Decades of legislation and court interpretations have left U.S. nuclear waste managers facing an intractable problem. Tasked with understanding science and skilled enough to work within constraints set by policy-makers, these managers sort various types of radioactive waste so they can be disposed of in accordance with the law. It’s a complicated job.
Now, waste management companies are urging the Nuclear Regulatory Commission (NRC) to take another look at the limitations of the current U.S. classification system and to possibly simplify it. This, in turn, raises questions about how the existing scheme works and how it compares with the international system.
“Waste classification is a really messy business to write about,” says Allen Croff, almost as soon as he answers a phone call from C&EN. Croff, now retired from Oak Ridge National Laboratory, led the National Council on Radiation Protection & Measurements (NCRP) in an effort to revamp the U.S. nuclear waste classification scheme more than a decade ago. But the U.S. government hasn’t adopted its recommendations.
The current classification system needs changing, the group concluded. NCRP called it “complex and not transparent to the public, who are increasingly involved in decisions about management and disposal of waste, and it is not understandable by anyone but a studied expert.”
Some of those waste classification experts work for NRC. Created by Congress in 1974, the commission regulates commercial nuclear waste and advises the Department of Energy on the management of DOE’s defense-related wastes, such as those from weapon production.
Commercial nuclear wastes are generally divided into high-level waste, low-level waste, and uranium mill waste. In addition to these, defense wastes also include a type of high-level material called waste incidental to reprocessing as well as transuranic waste, which is sometimes considered low-level waste depending on its radioactivity.
“The reason the system is so difficult to understand is because it has evolved based on qualitative definitions that are not intuitive,” Croff says. “The definitions that ended up in law are based on assumptions of what the nuclear enterprise would look like many decades ago, and those assumptions have not come to pass.”
In the U.S., all categories are defined in law based on the origin of the waste. For example, high-level waste is described as irradiated reactor fuel, highly radioactive material from reprocessing used nuclear fuel, and other high-level radioactive waste in the Nuclear Waste Policy Act of 1982.
Low-level waste, on the other hand, is defined by what it’s not. A 1985 law reserves the term low-level radioactive waste for material that is not high-level radioactive waste, spent nuclear fuel, or by-product material.
In its report, NCRP recommended that the U.S. set up three waste classes—exempt waste, low-hazard waste, and high-hazard waste. They would be based on chemical and physical properties of nuclear waste, including the type of radioactive decay and half-life. These considerations would affect the risk a particular waste poses to human health and the environment and would be used to determine the level of containment for storage or disposal, the council said.
The International Atomic Energy Agency (IAEA) has taken a similar approach to nuclear waste classification. Although the agency is not a regulatory body, it provides a set of generalized safety guidelines to governments that are intended to protect people and the environment, says Andrew Orrell, head of IAEA waste and environmental safety.
“Think in terms of safety,” Orrell says. “At the end, the requirements for protection are based on the potential radiological hazard the waste might pose to human health and the environment.”
IAEA has six categories for classifying waste that range from exempt waste to high-level waste and correspond to a recommended disposal path. The lowest class requiring radiation protection often is waste from the research and medical fields, and it can be disposed of as conventional waste once its radioactivity falls to an acceptable level for disposal in conventional landfills. The highest class contains short- and long-lived radionuclides that require disposal in an isolated, deep geological repository.
If the U.S. system for managing nuclear waste is confusing, that’s because the U.S. created the world’s first framework for sorting this material in all its varieties, Orrell says. Now long-standing laws and regulations governing this waste are intertwined and not easily undone, he adds.
But there’s a bright spot to that complex history.
“Other countries [that] are just beginning to have their very first research reactor have the luxury of a very simplified classification scheme,” the IAEA system, Orrell says. The U.S, which paved the way with nuclear technologies, has made it easier for countries with emerging nuclear energy programs to benefit from the experience, he says.
U.S. (DEFINED BY SOURCE):
Class: High-Level Waste
◾ Description: Includes irradiated reactor fuel, liquid wastes from reprocessing irradiated reactor fuel, and solids into which such liquid wastes have been converted, as well as other high-level radioactive waste.
◾ Subclass: Waste incidental to reprocessing, a type of high-level waste that results from reprocessing spent nuclear fuel. It is managed as low-level waste rather than high-level waste, and it is regulated by the state where it is located rather than by NRC.
Class: Low-Level Waste
◾ Description: Radioactive material that is not high-level radioactive waste, spent nuclear fuel, or by-product material. Transuranic waste may sometimes be disposed of as low-level waste depending on its radioactivity. This material includes contaminated laboratory supplies such as protective shoe covers, clothing, and gloves; mops, wipes, and filters; and medical and research wastes. It also includes large items, such as metals from decommissioned nuclear reactors.
◾ Subclasses: A, B, C, and greater than Class C, for which contents vary and radioactivity increases from near background to highly radioactive.
Class: Uranium Mill Tailings
◾ Description: The remaining portion of a metal bearing ore after some or all of such metal, such as uranium, has been extracted. This waste consists of residues that remain from processing uranium and thorium ore.
IAEA (DEFINED BY MATERIAL PROPERTIES):
Class: High-Level Waste
◾ Description: Generates heat from radioactive decay, thus requiring disposal in a deep, stable geological setting. This waste includes large concentrations of both short- and long-lived radionuclides.
Class: Intermediate-Level Waste
◾ Description: May contain long-lived α-emitting radionuclides. It requires greater engineered containment and isolation than provided by near-surface disposal. Waste in this class is to be disposed of at depths tens of meters to a few hundred meters below the surface of a landfill.
Class: Low-Level Waste
◾ Description: May include short-lived radionuclides at high concentrations and long-lived radionuclides at low concentrations. This waste must be isolated in an engineered facility for up to a few hundred years for disposal.
Class: Very Low Level Waste
◾ Description: Contains low levels of concentrated radioactivity and may be disposed of near the surface of a landfill. This waste may come from decommissioning nuclear facilities or naturally occurring deposits of ores and minerals.
Class: Very Short Lived Waste
◾ Description: Includes only radionuclides with extremely short half-lives that may be stored until their activity falls to the level of clearance for disposal as conventional waste. Examples include 192Ir and 99mTc—a radioisotope of technetium widely used in medical diagnostics—and other radionuclides with short half-lives from industrial and medical applications.
Class: Exempt Waste
◾ Description: Excluded from regulatory control for radiation protection purposes. It includes radionuclides with half-lives of less than 100 days, such as 90Y, 192Ir, and 198Au. This waste may be stored until its radioactivity subsides because of decay and is eventually disposed by conventional methods.
IAEA = International Atomic Energy Agency.
Source: NRC, IAEA