Yucca Mountain, Nevada - A proposed geologic repository for

high-level radioactive waste

Robert A. Levich and John S. Stuckless U.S. Department of Energy, Las Vegas, Nevada 89134

U.S. Geological Survey, Denver, CO 80225

ABSTRACT

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.

INTRODUCTION

Since the dawn of the Atomic Age more than 60 years ago, the operation of

nuclear powerplants, as well as the development and manufacture of nuclear weapons,

has generated large amounts of radioactive waste. Some of the radioisotopes in this

waste are in low concentrations or have short half-lives. Most of these "low-level"

wastes can be disposed of in shallow trenches. Other radioactive waste contains

radioisotopes in higher concentrations or isotopes with long half-lives, greater than 1,000

ykars. ~h?se"'high-level" wastes must be disposed of in a manner that will isolate them

from the biosphere for tens of thousands of years.

Worldwide, there has been a long-standing scientific consensus that the best

method for permanent disposal of high-level radioactive waste is in deep geologic

repositories (see for example National Academy of Sciences, National Research Council

report, 1957, and Nuclear Energy Agency report, 1995). There are many analogues that

support this conclusion, for example, ore deposits that have existed for millions of years,

organic materials that have existed in caves for hundreds of thousands of years, and

anthropogenic items that have been preserved underground for thousands to tens of

thousands of years (Winograd, 1986; Brookins, 1986a; Alexander and Van Luik, 1991 ;

Miller et nl., 1994; Stuckless, 2000, 2002)

Nuclear waste destined for disposal comes from several sources. The largest

quantity is commercial spent nuclear fuel (SNF), consisting of he1 assemblies from

civilian nuclear powerplants that contain enriched uranium fuel pellets that have been

removed after completing their useful life in the production of electricity. Approximately

20% of our Nation's electricity is produced at 74 sites in 33 States that host 11 8

con~mercial nuclear power reactors, more than 100 of which are still in operation.

Currently (2006), more than 40,000 metric tons of heavy metal (MTHM) are stored in 33

States at 72 commercial reactor sites and a single storage site (Commonwealth Edison's

consolidated storage facility at Morris, Illinois). It is estimated that if the existing nuclear

powerplants continue to operate for their license periods of 40 years, they would generate

about 87,000 MTHM of SNF. If each reactor were granted an additional 10 years by

license extension, they could produce a total of about 105,000 MTHM of SNF (c.f. Dyer

and Voegele, 200'1; U.S. Department of Energy, 2001).

Other sources of waste include:

1. U.S. Department of Energy (DOE) spent nuclear fuel - spent nuclear fuel

from reactors aboard naval vessels and irradiated fuel from weapons

production and research reactors.

2. High-level radioactive waste - radioactive by-products resulting from the

reprocessing of commercial or defense spent nuclear fuel, which fails to

separate small amounts of plutonium and other transuranic elements.

3. Surplus weapons plutonium.

4. Transuranic wastes - by-products from fuel assembly and the manufacture

of weapons.

HISTORY OF NUCLEAR WASTE MANAGEMENT

The Atomic Energy Act of 1954 assigned to the U.S. Atomic Energy Commission

(AEC) the responsibility of managing spent nuclear fuel from civilian reactors. This Act

also permitted private industry to construct and operate nuclear reactors for generating

electricity. In the following year, the National Academy of Sciences (NAS), at the

request of the AEC, began a study of waste disposal and in 1957 reported " . . . that

radioactive waste can be disposed of safely in a variety of ways and at a large number of

sites in the United States." The NAS also indicated that ". . . the most promising method

of disposal of high-level waste . . . is in salt deposits" (National Research Council, 1957).

As a consequence, the AEC comn~issioned the U.S. Geological Survey (USGS) to review

the Nation's salt deposits. On the basis of investigations between 1962 and 1969, an

abandoned salt mine near Lyons, Kansas, was selected for further study. However,

owing to the technical problems such as the discovery of old abandoned wells, as well as

intense local opposition to the development of a waste disposal site, the project was

canceled. As a consequence, the search for alternative geologic repositories was

broadened to investigate salt deposits in other States, as well as a variety of other rock

types, as discussed below.

