One of the fundamental challenges facing widespread utilization of nuclear power is the problem of waste. Operation of a nuclear reactor generates radioactive waste that can continue to produce dangerous levels of radiation for thousands and even millions of years.  This necessitates storage of radioactive waste on unprecedented time scales. Such permanent storage is not currently available in the United States, which naturally raises the question of where the country's radioactive waste actually goes.  The following is an overview of the fate of high-level and transuranic radioactive waste in the United States today.
Radioactive waste is broadly categorized as high-level, low-level, or transuranic waste.  High-level waste arises from spent reactor fuel, which contains significant quantities of leftover fuel elements such as uranium, as well as fission byproducts. [3-5] This spent fuel can in principle be reprocessed to extract usable elements and separate the longest-lived radionuclides from the bulk of the waste, although this is not done for commercial waste in the US due to concerns that plutonium from reprocessed fuel can be used for nuclear weapons manufacture. [3,4] The spent fuel or reprocessing byproducts are highly radioactive and are referred to as high-level waste.  The degree of radioactivity from high-level waste can remain acutely lethal for many years and present an environmental hazard for thousands to millions of years. [1,5]
The transuranic waste category includes non-high-level waste that contains elements with atomic numbers higher than that of uranium (i.e., "transuranic"), and despite not being classified as high-level waste is nonetheless dangerously radioactive and long-lived. [5,6]
Low-level waste does not fall into the above categories and consists mainly of material that is not inherently radioactive but that has become contaminated from contact with radioactive substances.  This overview focuses on high-level and transuranic waste, because low-level waste, while hazardous, does not represent the same level of danger as the other categories. 
The United States currently operates 104 commercial nuclear reactors for power generation.  Although the Nuclear Waste Policy Act of 1982 requires the US Department of Energy to provide a long-term storage site for high-level waste from spent nuclear fuel, the US government has yet to approve a site for this purpose.  Most recently, a permanent storage site was planned at Yucca Mountain, Nevada. [1,2,5] Radioactive waste in robust canisters would have been put into permanent underground storage at this facility. Department of Energy projections predicted that radioactive releases from the site would have remained well below EPA-allowable levels for over 1,000,000 years, but the reliability of these predictions is disputed, and the Yucca Mountain repository remains controversial for a variety of reasons.  The federal government has indicated that it no longer views the repository as a viable solution, and funding for the Yucca Mountain site was effectively eliminated in 2009. 
Absent a permanent option, waste from commercial reactors in the United States is stored at the reactor sites themselves. [2,4,5] Spent fuel is stored underwater in storage pools, where water serves to absorb both radiation and heat; older high-level waste that produces less heat is also sometimes stored in "dry casks" made of concrete or steel.  At present, spent nuclear fuel stored at US reactor facilities totals ~64,000 tons. 
The Department of Energy has judged that the current approach of on-site storage for high-level waste, conducted according to established standards, should be safe for up to 100 years, but is inadequate on the 10,000- and 1,000,000-year time scales considered for permanent disposal.  Furthermore, storage pools require active maintenance and operation to be effective; as a result, keeping high-level waste in on-site storage introduces potential risks from mistakes or malfunctions. 
Significant radioactive waste is also produced by US Department of Defense activities, such as those relating to nuclear weapons programs. Transuranic waste from these activities is currently disposed of underground at the Waste Isolation Pilot Plant (WIPP) in New Mexico.  This facility was established in 1979, based on the recommendation of the Nuclear Regulatory Commission that geologic disposal of radioactive waste be carried out in salt beds, and after other salt bed sites were rejected. [6,9] It has been proposed that the nation's waste disposal problem could be mitigated by opening WIPP to high-level waste from commercial reactors, though this suggestion is not without problems.  It has been met with resistance from New Mexico authorities, and current NRC guidelines call for high-level waste to be recoverable for 50 years at permanent disposal sites which geologic disposal in salt formations like that at WIPP prevents. [2,5,6]
In addition to transuranic waste, defense programs also produce high-level waste. In particular, the United States has built more than 200 nuclear-powered naval ships (most of them submarines, and most no longer in service), and the reactors onboard those ships represent another source of radioactive waste, ongoing in the case of those in service.  Like the waste from civilian power reactors, this waste was meant to go into long-term storage at Yucca Mountain and currently goes into temporary storage, in this case at a centralized location at Idaho National Laboratory. 
Hazardous radioactive waste is produced by nuclear power generation in the US, and no accepted permanent storage solution for this waste currently exists. High-level waste is currently in temporary storage that is designed to be effective for only a small percentage of the radioactive lifetime of said waste. If nuclear power generation is to be a viable part of the nation's energy future, it is crucial that a permanent disposal solution be found.
© Christian Lawler. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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