Just storing this yet unfinished official guide here:
Once upon a time, mankind used a block of metal, a battery and a stone furnace to create the first Generator. And he used Coal and there was electricity...
And then mankind realized that it wasn't enough, and it started creating Solar Panels from Coal Dust and glass...
And when the lag arrived, mankind averted from these incapable sources of low energy... and invented the Nuclear Reactor. But now...
IT'S TIME FOR THE INDUSTRIAL REVOLUTION, HAYO!
And since there's no revolution without sacrifices, we shall now remain quiet for 2 ticks to show our sympathy towards a lone, unnamed engineer, who managed to obtain the ultimate blueprints of Nuclear Engineering.
There, silence done, let's check out the blueprints! >>ACCESS GRANTED<<
Step I: Craft the future
First of all, you will need to craft a Nuclear Reactor itself. Of course you can't just summon a complex Reactor out of some iron and other stuff! That would be unrealistic. Instead, you first need to craft Nuclear Chambers. These chambers are, duh, CHAMBERS. Accordingly, you merely need a Machine Block and a half'o'stack of Copper. How to craft 33 elements together? Well, use your head, it's all about compressing numbers into quality.
(Be advised, I do not take any responsibility to injuries taken due attempts to compress Coppy by hammering it with your head.)
After you successfully crafted three, not two, not four, but three, to be spelled, 3, which is the number following after the 2 and going before 4, chambers, you can now easyly create a Nuclear Reactor, by combining the side-wards aligned Chambers with a Generator below and an advanced Circuit above.
You say that's much easier then before? Well, I say HAYO.
Due to improvements in various blueprints, we managed to cut down useless wasted ressources by 2%, resulting in the new and awesomely cheap recipe. Once you crafter your Reactor, it's already fully operational. Placing it down can be done anywhere, since the new Copper-based isolation will ensure the Reactor to be 100% immune to outward influences, accordingly it does neither heat up or cool down by itself or by surrounding blocks.
As you knew from before, a simple Reactor only contains 3 chambers and accordingly offers you 3 coloumns of space for installment of your personlaized reactor setup. You can expand this setup to up to 9 coloumns by placing more chambers (for the math-weak of you: 6) adjacent to the Nuclear Reactor core.
Unless you intend to use your Reactor as hayo-ish replacement for a TNT-cannon, I advise to use Reinforced Stone to encase the Reactor in a resistant layer to ensure minimal area destruction in case of 'slight misscalculations'.
Part II: Uranium and you (the radiated individual)
Of course the fuel, the source of energy, the symbol of life, the ultimate answer to the question of the sense of life, the universe and how to obtain enough power for everything else, is Uranium. Mined as raw chunks, compressed into craftable Brickets, filled into strangely durable tin cells, you obtain Uranium cells.
Be advised that, for your own security, Uranium cells do only do 'something' when the reactor is receiving a direct redstone signal.
Uranium cells last for 10.000 seconds (and accordingly 10.000 ReactorTicks) each. The lifetime of an Uranium cell is considered 'one reactor cycle'.
Uranium cells constantly and reliably (why? who cares?!) 'pulse' every full second. Every pulse causes an Uranium cells to send out a load of neutrons, whilst consuming 1/10000th of itself. Due to the critical-mass-of-compressed-uranium-in-small-tin-cells-for-whatever-reasons-hayo-rule, only a fractal of the Neutrons will actually cause Nuclear Reaction within the cell. (Reaction are good, they produce energy!).
In effect, this causes a single cell to merely produce one 'pulse' of energy. Every pulse of energy produces enough useable heat for the Nuclear Reactor to produce 100 EU, spread out amongst the next 20 ticks, effectively granting 5 EU/t.
However, if you place Uranium Cells adjacent to other Uranium Cells, the normally 'lost' Neutrons will hit the adjacent Uranium Cell, creating another pulse (for each adjacent Uranium cell). Therefore, 2 neighbouring cells will create a total of FOUR pulses, opposed to two pulses if they would be seperated.
