[NEW] Reactor System

Since it's proably required for proper testing and balance discussion, here a sum up of the reactor system:

The reactor does not have any sort of own/external cooling anymore.
It still contains (3+chambers)*9 inventory slots, as usual.
During a reactor tick, it will straightforward iterate through the slots (from top left to bottom right), calling a "updateTick" method on every item (if the Items are implementing IReactorComponent). EVERY IC² core compenent is coded by using that interface, thus it's quite mighty and sufficient for Addon Developers.
For reasons you will grasp upon reading this, Nuclear Output was HALVED (5EU/t / pulse) to compensate for the much more powerful and efficient reactors you can now build.

Uranium
There are 3 tiers of Uranium Cells: Single, Dual, Quad.
Single tells are your casual Uranium Cells, pulsing once + once for every pulseable object surrounding them. The heat generated by a cell is calculate by SSUM(pulses)*4.
SSUM :=
SSUM(1) = 1
SSUM(2) = 3
SSUM(3) = 6
SSUM(4) = 10
etc
Heat will be distributed to all surrounding components which accept heat (by default all which have a damage bar). If there is none, heat will be applied to reactor hull.
Dual cells are effectively 2 cells in the same slot (whole calculation will be doubled) and as well get +1 additional pulse for themselves.
Quad cells are 4x cells, which gain +2 additional pulses each, permitting efficiency 7.

Coolant Cells
are heat storages.
10k, 30, 60k.
They do not dissipate heat, don't cool and don't perform heat management on their own.

Plating
There are three kinds of plating.
The 'Integrated Plating' grants +1000 maxHeat to the Reactor, as well as reducing explosion range AND the chance to trigger heat-based effects (melting rock, setting stuff on fire) to 0.95 (multiplicative).
There are two modified Plating versions. The Heat Plating grants +2000 maxHeat, but only 0.99 modifier, whilst the Explosive Plating grants +500 maxHeat and 0.9 modifier.
Platings DO NOT take or redistribute any sort of heat and accordingly have no damage bar and are, as a result, stackable. Stacking them inside of a reactor does not have any effect.

HeatSwitch
HeatSwitches aka Heat Distributors are the new HD's of the old system, coming in various versions.
The standard Heat Switch 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 Diamon 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.

Vents
As you probably notice, there were so far no components providing any sort of cooling, at all. That's what Vent's are for.
Vents have a maxHeat of 1000 and a selfCooling and a reactorTransfer rate.
A vent will always first draw heat from the reactor in height of it's reactorTransfer rate, regardless of it's own heat level. They do not 'balance' as heatSwitches do. Second, they will reduce their own heat by the selfCooling rate, venting the heat into the air = Mystically gone.
Basic Vents do merely have a selfVent of 6.
CoreVents have 5 selfVent and 5 reactorTransfer (effectively applying continous -5Heat/tick to the reactor hull.
Golden CoreVents are tricky to use. They provide an amazing 20 selfCooling, but have 36 reactorTransfer. Effectively, this means they will always melt themselves if the reactor has enough heat avaible. It's up to you to figure out how to use them properly.
Diamond Vents have 12 selfCooling, but 0 reactorTrasnfer again.
There is one special, the SpreadVent. It can NOT take up any heat. However, it automatically cools down all adjacent components by 4 per tick.

Breeding
Breeding didn't change much from how it was before. Uranium cells have a 25% chance of generating depleted uranium (or you can create 8 depleted uranium from one ingot and 8 cells). Mixed with coaldust, this turns into an isotope cells. Isotope cells require 10000 pulses from uranium cels to become enriched uranium. Enriched uranium can be used for crafting of nukes or for new uranium cells.
However, there was one important change: Reactor heat does not add a x2 bonus for each, but merely a +1. Thus an isotope will need 10000 ticks on heat 0-2999, 5000 for 3000-5999, 3333.3 for 6000-8999, etc. The reasoning behin dthis: With heat plating, you can easyly create Reactors well past the 30k.

Heat Packs
However, to reach a constant 30k setup, you would need ridicolous amounts of lava in the old system. That's why you now can craft HeatPacks/HeatCells. These things are sort of cheap and stackable. Placing them inside of a reactor will cause them to heat up all surrounding components by 'stackSize' (=the amount of heatcells).
They will keep doing that, until the components heat level reached stackSize*1000. This way you can easyly configure your reactor to remain on a specific heat level.
Be advised you should use coolant cells next to the heatpacks, as heating f.e. vents to 30k doesnt really work.

