I know other people have suggested other ways to get Plutonium, but I wanted to throw my suggestions in too, perhaps they are good, but of course, they could be terrible too, and I'm okay with that. I appreciate people reading and thinking about it whatever way, so thank you for doing so regardless of your thoughts on my idea.
There exists a way to produce only Thorium with Uranium, via the route of producing 8 Depleted Isotope Cells from Uranium & 8 cells and then centrifuging them out 2 at a time to produce 4 Thorium per Uranium Ore. I feel that it would be nice to have a straightforward way to get Plutonium from Uranium while avoiding the waste of unwanted uranium cells.
Right now, as far as I know, the possible ways to get Plutonium from Uranium are:
1.) Centrifuging 16 Uranium Dusts with 21 Empty Cells yields 16 Uranium Cells, 4 Thorium Cells, 1 Plutonium Cell, and 1 Tungsten Dust.
2.) Pulverizers from Thermal Expansion have a 10% chance of giving a pile of Plutonium Dust when used with silk touched Uranium ore or Nether Uranium Ore (does not require silk touch). Gregtech's own excellent Industrial Grinder gives 2 tiny stacks of Plutonium dust per silktouched regular Uranium Ore or Nether uranium Ore
3.) Use of Re-enriched Uranium Cells from a Breeder Reactor in an Industrial Centrifuge. 8 Re-enriched cells nets 4 Thorium Cells, 3 Near-Depleted Uranium Cells, and 1 Plutonium Cell.
4.) The only 1:1 conversion to Plutonium is via direct conversion of Uranium by crafting it with 8 UU Matter. While this is a good possibility if you have a lot of UUM to spare, the fact that it uses so much UU Matter renders it at best a way to store UUM as energy for later.
As I tend to use Plutonium/Thorium mixed reactors, I generally find that the depleted cells left are usually enough for me to simply centrifuge them and receive back enough Thorium cells - I don't need more of them. So, I always end up with a huge surplus of Uranium I have no intention of using unless I have to, and far more Thorium than I would ever need. Maybe this bothers other people, maybe it's just me, but I've thought up a set of solutions that may be interesting. Here they are, moving from a relatively simple base to options of further possibly complexity.
(Simplest) Allow crafting 2 uranium ingots or dusts with a cell to produce a Transuranic Cell. Centrifuging one of these will yield a Plutonium Cell.
(More complicated) Transuranic Cells can also be placed inside a breeder reactor. After receiving a certain number of pulses, a Transuranic Cell becomes an Enriched Transuranic Cell. Enriched Transuranic Cells could then be centrifuged to produce a higher yield of Plutonium than a Transuranic Cell alone.
(The most complicated) An Enriched Transuranic Cell could be placed in the breeder reactor for another cycle, and in turn after it has received the requisite number of pulses, changes into a Highly Enriched Transuranic Cell. From here, you take it and centrifuge it - 
Where else? These Highly Enriched Transuranic Cell could yield the highest level of Plutonium, and in addition provide a source for other potentially useful Transuranic Elements, such as Neptunium and/or Americium Cells.
Neptunium Cells could possibly be used as a fuel that is used purely as a breeder fuel, producing heat & pulses, but no energy. Americium, used in real life in smoke detectors and ground density detectors could possibly be used as an analogue as an an ingredient in a ground density detector (maybe combined with a Computer Cube?), giving some text data to the player about the possibility of open caves, water, and lava below. Something I thought of that would be more fun would be to use Americium as a crafting component in producing a Nuclear Metal Detector. The player could carry in their hand, walk around with, and have it squeal when it detects metal in the direction & nearby vicinity the player is holding it. Using such a strongly powered tool to look for metals would carry a cost to the environment directly beneath the player's search area. Holding it over grass could turn it to soil. Plants, flowers, and leaves directly beneath the Detector would break without dropping an item. Highly flammable blocks like Netherrack may even catch fire.
(and a bonus mostly unrelated idea) Allow compression of Plutonium dusts into ingots, and in turn, crafting of Plutonium blocks, Plutonium blocks would appear silvery-green, but give off a faint greenish glow detectable in lower light levels (along the brightness of a redstone torch, perhaps, or maybe simply appearing faintly lit without producing light.) The block alone wouldn't cause harm, except possibly when a player decided to use a the Nuclear Metal Detector in its direction (boom!)
Crafting two such Plutonium blocks together would result in the production of the block Demon Core. The Demon Core is an actual subcritical mass of Plutonium that accidentally became critical twice after World War II. You can read a short bit about it on Wikipedia. Placing a Demon Core would produce temporary (lasting only while placed) negative effects like the aftermath of an in-game reactor explosion, but without the explosion. I thought it might be entertaining for some scenarios and maps, useful in others (placing a surprise deep pit around your base filled with water and demon cores would be far more memorable than an instakill), and also a way of offering a challenge to overcome for other people.
Anyway, I've edited this a few times to be sure I clarified a few things, and I've of course written too much. Thanks again all who have sat through my suggestions and read. They are just some thoughts and suggestions - I'd love to see any or all of it it in GregTech..Whether it does or doesn't, I'll continue to enjoy the new ways of doing things that GregTech offers. Thanks for making the mod, GregoriusT.
