Board Thread:Questions and Answers/@comment-173.77.235.213-20130621231319/@comment-10703376-20130630220524

You must have the previous achievements obtained before you can obtain the achivement. Do you have the required achievements obtained?

Another problem could be that you are automating the process. In order to obtain the achievement you must manually remove the Refined Uranium from the compressor. If you are automatically removing the Refined Uranium from the compressor with Buildcraft pipes or the like, you won't obtain the achievement.