Process Waste - A Continuing Chemical and Political Problem

What do we do with the byproducts of nuclear reactions and the chemistry of nuclear materials?  Every chemical and nuclear process, at a macroscopic level, yields both the desired product: fissibile uranium, plutonium, electricity, radioactive isotopes for medical use such as Co⁶⁰ or Sr⁸⁹ and a series of unwanted byproducts.  In contrast to the byproducts of other industrial efforts to support the ongoing culture - or to maintain defense or wage war - these byproduct materials are especially difficult to manage because of their complex composition of actively radiating nuclei.

Mankind has a history of leaving to subsequent generations the cleanup of its industry.  While roaming just one state, Colorado, one can visit the Windy Hill archeological site in the Park Range near Steamboat Springs.  There rests acres of quartzite flakes; the residue of centuries of tool making by the inhabitants of Colorado who followed the melting of the Ice-Age glaciers.  The men of prehistory took their points and knives and ax heads with them and left behind a benign byproduct, unchanged rock shards.

The 19th century miners of Colorado brought Zinc and Silver and Lead out of the ground near Leadville and the mounds of residual byproduct from their metal-freeing chemistry was not benign.  The snows of mountain winter melt and infiltrate the waste, extracting metals and reducing the pH to produce strongly acidic runoff that has found its way readily to the upper reaches of what was the pristine Arkansas River.  Fortunately the 20th century environment has chosen to clean up Leadville's California Gulch through the cooperative State and EPA Superfund activity.

California Gulch

Bartlett Mountain and the slump of the Glory Hole (left)

In the 20th century, near Leadville it was irresistible not to scoop out Bartlett Mountain and retrieve Molybdenum from the richest lode on the planet.  The underground mining of Bartlett Mountain that resulted in formation of the "Glory Hole" by the slow collapse of the mountain itself, left us enormous waste retention ponds undergoing reclamation with 21st century dollars.

Please understand, however, cleanup, is always a local political issue no matter how well meaning and seemingly obvious it is.  Leadville's long story is described so well by Gillian Kucas (LEADVILLE: THE STRUGGLE TO REVIVE AN AMERICAN TOWN, Island Press, 2004).

We understand these waste streams in intimate detail as result of examination of the microscopic.  We know the chemical equations for the chemical processes - both the processes we want and the byproduct processes inevitably resulting from thermodynamics.  So we can have confidence that applied chemistry and engineering can eventually develop schemes for the cleanup. 

Nuclear Process Waste - A Continuing Chemical and Political Problem

It should hardly surprise that strategy for and accomplishment of management of the waste products of the military nuclear effort (developed at its initiation in extraordinary haste) and the waste products from peacetime nuclear power and nuclear products has yet been completed.

The problems are extraordinary as compared to the illustrations of mine waste;

1. Nuclear waste problems are national rather than regional or local.  Waste is generated across the country and no one wants it or wants it transported through their community.
2. They initiate powerful personal fears resulting in a sweeping political debate and extraordinary levels of discussion and planning before action.
3. The isolation and treatment problem is exacerbated by the fact that many of the radioactive species have half-lives such that they will essentially never go away.
4. Any cleanup effort carries the risk of exposure to unseen, damaging radiation.

About the only consolation is that on a volume basis the amount of nuclear waste, though quite large, is small compared to major mine cleanups.  But by the nature of the nuclear physics, all transport containers or storage locations must take critical care not to mass materials together so that self-heating or even nuclear processes can begin.

According to the U.S. Department of Energy (DOE), the four major elements of the environmental legacy of nuclear weapons production are:

• waste,
• contaminated environmental media,
• surplus facilities, and
• materials in inventory

We will focus on the first two components. As we have seen in previous modules, nuclear weapons production in the United States was a complex series of manufacturing operations that generated large quantities of nuclear and chemical wastes. The term "waste" is defined as solids or liquids that are radioactive, chemically hazardous, or both. This waste consists of materials that have been disposed of previously, await disposal, or have been retrieved in site cleanups and are currently in storage. Waste is measured in terms of its volume (cubic meters) and its radioactivity (curies). Waste from nuclear weapons production managed by DOE includes 24 million cubic meters containing 900 million curies.

Hanford B reactor and waste barrels
(Courtesy of the Department of Energy)

The major categories of waste are:

• high-level waste,
• transuranic waste,
• low-level waste,
• mixed low-level waste,
• 11e(2) byproduct material,
• hazardous waste, and
• other waste.

High-level waste is the highly radioactive waste resulting from spent nuclear fuel, as well as the chemical processing of spent nuclear fuel and irradiated target assemblies. The radioactivity comes from fission fragments and their daughter products resulting from the fission of U²³⁵ in production reactors. Although radiation from short-lived fission products (fragments and their daughters) will decrease dramatically in the next hundred years, radiation risks associated with the long-lived products will remain high for thousands of years. In the initial decay period, most of the radioactivity is due to Cs¹³⁷, Sr⁹⁰, and their short-lived daughter products. Plutonium, americium, uranium, and their daughter products are the major contributors to long-term radioactivity.

