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Chapter 21 ‐ Electricity Part 3 ‐ Nuclear Power
Nuclear power is a relatively complex but highly effective way to generate large quantities of electricity. It is unlocked during the midgame with chemical science. In a nutshell, nuclear power requires you to mine and process uranium to create fuel cells, which are consumed by nuclear reactors. The reactors put out heat, which is transferred to heat exchanger units via special solid heat pipes. The heat exchangers, similar to boilers, take heat and water to create steam, but at high temperature. The high temperature steam is consumed to generate power at steam turbines, which are essentially high temperature steam engines.
All these processing steps are worth the effort because a single nuclear reactor produces enough heat to produce 40 megawatts of electricity by itself. In addition, putting multiple reactors side by side multiplies their effectiveness via a neighbor bonus. For example, 2 reactors side by side will produce 160 megawatts instead of 80 megawatts.
Nuclear material in vanilla Factorio does not damage players. Nuclear power is doable in Factorio Access but more work needs to be done to bring access to information such as temperatures.
To mine uranium ore, you need an electric mining drill that is supplied with sulfuric acid through any of its pipe interfaces. The acid requires oil and iron to produce, so it likely needs to come from your oil processing area. Usually it is a good idea to connect to uranium mines with trains, where one fluid wagon carries sulfuric acid to the mine and one or more cargo wagons carry the uranium ore back. The acid can flow through mining drills, allowing one to connect their pipe networks easily.
Uranium ore is processed inside a centrifuge. One centrifuge needs 4 electric mining drills to keep it continuously supplied. The refining process has a 99.3% chance to produce 1 unit of uranium-238 and a 0.7% chance to produce 1 unit of uranium-235. While the second material is rare, you only need small amounts of it anyway. In fact, one centrifuge is usually fast enough on average to keep one nuclear reactor continuously supplied, but it is more reliable to aim for 2 centrifuges per reactor so that you rely less on chance.
The processed uranium is used to make uranium fuel cells for nuclear reactors. This can be done in an assembling machine, requiring 19 units of uranium-238 and 1 unit of the rare uranium-235, and also 10 iron plates. This recipe produces 10 fuel cells, and each cell takes exactly 200 seconds to be used up in a nuclear reactor. Reactors put out their used up fuel cells in an output slot.
When you unlock nuclear fuel reprocessing, you can process your used up fuel cells in a centrifuge to reclaim some uranium-238. Later, when you unlock the Kovarex Enrichment Process, you can convert uranium-238 into uranium-235, which stops it from being rare, but you need a stockpile of the rare material already in order to begin the enrichment.
The nuclear reactor is a large and expensive 5 by 5 building that consumes uranium fuel cells to generate heat. The heat pipe connections of the nuclear reactor are found on all four sides, at the corner and middle tiles. You can connect heat exchangers or heat pipes at these points to drain heat from the reactor.
A single reactor produces enough heat to supply 40 megawatts of electricity when converted to steam power. If two reactors are side by side such that they share 3 heat connections, both of them receive a neighbor bonus which increases the heat produced by another 40 megawatts per reactor. Every shared side will give another neighbor bonus, such that a reactor can produce 160 megawatts by itself when 3 sides have active neighbors. Usually a 4th neighbor is not added because it makes it impossible to reach the reactor with inserters.
One uranium fuel cell is consumed by a nuclear reactor in exactly 200 seconds. During this time, the heat cell cannot be removed and the reactor continuously generates heat, which increases its temperature. In Factorio, this type of generated heat is never lost to the environment. Furthermore, unlike regular burner devices, nuclear reactors consume their fuel without pausing for any reason. The temperature of the nuclear reactor begins at 15 degrees centigrade and can increase all the way up to 1000 degrees centigrade, after which excess heat is dumped without damaging anything. The reactor itself also takes no damage from overheating, but high temperatures are still dangerous, because they make the reactor vulnerable against any other form of damage. If a nuclear reactor is damaged too much by other sources while it is above 900 degrees in temperature, it will explode violently and damage or destroy everything within about 200 tiles, including other reactors that may also explode in a deadly chain reaction. On the other hand, overheating nuclear reactors are generally safe to leave alone because usually nothing around will damage a reactor except for an enemy attack or a trigger happy player.
