Appendix D

Radioactive Waste Classifications and Waste Characteristics from Different Stages of the Fuel Cycle in the United States

In the United States, categories of radioactive waste include high-level waste, spent nuclear fuel, transuranic waste, low-level waste (which is further separated into Class A, Class B, Class C, and Greater Than Class C), depleted uranium, and uranium mill tailings. These classifications, defined in Table D.1, are generally based on the origin of the waste, but also on isotopic composition, radiotoxicity level, and concentration, and dictate how the waste must be treated, stored, transported, and disposed. Note that the United States does not have an Intermediate Level Waste (ILW) category as is the practice internationally¹; the closest U.S. category to ILW is Greater-Than-Class C (GTCC) waste, as defined in Table D.1.

WASTES FROM DIFFERENT STAGES OF THE FUEL CYCLE

Radioactive waste streams are generated throughout the fuel cycle, regardless of fuel and reactor type, including from uranium mining and milling, uranium enrichment, fresh fuel fabrication, reactor operation, reprocessing operations (if applicable), recycle fuel fabrication (if applicable), and decommissioning. The relative amounts (volumes) of waste generated from each stage of the nuclear fuel cycle differ significantly, as shown in Table D.2. This section provides a brief overview of the types of wastes generated during each stage of the nuclear fuel cycle; more detailed discussions of new and unique wastes that may be generated from advanced reactors and fuel cycles can be found in Chapter 5.

Wastes from the Front End of the Fuel Cycle

Wastes from the front end of the fuel cycle include those generated from mining and milling, enrichment, and fuel fabrication. In the United States, uranium mining and milling wastes are classified as Naturally Occurring Radioactive Material (NORM) by the U.S. Nuclear Regulatory Commission, not as radioactive waste; therefore,

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¹ According to the IAEA General Safety Guide, No. GSG-1, “Classification of Radioactive Waste”: “Intermediate Level Waste is waste that, because of its content, particularly of long lived radionuclides, requires a greater degree of containment and isolation than that provided by near surface disposal. However, ILW needs no provision, or only limited provision, for heat dissipation during its storage and disposal. ILW may contain long lived radionuclides, in particular, alpha emitting radionuclides that will not decay to a level of activity concentration acceptable for near surface disposal during the time for which institutional controls can be relied upon. Therefore, waste in this class requires disposal at greater depths, of the order of tens of meters to a few hundred meters.”

TABLE D.1 Radioactive Waste Categories and Definitions Used in the United States

they are not included in this report. Enrichment plants are characterized by low specific activity of the materials treated; they generate only low-level waste (LLW) and only in relatively small amounts. A modern centrifuge plant generates about 4 × 10^–5 m³/SWU of LLW (NEA-OECD, 2006b), where SWU is separative work unit, or the amount of separation done by an enrichment process. The amount of waste that will be generated by the production of high-assay low-enriched uranium (HALEU) is unknown at this time. Most of the U.S. fuel fabrication experience is in uranium oxide fuels, a process that generally involves the preparation and formation of fuel pellets, followed by the

assembly of those pellets into pins. LLW “from fuel fabrication includes filter media from water cleanup, waste oils, spent acids and bases, spent analytical solutions,” cleaning solutions, and discarded scrap metals and equipment. The volume of LLW from fuel fabrication is estimated to be 0.6 m³/metric tons of heavy metal (IAEA, 2019a).

Wastes from Reactor Operations

The nature and amount of waste produced during nuclear power plant operation “depend on the type of reactor, its specific design features, its operating conditions,” maintenance activities performed, and the fuel integrity. The radioactive waste consists of activated structures and components, “moderator and coolant materials, corrosion products captured” in plant components, filters and resins, maintenance materials and consumables, and fission product contamination arising from activated corrosion product transport or leaks in the fuel. “Corrosion products, which originate within the reactor core or out of the reactor and are carried through the reactor core by the coolant or moderator, are neutron activated isotopes” (NEA-OECD, 2006b). Within 8 days of shut down, these activated isotopes decay by about an order of magnitude and are almost all short lived (Zhang et al., 2016). “Both fission products and activation products are distributed throughout the coolant and moderator systems, becoming the primary contributors to liquid processing waste and decontamination and maintenance waste” (NEA-OECD, 2006b). When nonwater coolants such as liquid sodium are used, new unique waste streams are generated because of the hazardous characteristics of liquid sodium.

