You know how shittily unbalanced it would be if the Source dust did NOT disappear? You could feed the Source Dust back into the Centrifuge to get more and more Radioactive Isotopes out of something that should not have them anymore in the first place. Or with the 7 U235 + 1 Pu244 Recipe you would have a 1:1 ratio of Stuff being outputted what is WAY TOO FUCKING MUCH for this purpose.
There are only two valid choices:
1. The Mass vanishes, like it does now, or
2. The Centrifuge outputs a 100% useless byproduct, that can not be fed back into the Centrifuge and is ESPECIALLY NOT usable for any Nuclear related Stuff.
But your Suggestions are neither of those two options, and therefore extremely unbalanced.
Well, I meant that recipe just as an example, not as it has to be exactly like that.
Normally I would suggest to breed (pure) U 238 within Breeding Reactors (which should be added into GregTech if they aren't there already) into Pu 239 (and maybe as by-product Pu 240, Pu 241 and Pu 242) and to use then Pu 239 and/or Pu 241 as part of a MOX fuel.
That way you can consume U 238 very efficiently over a long time as it is possible already in real life.
Based on those facts the recipe could be something like (all dusts): 33x U 238 => 32x pure U 238 + 1x tiny pile of U 235 + 1x Ra (or just a small pile of it) + 25% chance of 1x tiny pile of Pu 244.
Pure U 238 could be used then within breeding reactors to gain Pu 239.
And the waste product out of the nuclear reactors that run on enriched U 235 or Pu 239 should be or contain a large amount of depleted U 238. Depleted U 238 can be used for radiation shielding or ammunition, for example, but there could be also a processing chain to filter out Ba and Kr to get pure U 238.
And Ra could be used as source of a processing chain to get Radon gas.
Does that sound more interesting than just (in my opinion senselessly) voiding U 238?
Pu 239, Pu 240 and Pu 241 should also be able to be finally breed somehow into Pu 242, maybe within a breeding reactor or within a Neutron Chamber by shooting on it with some kind of Neutron Cannon (like that thing in the Iron Man 2 movie).
Pu 242 can then be used as described below.
If you really want to produce Pu 244 in a significant manner then you have to create a nuclear explosion because you need a huge amount of free neutrons within a very short time to create a "production" chain of Pu 239 - 240 - 241 - 242 - 243 - 244.
The main drawback there is Pu 243 with its very short half time of just five hours.
For GregTech that could mean to build a Nuclear Explosion Chamber that resists a small nuclear explosion and to fuel it with "Mini" Nuclear Bombs made out of either U 235 and U 238 or Pu 239 and U 238 and maybe some Pu 242 for both recipes.
The Nuclear Explosion Waste should then be separated somehow into its ingredients - a somewhat lesser amount of the main products of the bomb together with some Pu 244.