Scientific and Technical Concerns




Seismic Risk Map of the United States

Seismic Risk Map of the United States




 
BOB MILLER
Governor
STATE OF NEVADA

Seal of the Great State of Nevada
ROBERT R. LOUX
Executive Director

AGENCY FOR NUCLEAR PROJECTS
NUCLEAR WASTE PROJECT OFFICE
Capitol Complex
Carson City, Nevada 89710
Telephone: (702) 687-3744
Fax: (702) 687-5277


 

In response to growing and legislative concern over the proposed high-level nuclear waste repository at Yucca Mountain, the 1985 Legislature established a formal structure by which the State would oversee federal waste program activities.

The legislate transformed the Nuclear Waste Project Office, which was established in 1983 by former Gov. Richard Bryan and previously functioned as part of the Governor's Office, into an independent, statutorily mandated Agency for Nuclear Projects. It is funded by a direct appropriation from the U.S. Congress.

The Agency's genera1 task is to oversee the Department of Energy's proposed high-level nuclear waste dump activities at Yucca Mountain. The Agency's division of technical programs and the division of planning have produced more than 135 published reports in more than 145 volumes covering some 35,000 pages documenting its research to date.

The research is the culmination of more than a decade of rigorous scientific inquiry from some of the finest researchers in the country. The work covers such diverse technical areas as the environment and the physical, chemical, volcanic, seismologic, mental and ground-water properties of Yucca Mountain. Transportation research has investigated cask design and testing accident conditions, risk assessment, and route analyses. Socioeconomic research includes data and impact analyses on issues such as characteristics of the visitor economy, risk management, and what effects the proposed repository would have on the economic and social fabric of Southern Nevada and the state.

We hope this this information proves useful to you. If you have my questions or comments, please do not hesitate to get in touch with me.

Sincerely;

Robert R. Loux
Executive Director

 


Contents

  • Earthquakes and Faulting
  • Volcanic Activity
  • Thermal Loading:
  • Mineral Resources
  • Groundwater Contamination
  • Climate Change
  • What You Can Do
  • Resources Available

  • Earthquakes and Faulting

    Yucca Mountain is located in an area that the U.S. Geological Survey classifies as very prone to earthquakes. in fact, the USGS designates the region as Class 4 earthquake zone, its highest rating. As recently as June 1992, a magnitude 5.6 quake struck an area just 12 miles southeast of Yucca Mountain itself, causing substantial damage to Yucca Mountain project surface facilities. The entire area that includes the site is rife with evidence of large numbers of earthquakes in the geologic past. There are at least 33 known earthquake faults within the study area for the repository, with at least two of the faults actually cutting through the proposed repository site.

    Earthquakes pose significant problems far a high-level nuclear waste repository for a number of reasons. They increase the risks associated with the handing and above-ground storage of the waste prior to emplacement underground. Above-ground facilities at Yucca Mountain will have to be built to withstand at least a 7.0 magnitude quake. Even with adequate engineering, a moderate or large event occurring during the transfer of spent fuel from transport to storage containers could pose significant safety risks to workers.


    There are 33 known earthquake faults in the Yucca Mountain area, two of which cut directly through the proposed repository block. Faults create pathways where water can flow and where gases can move. Fault movement within the repository could also cause waste containers to be breached and release the waste from the repository. This could make it easier for radioactive materials to find their way into the groundwater and eventually into the environment.

    Underground, earthquakes pose different problems. Quakes occur along faults, which are places where the rock has broken and slipped horizontally or vertically. these faults create pathways where water can flow and where gases can move. An earthquake occurring along a fault within the repository could increase the likelihood that water would find its way into the facility and speed the dissolution of the containers holding the waste.

    Fault movement within the repository could also cause waste containers to be breached and release the waste from the repository. This would make it easier for radioactive materials to find their way into the groundwater and eventually into the environment. It could also cause major problems for workers emplacing waste or who might need to access the repository to remove the waste in the event of repository safety problems.

