a Chemical Tank holding D-T Fuel, and it’ll take about half a second.

How to Ignite It

The plasma has to reach 100 million K before anything will burn, and the only way to heat it is by firing a Laser into the Laser Focus Matrix. Every 4 FE that hits the matrix adds 1 K, but the plasma is always leaking heat into the casing, so a single Laser firing by itself will level off at around 500,000 K and never get there.

This is why you’ll need a Laser Amplifier between the Lasers and the matrix. It’s charged by the beams that are fired into it, and it’s able to hold 2 billion FE, so it can save the energy up and then release it as one pulse. In its screen, set the Min threshold to a little over 400 million FE, and it’ll fire by itself when it has that much.

Each Laser adds 4,000 FE to the amplifier every tick, which is where those times come from. Before the pulse lands, make sure the full Hohlraum is in the controller and that there’s already Deuterium and Tritium in the tanks. The Hohlraum’s 10 mB will be burned in the first moment, and if there’s nothing to inject after it, the reaction will go straight back out.

Injection Rate and Output

The injection rate is set in the Fuel tab of the controller, and it’s how many mB of D-T Fuel the reactor will burn each tick. It’s always an even number, up to 98, and the reactor will burn half that amount of Deuterium and half of Tritium. A new reactor starts on 2, which is also the lowest rate that’ll keep it lit.

With no Water in it, the reactor is air-cooled, and it’ll make 200,000 FE/t for every point of injection rate. Those are the numbers it settles at once the casing has warmed up, so the output will climb for a while after it’s lit, and you’re able to watch it in the Heat tab.

If you pipe Water in, the casing will run cooler and the reactor’s own output will drop to a quarter, but it’ll also boil 150,000 mB/t of Water into Steam for each point of rate. That Steam is worth up to 4 FE per mB in an Industrial Turbine, so with enough turbines behind it you’re able to make over 3 times as much as an air-cooled reactor.

For any rate that’s not in the table, the calculator below will work it out for you. Set the injection rate and whether there’s Water in the reactor, and it’ll give the power, the Steam and how much Deuterium and Tritium you’ll be using each hour, along with the blocks for the shell.

The reactor holds 400 million FE, and it’ll keep burning fuel when that’s full, so the power needs somewhere to go, like an Induction Matrix. If either fuel runs out, the burn will stop on the same tick and it won’t start again when the fuel comes back. It needs a new full Hohlraum to relight, and another pulse as well once the plasma has cooled under 100 million K.

Upgrades and Automation

There aren’t any upgrades for the reactor, as the injection rate is the only thing that changes its output. For redstone, you’ll want a Fusion Reactor Logic Adapter in one of the face spots, which is only able to send a signal out, and it can’t be used to switch the reactor off.

The Insufficient Fuel mode is the useful one, as it’s able to warn you before the reactor goes out. A Comparator on a port will read how full the D-T Fuel tank is as well, which can be used in the same way.

A Fusion Reactor can’t melt down or explode, and it doesn’t make any radiation, so it’s far safer to live beside than a Fission Reactor. The only danger is the inside of it, as anything standing in the 3x3x3 space while it’s burning will be killed, so don’t break in through the Reactor Glass while it’s running. From here, the Laser page covers the amplifier settings in more detail.

FAQ