Rebalancing the fission reactors

Some time has passed since I implemented the reactor expansion and I’ve had enough time to experiment and think about the current balance of the system. There are some glaring issues I now see and can’t unsee.

The big bad balance blunder:

The biggest contender for “breaking the balance” or simply being overpowered as hell is the good ol 1x1 reactor core. The problem is simple: You can surround a 1x1 core with 4 2x2 cores. That mean the rod in the 1x1 core will be adjacent to eight other rods. So lets go through the scenarios of what this allows:

  • Surrounded by reflectors: Since the reflectors only receive half a side of neutrons each to double, the result is the same as if it were surrounded by just four reflectors, each receiving the full power of a side.
  • Surrounded by absorbers: Same as reflectors, since the output of the 1x1 core gets split over eight rods.
  • Surrounded by fuel rods: The rod in the 1x1 core would receive more neutrons, since there are twice as many rods surrounding it that provide these. This allows using the 1x1 core to quickly fill up breeder rods. That makes the breeding slightly more efficient, making the 1x1 core much better than the 2x2 for it, but could still be viewed as only a slight imbalance.
  • A moderator rod in the 1x1 surrounded by fuel rods: This is where the fun begins. Since the moderator rod reflects more energy based on the number of fuel rods surrounding it, there is a definite advantage in surrounding it in a 1x1, so it has eight neighbors instead of the usual four, effectively doubling the neutron output. But what about neutron maximum, shouldn’t the “output speed” be irrelevant since going over the maximum would reduce efficiency drastically? The maximum only cares about the output of the fuel rod, not about the extra neutrons created at reflectors or moderators. But doesn’t moderation from the moderator rod also reduce efficiency drastically, shouldn’t that balance it out? It reduces efficiency by 4 times. So, from a moderator you get 8 times more neutrons when surrounded by eight rods. Well, however see, that also means a fuel rod can only be adjacent to two of these, because it is in a 2x2 filled with fuel rods, meaning that only 4.5 times the neutrons get reflected (8 times 2 from the moderators plus 2 from adjacent fuel rods divided by four because that is per side, so total of 18/4), meaning it would almost be balanced out by the 4 times lower efficiency, only being an eight more efficient! Have you ever heard of surrounding a moderator in a 1x1 core with fuel rods in 1x1 cores? Did you know that in that case, the 1x1 reactor with the one fuel rod still counts as two sides to the moderator? Well, that means we speak of 8 times the neutrons reflected, even with the efficiency reduction from moderation that is still twice as efficient! And the solution can’t be to make moderation reduce efficiency even more, because that would punish the non-exploiting ways of using the moderator (in a 2x2 reactor for example) and water based reactors far too much.

So combing the 1x1 core and moderation is very problematic, especially because of how incomprehensible this behavior is for players. So how to fix this?

  • Make the neutron maximum take reflected/moderated neutrons into consideration. This would be a fine solution, the maximum would have to be based of the neutrons on the rod instead of the emitted ones. This would also make measuring if you go over the limit much more intuitive. The problem of the unintuitive behavior with moderators and fuel rods in 1x1 cores next to each other is however still unresolved.
    The balance of the whole system also gets shaken a but by this, because suddenly absorber rods will be much more efficient, since they effectively lower the neutrons on the fuel rod (since nothing gets reflected) and doubling the heat output of these, as well as reflectors now being nerfed comparatively, since their extra neutrons now count towards the neutron maximum. This would give absorbers the role of distinctly raising efficiency while reflectors (and moderators) are used for reaching criticality. Currently absorbers are kinda useless in critical reactors, because they are effectively equivalent to reflectors since reflectors also double the power output by doubling the neutrons instead of the heat, with no effect on the efficiency while also allowing to reach criticality.
    Generally this change would also count as a nerf to reactor efficiency overall, since neutron maximums are now reached earlier. This is also probably a good change, since reactors are pretty powerful right now anyway, so effectively cutting the efficiency in half (or more with moderation) isn’t that bad.
  • Removing the 1x1 reactor core (crafting recipe). This change would get rid of the weird interactions between it and moderations completely. The 1x1 core is generally more powerful than the 2x2 in any conceivable way: Easier to automate, more space to automate, less resource intensive, better for breeding, easier to reach criticality with moderation.
    Disabling it would tighten the balance and make reactors a bit more engaging an complex to build, since automation is much more difficult, having to use robot arms to interact with specific slots, while having to deal with less space for the automation (but certainly not impossible, because extenders exist).
  • Removing moderator rods (crafting recipe). This would also solve the problem with problematic behavior, but the superiority of the 1x1 reactor core over the 2x2 would still remain and water based reactors would be severely nerfed as well as the reactor system loosing a (in my totally unopinionated, not because I added this mechanic in the first place, opinion) really cool gameplay mechanic.

