Complex sentence: Uranium mining began in 1946, organized by the "Zapadnyi Mining and Chemical Combine", and two uranium processing plants would ultimately enrich more than of uranium ore for Soviet atomic bomb projects, both mined locally and imported from elsewhere in the Eastern bloc.
Split into simpler sentences: Uranium mining began in 1946, organized by the "Zapadnyi Mining and Chemical Combine". The processed ore was both mined locally and imported from elsewhere in the Eastern bloc.