| |
    
|
High-Level Radioactive Waste Disposal Efforts in the United States
by Gregory Lauer
Like the Hydra, the nine-headed serpent from Greek mythology that grew two heads after one was cut off, the debate over high-level radioactive waste in the United States is a seemingly invincible bureaucratic and scientific monster. After years of study and research, the construction and operation of a high-level radioactive waste repository is still decades away. Several researchers here at the University of Minnesota and a local consulting engineering firm are contributing answers, however, to a process perpetually producing questions.
The need to store high-level radioactive waste is a byproduct of America's nuclear energy program. In the 1950s, commercial nuclear reactors began producing electricity by harnessing the power of the atom. Proponents hailed nuclear power as a cheap, clean, and plentiful energy source capable of fulfilling the needs of a population accustomed to light bulbs, refrigerators, and television sets. Nuclear energy was a symbol of scientific and engineering excellence, and the concerns of critics were by and l arge ignored.
Unfortunately, there was little attention given to storing the highly radioactive waste products of nuclear power. In a typical nuclear reactor, fuel rods filled with thousands of uranium pellets are inserted into the reactor core. Nuclear fission occurs when the nucleus of an atom of an unstable isotope of uranium is bombarded by neutrons and splits into two parts. At this point mass is converted into energy and neutrons are liberated to continue the chain reaction. After the bulk of the available fissionable material is utilized, the fuel rods are depleted and must be replaced. The spent fuel casings, however, are still highly radioactive.
Finding an environmentally safe and politically palatable repository for "used" nuclear fuel constitutes the bulk of the debate concerning the disposal of high-level radioactive waste. By far the largest considerations are scientific and technical in nature; issues of safety, storage and retrieval, and cost must all be resolved. The corresponding political issues of storing nuclear waste, however, must also be addressed.
The burden of finding a repository for high-level radioactive waste falls primarily on the Department of Energy (DOE). In 1982, the Nuclear Waste Policy Act required DOE to characterize three potential repository sites and formally select one. In subsequent amendments to the National Waste Policy Act in 1987, DOE was directed to examine only one site at Yucca Mountain in Nevada. In terms of funding, the owners and generators of nuclear waste - primarily the utilities operating nuclear power plants are required to pay the costs associated with waste disposal efforts; since the program's inception, DOE has spent more than eight billion dollars. In the Energy Policy Act in 1992 Congress charged the Environmen-tal Protection Agency (EPA) to review earlier guidelines concerning the disposal of high-level radioactive waste and develop "findings and recommendations on reasonable standards for protection of public health and safety." That mandate led to the creation of a health-risk based standard for Yucca Mountain. The EPA's criteria include individual, population (local, regional, and global), and groundwater protection among other things. The repository must provide adequate safeguards for a period of 10,000 years, and it must minimize human exposure to carcinogenic and toxic agents.
The third major governmental agency to play a role in the disposal of high-level waste is the Nuclear Regulatory Commission (NRC) which is in charge of licensing the high-level radioactive waste repository after a site is selected by DOE. NRC conducts on-site inspections, evaluates safety procedures and contingency plans, and reviews quality assurance programs.
The Department of Energy, the Environmental Protection Agency, and the Nuclear Regulatory Commission are only the principal government organizations involved in the nuclear waste repository scavenger hunt. A plethora of committees, task forces, and representatives from other federal, state, and local agencies are also involved. Additionally the interests of corporations and utilities associated with nuclear power have a voice in the process. Not surprisingly, progress in establishing and operating a national repository for high-level waste is bogged down by bureaucratic inertia and the sticky nature of governmental red tape and regulations.
A preliminary site is currently being studied at Yucca Mountain in Nevada, approximately 100 miles northwest of Las Vegas. Yucca Mountain is similar to many outcroppings in this desert region with peaks just under 5,000 feet above sea level. The site is very dry and averages less than six inches of rainfall per year.
The Yucca Mountain Site Characterization Project will determine if the geologic and hydrologic setting of the site will effectively isolate spent nuclear fuel and high-level waste from the environment. Several issues must be addressed such as whether the geology of Yucca Mountain is capable of isolating high-level radioactive waste, whether volcanic activity or earthquakes pose a threat to the repository, and whether there is a threat of contaminating underground water tables. In addition to the technical issues under consideration, socioeconomic studies will also be conducted to assess the direct and indirect impacts on employment, communities, Native American populations, tourism, population distribution, social conditions, and government structures.
