The U.S. government plans to designate 6 metric tons of surplus plutonium now stored in South Carolina as waste and ship it to a storage facility in New Mexico, according to a preliminary notice filed on a federal website on Wednesday.

The notice, to be posted on Thursday by the U.S. Department of Energy (DOE), says its "preferred alternative" for disposal of the 6 metric tons of surplus plutonium would be to turn it into nuclear waste and store it in New Mexico.

Critics said the notice was a sign that DOE could decide to scrap a multibillion-dollar project in South Carolina that will mix 34 tons of surplus plutonium with uranium to form safer fuel pellets for use in commercial nuclear reactors.