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Stopgap solutions. Wastes in interim storage facilities at the Idaho National Engineering Laboratory await a final resting place. |
One can imagine that future generations may puzzle over the fortresses designed in the 20th century to entomb highly radioactive wastes. Perhaps schoolchildren of the 30th century will be taken on guided tours of the facilities, entering the historic tunnel ruins, speculating about their purpose or about the meaning of the ancient symbols and markers surrounding the giant tombs. Perhaps the facilities themselves have long been dismantled, their radioactive contents rummaged for reuse by societies more technologically advanced than our own. Or perhaps great geological and climatic changes have occured that broke open the tombs, sending radioactivity into the atmosphere.
Such speculation is not simply an idle exercise. The ability to protect future generations from 20th-century wastes is central to the technological and policy debate over nuclear waste disposal. A variety of options--from the imaginative to the mundane--have been explored for disposing nuclear wastes: launches into outer space, burial beneath the seabed, placement in the ice caps of Antarctica, land disposal in deep geologic formations.
Yet constraints and risks are inherent in all of these options. Space disposal is prohibitively expensive, and international law prohibits placement of wastes in Antarctica, according to a World Resources Institute report. Similarly, burial in subseabed sediments may run afoul of an international ocean dumping convention, although the option is under study, according to the WRI. Wastes buried in Antarctica and wastes submerged in ocean sediments would be difficult, at best, to retrieve. For these reasons, most countries have opted for the relatively low-tech option of geologic land disposal.
The United States has spent approximately $3 billion to study possible geologic disposal sites for two types of radioactive wastes: high-level wastes, which consist of intensely radioactive and thermally hot used fuel rod assemblies, primarily from commercial nuclear power plants, and transuranic wastes, which contain radioactive elements with atomic numbers higher than uranium, are generated primarily by nuclear weapons production, and, according to the Department of Energy, are less radioactive than high-level wastes.
The U.S. nuclear power industry estimates that it has produced 22,000 tons of spent fuel that is currently stored on-site at nuclear power plants. The DOE estimates that it is storing 396,000 cubic meters of high-level waste, 65,000 cubic meters of transuranic waste, and 68,000 cubic meters of low-level waste, which the DOE describes as wastes that contain a small amount of radioactivity in a large volume of material. The DOE also generates mixed wastes, which are radioactive wastes that contain chemically hazardous materials.
Although disposal sites exist for commercial and government low-level wastes, no permanent disposal facilities exist for high-level or transuranic wastes. The government wastes remain on-site at facilities such as Rocky Flats in Colorado which, until production was shut down in 1990, processed plutonium to produce nuclear weapon triggers, the Idaho National Engineering Laboratory, where wastes from Rocky Flats are stored along with spent fuel from naval reactors, or Hanford, Washington, where the DOE is concerned about potential explosions in tanks containing wastes from Hanford's plutonium production and processing activities.
Individuals living near these facilities frequently assume that any disease incidence in their communities is connected to the DOE sites, observed Paul Charp, senior health physicist with the Agency for Toxic Substances and Disease Registry, which conducts health assessments of DOE sites. Radiation exposure can sometimes be correlated with certain types of cancer and leukemia, but "any disease people have at Hanford they say is caused by the radiation," he said, "though scientists come in and say there's nothing in the literature" to support those claims.
Most of the human data on the effects of radiation are drawn from the experiences of the atomic bomb survivors at Hiroshima and Nagasaki. Studies of cancer incidence among the survivors reveal excess cases of leukemia, stomach, lung, liver, breast, and colon cancers, although no increases in cancer have yet been found in children of atomic bomb survivors, according to a report by the U.S. Council for Energy Awareness, a nuclear industry trade association. Charp said the strength of the radiation and cancer association among atomic bomb survivors stems from the high dose they received, which was "much higher than what we see in the environment."
Salt of the Earth
A salty grave. At the Waste Isolation Pilot Project, wastes will be buried in 2,000-feet- thick salt.