    Because earthquakes represent movement on faults, they have the potential to trigger significant changes in the characteristics of the underground environment. A key concern at Yucca Mountain is whether an earthquake -- even one that occurs relatively far from the site itself -- might result in fault movement which alters underground water levels. This phenomenon can occur when a fault slips and creates a dam that backs up water in an underground aquifer, causing the water table to rise. Should this occur under the repository, it could result in the flooding of the facility while the waste is there. Water coming into a very hot repository would turn into corrosive steam that could eat away at the canisters holding the waste and cause gaseous emissions through the fractures in the host rock. In a cooler repository or after the waste heat has lessened, the water itself would speed corrosion of the containers and help hasten the release and transport of radioactive waste materials into the environment.

    The Department of Energy contends that earthquakes would pose little threat to a repository because the shaking effects of such quakes are not severe in deep underground structures such as mines or repositories. DOE believes that the water table under Yucca Mountain is too deep to be altered sufficiently by fault movement to flood the repository.

    State of Nevada researchers have found evidence that the water table in the area has fluctuated considerably and that water has even flowed out of fractures at the surface of the site. It is also likely that earthquakes and fault movement played a role in these past water movements. It is also likely that combinations of geologic and hydrologic processes and events, in the future, will result in continued fluctuations in groundwater conditions at Yucca Mountain that could affect the site's ability to safely isolate nuclear waste during the thousands of years required

    Volcanic Activity


    Besides earthquakes, the Yucca Mountain area has a long history of volcanic activity. The most recent evidence of volcanic activity at the the Lathrop Wells Cinder Cone, only 7 miles from Yucca Mountain, could be only a few thousand years old. Any movement of molten rock that causes the groundwater under the repository to heat up and move upward through the fractures and fault zones could result in the intrusion of geothermal water and steam, which is highly corrosive and could eat away the waste canisters and subsequently carry the freed radioactive materials from the repository to the environment.

    In addition to earthquakes, the area around Yucca Mountain has a long history of volcanic activity. Yucca Mountain itself consists of material from violent volcanic eruptions a few miles to the north about 11 million years ago. Much more recently, there have been active volcanic centers in the immediate vicinity of the site. The most recent evidence of volcanic activity could be only a few thousand years old. (The repository will have to function to isolate waste for at least a 10,000 year period.)

    While the likelihood of a volcanic eruption at Yucca Mountain or within the repository seems unlikely (although not impossible), the potential for volcanic activity to damage the waste isolation capability of the facility does exist. Volcanoes occur when magma (or molten rock that forms the material beneath the Earth's crust) gets close to the surface and exhumes (or flows) out through faults and fractures. But even if the magma does not reach the surface, it has the potential to enter the repository along fractures or to heat the surrounding layers of underground rock and to cause groundwater to boil away through cracks and fissures. This phenomenon can cause hot springs and geothermal activity. The Earth's crust beneath the Yucca Mountain area is known to be relatively thin compared to other regions of the Great Basin.

    At Yucca Mountain, any movement of magma that causes the groundwater under the repository to heat up and move upward through the fractures and fault zones could result in the intrusion of geothermal water and steam into the repository and around the waste containers. Geothermal water is highly corrosive and could eat away the waste canisters and begin transporting the waste in a relatively short time. The water could then carry the freed radioactive materials from the repository to the environment.

    Volcanic activity can result in renewed faulting and earthquakes In its vicinity. Significant movement along faults can affect groundwater and, in some cases, result in a rise in the level of the water table. This could cause or contribute to groundwater flooding the repository and the transport of the waste to the environment.

    DOE contends that the chances of a volcanic event occurring at the repository are so small as to be insignificant, but does not discount the possibility of renewed volcanism in the area. State of Nevada researchers consider the potential for regional volcanic activity to indirectly compromise the repository, though geothermal or other processes, to be of significant concern.

    Thermal Loading:
    The Effects of Heat Generated by Spent Nuclear Fuel and High-Level Radioactive Waste

    Thermal Loading
    The rock at Yucca Mountain is highly fractured, containing numerous cracks through which water can pass fairly rapidly. Rain and snow melt flowing through these fractures could move through the repository, picking up radioactive material and carrying it to the water table. State scientists think that the groundwater travel time from the repository to the accessible environment could be less than 1,000 years, not many thousand years as DOE believes.

