radioactive waste, material containing the unusable radioactive byproducts of the scientific, military, and industrial applications of nuclear energy. Since its radioactivity presents a serious health hazard (see radiation sickness), disposing of such material is a great problem. Methods of disposal include dumping concrete-encased containers filled with radioactive waste in the ocean and burying the waste underground in old salt mines. In 1996 the United States opened a waste processing plant in Aiken, S.C. at the Savannah River nuclear-weapons complex. The waste will be converted into cylinders of radioactive glass, which will then be encased in steel containers that will be stored in an underground concrete vault. While the glass will still be radioactive, it will no longer be possible for the waste to leak into the soil, and there will be no possibility of a chemical explosion such as the one that occurred in the Soviet Union in the late 1950s. The United States has also agreed to accept about 20 tons of waste from research reactors in 41 countries. The spent nuclear fuel, supplied by the United States for medical and research purposes, includes about 5 tons of highly enriched uranium that could be extracted and used to produce nuclear weapons.