In addition to the search for geological repositories in the United States, there was

a perceived need to investigate other geologic and nongeologic means for nuclear waste

disposal, which included widely diverse alternatives as represented by the following:

1. Sub-seabed disposal - spent nuclear fuel andlor devitrified high-level waste

sealed in specially designed canisters and buried within deep sea sediments of

an abyssal plain in a tectonically stable area far from plate boundaries.

2. Island disposal - isolation of waste in a deep geologic repository beneath an

uninhabited island that lies in a remote area and lacks natural resources.

3. Ice sheet disposal - storage of waste in containers to be placed on the surface

of ice sheets (Greenland or Antarctica), with heat from radioactive decay

causing the container to melt its way toward the bottom of the ice sheet.

4. Deep-hole disposal - placement of waste-filled canisters in drill holes as much

as 10,000 m (6 mi) deep, below circulating ground water and far below the

accessible environment.

5. Rock-melt disposal - placement of waste in liquid or slurry form in a deep

drill hole or underground rock opening, with the heat of radioactive decay

eventually melting the surrounding rock to form a molten solution of waste

and rock that would eventually solidify into a relatively insoluble mass

resistant to leaching.

6. Deep well injection - injection of waste into a deep geologic formation

capped by a layer of impermeable rock.

7. Space disposal - several alternative concepts were considered, including (1)

transport to and injection of waste into the sun, (2) emplacement of waste on

the moon, and (3) sending reprocessed waste into orbit midway between Earth

and Venus.

8. Long-term surface storage - continued storage in (1) water pools that cool

spent f ~ ~ e l rods and shield workers from radiation, or (2) dry storage casks;

these are considered to be temporary measures requiring constant monitoring

and security.

Treatment methods to mitigate the waste-disposal problem also were considered.

Reprocessing of waste is a chemical process in which spent nuclear fuel is dissolved,

fissile uranium and plutonium are recovered, and the remaining high-level waste is .

vitrified (Cowley, 1997). The process is expensive but produces a greatly reduced

volunle of waste. During President Carter's administration (1977-1980), the United

States established the policy of not reprocessing commercial spent nuclear fuel.

Partitioning and transmutation of radioactive waste as an adjunct to reprocessing also was

considered (Cowley, 1997). In this method, the actinide waste is combined with uranium

(or uranium + plutonium), fabricated into mixed oxide, and reinserted into a reactor.

After numerous cycles the waste actinides would be converted to stable isotopes or ones

with very long half-lives; however, additional waste streams are generated during each

reprocessing cycle. Furthermore, transmutation does not reduce the quantities of long-

lived fission products including 9 9 ~ c and 1 2 9 ~ , and these must be disposed of in a geologic

repository.

Inherent technical difficulties and other serious disadvantages limit consideration

of most nongeological alternatives for waste disposal, and thus the effort to find an

acceptable geologic solution was expanded. In 1972, The AEC contracted with the

USGS to evaluate several different methods of geologic disposal, principally in geologic

media other than salt. Five modes of disposal were to be considered: (1) very deep drill

holes (9,140 to 15,250 m), (2) geometric array of shallow to moderate depth drill holes

(300 to 6,100 m), (3) shallow mined chambers (300 to 3,000 m), (4) cavities with man-

made (engineered) barriers, and (5) explosion cavities (6 10 to 6,100 m). The final report

(Ekren et nl., 1974) cited 30 previous reports on geologic disposal and concluded that

hydrologic isolation was of paramount importance. One specific recommendation was

"the Basin and Range Province of the western United States, particularly the Great Basin

exclusive of seismic-risk zone 3,' appears to have potential for mined chambers above

deep water tables in tuff, shale, or argillite" (Ekren et al., 1974, p. 2). The body of the

report provides several examples of favorable geologic features at the Nevada Test Site.

