Abstract Disposal of Czech institutional radioactive waste began in 1959. Waste (predominantly low level and short-lived) is disposed of in rock chambers that have been excavated in several different rock types, originally for different purposes, and subsequently used for radioactive waste disposal. All Czech radioactive waste repositories are operated by the Radioactive Waste Repository Authority (RAWRA). The oldest Czech repository is Alcazar near Beroun, a town in central Bohemia. This repository commenced operation in 1959. Two galleries in Devonian limestone were excavated between 1942 and 1944. Disposal at Alcazar ended in 1965. In 1994, the repository was closed. Bratrství, near the town of Jachymov in NW Bohemia, has been in continuous operation since 1974. Only waste contaminated by natural radionuclides is disposed of at this repository. Five chambers and the access gallery are parts of an abandoned uranium mine. The repository is situated in metamorphic rocks. The most important repository for institutional waste disposal is the Richard II facility near the town of Litomerice in northern Bohemia. Galleries and chambers currently used for disposal are part of an underground system excavated from an extensive lens of clayey limestone of Turonian age. The original purpose was the underground mining of limestone. Radioactive waste has been disposed of here since 1964.

Abstract In the Asse salt mine, a system with relatively small pillars and stopes was excavated between 1909 and 1964. From 1965 until 1978, low- and intermediate-level radioactive wastes were disposed there permanently. Most of the chamber volume (∼3.5 million m 3 ) was exposed to free convergence until 1995, when a backfilling campaign was started using pneumatic transportation of granular salt material. The barrier to the overburden rocks is formed by rock salt that has a minimal thickness of only 15 m in the upper part. The flank dips ∼70°SW. The Asse site has been monitored for decades by displacement observations, stress and strain measurements in the pillars, and recording of the backfill pressure built up in the chambers. Softening and damaging in the pillars and stopes of the mining horizon have led to stress redistributions into the overburden rocks, where rupture processes have occurred. Hence, because of the small dimension of the bearing elements on the southern flank and the close distance to the overburden, far-reaching geomechanical interactions exist.

Abstract In Germany, the former potash and rock salt mine Morsleben is so far the only underground repository for radioactive waste operated on the basis of the Atomic Act. In 1986, the Morsleben repository was licensed by the authorities of the former German Democratic Republic for the disposal of low- and intermediate-level waste. In 1999, the federal government of Germany decided to cease disposal operations. At present, a license for the closure of the repository is being pursued by the Federal Office for Radiation Protection (BfS). BfS initiated a comprehensive scientific and technical program to keep Morsleben a safe repository. This program resulted in greater insight into the geological structure of the site, the rock mechanical deformation of the underground excavations, and the origin and age of brine seeps at a few locations in the mine. To reduce the radiological consequences of a brine intrusion scenario, the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), contracted by BfS, investigated several concepts for effective backfilling and sealing. Material selection and—in view of the specific geological situation—adequate positioning of sealing systems underground contribute substantially to the long-term safety of the repository.

Abstract The Finnish power companies TVO and FPH currently operate four nuclear reactors, two each at the Olkiluoto and Loviisa sites. Both companies are responsible for the safe management of nuclear wastes. The underground repository program for low- and intermediate-level waste was commissioned in the late 1970s. From the start, the design basis has been geological disposal, the safety of which rests on natural and engineered barriers. The disposal system should isolate the waste for a few hundred years. During this time, the radiotoxicity of the waste will decline significantly. The critical radionuclides are 14 C, 239 Pu/ 240 Pu, 59 Ni, 90 Sr, and 137 Cs. The Olkiluoto site consists mainly of micaceous gneiss intercalated with sparsely fractured tonalite. A tonalitic portion of the site was chosen for more detailed characterization. The Loviisa site consists entirely of Rapakivi granite, which is coarse grained and porphyritic. The repository layout was in both cases constrained by the local geology. At Olkiluoto, the shape of the tonalitic body bounded by fracture zones led to a vertical silo-type concept 60–100 m below the surface. At Loviisa, the subhorizontal fracture zones above the planned disposal depth favored horizontal drifts 120 m below the surface. Thorough safety assessments were conducted during the licensing process. The Olkiluoto repository was built between 1988 and 1992, and the Loviisa repository was built between 1993 and 1997. Operation of Olkiluoto was commissioned in 1992, and Loviisa was commissioned in 1998. In the future, the repositories will also be used for disposal of waste when the nuclear power plants are decommissioned.