Heat pipes connect like regular pipes although they are more like solid metal rods. They are used to collect heat from reactor connections and deliver it to heat exchangers. The heat in these heat pipes spreads like a fluid inside fluid pipes, but much more slowly. Heat pipes also store the heat, and can go up to 1000 degrees centigrade while they never take heat damage. Heat is never lost to the environment.
Heat pipes have 2 unique constraints:
- They have no underground version.
- They have an effective range limit because of their inherent throughput limit, which comes from the heat transfer mechanics.
These constraints lead to the principle that heat exchangers in a nuclear power plant need to be close to the reactors. The range of a heat pipe can be extended somewhat by making it 2 or even 3 units thick instead of 1 unit thick, but increasing thickness further has diminishing returns.
A heat exchanger is like a super boiler. It is shaped like a boiler except that it has a heat pipe connection at its middle back side. It takes heat from a heat pipe or directly from a nuclear reactor heat connection, and produces high temperature steam. The exchanger must have a water supply and a temperature over 500 degrees centigrade in order to work and the steam it produces is always at 500 degrees. The heat exchanger consumes 10MW of heat at a time. This would mean that four heat exchangers are needed in order to match a single nuclear reactor.
A steam turbine is a super steam engine. It has the same size and pipe layout, but it can consume steam twice as fast, and also it can consume high temperature steam efficiently. A regular steam engine can also consume high temperature steam but it will do so while wasting energy. Meanwhile, steam at any temperature can be mixed together. This averages out the temperature but makes the steam less useful inside a turbine. The steam turbine at maximum speed produces 5.82MW of electricity.
- One sulfuric acid plant can produce enough acid for dozens of electric mining drills.
- Four electric mining drills produce enough uranium ore for one centrifuge.
- One centrifuge processes uranium ore quickly enough to supply one reactor on average. This may be surprising but the mathematics work out: Even though it takes half an hour on average to produce 1 unit of the rare uranium-235, that 1 unit is enough to make 10 fuel cells, which in total last for 33 minutes.
- A single nuclear reactor produces 40MW of heat, which is enough for 4 heat exchangers.
- A connected pair of nuclear reactors gives 100 percent bonus to both reactors, and produces 160MW instead of 80MW.
- A connected square of 4 reactors gives 200% bonus for each, and produces 480MW instead of 160MW.
- One heat exchanger produces steam fast enough to supply 1.72 steam turbines.
- 1 nuclear reactor by itself produces 40 megawatts. It needs 4 heat exchangers and 7 steam turbines, although it is simpler to just connect 2 turbines to each exchanger, and thus use 8 turbines in total.
- 2 nuclear reactors placed wall to wall will activate the neighbor bonus to give 80 megawatts each, and so 160 megawatts in total. This requires 2 offshore pumps, 16 heat exchangers, and 28 steam turbines, although again it is simpler to just connect 2 turbines to each exchanger, and thus use 32 turbines in total.
- 3 nuclear reactors in a row will produce 280 megawatts in total, requiring 3 offshore pumps, 28 heat exchangers, and 49 steam turbines, or 56 steam turbines using the simple design.
- 4 nuclear reactors in a row will produce 400 megawatts in total, requiring 4 offshore pumps, 40 heat exchangers, and 69 steam turbines, or 80 steam turbines using the simple design.
- 4 nuclear reactors in a 2 by 2 square will share more walls and maximize the neighbor bonus to yield 480 megawatts in total, requiring 4 offshore pumps, 48 heat exchangers, and 83 steam turbines, or 96 steam turbines using the simple design.
A very easy way to design a nuclear plant is to make a separate row for each type of machine. For example, let's demonstrate with a single reactor system that has 1 reactor, 4 heat exchangers, and 8 steam turbines, producing 40 megawatts. On the first row you have the reactor, which you can feed and empty with inserters and chests. On the second row you have a heat pipe that runs along the side of the reactor and is about 15 tiles long. On the third row you have 4 heat exchangers placed side by side, but it is good to have a gap of 1 tile between each pair of them so that you can fit electric poles in these gaps. As the fourth row, you can place a steam turbine at the output of each heat exchanger. For the fith row, place a second steam turbine after each first turbine. Finally, add electric poles within the 4th and 5th rows, to reach every steam turbine. When you add a water supply to the heat exchanger row, your power plant will be ready to run! Optionally, you can add a 6th row, made of storage tanks, with one for each steam turbine output, so that you can store steam to partially prevent the reactor from overheating and wasting fuel.
