Nuclear Energy - Types Of Radioactive Waste

Working in a laboratory in Chicago, Illinois, in 1942, Italian physicist Enrico Fermi assembled enough uranium to cause a nuclear fission reaction. His discovery transformed both warfare and energy production, but the experiment also produced a small packet of radioactive waste materials that will remain dangerous for hundreds of thousands of years. That "first" radioactive waste lies buried under a foot of concrete and two feet of dirt on a hillside in Illinois.

Radioactive waste material is produced at all stages of the nuclear fuel cycle, from the initial mining of the uranium to the final disposal of the spent fuel from the reactor. (See Figure 5.5.) "Radioactive waste" is a term that encompasses a broad range of material with widely varying characteristics. Some is barely radioactive and safe to handle, while other types are intensely hot in terms of both temperature and radioactivity. Some waste decays to safe levels of radioactivity in a matter of days or weeks, while other types will remain dangerous for thousands of years. The U.S. Department of Energy (DOE) and the NRC define the major types of radioactive waste.

Uranium Mill Tailings

Uranium mill tailings are sand-like wastes produced in uranium refining operations. Although they emit low levels of radiation, their large volumes (10–15 million tons annually) pose a hazard, particularly from radon emissions and groundwater contamination. Since it was not until the early 1970s that the dangers of uranium mill tailings were realized, many miners and residents in the western United States had unsafe exposure to them. Cancer incidences are high among miners who worked prior to the 1970s.

Low-level Waste

Low-level waste, which contains varying lesser levels of radioactivity, includes trash (such as wiping rags, swabs, and syringes), contaminated clothing (such as shoe covers and protective gloves), and hardware (such as luminous dials, filters, and tools). This waste comes from nuclear reactors, industrial users, government users (but not nuclear weapons sites), research universities, and medical facilities. In general, low-level waste decays relatively quickly (in ten to one hundred years).

High-level Waste

Spent nuclear fuel (used reactor fuel) is high-level radioactive waste. Uranium fuel can be used for twelve to eighteen months, and then it is no longer as efficient in splitting its atoms and producing heat, which ultimately is used to generate electricity. Therefore, it must be removed from the reactor and replaced with fresh fuel. Some of the spent fuel is reprocessed to recover the usable uranium and plutonium, but the radioactive material that remains is dangerous for thousands of years.

Transuranic (TRU) Wastes

Transuranic (TRU) wastes are eleven human-made radioactive elements with atomic numbers greater than that of uranium (ninety-two) and therefore beyond ("trans-") uranium ("-uranic") on the periodic chart of the elements. Their half-lives—the time it takes for half the radioisotopes present in a sample to decay to nonradioactive elements—are thousands of years. They are found in trash produced mainly by nuclear weapons plants and are therefore part of the nuclear waste problem but not directly the concern of nuclear power utilities.

Mixed Waste

Mixed waste is high-level, low-level, or TRU waste that also contains hazardous nonradioactive waste. Such waste poses serious institutional problems, because the radioactive portion is regulated by the DOE or NRC under the Atomic Energy Act (AEA; PL 83–703), while the Environmental Protection Agency regulates the nonradioactive elements under the Resource Conservation and Recovery Act (RCRA; PL 95–510).