Personally, I would remove the 1x1 core (maybe leave a optional config setting to leave it in) and also change to neutron maximum system, as I think it would generally really improve gameplay and provide some necessary streamlining to the nuclear system while providing more complexity in reactor automation. The other really nice thing with this change: Not breaking backwards compatibility (much). Since the block would still exist and heat/neutron mechanics wouldn’t be changed, old reactor designs would still work and output the same amount of heat, only their efficiency would have changed.

Coolant balance:

The big issue out of the way, there are also other changes I would make, more specifically to the balance of the coolants. While I’m generally happy with most of them, I feel like a few coolants don’t fit their intended role: The molten metal and gas reactors.

The molten metal coolants are supposed to fill the role for breeder reactors, however they fall short in comparison to the carbon dioxide coolant. Carbon dioxide has the huge advantage of raising the factor of the fuel rod. This allows using one adjacent reflector less to reach criticality, freeing the side up for breeder rods.

This allows a critical carbon dioxide breeder reactor with U235. U235 has a factor of 1/4, which gets increased to 1/3, which means only 3 sides need to have reflectors instead of 4 to reach criticality, allowing the remaining free sided to be used by the breeder rod. In a molten metal reactor however, since molten metal coolant doesn’t increase the factor, the rod would need all 4 sides to reach criticality and thus can’t be used for breeding, only allowing for high tier fuels with a factor of 1/3 to even be used there for critical breeding.

Since the stats of the molten metal coolant reactors are generally only useful in a critical breeder anyway, this is unacceptable. I would personally give the molten metals the bonus of increasing the factor, while taking it away from carbon dioxide coolant, probably with some smaller additional balance changes to the molten metal and gas coolants in general to make them better fit their niche (or establish one for the gases) while keeping their general balance in check.

This change would however be breaking and could in the worst case lead to explosion (noises and power outages, the explosions of the cores are still disabled iirc). The potential boomers would however only be the molten metal reactors, which I doubt anybody currently uses anyway, carbon dioxide would only be getting nerfed, so power outage in the worst case but no boom.


Removing the 1x1 seems like a good idea overall, considering how exploitable it can get.


For me byggest problem with nuclear energy is too much nuclear fuel in worldgen.
So I disabled all uranium/thorium ores and byproducts (no more uranium from azurite/rutile byproducts). Also made refined cobalt (Co-60 source) only available from copper in aqua regia (100 times lower chance, I think. I’ts 0.5% currently).
Also added 1% chance to get tiny refined thorium and 0.33% chance to get tiny refined uraninite from centrifuging 2 dark ashes. Also a way to get nuclear fuel from bedrock-mining coal.

Result is interesting. First reactor was moderated Co-60 “bomb”. 3 1x cores, 3 universal extenders, 1 moderator rod, 2 Co-60 rods, coolant: CO2. Enough for large invar boiler. I’m currently upgrading it to use 4 Th rods and feed 2 large invar boilers (currently stuck because of not enough iron).

I have another similar reactor running. 5 1x cores, 4 universal extenders, 1 moderated rod, 4 Co-60 rods, coolant: industrial coolant. So my base is currently powered :slight_smile:

I need to have 20 of tiny refined uraninite to get my first U-235, currently I have 18. I get most of my dark ashes from centrifuging komatiite dust. Only then I can start breeding Pu-239 (real fuel).

Yes, I like extracting nuclear fuel from crap :slight_smile:


I want Pu-239 mostly because it will allow me to build stable reactor (good for powering large centrifuge).


Hmm, that is a very good point. I’d argue the easy availability of good nuclear fuel (i.e. U235) is the biggest issue. While small, low power reactors like the ones you describe are still useful, they are really not that powerful. With the 1x1 reactor core being removed, that first reactor would (when rebuild using a single 2x2 core) output almost half as much power anyway (24HU instead of 44HU, though that design, since it is subcritical, works much better in a industrial coolant reactor, producing 52HU).

Cobalt-60 and Uranium 238 however can just go critical in a moderated reactor setup (using only 2x2 cores), though since the neutron maximum on those is quite low it may not be entirely worth it, also considering you need 6 2x2 reactor cores of space to get a single rod critical.

What is most important to lower however is the availability of Uranium 235, which would ideally be the gateway to more critical reactors and breeding reactors, allowing getting better fuels.