Nevertheless, residents' concerns about the impacts of DOE facilities on human and environmental health have increased pressure on DOE to open a permanent disposal facility. DOE has spent $1.5 billion to study a facility near Carlsbad, New Mexico, known as the Waste Isolation Pilot Project (WIPP), where wastes would be buried 2,100 feet underground in a salt bed. WIPP would house 6.2 million cubic feet of transuranic and mixed wastes, much of which was generated at Rocky Flats. The wastes wouldl be contained in steel drums and placed inside rooms mined out of the salt bed, which is 2,000 feet thick. Although the steel drums would eventually collapse, the DOE believes that salt would gradually encapsulate the wastes.
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Trash tunnel. Boreholes have been drilled 2,150 feet underground at the WIPP to test salt's ability to contain wastes. |
If the facility operates as it is designed, the potential for radioactive releases to which current nearby residents might be exposed is "extremely remote," according to Dennis Hurtt, an Energy Department spokesman. However, the DOE is exploring possible releases that could occur centuries, even millennia, from now.
Specifically, the DOE is studying whether oil and gas drilling at the facility could tap into a possible brine pocket, bringing brine up to the waste disposal area. Further drilling into the facility might then bring radioactive brine up to the surface or up to a rock formation through which the brine would flow to the repository's edge.
Oil and gas drilling is prevalent around the WIPP facility and is strictly controlled. But it will be almost impossible to maintain controls for thousands of years. The DOE is required to have an active program to control access to the site for 100 years, but thereafter only "passive" controls, such as fences and signs, would warn future generations of the dangerous wastes contained in the salt caverns.
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Don Hancock--The DOE may be overestimating the ability of salt to contain radioactive wastes. |
Don Hancock, director of the nuclear waste safety project of the Southwest Research and Information Center and a leading critic of WIPP, has raised several issues about the suitability of the site for nuclear waste, including questions about whether brine beneath the facility might be tapped by oil and gas drillers. He also believes the DOE may be underestimating the amount of brine that seeps through the salt bed. If enough water is present to corrode the drums, a buildup of radioactive gases could slow the salt encapsulation of the wastes. And, if the facility is closed and ventilation shut off, the corrosion may lead to a potentially explosive gas buildup.
Mike McFadden, experimental programs branch chief of the DOE's Carlsbad area office, said brine makes up only 1% of the formation in which the waste will be placed. When the facility is operating, ventilation systems will evaporate the moisture seeping through the rock, but once the ventilation systems are closed, moisture will build up, he said. "Moisture would be in contact with the drums and start corroding [them]. That is being studied to make sure it doesn't have any impact on the facility." The DOE expects to complete its study of the facility by January 1997.
Hancock believes the DOE may be too optimistic in its assumptions about the behavior of the salt that is supposed to contain the wastes. "Salt moves three times as fast as DOE had [initially] predicted and [it moves] in clumps," he said, which could lead to the fracturing of the roof of a facility and its collapse. "In addition to the brine reservoir problem and the fracturing problem, it's not clear whether salt itself will be a long-term barrier to movement of the waste."
Robert H. Neill, director of the Environmental Evaluation Group, which was established by the New Mexico state legislature to oversee the WIPP project, also believes that the DOE project is too reliant on the natural salt barrier and lacks engineered barriers. Neill said multiple barriers, or a "belt and suspenders" ap-proach to isolating the waste, are especially necessary given that the facility must meet release limits established by the EPA that apply for 10,000 years. "We're talking really long-term calculations," he commented.
10,000-Year Warranty
Before WIPP can open, it must demonstrate compliance with the EPA's nuclear waste disposal standards, which the agency was authorized to issue under the Nuclear Waste Policy Act of 1982. During the time the facility is accepting waste, the EPA standard limits annual doses in the general environment to 25 millirems to the whole body, 75 millirems to the thyroid, and 25 millirems to any critical organ. (A "rem" is a unit of measurement that quantifies the biological effectiveness of a dose of radiation.) The National Council on Radiation Protection and Measurement has estimated that the average American is exposed to 300 millirem annually from naturally occurring radiation sources including radon and cosmic rays. According to the U.S. Council for Energy Awareness, a whole-body dose of 500 rem or more in a short period will kill most humans within weeks. Severe radiation sickness would result from a dose of 100 rem.