During the 1970s and '80s, DOE (and predecessor agencies) investigated several

alternative sites and rock types:

1. Salt sites (other than Lyons, Kansas) -three salt domes (two in Mississippi

and one in Louisiana) and four bedded salt units (Paradox Basin in Utah and

Pern~ian Basin of West Texas) were evaluated (U.S. Department of Energy,

1984a,b; 1986a,b,c).

2. Basalt Waste Isolation Project, Hanford, Washington - investigation of

layered basalts of Miocene age in the Cold Creek Syncline of the Columbia

Plateau, on the Hanford Nuclear Reservation (U.S. Department of Energy,

1986d).

3. Crystalline rocks - following a survey of crystalline rocks largely in the

regions of the Appalachian Mountains and the North American Shield, 12

areas in Georgia, North Carolina, Virginia, New Hampshire, Maine,

I

' Seismic-risk zone 3 corresponds approximately to the east and west province margins, where extension is most active.

Minnesota, and Wisconsin were recommended for further study (OCRD,1983;

U.S. Department of Energy, 1986e).

4. Sedimentary rocks - widely distributed claystones and shales were considered

as appropriate media for geologic disposal of nuclear waste by the National

Academy of Sciences (1957). DOE supported several investigations in this

medium (Merewether et al., 1973; Shurr, 1977; Dames and Moore, 1978; and

Brookins, D.G., 1986b)

5. Tuffaceous rocks, Nevada Test Site - included tuffs in both the unsaturated

and saturated zones that had been examined in considerable detail as part of

other investigations on the Test Site (U.S. Department of Energy, 1986f,g).

This site received the endorsement of USGS Director McKelvey, who wrote

to DOE in 1976 pointing out the remoteness of the site, its varied geologic

environments, and the existence of 900 man-years of data collection and

interpretation.

Throughout the 1970s and 1980s, in addition to working with DOE in specific

areas, the USGS was tasked by Congress to study and comment on the problem of

disposal of high-level radioactive waste. A report released in 1978 concluded that (1) salt

was less than ideal as a disposal medium, (2) shales, tuffs, and crystalline rocks should be

considered, (3) major studies of flow and transport were needed, especially in fractured

rock, (4) more tools were needed for dating water and materials older than about 40,000

years, and (5) the severe limitations of Earth science predictions needed to be recognized

(Bredehoeft et al., 1978).

In 1980, the Office of Nuclear Waste Management of DOE and the USGS of the

Department of Interior (DOI) released jointly a draft plan for disposal of radioactive

waste in a mined repository (U.S. Department of Energy and U.S. Geological Survey,

1980). The report was written by 17 scientists from five organizations and concluded

that there was a need to redirect research from generic characterization to four or five

specific sites, that detailed study plans should be prepared for each site, and that research

and developn~ent at the current level should be sufficient to resolve major technical issues

within the next 10 years. They also noted a need for research on thermo-mechanical

effects on hydrology. The search for more specific sites was started in 198 1, when the

USGS, in cooperation with seven State agencies (Arizona, California, Idaho, Nevada,

New Mexico, Texas, and Utah), .began evaluating the Basin and Range Province for

possible repository sites. The results were published in eight Professional Papers in the

1370 series; the region encompassing Yucca Mountain is described by Bedinger et al.

(1 989).

THE YUCCA MOUNTAIN SITE

The Yucca Mountain site is located in Nye County in southern Nevada,

approxin~ately 160 km (1 00 mi) northwest of Las Vegas (fig. 1). The entire proposed

repository is located on Federal lands, a principal consideration in facilitating further

study. The eastern portion is located on the Nevada Test Site; the northwestern comer is

located on the Nevada Test and Training range of the U.S. Air Force; and the

southwestern corner is located on land managed by the Bureau of Land Management.