However currently U235 is obtainable in several ways:

  • Processing uranium bearing ores by centrifuging. While the output of U235 here is not too high, the process itself is quite easy and the ore readily available.
  • Processing uraninite using the uranium fluorite chain. The output of U235 is a bit bigger, but since the chain itself is so much more work compared to simply centrifuging it, it’s probably not used by anyone.
  • Breeding with lower tier fuels. Ok, while not providing U235, it provides even better fuels like U233 or Pu239. Currently breeding seems to be too easy, since it is totally feasible by just using low tier fuels, taking just some hours. And with the 1x1 reactor enabled it would be even quicker.
  • Extracting it from depleted U238. I think this is also much more powerful than I originally intended. You get one third the materials you need for a fuel rod from a depleted one, making just “burning” the fuel in a critical reactor extremely viable.

So here is what I would do considering these things:

  • Make breeding without U235 unfeasible. This could simply be done by increasing the neutrons required. This would of course require careful examination, so the “intended” way doesn’t become to tedious. Another way to archive this would be to rework the breeding efficiency system. Instead of becoming exponentially more efficient with higher neutron counts per tick, a “neutron barrier” would take its place. This mechanic for efficiency would be very simple: When adding neutrons onto a breeder rod every tick, a “neutron barrier” value gets subtracted from it. This value would be so high, that its only even possible to breed fuel with critical reactors. Obviously more neutrons per tick would mean more efficiency, as the breeder rod would then require less ticks and therefore less subtractions to convert, but it would no longer be exponential.
  • Less “decay products” from depleted fuel rods. Quite simple, I would probably reduce it to two 1/72 of a pile of dust. Makes it not completely unfeasible to gain good fuels this way, but definitely less viable.
  • Making uranium bearing ores bedrock drill exclusive. Gating uranium behind it makes thorium and cobalt-60 the starter fuels that could remain fairly available. Since regular U238 is now gated, decaying it into U235 is would now require first attaining it by decaying Th232, which would make the process much, much slower and less feasible, although still possible.
  • Removing the centrifuging method of extracting U235. This will force players to setup the uranium fluorite processing chain, adding another gate to U235.

This would mean the fission progression would look something like this:

  1. Subcritical thorium and cobalt-60 reactors. Moderated critical cobalt-60 reactor possible.
  2. Unlock U238 by bedrock mining. Allows for U238 subcritical and moderated critical reactors, better than cobalt-60.
  3. Unlock U235 by uranium fluorite processing chain or burner reactor. Allows for unmoderated critical reactors and thus breeder reactors.
  4. Unlock U233 and Pu239 with a breeder reactor. High tier fuels which allow getting even better fuels in burner reactors.

All in all, good fuels should be harder to obtain, taking multiple steps, but once you have the necessary infrastructure, they remain readily available. Though I would really appreciate feedback on this, since it isn’t really my area of expertise. How easy are cobalt-60 and thorium to obtain for example?


Co-60 was very extremely abundant, until Greg made it just extremely abundant fairly recently. Uranium is more common than thorium, (because of uraninite and pitchblende ores).

Be careful about nerfing nuclear reactors. Some people may just not bother, especially if they have captured bedrock natural gas.

Also, currently I use Co-60 for large boiler, using moderated reactor, which outputs increasing counts of neutrons (autostops at 4000/tick). I’m not sure if it’s critical, or supercritical.

Uraninite processing chain is not that hard. I finished it… today, I think. Started at one point yesterday. 6 mixers, 2 smelters, 1 shredder, 1 dust funnel, 1 titanium centrifuge, pipes, drums, etc. All electric, because I don’t have that much uraninite :slight_smile:


Hmm, Co-60 seems to be the somewhat unbalanced due to its overabundance and ability to create critical reactors. Personally I think, instead of nerfing them significantly by taking away their ability to go critical, much lower abundance, preferably even lower than thorium, would probably the best way to handle this. But maybe it isn’t and nerfing the factor to be 1/32 like thorium would be the way to go, making it the worst but also most abundant fuel, while locking critical reactors to uranium.

Regarding the subcritical, critical, supercritical wording: My way of describing the reactors for GT6 is not entirely realistic, technically all reactors sustain at least a stable chain reaction, so every reactor would at least be critical and the ones where the neutron counts rise would be supercritical (while they are rising, when stopped they would be subcritical for a while again until they become critical, i.e. stable, at some lower neutron count). I however like to call the ones with a stable neutron count subcritical and the ones with a rising one critical as categories for reactors rather than descriptions of the current state of the neutron reaction for simplicity. So calling them critical or supercritical is both fine imo.

Overnerfing the reactors is genuinely something I’m worried about. I suggest turning a lot of balance screws at the same time, but I think reactors currently are powerful enough to warrant such heavy measures. The ability to create critical reactors that can theoretically put out any arbitrary amount of power (if there weren’t fluid throughput limits, power conversion and reactor fuel efficiency) is still present after the changes, but it would just be a little harder. You just wouldn’t be able to archive everything with the most abundant and worst fuel available.