The Hanford, Washington, site manages the largest volume of high-level waste, but the Savannah River site in South Carolina contains more total radioactivity. At Hanford, high-level waste alkaline liquid, salt cake, and sludge are stored in 149 single-shell and 28 double-shell underground tanks. Double-shell underground tanks are also used to store waste at the Savannah River site. Hanford waste is less radioactive than Savannah River waste because much of the radioactive Cs and Sr has been removed, the waste is older and has had more time to decay, and it has been mixed with less radioactive waste.

High level waste is the reult of a few, well defined processes.  As such, stream compositions fall within a few, narrow concentration ranges

Transuranic (TRU) waste contains alpha-emitting transuranic elements with half-lives of greater than 20 years and a combined activity of 100 nanocuries per gram of waste. Because of the long half-lives of many TRU isotopes, TRU waste can remain radioactive for hundreds of thousands of years. Some common isotopes found in TRU are plutonium²³⁹, ²⁴⁰, ²⁴¹, ²³⁸, and ²⁴²; americium²⁴¹; and curium²⁴⁴. TRU waste from weapons production results from the fabrication of plutonium components, recycling of plutonium from scrap, retired weapons, and chemical separation of plutonium. Unlike high-level waste that results from a few specific processes with a narrow range of physical matrices and chemical characteristics, TRU waste exists in many forms with a spectrum of chemical properties.

A small percentage of TRU waste exhibits high direct exposure hazards and is referred to as "remote-handled" TRU waste. The majority of TRU waste emits low levels of direct radiation and is called "contact-handled" waste. The chief hazard of "contact-handled" waste is due to alpha radiation. Alpha particles can not penetrate the skin but cause serious localized tissue damage when inhaled or ingested. When inhaled, TRU elements tend to accumulate in the lungs; soluble TRU compounds migrate through the body, accumulating in the bone marrow and liver.

Mixed low-level waste contains both hazardous waste subject to the Resource Conservation and Recovery Act (RCRA) and nuclear materials. The radioactive component of mixed low-level waste is similar to low-level waste and thus less radioactive than high-level or TRU waste. Hazardous chemical components present in mixed waste include toxic heavy metals, explosives, halogenated organic compounds, and acids.

The other two categories are defined by government regulations. A variety of materials not covered previously fall into these categories. These materials include polychlorinated biphenyls, asbestos, and byproduct materials that have been mixed with chemically hazardous substances.

Waste Isolation Pilot Plant site in New Mexico
(Courtesy of the Department of Energy)

Waste storage (Courtesy of the Uranium Information Center)

Waste Storage Facilities in the United States Two locations in the United States have been identified to dispose of nuclear waste: one has been permitted for waste that results from defense activities (e.g., nuclear weapons development), while the other is proposed for waste from commercial activities (e.g., nuclear power generation).  The operational Waste Isolation Pilot Plant (WIPP) located in southeastern New Mexico is a geologic repository for the disposal of defense-related waste such as clothing, equipment, rags, and other items contaminated with transuranic (TRU) elements.  This TRU waste is defined as having activity greater than 100 nanocuries per gram due to transuranic isotopes. These isotopes have longer half-lives, extending from 20 to thousands of years. The waste is packaged in containers and emplaced in salt beds approximately 2,000 feet below ground. The salt will slowly close around the waste, permanently isolating it from the accessible environment. The Yucca Mountain site, located about 100 miles northwest of Las Vegas, Nevada, will be a geological repository for high-level spent nuclear fuel from civilian power plants and defense-related activities. This site is being studied carefully by DOE to ensure public health and safety. If DOE determines that the site is suitable, it will submit a construction application to the Nuclear Regulatory Commission (NRC). As the licensing agency, the NRC will use the standards currently being developed by the U.S. Environmental Protection Agency The first date for shipments of nuclear waste to Yucca Mountain is uncertain but was recently pushed to 2012. In June 2004 the Department of Energy released a stunning 5.6 million documents to the public in anticipation of initiating its licensing efforts with the NRC. As of early 2005, the license application itself is suffering with delay after delay. Not the least of the problems is the admission by the Secretary of Energy that certain data offered by the US Geological Survey may have been falsified. Yucca Flats sets extraordinary standards for control of radioactivity. A maximum value of 15 millirems/year of personal exposure was established and that value was to be held for the next 10,000 years. But the National Academy of Sciences had recommended that the exposure standards should extend far further into the future and standards are being developed as result of a ruling by the District of Cilumbia Court of Appeals for periods up to one million years! Scientific extrapolation of material and geilogical stability out to those extraordinary time periods is yet another cause for delay in initiating the storage that we need now. (See SCIENCE Vol310 21 October 2005, pg. 447) While awaiting approval of the construction license, waste continues to accumulate in the "temporary" storage sites at nuclear facilities around the country. Studies related to a permanent storage facility for nuclear waste began in 1983 and through 2004 more than $10 billion has been expended to get to the point of selecting Yucca Mountain, detailing its suitability (in the 5.6 million pages of information) and preparing the license.

Yucca Mountain Site in Nevada
(Courtesy of the Department of Energy)

Complete Bibliography on Nuclear W aste from the ALSOS Digital Library for Nuclear Issues