Abstract Geological disposal has been the basis for the Swedish program for disposal of radioactive waste since its beginning in the mid-1970s. Two underground facilities have been in operation since the late 1980s. The construction of the final repository for short-lived, low- and intermediate-level waste, SFR (Swedish final repository for radioactive operational waste), started in 1983, and it was put into operation in 1988. The facility is located 50 m below the sea, close to the Forsmark nuclear power plant, where the sea has a depth of ∼5 m. Low-level waste is placed in four rock vaults, each of which has a length of 160 m. Intermediate-level waste is stored in a concrete silo that has a height of 50 m and an inner diameter of 26 m. The disposal vaults are connected to the surface by two parallel access tunnels. The total disposal capacity is 63,000 m 3 , of which about one-half is currently in use. An expansion of the SFR is planned to accommodate radioactive waste from the decommissioning of the nation's power plants. Construction of the interim storage facility for spent nuclear fuel, Clab, started in 1980, and the facility was put into operation in 1985. The facility is located at the Oskarshamn nuclear power plant. The fuel assemblies are stored in water pools located in two 120-m-long rock chambers. The roof of the rock chambers is ∼30 m below the ground surface. Construction of a second storage vault has recently been completed. The Äspö Hard Rock Laboratory is an underground facility for developing and testing characterization methods and the different components of a system for deep geological disposal under realistic repository conditions. The facility reaches a depth of 460 m below the surface. After 5 yr of construction, it was put into operation in 1995. The licensing, construction, and operation of these facilities have provided valuable experience that is being used for the site characterization and design work currently in progress for the deep geological repository for spent nuclear fuel. The spent nuclear fuel will be disposed of in a repository located at depths between 400 and 700 m. The disposal concept is based on isolation of the spent fuel in copper canisters surrounded by a buffer of highly compacted bentonite placed in a borehole in granitic rock. Site investigations are currently in progress at two potential sites. This project is a major geoscientific undertaking that is planned to be completed in 2009 with the selection of one of the sites for the deep repository.

Abstract Site-specific investigations of bedded evaporites began at the Waste Isolation Pilot Plant site in New Mexico (USA) in 1976, and the first waste was accepted in 1999. Here, we describe and discuss some lessons learned from personal experience. “Fatal flaws” may not be fatal. Features, events, or processes are sometimes useful exclusionary factors, especially during site selection. Solution chimneys discovered northwest of the site in 1975 were possible vertical pathways for radionuclide transport. Intensive field studies since then have indicated no solution chimneys at the Waste Isolation Pilot Plant site. Known chimneys are related to a geologic unit not found at the Waste Isolation Pilot Plant, and chimney fill is not very permeable. Normal fluid flow should be downward if subevaporite formations are connected to near-surface units. If a solution chimney had been found early at the pilot plant, there might have been pressure to relocate it. Timing is important. Potash resources were assessed in 1976 by drilling 21 boreholes; four were completed as shallow hydrology observation wells. Data from all boreholes would have provided a comprehensive picture of the hydrology early in the project history. Resource conflicts were considered more important at the time than hydraulic parameters. Critics will always be with you. the Waste Isolation Pilot Plant is recertified every five years, offering multiple opportunities for outside review and comment. Repeated comments about dissolution of some halite beds, for example, rely on conclusions reached before site-specific studies. Intensive studies since 1984 of shafts, cores, and geophysical logs have shown that halite is distributed mainly by depositional processes. Some critics remain well behind the curve of technical work; we still must respond.

Yucca Mountain in Nevada represents the proposed solution to what has been a lengthy national effort to dispose of high-level radioactive waste, waste which must be isolated from the biosphere for tens of thousands of years. This chapter reviews the background of that national effort and includes some discussion of international work in order to provide a more complete framework for the problem of waste disposal. Other chapters provide the regional geologic setting, the geology of the Yucca Mountain site, the tectonics, and climate (past, present, and future). These last two chapters are integral to prediction of long-term waste isolation.