I hope the critical Co-60 reactor isn’t the one with just 2 or 4 fuel rods, that shouldn’t be able to go critical, even with the 1x1 reactor core, especially in industrial coolant.

The uraninite chain isn’t supposed to be very hard, but it represents at least some special effort setup that is required to get the better fuel.


so im not sure how to respond to your idea’s of change, first i felt the 2x2 core is annoying to automate with gregs robotic arms. i love some complex automation but i felt it sometimes worked and sometimes didnt work the way it should. not sure how to explain but ive seen it pull from wrong slots even when set correctly. maybe thats been fixed by now. but if your having issues with the 1x1 reactor why not hard cap it so your neutrons cant go above 5k? i feel that would fix the balancing issues and still allow people to make small powered reactors, ive only ever used it for a breeder, i prefer to avoid making a critical/super crit reactor all together other then for breeding anyways, sure you can get some stupid power out of it. but ive made a ton of neat designs for 2x2 reactor parts that already output enough power to run two MB heat exchanger/boilers. ive never felt the need to make over powered reactors other then those. and they are “Safe” reactors, not once do they go critical or need turned off once started. well untill they run out of fuel. also if you debuff the co2 then it wont have a use imo. i barely use any other coolants then co2 and industrial coolant. ive never seen the need. if anything maybe buff the other ones, they are not exactly the easiest to get, or maybe rebalance the whole thing from scratch. irl nuclear reactors are massive power generators. they are suppose to be powerful. if you need to make crafting recipes cost more or not thats up to you, but i also never use basic fuels and only use bred fuels. basic ones are easy too, its just i never felt the need in my gameplay to use them other then initial breeding. with or without the 1x1 core for my breeder reactor its not hard to make another kind of it, it will just make automating it even more of a choir. its hard enough as is to get item sensors to tell you items are in it or not. and then which ones are in there or not at that. we dont have easy item sorting and with bred fuels never being a “perfect” rod missing atleast one point of fuel etc, you cant exactly set filters. im not sure the neutron maximum you would go for, but i can get 12-20k neutrons per 2x2 core in a safe reactor so i hope that wouldnt be messing with the “max neutron” system you speak of. each rod in my safe reactors atleast hit 6k neutrons. and in a 2x2 thats two per core hitting 6k+ ive not even tested americium yet. and these are not going critical at all and only use industrial coolant…

if you watch the video of bear989 touring my base, you can see the old initial design on my safe reactor and the max neutrons im pulling out of my fuel. sure its my older world and ive made progress on automating and setup on another world. but that is the basic idea of a safe reactor with massive power output, im not sure if you should just remove the benefit of critical stuff or not then. maybe make it skip over neutrons for critical reactors if its outputting too many too fast? as in if a reactor that outputs 20k per 2x2 core just started up it would lose out on “heat” to fluid from the neutrons till it “stabilized” so you can still do high output safe reactors?


ok there is way to much to read for me here but reactors are not an early game thing, hell xarses made 3 fusion reactors before even touching fission do to the complexity and your wanting to nerf it? especially your idea of making Uranium bedrock drill only, automating the Uranium processing line is complex enuff i dont think many will attempt it. i still havent done it and making power from large gas turbines and diesel gennies or large solar grids why would anyone setup a reactor? and your wanting to nerf it to where we have to search the world over for a bedrock vein? that will just make less people bother in my opinion. when i setup a reactor it will be be small constant power, i probably wont even mess with critical reactors.


also i found this, Cobalt-60 - Wikipedia so i would say Co-60 should be more of a byproduct that would make a long low running reaction and doesnt come from Co itself. i would say safe, low neutrons, non critical.


It does appear out of balance of sorts but I don’t think nerfing many of the things you say you want to do are a good path forward. I want to remind you that there is a 7 page document attempting to describe how to work with fission reactors, its not nearly complete or effective in telling the masses how to build fission reactors in the game so I want to strongly caution you that the solution is already complicated and hard to enter.

I built 3 fusion reactors, 5 large centrifuges, 5 tanks, 55 huge carbon pipes, 90 drains, 4 bronze centrifuges, a lv and mv electorizer, and supporting pipes and motors to run 3 sustained reactions because its easier to enter than fission. This produces ~24Ki Eu with about 7Ki going to generating fuel for the reactions

Fusion reactors are stable and not complicated to maintain, they offer a consistent 8192 Eu/t across every fuel which seems fair due to the low effort to maintain them. Compared to fusion, fission allowing for insane outputs in more complicated builds seems more than fair. Keep in mind that sustained usage of the large matter fabricator draws 16Ki Lu → 32Ki Eu making Fusion not suitable for sustained matter manipulation.