After the WIPP facility is closed, the standard imposes a population dose limit which restricts the amount of radionuclides projected by computer model to leave the property over a 10,000-year period, within a specific range of probabilities, according to Bill Gunter, director of the criteria and standards division in the EPA's Office of Radiation and Indoor Air. Gunter said the EPA based its limits on the total releases that would be expected of the best geologic disposal facilities and on the human health effects that might be expected from those releases and then limiting the risk to 1000 additional deaths worldwide over 10,000 years.
The EPA's estimate of the increased number of deaths that would be caused by releases is based in part on data from Japanese atomic bomb survivors and on individuals who have received radiation treatments, Gunter said. Data from bomb survivors suggest a linear relationship between dose and health effects, he noted. The EPA relies on the linear relationship to estimate risk of any size dose, even low doses for which there are no human data.
Controversy exists about whether that relationship holds at low levels of exposure, according to John Ahearne, former commissioner of the Nuclear Regulatory Commission and currently executive director of Sigma Xi. The effect of low levels of exposure is an issue that's not settled, Ahearne noted, primarily because of the difficulty of assessing the specific role of radiation in causing cancer. "When you have hundreds of thousands of people dying of cancer," it is difficult to prove that a specific number of those cases stem from radiation exposure, he said.
Roger McClellan, president of the Chemical Industry Institute of Toxicology, believes that any uncertainty about the safety of disposal facilities lies strictly with engineering questions about how the site will perform, not with a lack of understanding or knowledge about radiation's health effects. He believes a linear extrapolation of the risks of low doses from the high-dose database produces standards that may be too conservative.
"The fact that we are able to see excess cancer cases at Hiroshima and Nagasaki is related to the fact that [many of the survivors] received large doses," McClellan said. Even so, "we didn't have people dropping dead on every street corner" from radiation-induced cancer. Instead, excess cancers numbered between 500 and 1000 in a population of 100,000, he said.
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Mortimer Elkind--Protracted exposures to low rates of radon may be more dangerous than short exposures at higher rates. |
The uncertainty surrounding health effects of low doses underscores the importance of research about the impact of low doses on the molecular structure of cells. Mortimer Elkind, a professor in the Department of Radiological Health Sciences at Colorado State University, has pioneered cell and molecular studies of protracted exposures to low doses of both low and high linear energy transfer (LET) radiation. Low-LET radiation is sparsely ionizing, such as gamma rays and X-rays. High-LET radiation is densely ionizing, such as alpha rays from radon decay. Elkind has studied radiation emitted by neutrons from nuclear reactors, whose radiobiological properties are similar to those from the alpha radiation present in the transuranic elements of nuclear waste.
Elkind's research has revealed that cells exposed to low-LET radiation over a protracted, rather than brief, period survive better because they repair the damage that leads to neoplastic transformation, which is a precursor to the production of cancer cells. Extending the exposure over time ameliorates the effects of the exposure to low-LET. When exposed to low-LET radiation in a brief period, more cells are damaged and left unrepaired.
In contrast, no ameliorating effect occurs when a dose of high-LET radiation is extended over time, Elkind said. With protracted, low exposures of high-LET, more cells may pass through mitosis, particularly in tissues that have been stimulated to divide, and are then more susceptible to transformation. As a result, "the net frequency of transformation goes up" when exposures of high-LET are extended over time, as compared to acute exposures.
These findings about protracted exposures may explain why uranium miners exposed to the alpha particles from breathing radon at low exposure rates have higher frequencies of lung cancer than miners exposed at higher rates and shorter times, Elkind said.