Planetary and synoptic-scale atmospheric features are important because they set the stage for differing climate regimes in the Yucca Mountain area—whether in past, present, or future time. Climate proxy records in the region show that numerous climate regimes occurred during the past 800 k.y. ranging from warm interglacial periods (similar to modern climate) to cool or cold and wet glacial periods. The current climate at Yucca Mountain is arid, with an annual average precipitation of ∼17.7 cm/yr. Most of the annual precipitation occurs during winter or during July and August monsoons. Annual average temperatures generally range from 15° to 18 °C but can exceed 40 °C during summer. Continuously deposited calcite at Devils Hole, Nevada, provides a precise chronology that can be used to calibrate other climate proxy data that provide estimates of the nature and magnitude of past climate events. During past glacial periods, mean annual temperature may have been as much as 10° to 15 °C cooler than present temperatures, with mean annual precipitation as much as 1.4–3 times present precipitation. These records of past climate are used to bound estimates of future climate to assess future potential infiltration. Five maximum infiltration scenarios are estimated to occur within the next 500 k.y. providing that anthropogenic disturbance does not modify or alter long-term climate change.

Yucca Mountain has been proposed as the site for the nation's first geologic repository for high-level radioactive waste. This chapter provides the geologic framework for the Yucca Mountain region. The regional geologic units range in age from late Precambrian through Holocene, and these are described briefly. Yucca Mountain is composed dominantly of pyroclastic units that range in age from 11.4 to 15.2 Ma. The proposed repository would be constructed within the Topopah Spring Tuff, which is the lower of two major zoned and welded ash-flow tuffs within the Paintbrush Group. The two welded tuffs are separated by the partly to nonwelded Pah Canyon Tuff and Yucca Mountain Tuff, which together figure prominently in the hydrology of the unsaturated zone. The Quaternary deposits are primarily alluvial sediments with minor basaltic cinder cones and flows. Both have been studied extensively because of their importance in predicting the long-term performance of the proposed repository. Basaltic volcanism began ca. 10 Ma and continued as recently as ca. 80 ka with the eruption of cones and flows at Lathrop Wells, ∼10 km south-southwest of Yucca Mountain. Geologic structure in the Yucca Mountain region is complex. During the latest Paleozoic and Mesozoic, strong compressional forces caused tight folding and thrust faulting. The present regional setting is one of extension, and normal faulting has been active from the Miocene through to the present. There are three major local tectonic domains: (1) Basin and Range, (2) Walker Lane, and (3) Inyo-Mono. Each domain has an effect on the stability of Yucca Mountain.

Yucca Mountain in southwestern Nevada is a prominent, irregularly shaped upland formed by a thick apron of Miocene pyroclastic-flow and fallout tephra deposits, with minor lava flows, that was segmented by through-going, large-displacement normal faults into a series of north-trending, eastwardly tilted structural blocks. The principal volcanic-rock units are the Tiva Canyon and Topopah Spring Tuffs of the Paintbrush Group, which consist of volumetrically large eruptive sequences derived from compositionally distinct magma bodies in the nearby southwestern Nevada volcanic field, and are classic examples of a magmatic zonation characterized by an upper crystal-rich (>10% crystal fragments) member, a more voluminous lower crystal-poor (<5% crystal fragments) member, and an intervening thin transition zone. Rocks within the crystal-poor member of the Topopah Spring Tuff, lying some 280 m below the crest of Yucca Mountain, constitute the proposed host rock to be excavated for the storage of high-level radioactive wastes. Separation of the tuffaceous rock formations into subunits that allow for detailed mapping and structural interpretations is based on macroscopic features, most importantly the relative abundance of lithophysae and the degree of welding. The latter feature, varying from nonwelded through partly and moderately welded to densely welded, exerts a strong control on matrix porosities and other rock properties that provide essential criteria for distinguishing hydrogeologic and thermal-mechanical units, which are of major interest in evaluating the suitability of Yucca Mountain to host a safe and permanent geologic repository for waste storage. A thick and varied sequence of surficial deposits mantle large parts of the Yucca Mountain site area. Mapping of these deposits and associated soils in exposures and in the walls of trenches excavated across buried faults provides evidence for multiple surface-rupturing events along all of the major faults during Pleistocene and Holocene times; these paleoseismic studies form the basis for evaluating the potential for future earthquakes and fault displacements. Thermoluminescence and U-series analyses were used to date the surficial materials involved in the Quaternary faulting events. The rate of erosional downcutting of bedrock on the ridge crests and hillslopes of Yucca Mountain, being of particular concern with respect to the potential for breaching of the proposed underground storage facility, was studied by using rock varnish cation-ratio and 10 Be and 36 Cl cosmogenic dating methods to determine the length of time bedrock outcrops and hillslope boulder deposits were exposed to cosmic rays, which then served as a basis for calculating long-term erosion rates. The results indicate rates ranging from 0.04 to 0.27 cm/k.y., which represent the maximum downcutting along the summit of Yucca Mountain under all climatic conditions that existed there during most of Quaternary time. Associated studies include the stratigraphy of surficial deposits in Fortymile Wash, the major drainage course in the area, which record a complex history of four to five cut-and-fill cycles within the channel during middle to late Quaternary time. The last 2–4 m of incision probably occurred during the last pluvial climatic period, 22–18 ka, followed by aggradation to the present time. Major faults at Yucca Mountain—from east to west, the Paintbrush Canyon, Bow Ridge, Stagecoach Road, Solitario Canyon, Fatigue Wash, Windy Wash, and Northern and Southern Crater Flat Faults—trend predominantly north, are spaced 1–5 km apart, have bedrock displacements ranging from 125 m to as much as 500 m, and exhibit Quaternary movements of several centimeters to a few meters. Displacements are predominantly down to the west, and bedrock/alluvium contacts commonly are marked by fault-line scarps. The predominant northerly fault trend changes to a more northeasterly trend in adjacent areas south of the site area owing to clockwise vertical-axis rotation. Structural blocks between the block-bounding faults are internally deformed by numerous minor faults, some oriented northwest and exhibiting strike-slip movements. Investigations to determine the natural resource potential of the Yucca Mountain area—metallic minerals, industrial rocks and minerals, hydrocarbon and other energy resources, and geothermal resources—resulted in findings indicating that a given commodity either (1) is not known to exist in the area, or (2) is present in such low concentrations as to be noneconomic.