Other late stage Energy generation basically only includes Tungstensteel or higher turbines. Gas Turbines can produce 24Ki EU with FeW. Sustained steam generation can be accomplished with traditional fuels, but is complex and appears to consume fuel quite quickly. I use Butane/Propane/Methane High/Low tanks and a high/low for NG (fed from ~60 springs scattered thought the vicinity). and iridium diesels and HV dynamos for the fuels. This is enough to keep my base battery mains filled, but would not be enough to run my base on EU (I mostly use turbo diesel for any RU application and Gas for heat) let alone deal with the power demands from matter fabrication. These combine to make the only viable power source for late game steam generation via heatant generated from fission reactors.

So I caution the approaches taken to reform the fission system so that its still feasible to generate the enormous amounts of power required in the later stages of the game

Ore Changes

Cobalt-60 is too abundant

This is very true, but given that the fuel appears to be piratically useless, I’m not sure the correct reaction here, you imply that you can make it critical, but I’m not sure how to do that, or what the maximum power here is

Thorium is too abundant

Maybe, I’m not sure here at ~60k Uraninite ore/~85k Uraninite dust , I only have 13.5k (15%) Thorium, it seems that there is much here, but not more than would be expected

Uranium (238) is too abundant

As direct byproduct processing, (uranium small ores) and the like I have just over 2k from the above uraninite load and another 6k large refined ore to seperate, given that it has the same byproduct rate as thorium (15%), there is far too much of this form of uranium available as its easy to process at 1024 RU

Uranium-235 is too abundant

As a direct byproduct processing U-235, my production gives an actual rate of 24%, which is the same as the chance rate of 24% ( 0.03*8) per 1/9th. This seems to be far to high for the ease of getting the material this way.

No one does uranium hexafloride

raises hand I run hexaflouride, its a beast of a loop requiring at least 18 machines, but ya, given the high rates of U-238 and U-235 as byproducts, no one is going to set it up. It consumes SiO2 and H (It does byproduct Si) like a mother but seems to be over producing in general (I’ll be back later after computing the exact cycle numbers) However the Rate of U-235 appears to be nearly 40% which is quite high, given the effort it seems reasonable.

Plutonium (244)

As a byproduct of centrifuging Uranium ore, Pu-244 clocks in around 10% the rate of Uranium, I’m not sure my math here, I ended up with 195 units, which appears to be 1.5% rate.


I ended up with 22, so not a lot of gain here compared the the crap ton of uraninite I processed.


I ended up with 19 here, again quite low gains.

Ore wise we are quite heavy on Co-60 and Th, those outputs can most likely be shortened, or have the ticks of the material changed to make up for the abundance. They may also need their power reduced, but I don’t understand enough there to comment at the moment.

Uranium is outright too easy to get, and the U-235 rate from ore is very high, we need to take steps to reduce that, either making ore less potent, or requiring another step (yellow-cake) to get U-238 out. We can also do centrifuge or other lossy reduction to get early amounts of U-235 out if we are going to need it for breeding.

However moving Uranium to only work with bedrock IS NOT a solution. The in world rates of Uraninite/Pitch/Thorium are actually on the low end, the three veins ive found are quite sparse. I ended up using an IE vein for “Uranium” which Greg “fixes” to uraninite when crushed.

Putting them behind bedrock mining seems interesting, but the rate of finding bedrock veins, or even the ones you need is quite low. I’d rather see the existing ores made less potent or require reduction recipies for the higher quality reactors

[ I will be back with more comments on the other aspects proposed ]


This is some really helpful feedback!

Requiring bedrock drills for uranium has definitely been a bad idea of mine, so that definitely won’t be coming. As far as ore abundance goes, the ores seem to all be at least a little too abundant.

As for cobalt-60 seeming useless: It is a more powerful fuel than thorium and the factor of 1/16 allows it to go critical by just surrounding it with four moderator rods (which all need to be fully surrounded by fuel rods). This theoretically allows extracting any amount of power wanted from cobalt, but as the neutron maximum is very low, you would be going through the fuel rods very quickly if running at high power, it is probably not worth the resources for what is quite a big reactor (at least 6 2x2 reactor cores) just to get less than 256 neutrons worth of output when staying under the maximum.

However, with the current system of the neutron maximum and having the 1x1 reactor core, it gets much more ludicrous. You will need only 13 single core reactors (which iirc are less resources than 6 2x2 cores), the setup is the same, but the numbers change drastically: Since the moderators are basically twice as strong in 1x1 reactors, you’ll be looking at not 4 but 8 times the neutrons. And since the neutron maximum only accounts for emitted neutrons (not the extra ones from the moderators), we are looking at an output of 2048 neutrons, while staying under the maximum.