This is called 'efficiency'. Since the lifetime of a cell is not dependant on the amount of pulses it effectively creates (but on it's 10k second lifetime, duh), one piece of Uraniumj can produce 1 or x million EU. Naturally, you will want a higher efficiency to maximize the energy gain of your Reactor.
However, the more efficient a cell is, the higher is the not-useable heat produced by it. Whilst useable heat is good, unuseable heat is not. It's like the dark side of good heat, just without cookies.
A cell creating 5 EU/t will produce 4 heat per second. 10 EU/t produce 12hps. 15 is 24hps, 20 is 40hps, etc... You will shortly learn how to deal with reactor heat.
Lastly, it should be mentioned there are theoretical approaches to condense more Uranium into less space. Of course way too dangerous to attempt this in practical applications, condensing Uranium Cells into more compact arrangements would permit users to reduce the amount of slots needed for actual Uranium Cells. Additionally, it would permit the Uranium Cells to more effectively use it's own emitted Neutrons.
For example a, theoretical!, setup of a 'Dual Uranium Cell', would not just produce twice as much energy (and heat) compared to a single cell, but it would additional pulse by itself TWO TIMES (per cell element!), for a total of up to 6 pulses per Neutron emission. With a 'Quad Uranium Cell', this would even increase to a maximum of 7 pulses, the highest efficiency theoretically possible. Though such a setup would create whopping 448 heat per second... which isn't exactly hayo...
Part III: Reactors in heat. ... Wait a second...
A reactor can only take so much heat before it will start melting and finally explode (which is a safety measure to prevent in from leaking dangerous radioactivity). Per default, the reactor hull can survive up to 10k heat without lasting damage. However, as the reactor's temperature rises, it will start affecting it's surrounding. Reactor heat can set wooden structures ablaze, melt stone into lava and harm living beings. It is ill-advised to approach hot reactors without full Hazmat-Equipment.
To prevent the reactor hull from heating up, you can make use of various Reactor Components. The most simple of those are Coolant Cells. Uranium Cells emit heat to all surrounding components (which can accept it) and will only heat the hull itself if there is no (suitable) component present. For example an Uranium Cell surrounded by four other cells will always heat the reactor hull.
Coolant Cells can be constructed in multiple layers of coolant water, permitting the cells to store 10k, 30k or even hayoish 60k of heat. However, by themselves these cells do merely STORE the heat, but don't DISSIPATE any heat and will eventually melt as well (causing the cells to heat the hull again).
For this reason, I hereby present you: HeatSwitches (commonly known as HD or HeatDissipator, HeatDistributer and Strange-Thing-Which-Can-Magically-Alter-Temeperatures).
The standard HeatSwitch can store 2500 heat, has a 'sideTransfer rate' of 12 and a 'coreTransfer rate' of 4.
All HeatSwitches work the same way: They calculate the % of heat stored in all surrounding tiles, themselves and the reactor hull, calculate a median and then attempt to reach that median on all components. A heatSwitch will first shift around (component <-> switch) the heat of adjacent components, to a max of sideTransfer. Then he will try to balance the heat between itself and the reactor to a max of coreTransfer.
The 'Core Heat Switch' does have a sideTransfer rate of 0 (thus no heat balance between adjacent components), but a coreTransfer rate of 72, and a maxHeat of 5000.
The 'Spread Heat Switch' does not have a coreTrasnfer, but instead 36 sideTransfer, and a maxHeat of 5000.
Lastly, the 'Diamond Heat Switch' has a sideTransfer of 24 and a coreTransfer of 8, and a maxHeat of 10000.
Opposed to the old HD's, the switches do NOT dissipate heat, have a LOW heat storage and do go by %, not my static values. F.e. you have a core heat switch (5000 max) and a reactor with some plating (20000 max). The system has a total of 5000 heat. The switch will balance 1000 heat to itself and 4000 to the reactor, resulting in 20% heat for itself and the reactor.