It is possible to create infinite thorium using just energy by using the following loop:
0. (Start one time only) Thorium Dust/Ingot

1. Thermal Centrifuge > Thorium-232 + Tiny Clump of Thorium-230(This is the "free" thorium)
2. Fluid Extractor > 144mB Thorium
3. Fluid Solidifier(Ingot) > Thorium Ingot
   Loop

Each loop creates a Tiny Clump of Thorium-230 that can be fluid extracted into thorium and then used for useful purposes. It's not free, but does create thorium using just energy.

The fissile loops are a little weird but not particularly gamebreaking. Thorium reprocessing will eventually run out, whereas the Uranium loop will infinitely generate U235. Neither is especially useful, particularly since it's so easy to get Thorium and you are gated in progress by the amount of U238 you have, not U235.

As far as I know, these are vanilla GTCE recipes. We'll take a look to see what the deal with them is. It might not be possible to rebalance them without breaking something else.

The easiest way to deal with this issue would be to make the liquid thorium an even mix of the two isotopes, at 1 part 230 9 parts 232, same goes for the ingot. If you wanted to convert the isotopes back into natural thorium, you would have to put them in a mixer to get them back into the standard dust form. The issue is that you can essentially convert isotopes back into the natural mix, which isn't supposed to happen.

Additionally, recipes could be added for the molten variants of thorium and uranium isotopes, and allow mixing of them back into the natural mixture at a 9:1 ratio.

import crafttweaker.item.IItemStack;
import crafttweaker.item.IIngredient;
import crafttweaker.oredict.IOreDictEntry;
import mods.contenttweaker.Fluid;

import mods.gregtech.recipe.RecipeMap;

val fluid_extractor = RecipeMap.getByName("fluid_extractor");
val mixer = RecipeMap.getByName("mixer");

fluidextractor.findRecipe(32, [<nuclearcraft:thorium:4>], null).remove();
fluidextractor.findRecipe(32, [<nuclearcraft:thorium:0>], null).remove();
fluidextractor.findRecipe(32, [<nuclearcraft:thorium:2>], null).remove();
fluidextractor.findRecipe(32, [<nuclearcraft:thorium:6>], null).remove();

mixer.recipeBuilder()
	.inputs(<ore:nuggetThorium230> * 1, <ore:nuggetThorium232> * 9)
	.outputs(<gregtech:meta_item_1:2069)
	.duration(160)
    .EUt(32)
    .buildAndRegister();

this hopefully should fix the issue

I think I'm going to de-schedule this from 1.2.2 since I don't really see this as a major problem; thorium is so easy to get from granite anyway that this slow duping process is really not that useful.

I'd also want more time to look at the potential balance ramifications of the recipe changes, so possibly I'll look into this for 1.3.