Well, the reactor wouldn’t really be controllable in that state, needing to shutdown more than half the rods for it to go subcritical, so realistically the build would only use two moderators, just enough to go critical in 1x1 reactors, so we would really only be able to produce 1024 neutrons at maximum efficiency. That doesn’t sound too bad, but remember this is one cobalt rod we are looking at and that these issues with the moderators and 1x1 reactor also scale to the better fuel rods. And that there are now two free slots next to it that can be used with absorber rods to get even more power from it. This setup probably not something most people know, much less use, so I count fixing this exploit not as really nerfing reactors.

So, when the 1x1 reactors is removed and the neutron maximum system changed, cobalt-60 isn’t that powerful, being quite expansive to build a critical reactor for and burning through fuel quite quickly when running at a high output. Lowering its abundance a bit might be a good change, but isn’t really required. However maybe making cobalt-60 less useful, turning it into the worst but most abundant nuclear fuel, would be a better alternative. Nothing would really be lost, as U238 can do everything Co-60 can, while only being a little rarer. I would really like to know what is the general consensus on this.

What I still feel however is required, is making breeding harder or rather require better fuels or critical reactors. Breeding just shouldn’t be something most players do with Co-60 (or U238 or thorium), as the breeding fuels are really powerful. A critical breeder reactor should imo be required. I mean, have you seen Pu239? That stuff is so powerful, it will go over its neutron maximum when surrounded by just four reflector rods in a floppin subcritical industrial coolant reactor! Critical breeding reactors are without a doubt the hardest to build and most complex and dangerous to operate, they should therefore not be made redundant by using a bit of Co-60 and time.

This also opens up some space for people to build burner reactors, as they are much simpler to automate and much less dangerous, while still being able to produce better fuel. It allows converting U238 into U235 at a rate of (currently) 3:1, while also producing lots of power, offering a good alternative to the uranium fluorite processing chain.

There also has been some worry that the changes I propose would make fission reactors less viable as the endgame energy source, but I think this is entirely unwarranted. The changes I propose don’t really effect the possible power output at all, apart from the removal of the 1x1 core making moderator rods less exploitable. The fission reactors and fuel themself arguably aren’t even the bottleneck, but the whole infrastructure required to convert the power into electricity is.

So, onto a very important point of critique: Complexity. The nuclear fission system is somewhat complex and lacks ingame documentation. Nerfs wouldn’t be required, because the complexity balances the potential of reactors. I have two counterpoints to this: First, fission reactors will still remain exceptionally powerful after the nerfs, just the exploits only experts would notice are fixed and there is maybe some more fuel consumption/less fuel available. Even after the nerfs, fission reactors will still be more powerful than when they were initially released (remember not even being able to automate them?).

Second, removing the 1x1 fission core and changing the neutron maximum to be based of the neutrons on the rod instead of total neutron output actually reduce complexity quite a bit. There are a bunch of weird and unintuitive behavior with the 1x1 reactor core, especially when combining it with the 2x2 reactor core. Those would be gone. Then, most notably, checking if a rod is above the neutron maximum would be much easier to do: Just read the neutron count on the rod. Right now, you have to calculate the real neutron output, which is much harder to even explain.

But some complexity would be introduced with the removal of the 1x1 reactor core, though not at understanding the reactors themself, but at automating them. I personally like the added challenge there but others like Ultima may see it as tedium. I can’t argue much against valid critique, other than arguing that the benefits of removing the 1x1 reactor core outweigh the negatives in my opinion.

And now for something completely different: Reactor coolant balance.
It is abundantly clear that the most used coolants are carbon dioxide and industrial coolant.

Industrial coolant excels at running subcritical reactors, allowing for really high energy outputs without much complexity.

  • Carbon Dioxide is one of the best options for running critical reactors and is the best option for breeders as well as easily obtainable. The other coolants seem to pale in comparison.
  • The heavy water coolants are probably to tedious to acquire while offering no huge benefits in any area. They act as a kind of baseline, but maybe they could use some buffs, like an even higher heat density?
  • Molten salt seem fine to me, just used less because CO2 is so good and easy to acquire.
  • Thorium salt is really good, especially when the changes to neutron maximum would slightly buff it, but requires a completely different design approach. Curious if anyone has one of these running.
  • Helium and molten metal are arguably useless.

Personally, I would only nerf CO2 and buff the others (except industrial coolant, I will leave it alone). The fear that CO2 would be useless and nobody would use critical reactors is in my opinion a bit unfounded, as there would ideally be more viable coolants after the rebalance, without CO2 becoming useless or industrial coolant being the only choice.

This post is already huge and I could still elaborate on some stuff or start on other issues (lack of ingame documentation, etc.), but I’m instead asking some questions:

  • What is your opinion on coolants other than CO2 and industrial coolant?
  • What are your suggestions for rebalancing the coolants?
  • What is the airspeed velocity of an unladen swallow?
  • How should breeding fuel rods be changed to discourage using Co-60 and other low tier fuels?

