I have one
https://mods.factorio.com/mod/NuclearScale

Interesting.
Anyway, I know how to "scale" things, so it's simple for me to add it (or any other machine) if it's needed.
I think I will provide up to nuclear reactor +2 (15×15, raw 640 MW) or +3 (20×20, raw 2.56 GW), in next version.

Just want to know how many nuclear reactors do you or other people use in their megabases?
Especially when a few thousand steam turbines are enough to kill UPS.

If you use huge and powerful turbines then your ups will be much higher. You can use the same part as it was made in Tiers 32 - if you collect 32 items, then you can make the new one, that is 32 times more powerful. With any factors, of coarse.

I see. Though I see limited throughputs when I made this mod, so I think I will not overscale things too much. Tiers of 4× is enough for my purpose.
For example, I tried heat exchanger +4 (2.56 GW), which has 5 water pipe connections per side. It would take 26392 units of water per second (u/sec) in order to work at full capacity, but 5 pipes can only provide 15000 u/sec at very ideal case. So it would be meaningless and I dropped it out.

Solar panels and accumulators would not face the throughput problems. So your mod don't have to be limited by this.
PS: Didn't realize these two mods are made by you, until you pointed them out here. :D

Scaled up nuclear reactors are now available in the latest version, 0.16.1.
Two overtiers are provided: +1 (160 MW) and +2 (640 MW).

I playtested 2×2 nuclear reactor +2 (total 7.68 GW). I found that it is already a tough challenge to connect enough water pipes, heat exchanger +3, and steam turbines +3, in order to run the whole plant at the designed rating (without "cheating" water source.) So I believe there is no need for nuclear reactor +3 at all.

PS: I feel increasing pipe throughput is "cheaty" rather than UPS-saving. So I did not touch the pipes or pumps.

Did you find the crash when amount of heat point connections is more than 12?

The limit reported during my test was 32.

That's why I did not scale up nuclear reactor like other machines, still having 3 connection points each side. (I wanted 6 points for +1, 9 points for +2 on each side.)