Shlomo Yaniv, senior technical advisor with the Nuclear Regulatory Commission, said studies of the mechanistic effects of radiation on cells may eventually lead to an improved basis for analyzing the effects of low levels of exposure. "The goal right now is to combine mechanistic studies at a basic level with whatever is gained from human epidemiological and experimental animal data," he said. Such a combination "may lead to a more intelligent extrapolation" from low doses to health risks, Yaniv said.
Mountain of Waste
Until a better extrapolation method is developed, the debate undoubtedly will continue over whether regulators of nuclear waste facilities are too protective of human health or not protective enough. That debate is reflected in the controversy over whether the EPA's nuclear waste disposal standard ought to apply at a proposed high-level nuclear waste repository at Yucca Mountain, Nevada, which is located about 100 miles north of Las Vegas.
Although the 1982 Nuclear Waste Policy Act gave the EPA authority to issue standards for all nuclear waste disposal facilities, subsequent legislation mandated that the EPA separately issue post-closure standards for WIPP and Yucca Mountain.
The DOE has already spent $2 billion studying Yucca Mountain as a permanent resting place for 23,000 metric tons of spent nuclear fuel, which would be placed within rooms bored into the mountain. In 1992, Congress instructed the EPA to obtain technical advice from the National Academy of Science before issuing a post-closure standard for Yucca Mountain. In particular, according to Ray Wassel, a project officer for the NAS Yucca Mountain committee, Congress instructed the NAS to examine 1) whether a standard based on doses to individuals would provide "a reasonable means of protecting the health and safety of the general public," 2) whether active institutional controls could prevent intrusion into Yucca Mountain, and 3) whether it is possible to make scientifically supportable predictions about possible breaches of site barriers over a 10,000-year period.
Bob Loux, director of Nevada's Agency for Nuclear Projects, believes Congress wanted the NAS to evaluate the EPA's post-closure standard because Yucca Mountain may not be able to comply with that standard. The NAS was instructed to examine whether an individual dose--such as the 25 millirem limit--would adequately protect public health, without imposing the global release limits that restrict additional deaths to 1,000 over 10,000 years. The global population dose "is the killer in the standard for DOE," Loux noted, because possible carbon-14 emissions would result in more than 1000 deaths over 10,000 years.
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Brett Leslie--The science is far from settled at Yucca Mountain. |
Yucca Mountain cannot meet the standard, according to Brett Leslie, senior scientist with the Institute for Energy and Environmental Research, because wastes at Yucca Mountain will be stored in a dry, porous environment, allowing carbon-14 from the spent fuel to be released into the air. Leslie said a committee of the EPA's Science Advisory Board examined the carbon-14 question at Yucca Mountain and determined that "releases may produce an appreciable global population dose over 10,000 years," which would translate into 4,000 cancer fatalities over that period.
Leslie believes the carbon-14 problem need not doom development of Yucca Mountain. The issue could be addressed with engineered barriers, such as improved containers that resist degradation. "It's not an intractable problem," he said. "That's the real kicker of this [controversy]."
Although much attention has been focused on the impacts of carbon-14 on the global population, nuclear physicist Harry Mortenson, formerly of Los Alamos National Laboratory and now president of Cygnus Scientific, a consulting firm in Las Vegas, believes too little attention has been focused on how the emissions might affect the local population.
The EPA has calculated a dose of 4.72 millirems to maximally exposed individuals within a 50-mile radius of Yucca Mountain, but Mortenson said his own calculations indicated that maximally exposed individuals would receive a dose of 266 millirem per year, or more than 10 times the EPA's 25 millirem standard. According to Mortenson, the EPA's estimated dose lies along the lower bounds of the range of possible doses; his own estimate lies in the middle to upper bounds. He believes the true dose will lie somewhere between the extremes, but will exceed the 25 millirem standard. Based on his dose estimates, Mortenson calculated a lifetime cancer risk of approximately 1.5 cancer deaths out of a population of 10,000.