Follow up for Uranium hexafloride Loop

I just went through the cycle numbers and as I lamented, produce far too much uranium from uraninite.

For an input rate of 28 uraninite we produce 28 units output or 100% of the input. 71% of the input becomes U-238 (20 units) and 28% U-235 (8 units). The ratio of outputs being U-235 is 40%

Starting with the Input, Uraninite is labeled as UO2, which implies that only 1/3 of the input can become any form of output. Fixing this rate alone may be enough to bring balance to the loop

Output rates; the ratio between 238 and 235 seems high at 40%. I would argue that it should be less and instead allow for further lossy reduction of the U-238 output to produce more U-235. Given stable access to a uraninite bearing ore, this is the fastest way to produce 235 for other fissile needs.

[ I will be back later to talk about fluids and other subjects ]


Uraninite in this case is the same as rutile, pyrolusite, garnierite, cassiterite. That is, get 1 unit of metal from 1 unit of that metal’s oxide.


Link? I’d love to read that.


I haven’t done much research on nuclear fission system. Personally, I prefer chemical industry (that’s why I’ve been putting forward those suggestions on Chemistry), and I don’t have much game time, so I’m not too interested. But I have some thoughts to say here:

  1. Cobalt 60 should not be used as nuclear fuel. As far as I know, although it has radiation, it will only decay, emit beta rays and gamma rays, not neutrons, and will not fission under neutron bombardment. So I don’t know why it’s used as a nuclear fuel, maybe just because it’s a radioisotope?
  2. The commonplace things about uranium-238 and uranium-235. Probably due to IC2, the uranium ingot in gt6 is not a mixture of a large amount of uranium-238 and a small amount of uranium-235, but uranium-238. However, in many other nuclear industry mod, uranium ingots are a mixture of two nuclides. This makes the isotope separation of gt6 very strange. Although this is really not a big problem, it may lead to a method of converting uranium-238 to uranium-235 through the mineral dictionary.
  3. For coolant, in addition to those added, Na-K alloy can also be considered. This is added in NC. In addition, there is ammonia in ReC, although I don’t seem to have seen that ammonia is used as coolant in real reactors, and ammonia can’t be synthesized now.
  4. This is my own UF6 loop and flow chart. I know this layout is a waste of space. There must be a better method, but at least it can operate normally. Recycling fluorite is really a troublesome thing. This cycle generally inputs uraniite and silicon dioxide, and outputs uranium-238, uranium-235, silicon and oxygen (I electrolyze water)


So, my change to the durability system is merged and will be in the next GT6 release and is in the current testing release. Don’t worry about your reactor exploding, this change doesn’t effect neutron counts. One thing to look out however, is that the neutron maximum calculation changed, you don’t need to compare it to the “real neutron output” of a rod anymore, but to the amount of neutrons on the rod.

Responding to some feedback:

The uranium fluorite processing chain seem to a tad too much work compared to the other way of obtaining U235, although it is more profitable. Realistically the player only needs one U235, being able to then breed better fuel (when breeding gets rebalanced), so removing the other method of obtaining U235 seems to be the most reasonable way to balance U235. Maybe then the output of U235 from the process could also be lowered a bit?

New coolants like Na-K or ammonia are possible, but I don’t really see much purpose for them. Na-K would be a liquid metal, so it would probably be “breeder coolant”. Realistically it is a terrible coolant for your reactor, while it is liquid at room temperature, it will react violently to water and catch fire when contacting air. In the vacuum of space, that may not be as great a problem, but in your backyard… Not that this wouldn’t make for an interesting coolant, but the effort to realistically and purposefully implement these things as mechanics is simply too great. As for ammonia, I’m not really sold on it as it would just be another gas coolant, although a less realistic one.

Next thing I’ll probably tackle is rebalancing breeding to need breeder reactors. There are generally two ways I could do this:

