Ah.
So you are not in fact playing Unleashed, you are not in fact on Minecraft 1.5.2, and you do not in fact have GregTech installed. What you do have is a 1.6.x world with IC2 Experimental, which is essentially a reboot of the mod after over a year of feature freeze. It's a completely different beast (and also heavily work in progress).
That's why, when someone asks you what version you run, please don't just make up random things. You're just preventing yourself from getting an answer. Instead, start up your Minecraft client (or quit your running game), and in the main menu, click the "mods" button. Then provide what you can see there.
In IC2 experimental, you need to extrude "fuel rods" from iron casings in a metalformer. Then you need to craft "enriched uranium fuel" by mixing U-238 and U-235 in the appropriate recipe. Finally, you need a canning machine to insert the enriched fuel into the fuel rods to receive uranium fuel rods. Those still work as they always have inside a reactor.
Oh, and get yourself a full hazmat suit, or you will die of radiation poisoning.