Performance of a high-level nuclear waste repository at Yucca Mountain hinges partly on long-term structural stability of the mountain, its susceptibility to tectonic disruption that includes fault displacement, seismic ground motion, and igneous intrusion. Because of the uncertainty involved with long-term (10,000 yr minimum) prediction of tectonic events (e.g., earthquakes) and the incomplete understanding of the history of strain and its mechanisms in the Yucca Mountain region, a tectonic model is needed. A tectonic model should represent the structural assemblage of the mountain in its tectonic setting and account for that assemblage through a history of deformation in which all of the observed deformation features are linked in time and space. Four major types of tectonic models have been proposed for Yucca Mountain: a caldera model; simple shear (detachment fault) models; pure shear (planar fault) models; and lateral shear models. Most of the models seek to explain local features in the context of well-accepted regional deformation mechanisms. Evaluation of the models in light of site characterization shows that none of them completely accounts for all the known tectonic features of Yucca Mountain or is fully compatible with the deformation history. The Yucca Mountain project does not endorse a preferred tectonic model. However, most experts involved in the probabilistic volcanic hazards analysis and the probabilistic seismic hazards analysis preferred a planar fault type model.

Abstract Military geology and national security projects are comparable, achieving their raison d'etre in support of national goals, military operations, and the systems that support them—all for vital national interests. The application of geoscience to these ends, especially engineering geology, has occurred from pole to pole and included every conceivable environment and natural condition. In the conduct of such projects, the geosciences have advanced, and vice versa. Desert trafficability, most notably regarding playa surfaces, is temporary and variable and not a persistent condition as some early authors believed. Playas in Australia, Iran, and the United States show that saline efflorescence is removed following surface water dissolution and subsequent deflation, resulting in very hard crusts. Magadiite, a hydrous sodium silicate and possible precursor of bedded chert, was first discovered in North America at Alkali Lake, Oregon, during a military project. Pleistocene Lake Trinity, a small and mostly buried evaporite basin in the northern Jornada del Muerto, New Mexico, was discovered during exploratory drilling in support of a military test program. The Strategic Petroleum Reserve (SPR), operated by the U.S. Department of Energy, has underground cavern storage of ~600 million barrels of crude oil in five Gulf Coast salt domes. The geologic characterization of the SPR sites is a major component of these comprehensive engineered works—unparalleled in modern times and on a comparable scale with the Panama Canal. Numerous studies of salt-stock heterogeneity, salt-karst features, and structural and physical attributes of salt deposits are broadening the database for use in the commercial storage industry. Geologists serving in military and national security endeavors are fully functioning members of the project technical teams and have made significant advances to the geosciences.