Thorium dust is one of the dusts added in GregTech
1 thorium dust can be obtained from 1 monazit ore put in an industrial grinder.
Can be shapelessly crafted with an empty cell for 1 thorium cell which can be used in a nuclear reactor for the same power output as 1 uranium cell. However, it outputs 5 times less energy per tick but lasts 5 times longer.
Another thing it can be used for, is amplifying the production speed of UU matter in a mass fabricator. The fact that processing 1 monazit ore gives you worth 550000 of amplification (equal to 110 scrap), makes it one of the best ways to increase your UUM production speed in the game.