  • Higher neutron amounts needed. We are talking many magnitudes higher here. Neutron outputs onto breeder rods can get ridiculous: When outputting 10_000 neutrons onto a breeder rod, that means 10_000 * 1.5^(10_000 / 500) = 10_000 * 1.5^20 = 10_000 * 3_325.2567 = 33_252_567 neutrons per tick towards breeding process. Only 144_000_000 neutrons are currently needed for breeding thorium into U233, so the process would only take a whopping 5 ticks, a quarter of a second. At 20_000 neutrons you get 221_146_646_418 neutrons of progress, which would still process the rod in only a single tick if the neutron count required would be increased by a 1000 times. Exponential growth is clearly a bit ridiculous.
    So lets say we want to balance thorium so it takes one minute at 15_000 neutrons per tick onto it. That is ~2_876_265_888 neutrons of progress per tick, meaning it would be 3_451_519_066_191 neutrons required for the rod to take one minute. I think this system is generally maybe a bit too complicated for the average user. Sure, higher neutron counts mean faster, but it is hard to gauge how much time it takes for a rod to breed with any neutron output at a glace, really needing a calculator.
  • The second approach would be to rework the breeding system completely with a new stat for breeder rods called “neutron loss”. It describes how many neutrons get lost when put onto the rod. So if you output 2000 neutrons from a fuel rod onto a breeder rod with a neutron loss of 1500, only 500 neutrons would arrive on the rod. Rods would only take exactly the neutrons onto them towards the breeding process, no exponential confusion.
    That means a couple of things:
    – Calculating how long it will take is significantly easier: just measure the neutron count on the rod and divide the neutrons required by that to get the number of ticks it needs.
    – There is no huge efficiency benefit of having multiple fuel rods supply neutrons onto a single breeder rod anymore. Previously that would mean greater neutron counts and exponentially faster breeding, making it also more efficient. But now, since the neutron loss is subtracted from the neutron output of any of these fuel rods, adding multiple fuel rods will only scale speed linearly, but efficiency stays the same.
    – Breeding efficiency doesn’t scale up as much, more neutron output from a adjacent rod will always mean more efficient, but the increase less significant the more neutrons are added.
    – Neutron counts on the breeder rod will be a tad bit lower (because they got subtracted by the neutron loss)

I’m leaning much more towards using the latter approach, because it makes breeding potentially a bit simpler to understand, as well as better to balance.

Another thing I would like to do is make handling the output of breeding a bit less tedious. Currently, especially with the new changes to the durability system that actually make rods update durability each tick rather than each second, there is not much hope that the new fuel rods produced by your breeder reactor will stack.

I would fix this by added a new intermediary stage between the breeder rod and the fuel rod, the enriched rod. The enriched rod has no durability, so will stack easily. Inside a reactor, the enriched rod will capture and convert neutrons to heat at a 1 to 1 ratio, making it effectively a worse absorber rod. With the change to breeder rods having a neutron loss, the number of neutrons on the rod would therefore slightly and suddenly increase when a breeder rod turns into an enriched rod, allowing you to automatically detect it and remove the rod from the reactor.

This would mean that breeder reactors are slightly less dangerous, as the reaction doesn’t rapidly get faster when a breeder rod converts. Alternatively, the enriched rod could act as a reflector, to get that sense of danger back, but I don’t want people to use them purposefully as reflectors, but maybe I’m worrying to much about this?

To turn these enriched rods into actual fuel rods, I have multiple ideas:

  • Turn enriched rods directly into fuel rods upon taking them out of the reactor. This would then also allow having them function as reflectors, as they wouldn’t be so exploitable. Though I will have to evaluate if this approach is even possible on automated extraction of the rod.
  • Have some really simple processing/crafting recipe to turn them into fuel rods.
  • Have a more complicated processing step, not turning them directly into the fuel rod, but into less than a fuel rod worth of the material the fuel rod would be made of.

What do you all think about this? What processing method for the enriched rod would you prefer? And what do you thing about the possible new breeding system?


With regard to the safety of NaK alloy, it is obvious that this will not happen in GT6. And you have added molten sodium coolant, so there will be no problem with potassium with similar natural properties. I think this can make potassium more useful. Its performance should be better than molten sodium.
For molten metal reactors, in addition to NaK, another commonly used coolant is eutectic molten lead-bismuth alloy, which has poor performance, low heat capacity and will absorb a lot of neutrons. The main reason for using in reality is that it will not cause danger like NaK, nor will it produce serious corrosion.
For the molten salt reactor, in addition to the lithium chloride currently available (it’s strange that I didn’t find lithium chloride as reactor coolant in reality, although it seems feasible in theory), it also includes FLiNaK and FLiBe. These two mixed salts will have higher heat capacity and performance, However, they are also difficult to obtain (they are added to the branch of GTCE Gregicality and can be used in their reactors).
In addition, for water-based reactors, there is another coolant option: boric acid solution coolant. It will have higher heat capacity and moderation. At the same time, it will absorb more neutrons, which is conducive to stabilizing the reactor. In reality, many are used. This may make the borax vein more useful, or add a boron neutron absorber like HBM.
As for breeding, in addition to the balance of neutron exponential growth, I also hope to use lithium to breed into tritium, so you don’t need to spend too much time on centrifugal water to obtain tritium. Adding more logistics machines will make it easier to automate the breeder reactor.I very much hope that adding logistics machines like Regulator can make the automation of reactors easier.


me, brain, hurt.