This mod lets you use (full) uranium cells or re-enriched uranium cells as well as uranium ingots (use either ingots or one type of cells, doesn't work if you mix them) when crafting nuclear weapons - assuming, of course, that the config file lets you build nukes in the first place. That's it.
I'll leave it as an exercise to the reader as to why you'd want this.
Works on both SSP and SMP. When connecting to a server which has this mod installed, you don't actually need to install it yourself to benefit from it. If you don't have it, you won't see the nuke item in the crafting output slot (but note that this doesn't stop you from crafting it, you just don't know that you're able to build a nuke).
Attached are client, server and the source. The mod_IC2.java file inside the source code is essentially a header file used during compilation to allow me to access IC2's config files - it contains no actual IC2 code and isn't included in the client/server mod files. Do whatever you like with the code - it's nothing special.
To install, stick the relevant .zip file in your .minecraft/mods/ directory along with IC2. To compile/edit, extract the IC2 API as normal into the src/[minecraft/minecraft_server]/net/minecraft/src/ directory of your Forge-decompiled Minecraft, then put the source in the same directory.
Thanks to AtomicStryker, who published the code for his version of Advanced Machines. Looking at that was a big help in seeing how things are done for IC2 mods.
2013-03-07: updated to support any version of IC2 that runs on Minecraft r1.4.6/7 and added a recipe using re-enriched cells.