Makes nuclear energy realistically overpowered. Also makes solar panels realistically worse, because solar panels have had it too good for too long.

Changes

Reduces solar panel production from 60 kW to 9 kW. (Note that this change dates back to when I played earlier, unpublished versions of this mod in 1.1. I haven't gotten to space yet, so if this makes early platforms unplayable I may change it.)

Removes reactor neighbor bonus, and increases nuclear reactor power to 160 MW to match what most extendable reactor setups will approach.

Increases energy content of uranium fuel cells from 8 GJ to 112 TJ. (See calculations below.)

Nuclear reactors now scale their fuel consumption to their energy consumption. Most real-world reactors are load-following as a means of controlling reactor power, even if they typically operate at max power for economic reasons. Other reactors are routinely operated in load-following mode, such as naval propulsion reactors. This change adds this capability to Factorio reactors.

Increases power of heat exchanges and steam turbines by 10x. Estimating the size of these buildings by comparing them to the Engineer puts them on the same scale as nuclear submarine steam generators and turbines, and this change brings their power in line with the published power output of those real-world systems. They consume a proportionately larger amount of water and steam.

Increases cost of heat exchanges and stream turbines by 10x, so that the increased power density doesn't also make them cheaper.

Reduce weight of U-235 and U-238 from 50 kg to 2 kg, to match that of coal, and carry the implications of this change to uranium ore and uranium fuel cells/cores, as well as Plutonium Breeding items, if present. At the same time, greatly increase the weight of nuclear reactors, heat exchangers, and steam turbines. With vanilla rockets, these will now need to be assembled on-platform to use in space.

Remove productivity from uranium fuel cells and reprocessing. It makes the energy and weight math easier. This removes the theoretical uranium efficiency gains that productivity would allow, but with realistic energy values this would be overkill in any case.

Greatly reduce the fissile material cost of atomic bombs to 4 U-235 and 2 U-238, but also add Rocket as an ingredient. If Plutonium Breeding is active, then they can also be made with 4 U-238 and 2 Pu-239. These values are roughly based on the content of the Davy Crockett's W54 warhead, which is closest to that shown in game (minus the absence of radiation damage).

Reduce weight of atomic bomb to be equal to the combined weight of its ingredients.

This mod makes no changes to portable fission cores and "nuclear fuel", as no plausible analysis can be made of such items.

Now With Hard Mode: Nuclear Cores

Do you feel that this mod makes nuclear power TOO powerful and easy?

Then consider the option to replace nuclear fuel cells with nuclear cores, which are 100x larger in materials and energy content, and require enrichment levels which correspond to those of real-world proposals that seek to achieve the high burn-up ratios seen in Factorio (20% U-235 for uranium-only cores, 10% Pu-239 for MOX cores if Plutonium Breeding is active). Besides being more realistic, this makes the transition to nuclear power more difficult, as a counter-balance to its power. A nuclear core that is consumed at full power will last about 2.2 real-world years.

As a matter of completeness and consistency, this option also applies to the plutonium-based fuel cycle from Plutonium Breeding, tho given the time-frame involved you will likely never see a depleted nuclear core to reprocess. If you ever do, please let me know in the Discussion tab!

The cores option only affects recipes, so you can safely enable or disable it on existing saves without removing any existing fuel cells or cores, and leaves the uranium fuel cell recipe available to support modded recipes that use it. To enforce the intended difficulty, also enable to option to make fuel cells unburnable. (This is a separate option because enabling it on an existing save will destroy fuel cells currently inside of a reactor, including the one currently being burned.)

Calculations

I'm assuming that a unit of U-235 or U-238 is 1 kg. This is consistent with the energy content of a unit of coal, which is what 1 kg of the best coal would contain with perfectly efficient energy capture. (As of Space Age, a unit of coal is canonically 2 kg. The following math still applies if we just assume 2 kg at 50% thermal efficiency rather than 1 kg at 100% thermal efficiency.)

1 kg of uranium contains 83 TJ/kg. Rounding down to 80 TJ for the sake of using a round number. U-235 and U-238 are different in how easy they are to fission, but if you do get them to fission, their energy content is about the same, so I'm treating them as equivalent.

10 uranium fuel cells are made from 20 uranium. Those 10 cells, once burned, can be reprocessed into a total of 6 U-238, for a net consumption of 14 kg uranium per 10 cells.

14 kg/10 cells * 80 TJ/kg = 1,120 TJ / 10 cells = 112 TJ / cell

As this mod now removes the reactor neighbor bonus, adjusting for it is not necessary.

Check out my other nuclear mods:

Deterministic Uranium Enrichment: Changes the uranium enrichment recipe to be deterministic, multiplying all recipe parameters by 1000 to maintain the same cost, time, and output ratio.

Plutonium Breeding: Adds Pu-239 to the nuclear fuel cycle and replaces Kovarex enrichment with plutonium breeding.