    In addition to being highly radioactive, spent nuclear fuel generates considerable heat. This "thermal" characteristic has important implications for an underground repository since the heat that is produced by the waste buried below the surface can fracture rock, affect water movement within the subsurface, and even cause environmental changes at the surface.

    Spent fuel from nuclear reactors is hottest when it first comes out of the reactor. It cools slowly as the radioactive waste products decay so that the longer the fuel has been out of the reactor, the cooler it becomes. However, this cooling does not occur evenly. Fuel temperatures beginning at hundreds of degrees drop off rapidly during the first 10 years or so after removal, and at a declining rate thereafter. After a hundred years, the spent fuel still could remain hot enough to boil water.

    By controlling the "age" of spent fuel that is emplaced in a repository, and by altering the distribution of the waste (how much waste is placed in a certain space), it is possible to make the peak temperature of the facility cooler or hotter.

    The "thermal" characteristics of high-level nuclear waste pose special problems with respect to Yucca Mountain. Because the rock is highly fractured -- meaning that there are many cracks in the rock that can become conduits for water and gases -- a repository that becomes hot enough to boil water will cause the water In the rocks to turn to vapor. The water vapor will be forced away from the heat source (the waste) until it cools and becomes liquid water again. At that point, it will begin to move back toward the repository, creating a convection pattern within the mountain similar to what happens when water evaporates from the land, forms clouds and returns as rain. Some of the water vapor will also move upward though the fractures and vent out of the mountain surface.

    Should water infiltrate the hot repository, it could be flashed into steam. In the event of a breach in the container holding the spent fuel and high-level wastes, this steam and water could carry radionuclides out of the repository though the fractures either downward into the water table or up through the mountain into the atmosphere.

    The Department of Energy is considering a repository design that would keep the facility above the boiling point of water for an extended period -- a few hundred to a few thousand years. DOE's rationale is that a hot repository would boil away the water that is in the rock pores and fractures near the waste and assure that the waste containers remain dry. That way, they would be less likely to corrode and release the waste that is inside. A hotter repository design also allows more waste to be emplaced in less space.

    State scientists are concerned that the DOE's decision to pursue a thermally hot repository at Yucca Mountain will drastically increase the scientific uncertainties surrounding the waste isolation performance of the site. High temperatures will expand and fractures the rock, creating new and less predictable pathways for water to enter and waste to escape.

    Should hot water or steam contact the waste containers and the waste itself, chemical processes that dissolve and transport the waste would be more severe and less predictable than in a cool environment. It is probably impossible to assure that the heat from the waste can be evenly distributed within the repository to provide the benefit of a uniform, dry environment around the waste that DOE desires for a thermally hot repository.

    A thermally hot facility could also result in changes at the ground surface above the repository. In addition to a rising ground surface because of thermal expansion in the rocks beneath (with the potential for increased surface fracturing and erosion of the desert soil), vegetation and animal habitats could be adversely affectedin unknown ways over the long term. Also, increased ground surface temperatures and emission of water vapor from the mountain could affect local weather conditions.

    The State of Nevada is concerned that the decision about repository thermal characteristics is being made more to increase the amount of waste DOE can emplace In Yucca Mountain than on the basis of what waste temperatures would be best for a safe waste isolation system.

    Mineral Resources

    One of the ways nuclear waste that has been buried in an underground repository can be released into the environment is through some form of human infusion during the time period when the waste remains dangerous. For this reason, one of the criteria for choosing the site for a repository is that the area not be one where there are potentially valuable mineral or oil and gas resources some future generation might decide to mine. By locating a repository away from any known or potential valuable resource deposits, the likelihood of someone inadvertently (or purposely) drilling or mining into the facility and breaching the waste canisters is greatly diminished.

    For some time, State of Nevada scientists have been concerned about the potential for commercially exploitable miners within or close to Yucca Mountain. The mountain is located within an area that has historically yielded valuable deposits of gold, silver and other minerals. the old Bullfrog mining district encompasses the site. Significant gold mining Operations are currently underway just 12 miles from Yucca Mountain at the Sterling mine, and the geology of the Yucca Mountain area is similar to that of some other mineral producing areas in the region.

