Risks and Issues of Concern to Nye CountyNye County's fundamental concern is whether a repository at Yucca Mountain or an interim storage facility at the Nevada Test Site would pose unacceptable risks and impacts to the health, safety, and well-being of Nye County residents.
To addresses these issues requires an understanding of (1) what the risks and impacts may be; and (2) how those risks and impacts might be managed.
A repository or interim storage facility would pose four kinds of potential risks and impacts to Nye County:
1. Risks to the health and safety of workers and the public;
2. Impacts on socioeconomic conditions and quality of life;
3. Impacts to the environment; and
4. An area of concern called "program risk."
Health and Safety RisksA high-level nuclear waste repository or an interim storage facility could pose health and safety risks to Nye County residents by (1) exposing them to harmful levels of radiation during routine operations or accidents, or (2) as a result of accidents not involving any release of radiation. These risks have both short and long term components.
Short term risks: Nye County residents could be exposed to varying levels of radiation from either routine transportation and facility operations, or through accidents involving release of radiation. With regard to transportation, small amounts of radiation are present at the surface of the casks used to carry spent fuel to the repository or interim storage site. Actual public exposure to this radiation decreases dramatically with increased distance from the cask. Drivers and other workers would receive a proportionately higher, if still very small, dose from routine transportation of spent fuel. In much the same way, workers at a repository or interim storage facility would be exposed to small amounts of radiation during routine waste handling at the operations center. Since these facilities would be isolated from members of the public, the public would receive virtually no radiation from routine operations.
Another concern is the risk of an accident that could result in a release of radioactive material. Many scenarios are possible, but all have a low probability of occurring. In the near term, a serious transportation accident or a failure in waste handling procedures or equipment at the repository or interim storage facility could result in the release of unknown amounts of radiation. HLW transportation casks are built to withstand extreme impacts, and the probability of an accident that could break open a canister is very small. A serious accident at the site would be highly unlikely.
Since these facilities would be isolated from population centers, the public would receive virtually no radiation from routine operations.
Long-Term Risks: Activities at the Nevada Test Site, including past testing of nuclear weapons and ongoing disposal of low-level radioactive wastes, could possibly result in radionuclide releases to the environment. Nye County believes that any assessment of potential radiological impacts should consider the cumulative exposures from all potential sources, including a repository, interim storage facility, transportation, and other past, present and future activities at the NTS.
The risks to health and safety after the repository is closed, are quite different in character than short-term or environmental risks. At some point, thousands or tens of thousands of years in the future, a portion of the radionuclides in the underground repository could escape from the waste packages. If this occurs, radionuclides could then be carried by groundwater to the human environment. Alternatively, radionuclides in a gaseous form could pass through so-called "pneumatic pathways" from the repository to the ground surface to reach the human environment. In both cases, the issues are how long it would take radionuclides to reach the environment, whether humans would be exposed to such releases, and whether those exposures would be harmful.
Several factors contribute to the ability of the repository to contain radionuclides. A key factor is that waste packages will generate a great deal of heat. These packages must be carefully arranged in the repository to manage the effects of this "thermal load." Characteristics of backfill materials and the design of repository tunnels will determine movement of radionuclides in the immediate vicinity of the waste packages. The geologic setting of the repository must provide the ultimate containment for the waste. The repository block is a rock type called "welded tuff" that was created by the eruption of volcanoes in the area millions of years ago. Minerals called "zeolites", that could absorb many of the radionuclides that might escape into the groundwater are present in the tuff. Zeolites help to slow movement of radionuclides from the repository to the human environment.
The repository block is located several hundred feet above the water table. This means there should be minimal or no contact between waste containers in the repository and the water table. However, some water is present in the repository block. One of the major questions is how the heat generated by the waste will affect the water. Fractures in the tuff could possibly work as "fast pathways" connecting the repository to the land surface or the water table. Although the site receives only four inches of rain a year, and much of that evaporates before it soaks into the ground, the possibility that surface water could reach the repository through these fast pathways must be considered.
Other events such as earthquakes, renewed volcanic activity, or climate changes could influence the performance of the repository system and groundwater behavior. At least two major faults are known to cross the repository block. Only about 150 years of Yucca Mountain earthquake history is known or available. This is a short time period, in geologic terms. Violent earthquakes, which may be possible over a period of thousands of years, could change groundwater pathways. This kind of activity could also raise the water table and shorten the time it takes for radionuclides to reach the human environment. The climate around Yucca Mountain could also become wetter in the future than it is today. This could increase infiltration of water into the repository or raise the water table.
There is also the remote possibility that volcanoes in the area could become active again. Volcanic activity near the site has been of both the explosive caldera type and the more inactive basaltic-flow type. Caldera-type volcanism occurred much earlier in geologic time than the flow type, and, according to the Department of Energy, would have a small probability of occurring during the next 10,000 years. The possibility of new basaltic-flow volcanic activity is greater, but still considered to be very low. The Lathrop Wells basaltic cinder cone, located less than twenty miles from Yucca Mountain and active as recently as 20,000 years ago, has been a subject of geologic research due to its close location and its comparatively young age.
Finally, future civilizations might accidentally access a repository in search of water or minerals, or intentionally intrude to recover radioactive materials. The National Academy of Sciences has concluded that, while it is impossible to make scientifically defensible estimates of the probability of human intrusion, it is possible to calculate the impacts of such an event. Although the repository system will be designed to warn future generations about its contents, the potential for human intrusion is only speculative and adds to overall uncertainties about the performance of the repository system.
Scientists must predict how all of these factors will interact over thousands of years. They will have limited and uncertain information about site conditions to use in making these predictions. It will be extremely difficult - and perhaps impossible - to demonstrate to the U.S. Nuclear Regulatory Commission and the pubic, that the repository can meet necessary performance and environmental standards. DOE’s analysis, to date, suggests only minute amounts of radiation would be released from a repository, and that it would take hundreds, or even thousands, of years for the radioactivity to reach the human environment.