In sci-fi literature, the threat of radioactive contamination is a frequently visited topic. Writers in the genre often conjure up scenarios where characters are exposed to massive doses of high-level radiation and suffer hideous mutations. Not surprisingly, the public has a deep-seated fear of all things radioactive. In order to satisfy these concerns, many studies are addressing possible modes of radioactive contamination.
Scientists and researchers are especially interested in the transport of radionucleides by groundwater flow. Dr. Charles Fairhurst of the Department of Civil Engineering is actively involved in the debate over high-level waste storage in the United States, and he chairs a committee of the National Research Council focusing on radioactive waste disposal; additionally Dr. Fairhurst advises both the French and Canadians on issues related to the disposal of radioactive waste. The transport of radioactive particles is a significant concern, he says, because of the threat of groundwater contamination. Current research has shown thus far that radionucleides travel more slowly than water due to chemical retardation and matrix diffusion which is encouraging news. Federal standards limit the movement of these particles to less than three miles over the course of ten thousand years.
Since 1983, a series of seventy-two deep and shallow holes were drilled at Yucca Mountain in order to understand the mechanisms associated with water flow. Several mineral barriers that inhibit the downward flow of water have been identified. Surface water is often kept from entering very deeply into the ground by layers of calcium carbonate. The layers are compact and often present a nearly impassable barrier to water. Rock formations formed millions of years ago from violent volcanic eruptions are a lso present near the surface and block the downward flow of water. By and large, rock comprising Yucca Mountain is very impermeable to water; typical rates of flow are on the order of inches per hundreds of years.
However, water may flow downward fairly quickly due to faults or fractures in the rock. Faults present conduits for water and accelerate the underground flow. There is concern that fractures may develop allowing water to come in contact with high-level waste in the repository. If the containers corroded, seeping water could become contaminated with radionucleides. Ultimately these particle could leach into underground reservoirs and travel southward with groundwater flow before finally resurfacing.
Understanding the mechanisms of rock fracture and fluid flow is important, especially in view of the unique engineering constraints related to the disposal of high-level radioactive waste. Itasca Consulting Group, a local engineering consulting firm here in the Twin Cities specializing in geo-engineering and rock mechanics, has prepared studies for the US. Nuclear Regulatory Commission analyzing various aspects of the Yucca Mountain repository. Itasca Consulting Group is unique among many engineering consulting companies because of its close ties to the University of Minnesota and its heavy emphasis on computational modeling.
In a typical study several years ago, Terje Brandshaug of Itasca Consulting Group investigated rock mass modification around a nuclear repository. By excavating material from existing rock formations, additional stresses are induced and joint deformations may occur. Thermal effects of disposal must also be considered because high-level nuclear waste generates enormous amounts of heat while decaying. Determining the behavior of the modified rock mass is important to scientists and researchers at Yucca Mountain as it may present special engineering or safety concerns that must be addressed.
In order to more fully understand the mechanisms and processes associated with excavation and thermal effects, computer codes based on boundary element and distinct element methods were employed. Using FLAC (Fast Lagrangian Analysis of Continua) it is possible to model a nuclear waste repository numerically and study the stress contours, temperature contours, and displacements of rock masses. In the rock mass modification study, zones above and below the repository were identified as likely candidates to have modified rock properties. In particular, these changes may alter the rock mass hydraulic characteristics and increase its permeability to fluid flow.
The work of researchers and consultants like Dr. Charles Fairhurst and Terje Brandshaug is providing answers to some of the questions in the high-level radioactive waste debate. The controversy surrounding Yucca Mountain, however, is likely to continue indefinitely. Politicians and the public are expecting perfection from science when it comes to radioactive waste disposal. Even with all of the exhaustive studies and voluminous reports, however, scientists and researchers can't guarantee the safety of the repository over the course of ten millennia.
Sadly enough, the United States' stockpiles of nuclear waste are sitting in temporary storage facilities at nuclear reactors around the country. Most experts agree this is an unsafe and insecure method of high-level waste disposal. Earlier this month, for example, NSP filled its second cask at the Prairie Island complex with highly radioactive, spent nuclear fuel. These stop-gap solutions will continue to be necessary until a permanent repository is established.
The future of the high-level waste repository at Yucca Mountain is certainly in question. Many different agencies, corporations, and public interest groups are actively competing to influence the final decision of politicians and policy-makers in Washington. Don't expect to see action soon, however, as the earliest start-up date of an American high-level radioactive waste repository is 2013.