Scientific investigations began at Yucca Mountain at the end of the 1970s. The

area had already been mapped at 1 :24,000 (Lipman and McKay, 1965; Christiansen and

Lipman, 1965), and the geology was known to be uncomplicated. The gently dipping

volcanic strata of fairly uniform thickness over a large area could be characterized easily,

and Yucca Mountain was well removed from the region of active nuclear weapons

testing. Initial efforts focused on the saturated zone, but preliminary drilling showed that

the water table was very deep (nearly 600 m), the temperature at the water table was

moderately elevated (30-35"C), and the rocks in the saturated zone were highly

trans~nissive, making containment of any leaked waste difficult if not impossible.

The general benefits of an unsaturated zone had already been pointed out by

Winograd (1 974, 198 l), including greater ease of (1) characterizing the site, (2)

monitoring stored waste, and (3) retrieving waste should it become necessary. In

February of 1982, USGS geologists indicated in a letter to DOE that the thick unsaturated

zone at Yucca Mountain might offer considerable advantages for disposing of radioactive

waste. The rationale was that only a small amount of water would reach the underground

reposito~y, and the repository could be designed so as to permit this water to pass through

into deeper permeable rocks and thus have only minimal contact with the stored waste

containers. Furthermore, there was a thick zeolitic unit above the water table that would

impede the movement of water to the saturated zone and sorb several of the radioactive

elements should there be any leakage. A more complete discussion of the advantages on

the unsaturated zone at Yucca Mountain is presented by Roseboom (1983). In July of

1982, DOE changed the target horizon for a possible repository to the unsaturated zone.

At the end of 1982, the focus of high-level radioactive waste disposal changed

with the passage of the Nuclear Waste Policy Act (NWPA), which directed DOE to

develop specific criteria for recommending candidate sites and prohibited

characterization work at any site until a site-characterization plan had been developed.

Work at Yucca Mountain was allowed to continue because it was already in progress.

DOE developed siting criteria, which were published as 10 CFR 960 (U.S. Department of

Energy, 1984c), and nine sites were selected for judging against the siting criteria. By

1986, three sites remained: a bedded salt at Deaf Smith, Texas; the basalt flows of

Hanford, Washington; and the ash-flow tuffs of Yucca Mountain, Nevada. At the end of

1987, Congress amended the Nuclear Waste Policy, Act, directing DOE to characterize

only Yucca Mountain.

The designation of Yucca Mountain as the only site for continued study was

based on several important factors. It is located at the west edge of the Nevada Test Site,

an area in which many years of geologic, geophysical, hydrologic, and related

investigations had been conducted in support of the underground nuclear weapons testing

program, as well as preliminary studies of various parts of the area as potential nuclear-

waste disposal sites. The preliminary studies had illuminated several favorable

conditions for siting a geological repository as noted previously, and no major adverse

conditions had been found. However, DOE was instructed to notify Congress

immediately and to stop work if anything was discovered that made the site unsuitable.

Hydrologic conditions in both the saturated and unsaturated zones were of major

importance in the designation of Yucca Mountain as the only site to be characterized.

These will be discussed in a companion volume. A series of papers covering aspects of

both zones can be found in Bodvarsson et al. (2003), and a description of the regional

flow system can be found in D'Agnese et al. (2002).

DOE, as directed by the NWPA, developed an extensive Site Characterization

Plan (U.S. Department of Energy, 1988), and the details of how characterization was to

proceed were written into more than 100 study plans. Studies included regional and site

geology, volcanic stratigraphy, Quaternary deposits, climate and paleoclimate, erosion,

unsaturated zone hydrology, saturated zone hydrology, mineralogy and petrology, rock

and fluid geochemistry, fracture fillings characterization, rock mechanics, thermal

testing, coupled processes testing, radionuclide transport, tectonics and tectonic models,

seismic and volcanic hazards analysis, geophysics, and natural resources evaluation.

Some of the results of these investigations are discussed in the following chapters of this

volunle. Combined, the results of the entire suite of investigations provide ample

docunlentation that Yucca Mountain is one of the most thoroughly studied geologic

features on Earth. Each of these subjects is discussed in detail in the Site Description

(Bechtel SAIC Company, 2004). This publication will discuss the regional and site

geology, tectonics, and climate (past, present, and future).