    State researchers, studying DOE core and rock samples from Yucca Mountain, have found evidence of gold and silver bearing rock. It is possible that Yucca Mountain could have mineral resources attractive enough to lure future extraction and mining activities and threaten the integrity of the repository.

    This would be especially likely in the more distant future, when gold reserves and supplies of other minerals possibly present at the site begin to dwindle or as extraction technologies advance to treat increasingly low quality deposits. Because a repository must remain undisturbed for thousands of years, the potential or known presence of any valuable minerals is cause for great concern.

    Groundwater Contamination

    A primary requirement of any high-level nuclear waste repository site is demonstration of its ability to effectively isolate radioactive wastes from groundwater that is or may be used by people for drinking, crop irrigation and other applications for thousands of years into the future.

    Since water moves downward from the ground surface through the underground layers of rock into aquifers, and a repository at Yucca Mountain would be located above the water table, the time it takes for water passing through the repository to reach the water table is an important predictor of a site's ability to adequately contain the waste. The canisters which hold the waste in the repository are required by regulations to last 300 - 1,000 years. They eventually will release the radioactive materials - the only questions are when, how and how fast that will happen. Once the canisters break down, the waste, which remains radioactive for thousands of years, can be exposed to water passing through the facility and then transported away from the repository to the surrounding environment.

    The rock within which the repository would be constructed is highly fractured, containing numerous cracks through which water can pass fairly rapidly. Water infiltrating from the surface (rain and snow melt), then flowing through these fractures and cracks (termed "fracture flow"), would move through the repository picking up radioactive material and carrying it to the water table. The rapidly flowing aquifer which underlies Yucca Mountain flows south through the Amargosa Valley and emerges through springs in Death Valley. State scientists think that the groundwater travel time from the repository to the accessible environment in Amargosa Valley could be less than 1,000 years, not many thousand years as DOE believes.

    For a repository that must isolate waste for a minimum of 10,000 years, the prospect of the waste contaminating the groundwater away from the repository site in less than 1,000 years would be a fatal flaw. This alone should disqualify he site from further consideration.

    Climate Change

    The area around Yucca Mountain shows evidence of changes in climate over recent geologic time. In the past, the southern Nevada region experienced periods when conditions were much wetter and colder than they are today. At one time, much of the southern Great Basin was covered by numerous lakes and surface water.

    Wet and dry climates characterize global climate. Some scientists believe that the present dry climate in the Yucca Mountain area represents a late phase of a dry cycle, and that future climatic conditions are likely to be much wetter. For a high-level nuclear waste repository designed for a dry environment, the prospect of increased rainfall and snow melt caused by natural climatic changes would mean higher rates of water infiltration into the repository. More water would flow through the fractures in the rock and into the repository coming into contact with the waste canisters. This could increase the speed at which the canisters break down and release the waste, while at the same time. hastening the transport of the radioactive waste to the groundwater and into the environment.

    Changes in climate also can cause alterations in the water table. There is evidence in the geologic record that water levels around Yucca Mountain have fluctuated over time, and some of these fluctuations were associated with changes in climate. Should wetter climatological conditions cause the water table under Yucca Mountain to intrude into the repository, radioactive waste could be released into the environment.

    While the potential for climate change would exist at almost any site chosen for a repository (because of the long time period required for isolation), such changes are especially problematic for a Yucca Mountain facility because it would be designed and built for unsaturated conditions above the water table. That means a Yucca Mountain repository, while not completely dry and free of water, would be designed for a long-term environment that is not underwater or saturated. Any change that would saturate the site could hasten release of the waste and damage the isolation capabilities of the repository.

    State scientists believe that, if evidence shows climate change resulting in a significantly higher water table is possible during the life of the proposed repository, the site should be disqualified.

    What You Can Do

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    This document is published by the State of Nevada Nuclear Waste Project Office and is funded through financial assistance provided by the United States Congress.

     


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