Reflectors
Good efficiency is something hard to obtain, usually requiring many uranium cells and thus creating unstable setups.
Neutron Reflectors solve this problem. An uranium cells nearby will consider Reflectors similar to Uranium cells and send out additional pulses. Whilst this increases the Uranium Cells heat output, the Neutron Reflector itself will of course not produce additionally heat (opposed to a second Uranium Cell).
Neutron Reflectors have a limited life length of 10000 ticks. You can, however, craft a 'Thick Neutron Reflector' with a lifetime of 40k ticks. Be advised: Neutron Reflectoers surrounded by multiple cells will diminish faster (2 cells adjacent to the same reflector will deplete it in half of a cell cycle).
Surrounding a single uranium cell with 4 Reflectors will grant it efficiency class 5.

Condensators
Condensators are a special tool to reduce Reactor heat. They come as Redstone and as LapisLazuli versions (latter one being an upgrade of former).
Condensators will accept any amounts of heat from surrounding components (though they don't balance heat around themseles), and INSTANTLY disperse the heat by using their fuel.
A Redstone Condensator can absorb 20k heat, refilling it (crafting) with redstone will restore 10k of it's capcity.
LapisLazuli Condensators can absorb 100k heat, redstone refills 5k and Lapis Lazuli 40k.

And now go forth and create even more industrial-hayoish reactors!

PS: For testing purpouses, the Nuclear Reactor'S tickrate is increased to 20 ticks per second (opposed to 1).
This way you can test setups and balance. Be advised this effectively 1/20th's the energy value of used Uranium!
(as usually, the reactor emits EU every tick, whilst only updating the setup every 20th tick)

4 times?

A Quad cell acts like 4 seperate cells in the same slot + every of these cells pulses 3 times 'in itself' opposed to the 1 basic pulse of single uranium.

Components do only take as much heat as they can take and simply disappear. In case of a Uranium cell, the remaining heat will be applied to a reactor hull.

Exception are the heatswitches, when drawing x heat, they can possibly exceed their maxHeat. Since the melting of heatswitches isn't really an applyable 'intended concept' it doesn't matter, though.

Quote from Gorni

540 cooling, can anyone get more?

http://i.imgur.com/EORQE.png

( i mean active heat venting, not single use.)

maybe its a bit overpowered that you can easly kill all excess heat of overclocked vents with adjectant component vents.

improved more:

http://i.imgur.com/XHYp7.png

656 cooling. (cant even generate so much heat with 3 quad cells. Those component vents are great. maybe too great....

Display More

Hmmm.. that definitely looks to easy.

Cell structure: OOO
First Cell has 3+1 pulses, the second has 3+2, third has 3+1 (since Quad Cells have a base pulse amount of 3).
This all is multiplied by 4 for each unit, as there are 4 cells located in a quad cell.
16+20+16=52

For heat calculation, you got 8*4P+4*5P
That's 8*(4*10)+4*(4*15)=320+240=560

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.

Now you can spread heat through all reactor components and balance it amongst all storage units. But unless you intend to constantly replace the storage components, the heat will merely accumulate all over the time. To solve this, our engineers designed HeatVents (aka Vents, Heat Ventilation, Ventilators, Fans, Followers...)
Vents have a maxHeat of 1000 and a 'selfCooling rate' and a 'reactorTransfer rate'.
A vent will always first draw heat from the reactor in height of it's reactorTransfer rate, regardless of it's own heat level. They do not 'balance' as heatSwitches do. Second, they will reduce their own heat by the selfCooling rate, venting the heat into the air = Mystically gone.
'Basic Vent's do merely have a selfVent of 6.
'CoreVent's have 5 selfVent and 5 reactorTransfer (effectively applying continous -5Heat/tick to the reactor hull.
'Golden CoreVent's are tricky to use. They provide an amazing 20 selfCooling, but have 36 reactorTransfer. Effectively, this means they will always melt themselves if the reactor has enough heat avaible. It's up to you to figure out how to use them properly.
'Diamond Vent's have 12 selfCooling, but 0 reactorTrasnfer again.
There is one special, the 'SpreadVent'. It can NOT take up any heat. However, it automatically cools down all adjacent components by 4 per tick.