REGULATORY INFORMATION

The Yucca Mountain project has been one of the most heavily regulated and scrutinized

projects in the history of geology. This section provides a brief overview of this aspect of

the project. The NWPA of 1982 ( I ) established a comprehensive national policy for

management and disposal of spent nuclear fuel and high-level radioactive waste, which

still remains the framework for the Nation's geologic disposal program; and (2)

designated three agencies with the authority and responsibility related to waste disposal:

(a) DOE, for siting, licensing, constructing, operating, and closing a repository; (b) the

U.S. Environmental Protection Agency, for developing and issuing standards for

radiological release from a repository; and (c) the Nuclear Regulatory Commission

(NRC), for establishing requirements and criteria for approving or disapproving a license

for a repository. The NWPA also established a fund derived from a 1.0 mil per kilowatt-

hour assessment on electricity generated by nuclear powerplants. This h n d would cover

costs associated with site characterization, licensing, and operation of a repository (with

some additional funding from the Department of Defense for handling of their radioactive

waste).

The NWPA also provided for use of the nuclear waste fund in the form of grants

for monitoring and independent characterization.activities by the State in which site

characterization was active as well as monitoring by other affected governmental

agencies and affected Indian tribes. In addition, funds have been made available to the

NRC for the same purposes. The NWPA required DOE to provide Congress with annual

reports on all site-characterization activities and findings.

The Nuclear Waste Policy Amendments Act added another layer of oversight by

creating the U.S. Nuclear Waste Technical Review Board. The 11 members of this board

are appointed by the President from a slate of nominees provided by the National

Academy of Sciences. The Board was also given investigatory powers by the Act.

A rigorous Quality Assurance (QA) program provides an internal oversight of all

Project work. All scientific activities must conform to several standards. Among these

are the following: Each activity must be fully described in a planning document before

any data collection can take place. The rationale as to why the study is needed is given.

The methods to be used are listed used along with an explanation of how these methods

will attain the desired answers or what should be done if unexpected results are found.

All personnel performing quality-affecting work must have their qualifications

documented and verified, and their training must be documented. Procurements

supporting quality-affecting work must be reviewed for appropriate QA requirements and

be procured from approved sources that are audited. All instruments to be used must be

calibrated; the tolerances for calibration must be given, and all calibrations must be

within the tolerance limits or else the data are discarded back to the date of the last

known acceptable calibration. All data are collected according to detailed written

procedures, and all samples are controlled and tracked. Finally, all data and records are

reviewed and entered into a project data base. Any part of the QA program is subject to

internal audit and/or audit by the NRC.

The NRC, in 10 CFR 63, mandated that the license application for the Yucca Mountain

site include a computer model that will assess how the engineered and natural systems, as

a whole, will act to isolate radionuclides from the accessible environment. All data

collected by the project have been synthesized into subsystem models and abstracted into

a Total System Performance Assessment (TSPA). Much of the data in this volume are

included in process models that form the basis for TSPA, either as frameworks within

which a model must operate (e.g., the basic geologic data for the site) or as input to a

model (e.g., future climate as an input to future unsaturated-zone flow and transport). For

a nlore comprehensive discussion of this complicated model and its results see Bechtel

SAlC Con~pany (2003).

Figure Captions

Figure 1 .-Map showing the location of the proposed repository at Yucca Mountain, Nevada.

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Acknowledgments

All of the authors of this memoir have been supported by the Department of Energy

(DOE), Office of Civilian Radioactive Waste Management. All of the research reported

here, except for most of the regional geology, also has been supported by DOE. Ardyth

Simmons (Los Alamos National Laboratory) was instrumental in creating the impetus for

publishing this work. The authors of this chapter wish to thank Eugene Roseboom and

Isaac Winograd (U.S. Geological Survey, retired), Michael Voegele (Science Application

Inter~~ational Corporation, retired), and Claudia Newbury (DOE), who collectively have

more than a century of work in high-level radioactive waste disposal, for very helpful

reviews and many helpful discussions.