Most of the risk would be borne by future generations, Mortenson pointed out. Since the carbon-14 emissions emanate from deteriorating canisters, the rate of canister failure will affect the amount of gas released from Yucca Mountain. Based on the EPA's specifications for the canisters, 73% would fail within 1,000 years, he said.
Unanswered questions also remain about the site's hydrology and about the level of tectonic and volcanic activity that could rupture waste canisters. "The science is far from settled at Yucca Mountain," said Leslie, noting that an "ongoing controversy" also exists about whether groundwater flows within the mountain. The existence of groundwater is important not just because of its role in corroding canisters, but because faults that cut across Yucca Mountain would swiftly carry any contaminated water throughout the mountain.
Leslie believes the DOE should conduct further studies above ground to characterize conditions at the site, rather than proceeding with boring tunnels, which, he said, will alter the natural conditions of the mountain, such as air circulation, and may prevent the DOE from identifying additional faults.
DOE spokesperson Samantha Richardson said that although faults at Yucca Mountain have been identified by characterizing activities above ground, "it's equally important to see underneath." The tunnels, she said, will provide a better view of the faults. The DOE is also continuing to explore the hydrology of the mountain, as well as how radioactive gases would flow through the mountain, Richardson said, adding that the department is five to seven years away from completing study of the site. Once the characterization is complete, the DOE must obtain a license from the Nuclear Regulatory Commission, which could be vetoed by Nevada, Richardson said, acknowledging that the project is not popular among Nevadans.
Political Pressures
Much of the opposition to Yucca Mountain may stem from the perception that the site was chosen because of Nevada's lack of political clout. Yucca Mountain was initially among several sites considered for a high-level repository. "Yucca Mountain was by no means the best site," said Nick Lenssen, senior researcher at the World Resources Institute and author of a WRI report on nuclear waste disposal. "It was very much a political decision, not a scientific one."
Several observers commented that political concerns are driving America's nuclear waste disposal program. CIIT's McClellan believes excessive concern about the risks of disposal could derail development of disposal facilities. The EPA's post-closure standard requiring no more than 1,000 deaths in 10,000 years is "an extraordinarily conservative approach," McClellan said, arguing that it is unrealistic to ask the DOE to guarantee how a facility will perform in 10,000 years. "Excessive stringency is killing the program," McClellan said. "It ensures that nothing is going to happen."
Theodore Bessman, research group leader at Oak Ridge National Laboratory, said the politicization of nuclear waste disposal is a uniquely American phenomenon; other countries take a "longer view," recognizing the environmental benefits of nuclear power as well as its drawbacks. But in the United States the nuclear waste issue "becomes political," as exemplified by a California law that prohibits new reactors until a waste facility is opened. "There are those kinds of political pressures to solve the problem, whether it needs to be solved tomorrow or not," he said.
Utilities are running out of storage space, Bessman acknowledged, but he said monitored retrievable storage (MRS) facilities, which would house huge casks of nuclear waste that are now being stored at nuclear plant sites, could provide long-term, safe storage above ground. An MRS could be as simple as a concrete pad on which casks of waste would be placed and monitored, or a more complex facility where fuel rod assemblies are disassembled and repackaged. "It's a simple engineering problem to safely store nuclear wastes for a long time," he said. But, "it's a tremendous political battle" to open an MRS or a disposal facility.
Leslie also believes the rush to dispose of nuclear waste is driven primarily by politics, but for different reasons. "There is no safety issue driving them," Leslie says of the states and utilities anxious to remove wastes to an MRS or disposal facility rather than retaining wastes on site at nuclear power plants. Leslie asserted that the risks from the waste stem largely from its transport. "The waste should stay where it is until it is scientifically decided what to do with it."
Mortenson also believes that, given the state of knowledge about nuclear waste, it should remain above ground. "We will spend a few billion to put it under ground. They [future generations] will spend a few trillion to bring it back up, and they will probably use it for something important that we can't conceive of."
Karen Breslin
Karen Breslin is a freelance writer in Lakewood, Colorado.