Wastes from Decommissioning of Power Plants

Decommissioning nuclear power plants generates a significant amount of LLW, which results from the removal of fuel and coolant, the dismantling of the reactor structure, the containment and associated buildings, components, and equipment. This LLW includes mostly

• “activated equipment and materials, such as reactor internals, reactor vessel, and concrete shielding surrounding the reactor vessel”;
• “corrosion products, such as deposits formed from corrosion and release into circulating coolants” and deposits on the various coolant system surfaces;
• environmental media contaminated from accumulation of radioactive isotopes released during operations, including soil, water, and building materials;
• on-site waste filtration and removal systems, such as off-gas charcoal adsorption beds (NEA-OECD, 2006b).

Most of the decommissioning wastes from advanced reactors may be similar to that of conventional reactors; however, waste from innovative coolant and reactor cores may differ significantly, as discussed in Chapter 5.

WASTE TREATMENT

Upon its initial generation, waste is usually treated directly at the facility to reduce volume for storage at the facility, reduce operational releases to the environment, and/or facilitate its further conditioning for storage or disposal. Waste treatments are well established and commercially available for most common waste streams, and vast operational experience has been accumulated.

Solid waste treatment technologies are used to predominantly reduce the waste volume to facilitate storage or reduce disposal costs. Aqueous liquid waste is verified to be within operational limits prior to discharge and diluted via the release pathway. Some aqueous liquid waste treatment technologies achieve further reductions in the bulk volume of liquid waste or in the amount of radioactivity discharge, mostly through evaporation or by separation of radionuclides using various filtration and sorption techniques (with the exception of tritium). The latter yields a substantially smaller volume of filtration materials and absorbents retained on site, although it results in higher concentrations of radionuclides. Gaseous waste streams are monitored to verify that releases are within limits and can be held for short-term decay prior to release or captured with filters and charcoal absorbers.

Treated waste also often requires additional conditioning before final disposal, with a goal of providing proper isolation of radioactive materials from the environment. Conditioning processes include transforming the waste into more stable solid forms or incorporating it into an inert matrix. For liquid waste conditioning, cementation and bituminization are well-matured and commonly used technologies.

WASTE DISPOSAL REQUIREMENTS AND MANAGEMENT PROGRAMS

Different disposal requirements exist for the different waste categories described in Table D.1. Transuranic waste generated from the nuclear defense program has been disposed of at the Waste Isolation Pilot Plant (WIPP) since 1999 (DOE, n.d.-b). Low-level activity waste streams are being or will be disposed of in near-surface disposal sites at four facilities: EnergySolutions Barnwell Operations in Barnwell, South Carolina; U.S. Ecology in Richland, Washington; EnergySolutions Clive Operations in Clive, Utah; and Waste Control Specialists, LLC, in Andrews, Texas (U.S. NRC, 2020k). DOE’s inventory of depleted uranium hexafluoride, located primarily at the Paducah Site in Kentucky and the Portsmouth Site in Ohio, is in the process of being converted to depleted uranium oxide, which is more stable and therefore better suited for disposal (U.S. DOE, 2016). Uranium mine and mill tailings also require specific disposal sites to prevent long-term contamination of soil, air, and groundwater around inactive mining and milling sites; for example, the Moab Uranium Mill Tailings Remedial Action Project is transporting approximately 15.5 million tons of tailings from the Moab site to a disposal cell near Crescent Junction, Utah (DOE-EM, 2021).

Per the Nuclear Waste Policy Act of 1982 (NWPA) (Public Law 97-425), high-level waste and spent nuclear fuel must ultimately be disposed of in a geologic repository, but they are currently stored at 113 sites across the country (Peters et al., 2020) since no such repository exists. Table D.3, reproduced from Peters et al. (2020), depicts the projected growth of spent nuclear fuel that will have to be managed and disposed of for the scenarios of (1) assuming 60 years of operations of the fleet of light water reactors as of 2012, (2) addition of two new reactor builds, (3) shutdown at end of current license period of 40 years, and (4) addition of two new builds plus 8 additional current reactors obtaining a second 20-year license renewal to 80 years of operations. For any of these scenarios, the projected inventory will exceed the current legislated capacity of Yucca Mountain’s repository, if licensed. Thus, an additional repository will be required.

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