Part IV: Have your uranium breed itself
By now, you should have run low on Uranium supplies. But luckyly, we still have Breeding to reenrich and reuse spent Uranium!
Whenever an Uranium Cell is used up, it has a 25% chance to turn into a Depleted Uranium Cells without enough uraniumized remains to be recycled. Refilling such a depleted cell with Coal Dust will provide the necessary raw material, resulting in an 'Isotope Cell'.
During normal Reactor operations, Uranium Cells send out Neutrons every full seconds (as mentioned above). If an Isotope Cell is struck by 10000 Neutrons, it will turn into an Re-Enriched Isotope Cell. Combine this result with some more coal dust and it will turn into a fully useable Uranium Cell again.
The process of re-enriching Isotope Cells, however, creates the same amount of heat as the interaction between Uranium Cells, WITHOUT actually producing the according energy. But considering you can obtain a full new Uranium Cell as a 'byproduct' it should still pay out. That's the way of Nuclear Engineering, GangnamHAYO style.
Even better though, the re-enrichment of Isotopes by Neutrons seems to be temperature-dependant. For each 3000 units of heat, basing on the reactor hull, there will be one additional Neutron affecting the Isotope. Accordingly, breeding Uranium with reactors on higher temperatures (f.e. 9001 heat) is much more effective (f.e. 4x fast).

However, with all your awesome coolant engineering... how could a reactor possibly heat up that much? The solution has a name: Lava Buckets Heating Cells!
Heating Cells, also known as HeatPacks, are special components, harnessing the intense heat of lava to act as UNDIMINISHING source of heat. These things are sort of cheap and stackable. Placing them inside of a reactor will cause them to heat up all surrounding components by 'stackSize' (=the amount of heatcells placed into the same slot).
They will keep doing that, until the components heat level reached stackSize*1000. This way you can easyly configure your reactor to remain on a specific heat level.
Be advised you should use coolant cells next to the heatpacks, as heating f.e. vents to 30k doesnt really work. At least not for me, HAYO.

Part V: How to turn your Reactor from hayo to HAYO!
You probably are asking, right now, 'What the hell? How can a reactor possible contain the heat necessary for successfull breeding?!'
The answer is Plating. There are three kinds of plating.
The 'Integrated Plating' increases the maximum amount of heat your Reactor can contain by 1000. Additionally, it serves as a buffer and stabilizer in case of emergencys, and will reduce a Reactor's explosion range by 5%. Since this is reallife and not some exploitable computer game, using 20 platings will NOT make your reactor unexplodeable, don't try! Additionally, it reduces the strength of heat-based reactor effects (burning your cookies and setting your factory ablaze) to the same degree.
There are, additionally, two modified Plating versions. The 'Heat Plating' grants +2000 maxHeat, but only a 1% modifier, whilst the 'Explosive Plating' grants only +500 maxHeat, but a 10% reduction.
Platings DO NOT take or redistribute any sort of heat and accordingly can be safely carried in larger stacks. These stacks (opposed to HeatPacks) don't influence the way they work, though.

And, to make things even 'more better', you can now directly enhance the effectivity of single Uranium Cells WITHOUT the use of other Uranum Cells, by the use of Reflectors.
Neutron Reflectors. As their name implies, they will 'reflect lost Neutrons', causing Uranium Cells to pulse equally as if they would be surrounded by more Uranium. Whilst this increases the Uranium Cells heat output, the Neutron Reflector itself will of course not produce additionally heat (opposed to a second Uranium Cell).
Neutron Reflectors have a limited life length of 10000 ticks. You can, however, craft a 'Thick Neutron Reflector' with a lifetime of 40k ticks. Be advised: Neutron Reflectoers surrounded by multiple cells will diminish faster (2 cells adjacent to the same reflector will deplete it in half of a cell cycle).
To give you an example of this astonishing techonology: Surrounding a single uranium cell with 4 Reflectors will grant it efficiency class 5.

And if all these methods just don't cut it: Condensators
Condensators are a special tool to reduce Reactor heat. They come as Redstone and as LapisLazuli versions (latter one being an upgrade of former).
Condensators will accept any amounts of heat from surrounding components (though they don't balance heat around themseles), and INSTANTLY disperse the heat by using their fuel. Yes, you heard right: INSTANT dispersion of UNLIMITE amounts of heat. Effecively a black hole. For heat. Within your Nuclear Reactor. Uhm... HAYO!
A Redstone Condensator can absorb 20k heat, refilling it (crafting) with redstone will restore 10k of it's capcity.
LapisLazuli Condensators can absorb 100k heat, redstone refills 5k and Lapis Lazuli 40k.

Part VI: Last and most likely least...
Due to copyright issues and nostalgic ideals, it's still recommended to use the 'old' system of labelling your Reactor designs. You can find the somewhat outdated notes here: Handbook for Reactor-Labelling.