The main issue with this design is that it will require very long rows if you use 3 or more reactors. You can resolve this by applying this design into two directions instead of one, starting from the row of reactors.
Nuclear fuel reprocessing is a recipe for centrifuges that allows you to recover some uranium-238 from used up uranium fuel cells. To start using this recipe, you need to unlock a production science technology with the same name. The recipe is useful because there is not much else you can do with the used up fuel cells and it decreases the need to do more mining.
This centrifuge recipe is expensive to unlock, using production science technology, but it is quite useful. It allows you to convert some uranium-238 into uranium-235 so that you can get more of the rare uranium type faster. However, to start using this recipe you need a stock pile of 40 units of uranium-235. These units are used to make the recipe work and are refunded when the crafting cycle finishes. Kovarex enrichment is not necessary in order to do nuclear power, but it makes it a lot easier to support a large number of nuclear reactors.
Kovarex enrichment is not trivial to set up because of most of the output being required as input again. Furthermore, the startup requirement for 40 units of 235 usually becomes 120 units per centrifuge, because the centrifuges keep accepting more of it until they each have enough to run 3 crafting cycles. The next sections offers guides for setting it up using the splitter priority feature or simply using chests.
This very simple setup is a quick but you need to be careful about how much Uranium you collect from the system because otherwise you might starve it. Note that the centrifuge requires 120 units of Uranium-235 before it is full and the collection chest begins to stay full. The setup can fit easily inside a 7 by 7 area. The idea is to build a simple loop from the centrifuge to itself using three stack inserters and two chests.
- Set up a steady input supply of uranium 235 and uranium 238. Use either a belt each or a belt lane each to supply them. They can be acquired via regular uranium processing.
- Feed the centrifuge from the supply system using regular inserters so that the input is relatively slow.
- At an empty corner of the cetrifuge, place a stack inserter and a chest for collecting all outputs.
- Place a second stack inserter that is aligned with the center of the centrifuge and is taking from the first chest and placing into a new second chest.
- Place the third stack inserter so that it takes from the second chest and puts into the other corner of the centrifuge, thus finishing the loop.
- The system is now done. The stack inserters will continuously resupply the centrifuge with its own output until the centrifuge is holding 80 units of Uranium-235 at its input slot and refuses to take more. Any excess Uranium of both types will begin to accumulate in the chest. You can collect the Uranium from here by hand but you need to make sure to leave at least 40 units of Uranium-235 inside the chest at all times so that you do not accidentally take the units that were on the way to resupplying the centrifuge.
This setup uses looping belts to feed the centrifuge output back into it. Splitter priority is used to take the excess Uranium-235 out of the system when the looping belt fills up. Note that the centrifuge requires 120 units of Uranium-235 before it is full and the belt begins to fill up. The setup can fit easily inside a 15 by 15 area.
- Set up a steady input supply of uranium 235 and uranium 238. Use either a belt each or a belt lane each to supply them. They can be acquired via regular uranium processing.
- Feed the centrifuge from the supply system using regular inserters so that the input is relatively slow.
- Set up a stack filter inserter to remove 235 and another one to remove 238.
- Behind each stack filter inserter, build a belt that loops back and feeds the centrifuge again, with a stack inserter each. Therefore the recycled output is fed back quickly.
- For one of the looping belts, add a splitter on it somewhere. One exit of the splitter will be on loop back to the centrifuge, and the new exit needs to continue at least 1 unit forward.
- Set the splitter output priority so that the looping belt exit has priority.
- The other exit belt of the splitter will go to storage, so you can put a chest at its end, or anything else.
- Do the same for the other looping belt.
- The system will begin to run when there are 40 units Uranium 235 in the centrifuge. It takes the system about 1.5 hours to become self-sufficient after that, but you can put speed modules in the centrifuge or supply more Uranium-235 at the start to make it self-sufficient faster.