Right, so there's been some rather... fundamental changes with nuclear engineering in the experimental fork. Of course, being experimental, there's no guarantee that this fork will ever actually be incorporated into the main IC2 development. The other caveat, of course, is that it is still a work in progress, so nothing is set in stone.
With that said...
First off, the amount of nuclear material produced per uranium ore is dramatically increased. Then it requires a bunch more nuclear material to produce the stuff that goes into the reactors. On the whole, it is a slight nerf, but somewhat mitigated by the fact that every fuel rod drops a depleted cell, so breeders just got a whole lot more useful. At the same time, however, heating cells got removed, which is a pretty stiff nerf-bat swung at breeders in general.
Now, fuel rods are currently made in the Canning Machine, and it takes for bloody ever... worse, it can't accept overclocker upgrades. Which means to make enough nuclear material to run a typical reactor, it's going to take for bloody ever. Oh, and because Canning Machines can't accept upgrades, that means no auto-eject upgrades either, which means automation of the task is going to be a PITA.
Heat and EU numbers haven't changed... which means all the old reactor designs should work just fine. Of course, with the additional nonsense involved in setting it up, this can only be seen as pushing Nuclear Power into an even less viable option for power generation... unless you use the MOX generators, which means having already run nuclear generators to get the depleted cells to generate the plutonium to make the fuel pellets for the passive EU income.
It's at least different and interesting. Lot of potential here, let's see if it pans out as well as I hope it will...